Metal finishing is the final step in the manufacturing process used to provide aesthetics and environmental protection. It is also used to reduce surface roughness beyond the capabilities of machining operations for parts that must mate or seal. It also includes methods of metal cleaning, descaling, deburring, etc. In short, numerous types of metal finishingprocesses are used for a variety of purposes. This guide reviews some major finishing methods, as well as applications and considerations for choosing a metal finishing process. Some of the general advantages of metal finishing treatments include:
Metal plating uses chemical baths to coat or alter the surface of substrates with thin layers of metal such as zinc, nickel, cadmium, or chromium. The electroplating method generates an electric current to coat the substrate, while electroless plating employs an autocatalytic process in which the substrate catalyzes the reaction. As plating is a chemically intensive, large scale process, it is almost invariably performed by plating service providers who specialize in the field.
Metal plating can improve a products durability, corrosion resistance, surface friction, and exterior appearance. In the case of galvanized metal, the zinc plating serves as a sacrificial anode, itself corroding while protecting the integrity of the underlying substrate. However, plating machines are generally not suited for smoothing out surface defects.
Sherardizing is a process used to coat small steel parts such as bolts and washers with a corrosion-resistant zinc-iron alloy. Parts are tumbled in a heated drum containing zinc dust, producing a highly corrosion-resistant finish. In high-volume production runs, a barrel-finishing machine is a fast and efficient coating solution.
Unlike plating, metal finishing with brushes is an effective method for removing surface imperfections. These finishing machines create a uniform, parallel grain surface texture to smooth out a products exterior. An abrasive belt or wire brush is usually employed to achieve this effect. In addition, the singular direction of the belt or brush can create slightly rounded edges perpendicular to the grain.
These abrasive methods are used to reduce surface roughness in metals after machining. Roughness is measured in micro-inches with about the most exacting machining processes (reaming, broaching) producing surface finishes of 16-125 -in. Precision or fine grinding (see below) can reduce surface roughness to 8-16 -in. using abrasive wheels or mounted points. Beyond that, abrasive powders are used in combination with leather or felt wheels to polish (1-32 -in.) and buff (0.5-16 -in.) as required. Honing and lapping use abrasive compounds to improve the surface roughness of mating parts by rubbing them against each other (such as lapped engine valves) or running a mating shape through a hollow (such as a honed cylinder).
The process that reduces surface roughness also increases a metals luster as reflected light is scattered less from smoother surfaces. Thus, these same methods are often employed simply for improving surface aesthetics.
Grinding machinesuse abrasive wheels to smooth out surfaces. There are several types of grinding machines designed to deliver different levels of finite smoothness. As noted above, grinding is used to reduce surface roughness left over from machining and as a final step in the machining process to close in on a tolerance. A surface grinder is the most common form of grinding machine but there are numerous specialty grinders such as centerless grinders and Blanchard grinders in everyday use as well.
Numerous varieties of hand grinders are used for metal removal, slag cleaning, etc. Die grinders are employed for detailed work in passages of intake manifolds, dies, etc. These are commonly fitted with special shaped abrasive wheels known as mounted points.
Vibratory finishing machines are used to deburr products and remove sharp edges, sprue, etc. They position parts inside a drum filled with abrasive pellets and apply tumbling vibration to create a uniform random texture. The machines cycle speed and magnitude of vibration are usually variable, allowing effective treatment for a range of small- to large-sized parts.
Blast machinery, such as sand-blasting machines, is typically employed in projects requiring a uniform matte texture. The sandblasting process (also known as bead blasting) forces sand, steel shots, metal pellets, or other abrasives onto a substrate at high speed. This results in a smooth, clean product texture, particularly in soft metals.
Shot peening is a blasting method used to impart compressive stress in the surface of metals as a way of improving fatigue resistance, stress corrosion cracking resistance, fretting resistance, etc. The cold working process imparts compressive stress to surfaces as a way of countering tensile stress induced during manufacturing. Burnishing is another cold-work surface modification method used to impart compressive stress for fatigue resistance.
