Improving the quality of products while reducing costs is the basis for continuous innovation and new investment in the production process. For the machinery factory, it is the production technology that develops towards higher performance.
The economically important factor for an extrusion line is the production characteristics. In the 70s and 80s, one production line took on the production of PVC profiles and the production of parallel twin-screw extruders was increased. In the mid-1990s, there was an alarming increase in production. In the 1980s, the average production line speed was between 1-2 m/min, and the extruder used an aspect ratio of 16-20D.
From 1990 to 1994, due to the development of die heads and calibration techniques, the line speed could be increased from 2 m/min to 4 m/min. The extruder with a screw diameter of 110mm and an aspect ratio of 20-23D has reached 150-350 kg/h.
After 1994, two trends were used at the same time: First, the single-line production line rate was increased to 6 m/min, followed by a tendency to increase the use of double-line extrusion to adjust to maximum output.
In 1995, the production with double strand extrusion was 450-500 kg/h (without internal cooling) and extrusion with a single strand (with internal cooling). The extruder has a screw diameter of about 130 mm and an aspect ratio of 23D.
At present, a new generation of parallel twin screw extruders with an aspect ratio of 26D has been developed. (Manufacturer: Kraussmaffei) This new generation of extruders has a screw diameter of 160 mm and an aspect ratio of 26 D. It has been further improved from 500kg/h to 1000kg/h. In production, the maximum output of double-line extrusion (without internal cooling) has now reached 750kg/h; the single-line die extrusion is 500kg/h (with internal cooling), but the single-line extrusion (without internal cooling) Most of the production line is 250kg/h.
The increase in output The output of an extruder with a set screw diameter depends on three important characteristics, namely:
· Set screw torque · Maximum screw speed · Specific drive energy in window profile extrusion. The main use is to improve the impact resistance of PVC formulations, it has a certain degree of shear sensitivity, found in the actual production, existing The screw design should not use the peripheral speeds specified above. Due to shearing and temperature variations in some of the super-materials, the maximum screw circumferential speed of the window profile extrusion is between 7.0 and 7.5 m/min. The new parallel profile extrusion has a maximum circumferential speed of 7.2 m/min. An extruder with a nominal screw speed of 6m/min can achieve guaranteed yield.
The minimum screw circumferential speed should not be less than 2.5m/min, otherwise insufficient shear energy (force) acts on the raw material, so that the final product does not reach the required mechanical strength.
Tubular Extrusion Twin Screw Extruder PVC Pipes produce conditions similar to those required for production of profiles: maximum efficiency and high quality can be achieved. Extrusion of pipes using the new 26D series of parallel twin screw extruders can also increase production. A certain peripheral speed must not exceed. The maximum circumferential speed of pipe extrusion is 10~11.5m/min. Therefore, the maximum screw peripheral speed of the extruder series has been measured to 11.5m/min. In fact, it has been found that the minimum should not be less than 4.0~6.0m/. In min, this corresponds to 15 rpm, the peripheral speed is too low, the shear energy (force) acting on the raw material is insufficient, and the final product does not have sufficient mechanical strength. The new parallel twin-screw extruder with a circumferential speed of 11.5 m/min achieves a guaranteed yield.
From the above discussion, it can be seen that the yield of a given screw diameter twin-screw extruder cannot be increased with the screw speed. Since the maximum possible screw speed should not be exceeded, the output of the extruder can only be increased by increasing the amount of extrusion.
To increase the aspect ratio, in order to fully plasticize the increased raw material extrusion, the residence time of the raw material in the extruder must be increased. This can be accomplished by lengthening the processing unit. For this purpose, the length of the processing equipment is Between the feed station and the center of the degassing hole should be increased by 45%.
In this section, in particular by barrel heating, more energy can be supplied to the raw material, so that the raw material can be preheated better, and special drive energy (force) can be reduced.
Increasing the screw torque As described above, increasing the productivity of a twin-screw extruder with a fixed screw diameter is an essential condition for increasing the screw torque.
With regard to the screw torque of the counter-rotating twin-screw extruder, it should be noted that their increase is proportional to the increase in extruder output, although in the 1970s and 1980s the screw torque increased linearly. Special increases can be seen in the 1990s. For example, the new series of parallel twin screw extruders has increased the screw torque to 25-45%. With a significant increase in the predetermined torque, the transmission must have sufficient power to adapt.
Extrusion of the profile extrusion feeding system window profile extrusion, in fact the extruder is a full hopper directly dominated the production, which can be constant feed and fill the screw. The volume of the feed zone is relatively easy to design, with the maximum possible yield for a particular dry mix. In general, the extrusion of high-performance profiles uses more than one formula for processing, and the range of mechanical equipment used is also narrow.
