Conical Screen Mills (also referred to as Cone Mills) are gentle size reduction mills which are often used to precondition the material prior to its entry into a process, either by delumping or coarse size reduction. These mills utilize a rotating propeller/stationary screen combination to gently compress material against the screen wall and size the material accordingly. Vacuum conveying is often used to move material through the conical screen mill, help improve overall throughput of the process, contain dust or exposure, and also to assist in improvement of end product quality.
Dilute Phase Principle
Typical dilute phase conveying operations involve materials where segregation in the conveying line is not a concern. Comparative velocities in a 3" pipe for dilute phase can range from 15 m/sec. (3000 ft/min) up to 35 m/sec. (7000 ft/min).
In many cases the conveying medium is air. However, in the pharmaceutical industry nitrogen is often used due to the relatively low volumes of gas used to convey relatively short distances. Nitrogen offers two benefits: it can inert the process when conveying highly explosive materials, and it is a naturally pure gas which does not need added filtration. As an alternative to the vacuum pump, a venturi can also be used for applications that require short conveying distances and minimal lift requirements.