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The design of pins and bushings is one of the important parts in the design process of excavator working devices. Since the excavator works in a continuous working system, the conditions are poor, there is a lot of dust, the working conditions are harsh, and the load between the pin and the sleeve is large, the wear of the matching pair is very serious. Therefore, the shaft sleeve must be reasonably designed in terms of material selection, surface hardness, core toughness, method, etc. to ensure that the matching pair of the pin and shaft sleeve works reliably.
1. Dimensional design of shaft sleeve
1.Inner diameter of shaft sleeve
The inner diameter of the bushing is generally determined by the diameter of the mating pin. The diameter of the pin shaft is designed and checked based on the hinge point force of the excavator working device, and will not be described in detail here.
2.Length of shaft sleeve
The length of the bushing is determined by the bearing surface pressure. When the inner diameter of the bearing is determined, the longer the length, the surface pressure it bears is relatively reduced, and the load on the bearing is reduced. However, at this time, due to the existence of geometric tolerance and deformation, offset contact will be caused, and cooling will be reduced, resulting in bearing failure. The service life is reduced; on the contrary, if the bearing length is too short, the surface pressure it bears will increase relatively, and the oil will easily flow out from the bearing end face, causing defects and reducing the bearing life.
Generally, L/d (bearing length/bearing inner diameter) = 0.5~3. Special attention should be paid to the fact that under high load conditions, it is easy to cause offset contact. Under such conditions, it is more appropriate to set L/d<1.0.
2. Design of the matching seat hole of the shaft sleeve
1. In order to facilitate the installation of the bushing, the matching seat hole must be chamfered.
2. Matching seat hole surface roughness
The surface roughness of the matching seat hole is usually Ra6.3, and the worst cannot be lower than Ra=12.5.
3. Matching seat outer diameter
The shaft sleeve matching the seat hole must withstand a large expansion stress after being pressed in. Therefore, the outer diameter of the seat hole of ferrous metal materials is generally 1.5 times the outer diameter of the shaft sleeve, while the outer diameter of the seat hole of aluminum alloy materials is generally required to be 1.5 times the outer diameter of the shaft sleeve. More than 2 times the outer diameter.
3. Relevant design of shaft sleeve matching shaft
The performance of self-contained shaft sleeves is largely affected by the surface roughness and hardness of the matching shaft material and whether the surface is electroplated. A high-quality matching shaft surface can prolong the life of the shaft sleeve. On the contrary, a rough matching shaft surface will degrade the shaft sleeve. life span.
1. Matching shaft surface roughness
① For bushings used under fluid conditions, when the surface roughness of the matching shaft is large, the protruding parts of the shaft and bushing will cut off the oil film, causing direct contact between the two. Therefore, the matching shaft surface is required to be mirror-finished to minimize the oil film gap. , making it close to the fluid state, so the performance of the bushing can be improved.
② Most self-bearing sleeves are used under dry friction or boundary conditions. They do not require mirror processing of the matching shaft surface as under fluid conditions. They only need to control the surface roughness of the matching shaft.
Generally, the material of the matching shaft of the bushing on the excavator is usually 45, 40Cr, etc., and the matching surface roughness requirement is Ra=1.6.
2. Matching shaft hardness
On excavators, matching shafts need to be heat treated to meet the requirements and adapt to the movement environment.
The general requirements are that the heat treatment is quenched and tempered 229-277HB, the mating parts are surface quenched, the hardness is 52~60HRC, the depth is 2~4mm, and the hardness at 2mm is above 450HV.
3. Matching shaft surface treatment
The main purposes of surface treatment of matching shafts are:
①Improve corrosion resistance
②Improve surface hardness
③Smooth the surface and improve the performance
Electroplating on the matching shaft can improve its corrosion resistance, effectively reduce rough wear, and improve stability. When the matching shaft rusts, the hard oxides and hard objects that are produced are also intrusive, which is also one of the causes of wear. Therefore, , it is recommended that users plate hard chrome on the matching shaft. If exposed to similar corrosive conditions such as sea water, the matching shaft must be electroplated with two to three layers of hard chromium.
4. Structural design of matching shaft
The surface roughness, sharp corner burrs, and grooves of the matching shaft will damage the sliding layer, so the matching shaft is required to have a smooth surface without sharp corner burrs, etc.
4. Shaft sleeve form
1. Fluid
When fluid is flowing, a viscous flowing oil film is formed due to the "clinch effect", and the surfaces of the shaft and sleeve are completely separated by an oil film. Since there is no direct contact between the shaft and the sleeve, the friction coefficient is very small, generally 0.001~0.01, and the amount of wear is also very small.
