Gravimetric screw feeders

DSL G gravimetric screw feeders

Q: What is the difference between gravimetric and volumetric feeding?

In the volumetric method the material is delivered at a constant screw speed, on the assumption of a constant bulk density - with no feedback loop. A gravimetric (loss-in-weight) feeder measures the loss of weight in real time and trims the screw speed with a PID controller. It therefore holds accuracy below ±0.5% even when the material properties vary, while the volumetric method manages only ±1–5%.

Q: What materials can be fed with the DSL G?

Practically every dry bulk material - from fine powders a few µm across to granulates and pellets. That covers well-flowing products (salt, sugar) as well as difficult-flowing ones (flour, soda), materials prone to aeration (carbonates, gypsum), abrasive ones (quartz sand) and brittle ones (flakes, soluble coffee). What matters is choosing the right feeding element - a screw with a centre shaft or a spiral.

Q: What happens during hopper refill in continuous mode?

While the hopper refills, the feeder switches automatically to volumetric mode - delivering material at the speed stored just before refilling began. Once the hopper is full, the system returns to gravimetric mode. The whole process happens without interrupting the feed.

Q: Is the feeder suitable for food or pharmaceutical applications?

Yes - even in the standard build every part in contact with the product is FDA-approved stainless steel. For more demanding applications we offer the hygienic EHEDG version - with ground welds (Ra<0.8 µm), 316L steel, aseptic motors and a structure that strips down quickly for cleaning. The build meets both GMP and HACCP requirements.

Q: How do I select the right feeder for my process?

We start by defining the material parameters: particle size, bulk density, moisture content, angle of repose and any tendency to cake or aerate. Next we establish the process requirements: the flow (continuous or batch), the accuracy needed, the batch size and the ambient conditions. On that basis we select the size of feeder (DSL35, DSL75 or DSL150 G) and the type of feeding element. We offer trials on the customer's actual material.

Q: What is the agitator and what does it do?

The agitator is a horizontal stirrer positioned above the feeding element. Its job is to stop bridges forming and material hanging up in the hopper, and to keep the metering screw completely and evenly filled. That matters particularly with cohesive, fine and difficult-flowing materials. DSL G feeders are fitted with one or two agitators.

Versatile loss-in-weight feeders for precise continuous and batch feeding of bulk materials — from fine powders just a few micrometres across to granulates and pellets. Continuous loss-in-weight measurement and PID control hold the accuracy steady whatever the raw material does.

Explore the DSL G family Gravimetric or volumetric?

<±0.5% continuous feeding accuracy 0.5 – 25000 kg/h feed rate range FDA · EHEDG · ATEX compliant builds

What loss-in-weight feeding is

Precision built on continuous loss-in-weight measurement

Gravimetric screw feeders working in loss-in-weight mode are one of the most versatile solutions for precise feeding of bulk materials. They suit processes that call for a constant mass flow (continuous feeding) just as well as applications where a set portion of material has to be weighed out exactly (batch feeding).

The whole feeding assembly — the hopper holding the material, the trough with the feeding element and the agitator — sits on load cells. The system measures the actual loss of weight, and a PID controller in a closed loop trims the rotational speed of the metering screw. The result is steady accuracy, unaffected by changes in the bulk density of the raw material.

<±0.5%

continuous feeding error against the set value

0.5–25000 kg/h

feed rate range of the DSL G family (turndown 1:10)

18–150 mm

diameters of screws and spirals, selected to suit the material

The DSL G feeder family

DSL35 G · DSL75 G · DSL150 G

The DSL35 G, DSL75 G and DSL150 G gravimetric screw feeders side by side

DSL G in service — click to enlarge

Stainless steel loss-in-weight gravimetric screw feeders at a combined heat and power plant — sorbent feeding installation with valves and pneumatic conveying lines — CHP plant

Gravimetric screw feeders at a chemical works — hoppers on weighing frames with drives and an access platform — Chemical works

Loss-in-weight screw feeders beneath silos at a refinery — outdoor installation with material taken away by pneumatic conveying — Refinery

Hygienic stainless steel gravimetric screw feeders at a food production plant — feeding recipe ingredients into a mixer — Food production plant

The DSL G family of gravimetric screw feeders covers versatile machines for the precise feeding of bulk materials of widely varying character — from fine powders to granulates and pellets. Each feeder comprises a main trough, a horizontal agitator, a precise load-cell weighing system and a hopper. Material flow is generated by the rotating screw, while the agitator keeps it fully filled and stops the material from hanging up.

