The pressure sensor can be installed in the nozzle of the injection molding machine, the hot runner system, the cold runner system and the cavity of the mold. It can measure the plastic from the injection molding machine nozzle to the Plastic pressure somewhere between the mold cavities. This data can be recorded in the monitoring system for real-time adjustment of the molding pressure, and inspection after molding or troubleshooting during the production process.
It is worth mentioning that this collected pressure data can become a general process parameter for this mold and this material. In other words, the data can be used to guide production on different injection molding machines (using the same mold). Only the case where the pressure sensor is installed in the cavity is discussed here.
Type of pressure sensor
Currently, there are two types of pressure sensors used in the mold cavity, namely, flat-mounted type and indirect type. The flush-mounted sensor is inserted into the cavity by drilling a mounting hole behind the cavity. Its top is flush with the surface of the cavity, and its cable passes through the mold and connects to the monitoring system interface located on the outer surface of the mold. . The advantage of this kind of sensor is that it will not be disturbed by pressure during demolding, but it is easily damaged under high temperature conditions, causing difficulty in installation.
Indirect type sensors are divided into sliding type and button type two structures. They can transmit the pressure exerted by the plastic melt on the ejector or the fixed pin to the sensor on the ejector plate of the mold or the movable template. Sliding sensors are usually installed on the ejector plate under the existing pusher pins.
In high-temperature molding, or when low-pressure sensors are used for small ejector pins, the sliding sensor is generally installed on the movable template of the mold. At this time, the ejector pin functions through the ejector sleeve or another one is used. Transition pin. The transition pin has two functions. One is that it can protect the sliding sensor from the interference of the demolding pressure when the existing ejector is used. Another function is that when the production cycle is short and the demolding speed is fast, it can make the sensor not affected by the rapid acceleration and deceleration of the ejector plate.
The size of the push pin on the top of the sliding sensor determines the size of the required sensor. When multiple sensors need to be installed in the mold cavity, the mold designer should use ejector pins of the same size for them to avoid setting errors or adjustment errors by the molder. Because the function of the ejector pin is to transmit the pressure of the plastic melt to the sensor, different products must use ejector pins of different sizes.
Generally speaking, the button sensor should be fixed in a recess in the mold, so that the installation position of the sensor must be the most interesting position of the processing personnel. If you want to disassemble this kind of sensor, you must open the template or make some special designs on the structure in advance.
Depending on the position of the button sensor in the mold, it may be necessary to install a junction box for cables on the template. Compared with the sliding sensor, the pressure reading of the button sensor is more reliable. This is because the button sensor is always fixed in the cavity of the mold, unlike the sliding sensor, which can move in the borehole. Therefore, button sensors should be used as much as possible.
Installation position of pressure sensor
If the pressure sensor is installed in the correct position, it can provide the molder with the most useful information. Except for some special cases, the sensor used for process monitoring should usually be installed in the back third of the cavity, and the sensor used to control the molding pressure should be installed in the first third of the cavity. For very small products, the pressure sensor is sometimes installed in the runner system, but this will make the sensor unable to monitor the pressure of the gate.
It needs to be emphasized that when the injection is insufficient, the pressure at the bottom of the cavity is zero, so the sensor at the bottom of the cavity becomes an important means to monitor the insufficient injection. With the use of digital sensors, sensors can be installed in each cavity, and the connection from the mold to the injection molding machine requires only one network cable. In this way, as long as the sensor is installed at the bottom of the mold cavity, without any other process control interface, the occurrence of insufficient injection can be prevented.
Under the above major premise, the mold designer and manufacturer must decide which cavity in the cavity to place the pressure sensor and the location of the wire or cable outlet. The design principle is that the wires or cables cannot be moved freely after passing through the mold. The general practice is to fix a connector on the mold base, and then use another cable to connect the mold with the injection molding machine and auxiliary equipment.
Post time: Nov-04-2021