Frequently Asked Questions (4)
9. Turbine flowmeter common problems and solutions First, the larger flow fluctuations Caused by the larger flow fluctuations can be considered from the following aspects:
1. Whether the water source is pulsating flow (1) Generally pumping raw materials, if the flow installation position is close to the pump, it is easy to generate pulsating flow, resulting in larger flow fluctuations, at this time solutions, increase the pump and flow meter The distance between the straight pipe makes the flow stable.
(2) The flow meter installation position is too close to the valve or elbow, when the raw material passes through the valve or elbow, causing flow fluctuations. At this point, it should be far away from the position of the valve and elbow to ensure a certain straight pipe section before and after
2. Is there an interference source such as a motor, frequency converter, and strong electric power near the flowmeter? Solution: flow meter grounding, or filter capacitor. If you cannot solve it, you should stay away from sources of interference.
Second, the flow meter does not show the flow solution (1) First check the line for any problems, such as the signal line off, there is a broken line.
(2) Separate the sensor from the signal amplifier, connect the signal amplifier to the meter, and use ferrous metal to move the distance from the bottom of the signal amplifier at a distance of 2~3mm. If the meter has a display, the display part is no problem. Please remove the flow sensor from the pipe and check whether the flowmeter impeller is entangled or the impeller is broken.
Third, the flow meter shows that the flow rate is small, and the actual flow rate is relatively large. The reason for this problem generally is that the rotation of the impeller is not slippery or the blades are broken. Remove the flow from the pipe and check that the flow meter is tangled or damaged.
Fourth, the flowmeter display error is relatively large (1) First check the flow sensor coefficient that is K value and other parameters of the instrument is set correctly (2) the customer conditions, the actual calibration with an electronic scale calibration. If the flow repeatability is poor or not calibrated at all, contact the supplier.
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10. Precautions for the use of high-temperature melt pressure sensors 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 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 setting the melt pressure sensor and pressure control device at the entrance of the mold, the yield can be made more stable and the material waste can be reduced. Melt pressure sensors play an important role in improving melt quality, improving production safety, protecting production equipment, and extending its 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 flows into the mold, the sensor under the filter will alert the operator. When the sensor on the filter travels an alarm, the internal pressure of 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 impediment 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 Normally, the pressure sensor is damaged due to its improper installation position. 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. Choosing the right tool to machine the mounting holes helps to control the size of the installation. In addition, a suitable mounting torque facilitates the formation of a good seal. However, if the mounting torque is too high, the sensor may slip off easily. To prevent this from happening, the anti-detachment compound is usually applied to 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 the appropriate mounting holes can avoid thread wear (Thread Industry Standard 1/2 UNF2B). Usually, mounting holes can be used to inspect mounting holes to make appropriate adjustments.
â— Keeping the mounting holes clean It is very important to keep the mounting holes clean and prevent the clogging of the melt 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, 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, measures 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 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 environment, but most sensors can not be absolutely waterproof, in the wet environment is also not conducive to normal operation. 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 materials, 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 avoid the risk from the perspective of safety of the equipment operation. It is better to choose 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.