JPH07314457A - Porous material for mold and its production - Google Patents

Abstract

PURPOSE:To develop a porous material for a mold realizing the easy removal of gas produced at the time of injection molding of a plastic and having a wear resistance. CONSTITUTION:In a mold material made of a tool steel and having such mechanical characteristics as a flexural strength of 500MPa or more and a hardness HRC of 35 or more, open pores having an average pare diameter of 5-20mum are formed in a ratio of 4-15%, by area, and the pores are tubular in parallel to each other and so structured as to be connected from one surface to the other surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous material for molds such as a mold for plastic injection molding and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, plastic injection-molded products have tended to be thinned, and as the resin material, a difficult-to-mold material having high strength and heat resistance is being used. These materials are not only difficult to mold, but also generate a large amount of gas during injection molding. Therefore, especially in the case of thin-walled products with a wall thickness of 0.5 mm or less, the resin material itself may be deformed due to such gas generation such as warpage and bending, and surface defects of the molded product such as wrinkles and cloudiness. Is a cause of.

The means for preventing such deformation of the injection-molded product and the generation of surface defects is basically to suppress the generation of gas from the material, but at present, it is necessary to select a proper resin material for the product. , It is difficult to prioritize its molding conditions etc.

Therefore, in order to prevent the occurrence of defects during the production of thin-walled injection-molded products, it is necessary to remove the gas generated during molding.

Also in the prior art, as a means for removing the gas, a method of forming a gap in a part of the mold, a method of utilizing the clearance of the ejector pin, and a method of forming the mold in a nested structure and utilizing the parting line thereof. and so on.

However, these gas removal methods are
Burrs easily occur, many pins cannot be provided,
It cannot be used particularly in the case of a thin-walled molded product because the parting line itself is not desirable.

The most effective method for this is to use a porous material for a part of the mold of the thin portion, and force the gas generated at the time of injection molding from the back surface through a mold surface with a vacuum pump. It is a method of suction and removal. However, since the porous mold material currently used in this method (see JP-A-3-28303 and JP-A-3-159708) is a stainless steel alloy, it has poor wear resistance. . Therefore, when it is used for injection molding of difficult-molding plastic, plastic containing filler, etc., the life of the mold is very short, and maintenance such as mold correction and replacement must be performed every time a fixed number of injection molding is performed.

As described above, the currently used porous die material has the effect of removing gas, but is inferior in wear resistance to the ordinary plastic die material and has a short die life. There are drawbacks.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mold porous material which facilitates the removal of gas generated during injection molding and is excellent in wear resistance, and a method for producing the same. .

[0010]

[Means for Solving the Problems] Here, the present inventor has conducted various studies to solve the above problems, and continued research and development focusing on the use of tool steel as a die material. The following findings were obtained. By the way, the conventional tool steel has not been used because it is difficult to process and there is a problem of corrosion due to gas generated during injection molding of plastic.

It has been found that the determinant of die life is wear rather than the traditionally considered corrosion. Based on that, when the material of the die material is high speed tool steel or alloy tool steel, a die with bending strength of 500 MPa or more and hardness of HRC35 or more is obtained, and contrary to what is generally recognized, It was found to have a longer life than a mold made of stainless steel material. This is because the tool steel was able to fully exhibit the wear resistance characteristics of the tool steel.

Conventionally, the sintered product of metal powder has been considered to have low strength, but unexpectedly, in the sintered product described later,
It was found that it is possible to make a mold having a bending strength of 500 MPa or more and a hardness of HRC35 or more.

In order to maintain the mold life and to ensure a predetermined air permeability, when the tool steel as described above is used as the mold material, the average diameter of the pores is 5 to 20 μm, and the existence rate is 20 to 20 μm.
It should be 40 vol.%.

In order to provide continuous pores from any surface to another surface, the size of the metal powder used as a raw material, the particle size distribution, the resin blending amount, etc. are critical.

As the metal powder, a raw material powder having a narrow particle size distribution with an average particle size distribution of 40% or more is suitable, and the binder resin to be added and mixed is EVA (ethylene-vinyl acetate copolymer) or polyethylene. , A mixture of resins such as paraffin wax is good, and the mixing ratio of resins is 1 to 10 wt.
% Is appropriate.

