The hottest gas auxiliary equipment and gas auxili

Gas auxiliary equipment and gas auxiliary control process

I. gas auxiliary equipment

gas auxiliary equipment includes gas auxiliary control unit and nitrogen generation device. It is another system independent of the injection molding machine, and its only interface with the injection molding machine is the injection signal connecting line. After the injection molding machine transmits an injection signal injection start or 13 positions of the screw new start registration project to the gas assisted control unit, it starts a gas injection process. When the next injection process starts, another injection signal is given to start another cycle, and so on

the gas used in gas assisted injection molding must be natural gas (usually nitrogen), the maximum pressure of the gas is 35MPa, and the special one can reach 70MPa, and the purity of nitrogen is ≥ 98%

the gas assisted control unit is a device that controls the gas injection time and pressure. It has a multi group gas circuit design, which can control the gas assisted production of multiple injection molding machines at the same time. The gas assisted control unit is equipped with a gas recovery function to reduce the gas consumption as much as possible. In the future, the development trend of gas assisted equipment is to build the gas assisted control unit into the injection molding machine as a new function of the injection molding machine

II. Gas assisted process control

1. Gas injection parameters

gas assisted control unit is a device that controls the size of gas pressure in each stage. There are only two values of gas assisted parameters: gas injection time (seconds) and gas injection pressure (MPA). Typical gas assisted parameter control is shown in the following figure:

gas assisted process pressure parameter curve (source: Baoer gas assisted company)

2. Gas assisted injection molding process is to inject high-pressure gas while injecting plastic melt into the mold. There are complex two-phase interactions between melt and gas, so process parameter control is very important, Next, we will discuss the control methods of various parameters:

A. injection volume

gas assisted injection molding adopts the so-called "short size" method, that is, first inject a certain amount of material into the mold cavity (usually 70-95% of full injection), and then inject gas to realize the full filling process. The amount of melt injection has the greatest relationship with the size of the mold airway and the structure of the mold cavity. The larger the cross-section of the airway is, the easier the gas is to penetrate, and the higher the hollowing rate is, so it is suitable to adopt a larger "short firing rate". At this time, if too much material is used, it is easy to accumulate molten materials, and shrinkage marks will appear in the places with too much material. Too little material will cause blow through

if the airway is completely consistent with the flow direction, it is most conducive to the penetration of gas, and the tunneling rate of the airway is the largest. Therefore, after the completion of land reclamation in the mold design, try to keep the airway consistent with the flow direction

b. injection speed and pressure maintaining

under the condition of ensuring that the product performance does not appear defects, use a higher injection speed as far as possible to make the melt fill the mold cavity as soon as possible. At this time, the melt temperature remains high, which is conducive to gas penetration and mold filling. After the gas pushes the melt to fill the mold cavity, it still maintains a certain pressure, which is equivalent to the pressure maintaining stage in traditional injection molding. Therefore, generally speaking, the gas assisted injection molding process can eliminate the process of using the injection molding machine to maintain the pressure. However, some products still need to use certain injection molding to ensure the quality of product performance due to structural reasons. However, it is not allowed to use high interval pressure holding, because too high pressure holding will seal the gas needle, and the gas in the cavity cannot be recovered, which is very easy to blow out when opening the mold. High pressure holding will also hinder gas penetration. Increasing injection pressure holding may cause greater shrinkage marks on the product performance

c. gas pressure and gas injection speed

gas pressure has the greatest relationship with the fluidity of materials. Materials with good fluidity (such as PP) adopt low gas injection pressure. The recommended pressures for several materials are as follows:

the gas pressure is high, which is easy to penetrate, but easy to blow through; If the gas pressure is small, there may be insufficient mold filling, insufficient filling or shrinkage marks on the surface of the product; With high gas injection speed, the mold cavity can be filled under the condition of high melt temperature. For molds with long process or small airway, increasing the gas injection speed is conducive to the filling of melt adhesive and the quality of product surface can be improved. However, if the gas injection speed is too fast, there may be blow through, and for products with large airway, there may be surface flow marks and gas lines

d. delay time

delay time is the time period from the beginning of glue injection of the injection molding machine to the beginning of gas injection by the gas assisted control unit, which can be understood as a parameter reflecting the "synchronization" of glue injection and gas injection. The short delay time, that is, when the melt is still at a high temperature, it is obviously conducive to gas penetration and mold filling. However, if the delay time is too short, the gas is easy to disperse, the hollowed shape is poor, and the hollowed out rate is not enough

III. gas assisted mold

gas assisted mold is not much different from traditional injection mold, only adding air inlet components (called air needles) and increasing the design of air passages. The so-called "airway" can be simply understood as the passage of gas, that is, the part through which the gas flows after entering. Some of the airway is part of the product, and some are specially designed glue positions for guiding the air flow

gas needle is a key component of gas assisted mold, which directly affects the process, but has a direct impact on the stability of general manufacturers and product quality

the core part of the air needle is a cylinder composed of many small gaps, and the size of the gap directly affects the air output. If the gap is large, the air outlet volume is also large, which is beneficial to injection molding filling. However, if the gap is too large, it will be blocked by melt glue, and the air outlet volume will decrease instead