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Reasons and solutions for defects in rubber products

🕙 2023-09-15 👆

Reasons and solutions for defects in rubber products

Common defects in rubber products include rubber cracks, poor metal bonding, bubbles, sticky rubber surfaces, lack of adhesive, shrinkage, frost spraying, layering, tearing, and burnt edges.

(1) : Crack

The product colloid cracks and often appears closed in its natural state. After being subjected to force deformation, product defects can be detected.

Main production reasons:

1. The hot plate temperature is too high.

2. The design of the mold structure is unreasonable: there are sharp corners in the mold cavity and the R at the mold corners is too small.

3. The demoulder has sharp corners.

4. The mold has severe dirt and is difficult to demould.


1. Adjust the temperature of the hot plate.

2. Repair the mold in a timely manner, polish the sharp corners and increase the R at the corners.

3. Sand the demoulder into rounded corners.

4. Regularly clean the mold.


Main production reasons:

1. The rubber material has poor thermal tearing resistance.

2. There is too much isolation agent on the molded part, with a high concentration of isolation agent or incorrect use.

3. Excessive spraying and accumulation of release agent can cause product cracks.

Decontamination measures:

1. Adjust the formula and add softeners appropriately.

2. Strictly follow the molding process.

3. During the production process, it is necessary to control the amount of release agent used.


Main production reasons:

1. The vulcanization temperature specified in the process is too high, the prescribed demolding method is improper, and the demolding tools are not specified.

2. The pre forming process does not specify the type and concentration of isolation agent, or the selection of isolation agent is improper.

3. The demolding speed is too fast.

4. The slow injection speed of the rubber material causes product cracks.


1. Conduct timely verification and improvement based on specific issues, and redesign reasonable processes.

2. Adopt the correct mold ejection method and strictly prohibit using blunt tools such as iron bars to strike the mold cavity.

3. Increase the injection pressure and flow rate, and return the rubber material to pre molding and refining before production.

(2) Poor adhesion between rubber and metal

1. The metal surface treatment fails, resulting in poor physical adsorption of the primer

① Coarse the metal surface to ensure a certain roughness of the metal bonding surface. The commonly used treatment methods are sandblasting, shot blasting, phosphating, and galvanizing, in descending order of surface roughness observed under a microscope;

② The metal surface should be free of rust, oil stains, dust, impurities, etc.

2. The stability of the adhesive coating process is poor, and the adhesive is too thin, missed, undercoated, and residual solvents are also present

① Pay attention to operation to prevent leakage or underapplication of adhesive;

② The metal parts coated with adhesive should be fully dried to allow the solvent to evaporate and prevent residual solvents from volatilizing during vulcanization, leading to bonding failure;

③ To ensure a certain adhesive thickness, especially the surface coating adhesive. On the one hand, there can be sufficient substances to fully promote mutual diffusion and co crosslinking; On the other hand, a certain modulus gradient layer can be achieved.

3 The formula is unreasonable, and the vulcanization speed of the rubber material is inconsistent with that of the rubber slurry

① Improve the formula to ensure sufficient scorching time;

② Improve the mold and formula to ensure that the adhesive reaches the bonding area as quickly as possible;

③ Try to use a regular and semi effective vulcanization system and increase the amount of sulfur to achieve polysulfide cross-linking bonds;

④ Improve vulcanization conditions (temperature, time, and pressure);

⑤ Reduce the use of frost prone substances and plasticizers to prevent their migration to the rubber surface, thereby affecting adhesion;

⑥ The rubber material has been parked for too long, so use fresh rubber material instead.

4. Insufficient pressure

① Increase vulcanization pressure;

② Pay attention to the position and size of the overflow port and vacuum tank to prevent excessive communication between local areas and the atmosphere, resulting in insufficient pressure;

③ Ensure that the mold fits tightly to prevent excessive local pressure loss.

5. Volatilization or solidification of the effective components of the adhesive

① For metal parts that require pre drying before vulcanization, attention should be paid to the time and temperature control of pre drying. Excessive pre drying can lead to the volatilization of reactive substances and the burning (or solidification) of the adhesive;

② Pay attention to preventing metal parts from staying in the mold for too long during operation.

6. Foreign objects such as vulcanized rubber skin and crumbs are mixed into the mixed rubber and vulcanized together with the rubber, causing a small area of degumming and causing a large area of peeling of the product

① Strengthen material management

(3) Bubbles

Main production reasons:

1. The process is formulated with too few exhaust times.

2. Improper operation methods for process development.

3. Deviations in the specifications of formed parts during process development.

4. Inadequate feeding (if some products are placed vertically during production, it will cause air leakage and generate bubbles).

