Posted by Chuck Awot on August 28, 2000 at 00:18:50:
In Reply to: Powdered metal hobbs posted by Don Jensen on March 05, 1999 at 12:56:01:
Most of the larger hob manufacturers in existance today, offer high speed steels made from "PM" or powder metallurgy type tool steels. The major manufacturer of this type of steel in the U.S. is Crucible steel, which is a division of Colt Industries. Their specific process is known as the CPM, or "compacted powder metallurgy" process. As I understand it, this is a proprietary process, where the molten tool steel is poured through a series of high pressure air jets, and causes the steel to rapidly solidify into small homogeneous particles. This is similar to what happens when lead is poured through a shot tower, to form buckshot. The particles are collected into a cylinder, which is then subjected to a hot isostatic compression which causes the particles to adhere to each other, and form a solid billet of tool steel. What is different between this, and a standard tool steel poured billet, is that the structure of the steel produced by the CPM process is totally the same throughout, unlike what you normally see in a standard tool steel, where you often get migration of the carbides in the steel. Chemically, a standard tool steel such as M4 is identical to CPM M4. Where the big difference lies is in the structure of the steel. Usually a CPM tool steel will have a much higher "Red Hardness" than a standard tool steel, and it will have a much greater resistance to heat and wear. If you need a good souce for "PM" type hobs, contact me at firstname.lastname@example.org and I can help you.
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