Vulcanization temperature is a key parameter in the vulcanization process of conveyor belts, directly affecting the crosslinking density, physical properties and service life of rubber materials. Reasonable control of vulcanization temperature is crucial for ensuring the quality of conveyor belts. The following is an analysis of the influence of vulcanization temperature on the cross-linking structure, physical and mechanical properties, aging performance and appearance quality of rubber:
First, the influence of vulcanization temperature on the crosslinking structure of rubber
Crosslinking density and vulcanization rate
An increase in vulcanization temperature will accelerate the crosslinking reaction of rubber molecular chains, resulting in a significant increase in crosslinking density. For instance, when natural rubber is vulcanized at 140℃, the crosslinking density increases by approximately 20% compared to that at 130℃, which directly affects the hardness and elasticity of the conveyor belt.
Excessively high temperatures may lead to excessive cross-linking, forming an overly dense network structure, making the rubber brittle and reducing its tear resistance.
Types and distributions of crosslinking bonds
At different vulcanization temperatures, different types of crosslinking bonds (such as single sulfur bonds, double sulfur bonds and polysulfur bonds) will form in rubber. During high-temperature vulcanization, the proportion of polysulfur bonds decreases while that of monosulfur bonds increases, resulting in a decline in the dynamic fatigue performance of rubber.
Uneven distribution of crosslinking bonds may lead to local stress concentration, affecting the durability of the conveyor belt.
Second, the influence of vulcanization temperature on physical and mechanical properties
Hardness and elasticity
An increase in vulcanization temperature will increase the hardness of rubber and reduce its elasticity. For example, after nitrile rubber is vulcanized at 150℃, its hardness may increase by 5-10 Shore A, but the elastic recovery rate decreases by 10%-15%.
Excessive hardness will cause the conveyor belt to be prone to cracking when bent, while insufficient elasticity will affect its impact resistance.
Tensile strength and elongation at break
An appropriate vulcanization temperature can enhance the tensile strength of rubber, but excessively high temperatures will lead to a decrease in tensile strength. For instance, when chloroprene rubber is vulcanized at 160℃, its tensile strength may decrease by 15% to 20% compared with that at 140℃.
The elongation at break decreases with the increase of vulcanization temperature, affecting the flexibility and tear resistance of the conveyor belt.
Wear resistance and fatigue resistance
Excessively high vulcanization temperature will cause the rubber surface to harden and its wear resistance to decline. For instance, after high-temperature vulcanization, the surface friction coefficient of conveyor belts may decrease by 20% to 30%, accelerating wear.
Excessive crosslinking will deteriorate the fatigue resistance of rubber, and it is prone to microcracks under dynamic loads, thus shortening its service life.
Third, the influence of vulcanization temperature on the aging performance of rubber
Thermal oxygen aging
High-temperature vulcanization will accelerate the thermal oxygen aging reaction of rubber, leading to the breakage of molecular chains and the destruction of crosslinking bonds. For instance, the rate of thermal oxygen aging of ethylene propylene diene monomer (EPDM) rubber after vulcanization at 170℃ is 30%-40% faster than that at 150℃.
After aging, the tensile strength and elongation at break of rubber decrease significantly, affecting the long-term performance of conveyor belts.
Ozone aging
Excessively high vulcanization temperatures will cause more unsaturated bonds to form on the rubber surface, increasing the risk of ozone attack. For instance, after high-temperature vulcanization of butyl rubber, the crack density of ozone aging increases by more than 50%.
Ozone aging can cause cracks on the surface of conveyor belts, reducing their service life.
Fourth, the influence of vulcanization temperature on the appearance quality of conveyor belts
Surface flatness
Uneven vulcanization temperature can cause bubbles, wrinkles or unevenness on the surface of the conveyor belt. For instance, excessively high local temperatures can cause scorching on the rubber surface, forming hard lumps.
Uneven surfaces will affect the smoothness of the conveyor belt’s operation and increase the resistance to material transportation.
Color consistency
High-temperature vulcanization may cause the rubber color to darken or develop color spots. For instance, when styrene-butadiene rubber is vulcanized above 160℃, its color may change from light yellow to dark brown.
Inconsistent color will affect the appearance quality of the conveyor belt, especially in occasions that require high cleanliness (such as the food and pharmaceutical industries).
Fifth, optimization strategies for vulcanization temperature
Select the temperature according to the type of rubber
Natural rubber: 140-150℃
Nitrile rubber: 150-160℃
Chloroprene rubber: 145-155℃
The vulcanization temperatures of different rubbers need to be adjusted according to their molecular structures and crosslinking characteristics.
Segmented vulcanization process
The combination of low-temperature pre-vulcanization (120-130℃) and high-temperature final vulcanization (150-160℃) can not only ensure the crosslinking efficiency but also avoid excessive vulcanization.
Temperature uniformity control
Use heat transfer oil or electromagnetic induction heating systems to ensure that the temperature uniformity of the vulcanized plate is within ±2℃, reducing local overheating or underheating.
The influence of vulcanization temperature on the quality of conveyor belts is multi-faceted, involving the cross-linking structure of rubber, physical and mechanical properties, aging performance and appearance quality. Reasonable control of vulcanization temperature is the key to ensuring the quality of conveyor belts, and it needs to be optimized according to the type of rubber, vulcanization process and equipment conditions. Excessively high vulcanization temperatures can lead to excessive crosslinking, performance degradation and accelerated aging, while excessively low temperatures will affect vulcanization efficiency and product quality. Therefore, in actual production, it is necessary to scientifically set the vulcanization temperature in combination with the characteristics of rubber, equipment conditions and process requirements, and strictly control the temperature uniformity to ensure the quality and performance of the conveyor belt.