JPS5852526B2 - Manufacturing method of bronze sintered bearing material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a bronze-based sintered bearing material having higher strength than conventional products.

In the production of bronze-based sintered alloys, there are cases where bronze powder is used as the raw material, and cases where mixed powder of copper and tin powders are used as the raw material, and the technology of the present invention targets the latter case. It was developed as.

First, to describe the general process of powder metallurgy, first, zinc stearate or other powdered lubricant is added to the raw material powder.
The standard method is to add 2 parts by weight, mix well, compression mold it into the desired shape using a mold, then sinter it in a sintering furnace, and then complete it by sizing and oil impregnation treatment. It is a process.

Here, we will touch on the sintering process, which is most closely related to the material properties of sintered alloys. First, there are two types of sintering furnaces: batch-type furnaces, which are usually used for small-scale sintering, and continuous-type furnaces, which are suitable for mass production. There are two main categories.

Continuous furnaces are horizontally long tube-shaped furnaces that use a mechanism to move the inserts (formed bodies), such as mesh belt furnaces that use heat-resistant alloy steel belts, or semi-continuous sintering boxes containing the formed bodies. There are various methods such as pusher type furnaces, roller type furnaces, lift beam type furnaces, etc., but all of them basically preheat and deheat the compact in order from the inlet side of the furnace. The structure has three zones: a wax chamber, a sintering chamber, and a cooling chamber.

Note that, as the atmosphere in the furnace, a reducing atmosphere such as hydrogen gas or ammonia decomposition gas is generally used.

Next, the sintering process is divided into two stages: an earlier dewaxing process and a later main sintering process.

That is, while the compact passes through the above-mentioned furnace, the lubricant in the compact is first evaporated and removed in a relatively low-temperature preheating/dewaxing chamber, and then in a sintering furnace maintained at a predetermined high temperature. After being sintered in earnest, it is gradually cooled to near room temperature to complete the sintering process.

Here, the conditions are that the dewaxing temperature is approximately 400°C, the temperature increase rate to reach this temperature is 10 to 30°C per minute, and the main sintering temperature is approximately 780°C. be.

The graph in Figure 1 shows the thermal history that the rolled compact undergoes in the above-mentioned sintering process. Equivalent to.

Now, the bronze-based sintered alloy obtained by dewaxing and sintering in a reducing atmosphere in this manner has a strength slightly exceeding 18V4/uIt2 in terms of radial crushing strength.

Therefore, since oil-impregnated bearings are also a type of mechanical element, it is desired to increase their strength as much as possible in order to increase the degree of freedom in design.

However, increasing the strength of bearing materials is not so easy.

This is because in the case of an oil-impregnated bearing, it is essential that it not only has its own wear resistance, but also that it does not wear out the shaft of the mating member, and that it is as porous as possible and capable of retaining a large amount of lubricating oil. , common strengthening methods in powder metallurgy, such as high alloying with the addition of reinforcing components 11, as in the case of mechanical components such as gears, or densification of parts by compression molding at high pressure. This is because it cannot be adopted.

Therefore, the inventor devoted his efforts to researching the sintering process of the compact, and by improving the preheating and dewaxing process that precedes it, he succeeded in improving the strength of the bearing while maintaining its original characteristics.

※※ This improvement, that is, the characteristic of the present invention, is that the dewaxing temperature in the dewaxing process is 41% higher than that of the conventional method.
5 to 710°C, dewaxing carried out in a reducing atmosphere, and the subsequent main sintering process.
The main point of this method is to include an oxidation reaction step in an oxidizing atmosphere.

Note that although a special oxidizing gas may be used as the oxidizing atmosphere here, the purpose can usually be easily achieved by using the atmosphere.

The present invention will be described below with reference to one embodiment thereof.

First, copper powder and tin powder are mixed in a ratio of 91% copper and 9% copper,
Add 0.3% zinc stearate as a lubricant to the total amount, mix thoroughly, put this mixed powder into a mold and compress it, and the shape is 18 m in outer diameter, 101 EJI in inner diameter, and 1 in length.
A large number of samples with a cylindrical shape of 4130 and a green powder density of 6.35 t/crIL are molded.

Next, regarding the sintering of the samples, a continuous sintering furnace of the type in which the dewaxing chamber and the main sintering chamber are separated and both are connected by a mesh belt is used, and the samples are divided into the above groups I to ■. Each was sintered based on the dewaxing conditions listed in Table 1.

That is, the sample group ① in the table is related to the present invention. First, the sample is sent to a dewaxing chamber with a reducing atmosphere, and the temperature is raised to 700 °C at a rate of 30 °C per minute, held for several minutes, and then lubricated. Evaporate the agent.

The temperature increase rate can be arbitrarily set by adjusting the temperature distribution in the furnace chamber and the feed rate.

Next, the dewaxed sample is transferred from the dewaxing chamber to the atmosphere (oxidizing atmosphere) to oxidize its surface.

Although the temperature of the sample decreases during this time, this has little effect on the sintering results.

Subsequently, main sintering of the sample is carried out in a reducing atmosphere by maintaining the temperature at 780° C. for about 15 minutes, and then a normal cooling process is performed to complete the sintering.

The graph in Figure 2 shows the thermal history that sample ■ undergoes in the above process.
For the oxidation reaction process in an oxidizing atmosphere, the range of ←
The range B→ corresponds to the main sintering and cooling steps in a reducing atmosphere.

For the sample ■ thus sintered, its radial crushing strength is J
Measurement according to IS Z2507 (ISO2739) showed a high value of 30 Ky/J.

