JPS6124459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a hollow porous metal material having a cylindrical shape or any cross-sectional shape.

The inventor has filed a patent application dated July 20, 1978-
No. 92180 discloses a porous metal material and a method for manufacturing the same. In this method, the cast alloy is maintained at a temperature range where the solid and liquid phases coexist, and by applying gas pressure to one side, the solid phase forms a network of dendrites. A method for obtaining porous metal materials with interconnected voids by separating a liquid phase from a surface is presented.
However, subsequent research has revealed that this method is not necessarily sufficient to obtain porous metal materials having general shapes such as cylindrical and plate shapes. In other words, depending on the method of gas pressurization, a tensile force may be generated within the material, forming a dendrite network that is considered to have a certain degree of mechanical strength. It was found that it broke and could not be separated. That is,
In a solid-liquid coexistence state, it has mechanical strength against compression, but breaks under tension with a force that is smaller than the force generated when the pressure necessary for separation is applied. Moreover, it has almost no ductility and is extremely brittle.

There is no quantitative data on the tensile properties of these alloys at solid-liquid coexistence temperatures, and in the special situation where the coexisting liquid phase is separated from the solid phase (by gas pressure), the solid phase No published materials have been found regarding whether it has such tensile properties. The present inventor has further improved this method by applying gas pressure so that when performing solid-liquid separation, a quasi-hydrostatic pressure state, that is, no tensile force is generated within the material, and a stress state close to hydrostatic pressure is created. Therefore, we developed a method to separate the liquid phase without destroying the solid phase and to produce general hollow porous metal materials such as cylindrical shapes. That is, the hollow porous metal material described above can be manufactured by applying gas pressure to the outer surface of a hollow alloy having an arbitrary cross-sectional shape and separating the liquid phase without destroying the solid phase. When separating by internal pressure, the outer surface of the metal material is restrained and supported by a porous filter that is finer than its wall thickness to prevent breakage of the solid phase, and the liquid phase is separated through the porous filter. As a result, hollow porous metal materials can be obtained.

Furthermore, in the above-mentioned method for producing hollow porous metal materials using internal pressure or external pressure, the axis of the hollow metal material is held horizontally while rotating during the temperature raising, lowering, or heating maintenance process, so that the entire metal material is more effectively distributed. A material with uniform porosity can be obtained, and at the same time, as will be described later, the life of the rotating device can be greatly extended.

Examples of the method according to this improvement will be described in detail below.

FIG. 1 is a detailed diagram of the experimental apparatus used in this invention.

This device can handle cylindrical cast specimens up to approximately 30 mm in outer diameter.
It was manufactured so that solid-liquid separation experiments can be performed using internal and external pressures, and it has a double-tube rotating system consisting of an outer tube 2 made of stainless steel and an inner tube 3 that supports the sample. It consists of a heater electric furnace 1, an argon gas piping system (gas source not shown), and a temperature measurement system. To explain in more detail, the portion of the inner cylinder 3 indicated by the broken line has large windows open on three sides, and is connected to the inner diameter threaded portion at the tip by three pillars. 4 is a sample support part provided inside the inner cylinder 3, 5 is an aluminum hook ring inserted to prevent pressure leakage,
6 is a sample support ring with an edge, 8 and 9 are sample support stands and screws, 10 is a flange sealed with a packing to connect the inner and outer cylinders, 11 is a rotation 2
14 is a stainless steel pipe, 15 is a turning roller, 16 and 17 are slips (yellow) for taking out the sample temperature thermocouple 25 to the external temperature recorder 27. 18, 19, 20, 21 are piping system valves, 22 and 23 are 10Kg/cm ³ pressure gauges, 24 is a beaker containing water to confirm separation, 26 is installed inside the sample Thermocouples, 28 and 29 are piping, 30
is a copper pipe spirally wound around a stainless steel support pipe 14.

The length of the sample was set to 30 mm in consideration of the soaking zone of the furnace. The samples used in this experiment were 99.9% A and 50A.
−Cu master alloy was heated to 700℃ and _CO2 process mold (45mm
It was cast to a diameter of φ x 28 mm x 200 mm (height) and processed to the specified dimensions.

Next, we will discuss the experimental method.

