Melt Pressure Sensors in Extrusion Production Role and Use Specifications In extrusion lines, melt pressure sensors play an important role in improving melt quality, increasing production safety, and protecting production equipment. At the same time, the melt pressure sensor is a very sensitive element. Only proper installation and maintenance can make full use of it.
During the extrusion process, some of the product's quality standards (such as dimensional accuracy or surface smoothness of mineral fillers, etc.) all require optimal control of the extrusion pressure. The melt pressure sensor fulfills this requirement. Important components. By arranging the melt pressure sensor and the pressure control device at the entrance of the mold, the yield can be made more stable and the waste of materials can be reduced. Melt pressure sensors play an important role in improving melt quality, improving production safety, protecting production equipment, and extending the service life.
In addition, measuring the pressure across the filter and the melt pump is also very important to ensure the safety of production and optimize the performance of the equipment. If the melt gets stuck in the mold, the sensor below the filter will warn the operator. When the sensor on the filter travels an alarm, it indicates that the pressure inside the extruder is too high, which may cause excessive wear on the screw. For manufacturers applying melt pumps, 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, because any obstruction may cause damage to the melt pump.
The melt pressure sensor assembled on the extrusion line can be a single sensor measuring only one point of pressure, or a series of sensors used to measure the entire production line. Melt pressure sensors are connected to data loggers and audible alarms. Process control systems can be used to adjust the processing parameters of the extruder. At the same time, the pressure sensor is also a very sensitive element that can easily be damaged if it is not properly installed and maintained. Several simple methods described below are conducive to prolonging the life of the pressure sensor and at the same time helping the user to obtain accurate and reliable measurement results.
â— Correct installation Usually the damage to the pressure sensor is caused by improper installation. If the sensor is forcibly installed in a hole that is too small or has an irregular shape, it may cause the shock film of the sensor to be damaged by impact. Selecting a suitable tool for machining the mounting holes facilitates the control of the size of the mounting holes. In addition, a suitable mounting torque facilitates the formation of a good seal. However, if the installation torque is too high, it can easily cause the sensor to slip off. To prevent this from happening, the anti-detachment compound is usually applied on the threaded portion of the sensor prior to installation. After using this compound, the sensor is difficult to move even if the mounting torque is high.
â— Checking the size of the mounting hole If the size of the mounting hole is not suitable, the threaded portion of the sensor during the mounting process is susceptible to wear. This will not only affect the sealing performance of the device, but also make the sensor not fully function, and may even cause potential safety hazards. Only suitable mounting holes can avoid thread wear (Thread Industry Standard 1/2-20 UNF 2B). Mounting holes can often be used to inspect mounting holes to make appropriate adjustments.
â— Keeping the mounting holes clean Keeping the mounting holes clean and preventing clogging of the melt are important to ensure the proper operation of the equipment. Before the extruder is cleaned, all sensors should be removed from the barrel to avoid damage. When the sensor is removed, the molten material may flow into the mounting hole and harden. If these residual melts are not removed, the top of the sensor may be damaged when the sensor is installed again. The cleaning kit can remove these frit residues. However, the repeated cleaning process may deepen the damage caused by the mounting hole to the sensor. If this happens, steps should be taken to increase the position of the sensor in the mounting hole.
â— Choosing the right location When the sensor is installed too close to the upstream of the production line, unmelted material may abrade the top of the sensor. If the sensor is installed too far, melting may occur between the sensor and screw stroke. In the stagnant zone of the material, the molten material 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 rotation and cause damage. In general, the sensor can be located on the barrel in front of the screen, in front of the melt pump, or in the mold.
â— Careful cleaning All sensors should be removed before cleaning the extruder barrel with wire brushes or special compounds. Because both of these cleaning methods may cause damage to the sensor's diaphragm. When the barrel is heated, the sensor should also be disassembled and wiped on top using a soft cloth that will not wear, and the hole in the sensor also needs to be cleaned with a clean drill and guide bush.
â— Keep dry Although the sensor's circuit design can withstand harsh extrusion processing environments, most sensors are not absolutely waterproof, nor are they conducive to normal operation in wet environments. Therefore, it is necessary to ensure that the water in the water cooling device of the barrel of the extruder does not leak, otherwise the sensor will be adversely affected. If the sensor has to be exposed to water or a humid environment, special sensors with extremely high water resistance must be selected.
◠Avoid low-temperature interference In the extrusion production process, for plastic raw materials, there should be sufficient “saturation time†from solid to molten state. If the extruder has not reached operating temperature before starting production, both the sensor and the extruder will suffer some degree of damage. In addition, if the sensor is removed from the cold extruder, the material may adhere 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 sufficiently high and the material inside the barrel is in a softened state.
â— Prevent pressure overload Even if the overload design of the pressure range of the sensor can reach up to 50% (rate exceeding the maximum range), it should be avoided from the safety point of view of the equipment operation. It is better to select the measured pressure within the range. sensor. Under normal circumstances, the optimal range for the selected sensor should be twice the measured pressure so that the sensor can be protected from damage even if the extruder is operated at extremely high pressures.
