The use of high-temperature melt pressure sensor precautions (Hu Wensheng 15549508068)
In the extrusion line, the PT series melt pressure sensors manufactured by Xiaogan Shanxiang Electronics Co., Ltd. play an important role in improving the quality of the melt, improving the safety of production, 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.
In the extrusion production process, some quality standards of the PT series products of Shanshan (such as the dimensional accuracy or the surface flatness of the mineral fillers added) all require the optimal control of the extrusion pressure. The sensor is an important element to achieve this requirement. 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, increasing production safety, protecting production equipment, and extending the service life.
In addition, measuring the pressure through 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.
Mounted on an extrusion line, the Yamatake PT321 melt pressure sensor can be a single sensor measuring only one point of pressure, or a series of sensors used to measure the entire production line. The Yamagata melt pressure sensor is connected to a data logger and an audible alarm device. The process control system 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 helping the user to obtain accurate and reliable measurement results.
â— Proper installation Normally 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, it is common to apply anti-detachment compound 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— Check 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 UNF2B). Mounting holes can often be used to test the 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 proper equipment operation. 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, the unmelted material may wear out the top of the sensor; if the sensor is installed too far, melting may occur between the sensor and the 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 using a wire brush or special compound to clean the extruder barrel. 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 sensor hole needs to be cleaned with a clean drill and guide bush.
â— Keep dry Although the sensor's circuit design can withstand the harsh extrusion processing environment, most sensors are not absolutely waterproof, nor conducive to normal operation in a humid environment. 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 the plastic raw material, there should be sufficient “saturation time†from the solid to the 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 50% (surpass the ratio of the maximum range), you should also avoid the risk from the perspective of safe operation of the equipment. 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.
1. Mounting the sensor The diaphragm of the sensor is the most vulnerable part. Please do not detach the protective cap before installation. At the same time, you should pay attention to protect the diaphragm of the sensor. The processing of the mounting holes shall be processed according to the technical requirements of the dimension drawings of the mounting holes and the dimension table, so as to prevent the normal operation of the sensor due to the scratches of the diaphragm caused by the non-standard mounting holes.
2. Demolition of Sensors Ensure that there are no metal foreign objects or plastics left in the correct installation hole during installation. Remove all sensors from the machine before cleaning the extruder. Remove the sensor only when the polymer is in a hot molten state. Immediately after removal, clean the sensor probe diaphragm with a soft cloth. At the same time, Shanghai Haoying Measurement and Control Technology Co., Ltd. can provide special cleaning tools for mounting holes to clean the materials in the holes for the next installation.
3, on the start of the equipment to ensure adequate heating and melting time before start-up to ensure that all the materials in the sensor membrane parts of the sensor before the extrusion machinery work has melted.
4. The probe part of the installation position sensor can withstand high temperature, and the temperature of the shell can be less than 80°C. Therefore, during the installation and use, it must be noted that the part of the mounted sensor shell is fixed at room temperature. The isolation of the enclosure from the high temperature area helps improve the measurement accuracy and lifetime of the sensor.
5. Impact of overload 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 interference on site.
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