Set the sample in a predetermined position and tighten with screw 9. Valves 18-21 are opened to replace the air in internal chambers 40 and 50 with argon. At this time, the mating flange 11 is sealed by a connecting jig (not shown). After the replacement, a small amount of argon is flowed through and the temperature is raised. When the temperature has risen to a certain degree, the connecting jig is removed, the mating flanges are brought into a state of light pressure contact, and a motor (not shown) is driven to slowly rotate the double tube at about 0.5 rpm while raising the temperature. The temperature increase rate was approximately 16°C/min. 10~ after the temperature reaches the predetermined solid-liquid coexistence temperature
Hold at this temperature for 15 minutes, stop rotation, connect and seal again, close valve 21 and valve 20 for internal pressure separation, and close valve 19 for external pressure separation and perform pressurized separation while adjusting valve 18. conduct. Thermocouple 25 is in contact with the sample surface, and thermocouple 2
The internal temperature according to No. 6 was slightly lower than this, and the surface temperature was taken as the sample temperature. Once the liquid phase is separated from the solid phase, chambers 40 and 50 are communicated through the porous sample, as can be seen by the bubbles in beaker 24. The separation pressure was read by pressure gauge 22 or 23. After separation, the power was turned off, and at the same time the furnace was opened, the pressure was raised for a short time and then lowered again to cool it below the A-CuA ₂ eutectic temperature. From then on, the sample was heated to room temperature with a small amount of argon flowing to prevent oxidation. After cooling, the sample was taken out. The separated liquid phase was blown out into the chamber 40 inside or outside the sample. The cooling temperature was approximately 15°C/min up to 400°C.

This experimental device can be held vertically by rotating it by 90 degrees (however, it does not rotate), and prior to experiments according to the present invention, we conducted a series of preliminary experiments in a vertical type, and these will be described below.

First, in order to investigate whether separation is possible by internal pressure, the A-4wt% Cu alloy was heated to 630℃, that is, Scheil
According to the formula for non-equilibrium solidification, when the solid phase ratio is 60% (all calculations for the solid phase ratio are based on this formula) and heated and held for about 10 minutes and internal pressure is applied, vertical cracks appear before the pressure is applied. (The same separation as found in hot tears in castings was not observed at all.A similar experiment was carried out in A-
The results were the same for 10% and 15% Cu alloys at a solid fraction of about 70%.

In other words, separation is virtually impossible because it breaks due to the tensile force generated by a pressure much lower than the pressure required for separation.

(1) Experiment without vertical rotation. Next, we conducted an experiment in which separation was performed while maintaining a quasi-hydrostatic pressure state, which is the basic technology of the present invention, that is, A. 1.5
%, 4%, 10%, and 15% Cu alloys were subjected to separation experiments using external pressure at solid fractions of approximately 50% or higher, and solid-liquid separation was achieved without cracking, with voids ranging from a few percent to approximately 20%. A porous material with a high density was obtained. However, complete separation may not always be possible depending on the alloy system or solid phase ratio.

To give an example, in the case of A-15% Cu, when the solid phase ratio is less than about 50% and it is separated by external pressure, about 1/5 of the top surface of the cylindrical sample is separated, and the other parts are not separated. A layer of liquid phase was formed on the inner surface of the lower part. The experiment was repeated under similar conditions, but the results were the same. The cause or mechanism of this is not completely clear, but it is thought that it is related to the liquid phase flowing through the dendrite skeleton during heating and holding due to its own weight, depending on the alloy system, solidified structure, or solid phase ratio. It will be done. It is considered that the larger the liquid phase ratio is, the more remarkable the liquid phase flow becomes.

(2) Experiments using horizontal rotation and external pressure method Based on the above experiments and considerations, the present inventor has developed a method in which the cylindrical sample is held horizontally and further rotated using an external pressure method in order to separate under quasi-hydrostatic pressure in order to eliminate these drawbacks. developed. Examples of this method will be described in detail below.

All sample methods are 25mm outer diameter x 5.5mm length x 30mm
It's height. All porosity in this specification was determined from the separated weight ratio (relative to the weight of the original sample) on the assumption that, for simplicity, the specific gravity of the porous sample and the separated liquid are the same.

Note that the rotation speed during temperature rise was 0.5 r.p.m.

Example 1 A-10% Cu alloy was heated and held at 580° C. for about 10 minutes (solid phase ratio 65%), and then separated under pressure. Separation pressure is approximately 1 atm. After separation, the mixture was further pressurized at 1.5 atm for about 10 seconds, and then cooled to 0.5 atm to the eutectic temperature, after which a small amount was allowed to flow. The porosity was 17%, and there was little shedding of the inner surface, and it was confirmed from stereoscopic microscopic observation of the sample surface and microscopic observation of the cross section that a uniform porous material was obtained.

