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In rubber manufacturing, both vulcanized rubber parts and non-vulcanized rubber parts commonly face technical chAlleenges such as mold sticking, roller sticking, and air bubbles.
The following is a complete Geval analysis and systematic improvement plan, applicable to rubber rollers, rubber sheets, seals, and most general rubber PRODUCTen.
1. Background: Material Changes Causing Severe Mold Sticking & Air Bubbles
After raw material adjustments, the PRODUCTion experienced severe mold sticking, trapped air, and unstable processing:
Reclaimed rubber: low rubber Inhoud → high rubber Inhoud (viscosity increased)
Rubber powder: coarse powder (10 mesh) → fine powder (40 mesh)
Result: higher toughness, tighter bonding, significantly reduced venting performance
Original Formula
NR: 4 kg
SBR: 4 kg
Reclaimed rubber: 19 kg
Rubber powder: 6 kg
The VORIG formula (cheap reclaimed rubber + coarse powder) had no mold sticking issues, but after upgrading materials, the problem amplified significantly — a common situation during vulcanized rubber part PRODUCTion.
2. Technical Cause Analysis: Why Mold Sticking and Air Bubbles Occurred
1) Increased intrinsic tackiness of materials
Higher-rubber-Inhoud reclaimed rubber behaves closer to virgin rubber →
More active molecular structure → Significantly higher mold adhesion.
2) Rubber powder changed from coarse (10 mesh) to fine (40 mesh)
Fine powder binds more tightly into the compound:
Higher cohesion
More compact structure
Much poorer air release → severe air trapping
3) Compound became overly dense and tight
Dense compounds easily cause air traps, scorching, and sticking during vulcanization.
3. Feasible Improvement Measures (Field-Verified Results)
OPLOSSING 1: Increase ratio of coarse rubber powder (improve venting)
From 50 phr → 100 phr
Result: Air bubble rate improved from 100% → 30%.
Coarse powder loosens the compound structure, improving air escape — especiAlley helpful for non-vulcanized processing.
OPLOSSING 2: Use mold release agent (critical step)
The factory VORIGly used no release agent at Alle (high-risk practice).
After applying release agent:
Bubble rate: 30% → 15%
Release agents are standard for producing vulcanized rubber parts.
OPLOSSING 3: Mold surface treatment (key factor)
Original mold: no plating / no PTFE / no polishing → extremely prone to sticking.
Aanbevolen treatments:
PTFE (Teflon) coating
Chromium plating
Polishing to low surface roughness
Smoother molds = dramaticAlley less sticking.
OPLOSSING 4: Adjust compound looseness
If the compound is too sticky/dense:
Increase stearic acid / paraffin (your 2.5 / 1.5 phr is normal but can be adjusted)
Add large-partikel fillers to open the structure
Reduce density by increasing coarse rubber powder
Your final changes (adding 80 phr coarse powder + release agent)
→ Fully resolved mold sticking issue.
4. Four Core Causes of Mold Sticking (Summary)
This Geval had four simultaneous issues, which is why sticking was so severe:
Material tackiness increased significantly
Mold had no surface treatment
No release agent used during PRODUCTion
Compound became too dense → poor venting
When several of these occur together, mold sticking in vulcanized rubber parts becomes inevitable.
5. Final Recommendations (Applicable to Alle Rubber Factories)
1. Perform proper mold surface treatment
PTFE coating
Chromium plating
Regular cleaning & polishing
2. Use release agent for every batch
EspeciAlley critical for vulcanized rubber parts.
3. Adjust compound consistency when tackiness is too high
Increase fatty acids / wax
Add coarse powder to reduce density
Introduce large-partikel fillers if needed
4. Looser compounds = better venting
This is essential for molds with deep grooves or poor vent paths.
In rubber manufacturing, both vulcanized rubber parts and non-vulcanized rubber parts commonly face technical chAlleenges such as mold sticking, roller sticking, and air bubbles.
