InterProcess Sp. z o.o. | Rozwiązania dla przemysłu
What loss-in-weight feeding is
Precision built on continuous weight-loss measurement
Gravimetric screw feeders working on the loss-in-weight principle are among the most versatile solutions for accurate feeding of bulk solids. They suit processes that call for a constant mass flow (continuous feeding) just as well as applications where a defined portion of material has to be metered out precisely (batch feeding).
The complete feeding assembly (material hopper, feeding chamber and agitator) is mounted on load cells. The system measures the actual loss in weight and a closed-loop PID controller trims the speed of the feeding screw. The result is a constant accuracy that is unaffected by variations in bulk density.
The DSL G feeder family
DSL35 G · DSL75 G · DSL150 G
DSL G installations · click to enlarge
The DSL G family of gravimetric screw feeders covers versatile machines for accurate feeding of bulk solids with widely differing characteristics, from fine powders through to granules and pellets. Each feeder comprises a main chamber, a horizontal agitator, a precision load-cell weighing system and a hopper. Material flow is generated by the rotating screw, while the agitator keeps it fully charged and stops the material from hanging up.
Accuracy 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 product-contact part is made of stainless or acid-resistant steel.
Key DSL G data
- Accuracy (continuous)feeding error typically <±0.5% of set point
- Accuracy (batch)±0.1–0.5% for batches above 1 kg
- Throughput0.5 to 25,000 kg/h (min/max turndown 1:10)
- Feeding elementsscrews and spirals, diameters 18–150 mm
- Load cellsclass C3 load cells, stainless steel, IP68/IP69K
- Materialssteel 1.4301 (AISI 304) or 1.4404 (AISI 316L)
- Agitatorone or two, prevents hang-ups and bridging
- Surface finishglass-bead blasting or electropolishing
- OptionsEHEDG hygienic version, ATEX design
- Suitable fordry bulk solids: free-flowing and poorly flowing, aerating, compacting
Downloads
Throughputs and dimensions: model comparison
Figures taken from the DSL35 G, DSL75 G and DSL150 G data sheets. Throughputs are volumetric [l/h]; for the mass flow rate multiply by the bulk density of the material (e.g. 200 l/h × 0.55 kg/l ≈ 110 kg/h).
| Parameter | DSL35 G | DSL75 G | DSL150 G |
|---|---|---|---|
| Throughput min. – max. | 0,5 – 450 l/h | 7 – 5 000 l/h | 70 – 25 000 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 | 1 327 – 1 609 mm | 1,967 mm (hopper ø850 mm) |
| Typical duty | micro-additives, colourants, flavourings, APIs | recipe ingredients, premixes, fillers | main raw materials, high mass flows |
The minimum throughput applies to the smallest full-flight screw at 10 rpm, the maximum to the largest spiral at 200–250 rpm. All models: 1:10 turndown, accuracy <±0.5%, SEW drives 3 × 400 V AC with inverter control. Weights, drive ratings and outlet diameters are given in the data sheets above.
Selecting the feeding element
Spiral or full-flight screw?
The choice of feeding screw or spiral has a decisive effect on the precision and stability of the process, which is why each type of feeding element is matched to the specific properties of the bulk solid.
Not sure which element to choose? We run feeding trials on the customer’s own material: the choice of screw or spiral is confirmed by measurement, not by catalogue data alone.
Arrange a material trialDesign variants
EHEDG hygienic version and ATEX design
EHEDG-compliant hygienic version
Even in the standard design our feeders are suitable for the food industry, because every product-contact material is FDA-approved or made of stainless / acid-resistant steel.
For more demanding duties we offer a design that follows the EHEDG guidelines. The feeding chamber and support frame are redesigned for maximum cleanability, and the feeding element and agitator can be removed quickly without tools. Acid-resistant 316L steel, interiors and welds ground to Ra<0.8 µm and aseptic motors (smooth, without cooling fins or fan) deliver the highest level of production safety.
We also use food-grade lubricants only (NSF H1 class), and electrical enclosures can be supplied to the Rittal HD (Hygienic Design) standard: stainless steel, sloping surfaces, able to withstand intensive high-pressure washdown.
Feeders for potentially explosive atmospheres (ATEX)
Many plants have areas classified as dust explosion zones. For these we supply feeders in an intrinsically safe design compliant with the ATEX Directive: all electrical components are certified and the construction maintains equipotential bonding throughout, so electrostatic charge is dissipated safely.
Gravimetric vs volumetric
Which feeding method should you choose?
In volumetric feeding the material is delivered at a fixed screw speed on the assumption that bulk density stays constant. There is no feedback loop, so any change in the material translates directly into a feeding error (typically ±1–5%).
A gravimetric (loss-in-weight) feeder, by contrast, measures the actual loss in weight from the hopper and trims the screw speed in a closed loop with a PID controller. This holds accuracy below ±0.5% even when the material properties vary, which matters greatly with multi-ingredient recipes and high-value raw materials.
| Parameter | Gravimetric loss-in-weight | Volumetric |
|---|---|---|
| Measuring principle | Continuous weight-loss measurement | Constant volume per unit of time |
| Accuracy (continuous feeding) | <±0.5% of set point | ±1–5% of set point after range linearisation |
| Accuracy (batch feeding) | ±0.1–0.5% (depends on load-cell range and batch size) | No direct control of batch weight |
| Compensation for density changes | ✓ Automatic, closed loop | ✗ None, requires recalibration |
| Real-time control | ✓ PID controller | ✗ Open-loop control |
| Flow documentation | ✓ Actual mass flow recorded | ✗ Screw 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, high-value materials, quality audits | Homogeneous materials with constant bulk density |
InterProcess DSL G feeders are designed as gravimetric machines but can also run volumetrically, for instance as a lower-cost starting point that can be upgraded later. Simpler duties are also covered by our volumetric screw feeders.