According to the present invention, the material is tool steel,
A die material having mechanical strength of 500 MPa or more in bending strength and 35 or more in hardness of HRC, having open pores having an average pore diameter of 5 to 20 μm and an abundance of 20 to 40 vol.%. Parallel tubes or straight tubes, 1
Is a porous material for molds having a continuous pore structure from the surface to the back surface. According to a preferred aspect of the present invention,
The above-mentioned porous material for a mold has pores which are linear pipes.

From another aspect, the present invention provides a method for producing the above-mentioned porous material for a die, which has a composition of tool steel and has an average particle size of 7 to 20 μm and a particle size of 10 to 20 μm. The resin powder having an average diameter of 50 to 110 μm is added to the steel powder having a ratio of the steel powder of 30 to 40% by weight, preferably 40 to 50% by weight of the particle size of less than 10 μm. 13% by area are mixed in parallel, the resulting mixture is molded into a green compact, and then the green compact is sintered, which is a method for producing a porous material for a mold.

Alternatively, the composition of the tool steel is
Steel powder having an average particle size of 7 to 20 μm and a ratio of steel powder having a particle size of 10 to 20 μm of 30 to 40% by weight, and preferably 40 to 50% by weight of less than 10 μm. , A plurality of steel wire bundles made by bundling steel wires with an average diameter of 80 to 140 μm are mixed in parallel, for example, in an area ratio of 2 to 10 area% in the cross section, and the obtained mixture is molded into a green compact. Then, the method is a method for producing a porous material for a die, which comprises sintering the green compact.

According to a preferred embodiment of the present invention, there is provided a method for producing the above-mentioned porous mold material using a press or CIP when forming the mixed powder into a green compact. According to another preferred embodiment of the present invention, in order to give the porous mold material the required mechanical properties described above, sintering to quenching and tempering may be performed in one furnace without being exposed to the atmosphere. . Examples of the tool steel include high speed tool steel and cold tool steel.

[0020]

Next, the operation of the present invention will be described more specifically. TECHNICAL FIELD The present invention relates to a porous material for a metal mold for injection molding of plastic, which is capable of removing gas (degassing) and has wear resistance, and a method for producing the same.

The porous material for a mold according to the present invention may be incorporated in a part of the mold, or may be used for a small diameter / long ejector pin or the like. At times, there is a risk of damage such as chipping or breaking. Therefore, the porous mold material according to the present invention also requires bending strength, that is, toughness. As a result of examining the required strength at that time, if the material has a bending strength of 500 MPa or more, since it is possible to prevent breakage even when used for an ejector pin, in the present invention, the bending strength is 500 MPa or more, Preferably 700 MPa or more, more preferably
800MPa or more.

Recent plastics tend to have higher hardness, and some of them have fillers added for the purpose of improving strength. Therefore, the die material is also required to have abrasion resistance. However, the porous materials currently used have a matrix hardness of about HRC30 (HV300) at the maximum, so that they have a short life and increase maintenance time. Therefore, the hardness of the die material according to the present invention is limited to HRC 35 or more, and more specifically to HRC 35 to 50. Preferably HRC 36
~ 42.

Here, as the tool steel used in the present invention, high speed tool steel (SKH) which has already been specified in JIS etc.
51, SKH57), cold tool steel (SKD11) and the like, and is not limited to a specific composition as long as it has been conventionally used as a tool steel, but in a broader sense, the tool steel according to the present invention is It has the following steel composition.

C: 0.5 to 2.5 wt%, Si: 0.5 wt% or less,
Mn: 0 to 1.2 wt%, Cr: 0.2 to 15.0 wt% (preferably
3.0 to 5.0 wt%), Mo: 0 to 10 wt%, W: 0 to 19 wt%,
V: 0 to 6 wt%, Co: 0 to 11 wt% More preferably, it has the following steel composition.

