JPH0873901A - Raw material composition for sintering and production of sintered parts formed by using this composition - Google Patents

Abstract

PURPOSE: To obtain sintered parts having excellent mechanical characteristics in a short binder removing time without using costly iron powders by composing the above compsn. of a binder consisting of reduced iron powder and specific components. CONSTITUTION: This compsn. is prepd. by kneading the binder components consisting, by weight%, of 1 to 2 polystyrene, 1 to 2 acrylic resin, 0.5 to 1 polyethylene, 1.5 to 2.5 paraffin and 0.5 to 1 stearic acid and the reduced iron powder for the balance. Such compsn. is injection molded in metal molds and is formed to a preform, which is then heated at a temp. below the m.p. of the reduced iron power and is thus subjected to the binder removing treatment; thereafter, the molding is subjected to a sintering treatment, by which the sintered parts are obtd. The reduced iron powder is obtd. by subjecting iron oxide to reduction by heating, then to decarburization refining followed by annealing. The reduced iron powder having an average grain size of 6.0 to 11.0μm and a specific surface area of 0.30 to 0.80m<2> /g is more preferable for averting the increase in the viscosity at the time of injection molding by the increase in the specific surface area and the degradation in the mechanical characteristics of the sintered parts by the increase in the particle size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material composition for sintering suitable for injection molding and a method for producing a sintered product by injection molding using this composition.

[0002]

2. Description of the Related Art Conventionally, machining has been applied to manufacture a metal molded product having a complicated three-dimensional solid shape, but in recent years, powder sinter molding using a plastic injection molding technique has been used. The workability is better than that of metalworking, and mass production is possible.

The method of manufacturing a sintered product by injection molding is as follows:
A mixture of raw material powder consisting of fine metal powder such as iron and a binder (binding material) is heated to form a kneaded body, which is injected from an injection molding machine into a predetermined mold to obtain a preformed body. After that, the binder is debindered by heating the preformed body at a temperature equal to or lower than the melting point of the raw material powder, and then the binder removed body is sintered at a high temperature to fill the voids after debindering. , A method for producing a contracted powder-sintered molded product having a shape similar to that of a mold.

However, in this manufacturing method, iron powder having a spherical shape or a shape close to that obtained by the atomizing method or the carbonyl method has been used as a molding material, but the iron powder is manufactured by these methods.
Due to its low production capacity and high cost, it has the drawback of not being suitable for mass production.

Therefore, as a technique for producing a sintered product with high mass productivity by using iron powder of irregular shape obtained at a low cost as a forming material and using a specific binder, high quenching A method of injection-molding a kneaded product of fine iron powder obtained by crushing carbon iron and subjecting to decarburization and a binder composed of paraffin, wax and polyethylene, and performing hydrogen reduction treatment between the binder removal treatment and the sintering treatment ( JP-A-2-270902) and a raw material powder comprising a mixture of reduced iron powder and carbonyl iron powder, and an ethylene / vinyl acetate copolymer, low density polyethylene, methacrylic acid ester copolymer, dibutyl phthalate or stearic acid, and A method of injection-molding a kneaded material including a paraffin / wack binder, and removing the binder and sintering the mixture (Japanese Patent Laid-Open No. 59-2). JP), etc. 9403 is proposed.

[0006]

However, in the above method, the binder removal treatment requires a long time of nearly 40 hours, and further the hydrogen reduction treatment step is required. It has a problem that the relative density is as low as about 92% and the mechanical properties are inferior.

Further, in the above method, since the raw material powder contains not only reduced iron powder but also expensive carbonyl iron powder,
There is a problem that the cost is increased and the relative density of the obtained sintered molded product is as low as about 87% and the mechanical properties are inferior as in the above method.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to apply it to reduced iron powder having various particle shapes so as to ensure fluidity suitable for injection molding, In addition, it is possible to shorten the heat treatment time for removing the binder, obtain a sintered product having excellent mechanical properties, and eventually reduce the cost, and a sintering raw material composition and a firing method. It is to provide a method for manufacturing a product.

[0009]

In order to achieve the above-mentioned object, the invention according to claim 1 is such that the raw material composition for sintering is 1 to 2% by weight of polystyrene, 1 to 2% by weight of acrylic resin,
Polyethylene 0.5-1% by weight, paraffin 1.5-
It is characterized by comprising 2.5 wt%, stearic acid 0.5 to 1 wt%, and the balance reduced iron powder.

