Introduction
Vulcanization is a critical process in rubber processing, improving material properties through cross-linking reactions. Accurate determination of vulcanization properties is of great significance for quality control and formulation development. As a commonly used equipment, the rotorless vulcanizer can continuously monitor the torque change during the vulcanization process, generate vulcanization curves, and provide data support for process optimization.
How it works:
The instrument places the specimen in a closed mold cavity, and the mold cavity maintains the set temperature. The upper mold oscillates with a fixed amplitude, and the lower mold measures the torque. As vulcanization progresses, the rubber modulus rises and the torque changes accordingly. The relationship between torque and time is recorded throughout the process, that is, the vulcanization curve is obtained. The torque change reflects the development of cross-linking density and indirectly characterizes the degree of vulcanization.
Test Standards
Domestic and foreign standards clearly stipulate the test conditions to ensure comparable results. Common standards include ISO and ASTM series, and the main parameters are as follows:
| Standard system | Typical standard number |
| International standards | ISO 6502 |
| American standard | ASTM D5289 |
| Chinese standard | GB/T 16584 |
Curve analysis
A typical vulcanization curve includes the following stages: first, the torque is maintained at a low level, which is called the scorching stage; Then the torque begins to rise and enters the vulcanization stage; Finally, the torque tends to be stable, which is the persulfurization stage. Several parameters can be extracted from the curve:
| Parameter symbols | Physical significance |
| ML | Minimum torque, reflecting the flow of unvulcanized rubber |
| MH | Maximum torque, reflecting the degree of cross-linking |
| ts1 | The scorching time is characterized as processing safety |
| t90 | Positive vulcanization time, commonly used process setting basis |
where t90Usually refers to torque up to ML + (MH - ML× 90% of the time required, calculated as:
t90 = t(ML + 0.9ΔM) ，ΔM = MH - ML
Influencing factors
Test results are influenced by multiple factors. The temperature changes the reaction rate significantly and needs to be precisely controlled. The shape and volume of the specimen affect the heat conduction; The oscillation frequency and amplitude change the shear conditions. In addition, the type of filler and the vulcanization system in the rubber formulation will lead to differences in curve morphology.
Applications:
This method is widely used in rubber products such as tires, seals, conveyor belts, etc. By comparing vulcanization profiles across different formulations or processes, vulcanization rates can be evaluated, energy consumption can be optimized, and product performance can be predicted. During production, regular testing helps monitor raw material stability and process consistency.
Notes:
Calibrate the temperature and torque sensors before testing; The specimen should be evenly filled with the mold cavity to avoid bubbles; The mold cavity needs to be cleaned during multiple tests to prevent residue. Different standards have specific requirements for specimen thickness, preheating time, etc., and should follow the corresponding specifications.
References
1. International Standards Organization. Rubber - Determination of vulcanization characteristics with a rotorless vulcanizer. ISO 6502.
2. American Society for Testing and Materials. Standard test method for rubber properties. ASTM D5289.
3. National Standardization Administration of China. Rubber - Determination of vulcanization characteristics with a rotorless vulcanizer. GB/T 16584.
4. Rubber Industry Handbook Editorial Board. Rubber testing technology. Chemical Industry Press.
5. Overview of vulcanization analysis techniques. Journal of Polymer Materials Science and Engineering.