Screw conveying for powders
Screw conveying is one of the most reliable methods for moving powders and bulk materials in a controlled way. A rotating screw inside a closed trough or tube pushes the product from inlet to outlet at a constant, dosable rate. For engineers, buyers and QA in pharma, chemical, food and the battery industry, screw conveying offers a robust, low-dust and highly controllable solution. HECHT designs screw conveyors and dosing screws tailored to your product, capacity and hygiene requirements.
How screw conveying works
A screw conveyor consists of a helical screw shaft rotating inside a housing. The rotation moves the product axially towards the outlet. Through speed control, the screw acts as both a conveyor and a precise dosing device. This makes screw conveying ideal for processes that require a constant, adjustable mass flow.
Because the product is fully enclosed, dust emission stays minimal and the working environment remains clean and safe.
Types of screw conveyors
The right design depends on product, capacity and layout.
- Trough screw — open or closed trough, suited to larger volumes and horizontal transport
- Tube screw — fully enclosed tube, dust-tight and suitable for inclined transport
- Dosing screw — short, precise screw for gravimetric or volumetric dosing
- Shaftless screw — for sticky or fibrous products without a central shaft
- Vertical screw — for conveying powders upward in compact layouts
Precise dosing with screw technology
Screw conveying excels at dosing. Coupling the rotation speed to a weighing system creates a gravimetric dosing screw that holds the mass flow within tight tolerances. This is critical for recipe formulation, continuous production and filling of critical ingredients.
- Volumetric dosing — constant speed delivers a fixed volume per revolution
- Gravimetric dosing — feedback from weighing corrects density variations
- Loss-in-weight — continuous weighing of the supply hopper for maximum accuracy
Product-friendly conveying
Not every powder tolerates the same handling. Break-sensitive granules, sticky substances and segregation-prone mixtures call for an adapted screw design. The pitch, profile and speed of the screw determine how gently the product is moved. HECHT matches the geometry to the break sensitivity and flow properties of your product.
Containment and operator protection
For highly active powders, a closed screw system is an effective containment strategy. Combined with split-butterfly valves at inlet and outlet, the product stays isolated from the environment and operator exposure is limited. Depending on the OEB band, seals, bearings and feed-throughs are validated for leak-tightness, verified to SMEPAC.
Hygienic design: GMP and EHEDG
In pharma and food, a screw conveyor must be fully cleanable. GMP and EHEDG-compliant designs have polished surfaces (Ra ≤ 0.8 µm), no dead zones and disassembly-free CIP/WIP cleaning. Stainless steel 316L and FDA-compliant seals prevent cross-contamination between batches and product changeovers.
ATEX and safety
For combustible powders, the screw conveyor must be ATEX-compliant. Earthing, spark-free bearings, temperature monitoring and correct zoning prevent ignition. For oxygen-sensitive products such as battery powders, the system can be run inert with nitrogen.
Frequently asked questions about screw conveying
What is the difference between a conveying screw and a dosing screw?
A conveying screw moves large volumes; a dosing screw is optimised for accuracy and delivers a controlled mass flow.
What accuracy does a gravimetric dosing screw achieve?
With loss-in-weight weighing, accuracies within a fraction of a percent are achievable, depending on product and capacity.
Is screw conveying suitable for sticky products?
Yes, with a shaftless screw or an adapted pitch; HECHT selects the geometry based on the flow properties.
Can a screw conveyor operate dust-free?
A closed tube screw with the right seals operates virtually dust-free and is suitable for containment up to high OEB bands.
How is a screw conveyor cleaned?
Via CIP or WIP, or for fast product changeovers through an easily disassembled design, depending on your hygiene requirements.
Related guides
Tailored advice from HECHT
A screw conveyor that suits your product starts with an analysis of your powder, capacity and dosing requirement. HECHT designs, tests and supplies screw conveying that is reliable, low-dust and hygienic, and integrates seamlessly with your dosing and filling systems. Contact us for a conveying analysis and a tailored proposal.