Many people wander this question , whether they purchase one laboratory mixing mill equipment ,then it can be suitable for both rubber and silicone material. It is econoic and can save a lot of investment, in addtion ,it may no need to take up so much space of your facility .
In fact ,it is not ideally — although a laboratory mixing mill equipment can be used for both material, yet the processing conditions, temperature settings, friction ratios, roller surface finishing, and cleaning requirements are significantly different.
If a laboratory need to switches the lab two roll mill equipment between these two material rubber and silicone mixing frequently , it’s best to use separate laboratory mixing mills respectively for each material, or you can customize the laboratory mixing machine with temperature control, special roll coatings, and easy-clean features ,so that handle both of the material efficiently.
1.Temperature Difference Between Rubber & Silicone Mixing
| Condition | Natural/Synthetic Rubber Mixing | Silicone Mixing | Main Effect |
| Processing Temperature | 60 °C – 120 °C depending on rubber type | 15 °C – 40 °C (lower to avoid premature curing) | Silicone requires cooler rolls |
| Roller Cooling | Light or moderate cooling | Strong water-cooling mandatory | Prevents crosslinking in silicone |
| Roller Surface | chrome-plated rolls | It is better adopt mirror-polished stainless steel | Silicone is sticky and needs smoother surfaces |
| Friction Ratio | Usually 1:1.2 ~ 1:1.3 for better mastication | Usually 1:1.1 or even equal-speed rolls | Silicone tears easily under high friction |
| Cleaning & Cross-Contamination | Rubber residual substances is easier to clean | Silicone is prone to absorb impurity very easily | Better use specialised lab mills |
| Viscosity Behavior | Viscosity decreases steadily with heat, enabling efficient filler dispersion. | Viscosity remains relatively stable but can suddenly spike if overheated, risking compound failure | Control the suitable temperature to keep the quality of mixture |
| Mixing Time | Usually longer due to high filler content | Shorter, as silicone flows more easily | Impacts production cycle time |
2. The Process of Laboratory Mixing Mill for Rubber Compounds
The process of two roll laboratory mixing mill for rubber mainly include mastication, filler or additives dispersion, and homogenization for compound material. Here , we list its main procedure as follows:
Step 1 — Preheating and Preparation
Firstly ,you need to set the temperature for roll to 40°C – 60°C ,which depends on the hardness of compound material.
Then adjust the friction ratio between front and rear rolls, usually the ratio for rubber material is 1:1.2.
Step 2 — Mastication
The raw rubber material is fed onto the gap between two rolls, and also the additives or other agents are fed if need , then start the two roll mill machine .
With these two rolls rotating at different speed in opposite direction , generating intensive shear forces ,which break down molecular chains and masticate the compound material , reducing viscosity.
The continue shearing action and mastication usually take about 3–5 minutes until desired plasticity is achieved.
Step 3 — Addition of Fillers and Additives
As these two counter roll rotating , you can gradually add other additives ,fillers , carbon black, silica, plasticizers, stabilizers, or antioxidants.
You can also adjust the gap of these two roll ,so that control the thickness of material each batch, depending on your specific needs .
Be sure to maintain the temperature of rolls to prevent premature vulcanization.
Step 4 — Final Homogenization
You confirm the compound material mix ,blend and masticated , all of the components are fully blended and uniformly dispersed.
Cut, fold, and feed rubber raw material repeatedly, each batch usually take around 5–8 times , until the compound material achieve homogeneity and uniform fully and evenly.
3. The Procedure of Laboratory Mixing Mill for Silicone
Silicone is a little easier ,it requires a lower temperature and more gentle mixing process in case of scorching and air or gas bubble .
Step 1 — Preheating and Preparation
Also ,it is the same as rubber procedure , firstly need to set the temperatures of roll to 15°C – 30°C , if possible ,it is better to use chilled water.
The material of cylinder rolls require polished stainless steel rolls to avoid material pollution.
Step 2 — Mastication
The silicone raw material is fed into the gap and gum evenly on the rolls.
Since it is specially for silicone material ,thus be sure to set the friction settings at 1:1.1 for smooth kneading and mastication.
Step 3 — Addition of Additives
As the rolls rotating , additive , stabilizers, fillers like fumed silica, pigments, or crosslinking agents are added to the material slowly ,then kneaded and dispersed evenly into the silicone material .
Since silicone is temperature-sensitive ,so be sure to maintain compound temperature strictly below 40°C ,or it would effect the quality of mixture.
Step 4 — Gentle Homogenization
Continuously cut and fold the processed mixture until it is completely homogenized and dispersed uniformly and evenly.
But you need to bear in mind avoiding over-milling as excessive shear and fold will cause molecular weight change.
3. Why The Conditions Of Two Rubber Differ
Rubber Compounding
Rubber material requires heat to soften polymers , so that mix and blend with other additive , fillers like carbon black, silica, or oils effectively and evenly.
→ Higher temperatures and slightly higher friction ratios help to the compound material are kneaded and dispersed fully and evenly .
Silicone Compounding
While silicone material is sensitive thermal ; if overheated, the silicone material prematurely cures and its molecular structure change and becomes unusable.
→ Cooling systems, smoother roll surfaces, and gentle mixing and mastication are very critical.
4. Recommendations for Manufacturers
If your lab mainly processes rubber material ,no matter for natural or synthetic rubber ,it is ok, choose a standard laboratory mixing mill with cooling system.
If your lab mainly processes silicone, then choose a specialized laboratory mixing mill feature with:
* Mirror-polished stainless steel rolls
* Efficient water-cooling
* Lower friction ratios
* Easy-clean surface design
If you need deal in two kind of materials for both rubber and silicone material,you need to consider prepare : Two separate two roll mills.
In conclusion , a laboratory mixing mill for rubber and silicone cannot operate under exactly the same conditions due to their special nature , the different process condition for different thermal behaviors, surface adhesion properties, and compounding requirements.