JP2012076185A - Manufacturing method of metal-bonded grindstone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing technology which can manufacturing a long-life metal-bonded grindstone.SOLUTION: There is provided a manufacturing method of a metal-bonded grindstone composed of abrasive grains as grinding materials, and cobalt and ceramic for improving the performance of teh grindstone and a binder. The method includes a cooling treatment step of obtaining the grindstone by stopping heating, and cooling a baked product while maintaining the pressure of compressed inert gas. The pressure of the compressed inert gas is set to 0.92 to 0.98 MPa at gauge pressure. When the pressure is equal to or higher than 0.92 MPa, a high temperature reduction rate is obtained, and the price of a hot press can be suppressed low by retaining the pressure at 0.98 MPa.

Description

  The present invention relates to a technique for manufacturing a metal bond grindstone suitable for honing roughing.

  In recent years, environmental efforts have been made in all fields. Even in vehicles, improving fuel efficiency is an important issue to be addressed. One measure for improving fuel efficiency is to reduce friction between the cylinder and the piston. This friction reduction not only improves fuel consumption but also leads to improvement of exercise performance.

The plateau honing method is effective for realizing the above-mentioned friction reduction.
FIG. 8 is an enlarged schematic view of a cross section of a cylinder that has been subjected to plateau honing. An infinite number of plateaus (hills) 101 and adjacent plateaus 101 and 101 are formed on the surface of the cylinder 100 that has undergone plateau honing. And a trough 102 formed between the two. The top surface 103 of the plateau 101 reduces the surface roughness to reduce wear, and maintains the lubrication between the top surface 103 and the piston with the oil accumulated in the valley 102. As a result, both slidability and lubricity can be achieved.

  A metal bond grindstone has been proposed as a grindstone suitable for the plateau honing process described above (see, for example, Patent Document 1).

In paragraph No. [0049] of Patent Document 1, “Manufacturing conditions were a sintering temperature of 500 ° C. and a molding pressure of 15 MPa of the grindstone of the example containing barium sulfate (BaSO ₄ ). (The original text. Heating seems to be correct.) It was manufactured by pressing (hot pressing). "

The present inventors pressure-sintered the metal bond grindstone material under the above-mentioned sintering conditions (500 ° C., 15 MPa). Although not explained in Patent Document 1 after sintering, a metal bond grindstone was obtained by stopping energization of the heater and cooling. The cooling rate at this time was 5.8 ° C./min.
The cross-sectional schematic diagram of the obtained metal bond grindstone is as follows.

FIG. 9 is a schematic cross-sectional view of a conventional metal bond grindstone. In the metal bond grindstone 110, cobalt (Co) particles 111, abrasive grains 112, and tungsten disulfide are contained in a metal-based binder Mb that is a base material. Although it is based on dispersing the (WS ₂ ) particles 113, it has been found that the agglomerates 115 are included therein.

  In this agglomerate 115, the filler added for the purpose of improving mechanical properties is insufficiently dispersed. It is generated by aggregation of tungsten sulfide particles 113. Such agglomerates 115 are more fragile than the surroundings.

  FIG. 10 is an explanatory view of the operation of FIG. For this reason, since the holding power is reduced and the amount of grinding is reduced due to the progress of falling off of the abrasive grains, and the wear is rapidly increased due to the progress of falling off of the agglomerates, the conventional metal bond grindstone 110 has a short life. I found out that

JP 2008-229794 A

  This invention makes it a subject to provide the manufacturing technique which can manufacture a long life metal bond grindstone.

The invention according to claim 1 is a method for producing a metal bond grindstone comprising abrasive grains as an abrasive, cobalt and ceramics for improving the performance of the grindstone, and a binder,
A heat treatment step of obtaining a fired product by firing the material in a compressed inert gas atmosphere while applying a press pressure to the material comprising the abrasive grains, cobalt, ceramics, and a binder by hot pressing;
A cooling treatment step of obtaining a grindstone by stopping heating and cooling the fired product while maintaining the pressure of the compressed inert gas.

  The invention according to claim 2 is characterized in that the pressure of the compressed inert gas is 0.92 to 0.98 MPa in terms of gauge pressure.

  In the invention according to claim 1, the fired product is cooled in a compressed inert gas. When the inert gas is compressed, the density increases and the collision frequency between the gas molecules increases, so that the heat transfer property increases. That is, the compressed inert gas serves as a heat carrier that efficiently transfers the retained heat of the fired product to the water-cooled jacket. When cooled at a high temperature-decreasing rate, generation of fragile agglomerates can be suppressed. As a result, the life of the grindstone can be extended. When the fired product is cooled in a compressed inert gas, a cooling rate of 10 ° C./min or more is obtained. Depending on the apparatus, a cooling rate of 20 ° C./min or more can be obtained. If the cooling rate is 10 ° C./min or more, preferably 20 ° C./min or more, the generation of aggregates can be suppressed.

