Introduction of special processing machine for sin

Introduction of special processing machine tools for single screw compressors

in the 1970s, Beijing first general machinery factory first introduced equipment and technology from abroad and began to develop single screw compressors. Single screw compressor has a series of advantages, such as long service life, high efficiency, low operating noise, small volume and so on, and is widely used in machinery, shipbuilding, petroleum, chemical industry, light textile and other industries. Therefore, since the 1990s, many domestic enterprises have been manufacturing single screw compressors

single screw compressor is composed of two star wheels and one screw. Each star wheel has 11 teeth and the screw has 6 slots. When working, the screw drives the star wheel to rotate, and the speed ratio of the screw and the star wheel is 11:6. Due to the complex tooth profile of the screw and the star wheel, at present, only special machine tools or five coordinate CNC machine tools can be used for processing

in the early stage, the star wheel was processed by special machine tools. At present, the star wheel parts have been sold in China, and the machine tools are no longer needed to process the star wheel

although five coordinate NC machine tools can be used to process screws, NC machine tools are expensive and complex to program. At present, there are few manufacturers in China. However, it is certain that using multi axis CNC machine tools for milling and grinding is the future development direction

the machine tool introduced in this paper refers to a special machine tool specially designed for processing single screw. Due to the constant ratio transmission mechanism, differential and rotary feed mechanism of single screw special machine tools, they have been widely used by many manufacturers, and the technology and structure adopted are roughly the same. This paper only introduces the differences in the layout and structure of the existing domestic single screw special machine tools from the following aspects

first, introduce the layout of the machine tool

the exhaust volume of the compressor determines the size of the diameter of the star wheel and screw and the size of the meshing center distance. Therefore, the rotation center of the spindle and the cutter of the machine tool are also different with the diameter of the screw. In order to process screws with different diameters, the layout of domestic single screw processing machine tools at present roughly has the following schemes

the first type: the center distance between the spindle of the machine tool and the tool rotation center is fixed

the center distance between the spindle of the machine tool and the tool rotation center is fixed, and the center distance cannot be adjusted. Machining screws with several diameters requires several machine tools with different center distance specifications

advantages: the structure of the machine tool is simple

disadvantages: each machine tool can only process screws of one specification. When there is a large demand for compressor screws of a certain specification in the market, one machine tool will process and other machine tools will be idle

the second kind: the spindle box of the machine tool is rotatable

the machine tool can rotate the spindle box by an angle before processing according to the diameter of the processing screw. This kind of machine tool whose spindle box can rotate is an improvement on the use method of the first machine tool mentioned above, and its structure is basically the same as that of the first machine tool

advantages: the machine tool is simple in structure and can adapt to the processing of screws of various specifications

disadvantage 1: after the spindle box rotates, the distance between the spindle rotation center line and the tool rotation center line is not easy to measure accurately

disadvantage 2: after the spindle box rotates, the distance between the front end face of the spindle and the rotation center line of the tool decreases, so the processing of screws with larger diameter is limited

the third kind: the spindle box of the machine tool is horizontally movable

a rectangular sliding guide rail is arranged between the bottom of the spindle box and the base, and the moving direction of the spindle box is perpendicular to the spindle rotation center line and perpendicular to the tool rotation center line. The power of the headstock is transmitted to the tool feeding mechanism in the base through the spline shaft

according to the diameter of the processing screw, move the spindle box to the appropriate position with the hand wheel lead screw feeding mechanism before processing, and then fix the spindle box on the base with screws. The moving distance of the headstock can be detected with a grating ruler, and the position error is ± 0.005mm

the diameter can be processed by a machine tool with a headstock that can move laterally φ 95 ~ so that the tow can be deformed by heating in the subsequent automatic layering process φ Screw of any specification between 385mm

due to processing φ 95～ φ The screw with a diameter of 385mm causes the distance difference between the front end face of the spindle and the rotation center line of the cutter to be too large. Therefore, in practical application, it is designed into two specifications of machine tools, one machine tool for processing φ 95～ φ 205mm diameter screw, processed by another machine tool φ 180～ φ 385mm diameter screw

advantages: the machine tool can adapt to the processing of various specifications of screws, and each specification of screws does not need to be equipped with a corresponding processing machine tool

disadvantages: the structure and assembly of the machine tool are more complex than the first two machine tools, and the cost of the machine tool is also higher than the first two machine tools

second, introduce the spindle structure of the machine tool

the accuracy of the horizontal spindle of the machine tool spindle box and the vertical spindle on the base determines the accuracy of the processed screw. At the same time, when the screw rotates at a high speed of thousands of revolutions in the compressor, the screw with poor accuracy will cause the compressor to produce heating, vibration, low efficiency, fast wear and other phenomena

at present, there are roughly two schemes for the spindle structure of domestic single screw processing machine tools

the first type: the main shaft structure with non adjustable radial clearance of the bearing

the front bearing of the main shaft adopts a combination of a double row cylindrical roller bearing and two thrust ball bearings. The main shaft uses a double row cylindrical roller bearing to bear the radial cutting force, and uses two thrust ball bearings to bear the axial cutting force

the rear bearing of the main shaft generally adopts a double row cylindrical roller bearing or a centripetal ball bearing

the advantages of this spindle structure: the spindle is simple to process and assemble, and the cost is low

