【Mechanical Equipment Technology Edition】Daily Question 201804013: Common Faults of Screw Refrigeration Compressors (2)

Every type of plastic has an ideal processing temperature range, and it is essential to maintain the temperature of the barrel at a level close to this range during processing. Granular plastic enters the cylinder from the hopper, and dry friction inevitably occurs during feeding. If these plastics are heated unevenly and melt unevenly, it can easily lead to increased wear on the surface of the screw. The speed of the barrel should be adjusted properly, as some of the plastic contains agents that reduce friction with metal surfaces. During injection molding, if the speed is too high, the wear rate increases; therefore, it is very important to control the speed appropriately. The screw rotates inside the barrel, and friction between the material and these surfaces reduces wear on the working surfaces of the screw and the barrel. The screw diameter will gradually decrease, while the barrel diameter will gradually increase. In this way, the clearance between the screw and the barrel gradually increases as wear occurs between them. If the material contains fillers such as calcium carbonate or glass fibers, it will increase the wear between the screw and the barrel. Because the material may not be uniformly plasticized on a monthly basis, or because metal particles may be mixed within it, this can cause the torque exerted on the screw to increase suddenly. When this torque exceeds the strength limit of the screw, it can lead to the screw breaking – this is a common type of damage that also results in wear on the screw, thereby reducing its service life.

I. Reasons for screw wear 1. As the screw rotates inside the barrel, the lubricating oil and compressed gas cause friction between the screw and the barrel walls, which gradually wears down the working surface of the screw; as a result, the diameter of the screw decreases while the diameter of the inner hole in the barrel increases. In this way, the diameter clearance between the screw and the housing gradually increases as both components wear down over time. However, since the resistance from the nose section and the shunt plate at the front of the machine remains unchanged, this increases the leakage rate as the compressed gas moves forward; in other words, the amount of gas and lubricating oil flowing from the diameter gaps in the direction of air intake increases. As a result, the flow rate out of the machine decreases. 2. If corrosive substances such as acids are present in the gas, it can accelerate the wear of the screw and the machine body. 3. Wear and abrasion of the machine, or the presence of metal particles mixed in the material, can cause the torque required to rotate the screw to increase suddenly. This torque exceeds the strength limit of the screw, leading to its breakage. This is a type of damage caused by an abnormal accident.

1. Poor lubrication 2. Dirty refrigeration system (lubricant not replaced regularly, oil, oil filters, suction filters, etc. not cleaned or replaced) 3. Wear particles from bearings entering the oil circuit 4. Deformation of the axes of the male and female rotors

1. The screw rotates inside the barrel; the lubricating oil and compressed gas cause friction with the screw and the barrel, leading to gradual wear of the screw’s working surface. As a result, the diameter of the screw decreases, while the diameter of the inner hole in the barrel increases. In this way, the diameter clearance between the screw and the housing gradually increases as both components wear down over time. 2. If corrosive substances such as acids are present in the gas, it can accelerate the wear of the screw and the machine body. 3. Wear and abrasion of the machine, or the presence of metal particles mixed in the material, can cause a sudden increase in the torque required to rotate the screw.

The oil quality is poor, resulting in inadequate lubrication; the alignment during installation is not proper, there are issues with the installation quality; there are defects in the manufacturing of the screw; and the bearings are damaged! Load increasing!

1. The screw rotates inside the barrel; the lubricating oil and compressed gas cause friction with the screw and the barrel, leading to gradual wear of the screw’s working surface. As a result, the diameter of the screw decreases, while the diameter of the inner hole in the barrel increases. In this way, the diameter clearance between the screw and the housing gradually increases as both components wear down over time. However, since the resistance from the nose section and the shunt plate at the front of the machine remains unchanged, this increases the leakage rate as the compressed gas moves forward; in other words, the amount of gas and lubricating oil flowing from the diameter gaps in the direction of air intake increases. As a result, the flow rate out of the machine decreases. 2. If corrosive substances such as acids are present in the gas, it can accelerate the wear of the screw and the machine body. 3. Wear and abrasion of the machine, or the presence of metal debris in the material, can cause the torque required to rotate the screw to increase suddenly. This torque exceeds the strength limit of the screw, resulting in its breakage. This is a type of damage caused by an abnormal accident.

