1. Assembly process
(1) Preparation before assembly
1) Learn and be familiar with the assembly drawing, and understand the structure of the equipment, the functions of parts and their interrelationships.
2) Determine the assembly method and sequence, and prepare the required assembly tools.
3) Clean and wash the parts.
4) For some parts, repair and sealing test or balance work should be carried out.
(2) Assembly classification
Assembly work is divided into assembly and final assembly, and partial assembly is the assembly process of assembling parts into parts; Assembly is the process of assembling parts into final products.
(3) Adjustment, precision inspection and trial operation
1) adjustment refers to the adjustment of the relative position, fit clearance and combination tightness of parts or components.
2) Accuracy inspection refers to the inspection of geometric accuracy and working accuracy.
3) Debugging refers to the operation test after the equipment is assembled according to the design requirements, including operation flexibility, working temperature rise, sealing, speed, power, vibration and noise, etc.
(4) Painting, oiling and packaging
Paint the decorative surface according to the required standards, protect the specified parts with antirust oil, and prepare for shipment.
2. Assembly method
In order to make the matching parts get the required matching accuracy, the following four assembly methods can be adopted according to different situations.
1) interchangeable components. In the assembly process, the assembly accuracy can be achieved without repairing, selecting or adjusting each matched part.
2) Grouping collection. In batch or mass production, when the parts of each pair of matching products are assembled in groups according to the measured dimensions, they can be assembled interchangeably according to the groups to achieve assembly accuracy.
3) Adjust the assembly method. In the assembly process, the relative position of the adjustable parts in the product is changed or the appropriate adjustable parts are selected to achieve the assembly accuracy.
4) Repair and assembly methods. In the process of assembly, the reserved repair quantity on the specified parts is removed to achieve assembly accuracy.
3. Main points of assembly work
1) cleaning. Cleaning refers to removing residual molding sand, rust and debris from parts; Cleaning refers to cleaning the surface of parts. These tasks are indispensable for assembly.
2) Add lubricant. Generally, lubricant should be added to the mating surface before mating or connecting.
3) The fit size is accurate. During the assembly process, it is often necessary to reinspect or sample some important fit dimensions, especially interference fit, and it is often necessary not to disassemble the reassembled parts after assembly.
4) Check during assembly. When the assembled product is complicated, it should be checked whether it meets the requirements after each part is installed. In the process of fastening threaded joints, we should also pay attention to the influence on other related parts.
5) Pre-inspection during debugging and monitoring during startup. Trial operation always means that the machine will start to run and stand the test of load, so you can't do it blindly, because this is the stage where problems are most likely to occur. Before the trial run, check the integrity of the assembly work, the accuracy and reliability of all connected parts, the flexibility of moving parts and whether the lubrication system is normal. And then start the car under the condition of ensuring everything is accurate and safe. Immediately after the machine is started, observe whether the main working parameters and moving parts move normally. The main working parameters include lubricating oil pressure, temperature, vibration and noise. Only when all the sports indexes are normal and stable in the start-up stage can the trial run be carried out.
(2) Assembly of fixed connection
1. Pre-tightening, locking and assembly of threaded connection
Threaded connection is a detachable fixed connection, which has the advantages of simple structure, reliable connection and convenient disassembly, and is widely used in machinery.
(1) Pre-tightening of threaded connection
In order to realize the tightness and reliability of threaded connection, a certain tightening torque is applied to the thread pair, so that the corresponding friction torque is generated between threads. This measure is called pre-tightening of threaded connection. The tightening torque can be obtained by the following formula:
m 1 = kp0d× 10-3( 1- 1)
Where: M 1 is the tightening torque; K is the tightening torque coefficient (k = 0. 13 ~ 0. 15 with lubrication and 0.18 ~ 0.21without lubrication); P0 is the pre-tightening force (n); D is the nominal diameter of the thread (mm).
