Improving LSR Medical Tube Production with a Customised Vertical Kneading Machine
A European medical device manufacturer was struggling to produce consistent LSR (Liquid Silicone Rubber) tubes containing 3‑5% of an active pharmaceutical ingredient (API) powder. Their existing horizontal mixer caused API agglomeration, inconsistent hardness values across batches, and visible air bubbles in the extruded tubes — leading to a rejection rate of approximately 12% at final inspection.
The company contacted us to find a solution. After detailed consultation, we recommended a customised vertical kneading machine with vacuum, heating/cooling jacket, and a modified blade design optimised for powder dispersion.
Challenges identified
API powder had a tendency to form micro‑agglomerates that were difficult to break
LSR base viscosity increased rapidly as API was added, requiring high torque
The process required strict temperature control (18‑22°C) to prevent premature curing
Air entrapment during mixing created pinholes in the final tube wall
GMP cleanroom operation demanded easy sterilisation and minimal operator contact
Solution – The customised vertical kneader
We supplied an SXJ‑100 model (100‑litre working volume) with the following modifications:
| Feature | Standard SXJ‑100 | Customised Solution |
|---|---|---|
| Blade design | Standard “S” shape | Extra‑wide blades with enhanced scraper edges |
| Disperser | 11 kW / 2100 rpm | 15 kW / 2980 rpm for higher shear on API powder |
| Jacket cooling | Single‑zone water | Dual‑zone (side + bottom) for uniform 18‑22°C |
| Vacuum system | Single‑stage pump | Two‑stage pump with ‑0.098 MPa and fast‑dump valve |
| Surface finish | Ra 0.8 µm | Ra 0.4 µm electro‑polished, crevice‑free welds |
| Control system | Basic PLC | PLC with recipe management and full FDA‑compliant data logging |
We also provided a dedicated API powder feeder that integrated with the vertical kneading machine‘s control system, allowing slow, controlled addition of the powder while the disperser was running at high speed.
Implementation and results
After installation and operator training, the manufacturer ran a 12‑batch validation study. The new vertical kneader consistently produced homogenous LSR/API compounds with:
No visible API agglomerates (verified by microscopic inspection at 50x magnification)
Batch‑to‑batch hardness variation reduced from ±5 Shore A to ±1.5 Shore A
Bubble‑free material after 8 minutes of vacuum mixing (compared to 20 minutes previously)
Rejection rate dropped from 12% to 1.8% — saving ~€85,000 per month in scrap and rework
Cleaning time reduced from 90 minutes to 35 minutes per batch, thanks to the open bowl design and CIP compatibility
Key performance metrics before and after
| Metric | Before (Horizontal Mixer) | After (Vertical Kneading Machine) |
|---|---|---|
| Mixing time (per 100L batch) | 45 min | 28 min |
| API dispersion quality | Inconsistent (agglomerates) | Uniform (no agglomerates) |
| Hardness tolerance (Shore A) | ±5 | ±1.5 |
| Rejection rate | 12% | 1.8% |
| Cleaning time | 90 min | 35 min |
| Annual scrap cost | ~€1,020,000 | ~€153,000 |
Customer feedback
“Switching to the vertical kneading machine was a game‑changer for our LSR tube production. Not only did we solve the API agglomeration problem, but we also gained better control over temperature and vacuum. The customised blade design and the dual‑zone cooling jacket made all the difference. Our operators find the machine much easier to clean, and the reduction in scrap has paid for the investment in less than six months.”
— Production Manager, Medical Device Division
This case demonstrates that a well‑designed vertical kneading machine, tailored to the specific challenges of LSR + API mixing, can deliver substantial improvements in product quality, operational efficiency, and cost savings. For any manufacturer facing similar issues with high‑viscosity, temperature‑sensitive, or powder‑loaded formulations, the vertical kneader represents a proven and reliable technology.
All technical data and performance figures are based on actual project records. For a customised proposal or to arrange a free material test on your own compounds, please contact our technical sales team.
