I. On-site Remedial Treatment
1. Dry wiping / Alcohol wiping (Recommended first choice for mild blooming)
- Use a clean, lint-free soft cotton cloth to dry-wipe away loose powder; for stubborn white bloom, use a cloth dampened with anhydrous ethanol (alcohol) to wipe gently.
- Allow to air-dry in a ventilated area after wiping; do not soak in large amounts of solvent, as this can cause rubber swelling, hardness changes, or deformation of the sealing surface.
2. Low-temperature baking (For wax or sulfur blooming; preferred for under-cured rubber)
- Bake in an oven at 60–80°C for 1–2 hours; the white bloom will re-dissolve into the rubber surface layer. Remove, let cool, and wipe away any surface residue.
- Strictly avoid excessive temperatures (>90°C); high heat accelerates aging and causes permanent deformation or collapse of the sealing surface in EPDM/NBR rubber.
3. Specialized rubber bloom remover (For heavy blooming on batches)
- Use a commercial rubber bloom remover; soak the part in the diluted solution for 10–15 minutes, rinse with clean water, and air-dry. This extracts free low-molecular-weight additives from the surface layer, significantly delaying the recurrence of blooming.
- **Perform a small-scale test** before full-scale treatment to ensure no swelling, no impact on hardness, and no contamination of the sealing surface; exercise caution with valves intended for food or drinking water applications.
II. Factory-level Root Cause Treatment (Resolving blooming at the source for valve seat batches)
1. Post-curing / Secondary vulcanization (Most effective for blooming caused by under-curing)
Under-curing is the most common cause of blooming in EPDM valve seats, resulting from incomplete cross-linking of free sulfur or accelerators.
- Apply a secondary vulcanization process tailored to the specific rubber type to ensure the vulcanizing agent reacts fully and to reduce free additives; wipe away surface exudates after the process is complete and the part has cooled. 2. Formulation Optimization (Root-cause solution; development of new rubber compounds)
1. Reduce the dosage of sulfur, accelerators, stearic acid, and protective waxes to levels within the rubber's solubility limits; consider switching the sulfur system to **insoluble sulfur**.
2. Add dispersing agents or PEG to improve the compatibility of additives within the rubber matrix.
3. Switch to low-migration antioxidants and high-molecular-weight additives to minimize the tendency for blooming (exudation).
4. For EPDM, consider using a peroxide curing system to reduce the risk of sulfur blooming.
3. Mixing Process Improvements
- Pre-disperse minor ingredients and add sulfur last; control mixing temperatures to prevent localized additive concentrations from exceeding limits.
- Implement slow, gradual cooling after vulcanization; rapid temperature drops can easily trigger blooming.
III. Storage and Protection (Preventing re-blooming; critical for long-distance export shipping)
1. Storage Environment: 0–25°C, 50%–70% humidity; keep away from light and avoid large diurnal temperature fluctuations or rapid cycling between hot and cold (common issues during long-distance container shipping).
2. Packaging: Seal in individual PE bags; do not store in the same container as PVC, oils/greases, or solvents.
3. Inventory Management: Prioritize "First-In, First-Out" (FIFO); for long-term stock of rubber valve seats, it is recommended to conduct quarterly spot checks of the surface condition.