The Cemented carbides(also called Tungsten Carbide)are a range of composite materials, which consist of hard carbide particles bonded together by a metallic binder cobalt (Co). Cemented carbides commonly use tungsten carbide (WC),titanium carbide (TiC), tantalum carbide (TaC) or niobium carbide (NbC) as the aggregate.Mentions of "carbide" or "tungsten carbide" in industrial contexts usually refer to these cemented composites. It is mainly used to make high speed cutting tools,cold working molds, measuring tools and high wear resistant parts.
Engineered hard chrome has been applied to aerospace parts to increase wear resistance and repair or rebuild worn sections. However, the use of hard chrome in aerospace and other applications is being phased out because of environmental and health concerns with hexavalent chrome emissions from the chrome plating process. As a result, high-velocity oxygen-fuel thermal spray coatings are replacing hard chrome on many aerospace parts. HVOF coatings can be used for newly manufactured parts and for repairing worn parts.
With worn parts, machinists typically remove a certain amount of material, eliminating the wear that has developed in the part. They rebuild that surface with HVOF coatings, according to Glen Rosier, applications engineering/business development, Abrasive Technology Inc., Lewis Center, Ohio, a superabrasives manufacturer.
The environmental reasons are important, but are not as big a driver as everyone thinks, said Keith O. Legg, a senior analyst at Rowan Technology Group, Libertyville, Ill., a marketing and analysis firm specializing in advanced technologies, materials and coatings. [Manufacturers] use HVOF coatings because they work better and last longer. With chrome, there are striations after a few years. The chrome becomes worn and damaged. With HVOF coatings, that is not the case.
The HVOF process is unlike plating, which can coat the entire part. HVOF coatings are deposited in a thermal-spray process where a powdered material is injected into a high-pressure, hot gas stream. The powder is sprayed with a gun onto the part surface and forms a dense, well-adhered coating. HVOF coatings are typically about 0.003 " to 0.005 " thick on original parts, and 0.015 " thick on rebuilt parts because manufacturers are building up the worn area.
The HVOF coating process can deposit a range of different alloys and cermets. A cermet is a composite material composed of ceramic and metallic materials. The most common alloy coating materials for aerospace applications are tungsten carbide cobalt (WC-Co) and tungsten carbide cobalt chrome (WC-CoCr).
You typically apply tungsten carbide on moving parts that have surfaces in constant contact, said Larry Marchand, aerospace account manager, United Grinding Technologies Inc., Miamisburg, Ohio, a grinding machine builder. You want something extremely hard and that will withstand the constant frictional forces.
The most common aerospace applications for tungsten-carbide HVOF coatings are landing gear parts, flight control and hydraulic actuators, landing gear and hydraulic system pins,flap and slat tracks andturbine engine shafts. [The list includes] almost any component subject to wear by rubbing or abrasion, which differs from aircraft to aircraft, said Legg.
The coated aerospace parts are typically made from HSS, although some titanium parts are HVOF-coated. The use of titanium in aerospace applications is growing because it weighs half as much as steel in similar applications. And for aircraft, weight is dollars, said Jon Devereaux, materials and processes engineer, NASAKennedy Space Center in Florida. (All opinions expressed by Devereaux in this article are his own and not necessarily those of NASA.)
One limitation with the HVOF coating process, however, is coating deep IDs. With chrome plating, any ID or OD can be coated because a part is immersed in a bath. But the HVOF spray does not reach into deep holes.
We can coat inner diameters, but it depends on the depth, size and location of these diameters, said Roger Maragh, process engineer for Hitemco, Old Bethpage, N.Y., which provides coating and grinding services. After all, this is a line-of-sight process.
Because HVOF coatings are denser and harder than hard chrome, they require a different approach to grind the material to achieve the required finishes and geometries. The coating has a thick, bumpy surface, so it has to be ground back to the correct geometry or with the proper finish, as far as smoothness and texture, Marchand said.
A process specification is availableAerospace Material Specification 2449for grinding tungsten-carbide HVOF thermal spray coatings applied to HSS for applications requiring wear, heat and corrosion resistance or dimensional restoration. However, usage is not limited to those applications.
NASAs Devereaux, who sponsored the specification, said, documenting all aspects of the grinding procedures in some sort of writtengrinding process controlsheet prior to the start of the grinding operation is vital.
Often, larger and more rigid grinding machines equipped with high-frequency drives are required. Also, minimizing vibration is especially important when grinding HVOF coatings. Machines with hydrostatic guide ways dampen vibration and offer much smoother grinding with these very hard materials, Marchand said. The machine moves on a film of oil and that layer of oil breaks the vibration energy.
While hard chrome is usually ground with an aluminum-oxide or silicon-carbide grinding wheel, the hardness of HVOF coatings requires that they be ground with a diamond wheel. As a result, the grinding machine requires higher static and dynamic stiffness.
The diamond wheel itself requires a higher threshold force to make it work, said Brian Rutkiewicz, manager of applications engineering, Saint-Gobain Abrasives Inc., Worcester, Mass., a manufacturer of high-performance materials, including abrasives. A wheel that has aluminum-oxide or silicon-carbide abrasives doesnt need as much force to make it cut.
Because diamond is as hard as it is, diamond wheels can grind substantially higher levels of the coating compared to silicon-carbide and aluminum-oxide wheels, said Abrasive Technologys Rosier. It maintains size and keeps the conformity of the part better.
The key to grinding HVOF coatings is following correct procedures for diamond wheels, including proper selection of the grinding wheel, grit size, grade and bond type, and proper mounting, balancing, truing and dressing of the wheel prior to grinding, according to NASAs Devereaux.
The first step is properly truing the wheel. You have to have that wheel running true before you start grinding parts, said Devereaux. If you dont properly true and dress it before you start, you will have problems. You cant just take a diamond wheel (from the manufacturer) and put it on your grinding machine.
While most people think a resin-bond diamond wheel should be applied, in many applications vitrified-bond wheels work better. Although these wheels are more expensive, they generally last longer than resin-bond wheels and condition more easily. Also, vitrified-bond diamond wheels can be diamond-dressed on the machine during the grinding process. Resin-bond wheels are typically trued first and then dressed in a secondary manual stick dressing operation.
Resin-bond diamond wheels traditionally have been used, said Rutkiewicz. However, resin- and hybrid-bond technologies have a drawback in that online truing and dressing can be difficult because of the frequency of truing due to form or finish loss and, more importantly, the need to dress or condition (stick-dress) the face after truing. This is because the resin- and hybrid-bond technology has little porosity and, when trued, the abrasive no longer has exposed cutting edges.
The newest technology employs vitrified-bond diamond wheels. Vitrified wheels are trued and dressed simultaneously with a rotary diamond disk. With a properly designed truing and dressing diamond rotary-disk dresser and by using the correct parameters, in many applications vitrified wheels may yield the lowest total process cost, said Rutkiewicz.
For dressing, the grinding machine must be set up for rotary dressing, not with a stationary tool. Stationary diamonds do not have the strength and hardness to efficiently dress vitrified diamond wheels. A rotary dressing tool is used when dressing a vitrified-bond diamond wheel because there are many more diamonds cutting and it acts like a cutting saw, said Beat Maurer, president of Complete Grinding Solutions, Springboro, Ohio, which grinds HVOF-coated aerospace parts.
The dressing system must be equipped with a high-frequency drive so it is adjustable in speed and direction to make the wheel cut properly and achieve desired surface finish requirements, according to Maurer. You can adjust parameters accordingly with the dresser because it is a rotary dresser that can go unidirectional or counterdirectional, he said. Unidirectional makes the wheel cut better and counterdirectional provides a better surface finish.
