1.1 Traditional Injection Cold Runner Moulds Traditional injection cold runner moulds, each injection is completed after the opening of the mold there will be a section of cooled and cured runners need to be taken out manually or mechanically. Through the heating method to ensure that the runner and the gate of the plastic to maintain the molten state, due to the runner near or in the center of the heating rod and heating ring, from the injection molding machine nozzle outlet to the gate of the entire runner are in a high temperature state, so that the plastic in the runner to maintain the molten state, the shutdown does not generally need to open the runner to take out the condensed material, and then boot only need to heat up the runners to the required temperature can be.
1.2 Hot runner system The hot runner system generally consists of several parts such as hot nozzle, manifold, temperature control box and accessories. Hot nozzles generally include hot tip type, sprue type and valve needle type three major types. Diverter plate in a mold multi-cavity or multi-point feeding, single-point feeding but material level offset when used, the material is usually used P20 or H13, generally divided into two categories of standard and non-standard, and its structural form is mainly by the distribution of cavities in the mold, the arrangement of the nozzle and the location of the gate to determine. Temperature control box includes host, cable, connector and wiring male and female sockets. Hot runner accessories usually include: heaters and thermocouples, runner seals, connectors and junction boxes.
1.3 hot runner technology Hot runner technology in our country gradually hot at the same time, its components show several major development trends. (1) parts miniaturization. Small products can be realized in a mold with multiple cavities and large products with multiple sprues punching mold. By reducing the nozzle space, more cavities can be configured on the mold to improve production and injection molding machine utilization. (2) Standardization of parts. Help to reduce the duplication of design work and reduce the cost of the mold, and easy to replace and repair wearing parts, to meet the user's mold design and manufacturing cycle is getting shorter and shorter requirements. (3) Pressure distribution, temperature distribution and sealing design of the overall reliability. (4) Precision of temperature control system to prevent overheating degradation of resin and reduction of product performance. (5) To improve the wear resistance of nozzles and hot runners and for molding sensitive materials. 2 Advantages and disadvantages of hot runner mold technology 2.1 Advantages of hot runner mold In the specific practice of production and operation, hot runner mold has the following advantages compared with cold runner mold. (1) When the wall thickness of the product is thin, to ensure that the melt can fully reach the part away from the gate, greatly reducing the degree of deformation of the product, greatly improving the product surface quality and the consistency of the product's surface aesthetics. (2) The pressure loss in the runner is small, the melt has good fluidity, the density is easy to be uniform, to avoid deformation of the injection molded parts, flying edge, as well as dimensional instability and color difference and other defects, to improve the surface quality of the products. (3) All or most of the elimination of runners, do not have to use three-plate molds that can be used to use the point of the gate, do not need to manually shear the gate, no need to crush, improve the utilization of materials, saving raw materials, improve production efficiency, improve the degree of automation. (4) Eliminate the additional heat brought by the waste material, the cooling cycle of the mold is only the cooling time of the product, which shortens the processing cycle and improves the efficiency of the machine. (5) All hot runners are automatic cut-off gates, available pin-valve gates to control gate sealing, improving the appearance of the gate and increasing the degree of automated operation. (6) Precise control of the temperature of the molten plastic, eliminating the degradation of the material, so that the holding time is more reasonable, the quality of the injection parts of the multi-cavity molds is consistent, reducing the internal stress of the product, improving mechanical properties, and reducing scrap.
2.2 Disadvantages of hot runner technology Every technology will have its own shortcomings exist, hot runner technology is no exception. (1) the mold structure is complex, the production process requires high equipment, mold cost increases dramatically. (2) It takes a period of time for the process to be stabilized, resulting in more start-up scrap. (3) The technical requirements for production and maintenance are high. Compared with cold runner molds, hot runner molds are complicated to operate and maintain. If the use of improper operation is very easy to damage the hot runner parts, melt leakage, heating element failure, the product quality and production schedule has a greater impact. Above item (3) disadvantages, through the correct production operation and maintenance, procurement of high quality heating elements, hot runner plates and nozzles, can reduce the emergence of these unfavorable situations. 3 hot runner supplier selection 3.1 supplier is very important hot runner mold conceptual design stage, to the mold of the actual manufacturing process, to the final use of the mold is a relatively complex technology in the field of injection molding. Therefore, mold manufacturing companies and mold users should have good technical knowledge related to hot runner and choose a good hot runner supplier, choose and buy the most appropriate hot runner system to ensure that the back of the injection molding production process smoothly and improve product quality.