The invention according to claim 2 is the raw material composition for sintering according to claim 1, wherein the reduced iron powder has an average particle diameter of 6.0 to 11.0 μm and a specific surface area of 0.30 to 0. .80
It is characterized in that it is m ² / g.

The invention according to claim 3 is the raw material composition for sintering according to claim 1 or 2, characterized in that the reduced iron powder contains graphite.

According to a fourth aspect of the present invention, the method for producing a sintered product comprises polystyrene 1-2% by weight, acrylic resin 1
˜2% by weight, polyethylene 0.5 to 1% by weight, paraffin 1.5 to 2.5% by weight, stearic acid 0.5 to 1% by weight, and the balance being a reduced iron powder. ,
Injection-molded into a predetermined mold to form a pre-molded body, and then the pre-molded body is heated at a temperature not higher than the melting point of the reduced iron powder to remove the binder, and then the de-binder molded body is sintered. It is characterized by processing.

Further, the invention according to claim 5 is the method for producing a sintered product according to claim 4, wherein the raw material composition for sintering remaining in the spool runner of the mold after the injection molding is reused. It is characterized by doing.

[0014]

Since the invention according to claims 1 to 5 has the above-mentioned structure, it has the following effect.

The raw material composition for sintering according to the first aspect of the present invention comprises polystyrene, acrylic resin, polyethylene, paraffin and stearic acid as binder components,
It is constituted as a kneaded product with reduced iron powder, and an appropriate amount of each binder component is added in order to exhibit the following actions.

That is, polystyrene is 1% by weight or more for securing the strength of the sintered product and maintaining fluidity during injection molding, and for shortening the binder removal processing time during sintering and preventing swelling of the sintered product. 2% by weight or less is added.

As the acrylic resin, it is desirable to use an acrylic acid ester copolymer or a methacrylic acid ester copolymer, which is 1% by weight or more for maintaining fluidity during injection molding.
In addition, 2% by weight or less is added to prevent swelling of the sintered product and to reduce the cost.

As for polyethylene, it is desirable to use low-density polyethylene, which is 0.5% by weight or more for maintaining fluidity during injection molding and preventing separation of a resin component and a wax component, and a binder removal treatment time during sintering. To shorten and prevent swelling of the sintered product, 1.0 wt% or less is added.

Paraffin is added in an amount of 1.5% by weight or more for maintaining fluidity during injection molding and stabilizing viscosity when the raw material is reused, and 2.5% by weight or less for preventing swelling of a sintered product. .

Stearic acid is added in an amount of 0.5% by weight or more for maintaining fluidity during injection molding and for stabilizing viscosity when the raw material is reused, and 1.0% by weight or less for preventing swelling of a sintered product. It

Further, the reduced iron powder is obtained by subjecting iron oxide to heat reduction, pulverization, decarburization purification, and subsequent annealing, and various forms of reduced iron powder can be used.

The invention according to claim 2 has an average particle diameter of 6.0 to 6.0.
11.0 μm, and specific surface area 0.30 to 0.80 m ² /
Since the reduced iron powder of g is used, it is possible to avoid the increase in viscosity at the time of injection molding due to the increase in the specific surface area and the deterioration of the mechanical properties of the sintered product due to the increase in the particle size.

In the invention according to claim 3, since the reduced iron powder contains graphite, the hardness can be improved by quenching.

In the method for producing a sintered product according to a fourth aspect of the present invention, the raw material composition for sintering is injection-molded in a predetermined mold to form a pre-molded body, and then the pre-molded body. Is subjected to binder removal treatment by heating at a temperature below the melting point of the reduced iron powder, and then this binder removal compact can be sintered to obtain a sintered product.

That is, first, reduced iron powder, polystyrene as a binder component, acrylic resin, polyethylene,
Paraffin and stearic acid are mixed in a predetermined ratio,
Using a pressure kneader or the like, the mixture is melt-kneaded at a temperature equal to or higher than the melting point of the binder component, followed by pulverization and granulation steps, and 1-2 wt% polystyrene, 1-2 wt% acrylic resin, 0.5-1 wt% polyethylene. %, Paraffin 1.5-2.
A raw material composition for sintering comprising 5% by weight, 0.5 to 1% by weight of stearic acid and the balance reduced iron powder is obtained.