Other factors to consider are proper application ofcutting fluidand selection of feeds and speeds. For the most part, companies are using emulsion over straight oil due to the cost savings. In general, emulsion is a better coolant but straight oil is a better lubricant, said Maurer. Diamond wheels are typically run at about 5,000 sfm, according to Maurer.
The coating must be ground without burning the base part, but that is less of an issue with HVOF coatings than chrome. These coatings are more heat resistant than hard chrome, Devereaux said. If you are grinding hard chrome, you definitely have to be careful not to burn the steel underneath it. But we have not seen that with HVOF coatings.
When ordinary grinding does not produce an acceptable surface finish on HVOF-coated aerospace parts, manufacturers turn to superfinishing. Superfinishing, or microfinishing, is a material-removal application that produces a very smooth, highly uniform surface finish, characterized by a high bearing area, while maintaining or improving part geometry, said Saint-Gobains Rutkiewicz. The superfinished surface is less than 8in.Ra, typically around 4in.Ra.
The AMS 2449 specification does not cover superfinishing, but an Aerospace Material Specification for HVOF-applied, tungsten-carbide coatingsis expected to be published this year, according to Devereaux.
Superfinishing may not always be required, depending on the application. However, tungsten-carbide coatings have hard, sharp peaks that emerge from the surface, according to Devereaux. The grinding process (with coarser grit sizes) inherently leaves some of these tungsten-carbide peaks exposed after grinding, he said. If not removed or smoothed by the superfinishing process, theseparticleswill damage a mating seal in a hydraulic system, such as landing gear or flight control actuators, which often results in a hydraulic oil leak and premature removal of aircraft components.
While superfinishing of hard chrome is not needed, the benefits of HVOF coatings over hard chrome still are apparent. They provide better wear and corrosion resistance, in addition to environmental benefits.CTE
Just as hard chrome platingis being replaced by HVOF coating, easier-to-grind microcomposite coatings may replace HVOF coatings, according to one coating supplier. Cermet powders from MesoCoat Inc., Euclid, Ohio, can be used to produce coatings that replace conventional HVOF thermal spray coatings, according to the company. They are designed to be a drop-in powder replacement for chrome-carbide or tungsten-carbide coatings and can be applied with the same equipment as HVOF coatings, said Curt Glasgow, general manager, thermal spray for MesoCoat.
Known as PComP, the powders are made with near-nanosize particles of titanium nitride, silicon nitride, tungsten carbide or titanium carbide combined with various metallic binders and sintered to form a hard composite core. The particle core is then further clad with a ductile or tough material, such as nickel or cobalt, forming a core-shell particle.
The coating structure provides a low coefficient of friction and excellent wear and corrosion resistance, according to the company. The coefficient of friction is orders of magnitude lower than that of tungsten carbide and chrome carbide, Glasgow said. The coating is also much more ductile then HVOF wear-resistant coatings. Therefore, it can be built up much thicker, say 0.030 " or 0.040 " thick, and used for repair where thicker buildups are required.
Also, the nanostructures in the core of the powder provide the coating with a lower modulus of elasticity than standard HVOF coatings. If you have an application where you have a lot of flexing of the part, such as long hydraulic cylinders or actuators, the lower modulus of elasticity allows it to withstand that flexing much better than tungsten-carbide or chrome-carbide HVOF coatings, Glasgow said.
Because the hard particles in PComP coatings are nanostructured, anywhere from 80nm to 600nm, the grinding wheel does not cut through them; they are instead removed with the grinding chips. This means that aluminum-oxide or silicon-carbide wheels can be used instead of diamond wheels. With the larger tungsten-carbide and chrome-carbide particle sizes, when you are grinding you have to cut those hard particles in half so you need a grinding media that is harder than the carbides, such as diamond, said Glasgow. Also, speeds and feeds typical for hard-chrome grinding can be applied as opposed to the slower feeds needed for carbides.
PComP coatings can be ground to finishes as fine as 8in. Rawith conventional grinding wheels. You dont have to superfinish it to get the desired surface characteristics, Glasgow noted. The coating is like hard chrome in that you can produce a 10in. Rafinish directly from grinding. If you have an application on hard chrome that requires 16in. Ra, if you were going to replace that with a tungsten-carbide coating and get an equivalent surface, youd probably have to be at 6in. Raor 8in. Ra. Youd have to grind that and superfinish it to get the surface equivalent of the hard chrome.
PComP can be used for wear coatings on aircraft parts, including landing gear and actuators. It can also be used for dimensional part restoration. We are going through the approval process with various customers in the defense and commercial aerospace markets, Glasgow said. We have development partnerships with the Air Force and others. We should have acceptance from customers in the next 3 or 4 months.
The ideal range is 20:1 (5% coolant, 95% water) to 10:1 (10% coolant, 90% water). Start out with a ratio of 20:1 for initial tank fills. Use clean, soft water if possible. If you have very hard water with lots of minerals, then increase the percentage of coolant to 15:1 or 10:1
Due to the evaporation of water in the coolant mixture, you should not top off the tank at the same dilution ratio that was used to fill the tank with fresh coolant. A good rule of thumb is to use one-half of the amount of coolant when topping up. If you start a fresh batch of coolant at a ratio of 20:1, then top off with a ratio of 40:1 (Brix reading of 0.5).
Coolant that is maintained at the correct dilution ratio and properly filtered by a centrifuge and/or filter type cartridge/paper should last up to 12 months. Note the translucent green color of a fresh batch of coolant. Unlike other brands of coolant, properly maintained coolant will keep its original color even after 6 months of use.
Grinders that have a small coolant tank (e.g., 20-gallon tank with inexpensive paper filter) will need to have their coolant changed more frequently (e.g., every 60 days), especially if grinding soils are continually re-circulated through the pump due to poor filtration.
First, calculate the volume (cubic ft) of your tank. Next, multiply the total by ft by 7.5 to convert to gallons. Then divide the total gallons by the dilution ratio to obtain the total amount of coolant to add. For example:
Todays grinding machines grind 2,3 and even 4 times faster than 10 years ago. Grinding wheel performance has been keeping up with technology with new high-temperature bonds and core designs. But until recently when it came to coolants you were faced with the same choices.
With coolant pressures now reaching in excess of 600 psi, the demand for high-performance specialized coolant programs has never been more intense. Thats why you need to turn to grinding Lubricants for real performance and productivity.
Water-soluble synthetic grinding coolant for companies grinding carbide or steel. Synthetic coolant is a concentrated high-performance coolant designed to dramatically reduce cobalt leaching in the machining and grinding of the tungsten carbide. If you have problems with your coolant turning pink due to cobalt leaching, then you should try synthetic coolant.
Synthetic coolant is an oil-free coolant that provides fast swarf removal, exceptional rust protection, and high cooling. Even when heavily diluted with water, it still provides excellent protection to freshly machined and ground surfaces. Synthetic coolant protects both machines and working parts against build-up of sticky residue associated with the grinding process, and contains ingredients that wont attach aluminum fixtures. The coolant has a high cleaning action that removes grinding fines thereby minimizing wheel loading. Synthetic coolant is a low foaming coolant that can be used with recycling or centrifuge systems.
Synthetic coolant is already in use by many leading carbide and HSS tool manufacturers throughout North America. When used in conjunction with a central coolant system, GrindClean GK 05 will increase diamond/CBN grinding wheel life and enable the wheel to produce a high-quality finish. The result is reduced grinding wheel costs and increased customer satisfaction with the finished product. Benefits of synthetic coolant include:
Oil grinding fluid/coolant. Oil coolant is a light viscosity, mineral-based oil designed for grinding or cutting steel, carbide, quartz, and crystal. Oil coolant is ideal where a high lubricity, low viscosity cutting or grinding oil is required. Oil coolant also finds use in honing and finishing of surgical knives and other products that require a very fine finish. The high flash point and non-toxic, biodegradable components of oil coolant make it safe to use.