On the other hand, for the group of samples (2) in the table, the dewaxing process was carried out using the conventional method, that is, the dewaxing chamber and the main sintering chamber were airtightly connected to create a reducing atmosphere in the furnace. The sample was dewaxed by raising the temperature to 400°C at a heating rate of 10°C, and then sintered under the same conditions as Sample 1, and its radial crushing strength was 19 to -2.

Next, the sample group (2) is one in which some of the conventional dewaxing conditions shown in sample (2) are changed, that is, the dewaxing temperature is increased from 400°C to 700°C. Although it is slightly higher than before, it is not significant enough.

Next, sample group (2) is an example based on the same method as the present invention (a dewaxing method separately proposed by the present inventor as an improved technique of the conventional method).

The difference between this method and the conventional method is that the dewaxing process is carried out in an oxidizing atmosphere throughout, and the temperature increase rate during dewaxing is faster than 50°C per minute, compared to the conventional 10-30°C. With this improvement, a radial crushing strength of 26 to 2 mem, which is significantly higher than the conventional one, can be obtained.

However, as described above, the sintered material according to the present invention exhibits even higher strength than this.

Furthermore, when the four types of samples mentioned above were sized and oil-impregnated into bearings and then subjected to a comparative test using a bearing performance tester, all of them showed almost the same characteristics, and no particularly significant difference was observed.

After repeated experiments, we determined the critical conditions under which the radial crushing strength of the present invention would be significantly improved.We found that the temperature increase rate could be 10 to 30 degrees Celsius per minute, as in the case of the conventional method, and that the temperature rise rate of the liquid phase at the 5-temperature of the removal temperature was sufficient. The temperature range in which this does not occur is higher than the L-ε→η peritectic temperature (415°C) in the copper-tin system equilibrium phase diagram, and the liquid phase generation temperature (the extension of the solidus line of γ and the composition of the ε phase in contact with the γ+L region) It was found that if the oxidation reaction step was carried out from this temperature within a lower range (corresponding to 710° C. at the intersection with the line), results superior to the conventional method typified by sample ① could be obtained.

As is clear from the above results, according to the present invention, a bearing material with higher strength than the conventional product can be obtained, and if the strength is the same as the conventional product, a bearing material with a higher oil content can be obtained. The present invention greatly contributes to expanding the range of application of bronze-based sintered oil-impregnated bearings.

Now, the structure of the present invention and its effects have been described in detail above, and finally, the principle of the operation and effect of the present invention will be considered.

First, if we focus only on the pure sintering phenomenon in a molded body in which no lubricant is present between the powder particles (that is, molded by the mold lubrication method), it is better to have the surface of the powder oxidized to some extent. Sintering progresses better.

This is because the oxide film is reduced during the sintering process in a reducing atmosphere and the grain surface becomes active.

Therefore, from this point of view, preheating and dewaxing in an oxidizing atmosphere is advantageous, but on the other hand, this method has the following disadvantages.

That is, as a result of coating the surface and internal pores of the molded body with oxides generated by heating in an oxidizing atmosphere, the evaporation and scattering of the lubricant from inside the molded body is inhibited, and furthermore, the lubricant composition The carbon material therein remains in the form of soot, and as a result, the powders are not sufficiently diffused and sintered.

And this minus is greater than the plus due to activated sintering.

This is the main reason why molded bodies are conventionally preheated and dewaxed in a reducing atmosphere.

On the other hand, before going into the explanation of the present invention, we will first discuss the advantages and disadvantages of the improved method shown in sample (2).

In this method, the entire process of preheating and dewaxing is carried out in an oxidizing atmosphere while raising the temperature at a high rate of 50°C or more per minute, so that the lubricant is first dewaxed, and then the molded body is dewaxed. By controlling both reactions so that the oxidation reaction progresses, high strength can be achieved without degrading the bearing properties.However, on the other hand, because the bearing undergoes a liquid phase in an oxidizing atmosphere, its structure and dimensions deteriorate. Problems include the tendency for changes to become unstable, the need to raise the temperature at high speeds, and the need to modify and extend the furnace body, especially in the case of series meshbelt furnaces.

However, in the present invention, since the atmosphere during preheating and dewaxing is reducing, the lubricant can be smoothly dewaxed.

In addition, the temperature increase rate at this time may be the conventional standard rate, and therefore there is no need to consider the furnace length or the like.

After the dewaxing is completed, the molded body is transferred to an oxidizing atmosphere to oxidize its surface, which is the solid phase region of 415 to 710.
Since the process is carried out in the temperature range of 1000 C, effects on the structure and dimensional changes are prevented.

In this way, it is believed that both complete dewaxing and the use of activated sintering are achieved, resulting in a bearing material with higher strength compared to conventional methods.

[Brief explanation of the drawing]

FIG. 1 is a temperature one-hour characteristic diagram showing the thermal history in a conventional sintering process, and FIG. 2 is a temperature one-hour characteristic diagram showing the thermal history in the sintering process of the present invention. AI... preheating/dewaxing process, AII... oxidation process,
...Main sintering process.

Claims (1)

[Claims] 1. A method for manufacturing bearing materials by powder metallurgy using copper powder, tin powder, etc. as raw materials, in which copper powder, tin powder, and lubricant are mixed in a predetermined ratio and formed into a predetermined shape. After that, the lubricant is maintained in a reducing atmosphere for a certain period of time within a temperature range higher than the L1ε→η peritectic temperature (415°C) and lower than the liquid phase generation temperature (710°C) in the copper-tin phase diagram. At the same time as evaporation and removal, temporary sintering is performed, and then this compact is held in an oxidizing atmosphere for several minutes to cause an oxidation reaction in the solid state, and then liquid phase sintering is performed in a reducing atmosphere. A method for producing a bronze-based sintered bearing material. 2. The method for manufacturing a bronze-based sintered bearing material according to claim 1, characterized in that the atmosphere is used as the oxidizing atmosphere.