Next, this sintering raw material composition is subjected to an injection molding machine and injection-molded in a predetermined molding die,
A preform is obtained.

The molding conditions in this injection molding are:
Molding temperature is 150-250 ° C, especially 170-210
C., injection pressure is 200 to 1900 Kg / cm < ² >, especially 550 to 1500 Kg / cm < ² >.

When the molding temperature is 150 ° C. or lower, the viscosity of the binder composition is high, and when the molding temperature is 250 ° C. or higher, the paraffin component evaporates sharply and the viscosity becomes high, which is not preferable.

When the injection pressure is 200 Kg / cm ² or less, it is difficult to obtain the uniformity of the preform, and the pressure is 1900 Kg / c.
If it is m ² or more, the preform may be cracked, which is not preferable.

In order to obtain an injection-molded product having a complicated shape having a hollow portion, a core having a predetermined shape for forming the hollow portion may be arranged in the mold, and the core has an injection molding temperature. It is desirable to use a material such as a thermosetting resin that does not soften, melts at the binder removal processing temperature, and does not react with the material contained in the preform.

The pre-molded body thus injection-molded and separated from the mold is then sent to a binder removal tank for binder removal processing under the conditions of binder removal under a non-oxidizing atmosphere such as nitrogen. In 400 to 800 ° C., particularly 450 to 700 ° C., preferably about 500 ° C., by heating for 10 to 40 hours.

When the binder removal treatment temperature is 400 ° C. or lower, the binder component cannot be completely removed, and when the binder removal treatment temperature is 800 ° C. or higher, the molded product may be nitrided at a high temperature because of the nitrogen atmosphere during the treatment, which is not preferable.

When the binder removal treatment time is 10 hours or less, the binder component cannot be completely removed as in the treatment temperature, and the binder component cannot be completely removed.
When the time is 0 hours or more, there is no problem in the characteristics, but the manufacturing cost increases, which is not preferable.

In this binder removal treatment step, the binder composition contained in the preform and the constituents of the core to be used if necessary are melted and effectively removed from the preform and removed. Although a binder molded body is formed, in the present invention, since the binder composition is defined as described above, the binder removal processing time can be significantly shortened as compared with the conventional case, and the binder removed molded body with less deformation can be obtained. Can be obtained.

In this step of removing the binder, the binder composition obtained by removing the binder composition and the constituent components of the core from the preform is suppressed as much as possible, and further the binder composition and the like are removed. In order to complete the above, it is preferable to perform the binder removal treatment in a state in which the preform is embedded in a binder removal tank filled with activated carbon. In this case, the same procedure can be performed by replacing a part of the activated carbon with alumina powder. You can expect an effect.

Further, it is desirable to cool the binder-removed molded body after the binder removal processing is performed in a non-oxidizing atmosphere as in the above.

The binder-removed molded body thus obtained is then sent to a sintering treatment step, and is subjected to 700 ° C. under a non-oxidizing atmosphere.
~ 1400 ° C, especially 1100 ~ 1300 ° C,
By contracting or sintering for 2 to 15 hours, especially 4 to 10 hours, the raw material powder is melted, the fine voids after the binder removal treatment are filled, and the contracted sintered article has a shape similar to the mold. Becomes

Here, when the sintering temperature is 700 ° C. or lower, the mechanical strength is low because the density does not increase and the sintered product is melted at 1400 ° C. or higher, which is not preferable.

If the sintering treatment time is 2 hours or less, the sintered product will be swollen or cracked, and if the sintering treatment time is 15 hours or more, there will be no problem with the characteristics, but the manufacturing cost will be increased, which is not preferable.

Further, in the invention according to claim 5, after the injection molding, the raw material composition for sintering remaining in the spool runner of the die is reused.

That is, the raw material composition for sintering remains in the spool runner in the mold after injection molding of the preform, but the residual raw material composition for sintering is recovered and crushed, Further, it can be granulated to prepare a recycled material of the raw material composition for sintering. In this recycled material, the binder composition in the sintering raw material composition is specified as described above, so that the flow characteristics during injection molding are almost the same as those of the new material, and the flow characteristics have a small viscosity fluctuation due to the number of times of regeneration. It is stable.