Oil coolant is used by many leading carbide and HSS tool manufacturers throughout North America. It can be used on most types of saw, tool, and rotary grinders. Oil coolant grinding coolant will increase both the grinding wheel and grinding machine life. In addition, the resulting surface finish will be better than grinding with water-based coolants. The major advantages of Oil coolant are reduced grinding wheel costs, reduced grinder maintenance costs, and increased customer satisfaction with the finished product. Benefits of oil coolant include:
Oil coolant has a long service life if filtered properly. It has a minimum flash point of 320 F and a specific gravity of 0.90. An air cleaning system (e.g., SMOG-HOG) for collecting coolant mist is recommended for grinders without a full enclosure. All CNC automatic grinders running oil-based coolants must have a spark arrester installed (check with grinder manufacturer for more details).
The following points highlight the eighteen main types of cutting tool materials used in industries. The types are: 1. Plain High Carbon Tool Steel 2. Low Alloy Carbon Tool Steel 3. High Speed Steel 4. Cast Cobalt Base Alloy Tools (Stellites) 5. Cemented Carbides 6. Ceramics 7. Non-Ferrous Alloys 8. Non-Tungsten Materials (Titanium Carbides and Titanium Nitrides) and a Few Others.
Before 1900, all types of tools were made of carbon tool steel. The chief characteristics of plain carbon tool steel are low hot hardness and poor hardenability. They are usually quenched into brine and even then only a thin layer can be fully hardened with the attendant risk of developing quenching cracks. The carbon steels are limited in use to tools of small section which operate at relatively low speed.
The higher the carbon content, the greater will be wear resistance of the tool. Actually when a hardened plain carbon steel tool having a tempered marten-site structure is heated, the smaller particles of cementite will dissolve and a corresponding amount of cementite will precipitate on the larger particles as soon as carbon in the vicinity of these particles has time to migrate into position.
The net result is fewer and coarser carbide particles dispersed in the ferrite matrix and hence a softer structure. This is overcome in high speed steels by adding tungsten and molybdenum which combine with iron carbide to form complex carbides.
Carbon tool steels are easy to machine. Keen cutting edge can be easily provided. It has high surface hardness with a fairly tough core. These lose their hardness above 200C and do not regain it even after cooling. These are used for manufacture of milling cutters, twist drills, turning and form tools for wood, magnesium, brass and aluminium. Cutting speeds with carbon steel tools are limited to about 0.15 m/sec using huge coolant supply.
In order to increase hardness of tools, simple addition of carbon content makes it brittle. Small amounts of chromium and molybdenum are frequently used to improve harden ability of tool steels. Upto 4% of tungsten is sometimes added to these steels in order to improve their wear resistance.
These types of materials are used where wear resistance is required. These steels are widely used for drills, taps and reamers. Their hot hardness is about the same as that of the carbon steels and are not satisfactory for high speed turning and milling.
The introduction of high speed steel made possible a significant increase in machining speed, which accounts for its name. The chief characteristics of these steels are superior hot hardness and wear resistance. These can retain their cutting edge hardness at temperatures upto 600C but soften rapidly at higher temperatures. Cutting speeds are limited upto 0.75 to 1.8 m/sec beyond which they fail rapidly. The high speed steels are of two major types, viz., tungsten and molybdenum type and cobalt type.
Under the first category, the most common type of high speed steel is 18-4-1 tool steel which is typical of the high tungsten class of high speed steels. 18-4-1 means that this tool steel contains 18 parts of tungsten, 4 parts of chromium and one part of vanadium.
During World War I, a shortage of tungsten was faced, and realising that tungsten and molybdenum behave in the same general way, attempts were made to substitute tungsten by molybdenum; thus giving rise to two more types of HSS in the first category. It may be noted that only half as much molybdenum as tungsten is required on a weight basis to achieve the same effect.
All the three elementstungsten, molybdenum and cobalt help in achieving high hot hardness; the first two do so by forming complex carbides and the cobalt forms an alloy by going into solid solution in the ferrite matrix and thus raises the recrystallization temperature so that the material can retain the hardness it obtains as a result of strain hardening at a higher temperature.
Vanadium in high speed steels forms very hard carbides (vanadium-iron-carbide being the hardest constituent in HSS) and thus increases the wear resistance of the tool at all operating temperatures. Vanadium also helps to inhibit grain growth at the high temperatures required in heat treatment.
Due to above reason, increased vanadium content in tools is used for machining a highly abrasive material such as a high carbon high chromium die steel containing chromium and vanadium as the major constituents. These are most desirable tools for machining highly abrasive stock.
As the cobalt and molybdenum have a tendency to promote decarburisation, steels containing these elements should be ground to a greater depth in finishing to remove the decarburised layer which will not become fully hardened. Such steel should also be packed in carbonanceous material when being heat treated.
The chromium and cobalt have the tendency to promote retention of austenite which has further tendency to transform into martensite at a low temperature when the tool is subjected to shock or cold work as by grinding or in use of cutting.
Due to this, large internal stresses are set up which frequently cause cracks to develop in the tool, resulting in the premature breakdown of the cutting edge in use. Such steels should, therefore, be tempered twice, or treated at very low temperature in order to reduce the amount of retained austenite to about 5%.
In case of conventional HSS, carbide segregation can take place which induces local variations in chemical composition and structure. Such problems can be overcome by manufacturing HSS by powder metallurgy which facilitates finer and more uniform distribution of carbide particles and better homogeneity of alloying elements.
HSS is also produced by electroslag refining process and this tool has uniform carbide distribution and is free from inclusions. The properties of HSS are affected by heat treatment and as such it should be done as per recommendation of manufacturer. Further hardening of surface is possible by work hardening treatment. HSS cutting tools are nowadays coated with layers of refractory metal carbide or nitride by chemical vapour decomposition technique.
Fig. 23.1 shows the effect of temperature on hardness of various tool-materials. It is interesting to note that carbon tool steel is harder than high speed steel at temperature below 250C. Thus from economic consideration, HSS tools should be used for high speed operation where tool tip temperatures will be more than 250C: otherwise carbon- tool steel should be used (for slow cutting processes where the cutting temperatures are relatively small). Nowadays indexible HSS inserts are manufactured which can be clamped, brazed to a low alloy steel body.
A number of non-ferrous alloys (usually known as stellites) high in cobalt have been developed for use as cutting tool materials. These materials cannot be heat treated and are used as cast at a temperature of about 1260C. These contain about 40-50% cobalt, 27-32% chromium, 14-29% tungsten and 2-4% carbon.
Though the cast alloys are not as hard as the tool steels at room temperature, but they retain their hardness at higher temperatures. Under certain conditions, the cast alloy tools gives somewhat better life than the high speed steels, but they are not in wide use, due to their fragile nature. Like all cast materials, these alloys are relatively weak in tension and hence tend to shatter when subjected to a shock load or if not properly supported.
From Fig. 23.1 it will be seen that stellite is harder than HSS at temperature above 500C. It maintains its hardness and cutting edge even at red heat (750C). Thus stellite tools are ideal for rapid machining of hard metals. These are used for making form tools.
Though it had been discovered long back that tungsten carbide is very hard material but difficulties were faced in joining fine crystals of tungsten carbides into tool bits by sintering (prolonged heating of the compressed material just below the melting point) because the required temperature was so high that the material decomposed.