If corrosive substances such as acids are present in the gas, it can accelerate the wear of the screw and the machine body. Wear and abrasion of the machine, or the presence of metal particles mixed in the material, can cause the torque required to rotate the screw to increase suddenly. This torque exceeds the strength limit of the screw, leading to its breakage. This is a type of damage caused by an abnormal accident.

I. Reasons for screw wear 1. As the screw rotates inside the barrel, the lubricating oil and compressed gas cause friction between the screw and the barrel walls, which gradually wears down the working surface of the screw; as a result, the diameter of the screw decreases while the diameter of the inner hole in the barrel increases. In this way, the diameter clearance between the screw and the housing gradually increases as both components wear down over time. However, since the resistance from the nose section and the shunt plate at the front of the machine remains unchanged, this increases the leakage rate as the compressed gas moves forward; in other words, the amount of gas and lubricating oil flowing from the diameter gaps in the direction of air intake increases. As a result, the flow rate out of the machine decreases. 2. If corrosive substances such as acids are present in the gas, it can accelerate the wear of the screw and the machine body. 3. Wear and abrasion of the machine, or the presence of metal particles mixed in the material, can cause the torque required to rotate the screw to increase suddenly. This torque exceeds the strength limit of the screw, leading to its breakage. This is a type of damage caused by an abnormal accident.

1. Damaged bearings cause the male and female rotors to come into contact, leading to wear. 2. An insufficiently clean medium results in wear of the screw. 3. An inappropriate clearance between the rotors, as well as too small a clearance between the rotors and the compressor cylinder walls, causes wear.

1. Each type of plastic has an ideal processing temperature range for plasticization; the temperature in the barrel should be controlled to be close to this range. Granular plastic enters the barrel from the hopper and first reaches the feeding section, where dry friction inevitably occurs. In the case of Guangzhou glue dispensing valves, when this plastic is not heated sufficiently and does not melt evenly, ab two-component glue dispensing valves, it can easily lead to increased wear on the inner walls of the barrel and the surface of the screw. Similarly, with glue dispensing valves, in the compression and homogenization stages, if the melting state of the plastic is uneven, it can also lead to accelerated wear. 2. The rotation speed should be adjusted properly. Some plastics contain reinforcing agents such as glass fibers, minerals, or other fillers. The frictional force of these materials on metal surfaces is often much greater than that of molten plastic. When injecting these plastics, using a high rotational speed increases the shear force on the plastic; this in turn leads to the formation of more fragmented fibers. These fragmented fibers have sharp ends, which significantly increases the wear rate. Inorganic minerals also exert a significant scraping effect when sliding at high speed over metal surfaces. Therefore, the rotation speed should not be set too high. 3. As the screw rotates inside the barrel, friction between the material and these components causes gradual wear of the working surfaces of the screw and the barrel; as a result, the diameter of the screw decreases gradually, while the inner diameter of the barrel increases gradually. In this way, the diameter clearance between the screw and the barrel gradually increases as both components wear down over time. However, since the resistance from the die head and the splitter plate at the front of the barrel remains unchanged, this increases the leakage rate of the material being extruded as it moves forward; in other words, the amount of material flowing from the diameter gaps in the feed direction increases. As a result, the production volume of plastic machinery declined. This phenomenon further increases the residence time of the material inside the barrel, leading to its decomposition. If it is polyethylene, the hydrogen chloride gas generated during decomposition exacerbates the corrosion of the screw and barrel. 4. If fillers such as calcium carbonate and glass fibers are present in the material, they can accelerate the wear of the screw and the barrel. 5. If the material is not uniformly plasticized, or if metal contaminants are present in the material, this can cause the torque exerted on the screw to increase suddenly. Such torque exceeds the strength limit of the screw, resulting in its breakage. This is a type of damage caused by an abnormal accident.