The manifestation and impact of edge shrinkage
The edge shrinkage usually manifests as incomplete or obvious shrinkage of the edge part of the product, resulting in missing edges or irregular shapes of the finished product. Its impact can be divided into the following aspects:
1. Decline in appearance quality
Rubber products with incomplete edges look rough and uneven, which directly affects the visual effect of the product. In industries that require high appearance standards (such as automotive parts, household appliances, etc.), such defects may cause the product to fail quality inspection.
2. Problems with dimensional accuracy
Edge shrinkage often causes the finished product size to not meet the design requirements, especially in applications that require precise dimensions. Such defects may cause the product to be unable to assemble or seal.
3. Impaired functionality
For functional rubber products such as seals and shock absorbers, edge shrinkage will directly destroy their functions. For example, a defect in the edge of a seal may cause air or liquid leakage, while an insufficient size of a shock absorber may not be able to effectively cushion.
4. Increased economic losses
Product shrinkage means a large increase in scrap rate, increasing raw material and production costs.
Main causes of edge shrinkage
1. Too high vulcanization temperature
Too high vulcanization temperature will accelerate the cross-linking reaction of the rubber, causing it to harden before the cavity is completely filled, resulting in the failure of the edge material to be in place. Especially when the cavity is complex or the edge is thin, high temperature will aggravate the shrinkage problem.
2. Too much rubber
Too much rubber will not only increase the overflow, but also cause uneven distribution of the material in the cavity, and shrinkage of the edge due to insufficient material diversion. In addition, excessive rubber will increase the pressure at the edge of the cavity, causing some material to be squeezed out of the cavity.
3. Too fast vulcanization speed
The vulcanization speed directly affects the filling time of the material. If the vulcanization speed is too fast, the rubber may begin to solidify before the cavity is filled, resulting in shrinkage in the unfilled edge area.
4. Mold design defects
Mold design without overflow grooves will hinder the discharge of excess material, resulting in uneven distribution of the rubber in the mold cavity. In addition, rough and uneven edges of the mold cavity, or insufficient mold sealing, will also cause edge shrinkage problems.
5. Mold exhaust problems
During the molding process, if the air in the mold cavity cannot be discharged in time, the flow of the rubber at the edge will be hindered, resulting in edge shrinkage. This situation is particularly obvious when the fluidity of the rubber is poor.
6. Improper control of process parameters
Insufficient pressure, too short vulcanization time, or improper mold temperature control will lead to insufficient fluidity and filling capacity of the rubber in the mold cavity, resulting in defects in the edge part.
Methods to solve the phenomenon of edge shrinkage
For different causes of edge shrinkage, the following solutions can be taken:
1. Optimize the vulcanization temperature
Appropriately lower the vulcanization temperature to allow the rubber to have more flow time in the mold cavity to ensure that the edge part can be fully filled. For example, adjusting the vulcanization temperature to a reasonable range (such as 160℃-180℃) through experiments can significantly improve the filling effect of the material.
2. Control the amount of rubber
Control the amount of rubber through precise weighing to ensure that it can fill the mold cavity without excessive overflow. In actual production, automatic weighing equipment can be used to improve the accuracy of the amount of rubber.
3. Adjust the vulcanization speed
Modify the ratio of vulcanizer in the rubber formula and reduce the vulcanization speed to extend the flow time of the rubber. This can be achieved by reducing the amount of accelerator or choosing a slower vulcanizer system.
4. Add overflow grooves and venting grooves
Add enough overflow grooves and venting grooves in the mold design to allow excess rubber to be discharged smoothly while ensuring that the air in the mold cavity can be discharged in time. Especially for products with complex edges, reasonable design of venting grooves can greatly reduce edge shrinkage.
5. Strengthen mold maintenance and optimization
Regularly check the sealing and edge flatness of the mold, and repair or replace the mold in time if problems are found. In addition, in the mold design stage, the use of numerical simulation technology to optimize the mold cavity design can also avoid the shrinkage problem in advance.
6. Adjust process parameters
According to actual production needs, optimize the process parameters, such as appropriately increasing the molding pressure, extending the vulcanization time, or reducing the mold temperature. These adjustments can effectively improve the fluidity of the material in the mold cavity and ensure that the edge part is filled.
7. Improve the rubber formula
By adjusting the formula, the fluidity of the rubber is enhanced. For example, increasing the plasticizer or reducing the filler content can significantly improve the flow ability of the material in the mold cavity. In addition, extending the scorch time can also prevent the rubber from solidifying prematurely before the filling is completed.
8. Strengthen production management and employee training
Formulate strict process standards and operating specifications, strengthen production management, and ensure that the process parameters of each link meet the requirements. At the same time, train production operators to make them familiar with equipment commissioning and problem-handling methods.
Conclusions
Edge shrinkage is a common problem in the production of rubber-molded products. Its causes are complex and involve multiple aspects such as vulcanization temperature, rubber dosage, mold design, and process parameters. To solve the edge shrinkage problem, it is necessary to start from multiple links, including optimizing the vulcanization process, improving the rubber formula, rationally designing the mold, and adjusting the process parameters. Through systematic analysis and continuous improvement, the edge shrinkage phenomenon can be effectively reduced and product quality and production efficiency can be improved.
