Dosing screw conveyors in stainless steel

What is a dosing screw conveyor?

A dosing screw conveyor is designed to deliver an exact and controlled quantity of material into a downstream process. It is typically used to feed a process machine, another screw conveyor, or a transport system such as a cup elevator or chain conveyor. The following five principles define what makes a dosing screw conveyor accurate, stable, and suitable for industrial applications:

1. Controlled throughput via frequency drive (VFD) — The dosing function is achieved by regulating the screw speed through a frequency‑controlled motor, allowing precise adjustment of the volumetric flow.
2. A completely filled screw rotor — Accurate dosing requires the screw to be fully filled; otherwise, the material flow cannot be controlled or predicted.
3. Volumetric principle and material density — The screw moves a defined volume per revolution. To calculate the mass flow, the density of the material must be known.
4. Application‑specific design — Dosing screws are optimized for each application, considering material type, industry requirements, physical layout, and capacity needs.
5. Flexible configuration and industry suitability — They can be built in various lengths and diameters and supplied with options such as ATEX rating and hygienic stainless‑steel design, making them suitable for both the process and food industries.

These principles form the foundation for designing a dosing screw conveyor that delivers predictable and economical control of material flow.

Read about another dosing screw conveyor here

Case: Precision Material Flow for a High‑Demand Production Line

A manufacturer in the food and process industry faced recurring challenges with inconsistent material flow into several machines in their production line. Their existing equipment produced irregular dosing, which led to variations in product quality, unnecessary waste, and frequent manual adjustments. The company needed a solution that could deliver stable, predictable throughput while meeting strict hygiene requirements and fitting into a compact production layout.

Challenge

The material being handled had a fluctuating bulk density, making it difficult to maintain a consistent mass flow. The previous conveyor system struggled especially at low dosing rates, where even minor variations caused significant downstream disruptions. The production environment required stainless‑steel construction to meet hygiene standards, and the system had to be flexible enough to integrate into an already tight physical layout without compromising performance.

BEMA’s engineered solution

BEMA designed and delivered six stainless‑steel dosing screw conveyors, each tailored to the customer’s specific application and material characteristics. The solution incorporated the core principles of dosing screw technology:

• Frequency‑controlled dosing ensured precise regulation of the screw speed, allowing the customer to fine‑tune the volumetric throughput and maintain stable flow despite density variations.
• Fully filled screw rotors guaranteed predictable dosing, as the screw could only deliver a consistent volume per revolution when completely filled.
• Hygienic stainless‑steel construction ensured durability, easy cleaning, and compliance with food‑industry requirements.
• Application‑specific optimization allowed each conveyor to be adapted in length, diameter, and material selection to match the customer’s layout and process conditions.
• Future‑ready configuration, including the option for ATEX‑rated components, ensured that the system could be upgraded if the production environment changed.

Results

After installation, the customer experienced a marked improvement in production stability. The dosing screws delivered a consistent and predictable material flow, reducing waste and minimizing manual intervention. Product uniformity improved, and the number of production stops decreased significantly. Because the conveyors were optimized for the specific material and environment, they also contributed to longer equipment life and reduced maintenance requirements.

The customer now operates a scalable and reliable dosing system that can be adapted for new materials or expanded to additional production lines. With BEMA’s support, they gained a clear understanding of how material density affects mass flow, enabling them to calculate throughput with confidence and optimize their process more effectively.

FAQ for Dosing Screw Conveyors

1. How is accurate dosing achieved in a dosing screw conveyor?

Accurate dosing is achieved by regulating the screw speed using a frequency drive (VFD) on the electrical motor. This allows precise control of the volumetric throughput. For the dosing function to work correctly, the screw must be completely filled with material; if it is only partially filled, the conveyor cannot deliver a predictable volume per revolution, and the material flow becomes unstable.

2. How is the mass flow calculated?

A dosing screw conveyor operates according to the volumetric principle, meaning it moves a defined volume of material per revolution. To calculate the mass flow, the density of the transported material must be known. If the density varies, the actual mass throughput will also vary, even if the screw speed remains constant. BEMA provides support for calculating flowrate when material data and capacity requirements are available.

3. Which design parameters are critical when selecting a dosing screw conveyor?

Dosing screw conveyors are application‑specific solutions, optimized for the material and the operating environment. Key design parameters include:

• Length and diameter, which determine the volumetric capacity and installation fit.
• Material selection, often stainless steel for food and process industries.
• Rotor design, which must ensure full filling and stable transport.
• Optional requirements, such as ATEX rating or hygienic design. These parameters ensure that the conveyor performs reliably in the intended application.

4. In which industries are dosing screw conveyors typically used, and why?

Dosing screw conveyors are used wherever controlled material flow is required. They are common in both the process industry and the food industry, where they feed material into process machines, other screw conveyors, or transport systems such as cup elevators and chain conveyors. Their flexibility in design, availability in many sizes, and cost‑effective operation make them suitable for a wide range of materials and production environments.