Several types of ball mill drives can be furnished, made up of various combinations of gearing, motors and transmission equipment. The correct combination to be selected takes into consideration power requirements, gear ratings, floor space, interference from other plant equipment and motor characteristics. The main types are described and illustrated on these pages.
Motors considered are the squirrel cage motor, wound rotor motor, and synchronous motor. One important advantage of the synchronous motor is the possible correcting of power factor within your operation, through its use. When using a synchronous motor we recommend having 200% starting torque, 120% to 130% pull-in torque, and 225% pull-out torque. These assume no greater than a 10% voltage drop at the motor terminals.
V-belt or poly-V drives are generally used on grinding mills consuming 350 HP or less. Where power exceeds this, drives become so large and motors become special, resulting in an uneconomical application. Generally the driven mill sheave is of split hub construction to facilitate field assembly. V-belt drives allow use of higher speed motors, generally low in initial cost. Motor speeds should be between 580 and 1160 rpm. The lower speeds apply to large diameter mills, the higher speeds to the smaller.
When power exceeds 300 HP a direct connected drive is recommended. This drive is also applicable for lower power requirements if desired. Synchronous motors are preferred, but in some cases wound rotor motors may be used. Motor speeds will vary from 225 rpm to 450 rpm.
The motor and pinion shafts are connected together through a flexible coupling. This drive is the most compact, resulting in minimum floor space. In cases where motors must be placed away from the mill a pilot shaft extension with flexible couplings can be provided.
This is essentially a direct connected drive permitting the use of higher speed motors. The motor shaft is connected to the high speed shaft of a reducer by a flexible coupling and similarly the low speed shaft and pinion shaft are coupled.
Any direct connected drive necessitates perfect alignment of all rotating shafts. With Marcy Mills the pinion shaft is fixed in position. Any gear adjustments are made by moving mill gear into proper mesh with the pinion.
The basic parameters used in ball mill design (power calculations), rod mill or anytumbling millsizing are; material to be ground, characteristics, Bond Work Index, bulk density, specific density, desired mill tonnage capacity DTPH, operating % solids or pulp density, feed size as F80 and maximum chunk size, productsize as P80 and maximum and finally the type of circuit open/closed you are designing for.
In extracting fromNordberg Process Machinery Reference ManualI will also provide 2 Ball Mill Sizing (Design) example done by-hand from tables and charts. Today, much of this mill designing is done by computers, power models and others. These are a good back-to-basics exercises for those wanting to understand what is behind or inside the machines.
W = power consumption expressed in kWh/short to (HPhr/short ton = 1.34 kWh/short ton) Wi = work index, which is a factor relative to the kwh/short ton required to reduce a given material from theoretically infinite size to 80% passing 100 microns P = size in microns of the screen opening which 80% of the product will pass F = size in microns of the screen opening which 80% of the feed will pass
Open circuit grinding to a given surface area requires no more power than closed circuit grinding to the same surface area provided there is no objection to the natural top-size. If top-size must be limited in open circuit, power requirements rise drastically as allowable top-size is reduced and particle size distribution tends toward the finer sizes.
A wet grinding ball mill in closed circuit is to be fed 100 TPH of a material with a work index of 15 and a size distribution of 80% passing inch (6350 microns). The required product size distribution is to be 80% passing 100 mesh (149 microns). In order to determine the power requirement, the steps are as follows:
The ball mill motorpower requirement calculated above as 1400 HP is the power that must be applied at the mill drive in order to grind the tonnage of feed from one size distribution. The following shows how the size or select thematching mill required to draw this power is calculated from known tables the old fashion way.
The value of the angle a varies with the type of discharge, percent of critical speed, and grinding condition. In order to use the preceding equation, it is necessary to have considerable data on existing installations. Therefore, this approach has been simplified as follows:
A = factor for diameter inside shell lining B = factor which includes effect of % loading and mill type C = factor for speed of mill L = length in feet of grinding chamber measured between head liners at shell- to-head junction
Many grinding mill manufacturers specify diameter inside the liners whereas othersare specified per inside shell diameter. (Subtract 6 to obtain diameter inside liners.) Likewise, a similar confusion surrounds the length of a mill. Therefore, when comparing the size of a mill between competitive manufacturers, one should be aware that mill manufacturers do not observe a size convention.
In Example No.1 it was determined that a 1400 HP wet grinding ball mill was required to grind 100 TPH of material with a Bond Work Index of 15 (guess what mineral type it is) from 80% passing inch to 80% passing 100 mesh in closed circuit. What is the size of an overflow discharge ball mill for this application?
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Ball mills are a special instrument used to break up hard solids into a fine powder. They are similar to rock tumblers in that the instrument is a rotating container filled with heavy balls to grind the substance into powder. Ceramic material, crystalline compounds, and even some metals can be ground up using a ball mill. Using a motor, container, belt, caster wheels, and some basic building supplies, you can make your own ball mill. X Research source
To make a ball mill, start by building a wooden platform and attaching a motor underneath it. Then, cut a slit into the wooden platform for the belt to pass through and attach casters to the platform for the container to sit on. Next, thread the belt through the slit and position the container so the belt is pulled tight. Finish by connecting the motor to the power supply, and filling the cylinder with metal balls and the substance you want to grind. For tips on how to operate your ball mill, read on! Did this summary help you?YesNo
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Menzel was to supply a spare slip ring motor for a cement plant in Canada and had to meet very exacting requirements. This was the third order of motors that this Canadian system integrator has recently placed at MENZEL. The new slip ring motor must be able to replace three existing crusher motors in case of a failure. To ensure smooth commissioning at the installation site, which is characterized by very tight space restrictions, Menzel's project manager took the measurements in Canada himself.
Menzel chose a 4.5 MW slip ring motor from stock and built an extended shaft. Furthermore we fitted special adapter plates with mounting holes for all three locations as well as brackets for plug and play mounting of vibration sensors for condition monitoring. The custom-made adapter plates were made in our in-house welding shop, which allows flexible production of special components and custom-made welded designs at all times. In addition, the terminal box of this spare slip ring motor was fitted with long feeder cables to facilitate the third-party connecting-up.
Through our many years of experience in the manufacturing of cement mill motors, we are familiar with a wide variety of requirements and can advise customers from the industrial cement sector around the world. MENZEL electric motors are being operated in numerous industrial plants, not only cement plants. Further reference projects from the industrial cement sector and others can be found here.
Menzel offers a comprehensive range of larger electric motors for the industrial cement sector. As a manufacturer of electric motors, we place our customers and their individual requirements at the heart of the focus of our engineering work. Our service packages covers far more than just delivering the correct drive. We also offer a wide range of services including support, maintenance, commissioning, consultancy, and logistics. We follow a clear objective, which is to be available to our clients at all times:
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