KR20020018716A - Manufacturing method of bi-metal bushing bonded for press-fit - Google Patents

Abstract

PURPOSE: A method for manufacturing complex-type bushing is provided to improve the endurance, impact resistance and load resistance even when used for a long time by strongly bonding inner and outer parts thereof. CONSTITUTION: A cylindrical steel pipe is fabricated by cutting pipe material in a required size. The cylindrical steel pipe is washed, and a sintered bushing fabricated through a powder metallurgy process is press-fitted into the cylindrical steel pipe. Then, the cylindrical steel pipe coupled with the sintered bushing is heated, so that the cylindrical steel pipe and the sintered bushing are bonded. After that, a bonding part of the bonded bushing is inspected for checking the fault and a heat treatment process is carried out. The bonded bushing, which has been passed through the heat treatment process, is subject to a vacuum inclusion process so that oil is coated on the sintered bushing.

Description

MANUFACTURING METHOD OF BI-METAL BUSHING BONDED FOR PRESS-FIT}

The present invention relates to a method for manufacturing a bushing used for supporting a rotating shaft, and more particularly, a heterogeneous material obtained by forcibly press-bonding a sintered bushing capable of self-lubricating inside a cylindrical steel pipe having excellent wear resistance. It relates to a method for manufacturing a composite bushing.

In general, a driving chain is used for industrial equipment, construction equipment, electronic equipment, escalators, etc., and a bushing for supporting a rotating shaft is used for the driving chain. In some cases, resin-type bushings having excellent lubrication properties such as PTFE may be used.

In particular, oil-free sintered bushings or resin-based lubricating bushings are used in oil-free chains where oil cannot be added or where there is a risk of fire due to lubrication equipment for continuous oiling or feeding. .

The oil-containing bushing used as described above has an advantage of containing oil in its own internal pores, but should be manufactured with low sintered density since oil is contained in the internal pores. Therefore, there is a problem that the inner diameter sliding portion of the sintered bushing may be expanded by plasticity or cracking may occur due to impact when high load and impact load are applied.

In addition, in the case of designing a small press-fitting tolerance to the housing in consideration of the above point there was a problem that the bushing is separated from the housing.

In addition, the method of adhering PTFE to the inner diameter of the steel pipe using a binder or coating the inner diameter of the steel pipe with MoS ₂ , which is a solid lubricant, has been introduced to improve the lubrication property and the load resistance. As a result of repeated high loads, impact loads, and thermal shocks, the joints were peeled off or durability of the coating layer was degraded.

The object of the present invention devised in view of the above problems can be self-lubricated on the inner surface in contact with the shaft, the outer surface friction with the sprocket is not only excellent in wear resistance, load resistance and impact resistance, but also inside and outside The present invention provides a method for manufacturing a composite bushing in which a heterogeneous material is press-bonded, which is strongly bonded and does not deteriorate durability even in long-term use.

1 is a flow chart showing the manufacturing procedure of the composite bushing press-bonded heterogeneous material of the present invention.

2 is a cross-sectional view of a steel pipe according to the present invention.

3 is a cross-sectional view of a sintered bushing according to the present invention.

Figure 4 is a cross-sectional view of the composite bushing press-bonded heterogeneous material produced by the present invention.

Figure 5 is a cross-sectional structure photograph of the junction of the sintered bushing and the steel pipe is bonded in the present invention.

Figure 6 is an assembled cross-sectional view of the paperless roller chain is applied to the composite bushing of the present invention.

7 is a cross-sectional view showing a modification of the composite bushing manufactured by the manufacturing method of the present invention.

* Explanation of symbols for the main parts of the drawings *

1: sintered bushing 2: steel pipe

In order to achieve the object of the present invention as described above, the step of forcibly pressing the sintered bushing into the inside of the cylindrical steel pipe, and by applying heat to the forced-bonded joint so that the contact between the steel pipe and the sintered bushing is made by diffusion. And a step of heat-treating the bonded assembly and vacuum impregnating the heat-treated joint to impregnate the oil in the sintered bushing. do.

The composite bushing press-bonded to the dissimilar materials manufactured by the above method is press-bonded and sintered bushing into the steel pipe, and then hardened heat treatment to improve the wear resistance of the sprocket and the steel pipe friction occurs, the sinter bushing is also hardened to improve wear resistance do.

In addition, by immersing the pores of the sinter bushing by vacuum-impregnating the bonded body in which the sinter bushing is forced-in, the self-lubrication is performed on the shaft rotating inside the sinter bushing, thereby improving the lubrication property in the non-lubricated state.