2. Boundary
At the boundary, the film between the shaft and the sleeve surface is very thin and a viscous flowing oil film cannot be formed. In this case the choice of bushing material is crucial.
3. Solid (or dry friction)
Solid (or dry friction), there is no viscous flowing oil film between the shaft and the shaft sleeve surface. When the shaft sleeve rubs against the dual piece, the solid agent on the shaft sleeve surface continuously transfers to the dual surface and forms a uniform solid film, thereby achieving It ensures good friction between the friction pairs and effectively reduces wear.
5. Advantages and Disadvantages of Various Shaft Sleeves
Excavator products have become increasingly mature, and various bushing designs have also been applied to the products. The following are the advantages and disadvantages of various commonly used bushings.
1. "8" shaped oil channel steel bushing
Commonly used materials: 45 steel, inner diameter after quenching and tempering, high frequency quenching
Advantages: mature technology, simple processing and low cost.
Disadvantages: The "island" area in the "8" oil tank interval is large, which will produce a whistling sound when there is a lack of oil.
2. Graphite inlaid copper sleeve (from)
Commonly used materials: ZCuZn25Al6Fe3Mn3.
It is commonly used at the root of the excavator arm stick and the root of the boom cylinder.
Advantages: It has certain self-performance when no butter is added for a short period of time, and the noise at the root of the boom and the root of the boom cylinder is low, and no whistling occurs.
Disadvantages: low pressure-bearing capacity, easy to wear, short life, and high cost.
3. Mesh steel sleeve
Commonly used materials: 42CrMo and other alloy steels, treated with QPQ.
Advantages: high hardness.
Disadvantages: The surface quality requirements are relatively high, and burrs are prone to appear during processing. The price is higher than the "8" slot, about 1.5 to 2 times the latter.
4. Oil hole steel sleeve
Commonly used materials: 20CrMnTi, 20Cr and other carburizing treatments.
Advantages: Large oil storage capacity, surface sprayed with MoS2 or graphite, which facilitates early "running-in" and increases wear resistance. High pressure-bearing capacity.
Disadvantages: Difficulty in processing.
5. Metal sintered steel bushing
The structure is a metal matrix inner circle sintered oil-containing metal powder.
Advantages: Has certain self-performance. There is no oil tank and the effective pressure bearing area is large.
Disadvantages: The sintered layer is easy to wear and the cost is high.
Please feel free to contactus Parts Sea engineers or sales for help if you have no parts No.
tse@partssea.com | sales@partssea.com
The design of pins and bushings is one of the important parts in the design process of excavator working devices. Since the excavator works in a continuous working system, the conditions are poor, there is a lot of dust, the working conditions are harsh, and the load between the pin and the sleeve is large, the wear of the matching pair is very serious. Therefore, the shaft sleeve must be reasonably designed in terms of material selection, surface hardness, core toughness, method, etc. to ensure that the matching pair of the pin and shaft sleeve works reliably.
1. Dimensional design of shaft sleeve
1.Inner diameter of shaft sleeve
The inner diameter of the bushing is generally determined by the diameter of the mating pin. The diameter of the pin shaft is designed and checked based on the hinge point force of the excavator working device, and will not be described in detail here.
2.Length of shaft sleeve
The length of the bushing is determined by the bearing surface pressure. When the inner diameter of the bearing is determined, the longer the length, the surface pressure it bears is relatively reduced, and the load on the bearing is reduced. However, at this time, due to the existence of geometric tolerance and deformation, offset contact will be caused, and cooling will be reduced, resulting in bearing failure. The service life is reduced; on the contrary, if the bearing length is too short, the surface pressure it bears will increase relatively, and the oil will easily flow out from the bearing end face, causing defects and reducing the bearing life.
Generally, L/d (bearing length/bearing inner diameter) = 0.5~3. Special attention should be paid to the fact that under high load conditions, it is easy to cause offset contact. Under such conditions, it is more appropriate to set L/d<1.0.
2. Design of the matching seat hole of the shaft sleeve
1. In order to facilitate the installation of the bushing, the matching seat hole must be chamfered.
2. Matching seat hole surface roughness
The surface roughness of the matching seat hole is usually Ra6.3, and the worst cannot be lower than Ra=12.5.
3. Matching seat outer diameter
The shaft sleeve matching the seat hole must withstand a large expansion stress after being pressed in. Therefore, the outer diameter of the seat hole of ferrous metal materials is generally 1.5 times the outer diameter of the shaft sleeve, while the outer diameter of the seat hole of aluminum alloy materials is generally required to be 1.5 times the outer diameter of the shaft sleeve. More than 2 times the outer diameter.