In all cases, not only powder but also pellets or regrinds are also used for processing, but feed equipment must be used. However, it can be seen that the proportion of weight feeding systems is increasing steadily because of the strict dimensional tolerances of the profiles and in particular the raw material saving potential.
Tube extruder feeds in pipe extrusion, different brands of pipe. Such as: pressure pipe, sewage pipe or wire conduit, etc., are produced with different formulations, the main difference between the formula is its different filler and specific gravity. For example: its bulk specific gravity is between 560 g/l and 820 g/l.
The maximum yield reported by Krauss-Maffei is for pressure pipe formulations. The low filler density for extrusion is to use low bulk density. This means that the screw feed zone is designed to have a volumetric specific gravity of 600±30 g/l. With this volumetric gravity and complete filling of the feed zone, the corresponding output rate is achieved. The compression ratio of the screw is compatible with these output rates.
If a higher bulk density formulation is used, the screw can be overfilled. This new 26D extruder can withstand this because of the high screw pitch. However, it causes increased wear. Due to the effective material compression is too large. So all 26D pipe extruders are equipped with a feeding system. The feed screw speed must be synchronized with the main screw speed to eliminate extruder screw overfeed. The use of weight feeding equipment is always increasing. These devices are used together with the hot wall thickness adjustment center and ultrasonic wall thickness measurement to save the same amount of raw materials. The weight feed device is properly adjusted on the extruder for accurate production.
Screw cooling In the past, extruders were often designed as external screw cooling systems. However, the current internal screw cooling has become a standard, and internal screw cooling has considerable advantages. Especially in the case of high aspect ratios.
The internal screw cooling (distilled water as a coolant) heat is transferred from the screw metering zone to the cold feed at the feed and pre-compression zone.
Not only through the barrel, but also through the screw. The profile melt has a very uniform temperature at the die entrance. In addition, the equipment is self-adjusting and does not require maintenance at all.
The processing equipment has been developed to 26D, and screw cooling has been adopted to provide energy-saving conditions. From the production practices and experience, it has been shown that the screw-in cooling method can reduce the transmission energy by about 10-15%.
Barrel cooling The barrel of the new extruder series is generally smooth on the outside, so the same barrel can be cooled with air or oil. The air-cooling method is commonly used, using aluminum blocks and cooling wings of an integral heat coil. Cooling with a cooling fan blows air down through the cover plate in the middle of the cooling fan. The temperature sensor is mounted on the cylinder from the side. In this way, the shortest control flow path can be achieved. Because of ease of maintenance, air cooling is definitely willing to adopt.
If oil is used to cool the barrel, the aluminum block is also used. According to the previous principle, the oil pipe is wound in the groove barrel. On the contrary, according to the new principle of the 26D extruder, the aluminum block with integral heating and cooling coils is mounted on a smooth barrel. This general principle achieves a good cooling effect. However, such equipment cannot be maintained without charge.
Screw shape (structure)
Due to the development of processing equipment, the structure of the screw and its product quality have been considerably improved. In particular, the length between the center of the feeding die of the cylinder and the center of the outlet diameter has been increased from 13D to 18D. Provides obvious advantages for extrusion processing, increasing the length can increase the number of precompression zones. It can be finer than before, and it is actually a continuous material compression from the feed zone to the exhaust zone, achieving a very fine material mix.
In order to increase the energy supply through the barrel, the heating area of ​​the barrel is also increased. Together with the increase in the cooling and residence time in the screw, this can lead to a reduction in the compression value. All of the points mentioned above not only reduce the transmission energy but also correspondingly reduce the wear of the screw and the barrel.
The traditional screw structure used for profile extrusion is generally 2 screw grooves and the entire screw has a screw groove. Only the high-compression zone is designed as a single-groove groove for reaction stability, and 98% of extruder brands in the world profile market require only two basic structures. It is only different in the high compression area.
The structure of the pipe (screw) and profile is usually 2-4 grooves and has a dynamic mixing head. The high-performance extruder structure must be closely matched to the special formulation. This is mainly due to the increase in the screw speed, ie, the increase in shear energy and yield.
The kneading trough will increase the transport of the counter-rotating twin-screw and the material will accumulate at the damper, often back to the pre-compression zone via the trough. This backflow extends the residence time, produces a good mixing effect, and makes the material more homogeneous and plasticized.
Increasing the uniformity of the melt to increase the output needs to improve the quality of the extrusion profile. The two most important parameters for determining the melt uniformity are the temperature uniformity of the melt and the changes in melt compression and time.