Further, in the present invention, a forced diffusion is performed in a state in which an appropriate amount of indentation tolerance is provided between the parts to be coupled so as to compensate for the difference in thermal expansion coefficient between dissimilar materials, and the diffusion is performed at a high temperature so that sufficient diffusion bonding is achieved. No deviation of the bushing due to the difference in shrinkage of dissimilar materials.

Hereinafter, with reference to the embodiment of the accompanying drawings, a method for manufacturing a composite bushing of the present invention heterogeneous materials as described above is as follows.

1 is a flow chart showing the manufacturing process of the composite bushing press-bonded heterogeneous material of the present invention, as shown, the composite bushing of the present invention heterogeneous press-bonded composite bushing is produced by cutting the tubular material to the appropriate size (2) After washing, the steel sintered bushing 1 produced by the powder metallurgy process is forcedly pressurized, and heat is applied to the forged press-bonded product so that the contact portion between the steel pipe 2 and the sintered bushing 1 is diffused. To make the joining.

Then, the joints of the bonded bushings are inspected to determine whether they are poorly bonded, and then heat-treated. The inner and outer diameters of the heat-treated bonded bushings are processed to a final size, and oil-impregnated in the sintered bushings by vacuum impregnation. Complete the bushing B without lubrication.

Figure 2 shows the above steel pipe (2), the carbon content of 0.02wt%, 50mm in diameter, 60mm in diameter of the pipe in the state of the material cut by 70mm length using a cutter to cut the size 50mm × 60mm × 70mm ( Inner diameter x outer diameter x length).

Figure 3 shows the sintered bushing (1), the iron, copper, and carbon as a raw material is mixed in a mixer (MIXER) to be Fe-38Cu-1.8C, and the mixed powder thus mixed is a molding press (COMPACTING PRESS ) Was molded to a density of 6.7 g / cm ² , size 40mm × 50mm × 70mm (inner diameter × outer diameter × length) using a mold to make a cylindrical molded product, and then the molded product was sintered in a sintering furnace (SINTERING FURNACE) The sintered bushing 1 in which a plurality of pores are distributed is manufactured.

The sintered bushing 1 manufactured as described above may vary in strength and properties according to content, molding density, and sintering conditions.

For example, when the copper (Cu) is 0.55wt% or less, the strength of the sintered body is high, but the compliance (COMFORMABILITY) is poor when the alignment of the shaft to be joined is not right or impact is applied. If the copper is 40 wt% or more, the sintered body may be damaged due to lack of strength during forced indentation, and the load resistance may not be used at high loads.

Graphite (C) diffused in the base metal iron (Fe) improves the load resistance by hardening the bushing by forming the carbide (Fe ₃ C) with the iron component of the carbon dissolved in the base metal during curing heat treatment. Therefore, when the graphite component is 0.4 wt% or less, the iron component, which is a known component, is not sufficiently cured, thereby lowering the load resistance and wear resistance of the bushing. And when the graphite component is 5.0wt% or more, the sintering ability of the sintered body is reduced, and the brittleness of the bushing increases after heat treatment, thereby reducing durability.

In addition, since the sintered body should contain oil in the internal pores, it should be manufactured at an appropriate density so that sufficient pores are formed. If the sintered density is 5.0g / cm ³ or less, the sintered body may be damaged in the indentation process due to low strength of the sintered body.

In addition, when the sintered density is 7.0g / cm ³ or more, the strength is excellent, but the number of pores is small and does not contain enough oil during impregnation.

Therefore, in order to have the appropriate strength and not to damage the sintered bushing 1 and to have a plurality of pores for containing oil, it is preferable to have a density range in the range of 6.0 to 7.0 g / cm ³ .

Forcing the sintered bushing 1 into the inside of the steel pipe 2 is performed at room temperature by using a press. In this case, the sintered bushing 1 can be easily pressed into the steel pipe 2 without breaking. It is preferable to perform a taper process on the inside surface of the press-fitting opening of 2), and to perform R processing on the outer edge part of the sintered bushing 1 to be press-fitted.

As described above, the joining operation for joining the combined steel pipe (2) and the sintered bushing (1) is a heat treatment in which nitrogen gas and hydrogen gas, which are reducing gas and inert gas, are injected, and the temperature of the hot portion is maintained at 950 ° C. By passing the joining product through the furnace, the joining part is joined by diffusion.

Figure 4 shows the steel pipe (2) and the sintered bushing (1) bonded as described above, the inspection of the bonded state can be a non-destructive inspection ultrasonic inspection, X-RAY inspection and fracture inspection, in this embodiment is a non-destructive inspection Ultrasonography and fracture testing were performed to determine the presence of bonding.

Figure 5 is a cross-sectional structure picture of the product made by the bonding process in the present invention, it can be seen that the diffusion layer is generated in the indentation of the sintered bushing (1) pressed into the steel pipe (2), By the bond strength is generated.