Precision comes from a weighing system built around a rigid support structure and two or three class C3 stainless steel load cells rated IP68/IP69K. Every part in contact with the material is made of stainless or acid-resistant steel.

Key specifications

Accuracy (continuous)feeding error typically <±0.5% of set value
Accuracy (batch)±0.1–0.5% for batches above 1 kg
Feed ratefrom 0.5 to 25000 kg/h (min/max working range = 1:10)
Feeding elementsscrews and spirals in diameters of 18–150 mm
Load cellsclass C3 strain-gauge, stainless steel, IP68/IP69K
Materialssteel 1.4301 (AISI 304) or 1.4404 (AISI 316L)
Agitatorone or two — prevents hang-ups and bridging
Finishglass-bead blasting or electropolishing
OptionsEHEDG hygienic version, ATEX build
Intended usedry bulk materials — well-flowing and difficult-flowing, aerating, compressible

Downloads

Datasheet DSL35 G (PDF) Datasheet DSL75 G (PDF) Datasheet DSL150 G (PDF) Questionnaire DSL(35-75-150) G (DOCX)

Feed rates and dimensions — model comparison

Figures taken from the DSL35 G, DSL75 G and DSL150 G datasheets. Feed rates are given by volume [l/h] — for the mass feed rate, multiply the figure by the bulk density of the material (for example 200 l/h × 0.55 kg/l ≈ 110 kg/h).

Parameter	DSL35 G	DSL75 G	DSL150 G
Feed rate min. – max.	0.5 – 450 l/h	7 – 5000 l/h	70 – 25000 l/h
Feeding element (ø × pitch)	ø18 – ø35 mm	ø35 – ø74 mm	ø74 – ø150 mm
Hopper capacity	30 · 40 · 65 l	100 · 200 · 300 l	400 · 600 l (ø850 mm) 1200 · 1800 · 2400 l (ø1200 mm)
Overall height	745 – 935 mm	1327 – 1609 mm	1967 mm (ø850 mm hopper)
Typical application	micro-ingredients, colours, flavourings, APIs	recipe ingredients, premixes, fillers	main raw materials, large mass flows

The minimum feed rate applies to the smallest solid screw at 10 rpm, the maximum to the largest spiral at 200–250 rpm. All models: turndown ratio 1:10, accuracy <±0.5%, SEW 3 × 400 V AC drives under inverter control. Weights, drive ratings and outlet diameters are given in the datasheets above.

Feeding element selection

Spiral or solid screw?

The right choice of metering screw or spiral has a decisive bearing on the precision and stability of the process. Each type of feeding element is therefore matched to the specific properties of the bulk material.

Spiral (helix)

Recommended for materials that are

—difficult-flowing (e.g. flour, soda, granulates)
—fine and sticky, building up on the shaft (e.g. cocoa, titanium white)
—coarse enough to cause friction between the shaft and the outlet pipe
—subject to raised hygiene requirements (e.g. the food industry)

Solid screw

Recommended for materials that are

—well-flowing and very loose (e.g. salt, sugar)
—prone to aeration and uncontrollable flow (e.g. carbonates, gypsum)
—highly abrasive (e.g. quartz sand)
—brittle and easily damaged (e.g. flakes, soluble coffee)

Not sure which element to choose? We run feeding trials on the customer’s actual material — the choice of screw or spiral is confirmed by measurement, not by catalogue figures alone.