5. The exhaust frequency is too low.


1. Conduct timely verification and improvement based on specific issues, and redesign reasonable processes.

2. Prevent the skeleton from being contaminated during the production process.

3. Conduct on-site training to enhance employees' skills, quality awareness, and self inspection awareness.

4. Strictly operate according to the process regulations and produce according to the work instructions


Main production reasons:

1. The oil temperature or electric heating temperature is too low.

2. The equipment does not maintain pressure.

3. The device operating system is not functioning properly.

4. Due to the unique structure of the mold, the formed parts are prone to causing "stuffiness" in the mold cavity during loading, and gas is not easily expelled during exhaust.


1. Adjust the temperature.

2. Repair equipment.

3. For molds with poor exhaust, drill exhaust holes in the deepest position of the mold cavity.


Main production reasons:

1. Insufficient parking time for rubber material.

2. The formed parts were not formed according to the process specifications.

3. There is water on the surface of the formed part.

4. Insufficient mixing.


1. Adhesive material with surface water not yet dry after refining, suitable for

When lowering the temperature of the material (5 ℃), feed it 2-3 minutes in advance.

2. Park the rubber material on schedule according to the process regulations.

3. Rework the formed parts.

(4) Sticky rubber surface

Adhesion on the rubber surface is manifested by the presence of sponge like or obvious sticky protrusions on the surface of the rubber part of the product

Local gas retention in the mold cavity affects heat transfer and vulcanization of the rubber material

① Vacuum the mold to ensure that the rubber enters the mold cavity in a vacuum state. Ensure that the vacuum is in good condition to extract gas from the mold;

② Increase the number of air releases after mold closure;

③ Install exhaust slots or overflow slots on the mold.

2. The mold cavity is asymmetric, with dead corners and uneven heat transfer, resulting in uneven vulcanization

① Adjust the formula of the rubber material and use rubber material with a long flat vulcanization curve;

② Adjust the curing conditions, extend the curing time or increase the curing temperature.

3. Press out or stretch the rubber material and insert gas

① Improve extrusion and rolling conditions and processes.

(5) Lack of glue

The lack of rubber is manifested as the shock absorber rubber not filling the entire cavity.

Main production reasons:

1. The rubber material is burnt, mixed unevenly, the parking period of the formed parts is too short, the fluidity of the rubber material is too good, and the hardness is low.

2. The formed parts were not formed according to the process requirements: low unit consumption and inconsistent specifications.

3. Poor fluidity of the rubber material and slow injection speed cause product shortage.

4. Sulfurization personnel do not operate according to the requirements of the work instructions, do not receive effective training, or the operator's skills are not proficient: such as inadequate feeding (incorrect feeding or deviation), excessive initial pressure, insufficient exhaust times, improper use of release agents; such as temporary use of other release agents or similar release agents of different concentrations, and uneven spraying.


1. Adjust the formula, improve fluidity, and control the hardness within the upper and middle limits.

2. Strictly follow the relevant processes for processing to ensure that the formed parts meet the process requirements.

3. Return the rubber material to molding and refining before production

4. Conduct on-site training to improve operator skills, quality awareness, and self inspection awareness.

5. If there is a shortage of release agents on the night shift and they are urgently needed, verification work should be done well.


Main production reasons:

1. Equipment oil leakage and pressure drop.

2. The pressure surface is uneven, the template is uneven, and the ultimate pressure cannot meet the process requirements.

3. The mold cavity has severe scaling, high adhesive flow resistance, or errors between equipment, resulting in different storage capacities for each equipment.

4. Unreasonable structural design: inconsistent cavity height, excessive or small mold fit gap, coarse sugar injection points, incorrect injection hole size, mold aging.

5. The gap between the injection mold material nozzle and the nozzle is large, causing material to run out during injection, and the mold spherical pressure ring.


1. Equipment maintenance or machine replacement for production.

2. If the template is slightly uneven, sandpaper can be used. If it is severe, the template should be replaced.

1. Clean or wipe the mold.

2. Mold repair or scrapping.

3. After repairing the equipment, maintain consistency or increase the flow rate to ensure that the cavity is filled.

(6) Thick fried edges and flash edges

Reasons and solutions for defects in rubber products.jpg

Manifestation is the appearance of large voids and grooves on the rubber surface of the product, such as the feeding port, overflow port, parting surface, or the bonding area between rubber and metal.

