Select Language 
In the production and processing of compression-molded rubber products, rubber molds are critical tools for controlling and ensuring product geometry, assembly dimensions, and compliance with dimensional tolerances. The design and manufacturing quality of molds directly determines the dimensional accuracy, surface appearance, and final qualification rate of rubber products, and serves as the fundamental basis for achieving high-yield rubber molds.
Rubber products are typically manufactured by mixing raw rubber with various compounding ingredients, followed by processing under high temperature and high pressure conditions. The compound is injected into the mold cavity, where it flows and fills the designed cavity and groove structures. Through crosslinking reactions, the compound is finally transformed into vulcanized rubber products with practical application value.
This process is widely used in rubber mold manufacturing and high-precision silicone rubber mold forming.
1. Mold Materials and Service Environment as Sources of Contamination and Corrosion
At present, most rubber molds are manufactured from P20 medium-carbon steel or 45# steel, which belong to typical hot-work mold steels. Under long-term high-temperature vulcanization conditions, mold cavities are prone to the following types of damage and contamination:
Thermal Oxidation Contamination
When molds are exposed to high temperatures, oxidation reactions occur between the mold surface and oxygen in the air, forming oxidation contamination spots on the cavity surface.
Non-polar rubbers: prone to softening degradation and adhesion to the mold cavity surface
Polar rubbers: tend to form localized hardened spots, negatively affecting demolding performance and surface appearance
Deposition of Compounding Agents and Low-Molecular Substances
Certain compounding ingredients or low-molecular components in rubber compounds generate new reaction products during vulcanization, which gradually deposit on the mold cavity surface.
Corrosive Gases and Halogen Effects
Some rubber types, such as chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), and fluororubber (FKM), release corrosive substances such as HCl, H₂S, and metal chlorides during vulcanization. These substances cause significant corrosion of mold cavities, with particularly severe effects on silicone rubber mold processing and precision mold service life.
These contamination and corrosion phenomena not only degrade the appearance and intrinsic performance of vulcanized rubber products, but also reduce production stability, potentially leading to interrupted continuous operation, which directly impacts mass-production performance after rapid rubber mold delivery.
2. Key Factors Affecting Mold Contamination and Corrosion (Weight Analysis)
Based on practical experience and weight factor analysis, mold contamination and corrosion are primarily driven by the rubber compounding system, including:
Vulcanization system additives (sulfur, accelerators, zinc oxide)
Accelerators with low solubility and high migration tendency
Migratory antioxidants
Activators such as stearic acid
External Release and Mold-Release Systems
Polysiloxane-based agents
Paraffin-based agents (most severe contamination)
Fluorinated release agents
In addition, the following factors significantly amplify mold contamination:
Selection of mold coating materials
Mold surface finish and sandblasting treatment
Vulcanization temperature, time, and continuous production cycle
Temperature and humidity conditions during compound storage
In high-precision silicone rubber mold applications, the combined effect of these factors is particularly critical.
3. Three-Stage Evolution Mechanism of Mold Cavity Contamination
Stage 1: Migration of Contaminants
Under high-temperature conditions, vulcanization additives and reaction by-products migrate from inside the rubber compound toward the mold cavity surface.
Stage 2: Adhesion and Deposition
These substances adhere to and deposit on the metal mold surface, gradually forming hard-to-remove oxidized layers through thermal oxidation reactions.
Stage 3: Aging and Transfer
With prolonged continuous use, contaminants undergo aging and degradation:
A portion becomes firmly adhered to the mold cavity
Another portion transfers to the surface of vulcanized rubber products, causing impurities, surface cracks, and appearance defects
This is extremely unfavorable for manufacturers pursuing high-yield rubber molds.
4. Influence of Mold Structure and Surface Treatment on Contamination
In rubber mold manufacturing and silicone rubber mold processing:
High-polish, chrome-plated, or alloy-coated molds → low contamination tendency
Sandblasted, matte, or textured molds → high contamination retention
Particular attention should be paid to the fact that sandblasting-induced surface roughness can create an “anchoring effect” during vulcanization, leading to mechanical interlocking between rubber and mold surfaces. This results in severe sticking, demolding difficulty, and secondary contamination.
To address this issue, the following surface enhancement solutions are recommended:
Chrome plating
Tungsten-chromium coatings
Vanadium-cobalt alloy coatings
These technologies have been widely validated in high-precision silicone rubber molds.
5. Comprehensive Strategies for Reducing Mold Contamination
1️⃣ Optimization of Compound Formulation
Select compounding ingredients with good rubber compatibility, low migration, and low blooming tendency
Reduce low-molecular substances prone to blooming and deposition
2️⃣ Optimization of Mold Structure Design
Ensure smooth rubber flow channels
Minimize dead corners and retention zones, allowing contaminants to be stripped away during rubber flow even if contamination occurs
3️⃣ Optimization of Mold Surface Engineering
Prioritize electroplated or alloy-coated surfaces
Avoid unnecessary rough sandblasting treatments
4️⃣ Cleaning and Maintenance Mechanisms
Common mold-cleaning methods include:
Mechanical cleaning (wet, dry, manual polishing)
Chemical cleaning (acid cleaning / alkaline cleaning)
Ultrasonic cleaning
Currently, chemical cleaning is the most widely used method, though environmental protection requirements and operator safety must be carefully considered. Commercial mold-cleaning liquids and mold-cleaning rubber compounds may also be used as auxiliary solutions.
Conclusion
Mold cavity contamination in compression-molded rubber products is universal, recurrent, and systematic in nature. Only through systematic optimization of:
Compound formulation design
Surface treatment technologies
can manufacturers truly achieve:
Stable mass production of high-precision silicone rubber molds
Sustained and reliable production performance after rapid rubber mold delivery
In the production and processing of compression-molded rubber products, rubber molds are critical tools for controlling and ensuring product geometry, assembly dimensions, and compliance with dimensional tolerances.