An important step in many metal manufacturing operations is heat treatment, which is used to procure desirable characteristics in the material after its finished shape is attained. For example, after gears are cut they are usually hardened through an inductive or flame heating process to increase wear resistance at the teeth surfaces while improving the strength of the underlying teeth. Hardening usually applies a quenching operation which is a critical step in transforming the grain structure of the metal. Case hardening is used on the shackles of padlocks, for example, to produce a shell that resists mechanical attack. Heat treating is applied too to remove any residual stresses left by manufacturing. Nitriding is another surface hardening process which can be done below the transformation temperature of steel, eliminating the need for quenching and any part distortion that could result.
Water- and oil-based paints are used to provide inexpensive protection to metals against corrosion. Special paints are available for harsh environments, such as anti-fouling paints for marine applications.
Powder coating applies a decorative finish that is similar to paint but with greater durability. The process involves UV or heat curing of dry thermoplastic or thermosetting polymer powder onto the metal to produce a textured, matte, or glossy coating. It is an electrostatic process wherein a charge placed on the substrate attracts the powder particles to it. A textured powder-coat finish is highly effective in hiding surface defects.
Hot blackening machines spread a thin layer of black oxide onto a products surface to create a matte black finish with high abrasion resistance. It is a high-temperature hot finishing process in which the product is inserted into a series of tanks containing cleaners, caustics, and coolants. Hot blackening is most commonly used in the production of automotive parts, tools,and firearms. Bluing is a subset of black oxide coating that is used to protect steel from corrosion.
This article presented a brief discussion of the different types of metal finishing. For more information on other products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.
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Cement is a finely milled mineral powder, usually grey in colour. The most important raw materials for the production of cement are limestone, clay, and marl. Mixed with water, cement serves as an adhesive to bind sand, gravel, and hard rock in concrete. Cement hardens both in the air and under water, and remains in its hardened state once reached.
Cement is usually available in the form of a homogeneous bulk dry good. Its characteristics are standardised in order to ensure the required stability, reliability, and processability in the application.
Cements are classified according to their early and final strength as well as their composition. In addition to cements that consist of 100% clinker, there are so-called composite cements, in which a portion of the clinker is replaced by alternative raw materials, such as fly ash, ground slag, or limestone. As the production of clinker is energy-intensive and releases large amounts of CO2, the use of alternative raw materials can conserve natural resources and reduce CO2emissions.
Depending on the desired application, different types of cement each with a specific composition are necessary. Cement characteristics can also be modified through the use of additives. We offer our customers a broad range of cement products, including quality cements, special cements with targeted characteristics, special geotechnical building materials and an expanded range of binders. Our product portfolio varies from country to country.
In 2020, cement and clinker sales volumes fell by 3.1% to 122.0 million tonnes (previous year: 125.9). With the exception of Africa-Eastern Mediterranean Basin, all Group areas recorded declines in sales. Countries in Northern Europe and Asia were most affected, followed by Western and Southern Europe and North America. As part of our portfolio optimisations, we expanded our market share in Morocco in 2020 by purchasing a grinding plant with an annual capacity of 0.5 million tonnes. In Bangladesh, we had already purchased a grinding plant with an annual capacity of 0.6 million tonnes in 2019.
In contrast, we sold our business activities in Mauritania in the reporting year. In 2019, we sold our activities in Ukraine, two cement plants and two grinding facilities in Italy, and the white cement plant in Egypt.Excluding these changes to the scope of consolidation, cement and clinker sales volumes in 2020 were 2.6% below the previous year.
The consumption of rechargeable batteries has been increasing rapidly. High demand on specific metals for battery manufacturing and environmental impacts from battery disposal make it essential to recycle and retrieve materials from the spent batteries. There have been some review articles on battery recycling, mostly on the technologies for the materials recovery and some on life cycle assessment (LCA). To develop a truly sustainable battery industry, however, battery recycling must be commercially viable. Yet, very limited information on the economics of battery recycling is available. This paper examines technologies and research efforts in battery recycling from the perspective of economic viability and life cycle inventory. With the support of up-to-date statistics, the paper also comments on the challenges facing battery recycling, and the role of battery design and circular economy in the sustainable development of battery industry where governments, manufacturers and consumers all play a part.