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How to make rubber products?

Edit: John 2020-02-11

  In rubber products, the main molding technologies are: compression molding, transfer molding, wrapping and injection molding.

  Among these methods, injection molding has significant advantages: ① simplify the process and reduce the number of operators; ② reduce energy consumption by about 10%; ③ improve production efficiency by 4 to 7 times; ④ improve product uniformity, stability, and accurate size And eligibility rate; ⑤ reduce flash and save rubber; ⑥ easy to operate, low labor intensity, high degree of mechanization and automation. Therefore, in recent years, injection molding technology has received more and more important attention, and has developed rapidly in the production of rubber products.


  1. Basic process flow

  With the rapid development of modern industry, especially the chemical industry, there are many types of rubber products, but the production process is basically the same. The products using general solid rubber (raw rubber) as raw materials, its production process mainly includes:

  Raw material preparation → plasticizing → mixing → molding → vulcanization → restoring → inspection

  2. Raw material preparation

  The main materials of rubber products are raw rubber, compounding agents, fiber materials and metal materials. Raw rubber is the basic material; compounding agents are auxiliary materials added to improve certain properties of rubber products; fiber materials (cotton, hemp, wool and various artificial fibers, synthetic fibers) and metal materials (steel wire, copper wire) It is used as the skeleton material of rubber products to enhance mechanical strength and limit product variations.

  In the raw material preparation process, the ingredients must be accurately weighed according to the formula. In order to make the raw rubber and the compounding agent evenly mix with each other, some materials need to be processed:

  Raw rubber should be softened in a drying room at 60-70 ℃, then cut and broken into small pieces;

  The bulk compound such as paraffin, stearic acid and rosin should be crushed;

  If the powdery compound contains mechanical impurities or coarse particles, it needs to be removed by screening;

  Liquid compounding agents (pine tar, coomarone) need to heat, melt, evaporate moisture, and filter impurities;

  The compounding agent should be dried, otherwise it is easy to agglomerate, and it cannot be dispersed uniformly during mixing, and air bubbles are generated during vulcanization, which affects the product quality;

  3. Sculpt

  Raw rubber is elastic and lacks the necessary properties (plasticity) during processing, so it is not easy to process. In order to improve its plasticity, it is necessary to plasticize the raw rubber; in this way, the compounding agent is easily dispersed uniformly in the raw rubber during mixing; at the same time, it also helps to improve the permeability of the rubber (infiltration) Fiber fabric) and molding fluidity. The process of degrading the long-chain molecules of raw rubber to form plasticity is called plasticizing. There are two types of raw rubber plastic smelting: mechanical plastic smelting and thermoplastic smelting. Mechanical plasticizing is to reduce the degradation of the long-chain rubber molecules by the mechanical extrusion and friction of the plasticizer at a not too high temperature, and change from a highly elastic state to a plastic state. Thermoplastic smelting is the introduction of hot compressed air into the raw rubber. Under the action of heat and oxygen, the long-chain molecules are degraded to shorten the plasticity.

  4. Mixing

  In order to adapt to various conditions of use, to obtain a variety of different properties, and to improve the performance of rubber products and reduce costs, different compounding agents must be added to the raw rubber. Mixing is a process in which the plasticized raw rubber is mixed with the compounding agent and placed in a rubber mill, and the compounding agent is completely and uniformly dispersed in the raw rubber through mechanical mixing. Mixing is an important process in the production of rubber products. If the mixing is not uniform, the role of rubber and compounding agents cannot be fully exerted, affecting the performance of the product. The rubber compound obtained after mixing is known as compound rubber. It is a semi-finished material for manufacturing various rubber products, commonly known as rubber compound, and is usually sold as a commodity. Buyers can use the rubber compound to directly process and vulcanize the rubber compound. Required rubber products. According to the different formulations, there are a series of different grades and varieties with different properties to provide choices.


  In the production process of rubber products, a calender or an extruder is used to make a variety of shapes and sizes in advance, which is called molding. The molding methods are:

  Calendering is suitable for making simple sheet and plate products. It is a method of pressing the mixed rubber into a certain shape and a certain size through a calender, which is called calendering. Some rubber products (such as tires, tapes, hoses, etc.) use textile fiber materials that must be coated with a thin layer of glue (gluing the fiber is also called glue or rubbing), and the coating process is generally completed on the calender. Fibre materials need to be dried and dipped before calendering. The purpose of drying is to reduce the moisture content of the fiber material (to prevent water evaporation and foaming) and increase the temperature of the fiber material to ensure the quality of the calendering process. Dip is a necessary process before hanging glue, the purpose is to improve the binding performance of fiber material and rubber material.

  Extrusion molding is used for more complex rubber products, such as tire treads, hoses, and wire surface rubber coating, which need to be manufactured by extrusion molding methods. It is a method of extruding the compounded rubber with a certain plasticity into the hopper of an extruder, and extruding it continuously through a variety of mouth shapes (also called templates) under the extrusion of a screw. Previously, the rubber must be preheated to make the rubber soft and easy to squeeze out, thereby obtaining rubber products with smooth surfaces and accurate dimensions.

