This week at the LRMIX factory in Shandong, China, two units of our 100L Vacuum Heating & Cooling Sigma Kneader have completed full production and quality inspection — and are now ready for delivery. Both machines are configured for silicone rubber compounding, with dual-function jacketed vessels, integrated vacuum systems and hydraulic tilt discharge.
This post walks through the key configuration choices for this build and why they matter for silicone rubber production.
Why Silicone Rubber Needs a Vacuum Heating Kneader — Not Just Any Mixer
Silicone rubber compounding is one of the most demanding mixing applications in industrial manufacturing. The base polymer — high-molecular-weight polydimethylsiloxane (PDMS) gum — has an extremely high viscosity that cannot be handled by paddle mixers, dispersers or ribbon blenders. It requires the specific counter-rotating Z-blade action of a sigma kneader to develop the shear, compression and folding forces necessary for complete fumed silica dispersion.
Three process requirements define the correct machine configuration for silicone rubber:
1. Temperature control throughout the entire mixing cycle Fumed silica incorporation generates significant frictional heat. Without active cooling, compound temperature rises above 60°C — dangerously close to the activation threshold of peroxide vulcanising agents (DCP, DBPH). The dual-function jacket on this machine circulates hot water from a mould temperature controller during the warm-up phase, and switches to chilled water for cooling during and after fumed silica addition. This keeps compound temperature below 50°C throughout the critical mixing stages.
2. Vacuum degassing to eliminate air bubbles Fumed silica has an extremely high surface area (150–400 m²/g) and entraps large volumes of air during incorporation. If not removed, these air pockets become voids in the cured silicone product — causing surface defects, reduced tensile strength and rejection in quality-sensitive applications. The vacuum system on this unit evacuates the sealed chamber to ≥ –0.09 MPa, removing entrapped air after the main mixing phase.
3. Efficient discharge of high-viscosity compound Fully compounded silicone rubber is extremely sticky and resistant to gravity flow. The 130° hydraulic tilt system discharges the complete batch in under 3 minutes — compared to 15–20 minutes of manual discharge. This reduces both labour cost and the risk of contamination during discharge.
Machine Configuration: What Was Built
| Parameter | Specification |
|---|---|
| Effective Volume | 100 Litres |
| Main Motor | 15 kW |
| Gear Reducer | ZLY Hard-Tooth Face, HRC 58–62 |
| Blade Type | Sigma Z-blade, Counter-Rotating, Differential Speed |
| Jacket | Dual-function — heating (mould temp controller) + cooling (chilled water) |
| Vacuum | ≥ –0.09 MPa |
| Discharge | Hydraulic Tilt 130° |
| Vessel Material | Carbon Steel (SS304 available) |
The ZLY Hard-Tooth Reducer: Why It Matters for Silicone Compounding
One detail often overlooked in kneader selection is the gear reducer. Silicone rubber gum loading creates extreme peak torque at the start of each batch — when the stiff, cold gum base first contacts the blades. Standard soft-tooth reducers are not designed for this repeated shock loading and will develop gear wear or failure over time.
The ZLY series hard-tooth face reducer uses carburising and quenching heat treatment to achieve gear surface hardness of HRC 58–62 — delivering 40% higher load capacity than soft-tooth alternatives. This is the correct specification for sustained heavy-duty silicone rubber compounding.
Suitable Applications for This Configuration
This 100L vacuum heating kneader is not limited to silicone rubber. The same combination of high torque, temperature control and vacuum degassing makes it suitable for:
- HTV silicone rubber compounding (primary application)
- Chewing gum and bubble gum mass preparation
- Hot-melt and structural adhesives
- BMC / DMC compound mixing
- Carbon electrode paste
- Ceramic clay body preparation with binder systems
Request a Quote
LRMIX supplies sigma kneaders from 5L laboratory scale to 3,000L production capacity. Standard and custom configurations are available including explosion-proof, steam heating, electric heating and SS316L food-grade options.
WhatsApp: +86 198 1875 7839 Email: info@lrmixer.com
→ View LRMIX Sigma Kneader Range: https://lrmixer.com/product-category/sigma-mixer/ → Silicone Rubber Application Guide: https://lrmixer.com/silicone-rubber-mixing/