The tightening torque can be looked up in table 1-2 1, and then multiplied by a correction factor (0.75 for 30 steel; 35 steel is1; 45 steel is 1. 1).
Table 1-2 1 Tightening torque of threaded connection
(2) Methods of controlling the tightening torque of threads
1) Use special assembly tools. Such as pointer-type torque wrench, electric or pneumatic wrench, etc. These tools can indicate the value of tightening torque when tightening threads, or automatically terminate tightening when a preset tightening torque is reached.
2) Measure the bolt elongation. As shown in figure 1-58, before the nut is tightened, the original degree of the bolt is L 1, and after the bolt is tightened according to the specified tightening torque, the length of the bolt is L2. Whether the tightening torque is correct can be determined according to the change of L 1 and L2 elongation.
3) Twist angle method. The principle of torsion angle method is the same as that of measuring bolt elongation, but the elongation is converted into the angle of nut torsion.
Figure 1-58 Measuring bolt elongation
(3) Assembly and locking of threaded connection
1) Before assembly, carefully clean the working face, chamfer sharp edges, and check whether it meets the drawings. The tightening sequence should be reasonable, and the connection sequence of squares and circles generally extends symmetrically from the middle to both sides.
2) Locking device for threaded connection. The thread itself has self-locking function and will not fall off under normal circumstances. However, in the case of shock, vibration, variable load or great change of working temperature, effective anti-loosening measures must be taken to ensure the reliability of the connection. ① Increase friction to prevent looseness. As shown in fig. 1-59, it adopts double nut locking or spring washer locking, with simple and reliable structure and wide application. ② Mechanical locking device. Fig. 1 60a shows the cotter pin and slotted nut device, which is mainly used in situations of variable load and vibration. In the stop washer device shown in fig. 160b, the protrusion of the inner circle of the stop washer is embedded in the square notch of the outer circle of the screw, and after tightening the round nut, the protrusion of the outer circle of the washer is bent 90 degrees and clings to the notch of the round nut to fix the round nut. Fig. 1-60c shows a stop washer device with an ear to prevent the nut from loosening under a small pressure. Figure 1-60d shows a series of steel wire devices, and the threads should be tightened when the steel wire is wound. (3) point riveting method to prevent loosening. Parts removed in this way can not be used again, and can only be used under special needs. ④ Bonding and locking. Apply anaerobic adhesive to the threaded connection surface. After tightening, the adhesive will solidify and stick, and the locking effect is good.
Figure 1-59 Increase friction to prevent loosening
Figure 1-60 Mechanical locking device
2. Key connection component
Keys are standard parts used to connect transmission parts and transmit torque. Keys have different structural characteristics and uses, which can be divided into three categories: loose key connection, tight key connection and spline connection.
Assembly of (1) loose key connection
Loose-key connection relies on the side of the key to transmit torque. Keys used for loose key connection include common Ping Jian, guide key, semi-circular key and spline. Ordinary Ping Jian connection is shown in figure 1-6 1.
Figure 1-6 1 ordinary Ping Jian connection
Key points of loose key assembly:
1) Remove burrs on keys and keyways, so as not to affect the reliability of fit.
2) For important keys, check the straightness of the key side and the symmetry of the keyway to the axis.
3) Try to match the key head and keyway to ensure their matching performance, and then file the key length and key head flat, leaving a gap of about 0.1mm. ..
4) Press the key into the mating surface after adding engine oil, and the bottom surface of the key should be in contact with the bottom of the shaft groove.
5) Pay attention to the clearance between the non-mating surfaces of the key and keyway of the trial assembly kit (such as gear and pulley).
(2) Tighten the key connection assembly
Tight key connection mainly refers to wedge key connection. There are two kinds of wedge keys: ordinary wedge keys and hook wedge keys (Figure 1-62), and the slope of its upper surface is generally L: 100. When assembling, the upper and lower working faces of the key should be attached to the bottom of the shaft groove and the hub groove, and there should be a gap on both sides. The inclination of the keys must be consistent, and the contact can be checked by coloring method. If the contact is not good, you can trim the keyway with a file or scraper. After the hook key is installed, there must be a certain distance between the hook head and the end face of the kit, which is convenient for disassembly during maintenance and adjustment.