C: 0.95 to 1.35 wt%, Si: 0.37 to 0.40 wt
%, Mn: 0.35 to 0.38 wt%, Cr: 4.0 to 4.3 wt%, Mo: 3.5
-5.1 wt%, W: 5.8-6.1 wt% Here, each component has the following actions.

C: In order to secure a predetermined hardness and strength (particularly hardness), it is limited to the above range. Si: Although it is effective in improving the hardenability, Si is a substitutional atom, so if the addition amount is too large, the hardenability decreases, so the range is limited to the above range.

Mn: MnS has a function of fixing S which deteriorates the steel, and MnS has a function of improving machinability. Further, it has an effect of improving the toughness because it has a structure refining effect in the above range. Cr: limited to the above range in order to improve hardenability and hardness.

Mo: limited to the above range in order to improve hardness and toughness. Mo is an element that causes precipitation hardening and has a great effect on ensuring hardness. W, V, Co: Limited to the above range for improving hardness.
W, V, and Co are carbide-forming elements, and the carbides have extremely high hardness.

In order to make it possible to perform gas removal from the back side with a vacuum pump during injection molding, there are pores in the mold material, and the pores from the surface of 1 to the back side (opposite side or side). It must be continuous (connected) to the other surface.

If the average diameter of the pores is too small, the gas removal ability becomes insufficient, while if it is too large,
Pore marks may be transferred to the skin of the molded product, and the strength may be reduced, causing damage to the mold. This is also related to the abundance ratio of the pores in the whole material, and if the abundance ratio is low, the gas removal capacity becomes insufficient, and if it is high, the material strength decreases.

Here, the existence rate is determined by using an electron micrograph.
It is the value obtained as follows. Existence rate = (total area of pores in arbitrary cross section / total area of arbitrary cross section) ^1.5 x 100 (%).

From the above, in the present invention, the average diameter of the parallel tubular pores is limited to 5 to 20 μm, and the abundance in the vertical cross section (simply referred to as the cross section) of the tubular pores in the longitudinal direction is limited to 4 to 15 area%. To do. Preferably, each is 12 to 17 μm, 7 to 15 area% (when resin thread is used)
Alternatively, it is 4 to 13 area% (when steel wire is used).

Here, "parallel tubular" means that a plurality of elongated tubular cavities are provided in parallel,
Specifically, it refers to the form of the space derived from the linear body when the powder mixture in which a plurality of linear bodies are arranged and embedded is pressed and sintered.

Next, a method of manufacturing the porous material for mold according to the present invention will be described. Generally, although there are some differences in the sintered metal produced by the powder metallurgy method, pores always exist. However, most of these pores are closed pores independent of each other and are not continuous with each other.

This is because the metal powder used as a raw material has a relatively small particle size and a wide distribution, and a binder (resin) is added to the minimum necessary amount in order to facilitate degreasing during sintering. In order to increase the density of the above, the reason is that the metal powder is heated and sintered under atmospheric conditions so that mutual diffusion of the metal powders sufficiently occurs.

Originally, in powder metallurgy, in order to improve mechanical properties and the like, except for special applications such as oil-impregnated bearings,
This is taken as a matter of course because it is a major premise to reduce the resulting pores as much as possible.

However, in the case of the plastic mold material, continuous pores (open pores) as described above, which are also continuous from the front surface of 1 to the back surface side (opposite side or side surface side) thereof, are required. Further, in order to efficiently remove the gas, it is desirable that the pores are connected in parallel pipes in a thick portion from the front surface to the back surface. More preferably, the pore may consist of a straight tube.

Here, according to the present invention, the parallel tubular pore structure derived from the occupied portion of the resin yarn or the gap between the steel wires constituting the steel wire bundle by manufacturing the sintered body by the following operation. Can be

(I) The grain size of the raw material steel powder is set to an average grain size of 7 to 20 μm.
The average particle amount in the whole is
It is 40% by weight or more, and preferably, the number of particles having a particle size of 10 to 20 μm is 30 to 40% by weight of the whole and the particle size distribution is narrowed.
More preferably, particles having a particle size of 11 to 16 μm occupy 15 to 20% by weight of the whole powder, and particles having a particle size of 8 to 11 μm occupy 14 to 19% by weight of the whole powder.

