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Screw Conveyors & Feeders

Transporting bulk materials within an industrial facility is generally achieved by using two conveying methods: mechanical and pneumatic conveying. Among the mechanical options, screw conveyors are among the most widely used and reliable systems for transporting dry bulk solids in a controlled and efficient manner. These systems are essential for ensuring continuous material flow across various stages of production, especially in operations requiring enclosed and dust-free transportation.

Bulk material handling processes in a variety of industries including plastics manufacturing, power generation, construction, food processing, and mining rely heavily on screw conveyors and screw feeders. These systems are designed to transport bulk solids in powdered and granular form between storage silos, processing equipment, and packaging lines. Their simple design, low maintenance requirements, and ability to handle a wide variety of materials make them an ideal choice for many industrial applications.

Screw conveyors function by using a rotating helical screw blade housed inside a trough or a fully enclosed tube. As the screw turns, it pushes bulk materials along the length of the conveyor in a steady and consistent flow. This mechanical action ensures that dry bulk solids are moved efficiently from one point to another within a production or processing facility. The design allows operators to regulate both the speed of the screw and the conveyor’s angle, providing precise control over the rate at which materials are fed into subsequent processing steps or packaging. Screw conveyors are adaptable to various layouts and process requirements, making them a versatile solution for bulk material handling across many industries.

Screw conveying systems can be installed horizontally, inclined, or vertically, depending on plant layout and process needs. Bulk solids commonly conveyed include cement, flour, sand, ash, plastic pellets, minerals, and chemical powders.
There are numerous types and configurations of screw conveyors, each tailored to specific operational needs. Common models include:

• Tubular Screw Conveyors

• U Type Screw Feeders

• Stainless Steel Screw Conveyors

• Hardox Screw Conveyors

• Screw Conveyors with Multiple Inlet Ports

• Screw Conveyors with Multiple Outlet Ports

• Mobile Screw Conveyors with Hopper

• Dosing Screw Feeders

• Microdosing Screw Feeders

• Custom Designed Screw Feeders and Conveyors

Choosing the right design among these types and configurations depends on several key operational factors, such as:

• Physical characteristics of the bulk material

• Desired conveying capacity

• Operating temperature

• Required horizontal or vertical conveying distance

Once these factors are defined, the conveyor’s technical design parameters must be selected accordingly. Important design considerations include:

• Screw diameter

• Screw pitch

• Shaft type

• Motor power

• Inlet and outlet dimensions

• Material and shape of the casing

With 45 years of experience in bulk material handling industry, Polimak designs and manufactures custom screw conveyors that meet the exact requirements of each application. Whether the task involves feeding small batches of fine powder or transferring large volumes of abrasive materials, Polimak’s engineering team ensures that each screw conveyor is optimized for durability, efficiency, and reliable performance. From compact dosing feeders to heavy-duty industrial screw conveyors, each system is built to deliver long-term value and seamless integration into the customer’s process.

Screw Conveyor vs. Screw Feeder:
Understanding the Difference

In bulk material handling, the terms screw conveyor and screw feeder are sometimes used interchangeably, but they serve distinct purposes despite having similar components. Both systems use a rotating helical screw enclosed within a tubular or U-shaped casing to move powders or granular materials from an inlet to an outlet. However, their operational goals and design priorities are different from each other.

The main distinctions between screw conveyors and screw feeders can be summarized as follows:
• Screw Conveyors:

o Primarily designed to transport bulk materials efficiently from one location to another.

o Operate at a maximum or optimized speed to move material quickly.

o Typically handle free-flowing or easily movable solids.

o Do not usually control or regulate the rate at which material is discharged.

o Commonly used in applications such as transferring material from silos, emptying dust collectors, loading trucks, and providing continuous feed to processes.

• Screw Feeders:

o Engineered to deliver materials in a precise and controlled flow.

o Designed to maintain a predetermined and often adjustable feed rate.

o Essential for accurate dosing and feeding tasks where consistent throughput is critical.

o Performance depends heavily on screw geometry, including diameter, pitch, and body shape, to achieve precise material handling.

o Widely used in volumetric or gravimetric dosing systems, ensuring exact quantities of bulk material are introduced into a process.

Understanding these differences is critical for selecting the right equipment to optimize process efficiency and maintain product quality in bulk material handling operations.

