NEWS
For the latest product consultation, technology application and exhibition information, please follow the official WeChat official account.
The Melt Pressure Transducer Must Be Mounted Correctly
Damage to a pressure transducer is commonly caused by their installation into an improperly machined hole. In forcing a transducer into a too-small or eccentric hole, the transducer diaphragm may be crushed and as a result the instrument will not function.
Tool kits available for machining the mounting hole will help to make sure the holes are properly sized. A mounting torque of 100 to 200 inch pounds (for ½-20 UNF) is essential to form an adequate seal; however, excessive mounting torque will cause seizing. To prevent problems with seizing, a high temperature anti-seize compound should be applied to the transducer threads prior to installation. Transducers installed at a mounting torque above 500 inch pounds will be difficult to remove even when anti-seize compound is applied.
Ensure That the Mounting Hole Thread Size is Correct
The abrasion from screwing a transducer into a mounting hole with an incorrect thread size will damage the instrument’s threads. This damage may prevent a good tight seal, resulting in material leakage, and the instrument will not function properly or safely. The proper dimensions for the mounting hole must be used to avoid thread galling. (The threads are, generally the industry standard of ½ - 20 UNF 2B.) A mounting well gage plug should be used to verify that the mounting hole is correctly machined and cleaned.
The Mounting Holes Must Be Clean
It is important that the transducer mounting holes are kept clean and free of any plastic buildup. Before an extruder is cleaned all of the transducers should be removed from the barrel to avoid their being damaged. When they are removed, plastic is likely to flow into the mounting holes and harden. If this hard plastic residue is not removed extensive tip damage will result when the transducers are re-inserted. A cleaning tool kit can be used to remove the contaminant plastic. It should be noted that repeated cleaning may produce “too deep” holes and result in damage to the transducer tip. If this is seen, spacers should be used to raise the transducer.
Select a Good Location
Transducers may be located in the barrel, before a screen changer, before and after a melt pump, or in the die. When a transducer is positioned too far upstream in the barrel, un-melted plastic pellets may abrade against the transducer tip, resulting in damage. If a transducer is positioned too far back in the mounting hole, a stagnant pool of melted plastic will build up between the transducer tip and the screw flights. Over time this plastic will degrade to carbon, which will prevent the transmission of an accurate pressure signal. On the other hand, if the transducer extends too far into the barrel the screw flights can shear off the unit’s sensor tip.
Clean the Transducer with Care
All of the transducers should be removed before cleaning an extruder barrel with either a wire brush or special cleaning compounds. Either one of these can ruin the transducer diaphragm. The transducer should be removed while the barrel is hot and tip wiped clean with a non-abrasive cloth. The transducer hole should be cleaned at this time with a cleaning drill/guide sleeve.
Avoid Cold Starts
Both the transducer and extruder can be damaged if the extruder is not brought up to operating temperature before the machinery begins operating. A sufficient “soak time” must be provided for the plastic to go from it’s solid to molten state. In addition, it should be noted that if a transducer is removed from a cold extruder, material might adhere to the transducer tip causing the diaphragm to tear off the unit. Make sure the barrel is warm enough, that any plastic present will be soft, before removing the transducer.
Don’t Overpressure the Transducer
Even though transducers are designed to withstand 1.5 times overpressure, avoid the risk of applying too much pressure by making sure that you are using the correct model designed for your range of extrusion operation pressures. A good rule of thumb is to use transducers that are built to withstand twice the rated pressure in your process. Then the extruder will have to be operating at an extremely high (and unsafe) pressure level for the transducer to fail.
In chemical fiber and plastic extrusion system equipment, melt pressure sensors can be single high-temperature melt pressure sensors that measure pressure at a single point, or a series of sensors used to measure pressure along the entire production line. High-temperature melt pressure sensors are connected to data loggers and audible alarm devices, and the extruder's processing parameters can be adjusted using a control system. At the same time, high-temperature melt pressure sensors are highly sensitive components, and if not properly installed and maintained, they are prone to damage. The following are some installation and usage precautions for high-temperature melt pressure sensors to ensure measurement accuracy and service life.
