Screw conveyors are an excellent option for conveying bulk materials. In fact, screw conveyors are one of the oldest known types of mechanical conveyors, dating all the way back to ancient Greece!
However, there is a lot to know to select the right screw conveyor for your application. We will take a look at the options out there today, which will help determine the right one for you. We’ll also share insights from our trusted conveying partner, KWS Manufacturing.
What is a Screw Conveyor?
A screw conveyor consists of three primary components – the screw, the housing it resides within, and the mechanical drive unit.
The screw typically consists of a center pipe with mounted helical flighting. The flighting wraps in a continual helix around the center pipe. Bulk materials are transferred along the length of the conveyor as the screw rotates.
The housing consists of troughs, covers, trough ends, and a minimum of one inlet and one discharge. Bulk materials are contained within the housing, preventing leakage and contamination.
The mechanical drive unit powers the screw conveyor. Typically, an electric motor transmits torque through a gear reducer and rotates the screw. Mechanical drive units can be located on either the inlet or the discharge end, allowing you to push or pull bulk materials.
Materials of construction vary, but generally, screw conveyors are manufactured using carbon steel, stainless steel, or specialty alloys. The type of construction is determined by your specific application.
Types of Screw Conveyors
Screw conveyors are extremely versatile, and can be used for conveying dry, free flowing to very wet and sticky bulk materials. Horizontal screw conveyors are the most common and operate on a flat or horizontal surface. Inclined conveyors operate on an inclined plane up to 45 degrees from the horizontal position.
Any incline over 45 degrees is considered a vertical screw conveyor. Additional horsepower and screw speed are required to convey a bulk material on an incline or vertically due to the effects of gravity and material fall back.
Shaftless screw conveyors do not have a center pipe and are an excellent choice for conveying wet and sticky bulk materials, such as dewatered biosolids or animal byproducts. Shaftless spirals will not plug and are very efficient at conveying problematic bulk materials. Many other screw conveyor configurations are available for mixing, heating, or cooling bulk materials.
Types of Flighting
Every screw conveyor has flighting, which is the continuous helix that wraps around the center pipe. Important considerations for flighting are pitch and diameter.
Pitch (P) is the distance between flights– the distance bulk materials travel with one full revolution of the screw.
Diameter (D) is the outside measurement of the screw flighting.
Pitch also correlates to the diameter of the screw. If the distance between flights is equal to the diameter of the screw, the screw is considered full pitch. (P = D).
Other common variations include half pitch (the pitch is 1/2 the diameter of the screw), short pitch (the pitch is 2/3rds the diameter of the screw), and long pitch (the pitch is 1.5 times the diameter of the screw). Variable pitch (where the pitch varies along the length of the screw) is also available for specialized applications.
Two types of flighting are helicoid and sectional. Helicoid flighting is typically made in one continuous piece of flighting for the full length of the screw. Sectional flighting is made in individual segments or sections. Flighting is then welded to the center pipe with either intermittent or continuous welds.
Why Screw Conveyors?
Screw conveyors are a popular option for moving bulk materials because of their efficiency and versatility. They can be made in an infinite number of ways, allowing for customization for all kinds of bulk materials. Because of this, screw conveyors can be found in a wide range of industries including:
- Agriculture and Grain Handling
- Chemicals
- Environmental
- Food and Beverage
- Aggregate
- Metals and Mining
- Pulp and Paper
- Recycling
Screw conveyors are also relatively simple in design, with robust construction and straightforward maintenance requirements.
The enclosed nature of most screw conveyors provides an extra layer of safety in your facility. For example, it prevents employees from contacting rotating equipment or hazardous bulk materials.
Additionally, screw conveyors are more cost-effective when compared to other conveying devices like belt conveyors or pneumatic conveying systems.
Considerations for Selecting a Screw Conveyor
KWS Manufacturing, a premium supplier of conveying solutions and licensed engineering firm, recommends the following steps as you consider your next screw conveyor:
- Determine bulk material characteristics. What is the type and condition of the bulk material? Maximum particle size? Specific bulk density? Also consider any environmental factors, such as temperature and moisture levels, and how they might affect the flow of your bulk material.
- Determine conveyor size and speed based on capacity. What is the capacity or feed rate of the bulk material to be conveyed? How does this output line up with other equipment in your facility? Calculate capacity in pounds per hour, tons per hour, or cubic feet per hour. What is the required distance and incline? This will help you determine your horsepower requirements as well.
- Verify torque rating of components. Screw conveyor components such as the center pipe of the screw must be designed for the full motor torque of the mechanical drive unit. Doing so will prevent unexpected mechanical failure during operation if the screw conveyor plugs.
For certain applications, liners can be a helpful addition to your trough, allowing a replaceable liner to take the wear and tear of the material handling process. Liners are typically made of UHMW, carbon steel or abrasion resistant alloys.
Screw Conveyor Applications
The possibilities are endless due to the customizable nature of screw conveyors.
A common place you will find many screw conveyors is in agriculture and grain handling. For example, it is common to use screw conveyors to transfer grain products to and from storage locations.
Food processing applications can also be well suited to screw conveyors. Shaftless screw conveyors are optimal for handling sticky or viscous food materials, and the lack of a center pipe helps reduce buildup. Polished stainless steel screw conveyors are used to convey finished food products such as flour, ingredients, and even ground meat.
Vertical screw conveyors are often found in the chemical industry for elevating various chemical products in the form of powders and granules.
If you have a bulk material handling application and need help selecting the right screw conveyor, we are here to help. KWS is known for their industry expertise and customized conveying solutions. They continue to innovate in the field, offering corrosion-resistant and high-temp conveyors. From their engineered screw conveyors and conveying systems, to CEMA standard screw conveyor parts, KWS is an excellent source for your screw conveyor needs.
Screw Conveyor Questions?
Our Conveying Systems experts would love to help you find the right KWS screw conveyor for your application. We can also help with replacement parts! Reach out to us directly, or request a quote here.
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We look forward to assisting you.
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