SOSHH® SF-WeighFlex™ Ultra-Flexible TPU Weighing Bellows for Loss-in-Weight Feeders
⚡ Executive Summary for Process & Instrumentation Engineers
- Zero Reaction Force (< 0.05 N): Diaphragm-style multi-convolutions absorb vertical, horizontal, and angular movements without exerting opposing mechanical resistance onto load cells, maintaining gravimetric dosing accuracy within ±0.1%.
- Ultra-Soft 70 Shore A Polyether-TPU: Custom-compounded soft elastomer provides maximum flexural compliance while delivering over 110 N/mm tear strength.
- 100% Dust-Tight & Gasket-Free: Integrated spring-steel snap bands lock directly into precision spigots, creating an airtight seal without loose gaskets or manual clamps.
- Full Food & Pharma Compliance: Certified compliant with FDA 21 CFR 177.2600 and EU Regulation 10/2011; crystal-clear transparent wall ensures zero product bridging.
![Ultra-flexible multi-convolution TPU weighing bellows with blue snap-in cuffs for loss-in-weight feeders]()
- Fig 1. SOSHH® SF-WeighFlex™ multi-convolution TPU weighing sleeve with integrated snap-in cuffs.
In automated continuous compounding, pharmaceutical tableting, and infant formula manufacturing, gravimetric feeders and loss-in-weight (LIW) hoppers rely on precision load cells to control material feed rates. However, standard thick-walled sleeves or rigid silicone connectors act like stiff mechanical springs, transferring mechanical vibration and tare resistance directly onto the weighing sensors.
The SOSHH® SF-WeighFlex™ Weighing Bellows solves this critical pain point through precision-formed multi-convolution geometry and an ultra-soft 70 Shore A polyether formulation, delivering near-zero reaction force to eliminate baseline drift and false weight readings.
1. Eliminating Load Cell Signal Drift: The Zero-Reaction-Force Advantage
Why Standard Sleeves Fail on Gravimetric Feeders
Conventional straight sleeves manufactured from 85A to 90A polyurethane or reinforced canvas exhibit high elastic memory. As the feed hopper fills and empties:
- Vertical Spring Force: Axial expansion and contraction generate 5 to 50 N of opposing mechanical force, directly distorting weight signals.
- Lateral Side-Loading: Structural tolerances cause minor pipe misalignment, exerting horizontal shear forces onto load cells designed exclusively for pure vertical loads.
- Dynamic Vibration Transmission: Mechanical vibration from upstream agitators transfers through stiff sleeves, destabilizing high-speed digital filtering algorithms.
How the Multi-Convolution Diaphragm Mechanics Work
The SF-WeighFlex™ features precision-molded multi-convolutions. When dynamic axial or lateral motion occurs, the convolutions expand and flex freely like an accordion. The measured reaction force transmitted to the load cell is less than 0.05 N, allowing the weighing system to respond exclusively to true gravimetric mass changes.
![Cross-section of transparent multi-convolution TPU weighing bellows showing smooth swept-root internal contour]()
- Fig 2. Engineered convolution geometry absorbing 3D displacement while preventing internal powder buildup.
2. Key Features & Engineering Specifications
Material Integrity & Sanitary Compliance
- 100% Virgin Polyether TPU: Completely free of plasticizers, phthalates, and heavy metal stabilizers; highly resistant to moisture and microbial growth.
- Regulatory Approvals: Certified compliant with US FDA 21 CFR 177.2600, EU 10/2011, EC 1935/2004, and 3-A Sanitary Standards.
- Wide Swept-Root Convolutions: Smooth internal radii eliminate sharp V-grooves, allowing bulk powders to slide freely without stagnating or forming dynamic deadload.
Technical Performance Matrix
- Elastomer Hardness: Ultra-Soft 70 to 75 Shore A
- Reaction Force on Load Cell: < 0.05 N (Virtually Zero Load Transmission)
- Operating Temperature: -25°C to +85°C (Intermittent steam/CIP washdown up to +100°C)
- Operating Pressure: Full vacuum (-500 mbar) to positive pulse (+0.35 bar / +35 kPa)
- Tensile Tear Strength: > 110 N/mm (Die C)
- Elongation at Break: > 700%
- Optical Transparency: > 90% Light Transmittance for real-time visual inspection
3. Product Selection & Interface Guide
Standard Diameter Matrix
- DN50 (2"): Micro-dosing feeders, laboratory batching, and pharmaceutical API dispensing stations.
- DN100 (4") & DN150 (6"): Standard continuous loss-in-weight screw feeders (e.g., Brabender, Coperion K-Tron style) and blender inlet chutes.
- DN200 (8") & DN250 (10"): Large gravimetric batch weighing hoppers and gain-in-weight mixing vessels.
- DN300 (12") to DN600 (24"): Heavy-tonnage bulk silo discharge hoppers and raw material reception stations.