  Compression molding You can also use the compression method to make some rubber products with complex shapes (such as leather bowls and seals). With the help of the formed male and female molds, the rubber is placed in the mold and heated to form.


  The process of converting plastic rubber into elastic rubber is called vulcanization. It involves adding a certain amount of vulcanizing agent (such as sulfur, vulcanization accelerator, etc.) to the semi-finished product made of raw rubber (in a vulcanization tank). Heating and holding at temperature allows the linear molecules of the raw rubber to crosslink to form a network structure through the formation of "sulfur bridges", so that the plastic compound becomes a highly elastic vulcanizate. Because the crosslinks are mainly composed of sulfur, it is called "vulcanization". With the rapid development of synthetic rubber, there are many types of vulcanizing agents. In addition to sulfur, there are organic polysulfides, peroxides, and metal oxides. Wait. Therefore, the process of converting the plastic rubber with a linear structure into the elastic rubber with a three-dimensional network structure is called vulcanization, and the substances that can play a "bridge" role in rubber materials are called "vulcanizing agents".

  The vulcanized elastic rubber is called vulcanized rubber, also called soft rubber, commonly known as "rubber". Vulcanization is one of the most important processes in rubber processing. Various rubber products must be vulcanized to obtain the desired performance. Unvulcanized rubber is of little use value in use, but under-sulfurization (insufficient vulcanization degree, insufficient vulcanization time, and failure to reach the optimal state) and over-sulfurization (excessive vulcanization time, and significantly reduced performance) both make Reduced rubber properties. Therefore, the vulcanization time must be strictly controlled during the production process to ensure that the vulcanized rubber products have the best performance and longest service life.

  7. Ancillary measures

  In order to achieve performance, auxiliary measures should be added to the production process:

  7.1 increase strength-with hard carbon black, mixed with phenolic resin;

  7.2 Increase abrasion resistance-with hard carbon black;

  7.3 High air-tightness requirements-use less highly volatile components;

  7.4 Increase heat resistance-use new vulcanization process;

  7.5 Increase cold resistance-through the degumming and inlaying of raw rubber to reduce the tendency to crystallize, use low temperature resistant plasticizers;

  7.6 Increasing flame resistance-no flammable additives, less softeners, flame retardants (such as antimony trioxide)

  7.7 Increase oxygen resistance and ozone resistance-using diamine protective agents;

  7.8 Improving electrical insulation-with high structure filler or metal powder, and with antistatic agent;

  7.9 Improving magnetic properties-using strontium ferrite powder, aluminum nickel iron powder, iron barium powder, etc. as fillers;

  7.10 Improving water resistance-using lead oxide or resin vulcanization system, with fillers with lower water absorption (such as barium sulfate, clay);

  7.11 Improve oil resistance-fully cross-linked, less plasticizer;

  7.12 Improve acid and alkali resistance-multi-purpose filler;

  7.13 Improving high vacuum--matching additives with low volatility;

  7.14 Decrease Hardness--Plenty of Softener

  8. Classification of rubber products and their application in automobiles

  Rubber products are widely used and there are many varieties. According to the use, it is usually divided into two categories: industrial and civilian. Industrial rubber products mainly include: tires, tapes, hoses, offset plates, tapes and tape products, seals, vibration damping parts, latex products, hard rubber products, rubber insulation products, rubber rollers and rubber linings.

  9. During the molding of rubber products, after coercive pressure, the cohesive force of the elastomer cannot be eliminated. When molding is released from the mold, extremely unstable shrinkage is often produced (the shrinkage of rubber varies depending on the rubber type). ), It will take some time before it can be gently stabilized. Therefore, at the beginning of the design of a rubber product, regardless of the formula or mold, it is necessary to calculate the coordination carefully. If not, the size of the product is likely to be unstable and the quality of the product will be lowered.

  10. Rubber is a hot-melt and thermosetting elastomer, and plastic is a hot-melt and cold-set. Due to the different types of sulfur compounds, the temperature range of molding and curing of rubber is also quite different. It can even be affected by climate change and indoor temperature and humidity. Therefore, the production conditions of rubber products need to be appropriately adjusted at any time. If not, there may be differences in product quality.

  11. Rubber products are made from rubber raw materials, which are made by mixing mixers with rubber mixers as raw materials. During rubber mixing, formulas are designed according to the characteristics of the required rubber products, and the required product hardness is determined. The product is molded by a rubber flat vulcanizing machine. After the product is formed, the flashing treatment is finally performed to smooth the product surface without burrs.

  Ordinary rubber is rapidly degraded by the ozone generated by corona discharge, while the silicone seal ring is not affected by ozone. And under long-term UV and other climatic conditions, its physical properties change little. Silicone sealing ring has high resistivity, and its resistance value remains stable over a wide temperature and frequency range. At the same time, the silicone seal ring has good resistance to high voltage corona discharge and arc discharge.