  In the invention according to claim 2, the pressure of the compressed inert gas is set to 0.92 to 0.98 MPa in terms of gauge pressure. If it exceeds 0.98 MPa, the pressure resistance of the hot press is strongly required by the laws and regulations related to the high pressure vessel, and the hot press becomes expensive. In this respect, by keeping the pressure at 0.98 MPa, a high temperature drop rate can be obtained while suppressing the price of the hot press. Moreover, if it is 0.92 Mpa or more, a high temperature-fall rate will be obtained.

It is sectional drawing of a hot press. It is a correlation diagram of a furnace pressure and a temperature drop rate. It is a correlation diagram of a temperature fall rate and a grinding ratio. It is a cross-sectional schematic diagram of the grindstone of Experiment 02 before grinding. It is a cross-sectional schematic diagram of the grindstone of Experiment 03 before grinding. It is a figure explaining the range of a suitable temperature-fall rate. It is a figure which shows the suitable range of a furnace pressure. It is the schematic diagram which expanded the cross section of the cylinder to which the plateau honing process was performed. It is the schematic diagram which expanded the cross section of the conventional grindstone. It is the schematic diagram which expanded the cross section of the grindstone after use.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The following notation is adopted for pressure. In the reduced pressure state, an absolute pressure with an absolute vacuum of zero is used, and (a) is written after the unit. For the pressurized state, a cage pressure with the atmospheric pressure set to zero is used, and (G) is written after the unit.

Embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a hot press 10 includes a water cooling jacket 11, a furnace shell 12 that can withstand an internal pressure of up to 0.98 MPa (G), and a lower punch 13 that is inserted upward from the bottom of the furnace shell 12. A cylindrical die 14 placed on the lower punch 13; an upper punch 15 inserted downward from the top of the furnace shell 12; and a graphite heater 16 disposed around the die 14; This is a sintering furnace (pressure resistant hot press) comprising a heat insulating chamber 17 surrounding the graphite heater 16.
The heat insulation chamber 17 is made of a ceramic fiber molded body that is rich in durability and has high heat insulation performance.

The lower part of the lower punch 13 is inserted into the cylinder 18, and when the pressure oil is sent from the hydraulic pump 19 to the cylinder 18, the lower punch 13 rises. The oil pressure is detected by the pressure detection means 21.
Water cooling jacket 11 is supplied with water by water pump 22. This water is discharged to the chiller 23, the temperature is adjusted, and then returned to the water pump 22.

  The graphite heater 16 is controlled by the furnace temperature control unit 25. That is, when the temperature detected by the furnace temperature detecting means 26 is lower than the set value, the power supply amount to the graphite heater 16 is increased, and when the temperature is higher than the set value, the power supply amount to the graphite heater 16 is decreased. By doing so, it is possible to control the furnace temperature including the control of the rate of temperature increase.

  Further, the furnace shell 12 is provided with a furnace pressure detecting means 27 for detecting the pressure in the furnace and an exhaust / pressurizing pipe 28, and an exhaust means 29 such as a vacuum pump or an ejector and an inert gas are provided in the pipe 28. A supply source 31 is connected. As the inert gas, argon gas or nitrogen gas is easily available. However, the exhaust means 29 and the inert gas supply source 31 are not used at the same time.

The furnace pressure detecting means 27 is desirably provided separately for the pressure reduction and the pressure application, but is here shared for convenience.
The following experiment was performed using the hot press 10 described above.

(Experimental example)
Experimental examples according to the present invention will be described below. Note that the present invention is not limited to experimental examples.
○ Material:
Abrasive grains (average grain size 69 μm): 10% by volume
Cobalt: 40% by volume
Ceramics: 20% by volume
Binder: 30% by volume

○ Material filling:
The material was filled in the die 14 of FIG. The maximum diameter of the die 14 is 120 mm.
○ Exhaust:
In order to exclude the air in the furnace, the inside of the furnace is reduced to a pressure of 20 Pa (a) or lower by the exhaust means 29 of FIG. This almost removes oxygen.

○ Inert gas filling:
Argon gas is blown into the furnace from the inert gas supply source 31 of FIG. 1, and the furnace pressure is maintained at a predetermined pressure.
○ Press:
A press pressure of 30 MPa is applied to the material by the punches 13 and 15 in FIG.