Operating modes
Continuous and batch feeding
DSL G machines work in both modes. In practice the choice depends on the nature of the production, the recipe flexibility required and the throughput expected.
Continuous feeding (continuous)
Material is delivered without interruption at a controlled mass flow rate. The system monitors the loss in weight continuously and trims the screw speed to hold the set point.
- —a steady, closely controlled material stream
- —feeding continuous mixers, extruders and reactors
- —automatic switch to volumetric mode during hopper refill
- —integration of several feeders in a master/slave system
- —a significant reduction in material giveaway
Batch feeding (batching)
An exact, pre-set mass of material is metered 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 metering of a target weight with final check
- —full traceability of every batch
- —support for multi-ingredient recipes
- —simplified validation in pharmaceutical production (GMP)
- —a proven answer where product changeovers are frequent
How loss-in-weight feeding works in detail
The weighed feeding assembly is connected to the refill equipment and the discharge pipework by flexible sleeves, so external forces cannot influence the measurement. During feeding the system measures the loss in weight and derives the actual mass flow from it. A PID controller compares the measured value with the set point and corrects the speed of the feeding screw.
When the material level in the hopper falls below the set minimum, refilling starts automatically without interrupting the feeding. For that short period the feeder switches to volumetric mode, running at the last recorded speed, and returns to full gravimetric control once refilling is complete.
Batch feeding
Recipe-based feeding
The versatile design of the screw feeders allows them to be built into a multi-ingredient feeding station where each machine handles a separate raw material. A central control system sets the batch size or the required flow rate from the recipe, both in batch (batching) operation and in continuous operation, depending on the nature of the production line.
The right solution depends on the type of process, the number of ingredients, the duty cycle, the feeding time and the accuracy required. We build both weighing concepts:
Gain-in-weight
Weighing into a central scale
The most common and most cost-effective batching arrangement: the ingredients are delivered one after another into a centrally located scale. Where requirements are exceptionally tight, intermediate scales (for example with a rotating bowl) or a rail-mounted travelling scale, positioned automatically under each feeder in turn, are used. Once dosed, the blend passes to a mixer for full homogenisation.
Loss-in-weight
Feeding straight off the scale
Each feeder has its own weighing system, so the ingredients can be delivered in parallel rather than in sequence. That shortens the cycle and the blend is already pre-homogenised as it is fed. In continuous operation the machines run simultaneously and hold the specified flow ratios, which means any additional in-line mixer can be far smaller and cheaper to run than a batch mixer.
Feeding accuracy
What disturbs the weight signal, and how we compensate
The accuracy of a loss-in-weight feeder depends not only on the electronics but also on the material and on what surrounds the scale. Below are the most common sources of error and the answers we build into DSL G feeders.
Vibration and shock
Vibration from neighbouring machines and the building structure is damped mechanically in the feeder frame, and the load-cell signal is filtered digitally in the controller.
Pressure differences
Negative or positive pressure in the discharge pipe, a running mixer or nitrogen inerting all falsify the reading. We use pressure compensation at the inlet and outlet together with flexible decoupling sleeves.
Bridging in the hopper
Cohesive materials hang up above the screw. The answers are agitators, correctly angled hopper walls and, for the most difficult powders, a hopper with an active loosening system.
Variable bulk density
Bulk density shifts with the delivery batch, the moisture content and the hopper fill level. The gravimetric controller trims the screw speed continuously, so the set mass flow stays constant.
Blockages in the feeding tube
Caking or fibrous products block the feeding element. We select variable-pitch screws or a shaftless spiral, which keeps the material loose by itself.
Short-term accuracy
At very low feed rates what counts is the evenness of the stream second by second. Multi-flight screws, higher speeds on a smaller cross-section and purpose-made discharge tube ends all improve it.
Ratio feeding
Multi-ingredient feeding systems
Loss-in-weight screw feeders are the ideal building block for continuous ratio-feeding systems, in which several ingredients are delivered simultaneously onto a common collecting conveyor or straight into the process. Each feeder measures the loss in weight of its own hopper, so the actual flow of every ingredient is known and controlled independently. One feeder acts as the master and the others run as slaves, holding a fixed mass ratio to the main ingredient.
A change of rate on the master automatically scales the rates of all slave feeders, so the system keeps the recipe proportions whatever the line throughput, and hoppers are refilled automatically without interrupting the feeding. InterProcess designs and integrates complete multi-ingredient feeding lines: feeder selection, control systems with industrial communication (4–20 mA, Profibus, Profinet, Modbus, EtherNet/IP) and recipe automation.
Industries and applications
Applications in key industries
FAQ
Frequently asked questions
Why InterProcess
Why choose our solutions
In-house manufacture
We design and build the DSL G feeders in our own works.
Engineered to the duty
Every system is designed around the customer’s process and material.
Turnkey delivery
From design and material trials through to commissioning and service.
Experience across industries
Food, chemical, pharmaceutical and cosmetics.
Safety and hygiene
Systems compliant with ATEX, HACCP, GMP and EHEDG.
Technical support and service
Fast response, 24/7 where required.
