Çin Qingdao Beishun Environmental Protection Technology Co.,Ltd son şirket blog Hakkında Rubber Mixing Process: How to Choose Between Open Mill and Internal Mixer

Rubber Mixing Process: How to Choose Between Open Mill and Internal Mixer

1. Basic Definition

Internal Mixer (Banbury Mixer) It is a closed pressurized mixing equipment. Inside the sealed mixing chamber, the rotor generates shear force, and the ram applies pressure to intensively blend rubber stock with compounding ingredients.
Two-Roll Open Mill It features an open twin-roll structure. Shear force is formed through the roll gap. Rubber is repeatedly milled for mixing under atmospheric conditions without a closed chamber.

2. Comparison of Core Advantages & Disadvantages

表格

Comparison Item	Internal Mixer	Two-Roll Open Mill
Mixing Efficiency	High. Supports mass batch or semi-continuous production with large single-batch capacity.	Low. Intermittent manual operation limits production output.
Shearing Strength	Powerful mixing under pressure, delivers outstanding dispersion of powdery fillers.	Mild shear force. Poor dispersion performance for fine powders such as carbon black.
Temperature Control	Poor heat dissipation in closed chamber. Rubber heats up quickly, with high risk of scorch; mixing duration must be strictly controlled.	Open structure facilitates heat dissipation. Temperature is easier to stabilize, lowering scorch risk.
Dust Emission	Closed chamber minimizes powder flying, improves workshop environmental conditions.	Open feeding causes obvious dust pollution, bringing higher environmental compliance pressure.
Formula Adaptability	Ideal for formulas with high loading of carbon black and fillers that require sufficient dispersion; suitable for mass production.	Suitable for lab sampling, color matching, supplementary sheeting, re-milling; works well for heat-sensitive rubber prone to scorching.
Operation & Investment	High automation, parameterized stable control; higher equipment investment cost.	Simple operation with lower equipment cost; mixing quality heavily relies on operator experience.
Subsequent Processes	Discharged compound normally requires an open mill for sheeting, cooling and supplementary refining.	Can complete mixing independently, mainly used for lab sample preparation and auxiliary working procedures.

3. Selection Guide for Practical Production

✅ Choose an Internal Mixer if:

You operate mass production lines for tires, rubber hoses, seals and other bulk rubber products.
The formula contains high content of carbon black, calcium carbonate and other fillers requiring uniform dispersion.
Stable rubber quality is required to reduce deviation caused by manual operation.
Dust emission control and environmental standards are strictly required in the factory.

Recommended configuration: Main internal mixer + sheeting open mill + cooling conveyor line

✅ Choose a Two-Roll Open Mill if:

Conducting laboratory R&D, formula testing and small-batch trial production (kilogram-level samples).
Processing heat-sensitive rubber compounds that are easy to scorch, such as certain CR and EVM formulations.
Performing color mixing and color matching to visually check the uniformity of rubber color.
Executing re-milling, hot milling, thin passing and pre-mixing auxiliary operations.
Running multi-variety, small-batch production with frequent formula changeovers.

4. Widely Adopted Combined Process in the Industry

Rough mixing via internal mixer → Final mixing & sheeting on open mill

The internal mixer completes intensive dispersion of raw rubber, carbon black and fillers in rough mixing stage.
Discharged stock is transferred to the open mill, where vulcanizing agents and accelerators are added and blended at low temperature via thin passing.

Critical Note: Vulcanization systems cannot be added inside the internal mixer under high temperature, otherwise premature scorch will occur. This process route is adopted by most rubber manufacturers.

5. Common Misconceptions

Misconception: An internal mixer can fully replace open mills → Incorrect. Operators cannot observe rubber status intuitively inside the mixer. High-temperature conditions forbid adding vulcanizing agents, so open mills are indispensable for final mixing.
Misconception: Mixing effect of an open mill equals that of an internal mixer → Incorrect. Under the same mixing time, open mills achieve far poorer filler dispersion. Mass-produced products may suffer inconsistent physical properties.
Misconception: All rubber compounds can be processed by internal mixers → Incorrect. Heat-sensitive and low-viscosity soft rubber may degrade or scorch after long-time closed high-temperature mixing, making open mills the better option.

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