3. Relevant design of shaft sleeve matching shaft
The performance of self-contained shaft sleeves is largely affected by the surface roughness and hardness of the matching shaft material and whether the surface is electroplated. A high-quality matching shaft surface can prolong the life of the shaft sleeve. On the contrary, a rough matching shaft surface will degrade the shaft sleeve. life span.
1. Matching shaft surface roughness
① For bushings used under fluid conditions, when the surface roughness of the matching shaft is large, the protruding parts of the shaft and bushing will cut off the oil film, causing direct contact between the two. Therefore, the matching shaft surface is required to be mirror-finished to minimize the oil film gap. , making it close to the fluid state, so the performance of the bushing can be improved.
② Most self-bearing sleeves are used under dry friction or boundary conditions. They do not require mirror processing of the matching shaft surface as under fluid conditions. They only need to control the surface roughness of the matching shaft.
Generally, the material of the matching shaft of the bushing on the excavator is usually 45, 40Cr, etc., and the matching surface roughness requirement is Ra=1.6.
2. Matching shaft hardness
On excavators, matching shafts need to be heat treated to meet the requirements and adapt to the movement environment.
The general requirements are that the heat treatment is quenched and tempered 229-277HB, the mating parts are surface quenched, the hardness is 52~60HRC, the depth is 2~4mm, and the hardness at 2mm is above 450HV.
3. Matching shaft surface treatment
The main purposes of surface treatment of matching shafts are:
①Improve corrosion resistance
②Improve surface hardness
③Smooth the surface and improve the performance
Electroplating on the matching shaft can improve its corrosion resistance, effectively reduce rough wear, and improve stability. When the matching shaft rusts, the hard oxides and hard objects that are produced are also intrusive, which is also one of the causes of wear. Therefore, , it is recommended that users plate hard chrome on the matching shaft. If exposed to similar corrosive conditions such as sea water, the matching shaft must be electroplated with two to three layers of hard chromium.
4. Structural design of matching shaft
The surface roughness, sharp corner burrs, and grooves of the matching shaft will damage the sliding layer, so the matching shaft is required to have a smooth surface without sharp corner burrs, etc.
4. Shaft sleeve form
1. Fluid
When fluid is flowing, a viscous flowing oil film is formed due to the "clinch effect", and the surfaces of the shaft and sleeve are completely separated by an oil film. Since there is no direct contact between the shaft and the sleeve, the friction coefficient is very small, generally 0.001~0.01, and the amount of wear is also very small.
2. Boundary
At the boundary, the film between the shaft and the sleeve surface is very thin and a viscous flowing oil film cannot be formed. In this case the choice of bushing material is crucial.
3. Solid (or dry friction)
Solid (or dry friction), there is no viscous flowing oil film between the shaft and the shaft sleeve surface. When the shaft sleeve rubs against the dual piece, the solid agent on the shaft sleeve surface continuously transfers to the dual surface and forms a uniform solid film, thereby achieving It ensures good friction between the friction pairs and effectively reduces wear.
5. Advantages and Disadvantages of Various Shaft Sleeves
Excavator products have become increasingly mature, and various bushing designs have also been applied to the products. The following are the advantages and disadvantages of various commonly used bushings.
1. "8" shaped oil channel steel bushing
Commonly used materials: 45 steel, inner diameter after quenching and tempering, high frequency quenching
Advantages: mature technology, simple processing and low cost.
Disadvantages: The "island" area in the "8" oil tank interval is large, which will produce a whistling sound when there is a lack of oil.
2. Graphite inlaid copper sleeve (from)
Commonly used materials: ZCuZn25Al6Fe3Mn3.
It is commonly used at the root of the excavator arm stick and the root of the boom cylinder.
Advantages: It has certain self-performance when no butter is added for a short period of time, and the noise at the root of the boom and the root of the boom cylinder is low, and no whistling occurs.
Disadvantages: low pressure-bearing capacity, easy to wear, short life, and high cost.
3. Mesh steel sleeve
Commonly used materials: 42CrMo and other alloy steels, treated with QPQ.
Advantages: high hardness.
Disadvantages: The surface quality requirements are relatively high, and burrs are prone to appear during processing. The price is higher than the "8" slot, about 1.5 to 2 times the latter.
4. Oil hole steel sleeve
Commonly used materials: 20CrMnTi, 20Cr and other carburizing treatments.
Advantages: Large oil storage capacity, surface sprayed with MoS2 or graphite, which facilitates early "running-in" and increases wear resistance. High pressure-bearing capacity.
Disadvantages: Difficulty in processing.
5. Metal sintered steel bushing
The structure is a metal matrix inner circle sintered oil-containing metal powder.
Advantages: Has certain self-performance. There is no oil tank and the effective pressure bearing area is large.
Disadvantages: The sintered layer is easy to wear and the cost is high.