Later on it was found that tungsten carbide crystals when mixed with cobalt powder could be sintered at a temperature near the melting point of cobalt (1980C) to provide a strong material for use in certain machining operations.
Thus cemented carbide is a typical powder metallurgy product. Cemented carbides are very effective in machining cast irons and certain abrasive non-ferrous alloys, but as such are not good for cutting steel because wear craters are developed on the face of the tool.
() The C-grade consisting of tungsten carbide with cobalt as a binder, for use in machining cast iron and non- ferrous metals. In this grade, cobalt concentration is varied from 3-16%. Higher is the cobalt content, greater is the resistance to shock.
(b) The S-grade consisting of tungsten carbide, titanium carbide and tantalum carbide with a cobalt binder for use in machining steel (Tantalum carbide: 0-10%, TiC: 0-16%). TiC reduces the tendency of chips to weld to tool, increases hot hardness. Tantalum carbide helps improve resistance to crater wear and make the structure fine grained. In this steel grain size also exerts great influence on properties of steel. The coarser grain produces soft metal but more resistance to shock.
The cemented carbides have high hardness over a wide range of temperature; are very stiff (Youngs modulus is nearly three times that of steel); exhibit no plastic flow (yield point) even on experiencing stresses of the order of 33300 kg/cm2, have low thermal expansion compared with steel; relatively high thermal conductivity: and a strong tendency to form pressure welds at low cutting speeds. However, these are weak in tension than in comparison. Their high hardness at elevated temperatures enables them to be used at much faster cutting speed (3-4 m/sec with mild steel).
These unusual properties of the cemented carbides call for special consideration in the design of carbide tipped tools. Due to the very high stiffness of the cemented carbides, they should be well supported on a shank of sufficient thickness. The tool should be so proportioned that tensile stresses are kept small.
The relatively small coefficient of expansion of the cemented carbides, makes it necessary to use a relatively thin layer of braze metal so that the braze will not crack upon cooling as a result of large tensile stresses which arise from differential contraction of the carbide and the braze metal. In view of the adverse- pressure welding characteristics of cemented carbide tools, they should be operated at speeds considerably in excess of those used with high speed tools.
It may be mentioned that carbide grade with different properties is required for machining cast iron and steel because the wear characteristics of cast iron machining are quite different from those of steel. No single grade can satisfy all the maximum values of three important desirable properties (edge wear resistance, crater resistance and shock). Thus compromise in selection has to be made.
The properties of carbides are governed by the tungsten-carbide grain size and the greater the cobalt, the lower the hardness and impact resistance. For longest tool life, the tool with the finest grain size and the lowest cobalt content, which just prevents chipping and fracture, should be used. For cutting steel, addition of titanium carbide improves the crater-wear resistance, but reduces the abrasive wear resistance. For increasing abrasion resistance, tantalum carbide is added.
The material removal capacity (accelerated metal removal with no loss in tool life) of convention carbides can be considerably increased by using coated inserts obtained by metallurgical bonding of a thin coating (0.005 mm thick) of titanium carbide to a tough carbide core.
This results in lowering of the coefficient of friction between tool and chip with consequent reduction of cutting forces (by 35% approximately) and temperature reduction of the order of 70C. Crater wear is also practically eliminated.
Ceramics consist mainly of sintered oxides (A12O3) and are prepared in the form of clamped tips and as throw away inserts. These can be used at very high speed (beyond carbide tools), resist built-up edge and produce good surface finish. These are extremely brittle, so their use is limited for continuous cuts. Friction at rake face is usually lower as compared to carbide tools but temperature is higher because these are poor conductors of heat. To strengthen the cutting edge, a small chamfer or radius is often stoned on the cutting edge and negative rake of about 15-20 is provided.
These consist of varying percentages of cobalt, chromium, tungsten and carbon and are used for machining hard metals at speeds slightly in excess of those used with HSS tools. These find wide application in drilling operation. Their properties are superior to HSS but inferior to tungsten carbide.
Shortage of tungsten has led to the introduction of titanium carbides and nitrides with nickel and molybdenum as bonding materials. Their life is high. These exhibit higher hot hardness and do not form built-up edge on their rake faces.
An important development of cemented carbides has been to improve wear resistance and at the same time retain high toughness. This is possible by coating carbides (titanium carbide and titanium nitride) in microscopic layers over tough carbide substrate.
In cast carbides, a hard carbide alloy is dispersed in a high strength refractory binder by electrode arc melting and spin casting of metal into graphite moulds. It is highly resistant to crater formation and plastic flow at high temperatures.
These are mixtures of oxides of aluminium, and small quantities of other oxides. These may consist of almost pure aluminium oxide (approx 97%), or they may contain 80% Al2O3 with titanium, magnesium and tungsten oxides and carbides. These are hard and have good resistance to abrasion wear and cratering. These can retain cutting hardness upto 700C and have high wear resistance. These are good only for uninterrupted cuts.
They are brittle and have poor shock- resistance. These cant be brazed to steel shank, but can be cemented by epoxy resins. These are best suited for maintaining close dimensional tolerances and surface finish when machining long shaft because these have very low tool wear.
It is a well-known fact that diamond is the hardest known substance which burns to CO2 when heated to about 810C. In addition, it has lowest thermal expansion (12% that for steel), high heat conductivity (2 times that for steel), very low coefficient of friction against metals and is poor electrical conductor. Due to these properties, diamond tipped tools are sometimes used for special applications such as the production of surfaces of high finish on soft materials that are difficult to machine. These produce finish of 0.05 to 0.08 m on non-ferrous metals like copper, aluminium etc.
Since very high hardness is always accompanied by brittleness, a diamond tool must be cautiously used to avoid rupturing to the point. This usually limits the use of diamond tools to light continuous cuts in relatively soft metals, and low values of the rake angle are normally used to provide a stronger cutting edge.
The very low coefficient of friction and high heat conductivity provide a low operating temperature and make it possible to use high speeds (> 150 surface metre per minute) inspite of the fact that a diamond will decompose in air at temperature above 810C.
The relatively high cost of diamonds that are satisfactory for tools are partially responsible for their limited use. Diamonds are commercially divided into four classes: carbons, ballas, boarts and ornamental stones. The first two of these categories comprise stones which are poly-crystalline.
These are less dense, less hard than perfect diamonds and are satisfactory for some industrial uses but not for cutting points. Diamond cutting tools are usually made from boarts, which are single crystals, less clear and fault free.
Synthetic polycrystalline diamonds are available as mechanically clamped cutting tips. These are used for machining abrasive aluminium-silicon alloys, fused silicon and reinforced plastics. The random orientation of their crystals gives them improved impact resistance making them suitable for interrupted cutting.
The abrasive grains are used in grinding wheels, abrasive belts, sand papers, sand blasting and other similar operations. These operations actually involve cutting in which the abrasive grains produce tiny chips from the work material.
The abrasive commonly used may either be natural or artificial (manufactured). Natural abrasives include corundum, emery, quartz, garnet and diamond. Manufactured abrasives include aluminium oxide, silicon carbide and boron carbide.
Aluminium oxide and silicon carbide are by far the most widely used for all grinding abrasives. Silicon carbide is harder than aluminium oxide but is, in general more friable. Hardness is of importance chiefly in the grinding of very hard materials. The choice between silicon carbide and aluminium oxide lies in balancing the attrition resistance with the body strength which determines the ability to fracture when dulled.
