1.Basic process flow

With the rapid development of modern industry, especially the chemical industry, there are various types of rubber products, but their production processes are basically the same. The production process of products made from general solid rubber (raw rubber) mainly includes:

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

2.Preparation of raw materials

The main materials of rubber products are raw rubber, compounding agents, fiber materials and metal materials. Among them, raw rubber is the basic material; Compounding agents are auxiliary materials added to improve certain properties of rubber products. Fiber materials (cotton, linen, wool and various artificial and synthetic fibers) and metal materials (steel wire, copper wire) are used as reinforcing materials for rubber products to enhance mechanical strength and limit the deformation of the products.

During the preparation of raw materials, the ingredients must be weighed accurately according to the formula. In order to ensure that the raw rubber and compounding agents can be evenly mixed with each other, certain materials need to be processed: the raw rubber should be softened in a drying room at 60- 70℃, and then the rubber should be cut and broken into small pieces. Blocky compounding agents such as paraffin, stearic acid, rosin, etc. should be crushed. When powdered compounding agents contain mechanical impurities or coarse particles, they need to be screened and removed. Liquid compounding agents (pine tar, coumarone) require heating, melting, evaporation of water and filtration of impurities. The compounding agents need to be dried; otherwise, they are prone to caking, cannot be evenly dispersed during mixing, and produce bubbles during vulcanization, thereby affecting the product quality.

3. Refining

Raw rubber is elastic but lacks the necessary properties (plasticity) for processing, and thus is not easy to process. In order to improve its plasticity, the raw rubber needs to be plasticized. In this way, during the mixing process, the compounding agents can be easily and evenly dispersed in the raw rubber. Meanwhile, during the calendering and molding processes, it also helps to enhance the permeability of the rubber compound (penetrating into the fiber fabric) and the molding fluidity. The process of degrading the long-chain molecules of raw rubber to form plasticity is called plasticizing. There are two methods for plasticizing raw rubber: mechanical plasticizing and thermal plasticizing. Mechanical plasticizing is a process carried out at a relatively low temperature. Through the mechanical extrusion and frictional force of a plasticizer, long-chain rubber molecules are degraded and shortened, transforming from a highly elastic state to a malleable one. Thermoplasticizing involves introducing hot compressed air into raw rubber. Under the influence of heat and oxygen, long-chain molecules are degraded and shortened, thereby achieving plasticity.

4. Mixing

In order to adapt to various usage conditions, obtain various performances, and also to improve the performance of rubber products and reduce costs, different compounding agents must be added to raw rubber. Mixing is a process in which the plasticized raw rubber is mixed with compounding agents and placed in a rubber mixer. Through mechanical stirring, the compounding agents are completely and evenly dispersed in the raw rubber. Mixing is an important process in the production of rubber products. If the mixing is not uniform, the functions of rubber and compounding agents cannot be fully exerted, which will affect the performance of the products. The rubber compound obtained after mixing is called mixed rubber. It is a semi-finished material for manufacturing various rubber products, commonly known as rubber compound. It is usually sold as a commodity. Purchasers can directly process and shape the rubber compound and vulcanize it to make the required rubber products. Depending on the formula, there is a series of different grades and varieties of compound rubber with various properties to choose from.

5. Forming

In the production process of rubber products, the process of pre-forming various shapes and different sizes using calendering machines or extruders is called molding. The forming methods include: calendering forming is suitable for manufacturing simple sheet and plate-shaped products. The method of pressing mixed rubber into a certain shape and size of film through a calendering machine is called calendering molding. For some rubber products (such as tires, rubber sheets, rubber hoses, etc.), the textile fiber materials must be coated with a thin layer of glue (applying glue on the fibers is also called attaching glue or rubbing glue), and the gluing process is generally completed on a calender. Before calendering, fiber materials need to be dried and impregnated with rubber. The purpose of drying is to reduce the moisture content of the fiber materials (to prevent water evaporation and bubbling) and increase the temperature of the fiber materials to ensure the quality of the calendering process. Impregnation is a necessary process before coating the rubber, with the aim of enhancing the bonding performance between the fiber material and the rubber compound. Extrusion molding is used for more complex rubber products, such as tire treads, rubber hoses, and the surface coating of metal wires, which need to be manufactured by extrusion molding. It is a method of continuously molding compound rubber with certain plasticity into the hopper of the extruder under the extrusion of the screw through various die shapes (also called templates). Before extrusion, the rubber compound must be preheated to make it soft and easy to extrude, thereby obtaining rubber products with smooth surfaces and accurate dimensions. Compression molding can also be used to manufacture some rubber products with complex shapes (such as rubber cups and sealing rings) by compression molding. With the help of the forming male and female molds, the rubber compound is placed in the molds and heated to form.

6. Vulcanization:

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 from raw rubber (carried out in a vulcanization tank), heating and holding it at a specified temperature, so that the linear molecules of the raw rubber are cross-linked into a three-dimensional network structure through the formation of "sulfur Bridges". Thus, the plastic rubber compound is transformed into a highly elastic vulcanized rubber. Since the crosslinking bonds are mainly composed of sulfur, it is called "vulcanization ". With the rapid development of synthetic rubber, there are now many types of vulcanizing agents. Besides sulfur, there are also organic polysulfides, peroxides, metal oxides, etc. Therefore, any process that can transform linear plastic rubber into three-dimensional network elastic rubber is called vulcanization. Any substance that can play a "bridging" role in rubber materials is called a "vulcanizing agent ". The elastic rubber after vulcanization is called vulcanized rubber, also known as soft rubber, and is commonly called" rubber ". Vulcanization is one of the most important technological processes in rubber processing. All kinds of rubber products must undergo vulcanization to achieve the desired performance in use. Unvulcanized rubber has no practical value in use. However, under-vulcanization (insufficient vulcanization degree, insufficient vulcanization time, and failure to reach the optimal state) and over-vulcanization (excessive vulcanization time, significant decline in performance) both lead to a decline in rubber performance. Therefore, during the production process, the vulcanization time must be strictly controlled to ensure that the rubber products after vulcanization have the best performance in use and the longest service life.