JP2011020242A - Metal-bonded grinding wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal-bonded grinding wheel having long lifetime. <P>SOLUTION: As shown in Fig. (a), the grinding ratio becomes more as the size of aggregates is smaller. The graph indicates a singular point at 16 in the X-axis scale, in other words, at the size of aggregate of 16 &mu;m, and that, if the size of the aggregate is &le;16 &mu;m, a high grinding ratio is obtained. If the size of the aggregate is &le;15 &mu;m with the allowance of 1 &mu;m, the grinding ratio of 1,000 can be obtained. In addition, if the size of the aggregate is &le;10 &mu;m, the grinding ratio of &ge;2,000 can be obtained. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to 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. 7 is an enlarged schematic view of the cross section of the cylinder subjected to the plateau honing process. The surface of the cylinder 100 subjected to the plateau honing process includes an infinite number of plateaus (hills) 101 and adjacent plateaus 101 and 101. 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. 8 is a schematic cross-sectional view of a conventional metal bond grindstone. In the metal bond grindstone 110, in a metal-based binder Mb as a base material, cobalt (Co) particles 111, abrasive grains 112 of about 5 μm, 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. 9 is an explanatory diagram of the operation of FIG. 8. After grinding for a while with the metal bond grindstone 110, the agglomerate 115 dropped off from the surface, and a large pocket 116 having 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 metal bond grindstone comprising abrasive grains as a grinding material, cobalt and tungsten disulfide for improving the performance of the grindstone, and a metal-based binder.
The metal bond grindstone includes an aggregate obtained by agglomeration of the tungsten disulfide, cobalt, and a metal-based binder, and an average size of the aggregate does not exceed 15 μm.

The invention according to claim 2 is a metal bond grindstone comprising abrasive grains as a grinding material, cobalt and tungsten disulfide for improving the performance of the grindstone, and a metal-based binder.
The metal bond grindstone includes an aggregate obtained by agglomeration of the tungsten disulfide, cobalt, and a metal-based binder, and an average size of the aggregate does not exceed 10 μm.

The invention according to claim 1 is characterized in that the metal bond grindstone includes an agglomerate in which tungsten disulfide, cobalt, and a metal-based binder are agglomerated, and an average size of the agglomerate does not exceed 15 μm. To do.
When the average size of the agglomerates is 15 μm or less, a high grinding ratio can be obtained and the life of the grindstone can be extended.

The invention according to claim 2 is characterized in that the metal bond grindstone includes an agglomerate in which tungsten disulfide, cobalt, and a metal-based binder are aggregated, and an average size of the aggregate does not exceed 10 μm. To do.
If the average size of the agglomerates is 10 μm or less, a higher grinding ratio can be obtained, and the life of the grindstone can be further extended.

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 sketch figure of the agglomerate expanded 3000 times. It is a correlation diagram of the size of the agglomerate and the grinding ratio. 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, the hot press 10 includes a water cooling jacket 11, a furnace shell 12 that can withstand an internal pressure of 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 comprising 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 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 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 includes 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. 8 described in the prior art, and has the problem as shown in FIG.

  As in the present invention, the size of the agglomerates (FIG. 8, reference numeral 115) could be reduced by cooling at a high cooling rate after sintering.

  As described above, it has been found that the size of the agglomerates can be reduced in proportion to the increase in the cooling rate. Then, an additional experiment was conducted to investigate the correlation between the cooling rate and the size of the agglomerates.

(Additional experiment)
○ Experiments 1 to 5:
As shown in Table 1, a grindstone was manufactured under the experimental conditions shown in the above (Experiment) section with a temperature drop rate of 5.8 to 26.4 ° C./min.
However, in FIG. 2, the temperature lowering rate was 11.9 to 19.3 ° C./min. However, the cooling rate can be lowered by using a large die, and the cooling rate can be increased by using a small die. In addition, the temperature lowering rate can be adjusted by changing the thickness of the heat insulating material constituting the heat insulating chamber 17 and changing the type. By performing such treatment, a temperature lowering rate of 5.8 to 26.4 ° C./min was realized.

The outermost surface of the obtained grindstone was observed with a SEM at a magnification of 3000 times.
FIG. 5 is a sketch of the agglomerate magnified 3000 times.
(A) is a sketch diagram related to Experiment 1, in which a considerably large agglomerate 48 was observed. The size L1 of the agglomerate 48 was 30 μm. This size was approximately equal to the average value of the number of agglomerates 48 distributed. Therefore, Table 1 lists 30 μm.

(B) is a sketch diagram related to Experiment 2, and the average size L2 of the aggregates 49 was 25 μm.
(C) is a sketch according to Experiment 3, and the average size L3 of the aggregate 50 was 16 μm.
(D) is a sketch diagram related to Experiment 4, and the average size L4 of the aggregates 51 was 8 μm.
(E) is a sketch according to Experiment 5, and the average size L5 of the agglomerates 52 was 8 μm.

By the way, 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.

When the grinding ratio was examined using the grindstone in Experiments 1 to 5, the values shown in Table 1 were obtained.
The correlation between the size of the agglomerates described in Table 1 and the grinding ratio is graphed.
As shown in FIG. 6A, it can be seen that the grinding ratio increases as the size of the agglomerates decreases. The graph shows that the horizontal axis scale is 16, that is, the size of the agglomerates is 16 μm, and if the agglomerate size is 16 μm or less, a high grinding ratio can be obtained.

If it is 15 μm or less with an allowance of 1 μm, a grinding ratio of 1000 can be obtained. Furthermore, if it is 10 μm or less, a grinding ratio of 2000 or more can be obtained.
Therefore, a favorable grinding ratio can be obtained by setting the size of the agglomerates inevitably distributed on the grindstone to 15 μm or less, preferably 10 μm or less.

FIG. 6 (b) is a graph showing the correlation between the temperature lowering rate in Table 1 and the size of the agglomerates. Needs to be 10 ° C./min or more.
However, when the cooling rate in Experiment 4 is 18.6 ° C./min or more, the size of the aggregate hardly changes. In order to increase the temperature lowering rate, it is desirable to set the upper limit at 20 ° C./min in order to impose a burden on equipment.
Therefore, a preferable temperature decreasing rate is 10 to 20 ° C./min.

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

  DESCRIPTION OF SYMBOLS 40 ... Metal bond grindstone, 41 ... Abrasive grain, 42 ... Cobalt particle, 43 ... Tungsten disulfide particle, 44 ... Metal-type binder, 48-52 ... Agglomerate, L1-L5 ... Agglomerate size (average size) Sa).

Claims (2)

In a metal bond grindstone composed of abrasive grains as an abrasive, cobalt and tungsten disulfide that improve the performance of the grindstone, and a metal-based binder,
The metal bond grindstone includes an agglomerate in which the tungsten disulfide, cobalt, and a metal-based binder are agglomerated, and an average size of the agglomerate does not exceed 15 μm. In a metal bond grindstone composed of abrasive grains as an abrasive, cobalt and tungsten disulfide that improve the performance of the grindstone, and a metal-based binder,
The metal bond grindstone includes an agglomerate in which the tungsten disulfide, cobalt, and a metal-based binder are agglomerated, and an average size of the agglomerate does not exceed 10 μm.

Images