Daily maintenance of thermocouples

Thermocouple is a kind of temperature sensor commonly used in industry. It not only suffers from external factors during the measurement process, but also is affected by some interference factors such as cleanliness, size and pressure overload. Constraints such as conditions. These factors combine not only to produce errors, but also to influence the measurement results, and also affect the life of the thermocouple itself. In order to avoid or reduce the occurrence of this adverse effect, we need to carry out routine maintenance of the thermocouple to ensure the normal application of the thermocouple.

1. Check the size of the mounting hole: If the size of the mounting hole is not suitable, the threaded part of the sensor will be easily worn during the installation process. This not only affects the sealing performance of the equipment, but also makes the pressure sensor not fully function, 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.

2. Keep the mounting holes clean: Keeping the mounting holes clean and preventing the clogging of the melt is important to ensure proper operation of the equipment. All pressure 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.

3. Choose the right position: When the pressure sensor is installed too close to the upstream of the line, the unmelted material may wear the top of the sensor; if the sensor is installed too far back, it may be between the sensor and the screw stroke There will be a stagnant zone of molten material, where the melt may degrade and the pressure signal may 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 or behind the melt pump, or in the mold.

4. 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.

5. 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.

6. 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.

7. Prevent pressure overload: Even if the overload design of the pressure sensor's pressure measuring range can reach 50% (out of the maximum range ratio), it should be avoided as much as possible from the safety point of operation of the equipment. It is best to choose the measured pressure in the range. The sensor inside. Under normal circumstances, the optimal range of the selected sensor should be twice the measured pressure, so that the pressure sensor can be prevented from being damaged even if the extruder is operated at extremely high pressure. The pressure transmitter is required to be inspected once a week, once a month, mainly to remove the dust inside the instrument, carefully check the electrical components, and the current value of the output should be checked frequently. The pressure transmitter is weak inside, must be the same The outside world is separated by strong electricity.