In the extrusion process, some quality standards of the product (such as dimensional accuracy or surface flatness of mineral filler parts) require optimal control of the extrusion pressure. Melt pressure sensors are required to achieve this. Important components. By providing a melt pressure sensor and a pressure control device at the mold inlet connection, the yield can be made more stable while reducing material waste. Melt pressure sensors play an important role in improving melt quality, increasing production safety, and protecting production equipment and extending their service life.
In addition, measuring the pressure through the filter and the melt pump is also important to ensure production safety and to optimize the performance of the equipment. If the melt is blocked when it flows into the mold, the sensor under the filter will alert you to the operator. When the sensor on the filter screen gives an alarm, it indicates that the internal pressure of the extruder is too high, which may cause excessive wear on the screw. For the manufacturer of the melt pump, it is necessary to measure the inlet pressure and outlet pressure of the melt to ensure that the melt can continuously flow into the mold, as any hindrance can cause damage to the melt pump.
The melt pressure sensor assembled on the extrusion line can be a single sensor that measures only one point pressure, or a series of sensors that measure the entire line. The melt pressure sensor is connected to the data logger and the audible alarm device, and the processing parameters of the extruder can be adjusted by the processing control system. At the same time, the pressure sensor is also a very sensitive component that can be easily damaged if it is not properly installed and maintained. The following simple methods are helpful to extend the life of the pressure sensor and help the user to obtain accurate and reliable measurement results.
â— Correct installation Normally the damage of the pressure sensor is caused by improper installation position. If the sensor is forcibly installed in an excessively small hole or an irregularly shaped hole, the vibration film of the sensor may be damaged by impact. Choosing the right tool to machine the mounting holes will help control the size of the mounting holes. In addition, suitable mounting torque facilitates the formation of a good seal. However, if the installation torque is too high, it is easy to cause the sensor to slip. To prevent this, it is common to apply the anti-separation compound to the threaded portion before the sensor is installed. After using this compound, the sensor is difficult to move even if the mounting torque is high.
â— Check the size of the mounting hole If the size of the mounting hole is not suitable, the threaded portion of the sensor is easily subject to wear during installation. This not only affects the sealing performance of the device, but also prevents the sensor from functioning fully and may even pose a safety hazard. Only the proper mounting holes can avoid thread wear (Thread Industry Standard 1/2-20 UNF 2B). Mounting holes can usually be tested with a mounting hole gauge to make the appropriate adjustments.
â— Keep the mounting holes clean Keeping the mounting holes clean and preventing clogging of the melt is important to ensure proper operation of the equipment. All sensors should be removed from the barrel to avoid damage before the extruder is cleaned. When the sensor is removed, the melt may flow into the mounting hole and harden. If the residual melt is not removed, the top of the sensor may be damaged when the sensor is mounted again. The cleaning kit removes these melt residues. However, repeated cleaning processes may deepen the damage to the sensor caused by the mounting holes. If this happens, steps should be taken to raise the position of the sensor in the mounting hole.
â— Choosing the right position When the sensor is installed too close to the upstream of the line, unmelted material may wear the top of the sensor; if the sensor is installed too far behind, there may be melting between the sensor and the screw stroke. In the stagnant zone of the material, the melt may be degraded there, and the pressure signal may also transmit distortion; if the sensor is too deep into the barrel, the screw may touch the top of the sensor during the rotation and cause damage. In general, the sensor can be located on the barrel in front of the screen, in front of or behind the melt pump, or in the mold.
â— Careful cleaning All sensors should be removed before cleaning the extruder barrel with a wire brush or special compound. Because both methods of cleaning may cause damage to the diaphragm of the sensor. When the barrel is heated, the sensor should also be removed and wiped with a soft cloth that does not wear out, and the sensor holes need to be cleaned with a clean drill and guide sleeve.
â— Keep dry Although the sensor's circuit design can withstand the harsh extrusion processing environment, most sensors are not absolutely waterproof, and it is not suitable for normal operation in humid environments. Therefore, it is necessary to ensure that the water in the water-cooling device of the extruder barrel does not leak, which may adversely affect the sensor. If the sensor has to be exposed to water or moisture, choose a special sensor that is extremely water resistant.
â— Avoid low temperature interference In the extrusion production process, for plastic raw materials, there should be sufficient "soaking time" from solid to molten state. If the extruder does not reach the operating temperature before starting production, both the sensor and the extruder will be damaged to some extent. In addition, if the sensor is removed from the cold extruder, the material may stick to the top of the sensor causing damage to the diaphragm. Therefore, before removing the sensor, make sure that the temperature of the barrel is high enough and the material inside the barrel is softened.
◠Preventing pressure overload Even if the overload design of the sensor's pressure measuring range can reach 50% (out of the maximum range ratio), it should be avoided as far as possible from the safety point of view of equipment operation. It is best to choose the measured pressure within the range of the range. sensor. Under normal circumstances, the optimal range of the selected sensor should be twice the measured pressure, so that the sensor can be damaged even if the extruder is operated under extremely high pressure. 1. Sensor Mounting The diaphragm of the sensor is the most vulnerable part. Do not drop the protective cap before installation. At the same time, pay attention to protect the diaphragm of the sensor. The processing of the mounting hole should be processed according to the technical requirements of the mounting hole size chart and the dimension table to avoid the normal operation of the sensor due to the film scratch caused by the non-standard mounting hole. 2. Remove and install the sensor. Ensure that there are no metal foreign objects or plastic left in the correct mounting hole. Remove all sensors from the machine before cleaning the extruder. The sensor can only be removed when the polymer is in a hot molten state. Immediately after removal, wipe the sensor probe diaphragm with a soft cloth. At the same time, Shanghai Yingying Measurement & Control Technology Co., Ltd. can provide special cleaning tools for the installation holes to clean the materials in the holes for the next installation. 3. Ensure sufficient heating and melting time before starting the equipment to ensure that all materials in the diaphragm part of the sensor have melted before the extrusion machine works. 4. The probe part of the installation position sensor can withstand high temperature, and the temperature resistance of the outer casing can be below 80 °C. Therefore, it is necessary to pay attention to fixing the installed sensor housing part in the room temperature environment during installation and use. The isolation of the housing from the high temperature area helps to improve the measurement accuracy and service life of the sensor. 5. Overload effect In the actual pressure control process, it is better to be within the rated pressure. Although the sensor has a certain overload capacity, when the long-term overload will affect the measurement accuracy and service life of the sensor. 6. Electrical connection of the transmitter During the electrical connection process, the signal output connection cable of the transmitter must be connected separately through the wiring slot to avoid disturbance on site.
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