1. Insufficient scorching time of rubber material can easily form vulcanized rubber particles and crumbs

① Extend the scorching time of the rubber material;

② Adjust the curing time (reduce the temperature to extend the curing time);

③ Avoid using adhesive that has been parked for too long;

2. The process is unreasonable, and there is too much rubber material to overflow. During vulcanization, the surface of the product is vulcanized before it is sandwiched between the parting surface and other parts

① Try to use transfer molding and transfer molding methods as much as possible;

② The rubber material should be accurately weighed and fed;

3. Mold contamination and unclean rubber material

① Clean the mold and adhesive;

4. The mold parting surface is not tightly matched, the design is unreasonable, and the overflow port is too large

① Improve the mold and try to avoid sensitive locations such as bonding areas on the parting surface of the product;

5. The heat transfer speed of the rubber material is slow, and the temperature rise of the inner and outer layers of the rubber material is inconsistent during vulcanization. The outer layer of the rubber material has already been vulcanized, but the inner layer of the rubber material expands due to heat, causing forced overflow and causing shrinkage cavities and interlayers

① Improve the formula of the adhesive material;

② Improve the vulcanization process conditions, such as using low-temperature long-term vulcanization. (Especially for thick products).

(7) Spray frost

Frost spraying refers to the formation of a white substance resembling frost mist on the surface of rubber products after being placed for a period of time

1. If the amount of raw materials such as vulcanizing agents, accelerators, and activators is too high, the dissolution in the rubber has become saturated and gradually migrates to the surface of the rubber

① Reasonably control the use of various raw materials through experiments;

2. Insufficient vulcanization and insufficient sulfur content of the product

① Fully vulcanized;

Reasons and Solutions for Rubber Frosting

(8) Layering

Layering is manifested as the inability of the rubber part of the product to form a whole, presenting a layered phenomenon.

1. Surface contamination of the adhesive material, especially oil stains

① Clean the surface of the adhesive or replace it with a clean adhesive;

2. Frost spraying

① Clean the surface of the adhesive or replace it with a clean adhesive;

3. Uneven mixing of different rubbers with poor compatibility

① When designing the formula, choose adhesive with good compatibility;

(9) Tears, burrs

Tearing and fuzzing are manifested by the rubber body of the shock absorber being torn or the surface of the rubber body being not smooth and flat.

1. Unreasonable demolding method, hard demolding, resulting in the product being torn or roughened

① Improve the demolding method and mold structure;

② Spray release agent;

2. The product is excessively vulcanized, resulting in a decrease in physical properties such as rubber strength and being torn or broken

① Adjust the vulcanization conditions to positive vulcanization;

3. The vulcanization temperature is too high

① Adjust the formula of the rubber material and reduce the curing temperature;

(10) Focal edge

Wrinkles and cracks at the parting.

Main production reasons:

1. The oil temperature or electric heating temperature is too high.

2. The equipment does not maintain pressure.

3. The device operating system is abnormal.

4. Lack of feeder or other auxiliary tooling, resulting in loading time exceeding the specified time.

5. The gap at the mold parting is too large.

6. The parting part of the mold cavity has a sharp edge or the cavity part R is too small.

7. The mold cavity is too close to the edge tearing groove.

8. The selection of mold parting method is not suitable.


1. Timely maintenance and repair of equipment.

2. Configure auxiliary tooling.

3. Repair the mold.


Main production reasons:

1. The formula of the rubber material has been changed, the content of the accelerator has decreased compared to the original content, and the process department has not been notified in a timely manner to change the vulcanization parameters.

2. The rubber material is overdue, resulting in a short scorching period.

3. The safety of the rubber formula is unreasonable.

4. Excessive molding of the adhesive material.

5. The unit consumption is relatively high.


1. Timely notify the process department for verification and changes

2. The rubber material shall be stored and refined according to the specified time in the process

3. Add antioxidant to remix or scrap the rubber material

4. Redesign the formula


Main production reasons:

1. The temperature for process development is too high.

2. The vulcanization time for the process formulation is too long.

3. Excessive exhaust frequency during process development.

4. Excessive loading time and exhaust frequency

Solution measures

1. Redesign the process based on specific issues.

2. Conduct inspections before going to work, and promptly verify and improve any issues found.

3. Conduct training according to requirements.