In order to more accurately verify the temperature uniformity in the melt, a special measuring cross is used. This measuring cross is installed between the die bushing and the die head. It can accurately laterally move from 8 points, 6 points vertically, and a middle point. Melt strands were measured.
The transverse melt temperature pattern is particularly important for indicating whether the temperature of the screw tip region is consistent with the pattern of the other portions of the screw groove. The detailed information given on various kinds of measurements on experimental devices is important for screw tip and core design. The goal is to arrive at a melt temperature pattern that is as uniform as possible and the same for all extruder types. This can increase the elasticity to be used on the die of different extruders.
In addition to melt temperature uniformity. Melt pressure also has a significant effect on the quality of the extrudate for changes in temperature. At this point, both the short-term and long-term melt pressures must be clearly distinguishable. For any reverse rotation, the sealing intermeshing twin-screw extruder operates like a pump, and the melt is discharged one cavity and one cavity, resulting in short-term results. The melt pressure fluctuates and appears to interfere with the inner surface of the cavity.
To minimize these short-term melt pressure fluctuations, the screw must be "opened" at the end of the metering zone. There are several ways to do this:
The uneven pitch at the end of the metering zone is used to make intermittent threads at the end of the metering zone. Using multi-threaded mixing heads to dry these measures, the short-term melt pressure fluctuations can reach 1% or less, and the normal pressure is 250-350 bar, except for short-term melts. Outside the pressure fluctuations, long-term melt pressure fluctuations may also occur. This is due to fluctuations in bulk density, changes in production, or due to inconstant temperature control of the barrel, die, or mold. Advanced control technology allows accurate temperature control to ±1°C.
About energy balance: 23D and the transmission energy of the new 26D profile extruder, 26D extruder is much smaller than the 23D shear energy for material plasticization, especially at low and medium screw speeds, in the maximum screw speed range 26D The extruder's transmission energy is still 15% lower. It can be seen that the screw speed is increased, the transmission energy is also increased a lot, but the thermal power is slightly reduced, and the screw structure must be compatible with the processing materials.
Filling for tube extrusion In order to reduce formulation costs, there is sometimes a tendency in the tube market to use the largest amount of chalk filler for sewage pipes and wire conduits. Experience to date shows that not only chalk usage, but also particle size and particle structure, play a decisive role in screw and barrel wear. There is one of the best chalks, the least wear is Omga 95T, the particles are round, top
The economically important factor for an extrusion line is the production characteristics. In the 70s and 80s, one production line took on the production of PVC profiles and the production of parallel twin-screw extruders was increased. In the mid-1990s, there was an alarming increase in production. In the 1980s, the average production line speed was between 1-2 m/min, and the extruder used an aspect ratio of 16-20D.
From 1990 to 1994, due to the development of die heads and calibration techniques, the line speed could be increased from 2 m/min to 4 m/min. The extruder with a screw diameter of 110mm and an aspect ratio of 20-23D has reached 150-350 kg/h.
After 1994, two trends were used at the same time: First, the single-line production line rate was increased to 6 m/min, followed by a tendency to increase the use of double-line extrusion to adjust to maximum output.
In 1995, the production with double strand extrusion was 450-500 kg/h (without internal cooling) and extrusion with a single strand (with internal cooling). The extruder has a screw diameter of about 130 mm and an aspect ratio of 23D.
At present, a new generation of parallel twin screw extruders with an aspect ratio of 26D has been developed. (Manufacturer: Kraussmaffei) This new generation of extruders has a screw diameter of 160 mm and an aspect ratio of 26 D. It has been further improved from 500kg/h to 1000kg/h. In production, the maximum output of double-line extrusion (without internal cooling) has now reached 750kg/h; the single-line die extrusion is 500kg/h (with internal cooling), but the single-line extrusion (without internal cooling) Most of the production line is 250kg/h.
The increase in output The output of an extruder with a set screw diameter depends on three important characteristics, namely:
· Set screw torque · Maximum screw speed · Specific drive energy in window profile extrusion. The main use is to improve the impact resistance of PVC formulations, it has a certain degree of shear sensitivity, found in the actual production, existing The screw design should not use the peripheral speeds specified above. Due to shearing and temperature variations in some of the super-materials, the maximum screw circumferential speed of the window profile extrusion is between 7.0 and 7.5 m/min. The new parallel profile extrusion has a maximum circumferential speed of 7.2 m/min. An extruder with a nominal screw speed of 6m/min can achieve guaranteed yield.
The minimum screw circumferential speed should not be less than 2.5m/min, otherwise insufficient shear energy (force) acts on the raw material, so that the final product does not reach the required mechanical strength.