Example 2 The same A-10% Cu alloy as in Example 1 was heated at 600°C x approx.
After being heated for 10 minutes (solid phase ratio 50%), it was separated under pressure. The separation pressure was approximately 0.8 atm. After separation, the mixture was pressurized to 1.5 atm for approximately 10 seconds, cooled to eutectic temperature at 0.5 atm, and then a small amount of argon was flowed. The porosity is 21%. A uniform porous material was obtained with very little inner surface shedding.

Example 3 A-10% Cu alloy was heated and held at 610° C. for about 10 minutes (solid phase ratio 38%) and separated under pressure. Separation pressure is approx.
0.2 atm, pressurized to 0.4 atm x 10 seconds after separation,
It was cooled to the eutectic temperature at 0.1 atm, and then a small amount was allowed to flow. A uniform porous material with a porosity of 24% was obtained.

Example 4 A-15% Cu was heated and held at 565° C. for about 15 minutes (solid phase ratio 50%) and separated under pressure. Separation pressure is approximately 0.4 atm.
After separation, the mixture was pressurized at 0.7 atm for about 10 seconds, cooled to the eutectic temperature at 0.2 atm, and then a small amount of argon was flowed. The porosity is 19%. Uniform porosity was obtained. Figure 2 shows one of the structures of the porous cylindrical material obtained in this way.
An example (Example 3) is shown. (a) shows the microscopic structure of the A-10% Cu alloy as cast, consisting of a network-shaped crystallized A-CuA ₂ eutectic and an A solid solution matrix.

(b) and (c) are scanning electron microscope images of the outer surface and cross section of the porous sample, respectively. The cast structure has become considerably coarser due to heating, and it can be clearly seen that the liquid phase mainly existing between dendrites has been separated. The eutectic, which is relatively fine compared to the size of the voids, remains, which causes the separation efficiency (the amount of separated liquid phase relative to the amount of liquid phase that should exist) to be low.

Although the mechanism of solid-liquid separation due to gas pressure has not yet been fully elucidated quantitatively, the pressure difference required for separation can be roughly considered to be the sum of σ/r and the pressure difference due to the resistance of the liquid flowing in the solid. can. Here, σ is the surface tension of the liquid phase, and r is the radius of curvature of the liquid interface when a plate-shaped void is formed, which is approximately half the width of the void. Considering this, it can be seen that a material having a relatively coarse solidified structure has a larger width of the liquid phase and a smaller resistance to the flow of the liquid phase even if the liquid phase ratio is the same, so that it can be separated at a lower pressure. It is also expected that the efficiency of separation will be increased.

It will be easily understood that the higher the liquid phase ratio, the lower the pressure required for separation.

The surface tension of the liquid phase and the flow resistance of the liquid phase in the solid phase do not differ greatly depending on the alloy system, and therefore the pressure required for separation does not differ greatly between general alloy systems. In other words, the pressure required for separation is the distance between the dendrites “dentophyte arm spacing”.
(dendrite arm spacing), its morphology, solid phase ratio, and sample shape. Furthermore, there are portions that are morphologically difficult to separate, which is considered to be the main cause of low separation efficiency. In addition to the reasons mentioned above, the reason for adopting the rotating horizontal method is to obtain a uniform temperature distribution over the entire sample, which is one of the important manufacturing control conditions, and to improve the heat resistance of the inner and outer cylinders, etc. This is also essential from the perspective of extending the life of the jig. In other words, in ordinary heating methods such as electric furnaces and gas furnaces, non-uniform temperature distribution in the circumferential direction of the heating element is unavoidable, and thermal stress distortion occurs in these jigs, coupled with creep deformation.
This shortens the life of the jig and makes separation difficult. This tendency becomes more severe as the diameter of the product increases or as the temperature increases.

The rotating horizontal method solves these problems at the same time.

Next, (3) we conducted an experiment to examine whether internal pressure separation is possible when a cylindrical sample is supported by a filter.

FIG. 3 is an enlarged cross-section of the cylindrical casting sample insertion part shown in FIG. 1, and shows a state in which stainless steel cylindrical filters 1 and 2, which have been drilled with a large number of holes, are set. Sample dimensions are 20mm.d x 3mmt x 30mm height.
External cylinder filter has 4 rows in the longitudinal direction x 14 rows in the circumferential direction =
56 pieces, the inner cylinder filter has 4 x 7 = 28 pieces of 3mmφ holes, the wall thickness is 2.5mm, and the gap with the sample is
It is 0.5mm or less.