As described above, according to the present invention, the metal powder raw material has 1) a relatively regular shape, and 2) an average particle size of 7 to
20 μm, 3) Select a steel powder raw material that also has the conditions that the range of particle size distribution is narrow, that is, the average amount of particles in the whole is 40% by weight or more.

(Ii) In the case of resin yarn as the pore-forming material, the average diameter is 50 to 120 μm, preferably 50 to 110 μm.
, More preferably 70 to 110 μm, and in the case of steel wire, the average diameter is 80 to 140 μm, preferably 80 to 100 μm.
μm.

The resin yarn is compounded in parallel in the powder, but it is vaporized by sintering, and the remaining pores shrink as the powder shrinks by sintering, and its shape is based on the shape of the parallel tubular pores after sintering. If specified, 15-50 lines / mm, preferably 20-45 lines / mm
mm resin threads are arranged at intervals of 20 to 70 μm, preferably 22 to 50 μm. The parallel compounding ratio of the resin yarns in the cross section is, for example, 4 to 13 area%, preferably 8 to 12 area%. At this time, the area ratio of pores after sintering is 4 to 15%, preferably 10 to
12%

In the case of steel wire, the composition of the array is 500 to 2000.
Book, preferably 600-1500, in a bundle of 15
~ 50 wires / mm, preferably 20 ~ 45 wires / mm steel wire bundle 20 ~ 70
It is arranged at intervals of μm, preferably 22 to 50 μm. The parallel compounding ratio of the steel wires in the cross section is, for example, 2 to 10 area%, preferably 5 to 9 area%. In the case of a steel wire, the steel wire itself serves as a matrix, and the holes are formed by the gap between the steel wires or the enclosure of the steel wires. Therefore, since the steel wire does not substantially shrink, the gap shrinks only slightly. For example, if the arrangement before molding is 2.5-10% by area, it will be 4.5-13% by area after molding. The pore area ratio after sintering at this time is 4 to 15%, preferably 10 to 12%.

1 (a) and 1 (b) are cross-sectional views of a green compact and a sintered body obtained from a mixture with a resin thread, for explaining the manner in which the parallel tubular pores are produced by the present invention. FIG.

As shown in FIG. 1 (a), a plurality of resin yarns mixed in parallel in a metal powder are installed at a preset density and a predetermined interval, and compacted in that state. After the sintering, the resin yarn and the binder added as necessary are gasified and removed, and the region occupied by the resin yarn remains as parallel tubular pores. Of course, as in the case of normal powder compact sintering, it is possible to form a porous structure as a whole by adjusting the sintering conditions, and at the same time, the form of the parallel tubular pores can be changed. .

FIGS. 2 (a), (b) and (c) also illustrate the formation of parallel tubular pores according to the present invention in the compaction and firing of a mixture of steel wire bundle and steel powder. It is an abbreviated explanatory drawing which shows a united thing in a cross section, respectively.

As shown in FIG. 2 (a), first, an appropriate number of steel wires are bundled to obtain a steel wire bundle. At this time, between each steel wire,
In the figure, a gap remains as shown by a white portion. This gap is
As shown in FIG. 2 (b), it remains even when the above-mentioned steel wire bundle as a green compact is embedded in the steel powder. The steel wire bundle is shown in Fig. 2 (c).
As shown in, a predetermined number of the steel powders are mixed in parallel at a predetermined interval. Even if each steel wire is integrated by mutual diffusion by sintering, the obtained green compact will have the above-mentioned gaps and become parallel tubular pores. However, if mutual diffusion goes too far,
The gap may also be filled. Therefore, the pore morphology can be changed to some extent by adjusting the sintering conditions. In this case as well, as in the case of FIG. 1, the surrounding steel powder portion may have a porous structure.