3.2Selecting a hot runner supplier to examine two basic aspects When selecting a hot runner supplier, focus on two basic aspects. (1) the hot runner supplier production of hot runner components of the number of varieties and quality, in the injection molding processing of plastic products, hot runner system and hot runner molds are in the high temperature and high pressure dynamic load state of work, leading to the failure of the hot runner system components of the many factors, and injection molding processing is mainly used in the production of large quantities of plastic parts, once there is any phenomenon of production stoppage, the economic loss is very serious, so the quality and reliability of the hot runner system is very important, so the quality and reliability of the hot runner system is very important, so the hot runner system is very important. Therefore, the quality and reliability of the hot runner system is very important. (2) The hot runner supplier in the mold user's region of technical support and after-sales service. To consider the hot runner in case of any problem, can get timely and effective technical support and after-sales service is an important factor. 4 hot runner system production operation and maintenance # p # page title # e # # 4.1 hot runner system switching operation (1) start to prepare the mold worker to connect the mold of the moving mold, mold and hot half-mold cooling water, such as the moving mold, mold temperature requirements on both sides of the mold is different, it must be connected to a separate water circuit. If the quality of product appearance is high, it is recommended to connect the mold temperature of both sides of the moving and fixed molds separately. Such as hot half-mold side of the hot runner heating heat generated by more, can be connected to its cooling water circuit separately; such as hot half-mold side of the hot runner heating heat absorbed by the template or transfer of more heat loss, can be connected to the appropriate temperature of the mold water in order to compensate for the loss of heat. The heating cable connection between the hot runner and the thermostat should be connected correctly according to the sign of the plug, and the plug lock should be fastened to prevent loosening. If the heating output cable and the temperature-sensitive cable line reversed, will lead to all thermocouples burned that is, open circuit; set up the mold after the first injection molding machine screw temperature to the required set temperature, but also open the mold heating machine to heat up the mold temperature to the production of the required set temperature, and then heat up the hot runner system to the working temperature of the plastic. It should be noted that after the hot runner of the new mold rises to the set temperature, it needs to wait for about 5 to 10 minutes (to ensure the heating is even), if the raw material contains fiberglass, it needs to take a longer time (about 10 to 15 minutes), because the tungsten steel tip of the nozzle is poor in heat transfer. (2) start boot First find out what kind of raw materials used in the last trial mold, the injection molding machine screw and nozzle temperature adjustment to the raw material in the molten state temperature, for the material to choose a suitable plastic to clean the screw. Such as the production of plastics containing glass fiber, for example: LCP + 30% glass fiber, this time the use of pure LCP material (does not contain glass fiber) to clean the hot runner; open the mold after the air shot, at this time you should see 8 out of the gate out of the glue are very smooth; when found that a certain or several hot nozzle is not out of the material: the gate has a cold material, can be used to bake the hot air gun to make the cold material melt, and then close the door to re-shooting glue; such as there is still a hot nozzle is not out of the material If there is still a hot nozzle does not produce material, according to the hot nozzle position schematic diagram, quickly find out the number of the nozzle, corresponding to the temperature of the nozzle in the original value on the basis of another 10 ~ 20 ℃ immediately after the air shot (not more than 3 times), the nozzle out of the rubber smooth immediately after the temperature drop to the production temperature, can be closed to try to play the product can be a solution to the problem; at this time, such as there are still sprues blocked, then immediately stop the production of the next mold removal of the blocked nozzle clear glue or notify the supplier to deal with. After reaching the temperature, the injection molding machine will use manual control to shoot out, for the new mold hot runner first to let the plastic fill up the runner cavity, the method is as follows: adjust the screw back pressure, let the plastic slowly squeezed into the runner, when the plastic out of the injection port is completed, the machine can be shot in accordance with the normal manual mode, and then the machine can be shot in accordance with the normal manual mode. When the product is shot out normally, count the molds, and turn back to the raw material containing fiberglass. (3) Stop and wait Immediately use pure LCP material to clean the rubber inside the hot runner, so as to keep the residual material inside the hot runner and the head of the hot nozzle, in the whole production process are relatively good fluidity of LCP material, at the same time to ensure that the next trial mold or production smoothly. Due to machine failure or other reasons, more than five minutes, the need to set the hot runner in the holding state of 250 ℃; if more than ten minutes, you can use 120 ℃. (4) raw materials to replace the color Clean up the barrel, with raw materials to clean up the screw, until the old color completely clear out, check the machine nozzle and hot runner gate, whether there is any old color residue, open the mold nut, the filling of the mouth of the plastic before the clear out. (5)Stop the machine to repair the mold Before separating the hot runner from the mold nut, you must make sure that the hot runner heating output has been turned off, and make sure that the temperature of the hot nozzle has been cooled down to the room temperature ( < 60℃); if the raw material contains glass fiber, use the raw material without glass fiber to clear out the original material with glass fiber, otherwise, the glass fiber material may be charcoalized in next time when it is heated up.