It is a nitrided refractory metal alloy having composition of 50% columbium, 30% titanium and 20% tungsten with no carbide. It has excellent thermal shock resistance, high hardness, and toughness. It exhibits excellent resistance to diffusion and chip welding. It is available in the form of throwaway inserts having 3-5 times more edge life than conventional carbides. It operates in the speed range of 250-500 m/min on steels of 200 BHN.
It consists of atoms of nitrogen and boron, with a special structural configuration similar to diamond. It has high hardness and high thermal conductivity. It is chemically inert. It is used as a grinding wheel for HSS tools and stellite. These are available in the form of index-able insert and are capable of machining hardened tool steel, chilled cast iron, high strength alloys. It is hardest material next to diamond.
The word Si AI ON stands for silicon nitride-based materials with aluminium and oxygen additions. It is produced by milling Si3N4, aluminium nitride, alumina and yttria. The mixture is dried, pressed to shape and sintered at 1800C. This tool material is tougher than alumina and thus suited for interrupted cuts. Aerospace alloys and nickel-based gas turbine discs can be machined using sialon tool bit at a cutting speed of 200-300 m/mt.
High speed machining operations make use of PCD and CBN tools for best results. In motor vehicle and aircraft manufacturing industries, component parts of non-metallic materials are being used extensively. PCD cutters achieve exceptional standards of surface quality at high feed and material removal rates with such materials. PCD tools are extensively used for machining aluminium components.
It ranks at the top in terms of difficulty, said Steve Storlie, vice president of business development for Mendell Machine and Manufacturing Inc. The Lake-ville, Minn., medical parts manufacturer specializes in implants, surgical instruments and diagnostic equipment, as well as serving the defense and aerospace industries. It is no stranger to tough jobs. We do all kinds of titanium, he added. We do titanium every day.
In addition to cobalt and chromium, the metals used in the medical industry contain various alloying elements with desirable wear- and corrosion-resistance properties for implants, such as shoulder, knee and hip replacements. For example, CoCr28Mo6 ASTM F75 contains 58.9 to 69.5 percent cobalt, 27.0 to 30.0 percent chromium, 5.0 to 7.0 percent molybdenum, up to 1.0 percent manganese, silicon and nickel, up to 0.75 percent iron and up to 0.35 percent carbon. Cobalt chrome is stronger than stainless steel, but weighs twice as much as stainless and is brittle under impact loading. Hardness ranges from 40 to 50 HRC or higher.
Cobalt chrome is extremely challenging to machine, concurred Russ Moser, machining manager for medical parts manufacturer Judson A. Smith Co., Boyertown, Pa. Although the material has a tendency to workharden, he said cobalt chromes high hardness causes the shop more problems. It becomes even more difficult once the hardness gets up in the 50-HRC range.
Moser noted the company tends to apply uncoated carbide ballnose and other endmills to cut cobalt chrome, with some tools having a titanium-nitride coating for enhanced wear resistance. When the metals hardness makes it too much of a pain to mill or turn, or part features are too small or delicate for those machines, the shop will wire or sinker EDM it. That way you dont have to worry about a very small cutting tool that just wants to ping right off once it touches the part, he said.
The challenge of cutting cobalt chrome is compounded when the workpiece has hard, abrasive intermetallic compounds in its microstructure. The hard spots are about 58 HRC, said Matt Dahms, founder and president of Oak View Tool Co. LLC. Thats the problem.
To enhance efficiency when cutting medical-grade cobalt chrome, the Columbia City, Ind.-based toolmaker developed the Ortho-Cut CC series of endmills. Oak View Tool also makes CC specials, such as keyway, form and dovetail cutters. The series is designed for cobalt chrome and those types of tough materials that workharden and tear up a typical tool, Dahms said.
Because cobalt chrome can workharden, CC tools have an edge prep combined with an effective shear angle, Dahms explained. Its so tough of a material, you have to hit it with the best of both worlds.
Oak View Tool designed its Ortho-Cut CC series endmills for machining medical-grade cobalt chrome. They are available with corner radii for added rigidity or for matching the size of the part feature.
The endmills also have unequal index geometry to minimize vibration and corresponding chatter. They have a carbide substrate with at least 10 percent cobalt to enhance tool toughness. The tools can be coated with aluminum titanium nitride or ordered uncoated if the orthopedic company has not yet validated the toolmakers coating, Dahms noted. He added that the coating, however, can extend tool life at least 30 percent. The substrate, coating, geometry and edge prep are key, he said. If youve got those four things figured out, you can make the tools work really well.
Jim Hoffman, director of manufacturing for Oberg Medical, Freeport, Pa., emphasized the importance of a tools corner radius. Youre not going to go in there with a sharp-corner tool, he said. It just breaks down too quickly.
To minimize workhardening and the damage it can cause to even a properly designed cutting tool, the tool must be kept loaded and continue to shear the workpiece rather than rub it, according to Hoffman. You have to bite into the material, but you cannot sit there and dwell, he said. You have to stay in the cut.
After machining a few parts for a job, Oberg has captured enough data to understand the process, making it a predictable job, Hoffman pointed out. Operators can then access the tool-life management data and change tools as needed based on the number of parts or minutes a previous tool lasted.
Hoffman noted cobalt chromes abrasiveness dulls cutting edges, but doesnt typically cause them to chip or break. A degraded surface finish is the telltale sign of a worn tool, he explained, adding that most implants require a 20 in. Ra finish off the machine to allow polishing to a 2 in. Ra finish if required by the customer. Oberg regrinds worn tools, but to ensure quality, the company doesnt use them to machine other implants.
The types of tool wear typically seen include abrasive, crater and notch, according to Judson A. Smiths Moser. Abrasive wear is primarily the result of hard particles in the workpiece rubbing or grinding the cutting edge. Crater wear occurs when hard-particle grinding removes tool material from the chip face, and can be remedied by selecting a positive geometry and reducing the speed to lower the temperature in the cut. Notch wear is concentrated at a tools DOC and generates burrs.
Compared to other difficult-to-cut materials, such as 17-4 precipitation-hardened stainless steel, Hoffman said Oberg might cut surgical implant-grade cobalt chrome 40 to 50 percent slower because its more challenging. Generally, the surface speed is about 200 sfm and the feed rate from 0.0004 to 0.005 ipt, depending on the DOC, when applying a 3- or 4-flute endmill.
Cobalt-chrome alloys are available as bar stock and can be cast into complex near-net shapes. The cast blank requires less material removal, but has a tough skin to get through or an inconsistent composition throughout the casting or both, noted Oak View Tools Dahms.
Bar stock is like butter compared to castings, Dahms said. The castings seem to vary, and when its that tough of a material, just a little difference makes a big difference. He added that the tools used for a cast application have stronger edge prep.
Oberg Medical produces an array of cobalt-chrome medical parts. From top to bottom: tibial augments used in knee replacements, a full tibial augment primarily used in total knee-revision surgery, and a trapezium implant used in the hand to replace the joint that controls thumb movement.
Oberg machines cobalt-chrome bar stock and castings and one challenge the company faces is securely holding the castings during machining. The near-net shapes have complex contours and typically there is no flat surface to grasp, Hoffman explained. As a result, the company spends a good deal of time designing and building fixtures to enable rigid workholding.
Hoffman added that Oberg creates the datum structure in the parts so the features that are held are held consistently throughout every step of the operation, including when a part moves from one machine to another. Therefore, variability is not introduced into the process.
Going a step further to ensure repeatability when machining cobalt-chrome and other parts, Moser said Judson A. Smith uses workholding receivers, including ones from Hirschmann, Erowa and System 3R. The receivers can be transferred from machine to machine, such as from a milling machine to a wire EDM, without removing the part from the fixture. You also have the ease of knowing where your datums are and not having to try to find a datum, he said.