Selecting the appropriate location
If the high-temperature melt pressure sensor is installed too close to the upstream end of the production line, unmelted material may wear down the sensor's top; if the sensor is installed too far downstream, a stagnation zone of melted material may form between the sensor and the screw's travel path, where the melt may degrade, and the pressure signal may be distorted; if the sensor is installed too deeply into the barrel, the screw may come into contact with the sensor's top during rotation, causing damage. Generally, the sensor can be located on the barrel before the filter screen, before or after the melt pump, or within the mold. The sensor's probe is heat-resistant, but the housing must be kept below 80°C. Therefore, during installation and use, it is essential to ensure that the sensor housing is securely fixed in a room-temperature environment. Isolating the housing from high-temperature areas helps improve the sensor's measurement accuracy and service life.
Proper Installation
Damage to pressure sensors is typically caused by improper installation. Forcing a high-temperature melt pressure sensor into a hole that is too small or irregularly shaped may cause the sensor's vibration diaphragm to be impacted and damaged. Using appropriate tools to machine the installation hole helps control the hole's dimensions. Additionally, proper installation torque facilitates a good seal. However, excessive torque may cause the sensor to slip out. To prevent this, apply anti-loosening compound to the sensor's threaded section before installation. After applying this compound, the sensor remains secure even with high installation torque. The sensor diaphragm is the most vulnerable component. Do not remove the protective cap before installation, and take care to protect the diaphragm during installation. The installation hole must be machined according to the technical requirements specified in the installation hole dimension diagram and dimension table to avoid diaphragm scratches caused by non-standard installation holes, which could affect sensor performance. Ensure that no metal debris or plastic residues remain in the installation hole during installation. All sensors must be removed from the machine before cleaning the extruder. Sensors can only be removed when the polymer is in a molten state. After removal, immediately clean the sensor probe diaphragm with a soft cloth. During electrical connection, the signal output connection cable of the transmitter must be routed separately through a cable tray to avoid interference at the site. Ensure sufficient heating and melting time before equipment startup to ensure that all material in the diaphragm area of the sensor has melted before the extruder begins operation.
Check the installation hole dimensions
If the installation hole dimensions are inappropriate, the threaded portion of the high-temperature melt pressure sensor is prone to wear during installation. This not only affects the equipment's sealing performance but also prevents the sensor from functioning properly, potentially creating safety hazards. Only appropriately sized installation holes can prevent thread wear (thread industrial standard 1/2-20 UNF 2B). Typically, an installation hole measuring instrument can be used to inspect the installation hole and make appropriate adjustments.
Maintaining the cleanliness of the installation hole
Maintaining the cleanliness of the installation hole and preventing melt blockage is crucial for ensuring the normal operation of the equipment. Before cleaning the extruder, all high-temperature melt pressure sensors should be removed from the barrel to avoid damage. When removing the high-temperature melt pressure sensor, melt may flow into the installation hole and harden. If these residual melts are not removed, they may cause damage to the top of the sensor when it is reinstalled. The Graeff cleaning kit can remove these melt residue. However, repeated cleaning processes may exacerbate damage to the sensor caused by the installation hole. If this occurs, measures should be taken to elevate the sensor's position within the installation hole.
Thorough cleaning
Before using a wire brush or special compounds to clean the extruder barrel, all high-temperature melt pressure sensors should be removed. This is because both cleaning methods may cause damage to the sensor's vibration membrane. When the barrel is heated, the sensors should also be removed and wiped with a soft cloth that does not cause wear.
Diaphragm damagedby a sharp edge
Causes:
· Damage through sharp edge contact (screwdriver or knife)
· Dropped
· Contact with degraded polymer in hole
Solutions:
· Use protective cap (transport, storage)
· Check hole with gauge plug for burrs or hardened plastic
· Clean hole with cleaning tool
About Graeff
Graeff is a British multinational group company specializing in the research and development, production and sales of melt pressure sensors, temperature sensors, industrial sensors, intelligent sensors, intelligent controllers and automation control systems.
Graeff (Jiaxing) Instruments Co., Ltd. (abbreviation: Graeff China) is a wholly-owned subsidiary of European enterprise Graeff Group in China. Graeff focuses on measurement and control in the field of pressure and temperature, and Graeff technology research and development The core members have many years of research experience in the fields of electronics and mechanics. It is an innovator in the field of