Figure 1-62 Wedge key connection
(3) Spline connection and assembly
Spline connection is shown in figure 1-63. Before assembly, the fittings shall be inspected according to the drawing tolerance and technical conditions. After heat treatment deformation, the kit can be trimmed by spline pushing or coloring. Spline connection can be divided into fixed connection and sliding connection: fixed connection has slight interference, which can be tapped with copper rod; When the interference is large, the sleeve should be heated to 80 ~120℃ before hot fitting; The sliding connection should be free to slide, flexible and free from jamming, and there should be no gap when turning the kit by hand.
Figure 1-63 Spline connection
3. Assembly of pin connection
Pin connection can play the role of positioning, connection and safety. According to the structure of the pin, it can be divided into cylindrical pin, conical pin and split pin.
1) cylindrical pin assembly. Cylindrical pin has the function of positioning, connecting and transmitting torque. The cylindrical pin connection is an interference fit, which is not suitable for repeated disassembly. When positioning cylindrical pins, it is usually necessary to drill two holes at the same time to ensure the matching accuracy, and make the surface roughness of the holes lower than Ra 1.6. When assembling, oil should be applied to the pin and the pin should be driven into the hole with a copper rod.
2) Assembly of tapered pins. The taper of the tapered pin is 1: 50. When reaming the taper hole, try to match the pin, and push in 80% ~ 85% of the length of the taper pin by hand. After the taper pin is pressed, the big end of the pin should be exposed from the plane of the workpiece (generally slightly larger than the chamfer size).
3) Assemble the cotter pin. After driving the cotter pin into the hole, open the small end opening to prevent it from coming out during vibration.
4. Assembly of interference connection
Interference connection is a method of fastening connection through interference after the container (hole) and the container (shaft) are matched. The advantages of interference connection are good alignment, strong bearing capacity and certain impact force, but it has high requirements for fit and is difficult to process and assemble.
(1) technical requirements for interference fit assembly
1) pipe fittings should have high form and position accuracy and ensure sufficient interference during assembly.
2) The matched surface should have a good surface roughness value.
3) When assembling, the mating surface must be coated with engine oil, and the pressing process should be carried out continuously, and its speed should be stable and not too fast, generally 2 ~ 4 mm/s..
4) For the cooperation of slender parts or thin-walled parts, the shape and position errors of the parts must be checked before assembly, and it is best to press them vertically.
(2) Assembly method of interference connection
1) press-in method. Hammer and pad can be used to press in or press in.
2) Thermal expansion method. Based on the principle that an object expands with heat and contracts with cold, the hole is heated to increase the aperture, and then the shaft is installed in the hole. The common heating method is to put the hole workpiece into hot water (80 ~ 100℃) or hot oil (90 ~ 320℃).
3) Cold shrinkage method. The cooling of the shaft is based on the principle that the object expands with heat and contracts with cold, and the shaft diameter is reduced before being put into the hole. The common cooling method is using ice and liquid nitrogen for cooling.
(3) Assembly of transmission mechanism
1. Assembly of belt drive mechanism
Belt drive relies on the friction between belt and pulley to transmit power.
(1) Technical requirements for assembly of belt drive mechanism
1) Strictly control the radial circular runout and axial movement of the pulley.
2) The end faces of two pulleys must be in the same plane (commonly used drives are V-belt and flat belt).
3) The surface roughness value of the pulley working face should be appropriate; if it is too large, the drive belt will wear quickly; If it is too small, it is easy to make the drive belt slip. Ra 1.6 is generally suitable.
4) The tension of the belt should be appropriate.