Arrange a material trial

Build variants

Hygienic EHEDG version and ATEX build

Gravimetric screw feeder in the hygienic version compliant with EHEDG

Hygienic version in accordance with EHEDG

Even in the standard build our feeders are suitable for the food industry — every material in contact with the product is FDA-approved or made of stainless or acid-resistant steel.

For more demanding applications we offer a build compliant with EHEDG recommendations. The feeder trough and the support frame have been redesigned for maximum cleanability, and the feeding element and agitator can be stripped out quickly without tools. Acid-resistant 316L steel, an interior and welds ground to Ra<0.8 µm and aseptic motors (with no cooling fins or fan) provide the highest standard of production safety.

We also use only lubricants approved for food contact (NSF H1 class), and electrical enclosures can be supplied to the Rittal HD (Hygienic Design) standard — stainless steel, with sloped surfaces, and able to withstand intensive high-pressure washdown.

Feeders in explosion hazard zones (ATEX)

Many production plants have areas classified as a dust explosion hazard. We therefore offer feeders in an explosion-protected build compliant with the ATEX Directive. In these machines every electrical component is certified, and the structure provides continuous equipotential bonding for the proper dissipation of electrostatic charges.

Gravimetric screw feeder in an ATEX build for explosion hazard zones

Gravimetric vs volumetric

Which feeding method should you choose?

In volumetric feeding the material is delivered at a constant screw speed, on the assumption that the bulk density does not change. The method has no feedback loop, so any change in the material’s properties translates directly into a feeding error (typically ±1–5%).

A gravimetric (loss-in-weight) feeder, by contrast, measures the actual loss of weight in the hopper and trims the screw speed in a closed loop using a PID controller. That holds the accuracy steadily below ±0.5% even when the properties of the raw material vary — which matters above all with multi-ingredient recipes and costly raw materials.

Parameter	Gravimetric loss-in-weight	Volumetric
Measurement principle	Continuous loss-in-weight measurement	Constant volume per unit of time
Typical accuracy (continuous)	<±0.5% of set value	±1–5% of set value after range linearisation
Typical accuracy (batch)	±0.1–0.5% (depending on the load cell range and the batch size)	No direct control of the batch mass
Bulk density compensation	✓ Automatic, closed loop	✗ None — requires calibration
Real-time control	✓ PID controller	✗ Open-loop control
Flow documentation	✓ Recording of the actual mass flow	✗ Speed monitoring only
GMP / HACCP compliance	✓ Full validation and traceability	Limited
Capital cost	Higher (weighing system + controller)	Lower — simpler design
When to choose it?	Multi-ingredient recipes, costly raw materials, quality audits	Homogeneous materials of constant bulk density

InterProcess DSL G feeders are designed as gravimetric machines, but they can also run volumetrically — as a cheaper starting option that can be upgraded later, for instance. Simpler applications are also covered by our volumetric screw feeders.

Operating modes

Continuous and batch feeding

Machines in the DSL G family work in both modes. In practice the choice depends on the nature of the production, the flexibility required of the recipes and the expected output.

Continuous feeding

The material is delivered without interruption at a controlled mass flow. The system monitors the loss of weight constantly and trims the screw speed to hold the set value.

—a steady, precisely controlled stream of material
—feeding continuous mixers, extruders and reactors
—automatic switch to volumetric mode while the hopper refills
—several feeders integrated in a master/slave system
—a marked reduction in material losses

Batch feeding

An exact, predetermined mass of material is weighed out. Once the target batch is reached, the feeder stops automatically and waits for the next cycle. Typical accuracy is ±0.1–0.5% for batches above 1 kg.

—precise weighing out of a target mass with a final check
—full traceability for every batch
—support for multi-ingredient recipes
—simplified validation for the pharmaceutical industry (GMP)
—a proven answer where products change frequently

Detailed operating principle (loss-in-weight)

The weighed feeding assembly is flexibly connected to the refilling equipment and the discharge pipe, which keeps external forces out of the measurement. During feeding the system measures the loss of weight and derives the actual mass flow of material from it. A PID controller compares the measured value against the set value and trims the rotational speed of the metering screw.

