The Differences (And Similarities) Between Coarse Material Screw Washers And Blade Mills

July 18, 2019
While they look about the same when completed in one of our manufacturing plants on the shop floor, Coarse Material Screw Washers and Blade Mills are different when installed in a washing plant.

Both Coarse Material Screw Washers and Blade Mills are used for washing rock and ore that have soluble mud and clay contaminants that can't be cleaned solely by a wet washing vibrating screen. How one is installed compared to the other depends on the downstream processing and if -4 mesh or 5mm fines need to be scrubbed or washed too.

Coarse Material Screw Washers

Coarse Material Screw Washers are used for washing coarse fractions only, meaning the fines (such as sand-sized material) have been removed by screening ahead of the unit. 


These machines are typically installed on a fairly steep incline, sort of like a sand screw, allowing dissolved silts and clays to overflow. In some instances, if already sized, this rock fraction can be directly conveyed to a stockpile. 

In a lot of instances, it is recommended that a Coarse Material Screw Washer product is further rinsed and sized (the latter if needed) on a wet vibrating screen, and then conveyed to finished product stockpiles.

Coarse Material Screw Washer shafts typically have one screw flight with replaceable wearing shoes at the feed end, followed by scrubbing paddles in the submerged pool/washing portion of the washer box. The remainder of the shaft consists of spiral flights, again having field-replaceable wearing shoes, that convey material to the machine's discharge.


Screw shaft speeds on these units are pretty consistent for most applications, turning at 250 to 280 feet per minute or 1.2 to 1.4 meters per second.

Capacities of the smallest single-shaft to the largest twin-shaft Coarse Material Screw Washers range from 35 to 550 metric tons per hour that can process feeds up to 4" or 100mm in size. 

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Blade Mills

Blade Mills are positioned fairly level in comparison to Coarse Material Screw Washers, ranging from 0 degrees to 5 degrees. As a result, with the addition of water to the solids feed and the discharge being in a slurry of about 65% to 75% solids by weight, these units must discharge to dewatering equipment, as there is no overflow of dissolved fines. 


This allows for many Blade Mills to be used as a top-size-feed-controlled sand and rock washing unit. There are a lot of units in the western United States where sand equivalency standards (often referred to as SE) are improved, allowing standard sand washing and dewatering afterward. 

Blade Mills have more paddles than Coarse Material Screw Washers. They have an alternating combination of screw flights and paddles the entire length of the shaft that provide the attrition and scrubbing action. 


Capacities of the smallest single-shaft Blade Mills to the largest twin-shaft Blade Mills range from 40 to 600 metric tons per hour than can process feeds up to 4" or 100mm in size. In some applications, higher capacities can be achieved with a paddle/screw shaft speed increase.

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While Coarse Material Screw Washers and Blade Mills may be similar in appearance, they have differences in application, design and capacity. 

Coarse Material Screw Washers are ideal for removing soluble clay, dirt, crusher dust and coatings, while Blade Mills scour, abrade and break down deleterious water-soluble material. For assistance determining which is the best for your application, contact us today.

Tags: Scrubbing, Washing & Classifying

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