Production process and sealing principle of plate heat exchanger gasket_
1014 plate heat exchanger (hereinafter referred to as the plate exchanger) effective heat exchange is not only carried out in the narrow space between the plates, but also in the many gaskets between the plates. In practical applications, the gaskets of plate heat exchangers are considered to be important and demanding parts in the plate heat exchanger. The gasket must not only seal the medium so that it does not leak to the external environment, but also prevent the heat exchange medium from mixing. The materials used for the plate changer sealing gasket include rubber, compressed asbestos fiber, expanded graphite, rubber coated and protected with polytetrafluoroethylene, and specially treated polytetrafluoroethylene. The utilization rate of plate heat exchanger gaskets in plate heat exchangers exceeds 98%. 1. Material composition and manufacturing rubber is a relatively complex polymer system, consisting of rubber polymers (or raw rubber), vulcanizing agents, fillers (for reinforcement), antioxidants, processing aids and diluents, etc. Component composition. The raw rubber polymer supplied by the polymer manufacturer is not the usual rubber, because the molecular chains of the high molecular polymer have not yet been cross-linked to form a three-dimensional network structure. The cross-linked network structure is formed during the vulcanization process. The vulcanizing agent that has a vulcanization reaction causes a chemical reaction between the rubber polymer under the action of heat, thereby completing the vulcanization process. Sulfur, organic resins and organic peroxides are all typical vulcanizing agents. In order to improve the physical properties of rubber gaskets, such as hardness, tear strength and tear strength, it is necessary to add reinforcing fillers. Carbon black is a commonly used filler. Carbon black can not only improve the physical properties of rubber gaskets, but also The price of gaskets is greatly reduced. Rubber gaskets, like all other organic systems, will age when they are exposed to harmful heat and oxygen. Therefore, it is necessary to add some effective anti-aging agents (antioxidants, antiozonants, etc.) to the rubber compound to extend the life of the rubber gasket. Although processing aids (softeners, mold release agents, etc.) cannot prolong the life of rubber gaskets, they are very effective in improving the mixing, extrusion and molding properties in the gasket manufacturing process. The selection of raw materials and their ratios will determine the performance of rubber gasket materials. The material, manufacture and sealing principle of rubber gaskets for plate heat exchangers. The manufacturing process of plate heat exchanger gaskets generally includes the following steps and Quality control point. (1) Mixing of rubber compound Weigh the raw materials accurately and mix them in a closed or open rubber mixer. Make each raw material component weighed according to the formula uniformly mixed, and after laboratory testing, the rubber compound is used for gasket production. (2) Due to the different cross-sectional area and length of the rubber gasket, the rubber blank can be made into a corresponding blank-cylindrical rubber strip by an extruder. (3) Molded plate changer rubber gaskets are manufactured by molding in a press, that is, placing unvulcanized semi-finished rubber strips into the cavity of a hot mold, and vulcanizing when the mold is closed. The molding temperature is 160 -185℃, time 3-15 min, depending on different rubber compounds, molding pressure should not be less than 9.8 MPa. (4) Post-vulcanization In order to improve the production capacity of the production line, the vulcanization is not completely completed during the molding process, and the molded vulcanized gasket is placed in an oven under static conditions to complete the vulcanization. The temperature in the oven must be uniform, and its holding time varies with different rubber compounds. Post-vulcanization is an extremely important step in the production process of rubber gaskets for plate changers. The oven must be equipped with a device with continuous temperature recording. (5) Finished product inspection The finished gaskets are taken from each oven and tested according to the finished product standards in the laboratory. 2. Sealing principle The common rubber O-ring is a self-sealing principle, and its sealing function is maintained until the O-ring is deformed and softened. This is because it is the pressure that the O-ring bears that seal the tiny defects. The seal of the rubber gasket of the plate changer is different. The sealing operation of the plate changer mainly depends on the comparison between the instantaneous sealing stress generated by the compression of the rubber gasket and the operating pressure of the plate changer. If the sealing stress is greater than the operating pressure, the seal can be maintained, and vice versa, leakage will occur. Therefore, the important thing for the plate changer seal is to make the seal stress as high as possible and keep it for as long as possible. The elasticity of the gasket rubber of the plate heat exchanger is different from that of the metal spring. It is a kind of viscoelastic material. This means that the rubber will undergo stress relaxation under long-term deformation, that is, under constant tension or pressure, the sealing stress will attenuate with time. Higher stress relaxation is an important factor that limits the service life of the rubber gasket of the plate changer.