In extrusion production lines, melt pressure sensors play an important role in improving melt quality, improving production safety, and protecting production equipment. At the same time, the melt pressure sensor is a very sensitive component, and only proper installation and maintenance can make it fully play its role.
In the extrusion production process, some quality standards of the product (such as dimensional accuracy or the surface flatness of the added mineral filler parts, etc.) require the optimal control of the extrusion pressure, and the melt pressure sensor is to achieve this requirement. important element. By providing a melt pressure sensor and a pressure control device at the mold inlet connection, it is possible to make the production rate more stable and reduce material waste. Melt pressure sensors play an important role in improving melt quality, improving production safety, and protecting production equipment and extending its service life.
In addition, measuring the pressure across the screen and melt pump is very important to ensure the safety of production and optimize the performance of the equipment. If the melt flow into the mold is blocked, a sensor under the screen will alert the operator. When a sensor upstream of the filter sounds an alarm, it indicates that the pressure inside the extruder is too high, possibly causing excessive wear on the screw. For manufacturers using melt pumps, the inlet and outlet pressures of the melt need to be measured to ensure a continuous flow of the melt into the mold, as any obstruction could result in damage to the melt pump.
The melt pressure sensor assembled on the extrusion line can be a single sensor measuring the pressure at only one point, or it can be a series of sensors measuring the entire line. The melt pressure sensor is connected with the data recorder and the sound alarm device, and the processing parameters of the extruder can be adjusted by the processing control system. At the same time, pressure sensors are also very sensitive components, which can be easily damaged if not properly installed and maintained. The following simple methods are beneficial to prolong the service life of the pressure sensor, and at the same time can help users get accurate and reliable measurement results.
● Correct installation
Usually the damage of the pressure sensor is caused by its improper installation position. If the sensor is forcibly installed in a hole that is too small or irregularly shaped, it may cause the vibration membrane of the sensor to be damaged by impact. Selecting a suitable tool to process the mounting hole is beneficial to control the size of the mounting hole. In addition, proper installation 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 out. In order to prevent this phenomenon, an anti-separation compound is usually applied to the threaded part of the sensor before installation. After using this compound, even with high mounting torque, the sensor is difficult to move.
● Check the size of the mounting holes
If the size of the mounting hole is not suitable, the threaded part of the sensor is easily worn during the installation process. This will not only affect the sealing performance of the device, but also make the sensor unable to function fully, and may even create a safety hazard. Only suitable mounting holes can avoid thread wear (thread industry standard 1/2-20 UNF 2B). Usually, the mounting hole can be tested with a mounting hole measuring instrument to make appropriate adjustments.
● Keep the mounting holes clean
Keeping the mounting holes clean and preventing melt clogging is very important to ensure the normal 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, it is possible for the molten material to flow into the mounting holes and harden. If this residual molten material is not removed, the top of the sensor may be damaged when the sensor is installed again. Cleaning kits can remove these melt residues. However, repeated cleaning procedures have the potential to deepen damage to the sensor from the mounting holes. If this occurs, steps should be taken to raise the sensor in the mounting hole.
● Choose the right location
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 back, a stagnant zone of molten material may be created between the sensor and the screw stroke, The melt may be degraded there, and the pressure signal may be distorted; if the sensor is too deep into the barrel, the screw may touch the top of the sensor during rotation and cause it to be damaged. Generally, the sensor can be located on the barrel in front of the screen, before and after the melt pump, or in the mold.
● careful cleaning
All sensors should be removed before cleaning the extruder barrel with a wire brush or special compound. Because both cleaning methods may cause damage to the sensor’s diaphragm. When the barrel is heated, the sensor should also be removed and the top of the sensor should be wiped with a soft, non-abrasive cloth. The sensor hole should also be cleaned with a clean drill and guide sleeve.
● keep dry
Although the sensor’s circuitry is designed to withstand the harsh extrusion process environment, most sensors are not completely 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 extruder barrel does not leak, otherwise it will adversely affect the sensor. If the sensor has to be exposed to water or moisture, select a special sensor that is extremely waterproof.
● Avoid low temperature interference
During extrusion production, there should be sufficient “saturation time” for plastic raw materials 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 damage. Additionally, if the sensor is removed from a cold extruder, material may stick to the top of the sensor causing damage to the diaphragm. Therefore, before removing the sensor, it should be confirmed that the temperature of the barrel is high enough and the material inside the barrel is in a softened state.
● Prevent pressure overload
Even if the overload design of the pressure measuring range of the sensor can reach up to 50% (the ratio exceeding the maximum range), from the perspective of the safety of equipment operation, risks should be avoided as much as possible, and it is best to choose a sensor whose pressure to be measured is within the range. Under normal circumstances, the optimal range of the selected sensor should be 2 times the pressure to be measured, so that even if the extruder is operating under extremely high pressure, the sensor can be prevented from being damaged.
Post time: Oct-09-2022