Scorch is essentially the accumulation of the influence of heat and time on the rubber compound during the process. It is the early vulcanization phenomenon of the rubber compound, which can also be called the thermal history of the rubber compound. The scorch time is often used to measure the difficulty of scorch. Scorch time can usually be determined by a Mooney viscometer. If the thermal history of the rubber compound is too long and the temperature is too high, the scorch time of the rubber compound can be gradually shortened.

1. How to judge rubber scorch?

In the rubber mixing process, if the film is found to be grainy or the rubber is found to be elastic or crepe-like, it is an omen of burning.

1. The scorched rubber, after vulcanization, the product is not bright (matte surface), the surface has obvious wrinkles, the surface is uneven, and it is very brittle and easy to crack.

2. The surface of the scorched rubber is also uneven and has hard lumps. And the scissors cut the constantly scorched rubber.

3. The scorched rubber can be measured by Mooney scorch test.

4. There are protruding lumps in the scorched part. Try cutting it and see that the hard block is cut continuously by the scissors.

Second, the prevention method of scorch

1. The design of the additive formula of the rubber compound should be appropriate and reasonable. As far as possible to adopt a variety of ways to use accelerators together,

In order to adapt to the high temperature, high pressure and high speed rubber mixing process, an appropriate amount (0.3-0.5 parts) of anti-scorch agent can be used. It is also possible to reduce the compounding amount of the vulcanization accelerator, but this will lead to a decrease in the physical properties of the rubber product. It is very important to understand this. The vulcanization accelerator is rarely used alone, and most of the two or three accelerators are used in combination. The way. Once there is a problem with the combination, the scorch of the rubber cannot be prevented. Generally speaking, the main accelerator for general-purpose rubber is the sulfenamide accelerator. The main accelerator DM is a universal accelerator; the accelerator M has high scorch property, and the sulfenamide accelerator has scorch resistance, but due to the slow starting speed of vulcanization, it should be selected according to the requirements of the rubber compound. . Thiuram is an auxiliary accelerator. In the summer and high temperature season, the auxiliary accelerator should be used in a reduced amount, while the main accelerator should not reduce its compounding amount as much as possible.

2. For the cooling measures of the rubber compound, the operating temperature can not exceed the critical point of scorch by strictly controlling the machine temperature, roller temperature and sufficient cooling water circulation.

3. The management of semi-finished rubber materials ensures that each batch of materials is followed by a flow card, follows the principle of "first-in, first-out" inventory, and stipulates that the maximum storage time of each vehicle material does not exceed. Also, keep the warehouse well ventilated.

3. Treatment of scorch

On the open mill, the roll temperature is low, and the glue loading capacity is small. It cannot be wrapped, packaged, rolled, parked for 24 hours, and then mixed with good materials for use, and the mixing amount is 15-20%. When the scorch is serious, add stearic acid and oil softener to destroy its cross-linked structure.

4. Scorch time

The scorch characteristics of rubber are usually expressed by Mooney scorch time ts at 120°C, and can also be expressed by t10 or ta1 and ta2 on the vulcanization curve measured by a vulcanizer. t10 is the scorch time. is the time it takes for the torque to reach 10%. The scorch time of the rubber compound is related to its technological process, rubber accelerator process conditions, rubber compound hardness and the return of the compound material and other factors. Generally, the soft compound is 10-20 minutes, most compounds (excluding high-filled hard compounds or compounds with high processing temperatures) are 20-35 minutes, and high-filled hard compounds are 35-80 minutes. Usually, when the rubber material is scorched, the film is partially vulcanized, and elastic bumps appear on the surface, which affects the apparent quality and physical and mechanical properties of the rubber product, and also increases the load on the processing equipment abruptly.