Image Gallery

Bulk Materials Handled by Screw Conveyors 

Starch
   
Minerals
  
Coffee Powder
Spices
  
Limestone
  
Copper Oxide
Cement
  
Salt
  
Sugar
  
Sand
  
Calcium Carbonate
Alumina
  
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Screw Feeder & Conveyor Applications Screw conveyors and feeders are widely used in bulk material handling operations to efficiently move bulk solids within industrial processes. Known for their reliability and adaptability, they support both continuous and controlled flow in applications across industries like food, chemicals, cement, plastics, and mining. Typical applications include silo and hopper […]

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OVER 40 YEARS OF SERVICE About Us Polimak is a leading engineering and fabrication company, specializing in bulk solids handling technologies for over four decades. Our wide range of versatile bulk material handling machinery is appropriate for value-added logistics as well as handling powders, granules and pellets in the food, chemical, plastics, minerals, and agriculture […]

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These valves are typically actuated by pneumatic actuators and are used to automatically open and close the product flow to discharge material to downstream equipment.
Installed below silos or hoppers, these valves are used for maintenance operations of equipment such as rotary valves, screw feeders, etc., that are positioned below the butterfly valve.
These valves are typically actuated by pneumatic actuators and are used to automatically open and close the product flow to discharge material to downstream equipment.
In this design, the butterfly valve is sandwiched between two flanges. Rubber sealing at both faces of the valve provides a tight seal between the flanges and the wafer butterfly valve.
One side of the valve has a bolted flange connection, while the other side features a built-in short pipe designed for fixing a flexible sleeve.
These valves have bolted flange connections on both sides, making them suitable for installation on silos, hoppers, screw feeders, and similar applications.
Bulk tanker trucks or open trucks can be filled with powdered materials delivered within FIBC bags. These systems generally consist of bulk bag discharging station, mechanical or pneumatic conveyor and loading bellow. Big bag discharge station transfers the bulk solid from big bag to conveying system. Conveying system transfers it to truck loading area. And loading bellow is used to fill tanker truck without any dust emission. Since truck loading operations are done within limited time, high capacity big bag discharge systems and bulk material conveying systems are used. For short distances, screw conveyors are preferred to transfer material from big bag discharge station to truck loading chute. For long conveying distances, pneumatic conveying systems provide better service. There may exist a storage hopper or silo above bulk truck loading bellow to compensate material flow between inlet and outlet. Bulk bag discharge and truck filling systems have automatic control system that monitors product level in truck and operates all equipment accordingly. Optional weighing system can be added to measure the amount of material that is filled to truck.
Big bag discharge systems can deliver dry bulk solids in powder and granular form to weighing and batching systems. The loading hopper of the weighing system should remain full during dosing and batching. Big bag discharge systems can monitor the product level in the loading hopper and maintain a constant level automatically. Depending on the dosing speed and conveying distance, mechanical conveying systems or pneumatic loading systems may be used. Dust collectors can be employed to prevent dust emissions during hopper loading, especially for materials with high dust content.
Dry bulk packaging systems are used to fill powdered or granular materials into bags, drums, jars, sacks, etc. Bulk materials delivered in big bags must be transferred to packaging machines without interruption. The loading hopper of the packaging system should remain full during the filling and packaging process. Big bag discharge systems can monitor the product level in the loading hopper and maintain a constant level automatically. Depending on the packaging speed, mechanical conveying systems or pneumatic loading systems can be selected. Dust collectors can be used to prevent dust emissions during hopper loading, especially for materials with high dust content.
Mixer automation systems are used to mix dry bulk solids according to specific recipes. Raw materials delivered in FIBC bags can be transferred to mixing units through a combination of conveying equipment and bulk bag discharge systems. Depending on the type of application, pneumatic conveying or mechanical feeding systems can be used to fill mixers. Big bag discharge stations can be manufactured with built-in dosing systems. The amount of raw material to be loaded into the mixer is automatically controlled with the help of a weighing and dosing system. Dust collectors can be used to prevent dust emissions during the mixer filling process.
Bulk material stored in big bags can be automatically filled into small bags. Big bag discharge systems come with optional built-in bag filling units. For low filling capacities, these units are installed below the big bag discharge hopper, providing a practical and cost-effective solution. Both big bag discharging and bag filling operations can be handled by a single, compact system. For higher bag filling needs, bag filling machines are installed near the bulk bag discharge stations. Pneumatic conveying systems or mechanical conveyors can be used to transfer bulk material from the FIBC bag discharge station to the bag or sack filling system.
Mechanical conveyors can be used for silo loading from big bag discharge stations. Screw feeders, bucket elevators, rotary valves, or chain conveyors are connected to big bag discharge stations to fill silos. The selection of conveying equipment directly depends on the conveying distance, height, transferred material, and capacity. Bucket elevators are preferred for high silos, while screw feeders are preferred for shorter silos and short distances. The big bag discharge system can be installed on top of the silo for faster filling. In this case, rotary valves or butterfly valves are better choices as they provide simple flow control. Dust collection systems may be required depending on the dust content of the bulk solid. During silo loading, air content in the silo escapes to the atmosphere and carries some dust along with it. Vacuum fans and jet filters in dust collectors prevent dust emissions into the environment. The collected dust is sent back to the silo, thus preventing product loss.
Pneumatic conveying systems installed after bulk bag discharge units transfer bulk material through conveying pipelines to fill silos. This configuration is useful in applications where high transfer rates and long conveying distances are needed. In production lines where raw materials are stored in warehouses far from storage silos, bulk bag discharge stations can be installed close to the warehouses, and pneumatic conveying systems are used to fill silos from long distances. This design reduces the need for forklifts and cranes for bulk material transfer on the production site and increases overall efficiency.

