Control of technological conditions in Wuhan Handern
DATE：2020/12/29 8:51:58 / READ： / SOURCE：This station
Control of technological conditions in Wuhan Handern
The most important process conditions of injection molding are temperature, pressure and corresponding time. Hollow board www.handern.com
1. Temperature
The injection molding process needs to control the temperature, including the barrel temperature, nozzle temperature and mold temperature. The former two are related to the plasticizing process of plastics, while the latter is related to the molding of plastics.
(1) The selection of material temperature should ensure that the plastic plasticizes well and can be injected smoothly without material decomposition. The material temperature should be determined according to the thermal properties of plastics, each plastic has different flow temperature. Therefore, the maximum temperature at the end of the plastic cylinder should be higher than the flow temperature for amorphous plastic, and higher than the pass point for crystalline plastic, but lower than the grouping temperature of plastic. If it is higher than the decomposition temperature, the molten material will decompose. Under the condition of smooth filling, the temperature of the material should be as close to the flow temperature as possible. In addition, the selection of material temperature should also take into account the duration of plastic heating. If the time is too long, even if the temperature is not finished, it will reach the decomposition temperature, which will also cause the decomposition of the plastic.
The plasticization process of plastics in the cylinder is different with different types of injection molding, so the selection of cylinder temperature is also different. In the plug-in injection molding machine, if the inner and outer layers of the fast plastic are heated and plasticized, a higher temperature of the cylinder is needed. In the screw injection machine, the plastic is mixed and mixed in the screw groove. In addition, the plastic is cut by the screw and generates friction heat. Therefore, the material temperature can be selected lower, which can be reduced by 10 ~ 20c.
The selection of material temperature should be combined with the structural characteristics of products and dies. The resistance of the cavity is narrow. Cooling fast, should improve the fluidity of plastic, in order to better fill the mold, so the material temperature should be higher. For thick wall products, it is more convenient to fill the mold, the cooling time of the parts in the mold is longer, and the material temperature can be lower.
The temperature distribution of the cylinder is usually from the hopper + side to the nozzle, from low to high, in order to facilitate the plastic flow. Hollow board www.handern.com
(2) Nozzle temperature plastic in the injection, quickly through the nozzle, there is still a certain friction heating effect, in order to prevent the nozzle material flow, the nozzle temperature is usually slightly lower than the material temperature, but the nozzle temperature is too low will cause the melt condensation plug nozzle, resulting in the flow of condensate in the mold cavity.
When the plastic melt passes through the injection nozzle, the hole diameter and injection molding pressure have certain influence on the melt temperature.
(3) Mold temperature, mold temperature depends on the characteristics of the material (especially for finished products), product size and structure, performance and process conditions.
In plastic injection molding, the mold is usually in two states, one is heated by electric heating coil, the other is the cold part of nitong cold water. Whether it is heated or cooled, the plastic melt is cooled inside the mold. Only when the culture body is condensed in the mold to obtain the required shape can the mold be demoulded. In order to ensure no deformation during demoulding, the plastic melt should be cooled from viscous flow state to crystalline state.
The influence of mold temperature on the mechanical properties of the products is relatively small in the injection molding of amorphous thermoplastic (such as polystyrene and its copolymer). On the premise of ensuring smooth injection, the cooling time can be shortened and the production efficiency can be improved by using lower mold temperature. In the injection molding of crystalline thermoplastic, the mold temperature has a great influence on the mechanical properties of the products. Generally speaking, the mechanical properties of polyolefin products increase with the increase of mold temperature. Mold temperature directly affects the cooling rate of products in the mold, so mold temperature directly affects the density of products. Hollow board www.handern.com
Author：admin