○ Heating and heating rate:
Heat from the atmospheric temperature (25 ° C.) to the sintering temperature (740 ° C.) at a heating rate of 12.5 ° C./min. By holding at 740 ° C. for a certain time, the sintering process is performed.
○ Heating stop:
The graphite heater 16 in FIG. 1 is stopped. This lowers the temperature in the furnace and the material. When the temperature is lowered, the pressure is monitored by the furnace pressure detecting means 27 to control the exhaust means 29 and the inert gas supply source 31 so that the pressure of the inert gas in the furnace is maintained.

The cooling rate was as shown in the following figure.
As shown in FIG. 2, when the pressure in the furnace is 0.01 MPa (G), the cooling rate is 11.9 ° C./min, 0.10 MPa (G) is 12.8 ° C./min, and 0.49 MPa (G). 16.0 ° C./min, 0.69 MPa (G) at 17.5 ° C./min, 0.80 MPa (G) at 18.7 ° C./min, 0.92 MPa (G) at 19.3 ° C./min there were.
In addition, the temperature decreasing rate measured the required time from 740 degreeC to 600 degreeC, and calculated | required by calculation of (740-600) / required time = temperature decreasing rate.

  Moreover, when the inside of the furnace was as high as 20 Pa (a), it was 5 ° C./min.

The difference in the temperature drop rate can be explained as follows.
Cooling means that heat is transferred (escapes) from the furnace center having a high temperature to the low outer periphery. The transmitting substance that fulfills this mediation is the atmosphere. In other words, heat transfer is performed by collision of gas molecules.

  In a general hot press manufacturing method, sintering is performed after reducing the oxygen partial pressure by reducing the pressure in the furnace or replacing the gas. This is to prevent deterioration due to oxidation. In a reduced pressure atmosphere, there are fewer substances (gas molecules) that transfer heat. In addition, regarding gas replacement, the number of gas molecules hardly changes even if the type of gas changes. Therefore, the cooling rate is not improved in a general hot press atmosphere. In the case of a high vacuum, as described above, the temperature lowering rate becomes half or less.

  In the present invention, the temperature drop rate is improved by performing a hot press manufacturing method in a pressurized state of the atmosphere in the furnace. Increasing the number of gaseous molecules by enclosing high pressure gas in the furnace. That is, it is possible to accelerate the heat dissipation by increasing the collision of molecules.

Next, the correlation between the cooling rate and the performance of the grindstone is examined.
With the hot press 10 described with reference to FIG. 1, the furnace pressure is set to 0.5 MPa (G). A grindstone was manufactured at a temperature decrease rate of 15 ° C./min obtained with this setting. The experiment number related to the obtained grindstone will be referred to as Experiment 01.

  Similarly, the pressure in the furnace is set to 20 Pa (a) with the hot press 10. A grindstone was manufactured at a temperature decrease rate of 5 ° C./min obtained with this setting. The experiment number relating to the obtained grindstone will be referred to as Experiment 02.

  Using the obtained grindstone (coarse grindstone), rough grinding was performed to examine the grinding ratio. The results are shown in Table 1. The definition of the grinding ratio is as follows.

When a workpiece is ground with a grindstone, the workpiece is ground and removed by a predetermined volume. This volume is called the grinding volume. Moreover, a certain amount of volume is worn on the grindstone side. This volume is called the wear volume.
(Grinding volume / wear volume) = defined as grinding ratio. Since the grinding ratio represents the life of the grindstone itself, a grindstone with a large grinding ratio, that is, a grindstone with a small amount of wear of the grindstone and a large amount of workpiece grinding is desired.

A larger grinding ratio was obtained in Experiment 01 than in Experiment 02. That is, it can be expected that the grinding ratio of the grindstone increases in proportion to the cooling rate.
Therefore, a grindstone is manufactured at a larger temperature drop rate and the grinding ratio is examined.

  In the facility of FIG. 1, the upper limit of the temperature drop rate remains at 20 ° C./min. In order to further increase the cooling rate, the heat insulating chamber 17 in FIG. 1 was replaced with a ceramic fiber felt having a heat insulating performance smaller than that of the ceramic fiber molded body. As a result, a large temperature decrease rate of 30 ° C./min could be obtained. A grindstone was manufactured at a temperature decrease rate of 30 ° C./min. The experiment number related to the obtained grindstone was called experiment 03, and the grinding ratio was examined. The results are shown in Table 2.