(2) Pulley assembly
Generally, the pulley hole and the shaft are transitional fit, and the fit interference is small, which can ensure that the pulley and the shaft have high coaxiality. When installing the pulley, clean the hole and shaft, install the key, gently tap the pulley with a hammer, and then fix it axially. After installing the pulley, check the radial circular runout and end circular runout of the pulley. In order to ensure that the two wheels are parallel and the middle planes coincide, the following drawing methods can be generally used for inspection:
Tie one end of the line to the rim of the wheel, and tighten the other end of the line to make the line stick to the end face of this wheel, and determine whether the other wheel sticks to the line, and then you will know whether it is correct. If the two wheels are different in size, check the gap between the end faces.
When the center distance is not large, use the ruler method to check, as shown in figure 1-64. In order to ensure that the middle planes of the two wheels coincide, the accuracy of the relative position should be ensured.
Figure 1-64 Check the correctness of the mutual position of pulleys.
(3) Adjustment of transmission tension
In the belt drive mechanism, the tensioning device is used to adjust the tension. The tensioning device can restore the tension to the specified requirements by adjusting the center distance between the two shafts. Appropriate tension can be judged according to empirical methods; Put your thumb in the middle of the V-belt trimming, you can press the V-belt down about 15mm, or you can add a force P in the middle of the V-belt trimming with a spring scale to make the V-belt droop for a distance s at the point where the force P acts. The corresponding sag distance s can be obtained by appropriate tension, which can be approximately calculated as follows:
S=A/50 ( 1-2)
Where: s is the sag distance of the triangle belt (mm); A is the center distance between two axes (mm).
Refer to Table 1-22 to select various V-belt forces.
Table 1-22V force on belt
When multiple V-belts are used for transmission, in order to make the tension of each belt as uniform as possible, it is required that the length of each belt should be consistent and the elasticity of each belt should be equal, and the new and old belts should not be mixed, otherwise the tension of each belt cannot be kept uniform.
2. Assembly of chain drive mechanism
Chain drive consists of two sprockets and a chain connecting them. Motion and power are transmitted through the engagement of chain and sprocket.
(1) Technical requirements for assembly of transmission mechanism
1) The axes of the two sprockets must be parallel, otherwise it will aggravate the wear of the sprocket and chain, increase noise and reduce stability.
2) The axial offset between two chains should not be too large. When the center distance between two wheels is less than 500mm, the axial deviation shall not exceed 2mm.
3) The radial circular runout and end circular runout of sprocket shall meet the following requirements: when the sprocket diameter is less than 100mm, the allowable runout is 0.3mm; when the sprocket diameter is 100 ~ 200mm, the allowable runout is 0.5mm; when the sprocket diameter is 200~300mm, the allowable runout is/.
4) The tightness of the chain should be appropriate, too tight will increase the load and accelerate the wear; Too loose can easily cause vibration or chain loss. The inspection method of high F chain sag is shown in figure 1-65. For horizontal or slightly inclined chain drive, sag f is not more than 20% of center distance l; When the inclination increases, the sag should decrease. For chain drive in vertical plane, f should be less than 0.02% of l.
Figure 1-65 Chain sag inspection
(2) Assembly of transmission mechanism
First, install two sprockets on the shaft and fix them as required, and then install the chain. The connection form of sleeve roller chain is shown in figure 1-66. When using the spring clip to fix the movable pin shaft, the opening direction must be opposite to the chain speed direction, otherwise it will easily fall off.
Figure 1-66 Joint Form of Sleeve Roller Chain
3. Assembly of gear transmission mechanism
Gear transmission transmits motion and power through the meshing between gear teeth. The invention has the advantages of accurate transmission ratio, compact structure, large bearing capacity, long service life and high efficiency, and can form a speed change mechanism and a reversing gear. The disadvantages of gear transmission mechanism are complex manufacturing process, high installation accuracy and high cost, which are not suitable for occasions with large center distance.
