JP5364486B2 - Manufacturing method of metal bond grindstone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing technology capable of manufacturing a metal-bonded grinding wheel having long lifetime. <P>SOLUTION: A calcinated product is cooled in compressed inert gas. When the inert gas is compressed, the density is increased, the frequency of collision of gas molecules is increased, and the heat conductivity is increased. In other words, the compressed inert gas plays a role as a heat carrier for efficiently transferring the potential heat of the calcinated product to a water-cooled jacket. When the calcinated product is cooled at high temperature dropping rate, generation of brittle aggregate can be suppressed. As a result, the lifetime of the grinding wheel can be prolonged. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a metal bond grindstone suitable for plateau honing.

  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. 5 is an enlarged schematic view of a cross section of a cylinder subjected to plateau honing. An infinite number of plateaus (hills) 101 and adjacent plateaus 101, 101 are formed on the surface of the cylinder 100 subjected to 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 inventors of the present invention compression-sintered a metal bond grindstone material under the above-described 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. 6 is a schematic cross-sectional view of a conventional metal bond grindstone. In this metal bond grindstone 110, cobalt (Co) particles 111, about 5 μm abrasive grains 112, and a metal-based binder Mb as a base material; Although it is based on the dispersion of tungsten disulfide (WS ₂ ) particles 113, it has been found that this contains an aggregate 115 of about 30 μm.

  In this agglomerate 115, the filler added for the purpose of improving the mechanical properties is insufficiently dispersed. Therefore, the agglomerate 115 and the cobalt particles 111 that are fillers in the coarse crystals of the metal-based binder Mb that is the base material are mixed. It is generated by aggregation of tungsten sulfide particles 113. Such agglomerates 115 are more fragile than the surroundings.

  FIG. 7 is an explanatory diagram of the operation of FIG. 6. After grinding for a while with the metal bond grindstone 110, the agglomerate 115 dropped off from the surface, and a large pocket 116 with a diameter of about 30 μm was formed. 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 tungsten disulfide for improving the performance of the grindstone, and a binder,
Hot pressing by the abrasive grains, cobalt, while applying pressing pressure on the material consisting of tungsten disulfide and binder, the material in a pressurized inert gas atmosphere 0.92~0.98MPa a gauge pressure, firing A heat treatment step of obtaining a fired product by processing;
Heating was discontinued and the features and the cooling process step to obtain a grinding wheel by cooling the calcined product while maintaining the pressure of the pressurized inert gas, in that it consists of.

  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 addition, in the invention according to claim 1 , 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 the hot press used by this invention. It is a correlation diagram of a furnace pressure and a temperature drop rate. It is the schematic diagram which expanded the cross section of the grindstone. It is the schematic diagram which expanded the cross section of the grindstone after use. 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 drawings are viewed in the direction of the reference numerals.
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 including a heat insulating chamber 17 surrounding the graphite heater 16.

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 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 preferably 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 5 μm): 8.75 vol%
Cobalt: 56% by volume
Tungsten disulfide: 5.25% by volume
Binder (phosphor bronze): 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.

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 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. In other words, we succeeded in accelerating heat dissipation by increasing molecular collisions.

○ Evaluation at 0.92 MPa (G):
The cross section (schematic diagram) of the grindstone manufactured at a furnace pressure of 0.92 MPa (G) was as shown in the following figure.
As shown in FIG. 3, the grindstone 40 is composed of abrasive grains 41, cobalt particles 42, tungsten disulfide particles 43, and a metal-based binder 44 that binds them, and also includes cobalt particles 42 and disulfides indicated by small black dots. The tungsten particles 43 and the abrasive grains 41 were evenly dispersed.

  FIG. 4 is an operation diagram of FIG. 3. When grinding was performed with such a grindstone 40, the tungsten disulfide particles 43 dropped off from the surface, and fine pockets 47 were formed.

  That is, the cobalt particles 42 that improve the wear resistance of the abrasive grains remain in the grindstone and exhibit a grindstone wear inhibiting action. Further, the fine pocket 47 prevents the chips from accumulating on the front surface of the abrasive grains, and the dropped tungsten disulfide particles 43 serve as a solid lubricant to promote the discharge of the chips. Is prevented. By these actions, good machinability is maintained.

○ Evaluation at atmospheric pressure (0.01 MPa (G)):
On the other hand, the cross-section (schematic diagram) of the grindstone manufactured at a furnace pressure of 0.01 MPa (G) is almost the same as FIG.

  As in the present invention, the size of the agglomerates (FIG. 6, reference numeral 115) could be reduced by cooling at a high cooling rate after sintering.

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

  DESCRIPTION OF SYMBOLS 10 ... Hot press, 11 ... Water cooling jacket, 31 ... Inert gas supply source, 40 ... Whetstone, 41 ... Abrasive grain, 42 ... Cobalt particle, 43 ... Tungsten disulfide particle, 44 ... Binder.

Claims (1)

A method for producing a metal bond grindstone comprising abrasive grains as an abrasive, cobalt and tungsten disulfide for improving the performance of the grindstone, and a binder,
Hot pressing by the abrasive grains, cobalt, while applying pressing pressure on the material consisting of tungsten disulfide and binder, the material in a pressurized inert gas atmosphere 0.92~0.98MPa a gauge pressure, firing A heat treatment step of obtaining a fired product by processing;
Heating was discontinued, and the cooling process step to obtain a grinding wheel by cooling the calcined product while maintaining the pressure of the pressurized inert gas,
A method for producing a metal bond grindstone comprising:

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