Fine Material Screw Washers

Fine Material Screw Washers wash, classify and dewater -10mm or 3/8″ solids material in one machine. They often accept feed slurry from Wash Screens, Sand Classifying Tanks, Hydrocyclones, Hydrosizers™ and other Fine Material Screw Washers. If an application calls for a greater level of dewatering, they are often placed in series with a Dewatering Screen.

Fine Material Screw Washers are especially simple for operations looking to wash dry screened fines. When compared to other sand washing systems, Screw Washers are a low-capital cost and low electric power user machine. They are widely used by construction sand producers, mining companies, solar salt/brine processors and glass recycling plants.

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Why McLanahan Fine Material Screw Washers

The design of a McLanahan Fine Material Screw Washer provides significant advantages over other sand screws you could consider that include: 

  1. Larger pool settling areas behind the feed box/baffle plate that provide higher retention of +75 micron (200 mesh) product sized solids
  2. A machine design that has a 65mm (2.5”) gap between the screw shaft spiral and the washer box/tub that eliminates abrasive wear on the tub. Competitors’ designs require periodic patching of the tub or complete replacement.
  3. McLanahan Fine Material Screw Washers have an extra-long dry deck area and longer screw shafts, providing more dewatering of material in comparison to others.

McLanahan offers an extensive range of sizes of Fine Material Screw Washers. Sizing and selection is based on several factors, including the type of feed solids, feed gradation, desired product specification, capacity required and volume of the feed slurry. It is extremely important that all of these factors are taken into consideration when selecting the proper size of screw washer. Poor design and planning can lead to overflow of desired fine material, resulting in lost product and profit. McLanahan Corporation’s utilises its vast experience in washing and classifying equipment to ensure proper machine size by reviewing application data that includes slurry volume and your feed gradation data of water coming in with the feed. 

High Water Volume Fine Material Screw Washers — Only From McLanahan

McLanahan offers a wider range of Fine Material Screw Washers than other manufacturers. High Water Volume Screw Washers provide the ability to mix and match screw shaft sizes and tub sizes, allowing a reduced capacity of sand solids and larger-than-normal water volume. This provides a lower cost option compared to a larger standard screw washer. If the sand capacity is 50 tph with 1,000 gpm of water, a 36" diameter screw shaft can be provided in a 54" washer box tub. 

In order to properly retain material in a screw washer, a calm pool area must be maintained. The feed box within the baffle plate is used to direct material away from the calm pool area; however, if the pool area is turbulent, finer material that may be desirable in the final product will overflow the weirs. The baffle plate helps to separate the washer box feed area and keep the pool area calm. In some applications, producers may remove the baffle plate and feed the material close to the back plate of the weir to help agitate the pool area and overflow undesirable material. 

The speed of the Fine Material Screw Washer is determined by the percent passing 50 mesh in the desired product. If the screw washer is running too fast, material does not have a chance to stay on the flight long enough to dewater. The material will fall off of the flight and return to the pool area, leading the box to eventually fill with sand and stall the screw shaft.  

How Fine Material Screw Washers Work

To achieve the desired results with a Fine Material Screw Washer, sand or other fine material is directed to the feed box in the baffle plate. Coarse, heavier materials settle to the bottom of the box, while ultra-fine waste fractions are carried by the up-current of water to the surface and overflow the weirs.

Heavier material that settles to the bottom is conveyed up an 18-degree slope toward the discharge end. The rolling and tumbling of the material releases fines and some lightweight fractions into suspension. It also mildly scrubs superficial clays from the sand/mineral surfaces. As the material is conveyed toward the discharge end, the water begins to separate from the material. A channel in the washer box/tub is provided opposite the conveying side to allow water to drain from the solids and overflow the weirs.

In order to properly retain material in a screw washer, a calm poll area must be maintained. The feed box within the baffle plate is used to direct material away from the calm pool area; however, if the pool area is turbulent, finer material that may be desirable in the final product will overflow the weirs. The baffle plate helps to separate the washer box feed area and keep the pool area calm. In some applications, producers may remove the baffle plate and feed the material close to the back plate of the weir to help agitate the fool area and overflow undesirable material.

The speed of the Fine Material Screw Washer is determined by the percent passing 50 mesh in the desired product. If the screw washer is running too fast, material does not have a chance to stay on the flight long enough to dewater. The material will fall off of the flight and return to the poll area, leading the box to eventually fill with sand and stall the screw shaft.

Popular Applications for Fine Material Screw Washers

Fine Material Screw Washers are widely used to wash and dewater: alluvial/natural sands, manufactured/crushed sands, frac sands, industrial/silica sands, iron ore fines, fine phosphate solids, solar evaporated salt solids and crushed glass.

Benefits of McLanahan Fine Material Screw Washers

  • McLanahan Twin-Seal Pak submerged rear bearing assembly incorporates Caterpillar Duo-Cone® seals that keep water and even the smallest particles from reaching the bearing. This is a far superior design rear bearing assembly design over any competitor’s offer.
  • Large pool area for fine solids retention
  • Longer screw shafts for better dewatering
  • Multiple screw shoe wear materials are available, including white iron and Hardmac iron alloys or polyurethane
  • Extended length wear shoes to protect more of the spiral flights near to the pipe shaft
  • Multiple rising current water injection points for better fines removal
  • Multiple wash back water connections for better solids dewatering
  • Off-the-shelf reducers for quick local procurement or factory support if necessary

Frequently Asked Questions

How much does it cost?

Contact McLanahan or your nearest authorised local dealer not only for pricing but for discussions on suitability and use for your application

What key options should I consider?

You can consider top protective safety covers, front supports and a discharge chute.

Are there any other technologies I should consider?

Hydrocyclones, Dewatering Screen systems using a Hydrocyclone, and bucket wheels. You’ll find that for the cost and low kW (hp) requirements, a Fine Material Screw Washer will be an extremely viable option and a good choice for you.