There are many kinds of waste rubber products, and there are usually non-rubber skeleton materials such as fibers or metals, so waste rubber should be pretreated before crushing, including sorting, removing, cutting and cleaning. After the waste rubber is sorted to remove non-rubber components, it cannot be directly crushed because of its different lengths and uneven thickness, so it must be cut. Generally, the whole tire slicer is widely used to cut the tire into 25mm×25mm rubber blocks. Waste rubber, especially tires and rubber overshoes, is mixed with a lot of impurities such as sediment due to long-term contact with the ground, so it should be washed with drum washing machine first to ensure the quality of rubber powder.
After pretreatment, waste rubber needs to be crushed to obtain rubber powder. There are two main methods of operation: freezing crushing and normal temperature crushing. The basic principle of freeze crushing method is that polymer materials such as rubber become brittle below the glass transition temperature, and are easily crushed into powder by mechanical action at this time. There are two low-temperature crushing technologies of waste rubber in China, one is air turbine refrigeration, and the other is liquid nitrogen method. The core technology of the former is to apply the turboexpansion refrigeration technology of aircraft manufacturing industry to the low-temperature crushing of waste rubber, using air as the cooling medium, which not only improves the fine powder rate, but also reduces the raw material cost, saves energy consumption and solves the inconvenience of storage and transportation when using liquid nitrogen as the medium. In the latter method, the waste rubber is deeply cooled with liquid nitrogen as the refrigeration medium, and then crushed at low temperature with a hammer mill or a roller mill. For example, LY-type liquid nitrogen freezing method developed by Shandong Qingdao Luye Rubber Co., Ltd. can produce 80-200 mesh fine rubber powder. Due to various cold energy recovery technologies, only 0.32kg of liquid nitrogen is consumed per production of 1kg fine rubber powder, which greatly reduces the cost and is conducive to popularizing the application of low-temperature fine rubber powder.
Normal temperature grinding method is characterized by low initial investment, low production cost and relatively simple maintenance, so it is promising in the market. So far, China has made many patent achievements in the field of room temperature grinding, such as drum, grinding wheel, spiral, grinding head, grinding disc and rolling cutting.
At present, some domestic enterprises are studying the preparation of fine rubber powder by physical and chemical methods. The key of this technology lies in the preparation and recovery of expansive agent and the process of high energy stirring and grinding. The rubber powder prepared by this method is much thinner than that prepared by ordinary technology, and its mechanical strength is obviously improved. These new technologies are helpful to improve the quality of rubber powder and reduce the cost, and will promote the further popularization and application of rubber powder.