Interface Configurations
- Blue Snap-In Rings: Standard industrial snap-in configuration for 30-second tool-free changeovers.
- White Snap-In Rings: Certified food/dairy contact configuration meeting strict FDA standards.
- Sanitary Tri-Clamp (TC): Precision 316L stainless steel ferrules welded to TPU for CIP/SIP washdown piping.
- ANSI / DIN Bolted Flanges: Custom drilled polyurethane or stainless steel flanges for rigid duct transitions.
- Plain Cuffs: Smooth ends compatible with standard heavy-duty band clamps for legacy retrofits.
![Before and after installation comparison of stiff canvas sleeve vs transparent TPU weighing bellows on gravimetric feeder]()
- Fig 3. Real-world upgrade: Replacing stiff legacy canvas sleeves with SOSHH® zero-reaction-force TPU weighing bellows.
4. Compatibility & Performance (Compatible with Standard Snap-in Systems)
040E Standard Sleeve
- Material Hardness: 90 Shore A (Stiffer elastomer)
- Tear Strength (Die C): 67 N/mm
- Elongation at Break: 593%
- Mechanical Reaction Force: Measurable spring stiffness on micro-load cells
- Optical Clarity: Translucent
SOSHH® SF-WeighFlex™ TPU Bellows
- Material Hardness: 70 to 75 Shore A (Ultra-Soft Formulation)
- Tear Strength (Die C): 110+ N/mm (Enhanced Tear Resistance)
- Elongation at Break: 700%+ (Extended Cyclic Flex Fatigue Life)
- Mechanical Reaction Force: < 0.05 N (True Zero-Force Mechanical Isolation)
- Optical Clarity: High-Clarity Transparent (100% Visual Flow Monitoring)
5. Frequently Asked Questions (FAQ)
Q1: Why do precision loss-in-weight feeders require zero reaction force?
A1: Loss-in-weight feeders calculate feed rates by monitoring milligram-level weight loss over fractional seconds. Stiff conventional sleeves exert opposing mechanical spring forces as the hopper shifts, leading to tare baseline drift, calibration errors, and costly batch rejections.
Q2: Will fine powder accumulate inside the convolutions and affect tare calibration?
A2: No. The SOSHH® multi-convolution profile features wide, smooth internal radii rather than sharp folds. Dry powders slide downward naturally without bridging. Furthermore, the crystal-clear wall enables operators to verify zero material stagnation with a quick visual check.
Q3: Can SOSHH supply custom lengths, non-standard diameters, or conical transitions?
A3: Yes. In addition to standard metric and imperial sizes, SOSHH provides full custom fabrication—including conical reducers and square-to-round transitions—with Zero Tooling Fees and rapid 7-day dispatch.
Q4: Can one sleeve do weighing AND vacuum at the same time?
No single sleeve is optimal for both. Weighing requires a soft 0.5 mm convoluted wall so the hopper can move without pushing or pulling the load cell. Vacuum requires wire or ring reinforcement to stop the wall collapsing — and that reinforcement adds the stiffness that drifts a scale. Use the weighing bellows at the scale head, and a wire-reinforced or ring-reinforced sleeve at the vacuum leg. State both duties and we specify the correct sleeve for each position.
Q5: Our feeder is loss-in-weight with a 0.002-class target — will this sleeve limit accuracy?
The sleeve does not “have” an accuracy rating; it either protects or disturbs the scale. A soft multi-convolution 70 Shore A bellows transmits negligible spring force, so the load cell responds to true mass change. The final precision (e.g. ±0.2%) is set by the controller, hopper, and calibration — not by the sleeve. If your current sleeve is 1.5 mm or 85A+ stiff, that is the drift source.
6. Related Powder Handling Solutions
SOSHH® SF-ClearFlex™ Transparent TPU Snap-In Sleeves – Standard straight flexible sleeves for vibratory sifters and rotary valves.
SOSHH® SF-StatFlex™ Permanent Anti-Static TPU Connectors – ATEX Zone 20/21 static-dissipative sleeves 10⁶ ~ 10⁹ Ω
Pure PTFE Convoluted Bellows – Heavy-duty chemical- and high-temperature-resistant weighing bellows up to +260°C.
Stainless Steel Grooved Spigots (304 / 316L) – Precision-machined weld-in adapters for snap-in sleeves.
7. Request Your Engineering Consultation & Free Sample Kit
Eliminate load cell calibration drift and achieve sub-percent dosing precision with SOSHH custom-engineered ultra-flexible weighing bellows. Contact our technical team with your connection dimensions for 24-hour CAD drawings and factory-direct pricing.
- Free Sample Kits available for qualified OEM & EPC engineering projects
- 24-Hour Engineering Quotations with custom 2D/3D CAD models
- Direct Factory Supply with reliable DDP international shipping to your plant site
- 📧 Technical RFQ & CAD Review: amin@soshh.com
