Technical Rubber Articles and Seals: A Matter of Tolerances.

Polymers, elastomers, and rubber do not behave like metal. Sounds obvious? Not quite, especially when we consider that designing technical components for molding requires a correct interpretation of the International Standard ISO 3302-1.

Which physical factors influence rubber dimensions during molding?

• Shrinkage:the compound vulcanized inside the mold at high temperatures (180°C) undergoes thermal contraction during cooling. This shrinkage is not constant; it varies depending on the type of polymer, the percentage of filler in the compound, and the direction of the injection flow.
• Post-vulcanization (Post-Curing): certain materials, such as silicones, require a post-molding oven cycle to complete cross-linking and optimize mechanical properties. This process leads to additional dimensional shrinkage.
• Hygroscopicity and environmental conditions: ambient humidity and temperature can cause slight variations in the component's dimensions even after production.

How should these variables be managed?

The ISO 3302-1 standard establishes the permissible tolerance classes for technical rubber molded parts regarding fixed dimensions F (which depend on the mold geometry) and closure dimensions C (which are affected by the mold split line and flash thickness).
Furthermore, it divides precision levels into four main classes for molding:

• M1 (fine): maximum precision, close to mechanical tolerances. Used for aerospace, medical applications, and critical micrometric mating clearances.
• M2 (medium): good precision level. A high standard for top-quality technical articles or industrial seals.
• M3 (coarse). commercial-grade precision. For bumpers, anti-vibration mounts, and protective bellows where a tenth of a millimeter does not affect functionality.
• M4 (non-critical): no specific precision required. For raw or large-scale structural components.

New Rubber and the importance of co-design.

In industrial manufacturing, we know that optimizing the cost/performance ratio is crucial. The best way to achieve the right balance and a profitable partnership is to involve our technicians right from the design phase.
NEW RUBBER is at your disposal for feasibility studies, recommendations on the most suitable compound for your application, and advice on component housing seats, taking into account the actual elastic behavior of the polymer.

NEW RUBBER Quality

At NEW RUBBER, in addition to maintaining a monitored quality system compliant with the UNI ISO 9001:2015 standard, we implement strict approval processes for finished products through the PPAP (Production Part Approval Process) procedure.
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