According to the present invention, as the tool steel powder having the above-mentioned characteristics, the metal powder having the above-mentioned composition ratio is used as the starting powder raw material. When using high-speed tool steels (SKH51, SKH57) and cold tool steels (SKD11), which have particularly excellent wear resistance, the matrix hardness after sintering of these alloys is unexpectedly the lowest in the example of SKH57. But with HRC40 and conventional products
Higher hardness was obtained (about HRC30). It should be noted that this conventional product is a porous mold material that is currently commercially available as one type, and is made of stainless steel.

In the production method of the present invention, in order to generate continuous parallel tubular pores, the diameter is 50 to 110.
Tens to hundreds of μm resin threads are arranged at regular intervals in the metal powder in the rubber mold, and then the rubber mold is molded by CIP.

When the molding pressure at this time is less than 98 MPa, the strength of the molded body is low, and the number of voids is large even after sintering, which is not practical. If the molding pressure exceeds 200 MPa, cracks due to backlash tend to occur in the molded body, which is not practical. From the above, 98 to 196 MPa is appropriate, preferably 120 to 18
It is 0 MPa, more preferably 145 to 150 MPa.

In the case of the above embodiment, in CIP molding,
It is not necessary to mix a binder (resins) with the metal powder, but a low molecular weight resin such as paraffin wax may be mixed in the range of 0.5 to 2.5 wt% if desired for handling.

For degreasing the resin yarn, it was effective to flow argon or nitrogen gas as a carrier gas. The most suitable atmosphere pressure was 260 Pa to 4 kPa, and the degreasing rate was as high as almost 100%.

The resin thread that can be used in the present invention is not particularly limited as long as the above-mentioned action is exhibited, but nylon-based, ABS resin-based, polyester, polystyrene and the like can be exemplified, but nylon-based and ABS are preferable. It is a resin type.

In the production method according to another aspect of the present invention,
In order to generate pores consisting of continuous straight tubes in parallel, for example, several tens to several hundreds of steel wires with an average diameter of 80 to 140 μm are densely bundled to form a steel wire bundle, and multiple steel wire bundles are arranged in parallel. Then, a rubber mold is filled with metal powder so as to surround it, and then the rubber mold is molded by CIP.

The molding pressure is not particularly limited, but for example,
If it is less than 98 MPa, the strength of the molded body is low, and there are many voids after sintering, which is not practical. On the other hand, when the molding pressure is 200 MPa or more, cracks due to backlash are likely to occur in the molded body, which is not practical. Therefore, the molding pressure is 98 to 196 MPa.
Is suitable, preferably 120 to 180 MPa, more preferably 145 to 150 MPa.

Also in the case of the above-mentioned embodiment, it is not necessary to mix the binder (resin) with the metal powder in the CIP molding, but it is necessary to prevent backlash after molding the mixture of the steel wire bundles mixed in parallel, and to handle it. 0.5-2.5 wt% if desired
A low molecular weight resin typified by paraffin wax may be mixed within the range.

The steel wire that can be used in the present invention is not particularly limited as long as the above-mentioned action is exhibited, but normally a piano wire, a hard steel wire, a stainless steel wire, etc. can be used, but a piano wire is preferable. .

In the manufacturing method according to the present invention, when a resin is used as a binder to be added when molding a steel powder mixture, the resin is present in the gap between the powder after molding and is gasified in the subsequent degreasing step. However, as described above, the gap between the particles is larger than in the case of the general powder metallurgy method, so that the gasified resin is easily removed. Therefore, in the case of the present invention, even if a large amount of resin is added, it is unlikely to remain as free carbon, or to be damaged or cracked due to deposition expansion of gasification.

When a resin thread is used, the proportion of pores can be controlled by adjusting the amount. After degreasing, the existing part of the resin thread inside the molded product
It becomes a tubular hole.

Furthermore, when a steel wire bundle is used, a gap between the steel wires before sintering remains after sintering. for that reason,
Voids (pores) made of parallel linear tubes are formed.

For degreasing the mixed resin as desired, it was effective to flow argon or nitrogen gas as a carrier gas. The most suitable atmospheric pressure was in the range of 260 Pa to 4000 Pa, and the degreasing rate was as high as almost 100%.