(1) assembly technical requirements for gear transmission mechanism
1) In order to ensure the accuracy of the coaxiality between the gear and the shaft, the radial circular runout and axial movement of the gear are strictly controlled.
2) Ensure that the gear has accurate center distance and proper backlash.
3) Ensure that the gear engagement has sufficient contact area and correct contact position.
4) Ensure the flexibility and accurate positioning position of the sliding gear on the shaft.
5) For high-speed and large-diameter gears, dynamic balance should be carried out before assembly.
(2) Assembly points of cylindrical gear transmission mechanism
1) gear and shaft assembly. There are three types of gear and shaft assembly: gear idling on the shaft, gear sliding on the shaft and gear fixed on the shaft. According to the matching nature of gear and shaft, the corresponding assembly method can be adopted. After the gear is assembled on the shaft, the common installation errors are gear eccentricity, skew and the end face not resting on the shaft shoulder. For gear pairs with high accuracy requirements, radial circular runout and end circular runout should be inspected, and the inspection method is shown in Figure 1-67.
Figure 1-67 Inspection of Radial Circular Runout and End Circular Runout of Gear
2) Assembly of gear shaft assembly. The assembly mode of the gear shaft assembly into the box should be determined according to the structural characteristics of the shaft in the box. Before assembly, the following three aspects should be checked: the dimensional accuracy and shape accuracy of holes and planes; Accuracy of mutual position between hole and plane; Surface roughness and appearance quality of holes and planes.
3) Check the meshing quality of gears. The meshing quality of gears includes backlash and contact accuracy. ① Check the backlash. The most intuitive and simple test method for clearance is the lead wire pressing method (Figure 1-68). On the tooth surfaces at both ends of the tooth width, two sections of lead wire with a diameter not less than 4 times the tooth side clearance are placed in parallel, and the lead wire is extruded by rotating the meshing gear. The thickness of the thinnest part of the lead after extrusion is the backlash. ② Inspection of contact accuracy. Contact accuracy refers to contact area and contact position. The contact surface of meshing gears can be tested by coloring method. During inspection, apply a uniform layer of display agent on both sides of the gear, then turn the driving wheel and brake the driven wheel slightly. For gears that work in both directions, check both positive and negative directions. The size of the embossed area on the gear side should be determined according to the accuracy requirements. The contact of transmission gears is generally not less than 30% ~ 50% of the tooth profile height and 40% ~ 70% of the tooth profile width, and their distribution positions are based on the pitch circle and symmetrically distributed up and down. The cause of the error can be judged by the position of the stamp.
Figure 1-68 Check the side clearance with lead wire.
(3) Assembly of bevel gear transmission mechanism
The assembly sequence of bevel gears should be determined according to the structure of the box. Generally, the driving wheel is installed first, and then the driven wheel is installed. The method of installing gears on the shaft is similar to that of cylindrical gears. Usually, the work to be done is the axial positioning of two gears on the shaft and the adjustment of meshing accuracy.
1) Determination of axial position of bevel gear. ① When determining the installation distance, it is necessary to make the indexing cones of the two gears tangent and the tops of the two cones coincide, so as to determine the axial position of the pinion. If the big gear is not installed at this time, it can be replaced by a process shaft, and then the axial position of the big gear can be determined according to the requirements of backlash. ② When assembling bevel gear with rear cone as reference, the rear cone should be aligned and leveled. As shown in figure 1-69, the axial position of the bevel gear l is adjusted by changing the thickness of the gasket; The axial position of bevel gear 2 can be determined by adjusting the position of the fixing washer.
Figure 1-69 Assembly Adjustment of Bevel Gear Transmission Mechanism
2) Check the meshing quality of bevel gear. The meshing accuracy is usually checked by coloring method. According to the different parts of tooth surface color display, different adjustment methods should be adopted.
4. Assembly of coupling and clutch
(1) assembly of coupling
According to different structural forms, couplings can be divided into taper pin sleeve type, flange type, cross slider type, elastic cylindrical pin type and universal coupling type (Figure 1-70).