The test materials had Cu contents of 4, 10 and 15%, and solid phase percentages of approx.
As a result of conducting internal pressure separation experiments at temperatures of 70% or lower, the separation was mainly centered around the holes, and uniform porosity could not be obtained, and the separation efficiency varied considerably, but compared to the case of external pressure separation without a filter. It has decreased considerably. Also, many fine axial cracks were generated.

These experiments also clearly revealed that in a solid-liquid coexistence state, the resistance to tensile force is extremely small, there is almost no ductility, and the material is extremely brittle. Next, a porous alumina cylindrical filter with fine voids was placed in contact with the outer surface of the sample to separate the internal pressure, and a uniform porous material without axial cracks was obtained. Even when an alumina filter was placed on the inner surface of the sample and separation was performed using external pressure, uniform porosity and separation efficiency were obtained, similar to the case of external pressure separation without a filter. However, in this case, the sample and filter became one and could not be separated. When a porous filter is placed in contact with the outer surface of a sample and the sample is separated by external pressure, the peelability between the outer cylindrical filter and the sample is good and the filter can be used repeatedly.

From the above experiments, we found that if the network-like dendrites of an elongated sample or an alloy system are weakly bonded and it is necessary to restrain and support the sample, a filter (for example, a porous Alumina, etc.) of high quality can be placed on the outside of the sample and separated using external or internal pressure. In this case, the inner filter does not necessarily have to be used.

As described above, by the method according to the present invention, a cylindrical porous material useful for oil-impregnated bearings and the like can be manufactured more easily than by conventional powder sintering methods.
The porous material according to the present invention has voids connected to each other,
It is characterized by being connected to the inner and outer surfaces, and independent pores exist in powder sintered porous materials.
Considering that it is a cause of a decrease in effective porosity, it is particularly advantageous when used in oil-containing materials, filters, etc.

In this example, A-Cu having a cylindrical shape is used.
Although only alloy systems have been described, it is clear that the method according to the present invention can be applied not only to these alloy systems but also to various hollow alloy systems having arbitrary cross-sectional shapes. The reason for this is that in these hollow metal materials, the stress state inside the material is in a quasi-hydrostatic state due to external pressure, and the liquid phase can be separated without generating any tensile force and therefore without destroying the solid phase. . Furthermore, by supporting the outer surface or both inner and outer surfaces of the metal material in contact with a porous filter that is finer than the wall thickness of these metal materials, separation can be performed uniformly by external or internal pressure without destroying the solid phase. This is because it is possible to produce a porous metal.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the entire experimental apparatus used in this invention. 1... Electric furnace that has become a split type, 2... Stainless steel outer cylinder, 3... Stainless steel inner cylinder, 4... Sample support flange, 5... Aluminum hack ring, 6... Stainless steel edge ring, 7... Cylindrical sample,
8, 9... Sample support stand and screw, 10... Outer cylinder and inner cylinder connecting flange, 11... Flange, 12,
13...Fixed inner and outer cylinder, 14...Stainless steel pipe, 15...Tarten growler, 16...Slip ring, 17...Carbon brush, 1
819, 20, 21... Valve, 22, 23...
Pressure gauge, 24... flask filled with water, 25,2
6... Alumel-chromel thermocouple, 27... Temperature recorder, 28, 29, 30, 31... Piping. Second
Figure a is a microscopic structure of the A-10% Cu cast material used in the present invention as cast, and Figures 2 b and c are scanning electron micrographs of the outer surface and cross section of the sample after separation, respectively. . Figure 3 shows the cylindrical sample support part, with stainless steel inner and outer cylinder filters, 2
and 1 are set.

Claims (1)

[Claims] 1. A cylinder made of an alloy in which a solid phase and a liquid phase coexist at a predetermined temperature;
A step of providing a hollow metal material having an arbitrary cross-sectional shape such as a rectangular tube or a gear shape, and applying pressure with a gas to maintain the metal material at the above temperature and maintain the metal material in a quasi-hydrostatic state, thereby A method for producing a hollow porous metal material having an arbitrary cross-sectional shape as described above, comprising the step of separating a liquid phase portion from a solid phase portion to make the metal material a porous metal material. 2. In the method for manufacturing a hollow porous metal material having an arbitrary cross-sectional shape as set forth in claim 1, a porous filter whose mesh is finer than the thickness of the metal material is brought into contact with the outer surface or both inner and outer surfaces of the metal material. It is also characterized by being supported. 3. In the method for manufacturing a hollow porous metal material having an arbitrary cross-sectional shape according to claim 1 or 2, the axis of the hollow metal material having an arbitrary cross-sectional shape is horizontal during the temperature raising, lowering, or heating holding process. The metal material is rotated while being held in place.