The bonded product bonded as described above was subjected to carburization heat treatment, and by this carburization heat treatment, the surface hardening of the steel pipe 2 and the sintered bushing 1 was performed. In the case of 0.40 wt% or more, a predetermined surface hardening effect may be obtained even when the steel pipe and the sintered bush are hardened by performing general tempering treatment.

And, the final vacuum impregnation is made in the vacuum impregnator and puts the product inside the impregnator containing the high viscosity oil, pumping the inside of the impregnator to maintain a vacuum for a certain time to maintain a sintered bushing (1 ) Contains oil in the pores. In particular, when the loading is large and a long unpaid period is required, a solid lubricant such as MoS ₂ or WS ₂ may be added to the oil.

In manufacturing the composite bushing (B) according to the present invention will be described in more detail because the indentation tolerance, the size of the indentation component, the coefficient of thermal expansion and the like can be a major variable to determine the quality of the component.

First, the most important point in the indentation process is the indentation tolerance, and therefore, the contents of the experiment of the relationship between the indentation tolerance and the bonding state in the post process will be described with reference to Table 1 below.

Table 1

division Sintered Body Outer Diameter (mm) Inner diameter of steel pipe (mm) Indentation Tolerance (mm) Junction Sample 1 50.0-50.05 50.0-50.025 0.025-0.05 Partial Junction Sample 2 50.0-50.05 49.70-49.90 0.10-0.25 Conjugation Sample 3 50.0-50.05 49.40-49.50 0.50-0.55 Conjugation Sample 4 50.0-50.05 48.80-48.90 1.1 to 1.15 Bonding failure

As shown in Sample 1 of Table 1, when the indentation tolerance of the sintered bushing 1 and the steel pipe 2 is 0.05 or less, the steel pipe 2 and the sintered bushing 1 are partially joined together, so that the steel pipe 2 due to the low bonding strength There was a problem in that the sintered bushing 1 is easily separated. However, in Samples 2 and 3 with indentation tolerances of 0.1 to 0.55, the sintered bushings 1 were well bonded without damage, and when the indentation tolerances were 1.1 or more, as in Sample 4, the sintered bushings were subjected to excessive indentation pressure. ) Has been partially broken.

And, according to the sample test, when the indentation tolerance is 0.1 to 0.55, the steel pipe 2 and the sintered bushing 1 are satisfactorily bonded at the high temperature portion of the furnace at 800 to 1200 ° C, whereas the temperature is below 800 ° C or above 1300 ° C. Bonding defect occurred at.

As such, there is almost no liquid phase appearance in the sintered bushing 1 at the bonding temperature of 800 ° C. or lower, and the solid dispersion is difficult, so that the bonding is difficult. Because.

The sintered bushing 1, which is press-fitted and joined to the steel pipe 2, has a bond strength such that it is not detached even by an external force, which means that the low-density sintered bushing 1 has a certain indentation tolerance in the steel pipe 2 As a press-fit, mechanical bonding is primarily performed, and heat is applied to the mechanically bonded joints so that the copper component of the sintered bushing (1) diffuses into the joint of the steel pipe (2), and the secondary bonding is performed. Because.

For example, when joining a combined product without ignoring the indentation tolerance, the sintering bushing 1 may be released from the steel pipe 2 due to the difference in the coefficient of thermal expansion of the steel pipe 2 and the sintering bushing 1. In the case of forced indentation with proper indentation tolerance as in the embodiment of the present invention, when the shrinkage occurs due to the difference in thermal expansion coefficient, the difference in thermal expansion coefficient is compensated by the compressive stress (P) formed in the indentation interface according to the forced indentation do.

That is, the compressive stress P acting on the interface of the press-fitted sintered bushing 1 can be expressed as follows.

P: Indentation interface stress between steel pipe and sintered bushing (kg / mm ² )

A: inner diameter of sintered bushing (mm)

B: Outer radius of sintered bushing (mm)

C: radius of outer diameter of steel pipe (mm)

I: Indentation tolerance of steel pipe and sintered bushing

Eb: modulus of elasticity of sintered bushing (10,000 ~ 15,000kg / mm ² )

νb: Poisson's ratio of sintered bushing (0.2 ~ 0.3)

Eh: modulus of elasticity of steel pipe (21,000kg / mm ² )

νh: Poisson's ratio of steel pipe (0.30)

That is, the compressive stress P increases as the indentation tolerance I increases as in the above formula. However, when the compressive stress is greater, breakage of the sintered body may occur, and when the compressive stress is too small, the joining of the steel pipe 2 and the sintered bushing 1 may not be possible.

Therefore, it is necessary to adjust the indentation tolerance according to the inner and outer diameter sizes of the steel pipe 2 and the physical and mechanical properties of the sintered bushing 1 so that the compressive stress applied to the interface acts constantly.