Figure 1-70 Common coupling forms
1) assembly technical requirements. No matter what kind of coupling, the main technical requirement of assembly is to ensure the coaxiality of the two shafts, otherwise the connected two shafts will produce additional resistance during rotation, increase mechanical vibration, and even deform the shafts in serious cases, leading to premature damage of the shafts and bearings. This requirement is particularly important for high-speed rotating rigid couplings. Because of its flexibility and ability to absorb vibration, flexible coupling has a slightly lower requirement for coaxiality than rigid coupling.
2) Assembly method. The flange coupling is shown in figure 1-7 1, and its assembly points are as follows: ① Install the flanges 3 and 4 on the shaft 1 and shaft 2 with Ping Jian, and fix the gear box. ② Fix the dial indicator on the flange 4, and make the probe of the dial indicator lean against the outer edge of the flange 3, so as to find out the coaxiality of the flanges 3 and 4. ③ Move the motor so that the boss of the flange 3 is slightly inserted into the concave hole of the flange 4. (4) rotating the shaft 2 to measure the gap z between the end faces of the two flanges; If the gap is even, move the motor to make the end faces of the two flanges close together, fix the motor, and finally fasten the two flanges with bolts.
Figure 1-7 1 flange coupling and its components
1, 2 axis; 3.4- Flanged Disc
(2) Assembly of clutch
The assembly requirements of the clutch are: sensitive engagement and disengagement, sufficient torque transmission and stable operation. For friction clutch, the problems of heating and wear compensation should be solved. The common friction clutch is shown in figure 1-72.
Figure 1-72 Ordinary Friction Clutch
In order to solve the problem of heating and wear compensation of friction clutch, attention should be paid to adjusting the gap between friction surfaces during assembly. Friction clutches are usually equipped with clearance adjustment devices. When assembling, it can be adjusted according to its structure and specific requirements.
The assembly points of conical friction clutch are as follows:
1) The contact of the conical surface must meet the requirements, and its spots should be distributed on the whole conical surface when tested by coloring method (Figure 1-73a).
Figure 1-73 cone coloring inspection
The contact point near the bottom of the cone (Figure 1-73b) or the contact point near the top of the cone (Figure 1-73c) indicates that the angle of the cone is incorrect and can be trimmed by scraping or grinding.
2) When combining, there should be enough pressure to compress the two cones, and when disconnecting, it should be completely separated.
(4) Assembly of bearing and shaft
1. Assembly of sliding bearing
Sliding bearings are reliable, noiseless and can bear large impact load, and are mostly used in precise, high-speed and heavy-duty rotating occasions.
There are many kinds of sliding bearings, which can be divided into integral type, split type and tile type according to different structural forms. According to the shape of working face, it can be divided into cylindrical, conical and multi-oil wedge.
The main technical requirements of sliding bearing assembly are to obtain a reasonable clearance between the journal and the bearing, ensure good contact between the journal and the bearing, and make the journal rotate smoothly and reliably in the bearing.
(1) Assembly of integral sliding bearing
The structure of the integral sliding bearing is shown in figure 1-74.
Figure 1-74 Composition of Integral Sliding Bearing
1) Deburr the shaft sleeve and bearing seat hole, and apply lubricating oil in the bearing seat hole after cleaning.
2) According to the size of the shaft sleeve and the interference during assembly, install the shaft sleeve into the bearing seat hole by tapping or pressing and fix it.
3) After the shaft sleeve is pressed into the bearing seat hole, it is easy to change the size and shape, so the inner hole should be trimmed and reamed or scraped to ensure a good clearance fit between the journal and the shaft sleeve.
(2) Assembly of split sliding bearing
The assembly sequence of split sliding bearing is shown in Figure 1-75. First, install the lower bearing bush into the bearing seat, then install the gasket, then install the bearing bush, and finally install the bearing cover and fix it with nuts.
