How to prevent injection molding machine from sticking?

Changing the angle of the extruded profile from the die can change the position where the adhesive is produced on the die, thus making it easier to clean. In addition, the chip adhesive can be transferred to the product manually and then completely removed. For thin plates, an automatic mechanical scraper can be used to scrape off the adhesive. However, operators often need to pay expensive fees such as parking to remove the chip adhesive. After cleaning, the release agent or silicone resin is coated on the exit area of the mold, which can reduce the generation speed of viscose and prolong the interval between two cleaning. In addition, reducing the running speed of the equipment can also reduce mold sticking, but this will affect the output. All the above methods are temporary solutions, but a better solution is to find out the reasons that lead to the formation of viscose. The chip adhesive is related to the stress at the chip outlet. On the inner surface of the mold, the flow rate of molten resin is relatively slow, and then it suddenly accelerates at the exit of the mold. This acceleration will create stress in the melt. Under the stress, the low molecular weight polymer components are separated from other components in the melt and deposited at the die outlet to form viscose. Therefore, the solution to the problem is to reduce the outlet stress of the die or reduce the trend of separation of melt components. This may involve changes in technology, raw materials or molds. Figure 1 thick soft mold compound may be formed because of local foaming of melt, compatibility of resin or excessive die stress. Changing the process to increase the temperature of die and melt is one of the methods to reduce the outlet pressure of die, but it may cause additional degradation and lead to the increase of low molecular weight components. Therefore, the adjustment of melt and mold temperature needs to be carried out separately. However, it should be noted that sometimes if the mold temperature is too low, a resin cold flow layer with slow flow rate may be formed on the inner surface of the mold, which will be separated from the main stream of resin and eventually lead to the formation of viscose. Fig. 2 The stress change of resin at the exit of the die can be studied by simulating the flow of the die, which will eventually lead to the formation of mold glue (picture from Compuplast Company). To set the mold temperature, we must first determine the real melt temperature. Because the standard melt thermocouple often makes mistakes, it is necessary to measure the melt temperature manually. Although this method is difficult, we need to find the cause of the failure. In addition, because the surface temperature at the exit of the die is much lower than the temperature of the die itself, the surface thermocouple should be used as much as possible when checking the exit temperature of the die. Blowing air at the die outlet can reduce and control the production of viscose, and at the same time, it can also take all kinds of flue gas and condensable gas away from the die. In addition, the blast also helps to cool the mold adhesive, so that it is not easy to be oxidized and blackened. N2 can also be used to prevent oxidation. However, it should be noted that the extruded profile should not be deformed by blowing too hard or lowering the die temperature too low. Changing different raw materials will produce different forms of mold adhesives, some thin and sticky, and some thick and loose. Thin viscous viscose is formed by vaporization at the die outlet and condensation on the die surface, usually from low molecular weight components in raw materials. Viscous and loose viscose is usually caused by partial foaming in the melt, compatibility problems or high pressure in the mold. Therefore, in the extrusion process, excessive moisture or resin degradation, as well as possible melt fracture or improper exhaust should be avoided. Some suppliers' resins will produce more viscose than other sources, even though these resins have exactly the same technical specifications. When the chip adhesive appears, try to use similar grade resin provided by other suppliers. If the adhesion problem is improved, the initial resin may have performance problems. Resins from different suppliers may have similar shear viscosity, but very different elongation viscosity. If no other performance differences are found, try to test its elongation viscosity. Due to the increase of die outlet pressure, the resin with higher elongation viscosity may produce more viscose. Sometimes, the resin with large die expansion change will have a higher die adhesive formation rate. When the resin has a narrow molecular weight distribution, its extrusion swell may be lower, but this does not necessarily mean that less viscose is produced. Generally, the resin with narrow molecular weight distribution is difficult to process, and may produce low molecular weight components, which will eventually lead to the production of chip glue. For the regeneration of resin, it usually contains low molecular weight components produced by thermal degradation in previous processing. In this regard, additives that inhibit degradation may be added, or chain extenders that can repolymerize the degraded components may be used. If none of this works, these recycled materials are not suitable for use. Sometimes, adding lubricant is helpful to reduce viscose, but too much lubricant may also increase the output of mould viscose. The chemical compatibility of different components in the formula is also one of the important factors affecting the viscose problem. For example, when highly incompatible polymers are melted and mixed together, serious die sticking often occurs. In this case, the use of compatilizer will help to reduce the formation of viscose. In addition, adding a small amount of fluoropolymer processing AIDS can also reduce the stress diagram of die exit. Improved die exit geometry (some of which have been patented) can reduce the formation of die adhesive. For the yellow or black chip adhesive that will oxidize quickly, antioxidants can be added to the formula. Although this will not solve the problem of mold sticking, it can make the glue attached to the product invisible. Replacing the mold and coating fluoropolymer, such as PTFE, on the surface of the mold can prevent the formation of viscose to some extent. A more effective method is to use metal coating to make fluoropolymer penetrate into the mold to reduce the stress at the exit of the mold. On the other hand, die flow simulation has been successfully applied to solve the problem of die sticking. By simulating the flow state of resin at the die, we can study the causes of stress at the die outlet, and also evaluate the influence of changing the geometry of the die outlet on viscose. It is a widely used method to improve the geometry of die exit to reduce stress. The exit shapes of some molds have been patented by processors and resin manufacturers. It is said that the improved die outlets that can reduce die sticking are: sharp square outlet, sharp mouth outlet, rounded corner outlet, outer step outlet, inner step outlet and outer funnel-shaped outlet. In addition, by increasing the length of the molding section of the die, the variation amplitude of the resin at the die outlet is reduced, which is also helpful to reduce the die outlet stress.