Pit & Quarry, January 2018
SCREENING W hen the general population thinks of screens or sieves some people think of a small child at the beach using a screen to sift through sand to find seashells or other hidden treasures When it comes to rock screens for the aggregate industry however they really are quite technical and scientific THE ROLE OF SCREENS In actuality rock screens are vitally important to any company that deals with rock crushing Crushers wont crush rocks to a consistent size every time Once rocks are crushed theyre going to run through a screen for two reasons First you want to get the sizes you need Second they are used to either wash or dewater material The rock itself is filtered and isolated to the correct size to meet the customers specifications for base asphalt or concrete One quarry might make a lot of product specifically for concrete while another quarry might focus heavily on making product of a smaller size for asphalt At yet other times a quarry might need the flexibility to make both Furthermore customer product specifications are becoming even tighter meaning smaller margins of error and can vary widely even across very geographically similar markets For these reasons among others aggregate producers must understand the significance of the rock screen to the success of their operation FROM CRUSHER TO SCREEN At their simplest rock screens are made up of a screen box a specific amount of screen decks screen media and a vibrating mechanism that shakes and moves rocks through the screens The wearable layers that size the material and protect each deck inside the screen box are called media Media is the screen metal cloth rubber or polyurethane that have specified openings allowing stone to either be passed through or discharge over the decks All of those openings will be set to a certain size that will achieve the dimensional threshold that the quarry needs per product The process starts when the rocks that pass through the crusher land on a conveyor belt that takes the material up to whats called a screen tower The rocks drop onto the screens and the physical screening begins The most typical screens used in a quarry are inclined set at a 20 degree angle The rocks fall into the feedbox at the top of the screen and then cascade onto the first screen deck S6 PIT QUARRY January 2018 pitandquarry com PHOTO COURTESY OF MELLOTT COMPANY A starters guide to SCREENS and SCREEN MEDIA Why rock screens are essential to your rock crushing company BY CHRIS ANDREWS
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