When holding the cutting tool itself, Dahms recommends toolholders that minimize total indicator runout when machining cobalt chrome. Shrink fit is the perfect world, he said, adding that high-quality milling chucks are suitable. Those chucks are much better than the standard Weldon-flat, slip-fit holders. Thats out and old school. With the correct tool geometry, tool pullout is not an issue, according to Dahms.
Hoffman agreed that shrink-fit holders work well when cutting cobalt chrome. Everything we machine from the medical side is HSK 63, all Haimer shrink fit, he said. This allows us to maintain a 0.0001 " TIR on our cutting tools, which is vital for achieving fine surface finishes and improved tool life when cutting cobalt chrome.
After a cobalt-chrome chip is produced, its critical to evacuate it from the tool so the heat in the chip doesnt penetrate the tool, Moser pointed out. He added that he judges if the process is creating proper chips by their color and looks for a tan to bluish-black shade.
Radial chip thinning is the effect of taking a radial WOC less than 25 percent of the milling tools diameter. The chip thickness based on the calculated feed per tooth will diminish as the radial width decreases, resulting in a lighter actual feed per tooth. This causes the tool to rub the workpiece rather than cut it, so the feed needs to be increased as the radial depth decreases. The result is a lower temperature at the tool/workpiece interface, a decrease in cycle times and longer tool life.
We do light step-overs with full-flute depths to try to buzz the material off quickly, Dahms said. It gets the surface footage back up to where the heat is right for the coating. Also, we get a high enough feed rate to make parts fast enough, so everybody is excited.
In addition, Dahms promotes using the full-flute length when machining cobalt chrome, and noted Oak View Tool designed the CC series tools to handle that type of cutting. A lot of people do surfacing where theyll use Z-level depths to remove material, he said. We want to get in and out quickly, because every time you use a Z-level depth, youre putting more heat into the part and getting workhardening.
Regardless of the machining methods, cobalt chromes high cost makes scrap unacceptable, and up-front process design is critical to producing good parts, according to Obergs Hoffman. What shouldnt be considered an unnecessary expense is the cost premium for high-performance cutting tools to effectively cut the metal.
You can try to cut tool costs but youll lose money in scrap and just induce more risk in terms of more tool changes and tool adjustments, tool breakage, poor surface finishes and rework. Weve seen all of that happen if not using the right cutting tool, Hoffman said. I tell my guys all the time: Dont step over a dollar to pick up a dime.
Mendell Machines Storlie also understands the value of the right high-quality tool for the job. Getting the proper tool is so critical because, if you dont have it, you might only last 20 parts, he said. With the proper tool, you might get a few hundred parts.
Nonetheless, tool selection is only one piece of the machining system puzzle. What is most important to be successful is to have a robust process that incorporates effective workholding, a solid machining approach and the latest in cutting tool technology, Hoffman emphasized. CTE
When milling understructures for dental restorations, titanium is often the workpiece of choice, but cobalt chrome is another option that offers advantages, according to Felix S. Chung, president/owner of Imagine Milling Technologies LLC, a Reston, Va.-based dental milling center.
Compared to titanium, cobalt chrome infuses more effectively with other materials, such as a ceramic or composites, which covers the understructure and makes the restoration look more aesthetically pleasing. You mimic the natural tooth color, Chung said. Titanium doesnt have very good bonding with porcelain, so some people stay away from using it.
According to Chung, cobalt chrome is also not as challenging to machine as titanium because titanium chips dont effectively absorb and transport heat away from the tool/workpiece interface. This means coolant is typically required. Cobalt chrome, on the other hand, can be machined dry, he pointed out, adding that the company applies a silicone-based cooling agent when producing titanium restorations on its Datron dental milling machine. Theres not a lot of water mixture with it, Chung said, and that [cooling agent] can get very messy.
The majority of the cutting tools used by Imagine for machining cobalt chrome are coated, 2-flute, ballnose endmills, ranging in diameter from 0.5mm to 3mm, with neck lengths from 4mm to 14mm. Spindle speeds range from 15,000 to 35,000 rpm, depending on tool diameter.
In addition to machining titanium and cobalt chrome, Imagine also makes zirconia understructures, which require minimal material to be added because zirconia is similar to ceramic. Regardless of the workpiece material, each understructure has its own unique, organic shape to match the patient.
Las Vegas-based Core3dcentres USA is located near the Las Vegas Institute for Advanced Dental Studies, where restorative and cosmetic dental techniques are taught to practicing dentists and laboratory technicians.
At its facility, Core3dcentres prepares CAD files developed from data typically gathered with an iTero oral scanning wand or CAD files from scans of conventional dental impressions from a patients mouth, which are then digitally captured in a dental scanner. Software is used to image the impression, beginning the process of creating a crown, bridge, abutment, coping, implant or full denture restoration.
The DMG Sauer 20 ultrasonic machine with a robot loader at Core3dcentres has a Siemens Sinumerik 840D sl CNC. The CNC recognizes the workpiece pallet, which is coded by patient name to reportedly eliminate error.
The next step is translation of the digital impression to a RenShape mold, using conventional machine tools. Usually, the required structures are simultaneously designed, and then the mold with coping is sent to the DMG Sauer ultrasonic dental machine for preparation of the final structures. This is where Core3dcentres processes advanced and expensive substrates, such as cobalt chrome, ceramics, lithium disilicate and zirconia.
Tim McKimson, the companys worldwide director of engineering, explained that the decision to cut ultrasonically rather than use other techniques was relatively easy, given the inherent wear conditions and high cost of conventional cutting tools. In the ultrasonic process, a combination of electrolysis and fluid lubrication act in concert to create an ionic attraction of particles, removing material in a predictable and accurate way, without the mechanical stress implicit in conventional machining.
The process is more or less a grinding process, said Dr. Uli Sutor, senior account manager for DMG Vertriebs und Service GmbH Deckel Maho Gildemeister, Pfronten, Germany. He added that the ultrasonic tools move 2m to 4m about 50,000 times a second and only remove material thats sintered or harder than 62 HRC. It is not possible in material like titanium.
In detailing the accuracy of ultrasonic machining, McKimson noted each ultrasonic tool is obtained from a 25-position toolchanger and a Renishaw probe monitors its position. Technicians often load three sets of the tools needed for the 66-piece runs, ensuring virtually 24/7 unattended operation. According to McKimson, accuracies are from 2m to 4m, and process reliability has significantly reduced scrap.
When considering an ultrasonic machine, Sutor emphasized looking at the advantages of the equipment, such as extended tool life, high surface quality and accuracy. If these points are interesting for you, the ultrasonic technology is a step forward for your company.
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CNC surface grinding machine brand: Aba; type: Multiline 1507; year: 1996; description: CNC surface grinding machine; serial number: 208692; details: ; Dead weight: 12,000 kg; Total power: 40 kW; Control system: ...
Surface grinding machine make ABA type FF 625Masch. No: 3325 year 1960gr. Working area: 600 x 250 mmSize of the table surface: 620 x 250 mmTable movement lengthwise: 675 mmTable speed longitudinal: 1 - 30 m / min...
E.P magnetic plate 1250mm x 500mm Workpiece weight 1200kg spindle drive 7,5KW grinding wheel diameter 400mm Folding dresser Oil recooler Paper belt filter PFA 60 Partially overhauled: -linear guides longitudinal ...
Surface grinding machine make ab. Year 1965 grinding range: 500 x 200 mm table clamping surface: 500 x 200 mm grinding wheel size: 200 x 30 x 51 mm weight approx.: 1500 kg dimensions ca .: 1700 x 1050 x 1700 mm d...
