Temperature measurement and control is very important in injection molding. Although these measurements are relatively simple, most injection molding machines do not have enough temperature sampling points or lines.
On most injection molding machines, the temperature is sensed by thermocouples. A thermocouple is basically made up of two different wire tails. If one end is hotter than the other, a tiny telecommunication will be generated; The more heat, the stronger the signal.
Thermocouples are also widely used as sensors in temperature control systems. On the control instrument, set the required temperature, and the display of the sensor will be compared with the temperature generated on the set point. In this simplest system, when the temperature reaches the set point, it will turn off, and the power will turn on again when the temperature drops. This system is called open close control because it is either on or off.
The melt temperature is very important, and the temperature of the injection cylinder used is only instructive. The melt temperature can be measured at the nozzle or by air injection. The temperature setting of the injection cylinder depends on the melt temperature, screw speed, back pressure, injection volume and injection cycle.
If you have no experience in processing a certain level of plastic, please start with the lowest setting. For easy control, the injection cylinder is divided into zones, but not all of them are set to the same temperature. If operating for a long time or at a high temperature, set the temperature of the first zone to a lower value, which will prevent premature melting and segregation of plastic. Before injection, make sure that the hydraulic oil, hopper closer, mold and injection cylinder are at the correct temperature.
This is the pressure that causes the plastic to flow and can be measured by sensors on nozzles or hydraulic lines. It has no fixed value, and the more difficult the mold filling is, the higher the injection pressure is. The injection line pressure is directly related to the injection pressure.
·First stage pressure and second stage pressure
During the filling phase of the injection cycle, high injection pressure may be required to maintain the injection speed at the required level. High pressure is no longer required after the mold is filled. However, when some semi crystalline thermoplastics (such as PA and POM) are injected, the structure will deteriorate due to the sudden change of pressure, so it is sometimes unnecessary to use the secondary pressure.
In order to counter the injection pressure, it is necessary to use the clamping pressure. Instead of automatically selecting the maximum value available, it is necessary to consider the projected area and calculate a suitable value. The projected area of the injection part is the largest area seen from the application direction of the clamping force. For most injection molding cases, it’s about 2 tons per square inch, or 31 trillion Newtons per square meter. However, this is only a low value and should be taken as a rough empirical value, because once the injection part has any depth, then the sidewall must be considered.
This is the pressure that needs to be generated and exceeded before the screw retreats. Although high back pressure is conducive to the uniform distribution of pigment and the melting of plastic, it also prolongs the return time of the middle screw, reduces the length of fiber contained in the filled plastic, and increases the stress of the injection molding machine; Therefore, the lower the back pressure, the better. Under no circumstances can it exceed 20% of the injection pressure (maximum quota) of the injection molding machine.
Nozzle pressure is the pressure inside the nozzle. It’s about the pressure that causes the plastic to flow. It has no fixed value, but increases with the difficulty of mold filling. There is a direct relationship among nozzle pressure, line pressure and injection pressure. In the screw injection molding machine, the nozzle pressure is about 10% less than the injection pressure. In the piston injection molding machine, the pressure loss can reach about 10%. In piston injection molding machine, the pressure loss can reach 50%.
This refers to the filling speed of the die when the screw is used as a punch. When injection molding thin-walled products, it is necessary to use high shooting speed, so that the mold can be completely filled when the melt glue is not solidified, and the smooth surface can be produced. During filling, a series of programmed firing rates are used to avoid defects such as jet or trapped air. Injection can be carried out in open-loop or closed-loop control system.
No matter what kind of injection speed is used, the speed value and injection time must be recorded on the record sheet. Injection time refers to the time required for the mold to reach the predetermined first stage injection pressure, which is a part of the screw advance time.
About JasonMould Industrial Company Limited
Jasonmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.
Person: James Yuan
Company: JasonMould Industrial Company Limited
Add: LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Email: [email protected]