Figure 1-75 Structure of Split Sliding Bearing
1-nut; 2- Stud; 3- bearing seat; 4— Lower bearing bush; 5— Washer; 6— Bearing bushing; 7— Bearing cover
Assembly points of split sliding bearing:
1) When assembling the bearing bush and the bearing body (including the bearing seat and the bearing cover), the upper and lower bearing bushes must have good contact with the inner hole of the bearing body. If it does not meet the requirements, the back of the thick-walled bearing shell should be scraped off based on the inner hole of the bearing body. At the same time, the steps of the bearing should be close to the two end faces of the bearing body. The fit between them is generally H7/f7. If it does not meet the requirements, it should be scrapped. For thin-walled bearing shells, scraping is not required, as long as the median plane of the bearing shell is higher than the median plane of the bearing body by a certain value (δ h), δ h = nδ/4 (δ is the fit interference between the bearing shell and the bore in the bearing body), and generally δ h = 0.05 ~ 0. 1mm (Figure 1-76).
Figure 1-76 height of split surface of thin-walled bearing bush
2) Positioning of bearing bush. The bearing bush is installed in the bearing body, and no displacement is allowed in the circumferential or axial direction. It can usually be stopped by locating pins and steps at both ends of the bearing bushing.
3) Scraping of bearing holes. Generally speaking, split bearing shells are equipped with matching shaft grinding points. Usually, first scrape off the bearing bush, and then scrape it with a scraper. In order to improve the scraping efficiency, the bearing cover can be removed when scraping the bearing bush. When the contact point of the lower bearing bush basically meets the requirements, press the bearing cover tightly, and further correct the contact point of the lower bearing bush while scraping the bearing bush. With the increase of scraping times, the tightness of the shaft can be adjusted by changing the thickness of the gasket. After the bearing cover is fastened, the shaft can rotate easily without obvious gap, and the contact point meets the requirements, indicating that scraping is completed.
4) Measurement of bearing clearance. The size of the bearing clearance can be adjusted by the split gasket, or it can be obtained by scraping the bearing bush directly. Bearing clearance is usually measured by pressing lead wire. Put several sections of lead wire with a diameter larger than the bearing clearance on the split face of the journal, then close the bearing cover, evenly tighten the nut to press the split face, then unscrew the nut, take off the bearing cover, and carefully take out the lead wire flattened everywhere. Measure the thickness of each section with a micrometer, and the clearance of the bearing can be known according to the average thickness difference of the lead wire.
2. Assembly of rolling bearing
Rolling bearings have been widely used in machinery manufacturing because of their advantages of small friction, small axial size, convenient replacement and simple maintenance.
(1) Technical requirements for rolling bearing assembly
1) The end face marked with code on the rolling bearing should be installed in the visible direction for correct inspection when replacing.
2) After the bearing is installed on the shaft or in the bearing seat hole, it is not allowed to skew.
3) Among the two coaxial bearings, when the important official expands when heated, one bearing must have room for axial movement.
4) When assembling the bearing, the pressure (or impact force) should directly act on the end face of the ring to be matched, and it is not allowed to transmit the pressure through the rolling body.
5) Keep it clean during assembly to prevent foreign objects from entering the bearing.
6) The assembled bearing shall operate flexibly, with low noise, and the working temperature shall not exceed 50℃.
(2) Assembly method
When assembling a rolling bearing, the most basic principle is to make the applied axial pressure directly act on the end face of the bearing ring, without affecting the rolling body as much as possible.
There are many ways to assemble bearings, such as hammering, screw press or hydraulic press assembly, hot-fitting and so on. The most commonly used method is hammering.
1) hammer method. As shown in figure 1-77a, a special sleeve is padded with copper bars, and the bearing inner ring is mounted on the journal with a hammer. As shown in figure 1-77b, install the bearing outer ring into the bearing seat hole by hammering.