Pneumatic conveying systems used for silo loading utilize blower pumps or compressors. Motor power, pipeline diameter, and equipment selection depend on the type of bulk material, transfer distance, silo height, and transfer capacity. Level sensors, jet filters, and other equipment are installed on storage silos to ensure the proper operation of the silo filling system.
Pneumatic conveying systems installed after bag dump units transfer bulk material through pipelines to fill silos. This configuration is ideal for applications requiring high transfer rates and long conveying distances. In production lines where raw materials are stored in warehouses far from storage silos, bag dump stations can be installed close to warehouses, allowing pneumatic conveying systems to transport materials over long distances. This design reduces the excessive use of forklifts and cranes for bulk material transfer within the production site, improving overall efficiency.

Pneumatic transfer systems used for silo loading utilize blower pumps or compressors. Motor power, pipeline diameter, and equipment selection depend on factors such as the type of bulk material, transfer distance, silo height, and transfer capacity. Level sensors, jet filters, and other equipment are installed on storage silos to ensure the proper operation of the silo filling system.
Mechanical conveyors can be used for silo loading from bag dump stations. In this configuration, screw feeders, bucket elevators, rotary valves, or chain conveyors are connected to bag dump stations to fill silos. The selection of conveying equipment depends on factors such as conveying distance, height, material properties, and capacity. Bucket elevators are preferred for high silos, while screw feeders are ideal for shorter silos and short distances. Bag dump systems can be installed on top of the silo for faster filling. In such cases, rotary valves or butterfly valves are better choices as they provide simple flow control.

Dust collection systems may be required depending on the dust content of the bulk solid. During silo loading, air inside the silo escapes to the atmosphere, carrying dust particles with it. Dust collectors equipped with a vacuum fan and jet filter capture airborne dust. The collected dust is returned to the silo, preventing product loss and ensuring a cleaner environment.
The inlet skirt is an optional feature designed to extend the lifespan of the flexible connector sleeve. Its upper portion is attached to the outlet port of the upstream equipment and extends down into the bin activator’s inlet port. The primary function of the inlet skirt is to serve as a protective shield, safeguarding the flexible connector seal from wear and damage.
A vibratory motor is externally mounted to the bin activator. When powered, the motor generates vibrations that facilitate a steady flow of dry bulk materials within the system. Depending on the application requirements, one or two vibratory motors can be installed externally.
To accommodate a bin activator, the cone of a silo must be shorter than usual, resulting in a wider outlet. A flange supplied with the bin activator is separately welded to the silo’s outlet, slightly above the opening, at the production site. Once installed, the vibrating bin discharger is securely bolted to the flange, ensuring a stable and reliable connection.
Special spring suspension links and an engineered polymer seal work together to create a flexible connection between a vibrating bin discharger and the equipment positioned above it.

The proper design and installation of the polyurethane seal prevent it from slipping off and ensure a secure seal, eliminating the risk of dry bulk material leakage. Additionally, the seal offers high stress resistance and long-term durability, withstanding stresses caused by motor vibrations, pressure conditions, and other operational factors.

Externally installed spring suspensions provide full resilience to the vibrations of the cone head. They ensure that the generated vibrations affect only the cone itself rather than the upstream equipment structure.
An internally tapered, conical-shaped baffle plate is positioned at the center of the bin activator’s diameter. The baffle is rigidly attached to the equipment body using structural steel components. It facilitates bulk material flow from upstream equipment by directly inducing vibrations into the material.

A secondary deflector plate reduces the weight of the bulk material in the lower portion of the bin activator by acting as a wedge beneath the material, directing it around the areas adjacent to the cone’s surface.

Polimak baffle plates are available in various configurations, including convex and cone plates, and in different angles (15°, 30°, 45°, or even 60°) depending on the flow characteristics of the handled bulk material and the specific application requirements.