  FIG. 3 shows the correlation between the cooling rate and the grinding ratio. It was confirmed that the grinding ratio dramatically increased when the temperature decreasing rate was 15 ° C./min or more.

Since the grinding ratios were greatly different, the grindstone in Experiment 02 and the grindstone in Experiment 03 were observed with a microscope. The state of the cross section will be described with reference to schematic views.
FIG. 4 is a schematic cross-sectional view of the grindstone of Experiment 02 before grinding. The grindstone 40 of Experiment 02 includes abrasive grains 41, cobalt particles 42, ceramic particles 43, and a metal-based binder 44 that binds them. Although it was a basic element, this included an agglomerate 45.

  As described in the section of the prior art, the agglomerate 45 is not sufficiently dispersed in the filler added for the purpose of improving mechanical properties, so that coarse crystals of the metal-based binder as the base material are formed. It is produced by agglomeration of cobalt particles 42 and ceramic particles 43 as fillers. Such agglomerates 45 are more fragile than the surroundings.

  When the grinding operation is performed, the fragile agglomerates 45 fall off. Then, the supporting force with respect to the abrasive grains 41 decreases, and the abrasive grains 41 fall off the grindstone 40. Since the wear volume increased and the grinding volume decreased, the grinding ratio represented by (grinding volume / wear volume) was reduced, and as shown in Table 1, the grinding ratio remained at 4800.

  FIG. 5 is a schematic cross-sectional view of the grindstone of Experiment 03 before grinding. The grindstone 50 of Experiment 03 is composed of abrasive grains 51, cobalt particles 52, ceramic particles 53, and a metal-based binder 54 that binds these. And no agglomerates were observed.

  When the grinding operation was performed, the abrasive grains 51 were not dropped out and good grinding was possible. As a result, the grinding ratio increased dramatically, and as shown in Table 2, the grinding ratio became 14000.

Based on Table 1 and Table 2, the correlation between the furnace pressure and the grinding ratio was graphed.
As shown in FIG. 6, the grinding ratio cannot be expected to increase so much when the temperature drop rate is in the range of 5 to 15 ° C./min. On the other hand, when the temperature decrease rate is in the range of 15 to 30 ° C./min, a large grinding ratio proportional to the temperature decrease rate is obtained.
Therefore, in terms of the grinding ratio, the temperature lowering rate is preferably 15 ° C./min or higher, and the higher the better.

Moreover, since the heat insulation performance was lowered as described in the remarks column of Table 2, the electricity cost required for heating increases. Moreover, since the ceramic fiber felt is less durable than the ceramic fiber molded article, the replacement cost of the heat insulation chamber 17 increases.
Therefore, in order to carry out the experiment 03, the operation cost increases and it becomes difficult to carry out the experiment. That is, it is desired that the temperature lowering rate is 20 ° C./min or less in order to suppress an increase in operating cost.

The maximum value of the black circles plotted in FIG. 2 was 0.92 MPa (G). Moreover, the vacuum pressurization type | mold in FIG. 3 can raise the pressure in a furnace to 10 atmospheres (0.98MP (G)).
Therefore, as shown in FIG. 7, a furnace pressure of 0.92 to 0.98 MPa (G) is recommended as a preferred range.

  The present invention is suitable for a metal bond grindstone used for honing roughing.

  DESCRIPTION OF SYMBOLS 50 ... Metal bond grindstone, 51 ... Abrasive grain, 52 ... Cobalt particle, 53 ... Ceramic particle, 54 ... Binder (metal type binder).

Next, the correlation between the cooling rate and the performance of the grindstone is examined.
In the hot press 10 described with reference to FIG. Set to 4 MPa (G). A grindstone was manufactured at a temperature decrease rate of 15 ° C./min obtained with this setting. The experiment number related to the obtained grindstone will be referred to as Experiment 01.

Claims (2)

A method for producing a metal bond grindstone comprising abrasive grains as an abrasive, cobalt and ceramics for improving the performance of a grindstone, and a binder,
A heat treatment step of obtaining a fired product by firing the material in a compressed inert gas atmosphere while applying a press pressure to the material comprising the abrasive grains, cobalt, ceramics, and a binder by hot pressing;
A cooling process step of obtaining a grindstone by stopping heating and cooling the fired product while maintaining the pressure of the compressed inert gas;
A method for producing a metal bond grindstone comprising:   The pressure of the said compressed inert gas is 0.92-0.98MPa in gauge pressure, The manufacturing method of the metal bond grindstone of Claim 1 characterized by the above-mentioned.

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