There are two main methods for recycling waste rubber: mechanically crushing or grinding waste tires into fine particles, so-called rubber particles and rubber powder; and destroying the chemical network structure of vulcanized rubber by desulfurization technology to produce so-called recycled rubber. This article briefly introduces the production technology of rubber powder.
1. Method for manufacturing rubber powder
Pre-processing of waste rubber. Waste rubber products generally have non-rubber skeleton materials such as fibers and metals, and a wide variety of rubber products. Therefore, pre-processing must be carried out before the waste rubber is crushed, including sorting, removal, cutting, cleaning and so on. Waste rubber should be inspected and classified. The waste rubber and its products from different categories and sources should be classified according to requirements. It is most desirable to adopt a recycling management cycle method and handle it according to the source of the waste rubber. For larger products such as waste tires, the bead is removed, and the tread separator is used to separate the tread from the carcass. The rubber shoes mainly collect the soles, and the inner tubes remove the valve fittings.
After sorting and removing the non-rubber-containing waste rubber, since the length is different, the thickness is uneven, and it is not possible to directly pulverize, and the waste rubber must be cut. Foreign tires are generally cut into 25MMX25MM rubber blocks by whole tire cutting machine.
Waste rubber, especially tires and rubber footwear products, due to long-term contact with the ground, mixed with a lot of impurities such as sediment, should be washed first with a drum washing machine to ensure the quality of the rubber powder.
Freeze pulverization method. The basic principle of the low-temperature freeze-grinding method is that when a polymer material such as rubber is at a glass transition temperature (TG) or less, it is embrittled by itself, and at this time, it is easily pulverized into a powdery substance by mechanical action, and the vulcanized rubber powder is pressed. This principle is made.
There are two kinds of freeze pulverization processes: one is the low temperature freeze pulverization process. The other is a combination of low temperature and normal temperature. The former uses liquid nitrogen as the refrigerant. After the waste rubber is cryogenically cooled, it is pulverized by a hammer mill or a roller mill. The fine rubber powder production line is produced by the latter method. The liquid tire deep cooling technology is used to process the waste tire into a fine rubber powder of 80 mesh or more. The temperature, speed and overload in the production process are controlled by a closed-loop interlocking microcomputer, and the environment is not polluted. The whole process of production of the production line adopts compressed air-powered feeder and closed pipeline transportation. The whole line is closed except for the contact between the waste tires and the product packaging. In addition, since it is produced by the freezing method and has no high-temperature odor, secondary pollution is not generated. And through the heat exchange process of fine rubber powder and coarse powder, the purpose of fully utilizing energy, reducing energy consumption and reducing product cost is achieved.
Normal temperature pulverization method. After being pre-processed, the waste rubber is pulverized at room temperature, and is generally divided into coarsely divided and finely divided. At present, China's reclaimed rubber factories often use two kinds of crushing methods, one is coarse crushing and fine crushing on the same equipment; the other is coarse crushing and fine crushing on two different equipments. The former is suitable for production in small factories.
The method of simultaneous coarse and fine crushing: the two rolls performing this operation have grooves on one surface and no grooves on the other surface, which is a groove roller machine. Firstly, the washed rubber block is sent to the two rolls through the conveyor belt to break the glue, and then the broken rubber block and the rubber powder are dropped into the reciprocating sieve at the bottom of the device to be sieved, and the particle size requirement is dropped from the screen. Through the conveyor into the warehouse; the required rubber block is not reached, and the crushing is continued by turning the material into the groove roller machine.
The method of coarse and fine crushing on two machines: coarse crushing is carried out on a groove roller machine with grooves on both rolls, and the size of the coarsely crushed rubber is generally 6-8 mm. Then it is cut into a light roller fine crusher for fine crushing, and its particle size is generally 0.8-1.0 MM (26-32 mesh). The rubber powder factory crushing equipment is different from the traditional recycled rubber crushing equipment, and is a special waste rubber crusher, medium crusher and fine crusher.
2. Activation and modification of rubber powder
The so-called activated rubber powder is a rubber powder whose surface is chemically treated in order to improve the performance of the rubber powder complex. There are many methods for activation and modification of rubber powder, which are roughly divided into: grafting method; interpenetrating polymer network (IPN) method; surface degradation regeneration method; oligomer modification method; adjustment of vulcanization system; For example, a saturated amount of vulcanization accelerator treatment. This method is prepared by mechanically treating 420 & MU; M (40 mesh) rubber powder with 2-3 parts of vulcanization accelerator, and the surface of the treated rubber powder is uniformly adhered with a vulcanization accelerator, thereby making the rubber powder The cross-linking bond at the interface with the matrix rubber increases, and the entire rubber compound is vulcanized to become a uniform cross-linking material. The rubber powder is applied to the tire, and although its static performance is slightly decreased, its dynamic performance is improved.
Liquid polymer material plus vulcanizing agent treatment method. This method is to use 12 parts of liquid unsaturated vulcanizable polymer material and vulcanizing agent, and then mechanically treat the rubber powder. The liquid polymer materials that can be used include liquid nitrile rubber, liquid styrene butadiene rubber, liquid ethylene propylene rubber, etc., and the liquid polymer material used may be determined according to the type and use of the rubber powder. The treated rubber powder can be well crosslinked with the matrix rubber, and is rendered resistant to oil and ozone depending on the type of liquid polymer used. According to the application test, it can be blended in a high proportion (40%-80%) within the range where the physical properties do not exceed the allowable range.
3, the application of rubber powder
The application of rubber powder can be divided into two major areas: one is direct molding or combined with new rubber to make products, which belongs to the rubber industry; the second is applied in the broad field of non-rubber industry. Nowadays, more and more manufacturers around the world use rubber powder instead of raw materials, which is not only beneficial to environmental protection, but more importantly, the use of rubber powder can effectively reduce costs, improve performance, and obtain effects that other materials cannot obtain. It can be widely used as a rubber, filler and composite material in tires, hoses, tapes, rubber shoes, rubber industrial products, wires, cables and building materials. The rubber powder can also be used together with plastics such as polyethylene, polyvinyl chloride, polypropylene, polyurethane, etc. to improve performance and reduce costs.
The use of rubber powder to modify the asphalt pavement is also widely used. Roads coated with rubber powder modified asphalt are used in many developed countries in Canada, the United States, Belgium, France, the Netherlands and other countries. Some provinces and cities in China have also entered Jiangxi, Hubei, Guangzhou, Beijing and other places, and successively laid experimental sections. Practice has proved that roads paved with rubber powder modified asphalt can reduce road surface cracking and softening, road surface is not easy to freeze and slip, improve driving safety, and can improve road life, at least improve the service life of ordinary asphalt roads. Doubled.
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