İhsan Gökhan Serin - 503111309 - 4th Week's Unanswered Words

Impact Milling (Size Reduction Operation) 

Previous Answer:

In Impact milling, metal particals are driven against a metal target using a high velocity gas stream. A blocky powder particle is produced that has less tendency to align preferently during powder compaction than those produced by ball or attrition milling. When the powder is compacted under heat and pressure, it is more uniform, resulting in greater ductility. Since the low ductility of metal has always been a concern, improvements in room temperature ductility have been achived by control of preferred orientation, improved purity, reduction of

insclusions, control of inclusion distribution, and by reducing grain size.


(Campbell F.C., Manufacturing Technology for Aerospace Structural Materials, 2006, p. 112)

New Answer: (Better)

Whether your material must be reduced to a particle size measured in millimeters or microns, there is a machine that can handle the job. This article introduces size reduction methods and describes common examples of equipment based on each method.

Most powders that are part of our everyday lives -in the medicines we use, the foods we eat, and the plastic parts in the appliances and computers we operate - start out as larger particles or agglomerates that must be reduced to a specified size. But each dry bulk material has its own characteristics, and those determine which type of size reduction machine is suited to reducing it. Dry bulk materials can be reduced by equipment based on one of three methods: shear milling, compression milling, or impact milling.  Shear milling produces relatively larger particles. Compression milling produces smaller particles, and impact milling typically produces the smallest particles. However, impact milling is the most energy-intensive. In fact, the smaller the particles you need, the more energy you will typically use to produce them.

(Kıran D. Patil, Mechanical Operations Fundamental Principles and Applications, pg. B12)

Impact milling occurs when a hard object that applies a blunt force across a wide area hits a particle to fracture it. This milling action is produced by a rotating assembly that uses blunt or hammer-type blades. Another type of impact mill is a jet mill. A jet mill uses compressed gas to accelerate the particles, causing them to impact against each other in the process chamber. Impact mills can reduce both fine powders and large chunks of friable material such as pharmaceutical powders, sugar, salt, spices, plastics, coal, limestone, chemical powders, and fertilizer — down to 50 microns with mechanical impact mills and less than 10 microns with jet mills. Mechanical impact mill types include hammermills, pin mills, cage mills, universal mills, and turbo mills.

(Scott Wennerstrum, Size Reduction Solutions for Hard-To-Reduce Materials, Powder and Bulk Engineering Magazine, pg. 1)

Roll Crushing (Solid Waste Seperating Process ) 

Previous Answer:

This process is used in material recovery operations to grind brittle materials such as glass and flatten malleable materials such as metal cans and plastic bottles. This allows for subsequent separation by screening. Roll crushers were first employed for the reclamation of materials from incinerator residue and more recently are being used to process source separated recyclables, mainly glass containers and aluminum and steel cans. Once crushed this mixture can be sorted using screens and magnets, the material remaining being aluminum cans.

(McDougall F.R., White P.R., Integrated Solid Waste Management: A Life Cycle Inventory, p.232) 

New Answer: (Better)

Roll crushers are used in resource recovery operations for the purpose of crushing brittle materials (such as glass) while merely flattening ductile materials (such as metal cans), hence allowing for subsequent separation by screening. Roll crushers were first employed in materials recovery facilities for the reclamation of metals from incinerator residue and have found use in processing partially source-separated refuse composed of glass containers and aluminum and steel calls.

A variation of the roll crusher is the roll crusher/perforator. Curbside recycling programs typically collect PETE (soda bottles) and HDPE (milk containers) from residents. Even though instructed not to, some residents Screw the lids back onto the empty containers. When these containers are baled, they then do not compress and can cause problems with the finished bales. To solve this problem, some processors have placed roll crushers/perforators In front of the baler. Puncturing the container prior to balling eliminates problem.

(William A. Worrell, P. Aarne Vesilind, Solid Waste Engineering, pg. 192)