Control: ABAmatik 1 N.D. | Freight basis: Delivery ex location. | Grinding length: 1000 mm | Grinding width: 600 mm | Total power requirement: kW | Weight of the machine ca.: 6.500 kg | Dimensions of the machine...
Make ABA mod. FFU 1500/60 New 1988 CNC Abamatic Worker: 1500 x 500 x 600 mm Main motor: 11 kW Equipment: coolant Remarks: table size 1500 x 500 mm, table speed 3 - 25 m / min, Grinding stone 400 x 50 x 12...
Table:: 1020 x 250 mm | Table travel: 675 mm | Grinding width: 300 mm | Grinding length: 600 mm | Type of control: conventional | Type of machine: Surface Grinding Machine - Horizontal | Workpiece height: 560 mm...
with automatic vertical feed, vertical rapid traverse, central lubrication, demagnetising device, wet grinding device, automatic dressing device, stepless cross feed, automatic tip feed, separate hydraulic drive ...
Grinding machines have been known since ancient times. The original manual machines for shaping, sharpening or smoothing are used today as conventional or CNC grinding machines in various industries. Generally, grinding wheels and grinding belts reach higher accuracies than machining with geometrically undefined cutting edges. For this reason, tool grinding machines, circular grinders, surface grinders, bench grinders, etc., are essential for many stages of production for the industry and crafts. At Surplex you will find a great variety of grinding machines and its corresponding accessories such as used grinding wheels, wheel spindles and many more. High quality for the best price!
In the metalworking industry, dimensions need to be precise down to a thousandth of a millimetre. Even a surface that feels smooth to the touch may be far too rough for the intended application. Milling machines and lathes, for instance, can produce outstanding dimensional accuracy, but the final touch can only be applied using an appropriate grinding machine.
This particularly applies to surfaces subject to narrow tolerances: piston tracks in combustion engine cylinders, for example. They need to precisely and securely guide the piston rings within a wide temperature and speed range without jamming, which can only be ensured through use of a metal grinder.
Grinding machines work without tools: all they need is the corresponding abrasive medium, such as types of paper and textiles with an abrasive surface. Grinding stones are also used and consist of a pressed and fired abrasive medium mostly quartz sand. The finer the abrasive medium, the less surface that will be removed per grinding cycle.
And if solid abrasive media are insufficient to achieve the desired dimensions, fluid abrasive agents are another alternative. Wet polishing machines and lapping machines facilitate this type of abrasion.
Polishing and lapping processes are used for achieving the best dimensional accuracy and a consistently smooth surface, which is ideal for galvanising applications, for example. A product can only be galvanised or chrome-plated if it has been polished to a very high sheen.
Round grinding media carriers are used in eccentric and plate grinders. They consist of a circular surface and the media are either moved radially or eccentrically. Radial grinding machines are designed very simply and are affordable.
Grinders with a belt-type abrasive medium carrier are called belt grinding machines. These types of grinder involve a grinding belt being tensioned between a drive roller and one or two tensioning rollers. They are used to remove outer layers from materials consistently and smoothly. Belt grinding machines remove a pre-defined quantity of material per work cycle, which makes it easy to maintain dimensional accuracy by spreading the abrasion process across different work cycles with varying grinding heights. Belt grinding machines are also designed to be simple and are thus easy to maintain.
A metal grinder always consists of cooling lubrication and powerful extraction. The particles removed from the workpiece need to be transported away as quickly as possible since fine metallic dust can quickly lead to heavy wear and tear. This particularly applies to iron-containing dusts, which increase in volume as they corrode and lead to further damage.
Surface grinders are used when an extremely flat surface is needed. They work using a grinding disc that is consistently guided across a workpiece. These machines are key to the tool-building and mould construction industries and can be relied on to achieve the required dimensional accuracy.
Guideway grinding machines, as the name suggests, are used to grind guideways and are deployed wherever very large cutting machines are being manufactured. Mechanical guideways need to be very precise and the guideway grinders on offer today can achieve tolerances of 1/1000 of a millimetre across seven metres of length.
Internal (cylindrical) grinding machines are used to create consistent and accurate internal radii. They work using roll-shaped grinding bodies. The internal grinding machines available today feature computerised numerical control (CNC) and can thus achieve the strictest of tolerances.
Jig grinders feature CN controls and a very small grinding body. They are used to grind away at specific points on a workpiece as required by the respective production process. As such, jig grinders feature a very similar design to CNC mills.
Cylindrical grinders serve to grind profiles, pipes and round steels in a cylindrical manner. Tensioning cylindrical grinding machines use centre tips similar to the tail stocks of lathes. Centreless grinding machines, by contrast, can be used to indefinitely process profiles without any clamping process being required.
Bench grinders are standard grinding tools that are found in every workshop. A bench grinder can be used to sharpen, grind, plane, or deburr a workpiece by hand. They consist of a motor to which one or two grinding discs are attached. They are produced in single- and double-sided variants.
A Roll grinding machines serve to precisely grind press rollers to the desired dimensions. They can be used to grind new, used and freshly turned rollers to achieve the required tolerance. Precision rollers can only be created using a roll grinding machine.
The wide variety of grinders for sale does not make it easy to choose the right device, but there are some general tips that any prospective buyer of a second-hand grinding machine should know. The first consideration is what applications the (used) device should perform a simple bench grinder is incomparable to a complex jig grinder.
A good starting point is to look at the general condition and cleanliness of the machine. Even with comprehensive rinsing and extraction units, grinding machines require a great deal of cleaning daily, thorough cleaning is essential for any frequently used grinder. If the first thing you notice about a second-hand grinding machine is that it is soiled, you should definitely take a very close look at the machine from all aspects.
Unless you buy a metal grinding machine from a trader in used machinery who has taken care of the maintenance and repair tasks, it will be necessary to completely dismantle and clean the equipment. If those intending to repair/maintain a used metal-grinding machine are lacking in qualifications to do so, a specialist service provider should be commissioned.
The weakest points in all used grinding machines are the bearings: the high speed experienced by the grinding spindles, the continual one-sided impact, and grinding heads that frequently lose their shape have a major effect on the bearings. It is therefore important that the bearings are inspected and, if there is the slightest amount of rattling, replaced. Once equipped with new bearings, a used metal grinder can continue operating for thousands of hours to come.
Those looking to buy a used grinding machine will find everything they need at Surplex. We regularly have second-hand grinders for sale. You can purchase machines via our portal where you will regularly find online auctions featuring a wide range of grinding machine types for a variety of needs and at attractive prices. The metal grinders for sale are generally in a good to very good condition.
1. If you breathe in chunks of these materials they get into your lungs and can tear up the lung tissue. This is pure physical damage. In wet grinding it is chunks in the grinding fluid droplets. In dry grinding it is airborne chunks.
Cadmium boils at 1409 degree F. The solder melts from 1170 to 1270 F. The torch runs considerably hotter than this. One other factor is that Cadmium fumes before it boils just as water does. When carbide saws are ground the solder gets hot enough to cause the Cadmium to come out and collect in the grinding coolant.
Chromium is dangerous. It is found in certain carbides in very small amounts. It is a major part of some alloys such as Stellite. Chromes have a very high boiling point. It is mostly a danger during the welding of Stellite onto saws. The welding process is a metal melting process. Melting these alloys causes the fumes to get into the air.
Cobalt is the matrix that holds carbide grains together. It gets into the coolant when saws are ground. It is in the coolant as chunks and it also dissolves into the coolant. A lot of the Stellite type metals also contain cobalt. It is not so dangerous here because it is alloyed with the other metals and does not come out as easily.
