The phenomenon of obvious cracking and poor fusion at the parting line position of rubber products during vulcanization is generally called "burning edge". Once it occurs, a large number of waste and defective products are often generated, which seriously affects the normal production. This phenomenon is analyzed, hoping to help solve the problem.
1. Reason Analysis The vulcanization of rubber is a complex chemical reaction. Due to the effect of high temperature, a large amount of volatiles will be generated. When the rubber is clamped and vulcanized, due to the action of high pressure, the rubber is formed and reacted in a closed cavity, and the volatiles generated by vulcanization cannot escape and form a certain pressure. With the progress of the vulcanization reaction, more and more volatile matter, the internal pressure is also increasing, finally breaking through the closed cavity and leaking out along the parting line. At this time, the vulcanization has been going on for a period of time, and the rubber on the surface has been vulcanized. Loss of fluidity, the defects formed by the impact of a large amount of volatiles leakage cannot be compensated, and they remain on the final product, resulting in "burning edge".
The above analysis is just an assumption. If it is correct, then the phenomenon of "burning edge" is likely to occur on products with the following characteristics:
1. For thick-walled products, because the heat conduction of rubber is difficult, the inner and outer layers are not easy to be vulcanized simultaneously. Therefore, such products are likely to cause edge burning conditions in which the surface layer of the product has been vulcanized but the interior has not been vulcanized.
2. Low-hardness products, because a large amount of softener is often added to the formula design of such products, which will contain more low-boiling volatiles, which will escape in large quantities during vulcanization. Compared with high hardness compounds, the phenomenon of "burning edge" is more likely to occur.
3. The mold structure design is easy to cause products with concentrated exhaust. For example, for cylindrical and cylindrical products, a combination of two semicircles is used for parting. All the volatiles generated by vulcanization are concentrated and discharged from the middle parting line, which often causes "burning edges" due to excessive concentration of exhaust gas.
Production practice shows that products with burnt edges often have the above characteristics. If they have both, the chances of "burnt edges" appearing are even greater.
Once you understand the cause of the problem, you can take appropriate measures to prevent and avoid it.
From the perspective of technology research and development, the best way to solve problems is to prevent them from appearing, rather than trying to solve them when they occur.
1. The production process is from the three commonly used molding methods of molding, injection molding and injection. For the same rubber compound, the chance of edge burning decreases in turn. In particular, the injection method can accurately preheat the compound to a higher temperature before injecting it into the cavity, which effectively shortens the process of heat transfer and vulcanization reaction after the compound enters the cavity, especially for low-hardness thick-walled products. , has unparalleled superiority in preventing and solving the burning edge problem. A product called BX024 produced by our company is a typical example, with low hardness (SHA35) and thick wall (15.2mm*24.2mm*39mm). It is produced by injection molding process, and there is obvious burning edge phenomenon. After various formula combinations, the burning edge phenomenon of the product cannot be effectively eliminated. Therefore, a low-temperature and long-term vulcanization process has to be adopted. The production efficiency is low, and the curing time of each mold product is long. After 10 minutes, microwave preheating was used to heat the rubber compound before injection. As a result, the vulcanization time was effectively shortened, and the edge burning phenomenon was also reduced. However, this method still has disadvantages compared with injection: It takes a period of operation to inject into the cavity. Because of the danger of scorch, the rubber compound cannot be preheated to a very high temperature, and the preheating temperature cannot be precisely controlled to preheat the rubber compound evenly, so it still cannot be used. The effect of the injection process.
2. Formulation design is the basis for the production of rubber products. A good formula must not only meet the performance requirements of the product, but also have good process performance and low cost, so that the product can be produced smoothly and efficiently. For thick-walled low-hardness products, special consideration should be given to the possibility of "burning edge" in formula design. Try to choose softeners with low boiling point and low volatile content and pay attention to controlling the dosage; in the selection of the sulfur-promoting system, pay attention to the selection of after-effect varieties as much as possible to obtain longer scorch time and vulcanization flat period; if possible, you can also Add additives that can improve the thermal conductivity of the rubber compound, so that the inner and outer layers of rubber can be vulcanized simultaneously as much as possible to avoid the condition of "burning edge".
3. Mold design It is also an effective way to avoid edge burning in mold design. For the mold structure of products with the above characteristics, try to adopt the mode of mold separation that can disperse the exhaust gas to avoid centralized exhaust. "burning edge" problem, and at the same time, it can also avoid the phenomenon of lack of glue pockets that are easy to form.
4. The vulcanization process can also be adjusted by taking measures. The low-temperature and long-term vulcanization process is the most commonly used method. Since the vulcanization temperature is reduced, the difference in the vulcanization speed of the inner and outer layers of the rubber is shortened; at the same time, due to the decrease in temperature, the volatile matter produced by vulcanization is reduced, and the resulting edge burning phenomenon is also reduced. . Reducing the clamping pressure, to a certain extent, disperses the concentrated leakage of vulcanized volatiles, and also has the effect of reducing the "burning edge".
The above methods all help to solve the "burning edge" problem. The solution from formula design is often limited by product performance and material cost, it is not easy to achieve results, and the cost of solving the problem is also high. Solving from the vulcanization process also often brings about the problem of reduced production efficiency. In contrast, choosing an appropriate production process, especially the advanced molding process of injection, and fully considering the mold parting method, can achieve twice the result with half the effort.
Disclaimer: The picture materials and articles on this platform come from the Internet, so the copyright belongs to the original author. If there is any infringement on your copyright and interests, please contact us, we will apologize and delete it quickly. Article source: Rubber Technology Network
Latest news
- The Combination and Foaming Process of
- Famous tire enterprise with multiple d
- Ministry of Commerce Initiate a final
- The Effect of Carbon Black on the Cutt
- Stop work orders encounter rising pric
- Lanzhou Petrochemical's carboxylated n
Contact us
- ADD: Room 4210, CEC Business Hall, No. 121-4, Nanjing South Street, Heping District, Shenyang
- TEL: 13644907299
- FAX: 024-25361668
- E-mail: boss@long-green.cn
> Company new