Rubber special-shaped parts are a kind of rubber seals with special shapes, which are widely used in various industrial and living fields, such as auto parts, mechanical seals, building materials, etc.; Natural rubber is an important raw material for making all kinds of special-shaped rubber parts. As an option raw material for natural rubber, natural reclaimed rubber can be used alone or combined with natural rubber and synthetic rubber to produce special-shaped rubber parts, effectively reducing the cost of raw materials.
Compared with natural rubber, the elasticity, hardness, tensile strength, tearing elongation and other indicators of natural reclaimed rubber with high rubber content can be comparable to natural rubber, with low price, good performance, sufficient supply of waste rubber and stable supply. Therefore, natural reclaimed rubber is an ideal raw material to replace natural rubber to produce special-shaped rubber parts; The vulcanization formula and process of natural reclaimed rubber directly affect the performance and stability of special-shaped rubber parts.
1. When designing the vulcanization formula of natural reclaimed rubber special-shaped rubber parts, it is necessary to consider the vulcanization system, reinforcing filling system, plasticizer, antioxidant, etc.
(1) Vulcanization system: The commonly used vulcanization system of natural reclaimed rubber includes sulfur vulcanization system and peroxide vulcanization system, of which the sulfur vulcanization system is divided into ordinary sulfur vulcanization system (sulfur dosage 2-3 parts), semi-effective sulfur vulcanization system (1-1.5 parts) and effective sulfur vulcanization system (0.3-0.5 parts of sulfur and 3-5 parts of accelerator combination, or no sulfur). When using natural reclaimed rubber as the main raw material to produce special-shaped rubber parts, the appropriate vulcanization system can be selected according to the specific performance requirements of rubber parts.
In actual production, the rubber material vulcanized by ordinary sulfur vulcanization system has good mechanical properties, high tensile strength, wear resistance, fatigue crack resistance, etc.; Natural reclaimed rubber has good anti-reflex and vulcanization uniformity when vulcanized by effective vulcanization system, and has good heat resistance, compression deformation resistance and aging performance of vulcanized rubber; The vulcanization process characteristics and physical properties of vulcanized rubber of natural reclaimed rubber using semi-effective sulfur vulcanization system are among the two. If natural reclaimed rubber is used to produce special-shaped rubber parts with high requirements for heat resistance and compression set, peroxide vulcanization can also be used, and vulcanized rubber has good thermal stability, high temperature resistance, small creep and small compression set.
(2) Reinforcement filling system: carbon black or white carbon black can be used in the production of natural reclaimed rubber special-shaped rubber parts to further improve the strength and wear resistance of rubber; Calcium carbonate, clay and other fillings are used to increase the volume of rubber and reduce the cost of rubber materials.
(3) Softening and plasticizing system: the commonly used softening plasticizers for natural reclaimed rubber include pine tar, petroleum-based softeners, etc., which can improve the viscosity and softness of the rubber compound, and facilitate subsequent process operations such as mixing, calendering, and extrusion molding; In the production of special-shaped rubber parts, the hardness of natural reclaimed rubber vulcanized rubber can be adjusted by adjusting the amount of softener and plasticizer. It should be noted that when using natural recycled rubber to produce light-colored special-shaped rubber parts, the influence of plasticizers on rubber color also needs to be considered.
(4) Antioxidant system: antioxidant can improve the heat resistance, oxygen resistance and aging resistance of natural reclaimed rubber, commonly used antioxidants are antioxidant RD, antioxidant A, antioxidant DNP, antioxidant 4020, antioxidant 4010NA, antioxidant AW, antioxidant MB, antioxidant SP, antioxidant SP-C, antioxidant 3100, etc., can be used alone or together.
When using natural reclaimed rubber to produce special-shaped rubber parts that require heat and oxygen resistance, the dosage of antioxidant RD and antioxidant A is 1-2 parts; Ozone resistance is required, and a large amount of antioxidant 4020, antioxidant 4010NA, antioxidant AW, antioxidant 3100, etc., should be used, the dosage is 3-5 parts, and 0.5-1 part of physical antioxidant microcrystalline wax should be used. For the production of light-colored special-shaped rubber parts of natural reclaimed rubber, it is necessary to pay attention to the selection of non-polluting antioxidants, antioxidant B, antioxidant SP, antioxidant SP-C, antioxidant 264, antioxidant 2246, etc.
When natural reclaimed rubber or natural rubber/natural reclaimed rubber is used together to produce special-shaped rubber parts, manufacturers can also reduce material waste and improve production efficiency by optimizing process steps such as mixing, extrusion, molding and vulcanization.
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