1. The rubber product is composed of a proper amount of a compounding agent based on the raw rubber.
(1) Raw rubber without added compounding agent or unvulcanized natural or synthetic rubber is collectively referred to as raw rubber. Natural rubber has good comprehensive performance, but the output cannot meet the needs of the industry, and it can not meet certain special performance requirements. Therefore, synthetic rubber is used more.
(2) A compound to be added in order to improve and improve various properties of a rubber product is called a compounding agent. The compounding agent mainly includes a vulcanized thorn, a filler, a vulcanization accelerator, a plasticizer, an anti-aging agent and a foaming agent.
1 vulcanizing agent acts similarly to the curing agent in thermosetting plastics, which forms a transverse chain between the rubber molecular chains, and is properly crosslinked to become a network structure, thereby improving the mechanical properties and physical properties of the rubber. Commonly used sulfides are sulfur and sulfide.
2 filler is to improve the mechanical properties of rubber, such as strength, hardness, wear resistance and rigidity. The most common fillers used are carbon black and textiles, fibers, or even wire or metal braids as a framework material. The addition of fillers can also reduce the amount of raw rubber and reduce the cost of rubber.
3 Other compounding agents vulcanization-promoting can accelerate the vulcanization process and improve the vulcanization effect; plasticizers are used to increase rubber plasticity and improve the molding process performance; anti-aging agents (antioxidants) are used to prevent or delay rubber aging.
2. Characteristics and application of rubber products
Rubber products have high elasticity, high resilience, high strength and high wear resistance. Its elastic modulus is very low, only 1-10MPa, the amount of elastic deformation is very large, up to 100% ~ 1000%, with excellent flexibility and ability to store energy. In addition, there is good wear resistance, sound insulation, damping and insulation. However, the rubber has poor heat resistance and cold resistance (cursive at high temperatures, cold and brittle), and dissolves in the solvent.
1. High elasticity: low modulus of elasticity, large elongation and deformation, reversible deformation, and flexibility in a wide temperature range (-50~150 °C).
2. Viscoelasticity: The rubber material is affected by temperature and time when it is deformed and restored, and exhibits obvious stress relaxation and creep phenomenon. Under the action of vibration or alternating stress, hysteresis loss occurs.
3. Electrical insulation: rubber is an electrically insulating material like plastic.
4. There are aging phenomena: such as metal corrosion, wood decay, and rock weathering, rubber will also cause aging due to changes in environmental conditions, resulting in deterioration of performance and a decline in life.
5. Must be vulcanized before use, except for thermoplastic elastomers.
6. A compounding agent must be added.
Other characteristics such as small specific gravity, low hardness, good flexibility, and good air tightness are all valuable properties of rubber.
Indicators for characterizing the physical and mechanical properties of rubber:
1. Tensile strength: also known as tear strength, tensile strength, refers to the load on the unit section when the test piece is stretched to break, the unit is megapascals (MPa), and the previous kilogram force / square centimeter (kgf / cm2).
2. Fixed tensile stress: The old known tensile strength refers to the load per unit area when the sample is stretched to a certain length. The unit of measurement is the same as the tensile strength. Commonly used are 100%, 300% and 500% modulus. It reflects the ability of rubber to resist external force deformation.
3. Tear strength: The load per unit thickness when tearing a special test piece (with a cut or a right angle), indicating the tear resistance of the material, the unit is kN/m.
4. Elongation: When the test piece is broken, the ratio of the elongation to the original length is called elongation; expressed as a percentage.
5. Permanent deformation: After the sample is stretched to break, the unrecoverable part of the gauge length deformation is a percentage of the original length. The external force is released and placed for a certain period of time (usually 3 minutes), expressed in %.
6. Resilience: Also known as impact elasticity, refers to the ability of rubber to return to its original state after impact, expressed in %.
7. Hardness: It indicates the ability of the rubber to resist the intrusion of external force and is usually measured by a Shore hardness tester. The hardness of rubber is generally between 20 and 100, and the unit is Shore A.