The powder compacting means, conditions, sintering conditions and the like are not particularly limited in the present invention, but preferably the powder compact density is 50% or more, preferably by press molding or CIP molding.
A green compact of 65 to 90% is molded and then sintered in a normal vacuum atmosphere or a reducing gas atmosphere. At this time, it is preferable to select sintering conditions so that the powders are not completely integrated.

If these conditions are combined and manufactured,
A sintered body having continuous open pores will be obtained. Sintering of the molded body according to the present invention is characterized in that processing from degreasing to sintering and cooling is performed in one furnace. That is, since the green compact that has been molded can be heat-treated (quenching and tempering) without exposing it to the atmosphere, not only is material deterioration prevented, but also the process is shortened.

The sintering holding temperature differs depending on the material of the metal material, but it is 75 to 85% of the melting point, for example, SKH57.
Alternatively, in the case of SKD 11, it is desirable to set the temperature at 1050 to 1150 ° C, which is lower than the sintering temperature by the general powder metallurgy method. This is to prevent the inter-diffusion between the metal powders that are in contact with each other when sintering is performed at a general sintering temperature, and the pores intentionally provided are contracted.

Following the crystal holding, the treatment temperature is further reduced to 0.
After raising the temperature in the range of ~ 100 ° C and holding it for a certain period of time,
Introduce argon or nitrogen gas to a pressure of ~ 0.6MPa and quench. Since the die material according to the present invention is a porous body, it cannot be subjected to a normal quenching method, that is, oil cooling or water cooling. This is because oil or water penetrates into the alloy through the pores. Therefore, gas cooling is required.

Therefore, in the manufacturing method of the present invention, it is preferable to perform direct quenching from the sintering so that the thermal energy at the time of sintering can be used as it is. Further, after cooling, the temperature is maintained at a certain temperature or lower, then reheated and tempered.

According to this method, the deterioration of the material can be minimized without exposing the processed material to the atmosphere. In addition, the process will be greatly shortened. Next, the function and effect of the present invention will be described more specifically based on Examples.

[0068]

【Example】

(Example 1) Nylon threads having a diameter of 104 μm are arranged 600 at an average interval of 40 μm per square centimeter, put in a rubber mold for CIP molding, and further, high-speed tool steel made of metal powder having an average particle diameter of 10.8 μm. (Material SKH51) Powder (particle size distribution in which particle size of 10 to 20 μm occupies 37.4% by weight) was vibration-filled into this rubber mold, sealed, and then CIP molded at a pressure of 147 MPa. The green density was 90%. The mixing ratio of the Naoron yarn was 10 area% in the cross section.

Next, this green compact was sintered at 1150 ° C. under a N ₂ gas flow kept at a vacuum degree of 660 Pa, held for 2 hours, and then a pressure of 0.5 MPa was applied to it at 2 ° C./s. It was quenched at the cooling rate.
Then, after holding at 150 ° C for 1 hour under a vacuum of 1.3 × 10 ^-3 Pa,
After tempering at 550 ° C., it was taken out of the furnace.

The matrix hardness of the treated product of this example, which has been sintered and heat-treated, is significantly higher than HV 400 to 450 (HRC 41 to 45) and the commercially available product (HV 300) of the same composition by the melting method, and the bending strength is high. Was 900 MPa.

The average diameter of the tubular pores continuous in one direction is 15 μm, and the abundance rate is 11% (area ratio). Tubular pores that are not parallel to this pore, single pores existing in another portion, etc. The existence was not recognized.

This processed product was processed into a predetermined size, incorporated into a mold for injection molding, and subjected to plastic injection molding having a 0.5 mm thick portion. Conventionally, deformation of a thin portion where warpage and bending occurred Could be prevented. In addition, the commercially available stainless steel porous material was used 40,000 times continuously, but was extended 2.5 times to 100,000 shots. The total number of times of use was 400,000 shots in the case of the conventional one, but 600,000 shots in the example of the present invention.

Further, it was easier to remove the gas by a vacuum pump than the commercially available stainless steel porous material, and no defects such as wrinkles and cloudiness were observed on the surface of the injection molded product. Conventionally, a warp of about 3 mm was observed every 5 cm, but no warpage was observed in this example, as in the case of other porous materials. No rough skin was observed as well.