disadvantage 1: because the radial clearance of the main shaft bearing cannot be adjusted, the accuracy of the main shaft is poor. Although the interference fit between the inner diameter and shaft diameter of the bearing can be used to eliminate the radial clearance of the bearing, the inner diameter and radial clearance of each bearing are not a fixed value, so it is difficult to give the fit tolerance between the quasi shaft diameter and the inner diameter of the bearing during design and processing

disadvantage 2: it is difficult to buy domestic or imported thrust ball bearings of grade C, D or P4, P5 in the market. Machine tool manufacturers often use ordinary grade bearings instead, which also affects the improvement of spindle accuracy

the spindle structure with non adjustable radial clearance of bearings is suitable for ordinary machine tools with general accuracy, and is not suitable for machine tools with high requirements for spindle accuracy

the second type: the spindle structure with adjustable radial clearance of the bearing

the front bearing of the spindle adopts a combination of a P4 level double row cylindrical roller bearing with tapered holes and a P4 level double row radial thrust ball bearing. The spindle uses double row cylindrical roller bearings with tapered holes to bear radial cutting forces, and double row radial thrust ball bearings to bear axial cutting forces and partial radial cutting forces

the rear bearing of the main shaft generally adopts a double row cylindrical roller bearing with P5 conical hole

the inner ring and mating shaft diameter of double row cylindrical roller bearing with tapered hole are both 1:12 tapered. Locking the bearing with round nut will make the bearing produce a displacement in the axial direction and expand the inner ring of the bearing, so as to achieve the purpose of reducing or eliminating the radial clearance of the bearing

advantages of this spindle structure: high spindle accuracy. On the front face of the spindle φ The lateral runout value of the spindle measured on the 230mm diameter is 0.010mm. At the front of the spindle φ The radial runout value of the main shaft measured on the 230mm outer circle is 0.005mm. The spindle accuracy of the second structure is about 50% higher than that of the first one

disadvantages of this spindle structure:

the machining process of the spindle is complex, and the assembly of the spindle also requires experienced workers to operate in order to make the spindle accuracy reach the ideal value

III. control of tool feed depth

screws with different diameters need to process different depths of spiral grooves. Screw 10. Deformation measurement accuracy displacement accuracy: within ± 0.5%, the depth of spiral grooves ranges from tens of millimeters to more than 100 millimeters. The tool feed mechanism needs to rotate and feed thousands of rounds to complete the processing of a screw part

because the tool feed mechanism needs to complete the feed action while the tool rotates, some methods of mechanical and electrical control of cutting depth commonly used in ordinary machine tools are not applicable to single screw machine tools

the tool feed mechanism of single screw machine tool can control the feed depth by adopting the following different methods

the first kind: friction clutch and electric switch control the tool feed depth

its control principle is that when the tool cut depth increases, the load torque of the tool feed mechanism increases, making the friction clutch in the transmission chain of the tool feed mechanism slip, and a mechanical linkage mechanism contacts the gas switch and sends out sound and light signals to prompt the operator. At this time, the operator manually disconnects the power of the tool feed mechanism

the advantages of this control method are: the control method is simple and the processing and operation of parts are not affected by sudden power failure

the disadvantage is that the preload of the compression disc spring of the friction clutch needs to be adjusted for processing screws with different diameters

due to the slight differences in the density and hardness of each screw material and the sharpness of the tool, the accuracy of this control method is not very accurate, which may lead to the excessive depth tolerance of the screw spiral groove

the second kind: use the combination of electromagnetic clutch and encoder to control the tool feed depth

the tool feed system is equipped with electromagnetic clutch, a pair of speed measuring gears for detecting the number of tool turns and an encoder

its control principle is to manually start the encoder counting switch when the tool just touches the screw surface, and the counting device starts counting. When the tool rotates to the preset number of turns, that is, when the cutting depth is reached, the electromagnetic clutch automatically disconnects the power of tool feeding and sends out acoustic and optical signals to remind the operator that the parts have been processed

the detection device displays the number of feed cycles or feed rate through the digital display meter. After the electromagnetic clutch is disengaged, the tool only rotates with the vertical shaft without feeding movement

the advantage of this control method is that the depth tolerance control of the screw spiral groove is more accurate. Because the digital display shows the depth or number of turns to be processed and the depth or number of turns processed, the operation is also very intuitive and convenient

the disadvantage is that the electrical control of the machine tool is complex. At the same time, this control method will lose the preset data if the power is suddenly cut off in the factory during part processing

if a battery is added to the electrical control to maintain the operation of the detection device at the initial stage of power failure maintenance, the above problems can be solved

IV. control of gear transmission clearance

when processing screws, the spiral groove is processed under the combined action of tool rotation and workpiece rotation. When just cutting into the workpiece, the tool receives a large resistance in the tangential direction of rotation. When the tool is about to cut out the workpiece, under the action of the spiral groove, the tool receives a small resistance in the tangential direction of rotation, even the thrust of the spiral groove of the workpiece

due to the existence of machine tool box hole processing, gear processing and other errors, the transmission clearance of the tool rotating shaft is too large, commonly known as large clearance

the method to detect excessive transmission clearance is to fix the power input shaft and rotate it left and right to shake the output shaft. If the machine tool is designed and manufactured with a conventional transmission structure, the transmission clearance swing angle of the output shaft is more than ten degrees to dozens of degrees. Excessive transmission clearance causes obvious tool marks on the machined surface of the spiral groove of the screw, which affects the machining accuracy of the screw

the transmission clearance of the tool rotating shaft is too large after the machine tool is assembled,