The compression ratio of the screw, what is the compression ratio of the screw compressor related to

Extruders required for various plastics.

The compression ratio is not fixed and can have a range. Depending on the raw material, the required compression ratio is also different. For example, when extruding soft PVC plastic, if it is a granular material, the screw compression ratio is often taken, and if it is a powder mixture, the compression ratio can be 4 5.

The selection of screw compression ratio can be referred to Table 4.

The compression ratio can be obtained in the following ways:

1) Pitch. Variation (isodepth not equidistant). The advantage of this structure is that it does not affect the strength of the screw when the compression is relatively large, and the disadvantage is that the screw processing is difficult, and the helix angle is too small when approaching the end of the screw so that the material flow can not be smooth, and it is easy to produce nest material.

2) The depth of the screw groove changes (equidistant and unequal). Its advantages are easy processing and manufacturing, large contact area between the material and the barrel, and good heat transfer effect. The disadvantage is that the strength is weakened greatly, and special attention should be paid when using long screws and large compression ratios.

3) Both pitch and groove depth vary (unequal distance and unequal depth). If properly designed, such a screw can get the maximum advantages and the least disadvantages. In actual production, it is mainly considered from the convenience of processing and manufacturing, and the equidistant unequal depth screw is the most widely used.

The compression ratio of screw refers to the ratio of the volume of the first threaded groove of the screw feed section to the volume of the last threaded groove of the screw homogenization section. In the equidistant gradient screw, the compression ratio can also be understood as the ratio of the first spiral groove depth of the feed section to the last thread groove depth of the homogenization section, that is, the compression ratio of the compression ratio screw is magnitude, which has a great influence on the process control conditions of extrusion plasticizing raw materials.

The difference between a screw machine and a piston machine is that a piston machine will only undercompress, whereas a screw machine will have more overcompression.

Affected by the structure, there is an important data of the screw machine, that is, the internal volume ratio, the English abbreviation VI, for most screw compressors VI is fixed. From the perspective of maintenance and operation, the value of its internal product ratio is the same as the external compression ratio.

(the ratio of condensing pressure to evaporation pressure) is very similar, and this compressor is the most efficient.

So what happens when the compression ratio is large or small?

Too large, or too large a pressure difference, proves that the system completely deviates from the design value, the main phenomena are, the exhaust pressure temperature is too high, the suction pressure is low, and the temperature is too high.

If the exhaust pressure temperature is too high, the adverse consequences are mainly for the lubricating oil in the system to be easy to coke, not suitable for the formation of oil film, can not fully lubricate the rotor, the rotor can not be effectively cooled, lubrication, it will be blocked, and then cause motor damage.

Low suction pressure, high suction pressure temperature mainly affects motor cooling, and high exhaust temperature. The consequence is basically equivalent to a high exhaust temperature pressure.

Too small, the main impact is the wet stroke.

Tide car, inverted frost), in some materials, screw compressor wet stroke resistance, including some of our designs, sales staff also like to promote this. In fact, the screw machine is more afraid of wet stroke, if a large amount of liquid returns to the compressor, it will cause the dilution of the lubricating oil, and the consequences are the same as the high exhaust temperature.

Of course, the compression ratio is smaller than the partial rock lift, and some are caused by serious rotor wear and failure of load addition and reduction. Tilingte compressors.

Compression ratio of a single screw extruder: (empirical formula) n = k d d n.

Screw compression ratio: The ratio of the volume of each screw slot in the screw feed section to the volume of each screw slot in the metering section. It can characterize the degree of compression and work of the screw on the material, the stacking density of the material in different forms (powder, granularity or flake) is different, and the change of volume after compression and melting is also different, and the design and selection of the compression ratio of the screw should be adapted to take it back.

The compression ratio of the screw extrusion machine for melt spinning is generally 3 35, and the required compression ratio can be obtained by changing the pitch or the depth of the screw groove or both at the same time, because it is difficult to change the processing of the pitch in the screw manufacturing, the method of changing the depth of the screw groove is commonly used to change the compression ratio.

The compression ratio can be obtained in the following ways:

1. The pitch changes (equal depth is not equal distance), the advantage of this structure is that it does not affect the strength of the screw when the compression is relatively large. The disadvantage is that the screw processing is difficult, and when approaching the end of the screw, the spiral angle is too small, so that the material flow can not be smooth, and it is easy to produce nest materials.

2. The depth of the screw groove changes (equidistant and unequal depth), its advantages are easy processing and manufacturing, large contact area between the material and the barrel, and good heat transfer effect. The disadvantage is that the strength is weakened greatly, and special attention should be paid to the use of long screws and large compression ratios.

3. The pitch and the depth of the screw groove are changed (unequal distance and unequal depth), if properly designed, this screw can obtain the greatest advantages and the smallest disadvantages, the actual production is mainly considered from the convenience of processing and manufacturing, and the equidistant unequal depth screw is the most used. <>

There are many reasons for the high intermediate pressure of screw compression, among which the most common original excitation causes are: 1. The function of the exhaust valve is not good enough, resulting in the air of the compressor cannot be discharged in time, and the intermediate pressure will rise. 2. The amount of blind lead reed lubricating oil in the casing and screw is insufficient, which will cause friction loss and temperature increase over time, resulting in an increase in intermediate pressure.

3. The speed regulating device of the screw compressor is not properly adjusted, and improper adjustment will cause the speed of the screw compressor to be too high, resulting in an increase in the intermediate pressure. 4. The air filter of the screw compressor is blocked, and the dirt with a large amount of grinding belt cannot be filtered out, resulting in an increase in intermediate pressure.

1. The exhaust valve or safety cover is not sealed and there is leakage, which increases the suction pressure of the screw compressor. 2. The gas transmission efficiency of the compressor is reduced, the gas transmission volume is reduced, the gap is large, the sealing ring is worn too much, and the suction pressure is increased. 3. If the heat load of the warehouse increases suddenly, the refrigeration capacity of the compressor is insufficient, which will lead to too high suction pressure.

4. The expansion valve of the system is improperly adjusted or the temperature sensing bag is tightened, the suction pipe or throttle valve is opened too large, the float valve is faulty or the ammonia pump system is circulated too much, resulting in too much liquid. The compressor suction pressure is too high. When the pressure of the screw compressor is too high or too low, check whether the intake valves are all open, whether the current is within the normal range, whether the amount of external useful air increases, or whether there is leakage in the belt.

The ratio of the volume of the first screw groove in the charging section to the volume of the last screw in the homogenization section.

in the extruder. The screw can be divided into three sections: feeding section (40% screw length), compression section (35%), homogenization section (metering section) (25%).

Feeding section - the bottom diameter is small, and the main function is to convey raw materials to the rear section. Compression section - the bottom diameter changes, the main role is to compact, melt the material, and establish pressure. Homogenization section (metering section) - the melted material in the compression section is squeezed to the front of the screw at a fixed temperature.

The geometric compression ratio of the screw refers to the ratio of the volume of one screw groove in the feeding section of the screw to the volume of the last screw in the homogenization section (metering section). Its value is generally 2 4. Comparatively speaking, the larger the compression ratio, the more uniform the plasticization of the plastic.

It refers to the ratio of the volume of a screw groove in the feeding section of the screw to the volume of a screw groove in the homogenization section (metering section). Its value is 2 4

Screw geometric compression ratio: the ratio of the volume of the first screw groove in the screw charging section to the volume of the last screw groove in the homogenization section.