These secondary collisions cause more destruction and decelerate the particles. The screens are fitted in close tolerance to the hammers, providing a web into which accelerated particles collide. As the rotor spins, hammers affixed to support pins at its circumference extend outward, striking particles introduced through the machine’s inlet. A hammermill, for instance, includes a grinding chamber defined by a rotor fitted inside one or more screens (Figure 1). While milling machines vary from one type to another, the screens they use serve a common purpose: 1) to retain material in the grinding zone and 2) to provide additional cutting/impact surface. This article will discuss the various aspects of screen selection along with their effect on mill performance, providing end users with a foundation to make informed choices when optimizing their equipment.

Typically, this screen is chosen by the original equipment manufacturer based on application experience and testing. The market offers a variety of machines for size reduction, and many of them utilize a screen to aid in the size-reduction process. For example, granular sugar can be pulverized into a powder, improving texture for use in icings, while scrap wood can be shredded then reduced through one or more hammermilling steps to manufacture secondary products such as oriented strand sheeting or particle board. Bulk solids processing often includes one or more size reduction steps to improve a material’s value or functionality.

Bulk safety pins