In addition, shrinkage generated in the sintered bushing 1 forcibly pressed by the interfacial stress acting on the sintering bushing 1, the size of the sintering bushing 1, and the material properties of the sintering bushing 1 may be represented by the following equation. .

here,

P: interfacial stress between steel pipe and sintered bushing (kg / mm ² )

D: outer diameter of sintered bushing

Eb: modulus of elasticity of sintered bushing (10,000 ~ 15,000kg / mm ² )

Tb: thickness of sintered bushing

Therefore, a certain portion of the indentation tolerance during indentation is deformed into plastic or elastic deformation as described above.

In addition, the shrinkage and expansion amount are changed by the difference in thermal expansion coefficient of two dissimilar materials during heat treatment. Therefore, the setting of indentation tolerance is very important in order to obtain a good joint surface at the time of indentation welding.

The relationship between the difference in thermal expansion coefficient and diameter change between dissimilar materials can be expressed by the following equation.

here,

ΔT: Difference in diameter change of sintered bushing (mm)

αA: Coefficient of thermal expansion of steel pipe (10 ^-6 / ℃)

αB: Coefficient of thermal expansion of sintered bushing (10 ^-6 / ℃)

D: Outer diameter of sintered bushing (= inner diameter of steel pipe) (mm)

ΔT: Temperature deviation (℃)

As shown in the above equation, it can be seen that the change in diameter is caused by the change in diameter by the difference in the coefficient of thermal expansion between different materials.

For example, the sintered bushing having a diameter of Φ 50 was cooled in a state in which a steel tube forcedly pressurized was heated to 900 ° C., and the change in diameter was confirmed as shown in Table 2 below.

Table 2

division αA αB D ΔT ΔD Measures 11.7 15 50 900 0.01

As shown in the experimental results shown in Table 2 above, when heated to 900 ° C. and cooled, it could be confirmed that 0.01 mm expansion-shrinkage occurred. In such a case, the junction part may fall.

Therefore, in the case of forcibly press-bonding dissimilar materials as in the present invention, it is very important to design the press-fitting tolerance in consideration of the size of the sintered bushing, the coefficient of thermal expansion, the joining temperature, the amount of shrinkage during the press-fitting, and the like.

Figure 6 shows a paperless roller chain having a composite bushing of the present invention, as shown, the composite bushing (B) according to the present invention is rotatable to the shaft (5) fixed to the outer link plate (4) The inner link plate 6 which is inserted and connected to both ends of the compound bushing B thus installed is fixed so as to be used in an oil-free state in a chain continuously rotating.

7 shows a modified example of the composite bushing in which the heterogeneous material of the present invention is press-fitted, in which two sintered bushes 12 are joined to both inner ends of the steel pipe 11, which is manufactured by a large sintered bush 12. Considering the difficulty of the phase, the two short manufactured sintered bushes 12 can be used by press-fitting, bonding, heat treatment, and impregnation on both sides. This type of composite bushing (B ') is not only easy to manufacture, but also raw materials There are also savings.

As described in detail above, in the manufacturing method of the composite bushing in which the heterogeneous material of the present invention is press-fitted, the sintered bushing is forcedly pressed into the inside of the steel pipe cut to a predetermined size, and the forced pressurized product is heated to join by diffusion. After heat-treating the bonded product, and vacuum-impregnated, the sintered bushing is produced in order to impregnate oil. The outer side has wear resistance and high strength characteristics and the inner side does not need lubrication. There is an effect that can be easily used in the chain.

Claims (4)

Forcing the sintered bushing into the inside of the cylindrical steel pipe, applying heat to the forced-bonded joint so that the contact portion of the steel pipe and the sintered bushing is formed by diffusion, and heat-treating the joined joint. And vacuum-impregnating the heat-treated joint to impregnate the oil in the sintered bushing. The method of claim 1, wherein the sintered bushing has a density of 6.0 ~ 7.0 g / cm ² , the content of the material is copper (Cu): 0.55 ~ 40 wt%, graphite (C): 0.4 ~ 10.0 wt%, the rest: iron Method for producing a composite bushing press-bonded dissimilar materials, characterized in that consisting of (Fe). The method of claim 1, wherein the press-fitting tolerance when forcing the sintered bushing into the steel pipe is 0.1 to 0.55. 2. The heterogeneous material as claimed in claim 1, wherein the sintered bushing forcibly pressed into the steel pipe is formed in a continuous furnace having a temperature of 800 to 1200 ° C at a high temperature, in which nitrogen gas and hydrogen gas are injected, and an inert and reducing atmosphere. Method of manufacturing this press-fitted composite bushing.