[0042]

EXAMPLES The present invention will be specifically described below based on examples.

First, a raw material composition for firing and sintering (raw material of the present invention) as one example and a raw material composition for sintering (comparative raw material) as a comparative example were subjected to raw material weighing, kneading, pulverization, and granulation. Through the steps, the composition shown in Table 1 was adjusted.

[0044]

[Table 1] The reduced iron powder used at this time contained 0.6% by weight of graphite powder in both the raw material of the present invention and the comparative raw material, and the raw material of the present invention had an average particle size of 9.40 μm and a specific surface area of 0.7.
The particle shape of 5 m ² / g is irregular, and the average particle diameter of the comparative raw material is 7.30 μm and the specific surface area is 0.3.
The particles are substantially spherical particles of 5 m ² / g.

Next, these raw materials have a screw temperature of 180.
Supplied to the injection molding machine set to ℃, injection pressure 1300
Under a condition of Kg / cm ² , it was injected from a nozzle into a mold to form a preform.

Then, the preformed body thus obtained is buried in a binder removal treatment tank filled with activated carbon, and the temperature is gradually raised from room temperature to 700 ° C. over 20 hours in a nitrogen gas atmosphere, The binder composition was held at 700 ° C. until completely vaporized and removed, and then debindered under cooling conditions. At this time, the heat treatment time required for the binder removal treatment was 14.5 hours for the raw material of the present invention and 20 hours for the comparative raw material. It is shortened due to the low content. Moreover, the heat treatment time required for the binder removal treatment using the raw material of the present invention can be greatly shortened as compared with the binder removal treatment (40 hours or more) in the conventional manufacturing method.

Then, the binder-removed molded body was treated with 1 × 10.
Room temperature to 1300 ℃ under non-oxidizing atmosphere below ^-3 Torr
The temperature was gradually raised over 2 hours, the temperature was held at 1300 ° C. for 3 hours, and then cooled to obtain a powder sintered product 1 shown in FIG.

This sintered product 1 is formed in a substantially T-shape with thin portions 3 on both sides of the thick portion 2 in the central portion.

Further, as the raw material composition for sintering, the same steps as described above are carried out by using a recycled material obtained by collecting and regenerating the raw material composition for sintering remaining in the spool runner of the mold after injection molding. After that, a sintered product 1 was obtained. This recycled material is prepared by crushing the raw material composition for sintering recovered from the spool runner and then granulating it. In this embodiment, the recycled material that has been recycled once to four times is used. .

Tables 2 and 3 show the fluidity evaluations of the raw material composition for sintering as a new material which has not been regenerated in the raw material of the present invention and the comparative raw material and the regenerated material once to four times. Table 4 shows the appearance evaluation of the sintered product 1 obtained from each of these raw materials. The fluidity was evaluated by a shear rate at a measurement temperature of 190 ° C. of 9.728 × 10 ³ (sec ⁻¹ ) and 1.946 ×.
The viscosity is shown below 10 ⁴ (sec ⁻¹ ).

[0051]

[Table 2]

[Table 3]

[Table 4] As can be seen from Tables 2 and 3, the raw material of the present invention (Table 2) has a lower viscosity and a higher fluidity than the comparative raw material (Table 3), despite using the reduced iron powder having an irregular particle shape. Since it has properties, it can be applied to reduced iron powder having various particle shapes to secure fluidity suitable for injection molding. Therefore, the raw material of the present invention can use reduced iron powder, which has an irregular particle shape and can be obtained at a low cost, as a molding material, and thus can reduce the cost.

In addition, the recycled material of the raw material of the present invention has substantially the same fluidity at the time of injection molding as the new material (Table 2), and this fluidity is less viscous than the comparative raw material (Table 3) due to the number of regenerations. Since it is small and stable, it is easy to set the molding conditions for the preform. Therefore, the raw material of the present invention can further reduce the cost by using the recycled material, and a sintered product of stable quality can be obtained despite the use of the recycled material (see Table 4).