Tubular Extrusion Twin Screw Extruder PVC Pipes produce conditions similar to those required for production of profiles: maximum efficiency and high quality can be achieved. Extrusion of pipes using the new 26D series of parallel twin screw extruders can also increase production. A certain peripheral speed must not exceed. The maximum circumferential speed of pipe extrusion is 10~11.5m/min. Therefore, the maximum screw peripheral speed of the extruder series has been measured to 11.5m/min. In fact, it has been found that the minimum should not be less than 4.0~6.0m/. In min, this corresponds to 15 rpm, the peripheral speed is too low, the shear energy (force) acting on the raw material is insufficient, and the final product does not have sufficient mechanical strength. The new parallel twin-screw extruder with a circumferential speed of 11.5 m/min achieves a guaranteed yield.
From the above discussion, it can be seen that the yield of a given screw diameter twin-screw extruder cannot be increased with the screw speed. Since the maximum possible screw speed should not be exceeded, the output of the extruder can only be increased by increasing the amount of extrusion.
To increase the aspect ratio, in order to fully plasticize the increased raw material extrusion, the residence time of the raw material in the extruder must be increased. This can be accomplished by lengthening the processing unit. For this purpose, the length of the processing equipment is Between the feed station and the center of the degassing hole should be increased by 45%.
In this section, in particular by barrel heating, more energy can be supplied to the raw material, so that the raw material can be preheated better, and special drive energy (force) can be reduced.
Increasing the screw torque As described above, increasing the productivity of a twin-screw extruder with a fixed screw diameter is an essential condition for increasing the screw torque.
With regard to the screw torque of the counter-rotating twin-screw extruder, it should be noted that their increase is proportional to the increase in extruder output, although in the 1970s and 1980s the screw torque increased linearly. Special increases can be seen in the 1990s. For example, the new series of parallel twin screw extruders has increased the screw torque to 25-45%. With a significant increase in the predetermined torque, the transmission must have sufficient power to adapt.
Extrusion of the profile extrusion feeding system window profile extrusion, in fact the extruder is a full hopper directly dominated the production, which can be constant feed and fill the screw. The volume of the feed zone is relatively easy to design, with the maximum possible yield for a particular dry mix. In general, the extrusion of high-performance profiles uses more than one formula for processing, and the range of mechanical equipment used is also narrow.
In all cases, not only powder but also pellets or regrinds are also used for processing, but feed equipment must be used. However, it can be seen that the proportion of weight feeding systems is increasing steadily because of the strict dimensional tolerances of the profiles and in particular the raw material saving potential.
Tube extruder feeds in pipe extrusion, different brands of pipe. Such as: pressure pipe, sewage pipe or wire conduit, etc., are produced with different formulations, the main difference between the formula is its different filler and specific gravity. For example: its bulk specific gravity is between 560 g/l and 820 g/l.
The maximum yield reported by Krauss-Maffei is for pressure pipe formulations. The low filler density for extrusion is to use low bulk density. This means that the screw feed zone is designed to have a volumetric specific gravity of 600±30 g/l. With this volumetric gravity and complete filling of the feed zone, the corresponding output rate is achieved. The compression ratio of the screw is compatible with these output rates.
If a higher bulk density formulation is used, the screw can be overfilled. This new 26D extruder can withstand this because of the high screw pitch. However, it causes increased wear. Due to the effective material compression is too large. So all 26D pipe extruders are equipped with a feeding system. The feed screw speed must be synchronized with the main screw speed to eliminate extruder screw overfeed. The use of weight feeding equipment is always increasing. These devices are used together with the hot wall thickness adjustment center and ultrasonic wall thickness measurement to save the same amount of raw materials. The weight feed device is properly adjusted on the extruder for accurate production.
Screw cooling In the past, extruders were often designed as external screw cooling systems. However, the current internal screw cooling has become a standard, and internal screw cooling has considerable advantages. Especially in the case of high aspect ratios.
The internal screw cooling (distilled water as a coolant) heat is transferred from the screw metering zone to the cold feed at the feed and pre-compression zone.
Not only through the barrel, but also through the screw. The profile melt has a very uniform temperature at the die entrance. In addition, the equipment is self-adjusting and does not require maintenance at all.
The processing equipment has been developed to 26D, and screw cooling has been adopted to provide energy-saving conditions. From the production practices and experience, it has been shown that the screw-in cooling method can reduce the transmission energy by about 10-15%.