(Example 2) ABS resin threads having a diameter of 80 μm were arranged at an average interval of 25 μm and 1500 pieces per square centimeter.
Put in a rubber mold for CIP molding, and then use cold tool steel (material SKD11) powder of metal powder with an average particle size of 9.9 μm (average particle size 9.9
(34 wt% of particles with a particle size of 10 to 20 μm) was vibration-filled into this rubber mold, and after sealing, a pressure of 196 MPa was applied to give a diameter of 8 mm.
CIP molding was performed to a size of × 120 mm. The green density was 87%. The compounding ratio of the resin yarn was 10.5 area%.

Next, this green compact was sintered at 1150 ° C. under N ₂ gas flow maintained at a vacuum degree of 660 Pa, held for 2 hours, and then applied with a pressure of 0.5 MPa at 2 ° C./s. It was quenched at a cooling rate of.
Then, after holding at 150 ° C for 1 hour under a vacuum of 1.3 × 10 ^-3 Pa,
Tempering was performed at 550 ° C.

The matrix hardness of the treated product of this example which had been sintered and heat treated was HV 400 (HRC 41), and the bending strength was
It was 800 MPa. Further, the average diameter of the pores was about 10 μm, the abundance rate was 12% (area ratio), and a continuous tubular shape was obtained in the longitudinal direction.

When an ejector pin was processed and manufactured from this processed product and incorporated into an injection molding die so that degassing could be performed through the pin, degassing could be performed more efficiently than when using the conventional clearance. Moreover, the occurrence of burr was also suppressed. The number of continuous uses until cleaning was doubled to 80,000 shots, compared to 40,000 shots for commercially available stainless steel porous bodies. Also,
The total number of times of use was 600,000 shots after 8 times of maintenance. The quality of the molded product was the same as in Example 1.

Example 3 1500 piano wires with a diameter of 80 μm were bundled into one bundle, 10 bundles were dispersed in powder at 1 cm intervals, and this was placed in a rubber mold for CIP molding, and the average particle size was further calculated. High-speed tool steel (material SKH57) powder of 9.6 μm metal powder
(Average particle size of 9.6 μm, particle size of 10 to 20 μm was 35.5% by weight) was filled in this rubber mold by vibration, sealed, and then CIP molded at a pressure of 196 MPa. The green density was 65%. At this time, the steel wire compounding ratio was 47 area%, and the hole existence rate was 5 area%.

The obtained green compact was sintered at 1150 ° C. under a N ₂ gas flow kept at a vacuum degree of 660 Pa and held for 2 hours, then a pressure of 0.5 MPa was applied to it at 2 ° C./s. It was quenched at the cooling rate.
Next, after holding at 150 ° C. for 1 hour under a vacuum of 1.3 × 10 ⁻³ Pa, tempering was performed at 550 ° C., and then the product was taken out of the furnace.
During this time, the processed material never exited the furnace.

The matrix hardness of the treated product of this example which has been sintered and heat treated is HV 400 to 450 (HRC 41 to 45), which is a commercially available product.
(HV300) was significantly exceeded, and the bending strength was 1010 MPa. Also, the average diameter of tubular pores that are linearly continuous in one direction is 10 μm, and the abundance rate is 9% (area ratio). Tubular pores that are not parallel to this pore, single pores that exist in another portion, etc. The existence was not recognized. The steel wire existence rate is
It was 72%.

This processed product was processed into a predetermined size, incorporated into a mold for injection molding, and subjected to plastic injection molding having a 0.5 mm thick portion. Conventionally, deformation of the thin portion where warpage and bending occurred Could be prevented. The number of continuous uses until maintenance was 30,000 shots for the conventional one, but
90,000 shots, three times longer. Further, the total number of times of use was 450,000 shots in the conventional case, which was 950,000 times, but was 650,000 shots in the present invention example after 7 times of care. The quality of the molded product was the same as in Example 1.

