Crushing of thermoplastic elastomers (ZT)

Thread Content

Crushing of thermoplastic elastomers [Question] We are a company that processes products made from thermoplastic elastomers, but it is difficult to crush TPE scraps using conventional crushers. Is there a better method? 【Answer】TPE has seen rapid market growth in recent years due to its combination of the plasticity of plastics and the high elasticity of rubber. However, the recycling of soft materials such as TPE often faces many difficulties; other such materials include various soft plastic films, soft PVC, rubber diaphragms, and so on. For soft plastics and rubber, the main recycling methods commonly used are three: direct extrusion granulation, freeze crushing, and room-temperature crushing. PE and PP films produced by direct extrusion granulation are materials with excellent toughness, and they are not easy to crush using ordinary plastic crushers. Ordinary plastic crushers: one type uses a hammering method and is suitable for crushing materials that are hard but low in toughness ； Another method is cutting with knives; a row of fixed knives and a set of rotating knives make up the cutting tool, which is suitable for processing materials with certain toughness and high melting points. Since PE and PP films are soft and flexible and not easy to cut, coupled with the high temperature of the cutting tool at high speeds, which causes LDPE to melt and stick to the blade. Therefore, for the granulation of PE and PP films, it is common to feed them directly in strip form into the feeder of the extruder; the shear force of the screw is then used to pull the PE and PP films into the barrel, where they are heated, melted, and extruded to form granules. This is generally applicable to large quantities of recycled material that are well-organized. Freeze grinding method: The basic principle of the low-temperature freeze grinding method is that when polymer materials such as rubber are below their glass transition temperature (Tg), they become brittle, and under mechanical action they can be easily ground into a powder form. Vulcanized rubber powder is produced using this principle. There are two types of cryogenic grinding processes: one is the low-temperature cryogenic grinding process, and the other is the process that uses both low temperature and normal temperature. The former uses liquid nitrogen as a refrigerant to deeply cool the waste rubber, which is then crushed at low temperatures using a hammer mill or a roller mill. The fine rubber powder production line uses the latter method for production. Using liquid nitrogen cryogenic technology, used tires are processed into fine rubber powder with a particle size of over 80 mesh. The temperature, speed, and overload during the production process are all under closed-loop microcomputer control, resulting in no environmental pollution. The entire production process of this line utilizes compressed air-powered feeders and closed piping for transportation; with the exception of the moment old tires are fed in and during product packaging when it comes into contact with air, the whole line remains in a sealed state. Due to production using the freezing method, there is no high-temperature odor, thus preventing secondary pollution. Furthermore, through the heat exchange process between fine powder and coarse powder, it is possible to make full use of energy, reduce energy consumption, and thus lower the cost of the product. Room-temperature crushing method: The waste rubber is pre-processed and then crushed at room temperature, usually involving coarse crushing and fine crushing. Currently, two types of crushing methods are commonly used in rubber recycling plants in China: one involves performing coarse crushing and fine crushing on the same machine ； Another approach is to perform coarse crushing and fine crushing on two separate machines. The former is suitable for production in small factories. Method of performing coarse crushing and fine crushing simultaneously: In this approach, one of the two rollers used for this operation has grooves on one of its surfaces while the other surface is groove-free; this is what is known as a grooved-and-smoothed roller machine. First, the washed rubber blocks are fed between two rollers via a conveyor belt to be broken down. The resulting broken rubber blocks and rubber powder then fall into a reciprocating screen at the bottom of the equipment; those that meet the required particle size criteria fall through the screen and are sent to the storage bin using a conveyor ； The gel blocks that do not meet the requirements are turned over and fed back into the grooved grinding roller machine for further crushing. Coarse and fine crushing are carried out using two different machines: coarse crushing takes place on a roller crusher with grooves on both surfaces of the rollers, and the size of the rubber pieces after coarse crushing is generally 6–8 mm. Then, it is fed into a photo roller crusher for grinding, with a particle size generally ranging from 0.8–1.0 mm (26–32 mesh). The crushing equipment in rubber powder factories differs from that used in traditional recycled rubber processing; it consists of specialized crushers for waste rubber, including medium-size crushers and fine crushers. It is recommended that, considering your company’s products, having a technology for crushing at room temperature would be the most convenient option. Recently, I came across in some information that Shanghai Suowei Crushing Machinery Co., Ltd. produces a GJ/OJ combined high-power crusher. The machine consists of the upper unit GJ, which performs powerful rough crushing (low speed, high torque, high crushing force), and the lower unit OJ, which cuts the material into fine pieces. The discharge mechanism at the end of the machine is equipped with a screen to adjust the fineness (usually 1–5 mm); the fine material is discharged around the entire circumference of the machine (360° discharge), resulting in an efficiency 3–5 times higher than that of horizontal machines. The boarding and alighting functions can be used separately. Simply unscrew the quick-release bolts at the top and bottom, turn the ladder bolt, and push the machine down. It is said that this machine can be used for crushing rubber, engineering resins, municipal waste, wood, hoses, sheet materials, and even films. I hope we can meet your company’s crushing requirements.