There are two main methods for the recycling of waste rubber: crushing or grinding waste tires into particles by mechanical means, the so-called rubber particles and rubber powder; destroying the chemical network structure of vulcanized rubber by desulfurization technology to make so-called recycled rubber. This article briefly introduces the production technology of rubber powder.
1. Manufacturing method of rubber powder
Preprocessing of waste rubber. There are generally non-rubber skeleton materials such as fibers and metals in waste rubber products, and there are many types of rubber products. Therefore, pre-processing must be carried out before waste rubber is crushed, including sorting, removal, cutting, cleaning and other processing. The waste rubber should also be inspected and classified, and the waste rubber and its products of different types and sources should be classified according to the requirements. Ideally, the recycling method should be adopted, and the waste rubber should be processed purposefully according to the source of the waste rubber. For larger products such as waste tires, the bead must be removed, and a tread separator is also used to separate the tread from the carcass. The rubber shoes mainly recycle the soles, while the inner tubes need to remove the valves, etc.
After sorting and removing non-rubber components, the waste rubber cannot be crushed directly due to its different lengths and uneven thicknesses. The waste rubber must be cut. Foreign countries generally use the whole tire cutting machine to cut into rubber blocks ranging from 25mmx25mm. The large rubber blocks are returned to the cutting machine and cut again.
Waste rubber, especially tires and rubber footwear products, due to long-term contact with the ground, is mixed with a lot of impurities such as sediment, so it should be cleaned with a rotary drum washing machine to ensure the quality of the rubber powder.
Freeze crushing method. The basic principle of low-temperature freezing and crushing method is: when rubber and other high-molecular materials are below the glass transition temperature (Tg), it becomes brittle. At this time, it is easily crushed into powdery substances by mechanical action, and the vulcanized rubber powder is pressed Made on this principle.
There are two types of freezing and crushing processes: one is the low-temperature freezing and crushing process. The other is low temperature and normal temperature combined with crushing process. The former uses liquid nitrogen as the refrigeration medium. After the waste rubber is cryogenically cooled, it is crushed at low temperature with a hammer mill or a roller mill. The fine rubber powder production line is produced by the latter method. Using liquid nitrogen cryogenic technology to process waste tires into fine rubber powder of more than 80 meshes, the temperature, speed and overload in the production process are controlled by closed-loop interlocking microcomputers, which have no pollution to the environment. The entire production process of this production line adopts the feeder powered by compressed air and the closed pipeline transportation. Except for waste tires input and product packaging, which are in contact with air, the whole line is in a closed state. In addition, because it is produced by the freezing method, there is no high-temperature smell, so there is no secondary pollution. And through the heat exchange process of fine powder and coarse powder, the purpose of making full use of energy, reducing energy consumption, that is, reducing product cost is achieved.
Normal temperature crushing method. Waste rubber is crushed at room temperature after preprocessing, generally divided into coarse crushing and fine crushing. At present, two crushing methods are often used in reclaimed rubber factories in China. One is that coarse crushing and fine crushing are completed on the same equipment; the other is that coarse crushing and fine crushing are completed on two different equipment. The former is suitable for production in small factories.
The way of coarse crushing and fine crushing at the same time: one of the two rollers for this operation has grooves on the surface, and the other has no grooves on the surface, which is the groove smooth roller machine. First, through the conveyor belt, the washed rubber blocks are sent between the two rollers to break the rubber, and then the crushed rubber blocks and rubber powder are dropped into the reciprocating sieve at the bottom of the equipment for sieving, and those that meet the particle size requirements fall from the screen. It is put into the warehouse through the conveyor; the rubber blocks that do not meet the requirements are turned over and then enter the groove roller machine for further crushing.
Coarse crushing and fine crushing are carried out on two sets of equipment: coarse crushing is carried out on a groove roller machine with grooves on the surface of both rollers, and the size of the coarsely crushed rubber blocks is generally 6-8mm. Then enter the smooth roller crusher for fine crushing, the particle size is generally 0.8-1.0mm (26-32 mesh). The crushing equipment of the rubber powder factory is different from the traditional reclaimed rubber crushing equipment. They are all dedicated waste rubber crushers, secondary crushers, and fine crushers.
2. Activation and modification of rubber powder
The so-called activated rubber powder is the rubber powder whose surface is chemically treated in order to improve the performance of the rubber powder complex. There are many activation and modification methods of rubber powder, which can be roughly divided into: grafting method; interpenetrating polymer network (IPN) method; surface degradation regeneration method; oligomer modification method; adjustment of vulcanization system; other activation methods. For example, saturated amount of vulcanization accelerator treatment. This method is obtained by mechanically treating 420 μm (40 mesh) rubber powder with 2-3 parts of vulcanization accelerator, and a layer of vulcanization accelerator is evenly attached to the surface of the treated rubber powder, so that the rubber powder and the matrix The cross-linking bond at the interface of the rubber increases, so that the entire rubber compound becomes a uniform cross-linked product after vulcanization. This rubber powder is applied to the tire, although its static performance is slightly reduced, but its dynamic performance is improved.
Liquid polymer material plus vulcanizing agent treatment method. This method is made by blending about 12 parts of liquid unsaturated vulcanizable polymer material with vulcanizing agent, and then mechanically treating the rubber powder. The liquid polymer materials that can be used include liquid nitrile rubber, liquid styrene-butadiene rubber, liquid ethylene-propylene rubber, etc. As for which liquid polymer material to use, it can be determined according to the type and use of the rubber powder. The treated rubber powder can be well cross-linked with the matrix rubber, and endowed with oil resistance, ozone resistance and other properties according to the type of liquid polymer used. According to the application test, it can be blended in a high proportion (40%-80%) if the physical properties do not exceed the allowable range.
3. Application of rubber powder
The application of rubber powder can be summarized into two major fields: one is direct molding or combined with new rubber to make products, which belongs to the rubber industry category; the other is application in a wide range of non-rubber industries. Now more and more manufacturers around the world use rubber powder to replace raw materials, which is not only beneficial to environmental protection, but more importantly, because the use of rubber powder can effectively reduce costs, improve performance, and achieve effects that other materials cannot obtain. It can be widely used as rubber, filler and composite materials in tires, hoses, tapes, rubber shoes, rubber industrial products, wires, cables and building materials. Rubber powder can also be used with plastics, such as polyethylene, polyvinyl chloride, polypropylene, polyurethane, etc., to improve performance and reduce costs.
It is also widely used to modify asphalt with rubber powder to pave roads. Roads paved with rubber powder modified asphalt are used in many developed countries including Canada, the United States, Belgium, France, the Netherlands and other countries. Some provinces and cities in China have also laid experimental road sections in Jiangxi, Hubei, Guangzhou, Beijing and other places. Practice has proved that the road paved with rubber powder modified asphalt can reduce cracking and softening of the road surface, the road surface is not easy to freeze and slip, improves driving safety, and can also improve the service life of the road surface, which is at least longer than that of ordinary asphalt pavement. doubled.