During the extrusion process, some of the product's quality standards (such as dimensional accuracy or surface smoothness of mineral fillers, etc.) all require optimal control of the extrusion pressure. The melt pressure sensor fulfills this requirement. Important components. By arranging the melt pressure sensor and the pressure control device at the entrance of the mold, the yield can be made more stable and the waste of materials can be reduced. Melt pressure sensors play an important role in improving melt quality, improving production safety, protecting production equipment, and extending the service life.
In addition, measuring the pressure across the filter and the melt pump is also very important to ensure the safety of production and optimize the performance of the equipment. If the melt gets stuck in the mold, the sensor below the filter will warn the operator. When the sensor on the filter travels an alarm, it indicates that the pressure inside the extruder is too high, which may cause excessive wear on the screw. For manufacturers applying melt pumps, 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, because any obstruction may cause damage to the melt pump.
The melt pressure sensor assembled on the extrusion line can be a single sensor measuring only one point of pressure, or a series of sensors used to measure the entire production line. Melt pressure sensors are connected to data loggers and audible alarms. Process control systems can be used to adjust the processing parameters of the extruder. At the same time, the pressure sensor is also a very sensitive element that can easily be damaged if it is not properly installed and maintained. Several simple methods described below are conducive to prolonging the life of the pressure sensor and at the same time helping the user to obtain accurate and reliable measurement results.
â— Correct installation Usually the damage to the pressure sensor is caused by improper installation. If the sensor is forcibly installed in a hole that is too small or has an irregular shape, it may cause the shock film of the sensor to be damaged by impact. Selecting a suitable tool for machining the mounting holes facilitates the control of the size of the mounting holes. In addition, a suitable mounting torque facilitates the formation of a good seal. However, if the installation torque is too high, it can easily cause the sensor to slip off. To prevent this from happening, the anti-detachment compound is usually applied on the threaded portion of the sensor prior to installation. After using this compound, the sensor is difficult to move even if the mounting torque is high.
â— Checking the size of the mounting hole If the size of the mounting hole is not suitable, the threaded portion of the sensor during the mounting process is susceptible to wear. This will not only affect the sealing performance of the device, but also make the sensor not fully function, and may even cause potential safety hazards. Only suitable mounting holes can avoid thread wear (Thread Industry Standard 1/2-20 UNF 2B). Mounting holes can often be used to inspect mounting holes to make appropriate adjustments.
â— Keeping the mounting holes clean Keeping the mounting holes clean and preventing clogging of the melt are important to ensure the proper operation of the equipment. Before the extruder is cleaned, all sensors should be removed from the barrel to avoid damage. When the sensor is removed, the molten material may flow into the mounting hole and harden. If these residual melts are not removed, the top of the sensor may be damaged when the sensor is installed again. The cleaning kit can remove these frit residues. However, the repeated cleaning process may deepen the damage caused by the mounting hole to the sensor. If this happens, steps should be taken to increase the position of the sensor in the mounting hole.
â— Choosing the right location When the sensor is installed too close to the upstream of the production line, unmelted material may abrade the top of the sensor. If the sensor is installed too far, melting may occur between the sensor and screw stroke. In the stagnant zone of the material, the molten material 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 rotation and cause damage. In general, the sensor can be located on the barrel in front of the screen, in front of the melt pump, or in the mold.
â— Careful cleaning All sensors should be removed before cleaning the extruder barrel with wire brushes or special compounds. Because both of these cleaning methods may cause damage to the sensor's diaphragm. When the barrel is heated, the sensor should also be disassembled and wiped on top using a soft cloth that will not wear, and the hole in the sensor also needs to be cleaned with a clean drill and guide bush.
â— Keep dry Although the sensor's circuit design can withstand harsh extrusion processing environments, most sensors are not absolutely waterproof, nor are they conducive to normal operation in wet environments. Therefore, it is necessary to ensure that the water in the water cooling device of the barrel of the extruder does not leak, otherwise the sensor will be adversely affected. If the sensor has to be exposed to water or a humid environment, special sensors with extremely high water resistance must be selected.
◠Avoid low-temperature interference In the extrusion production process, for plastic raw materials, there should be sufficient “saturation time†from solid to molten state. If the extruder has not reached operating temperature before starting production, both the sensor and the extruder will suffer some degree of damage. In addition, if the sensor is removed from the cold extruder, the material may adhere 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 sufficiently high and the material inside the barrel is in a softened state.
â— Prevent pressure overload Even if the overload design of the pressure range of the sensor can reach up to 50% (rate exceeding the maximum range), it should be avoided from the safety point of view of the equipment operation. It is better to select the measured pressure within the range. sensor. Under normal circumstances, the optimal range for the selected sensor should be twice the measured pressure so that the sensor can be protected from damage even if the extruder is operated at extremely high pressures.