The effect of increasing back pressure
To achieve a high-quality adhesive, it is crucial to ensure the plastic is uniformly heated or melted and mixed thoroughly. The key lies in using the correct screw that enables proper melting and mixing. It is also important to have sufficient pressure, or back pressure, in the injection cylinder to consistently achieve the desired level of mixing and heating.
To avoid undue stress on the driving system of an injection molding machine, it is best to maintain back pressure at a consistent level. However, when the resistance of the return oil is increased, back pressure can result in the firing cylinder. It is crucial to ensure that the adhesive temperature and mixing degree remain constant, and that the back pressure is isolated from air. One thing to keep in mind is that increasing back pressure means the screw takes longer to reset, leading to more wear and consumption of the driving system. Therefore, it is necessary to strike a balance between maintaining back pressure and preserving the lifespan of the machine's components.
1. Stop valve
To ensure that plastic is properly molded, the tip of the screw used in the process is typically equipped with a stop valve. Additionally, a pressure reducing device or a specialized nozzle is installed to prevent any plastic from leaking out of the nozzle. Regular inspections of the firing cylinder are necessary, particularly if using anti-abortion supply and marketing. It's worth noting that switch type shooting nozzles are currently not used as often since they tend to experience plastic leakage and decomposition inside the shooting nozzle equipment. Different types of plastic require different shooting nozzle types, and there are specific lists available for each.
2. Screw backward (reverse cable)
To optimize injection molding processes, many machines are fitted with suction devices or screw retraction mechanisms. When the screw stops rotating, the hydraulic retraction can pull back the plastic from the nozzle tip. Thanks to this feature, open nozzles can be used, although the amount of suction can be adjusted to prevent air ingress which may cause issues with certain types of plastics.
3. Screw pad material
When undertaking an injection molding cycle, it is crucial to adjust the screw rotation appropriately. This is because you need a small amount of soft plastic left at the end of the screw injection. This guarantees that the screw reaches an effective pushing time and maintains a fixed shooting pressure. For small machines, the padding is about 3mm, while for more extensive machines, it is 9mm. However, the screw pad material value must remain unchanged, irrespective of its size. Nowadays, the screw pad size can be controlled within 0.11mm.
4. The rotational speed of the screw
The speed at which the screw rotates can have a big impact on how stable the injection molding process is, as well as how much heat is applied to the plastic. The faster the screw is rotated, the hotter the temperature becomes. This high speed can transmit more friction energy (shear) to the plastic, which improves the efficiency of plasticization, but also increases the unevenness of the temperature of the melt. It's important to take into account the speed of the screw surface, so a lower screw rotation speed should be used with large injection molding machines compared to small ones, because the shear heat generated by the larger screws is much greater than that of smaller screws at the same speed of rotation. With different types of plastic, the speed of the screw rotation will also vary.
5. Injection amount
The assessment of syringe molding machines typically revolves around the injection capacity, which is often measured in ounces or grams of PS. Alternatively, some ranking systems are based on the amount of molten adhesive injected by the injection molding machine.
6. Plasticizing ability
Injection molding machines are typically evaluated based on their plasticizing capacity, which refers to the ability to uniformly melt a certain amount of PS within one hour or heat it to a consistent melting temperature. This evaluation criterion is measured in pounds and kilograms.