Further, it was easier to remove the gas with a vacuum pump than the commercially available stainless steel porous material, and the pressure control thereof could be performed easily. As a result, no surface defects such as wrinkles and cloudiness were observed on the surface of the injection molded product.

Example 4 1000 piano wires with a diameter of 100 μm were bundled into one bundle, and in the center of the CIP rubber mold, a cold tool steel (material SKD11) powder of metal powder with an average particle size of 9.9 μm was further added.
(Average particle size 9.9 μm, particle size 10 to 20 μm is 34% by weight) This rubber mold was vibration-filled, sealed, and then CIP-molded with a pressure of 196 MPa to a diameter of 10 mm and a length of 120 mm. did.
The green density was 70%. The steel wire mixture ratio was 49% (area ratio). The pore existence rate at this time was 4 area%.

Next, this green compact was sintered at 1150 ° C. under N ₂ gas flow kept at a vacuum degree of 660 Pa, held for 2 hours, and then pressurized at 0.5 MPa to 2 ° C./s. It was quenched at a cooling rate of.

Then, under vacuum of 1.3 × 10 ⁻³ Pa at 150 ° C., 1
After holding for a period of time, tempering was performed at 550 ° C.

The matrix hardness of the treated product of this example which had been sintered and heat treated was HV 400 (HRC 41), and the bending strength was 11
It was 00MPa. Further, the pores had an average diameter of about 15 μm and an abundance rate of 8% (area ratio), and a linearly continuous tubular shape was obtained in the longitudinal direction. The existence rate of steel wire is 70% by area.
Met.

From this sintered product, an ejector pin was processed and manufactured, and it was incorporated into an injection molding die so that gas could be released through the pin. As a result, gas could be released more efficiently than when using conventional clearances. Furthermore, the occurrence of burrs could be suppressed. The number of continuous use is 4 for the conventional one
The number of shots increased from 60,000 to 1.5 times. The total number of uses is 300,000 shots (7 times of maintenance)
Increased to 500,000 shots (8 maintenances). The quality of the molded product was the same as in Example 1.

Further, the pressure control of gas removal by the pump could be easily carried out, and wrinkles and fogging on the surface of the injection molded article could be prevented.

[0089]

As described above, according to the present invention,
Conventionally, the mold life is short and it is a problem that tool steel can be used as a porous mold material for injection molding, not to mention breathability,
In terms of both hardness and strength, a product superior to the conventional melted product can be obtained, and the life of the porous mold can be remarkably extended, resulting in great practical advantages.

[Brief description of drawings]

1 (a) and 1 (b) are schematic explanatory views each showing in cross section a green compact and a sintered body obtained from a mixture with a resin system.

2 (a), 2 (b) and 2 (c) are schematic explanatory views each showing a green compact and a sintered compact of a bundle of steel wires and a mixture of the steel powder in cross section.

Claims (4)

[Claims] 1. A mold material having a material of tool steel, a mechanical property of which is a bending strength of 500 MPa or more, and a hardness of which is HRC 35 or more,
It has open pores with an average pore diameter of 5 to 20 μm and abundance of 4 to 15 area%, and the pores are in parallel tubular form.
A porous material for molds having a continuous pore structure from the surface of the mold to the opposite surface. 2. The porous mold material for injection molding according to claim 1, wherein the pore structure has pores which are linear pipes. 3. The composition of tool steel has an average grain size of 7 to 20.
An average diameter of 50 to 120 is applied to steel powder in which the proportion of steel powder with a particle size of 10 to 20 μm is 30 to 40% by weight of the total steel powder.
A method for producing a porous material for a die, comprising: mixing resin yarns of μm in parallel, molding the obtained mixture into a green compact, and then sintering the green compact. 4. A tool steel composition having an average grain size of 7 to 20.
80 to 140 μm average diameter for steel powder in which the ratio of steel powder with a particle size of 10 to 20 μm is 30 to 40% by weight based on the total steel powder.
A porous material for a die, characterized in that a plurality of steel wire bundles formed by bundling m steel wires are mixed in parallel, the obtained mixture is formed into a green compact, and the green compact is then sintered. Manufacturing method.