How to deal with impurities and cracks in sealing rings?

The problems of impurities and cracks directly affect its sealing performance and service life, and need to be systematically addressed from three aspects: defect types, treatment methods, and preventive measures. The following are the specific handling methods:

I. Treatment of Impurity Issues

1. Surface impurities

Feature: Foreign substances such as carbon black particles, metal shavings, and fibers adhere to the surface of the sealing ring.

Treatment method:

Mechanical removal: Use tweezers or a blade to gently remove impurities to avoid damaging the surface.

Surface grinding: Use sandpaper with a grit of 800 or higher to grind the impurity area to make it smooth with the surrounding surface.

Solvent cleaning: Wipe the surface with alcohol or acetone to dissolve soluble impurities.

2. Internal impurities

Feature: Foreign substances are mixed inside the sealing ring, usually caused by uneven mixing of raw materials or contamination of the mold.

Treatment method:

Scrapping treatment: If internal impurities cannot be removed, it will be scrapped directly.

Raw material filtration: Check whether the mixed rubber has been filtered through a 200-mesh or larger filter screen to prevent impurities from mixing in.

Mold cleaning: Regularly clean the mold with sandpaper or solvent to prevent the residue of rubber compound.

Ii. Treatment of Crack Problems

Surface cracks

Feature: Fine cracks appear on the surface of the sealing ring, usually caused by insufficient vulcanization or stress concentration.

Treatment method:

Grinding and repair: Gently sand the cracked area with sandpaper of 800 mesh or above to remove surface defects.

Surface coating: Apply silicone oil or fluororubber solution to fill tiny cracks.

Secondary vulcanization: Re-place the sealing ring into the vulcanization tank and vulcanize it at 170-180 ℃ for 2-4 hours to enhance the surface strength.

2. Internal cracks

Feature: Cracks appear inside the sealing ring, usually caused by insufficient vulcanization pressure or uneven cooling.

Treatment method:

Increase the vulcanization pressure: Ensure that the pressure during vulcanization reaches 15-20 mpa.

Optimize the cooling process: Adopt staged cooling, first water cooling to 80 ℃ , and then natural cooling to room temperature.

Scrapping treatment: If the internal cracks cannot be repaired, it will be scrapped directly.

Iii. Defect Prevention Measures

1. Process control

Vulcanization parameters:

Temperature: Keep it at 160-180 ℃ to prevent material decomposition due to excessive temperature.

Time: Adjust the vulcanization time according to the thickness of the sealing ring to ensure complete vulcanization.

Pressure: Maintain 15-20 mpa to ensure that the material fills the mold and the gas is discharged.

Mold design

Exhaust groove: Set an exhaust groove of 0.05-0.1mm on the parting surface of the mold to prevent bubbles and cracks.

Surface treatment: Chrome plating or polishing of the mold surface to reduce the adhesion of the rubber compound.

2. Raw material Management

Mixed rubber

Filtration: The mixed rubber needs to be filtered through a filter screen with a mesh size of 200 or above to remove impurities.

Storage: Keep sealed to avoid moisture or contamination.

Additive

Antioxidant: Add 0.5-1% antioxidant to delay material aging.

Plasticizer: Add an appropriate amount of plasticizer to improve the fluidity of the material and reduce stress concentration.

3. Equipment maintenance

Vulcanizing machine

Regular calibration: Calibrate the temperature and pressure sensors monthly to ensure accurate parameters.

Sealing inspection: Check the sealing ring of the vulcanizing machine weekly to prevent gas leakage.

Mold

Regular cleaning: After each shift, clean the mold with sandpaper or solvent.

Wear inspection: Use a three-coordinate measuring machine to inspect the mold dimensions every quarter and repair the wear in a timely manner.

Iv. Example of Processing Flow

Steps, operation contents

Defect identification: Observe the surface of the sealing ring with a 10x magnifying glass to determine whether it is an impurity or a crack.

Impurity treatment: Surface impurities: Remove with tweezers + sand with sandpaper; Internal impurities: Scrap directly.

Crack treatment: Surface crack: Grinding + coating; Internal cracks: Scrapping + process improvement.

Process adjustment involves adjusting the vulcanization temperature, time, pressure or mold design based on the cause of the defect.

After re-vulcanization for quality verification, the leakage rate of the sealing ring is detected with a gas tightness tester to ensure it is <000000>le; 0.1mL/min.

V. Key Points to Note

Scrapping standard:

Internal cracks, bubbles with a diameter greater than 1mm, and metal impurities with a diameter greater than 0.5mm need to be scrapped directly.

Rework restrictions

The same sealing ring can be reworked at most twice. If it is reworked more than twice, it needs to be scrapped.

Personnel training:

Operators need to undergo training in the ISO 9001 quality management system and master the methods for identifying and handling defects in sealing rings.

Vi. Summary

Impurity treatment: Surface impurities can be repaired, while internal impurities need to be scrapped and raw material and mold management improved.

Crack treatment: Surface cracks can be repaired, while internal cracks need to be scrapped and the vulcanization process optimized.

Prevention first: Reduce the defect rate to below 0.5% through process control, raw material management and equipment maintenance.

Through the above methods, the problems of impurities and cracks in the sealing rings can be systematically solved to ensure that the product quality meets the requirements of standards such as GB/T 3452.2.