tips for specifying a pin mill
A pin mill is one of the most commonly used impact mills for grinding bulk solid materials to medium fineness. The mill can accept feed materials with a particle size from 20 microns to 0.5 inch and a Mohs hardness up to about 4, reducing them to particles as small as 10 microns, depending on the mill type and feed size. This versatile machine handles a wide range of materials; some typical examples are hydrated lime, sugar, wet corn slurry, food ingredients, and fertilizers.
By specifying the right components and operating features for your pin mill, you can not only optimize the mill to reliably grind your material to the desired fineness but reduce equipment downtime for parts replacement and repairs. This can help your mill yield a final product with a very fine or homogeneous particle size distribution, stand up to an extremely abrasive or corrosive material, or safely reduce a heat-sensitive material without damaging it.
Your best source of help in specifying the mill is the pin mill supplier. With many years experience in supplying units that can successfully handle tough materials and operating conditions, the supplier can help you determine what it will take to keep your pin mill running smoothly with minimal downtime. Before you specify the mill, it's always a good idea to have the supplier test your material in pilot mills equipped with different pin configurations and construction materials, components made of appropriate wear- or corrosion-resistant materials, and other options. Running the test will typically require from 400 to 1,000 pounds of your material, depending on the results you need.
Once you have the test results in hand, you're ready to work with the supplier to specify a pin mill for top grinding performance with minimal maintenance downtime. Here are three practical tips for specifying your mill.
Specify the right number and arrangement of pins.
Selecting the right number of pins and the appropriate pin arrangement (typically in rows) for your pin mill discs can not only help produce the final particle size distribution you need, but help control the narrowness of that distribution to meet your product requirements. The right number and arrangement of pins can minimize material buildup in the mill during grinding, reducing washdown requirements and the associated downtime. Careful pin specification can also reduce the amount of heat generated during grinding, helping you avoid heat-related material buildup problems and softening or melting of heat-sensitive particles or other particle damage. Rely on your pin mill supplier's experience for help determining what number and arrangement of pins are best for your application.
Specify high-quality wear parts and appropriate options for your application
Any internal mill surface in contact with the material during grinding is subject to wear, and in a pin mill this includes the pins, the wear plate (that is, the disc surface on which the pins are mounted), the rotor, and the impact wall at the disc periphery. These parts can also be subject to corrosion if your pin mill handles a corrosive material.
Halting your grinding process to replace parts is costly; the lost production, maintenance labor cost, and parts cost can quickly add up. Choosing high-quality parts made of an appropriate wear- or corrosion-resistant material will reduce the replacement frequency and maintain your product quality while minimizing downtime and maintenance costs.
You can specify any of several construction materials for the pins, wear plates, and impact wall so they can resist wear and corrosion. Common wear-resistant materials include the following, ranging from those for less abrasive to more abrasive particles: mild steel, 40-RC (Rockwell C) tool steel, 60-RC case-hardened tool steel, chrome-oxide-coated 60-RC case-hardened tool steel, chrome carbide, tungsten carbide coating, and tungsten carbide. Corrosion-resistant materials include Type 304 and Type 316 stainless steel and special deep surface treatments like Stellite and other coatings.
Order wear parts to keep on hand.
Stocking spare wear parts — pins, wear plates, impact walls, and rotors — in your plant's maintenance department will save you time and money by keeping your parts-replacement downtime to a minimum. Keeping parts on hand eliminates the time required for ordering parts from the pin mill supplier. While it's true that most suppliers stock critical spare parts for fast delivery to their customers, most of your pin mill's wear parts are likely to be specified for your unique application, so your supplier probably won't have all the parts you need for immediate delivery.