Rubber compounding is a critical step in manufacturing various rubber products. Two primary machines dominate this field: the internal mixer (such as the Banbury mixer) and the open two-roll mill. Though both aim to disperse additives into a rubber base, their operating principles, procedures, and outcomes differ significantly.china supply high quality long rubber strip feeder, This article outlines the step-by-step processing flows for each.
Internal Mixer Processing Procedure
The internal mixer operates as a closed, high-intensity blending system. The process begins with preheating the mixing chamber to around 50–80°C and ensuring the rotors are clean. Next, the rubber polymer (e.g., natural rubber or SBR) is fed through the hopper. The ram descends, applying pressure, and the rotors start rotating at variable speeds (typically 20–60 rpm). The intense shear and friction generate heat, carbon fiber roller rubber roller manufacturer,softening the rubber within 1–2 minutes.
After the polymer breaks down, the operator lifts the ram and adds solid additives – carbon black, silica, oils, and processing aids – through the hopper in a predetermined sequence. Zinc oxide and stearic acid often follow, then accelerators and sulfur are added later (unless using a two-stage mixing process to avoid scorch). The ram is lowered again, and mixing continues for 3–5 minutes total. The chamber temperature may reach 120–160°C. Efficient heat exchange via water-cooled jackets prevents overheating.
Once dispersion is achieved, the operator opens the drop door at the bottom, and the mixed compound is discharged as a lump. silicone rubber roller made in china,The entire cycle typically lasts 5–8 minutes. The internal mixer excels in high-volume production, providing consistent dispersion, reduced dust, and lower labor requirements. However, it cannot easily accommodate temperature-sensitive ingredients without proper sequencing.
Open Mill (Two-Roll Mill) Processing Procedure
The open mill features two counter-rotating horizontal rolls with adjustable gap and friction ratio. Preheating the rolls to 40–60°C is essential for adhesion. The procedure starts with feeding the raw rubber into the nip (the gap between rolls). The rubber forms a rolling bank and wraps around the front roll. The mill operator manually cuts, folds, and re-feeds the rubber to promote breakdown and softening – a process called “milling” that lasts 3–5 minutes.
Additives are then introduced gradually. Powders like carbon black are sprinkled onto the rolling bank, while oils are poured slowly to avoid slippage. Unlike the closed mixer, the operator constantly uses a spatula or knife to trim the compound, fold it, and form a “rolling bank” to incorporate materials. For thorough mixing, the operator may perform “cross-blending” (cutting and turning the sheet) or “triangling” (folding into a triangular shape). The mill gap is progressively narrowed to increase shear.
Once all ingredients appear uniformly dispersed (typically after 10–20 minutes), the compound is sheeted off as a continuous strip or cut into slabs. Temperature control is manual – water circulation through the rolls removes heat, but overheating can occur if mixing is prolonged. The open mill offers flexibility for small batches, color changes, and sensitive compounds (e.g., those with very fast accelerators). However, it requires high operator skill, exposes workers to dust and heat, and has lower productivity.
Key Differences in Process Flow
Feature Internal Mixer Open Mill
Cycle time 5–8 minutes 10–20 minutes
Labor intensity Low (automated) High (manual)
Dust exposure Minimal Significant
Temperature control Excellent (jacketed) Moderate
Batch size Large (50–500 kg) Small (1–50 kg)
In summary, the internal mixer is preferred for large-scale, efficient, and clean compounding, while the open mill remains indispensable for small batches, specialty compounds, and laboratory work. Many factories actually use both in sequence: internal mixing for initial dispersion, followed by open milling for cooling, adding curatives, and final sheeting. Understanding these procedures allows compounders to select the right tool for each task.
Post time: Apr-03-2026