Which is most dangerous or least dangerous depends on which agency you are dealing with. The point is that these are all dangerous. Nickel is maybe safer than cobalt unless you are allergic to nickel and not to cobalt.
Breathing Cadmium, Chromium, Cobalt and Nickel as fumes, as dust form grinding or as material in grinding coolant can and will hurt you. Breathing coolant and breathing coolant with metals in it causes short-term health problems and long term health problems.
Cadmium, Chromium, Cobalt and Nickel in grinding mist bother everybody. Dr. Susan Kennedy of the University of British Columbia did a study on filing rooms. She measured saw filers against bus mechanics because the work areas were similar and the people doing the work were similar. Saw filers cough and wheeze and generate phlegm (thick stringy mucous) two to three times as much as bus mechanics do. In addition saw filers wet grinding tungsten carbide and filers welding Stellite had reduced lung capacity. They could not breathe as deeply or as easily. This part bothers everybody the way smoke from a campfire bothers everybody.
A certain percentage of the population has an allergic reaction to Cadmium, Chromium, Cobalt and Nickel. When inhaled, these metals can kill people slowly and horribly. Cadmium, Chromium, Cobalt and Nickel get into the lungs and scar the lungs. They tear up the lung tissue. The lung tissue then forms scars like scars form on the outside of your body. Lung tissue scars do not allow for breathing. Eventually more and more of the lung gets scarred and it is harder and harder to breathe until the person dies. This is more like the way that smoke from a campfire bothers someone with asthma.
Chromium, Nickel and Cobalt get into your lungs when you breathe in grinding coolant or welding fumes. Chromium, Nickel and Cobalt are in grinding coolant in two ways. They get in as really little particles in size from one -- one thousandth (1/1,000 or 25 microns) of an inch down to one --twenty five thousandth (1/25,000 or one micron) of an inch. They also dissolve in grinding coolant and get into your lungs that way.
It is pretty easy and simple to get much cobalt out of grinding coolant. If you run coolant through a clean filter you can get out up to 90% of all cobalt. This depends on the filter, the coolant and the whole system. The 90% figure is what we found in our actual tests.
Do not splash grinding coolant any harder or further than you have to. What happens is that grinding coolant is sprayed onto the work as a liquid then the splashing breaks the liquid up into very small drops (aerosols) and this is what you breathe.
There are other materials in grinding coolant that can be dangerous. There are bits of diamond or CBN from the wheel; there is resin from the wheel and chunks of broken carbide as well as just general grit and dirt. We found that there could be up to 75,000,000 or 80,000,000 pieces of crud in a cubic centimeter. This would be 150,000,000,000 (150 billion) particles in a two liter soda pop bottle. Filtering can get out over 99% of these particles.
Twenty years ago I could put my kids and the neighborhood kids in the back of the pickup and take them for ice cream. Not only was it legal but I was a good Dad for doing it. Now the state of Washington requires that all dogs in the back of a pickup be anchored to both sides of the bed. Dogs and kids and pickups havent changed but the attitude of society and thus the law have changed.
People come in an amazing varsity of sizes and shapes. This reflects their internal chemistry and gives some idea of the range of individual sensitivities to things like sunburn and industrial chemicals.
You take 200 rats. 100 you leave alone. The others you start testing. You feed them a chemical, subject them to a loud noise or fumes or heat or almost anything. When you find a dose that reliably kills half the rats you have an LD50 (lethal dose of 50%) This is sort of how they get the LD50 figure on MSDS sheets and other.
Lab rats arent people. However you can gain meaningful data anyway. If you hit your hand with five different hammers and they all hurt then you can pretty well guess that the sixth hammer will hurt as well. Something that kills rats is more likely to be dangerous to people than something that doesnt kill rats.
It is statistics and statistics works best in large numbers. Statistics makes almost no sense in an individual case. You can pretty well bet that a coin flip will come up heads half the time if you flip it often enough.
Chemicals have to be breathed, eaten or absorbed through the skin to hurt you. You can control breathing by face masks or by air collection. Personally I prefer air collection. The initial cost is higher but it works much better and it protects the equipment as well as he operator. Clean air can well pay for itself by extended equipment life.
United Air Specialists (800) 551-5401 Cincinnati, Ohio Invented the original smoke eaters for bars, etc. Good equipment good literature and great technical help. Recommended for literature. http://www.uasinc.com/
Dr. Susan Kennedy, at the University of British Columbia has recently done industrial hygiene surveys that indicate that the problems with cobalt exposure in coolants are much greater than the government recognizes.
There is a problem with dissolved cobalt. It causes hard metal disease. (Hard metal diseases are different from heavy metal diseases although both are often linked to industrial practices.). According to Ed Chessor of the British Columbia Workers Compensation Board, about 1 or 2 % of the population is particularly susceptible to cobalt. Others have put the figure much higher. They are in much greater danger than the average person is. This is somewhat similar to the fact that some people are much more susceptible to damage from bee stings.
The safety and health issues are incredibly important and very complex. If you have any concerns you should call in a consultant from the government or a private consultant to do a hypersensitivity reaction to inhalation of particles of hard metal. Hard metal is a material composed predominantly of tungsten carbide (WC) and cobalt (Co). Hard-metal lung disease occurs mainly in workers engaged in the manufacture of hard metal, but also in workers engaged in resharpening hard metal tools (saws, drilling tips, etc.). Hard metal lung is sometimes labeled as cobalt lung, because cobalt is probably the critical offending agent in hard metal and because the same disease has also been described in diamond polishers who use polishing disks made of diamond cobalt (i.e. not really hard metal).
Unlike most other mineral pneumoconioses, hard-metal lung does not appear to be caused principally by the reaction of excessive dust accumulation in the lungs, but it presents many features of a hypersensitivity reaction. Consequently, hard-metal lung may occur in young subjects with relatively short exposure histories. It may present (sub)acutely, with work-related clinical and radiological features similar to those of hypersensitivity pneumonitis (extrinsic allergic alveolitis). However, hard metal lung differs from hypersensitivity pneumonitis in its pathology, which is characterized by the presence in the lung interstitium and the alveolar spaces (and hence in the bronchoalveolar lavage) of 'bizarre' multinucleated giant cells with 'cannibalistic' features thorough analysis.
Comments Hard metal disease is a "giant cell interstitial pneumonitis" that affects a small minority of workers who manufacture or use high-speed tungsten carbide saw tips, drill tips, or discs. These tools are used to polish diamonds and to cut hard materials such as metals, hardwoods, and cement. The workers are exposed to fume or dust from the cobalt used as a binder in the cemented tungsten carbide metal. The usual symptoms are dyspnea on exertion, cough, and fatigue. The chest x-ray may show infiltrates, and the pulmonary function test may reveal a restrictive defect. The same workers are at risk for cobalt-induced asthma.
Symptoms/Findings associated with this disease: chest tightness, clubbing, cough, diffuse infitrates, interstitial pattern, dyspnea, exertional fatigue, inspiratory rales, restrictive defect, sputum production, weight loss
Cobalt In Tungsten Carbide Is Different Than Cobalt In Talonite , Stellite , Etc. Cobalt is the same in both uses but in Talonite it is chemically locked up to other elements while in tungsten carbide it is unlocked and can move freely.
Atoms have electrons that work sort of like the hooks and loops in Velcro. If the two halves of Velcro as separate then it can pick up fuzz, etc. If the two halves of Velcro are pressed together then it wont pick up anything.
In tungsten carbide cobalt is used as a binder as pure cobalt. It melts and glues the carbide grains together like hot melt glue holding marbles together. It never reacts with anything so it still has the capacity to react.