Figure 1-77 Assembly of Rolling Bearing by Hammer Method
2) Screw press or hydraulic press assembly method. For bearings with large interference, screw press or hydraulic press can be used for assembly. Before press-fitting, lay the shaft and bearing flat and apply a little lubricating oil to the shaft. Don't press in too fast, and quickly remove the pressure after the bearing is in place to prevent damage to the shaft, especially the slender shaft.
3) Hot-fitting method. Hot-fitting method can be used when there is a large amount of surplus, large assembly batch or limited assembly conditions. Hot-fitting method is to put the bearing in oil and heat it to 80 ~ 100℃, so that the inner hole of the bearing is expanded and sleeved on the shaft, which can ensure that the bearing and the shaft are not damaged during assembly. Bearings filled with grease with dust cover and sealing ring cannot be assembled by hot assembly method.
When assembling thrust ball bearings, we must first distinguish between loose rings and tight rings. When assembling, the tight ring should be close to the end face of the rotating part and the loose ring should be close to the end face of the static part (or box) (Figure 1-78).
Figure 1-78 Assembly of Thrust Ball Bearing
1, 5- tight cycle; 2,4—Loose; 3 boxes; 6 nut
(3) Adjustment of rolling bearing clearance
Many bearings must strictly control and adjust the clearance when assembling. Usually, the inner ring of the bearing makes appropriate axial relative displacement relative to the outer ring to ensure clearance. There are several ways to adjust: as shown in figure 1-79, adjust with gasket; As shown in figure 1-80, adjust with screws.
Figure 1-79 Adjust the gap with a gasket.
Figure 1-80 Adjust the clearance with screws
1-gland; 2- nut; 3 screws
3. Assembly of the shaft
Shaft is an important part in machinery, and all parts that do rotating motion must be mounted on the shaft to work. In order to ensure the normal operation of the shaft and its components, the shaft itself must have sufficient strength and stiffness to meet certain machining accuracy. The parts on the shaft should also reach the specified assembly accuracy after assembly.
Accuracy of (1) axis
The accuracy of the shaft itself mainly includes the roundness, cylindricity and radial runout of each journal, the radial runout of the cylindrical surface matched with the parts on the shaft, and the verticality between the important end surface of the shaft and the journal.
The roundness error of journal is too large, which will cause jumping (vibration) when running in sliding bearing; When the cylindricity error of important official neck is too large, the journal will cause uneven oil film thickness in the bearing, and the local load on the bearing surface will be too large, which will aggravate the wear. When the radial circular runout error is too large, it will cause radial vibration during operation. The above errors are reflected in the support of the rolling bearing, which will cause the deformation of the rolling bearing and reduce the assembly accuracy. Therefore, these errors are generally strictly controlled within 0.02 mm
When the cylindrical surface matched with other rotating parts on the important official is too large, the radial circular runout error of the journal or the verticality error of the important end face of the shaft is too large, the rotating parts will be eccentric after being installed on the shaft, resulting in the vibration of the shaft in operation.
(2) Check the accuracy of the shaft
After measuring the journal with a micrometer, the roundness and cylindricity errors of the shaft can be obtained directly. The radial circular runout error of each cylindrical surface on the shaft and the verticality error of the upper end surface of the shaft can be determined by measuring the radial and end surface circular runout on the V-frame, lathe and grinder or on two centers.
Figure 1-8 1 shows the accuracy of checking the shaft on the V-frame. Put the two journals of the shaft on the V-shaped frame on the flat plate, put a steel ball in the central hole at the left end of the shaft and hold it with angle iron to prevent axial movement during inspection. Measure the runout of each outer cylindrical surface and end face with a dial indicator or dial indicator to get the error value.
Figure 1-8 1 Check the accuracy of the shaft on the V-shaped frame.
(3) Assembly of the shaft
The assembly work of the shaft includes cleaning and checking the shaft itself and connecting some parts on the shaft (such as the plug of the central hole, etc.). ), and prepare to assemble other transmission parts or impellers on the shaft.