When the material level in the hopper falls below the set minimum, refilling starts automatically — without interrupting the feed. During that time the feeder switches briefly to volumetric mode, running at the last stored speed, and returns to full gravimetric mode once refilled.

Proportional feeding

Multi-ingredient feeding systems

Loss-in-weight screw feeders are the ideal building block for continuous proportional feeding systems, in which several ingredients are delivered at the same time onto a shared receiving conveyor or straight into the process. Each feeder measures the loss of weight in its own hopper independently, so the actual flow of every ingredient is known and controlled separately. One feeder acts as the master and the rest work as slaves, holding a constant mass ratio to the main ingredient.

A change of flow on the master automatically produces a proportional correction on every slave feeder — the system keeps the recipe proportions constant whatever the line output does, and hoppers refill automatically without interrupting the feed. InterProcess designs and integrates complete multi-ingredient feeding lines: feeder selection, control systems with industrial communications (4–20 mA, Profibus, Profinet, Modbus, EtherNet/IP) and recipe automation.

Industries and applications

Key industry applications

🍞 Food Industry

Feeding spices, flour blends, milk powders, dietary supplements, instant products and premixes. Every system complies with HACCP and the materials are FDA-approved. An EHEDG build is available as an option.

💊 Pharmaceutical Industry

Precise feeding of active pharmaceutical ingredients (APIs), excipients and premixes. The machines provide full GMP compliance, process validation and batch traceability. The hygienic version is suitable for cleanroom conditions.

⚗️ Chemical Industry

Feeding pigments, fillers, crop protection products, fertilisers and speciality chemicals. Corrosion-resistant builds are available, as are ATEX variants intended for dust explosion hazard zones.

FAQ

Frequently asked questions

What is the difference between gravimetric and volumetric feeding?+

In the volumetric method the material is delivered at a constant screw speed, on the assumption of a constant bulk density — with no feedback loop. A gravimetric (loss-in-weight) feeder, by contrast, measures the loss of weight in real time and trims the screw speed with a PID controller. It therefore holds accuracy at <±0.5% even when the material properties vary, while the volumetric method manages only ±1–5%.

What materials can be fed with the DSL G?+

Practically every dry bulk material — from fine powders a few µm across to granulates and pellets. That covers well-flowing products (salt, sugar) as well as difficult-flowing ones (flour, soda), materials prone to aeration (carbonates, gypsum), abrasive ones (quartz sand) and brittle ones (flakes, soluble coffee). What matters is choosing the right feeding element — a screw with a centre shaft or a spiral.

What happens during hopper refill in continuous mode?+

While the hopper refills, the feeder switches automatically to volumetric mode — delivering material at the speed stored just before refilling began. Once the hopper is full, the system returns to gravimetric mode. Importantly, the whole process happens without interrupting the feed.

Is the feeder suitable for food or pharmaceutical applications?+

Yes — even in the standard build every part in contact with the product is FDA-approved stainless steel. For more demanding applications we offer the hygienic EHEDG version — with ground welds (Ra<0.8 µm), 316L steel, aseptic motors and a structure that strips down quickly for cleaning. The build therefore meets both GMP and HACCP requirements.

How do I select the right feeder for my process?+

We start by defining the material parameters: particle size, bulk density, moisture content, angle of repose and any tendency to cake or aerate. Next we establish the process requirements: the flow (continuous or batch), the accuracy needed, the batch size and the ambient conditions. On that basis we select the size of feeder (DSL35, DSL75 or DSL150 G) and the type of feeding element — a solid screw with a centre shaft or a shaftless spiral (helix). Do fill in the selection questionnaire or get in touch — we offer trials on the customer’s actual material.

What is the agitator and what does it do?+

The agitator is a horizontal stirrer positioned above the feeding element. Its main job is to stop bridges forming and material hanging up in the hopper. At the same time it keeps the metering screw completely and evenly filled. That matters particularly with cohesive, fine and difficult-flowing materials. Depending on the configuration, DSL G feeders are fitted with one or two agitators.

Why InterProcess