Barrel cooling The barrel of the new extruder series is generally smooth on the outside, so the same barrel can be cooled with air or oil. The air-cooling method is commonly used, using aluminum blocks and cooling wings of an integral heat coil. Cooling with a cooling fan blows air down through the cover plate in the middle of the cooling fan. The temperature sensor is mounted on the cylinder from the side. In this way, the shortest control flow path can be achieved. Because of ease of maintenance, air cooling is definitely willing to adopt.
If oil is used to cool the barrel, the aluminum block is also used. According to the previous principle, the oil pipe is wound in the groove barrel. On the contrary, according to the new principle of the 26D extruder, the aluminum block with integral heating and cooling coils is mounted on a smooth barrel. This general principle achieves a good cooling effect. However, such equipment cannot be maintained without charge.
Screw shape (structure)
Due to the development of processing equipment, the structure of the screw and its product quality have been considerably improved. In particular, the length between the center of the feeding die of the cylinder and the center of the outlet diameter has been increased from 13D to 18D. Provides obvious advantages for extrusion processing, increasing the length can increase the number of precompression zones. It can be finer than before, and it is actually a continuous material compression from the feed zone to the exhaust zone, achieving a very fine material mix.
In order to increase the energy supply through the barrel, the heating area of ​​the barrel is also increased. Together with the increase in the cooling and residence time in the screw, this can lead to a reduction in the compression value. All of the points mentioned above not only reduce the transmission energy but also correspondingly reduce the wear of the screw and the barrel.
The traditional screw structure used for profile extrusion is generally 2 screw grooves and the entire screw has a screw groove. Only the high-compression zone is designed as a single-groove groove for reaction stability, and 98% of extruder brands in the world profile market require only two basic structures. It is only different in the high compression area.
The structure of the pipe (screw) and profile is usually 2-4 grooves and has a dynamic mixing head. The high-performance extruder structure must be closely matched to the special formulation. This is mainly due to the increase in the screw speed, ie, the increase in shear energy and yield.
The kneading trough will increase the transport of the counter-rotating twin-screw and the material will accumulate at the damper, often back to the pre-compression zone via the trough. This backflow extends the residence time, produces a good mixing effect, and makes the material more homogeneous and plasticized.
Increasing the uniformity of the melt to increase the output needs to improve the quality of the extrusion profile. The two most important parameters for determining the melt uniformity are the temperature uniformity of the melt and the changes in melt compression and time.
In order to more accurately verify the temperature uniformity in the melt, a special measuring cross is used. This measuring cross is installed between the die bushing and the die head. It can accurately laterally move from 8 points, 6 points vertically, and a middle point. Melt strands were measured.
The transverse melt temperature pattern is particularly important for indicating whether the temperature of the screw tip region is consistent with the pattern of the other portions of the screw groove. The detailed information given on various kinds of measurements on experimental devices is important for screw tip and core design. The goal is to arrive at a melt temperature pattern that is as uniform as possible and the same for all extruder types. This can increase the elasticity to be used on the die of different extruders.
In addition to melt temperature uniformity. Melt pressure also has a significant effect on the quality of the extrudate for changes in temperature. At this point, both the short-term and long-term melt pressures must be clearly distinguishable. For any reverse rotation, the sealing intermeshing twin-screw extruder operates like a pump, and the melt is discharged one cavity and one cavity, resulting in short-term results. The melt pressure fluctuates and appears to interfere with the inner surface of the cavity.
To minimize these short-term melt pressure fluctuations, the screw must be "opened" at the end of the metering zone. There are several ways to do this:
The uneven pitch at the end of the metering zone is used to make intermittent threads at the end of the metering zone. Using multi-threaded mixing heads to dry these measures, the short-term melt pressure fluctuations can reach 1% or less, and the normal pressure is 250-350 bar, except for short-term melts. Outside the pressure fluctuations, long-term melt pressure fluctuations may also occur. This is due to fluctuations in bulk density, changes in production, or due to inconstant temperature control of the barrel, die, or mold. Advanced control technology allows accurate temperature control to ±1°C.
About energy balance: 23D and the transmission energy of the new 26D profile extruder, 26D extruder is much smaller than the 23D shear energy for material plasticization, especially at low and medium screw speeds, in the maximum screw speed range 26D The extruder's transmission energy is still 15% lower. It can be seen that the screw speed is increased, the transmission energy is also increased a lot, but the thermal power is slightly reduced, and the screw structure must be compatible with the processing materials.
Filling for tube extrusion In order to reduce formulation costs, there is sometimes a tendency in the tube market to use the largest amount of chalk filler for sewage pipes and wire conduits. Experience to date shows that not only chalk usage, but also particle size and particle structure, play a decisive role in screw and barrel wear. There is one of the best chalks, the least wear is Omga 95T, the particles are round, top
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