What common problems will rubber transmission belts encounter during the vulcanization process

In the manufacturing process of rubber transmission belts, the vulcanization process is a key step in determining its performance stability, service life and appearance quality. The vulcanization process mainly forms a cross-linked structure of rubber molecular chains through high temperature and high pressure environment, thereby giving the material good elasticity, heat resistance, wear resistance and mechanical strength. However, due to the influence of many factors such as equipment, formula, and operation, rubber transmission belts often have various quality problems during the vulcanization process, which may cause product scrapping or substandard performance in severe cases.

Incomplete vulcanization (undervulcanization)
Incomplete vulcanization is one of the most common problems in the manufacture of rubber transmission belts. It manifests itself as sticky surface of the belt, poor elasticity, insufficient hardness, and decreased mechanical strength. Undervulcanization can cause premature breakage, delamination or tensile deformation of the transmission belt during use.
The main causes of undervulcanization include: too low vulcanization temperature, insufficient vulcanization time, insufficient vulcanizer ratio, or uneven temperature control of vulcanization equipment. Undervulcanization areas are usually distributed in thicker parts or mold corners.

Over-vulcanization (over-sulfurization)
Over-vulcanization will damage the molecular chain structure of the rubber, make the material brittle, reduce the fracture strength, and the belt body is prone to cracks or even belt breakage. The rubber surface will show burnt, hardened, and dull phenomena.
The main causes of over-sulfurization include: too long vulcanization time, too high temperature setting, and improper proportion of vulcanization accelerators in the formula. Especially in automated batch production, if the vulcanization parameters are not adjusted for belts of different specifications, batch over-sulfurization problems are likely to occur.

Vulcanization bubbles
Bubbles are closed cavities formed inside or on the surface of rubber transmission belts, which have a great impact on structural integrity. Bubbles will reduce tensile strength and may cause delamination or bulging problems.
The causes of bubble formation include: uneven mixing leading to retention of volatile components, insufficient preheating leading to insufficient discharge of water vapor, unreasonable design of mold vents, insufficient vulcanization pressure, etc. Bubbles usually appear in the center area or on the plane near the reinforcement layer.

Surface cracking and scorching
After vulcanization, small cracks or scorching marks appear on the rubber surface, indicating that the local temperature is too high or the heat distribution is uneven during the vulcanization process. Such defects not only affect the appearance, but may also cause the rubber surface to harden, reducing wear resistance and ductility.
Common causes include: uneven mold preheating, poor control accuracy of the heating system, unscientific vulcanization time setting, and uneven belt thickness distribution causing heat conduction differences.

Dimensional shrinkage and deformation
After vulcanization, the rubber transmission belt has abnormal shrinkage, deformation or warping, which will lead to installation difficulties, transmission deflection, increased noise and other problems, seriously affecting customer experience and product reputation.
The main causes of dimensional abnormalities are: high oil content in the rubber compound, unbalanced ratio of formula fillers, failure to use appropriate shrinkage compensation design, insufficient molding mold precision, and improper control of the demolding process.

Poor vulcanization at the joint
The joint part of the rubber transmission belt is the weak point of the entire belt. If the vulcanization is poor, it is very easy to crack, delaminate, tear and other failure problems, which seriously affect the strength and stability of the belt.
Joint problems are mainly caused by factors such as insufficient joint hot pressing time or pressure, incomplete joint surface treatment, uneven thickness of vulcanized rubber layer, and unstable equipment clamping force. Especially in high-strength synchronous belts or multi-layer structures, the quality of joint vulcanization directly determines the service life of the entire belt.

Delamination of skeleton material
The skeleton layer of the rubber transmission belt is usually composed of reinforcing materials such as polyester, aramid, and steel wire. If the skeleton and rubber layer are not firmly bonded during the vulcanization process, it is easy to delaminate, peel or break after being stressed.
This problem generally stems from: improper design of the rubber bonding system, surface contamination or inadequate treatment of the reinforcing material, uneven lamination process, and insufficient vulcanization pressure. It is particularly obvious in combined belts or wide flat belts.

Mold contamination and demolding difficulties
Mold contamination causes visual defects such as impurities, bubble marks, and color spots on the surface of the rubber belt, affecting the product grade assessment. Difficult demolding may cause the rubber surface to be pulled during demolding, causing dimensional deviation or mold damage.
The reasons include: incomplete mold cleaning, incompatible release agent, violent vulcanization reaction of rubber with a lot of residue, rough mold surface, etc.

Inconsistent local hardness
After vulcanization, the hardness of different areas of the belt body is obviously different, which may cause jumping, vibration or noise problems during operation. In severe cases, the low hardness area will become the starting point of fatigue damage.
The reasons for such defects are usually uneven mold temperature distribution, uneven dispersion of rubber fillers, complex belt structure design leading to asymmetric heat conduction, or unstable vulcanization system pressure.