Further, as can be seen from Table 4, the product of the present invention obtained by using the raw material of the present invention has excellent appearance evaluation and mechanical properties as compared with the comparative product obtained by using the comparative raw material. There is. That is, the sintered product 1 as a comparative product is
Swelling and cracking occur over the entire surface (new material), or swelling and cracking occur in the thick portion 2 (recycled material 1 to 4 times), and these swelling and cracking do not occur The appearance evaluation and mechanical properties are inferior.

Relative density of the product of the present invention (relative density with respect to the blunt iron density of 7.86 g / cm ³ ) and tensile strength (JIS standard No. 4 test piece shape was prepared and measured according to JIS standard. ) Are 98% and 670 MPa, respectively, and the mechanical properties are improved.

[0055]

As described in detail above, the present invention has the following effects.

That is, according to the invention of claim 1,
The raw material composition for sintering was polystyrene 1-2% by weight, acrylic resin 1-2% by weight, polyethylene 0.5-1% by weight, paraffin 1.5-2.5% by weight, stearic acid 0.5-1. Since the composition is such that the weight% and the balance are reduced iron powder, it can be applied to reduced iron powder of various particle shapes to ensure fluidity suitable for injection molding, and heat treatment for binder removal. It is possible to shorten the time and obtain a sintered product with excellent mechanical properties,
As a result, it is possible to provide a raw material composition for sintering which can also reduce the cost.

According to the second aspect of the invention, the average particle size is 6.0 to 11.0 μm, and the specific surface area is 0.30 to 0.8.
Since 0 m ² / g of reduced iron powder is used, it is possible to avoid the increase of the viscosity at the time of injection molding due to the increase of the specific surface area and the deterioration of the mechanical properties of the sintered product due to the increase of the particle size. It is possible to provide a raw material composition for sintering that exhibits the same effect as that of the invention of claim 1.

According to the invention of claim 3, since the reduced iron powder contains graphite, the hardness can be improved by quenching. As a result, in addition to the effect of the invention of claim 1, the machine It is possible to provide a raw material composition for sintering capable of obtaining a sintered product having excellent dynamic characteristics.

According to the invention described in claim 4, the sintering raw material composition is injection-molded in a predetermined mold to form a preformed body, and the preformed body is then made of reduced iron powder. After removing the binder by heating it at a temperature below the melting point, the binder-removed compact was sintered to obtain a sintered product, so it can be applied to reduced iron powder in various shapes for injection molding. Suitable fluidity can be secured, complex shaped sintered products can be easily molded, heat treatment time for binder removal can be shortened, and cost can be reduced, and mechanical It is possible to provide a method for producing a sintered product that can obtain a sintered product with excellent characteristics.

Further, according to the invention of claim 4, after the injection molding, the raw material composition for sintering remaining in the spool runner of the mold is reused. Therefore, the effect of the invention of claim 4 In addition to further cost reduction,
The fluidity of the recycled material composition of the sintering material composition during resin molding is almost the same as that of the new material, and this fluidity is stable with little viscosity fluctuation due to the number of regenerations. It is possible to provide a method for manufacturing a sintered product in which the setting of is easy.

[Brief description of drawings]

FIG. 1 is a perspective view of a sintered product.

[Explanation of symbols]

 1 Sintered product 2 Thick part 3 Thin part

Claims (5)

[Claims] 1. Polystyrene 1-2% by weight, acrylic resin 1-2% by weight, polyethylene 0.5-1% by weight, paraffin 1.5-2.5% by weight, stearic acid 0.5-1.
A raw material composition for sintering, characterized in that the weight percentage and the balance consist of reduced iron powder. 2. The raw material composition for sintering according to claim 1, wherein the reduced iron powder has an average particle diameter of 6.0 to 11.0 μm and a specific surface area of 0.30 to 0.80 m ² / g. A raw material composition for sintering, characterized in that 3. The sintering raw material composition according to claim 1 or 2, wherein the reduced iron powder contains graphite. 4. Polystyrene 1-2% by weight, acrylic resin 1-2% by weight, polyethylene 0.5-1% by weight, paraffin 1.5-2.5% by weight, stearic acid 0.5-1.
A raw material composition for sintering, which is composed by weight% and the balance is reduced iron powder, is injection-molded in a predetermined mold to form a preformed body, and the preformed body is then heated to a temperature not higher than the melting point of the reduced iron powder. A method for producing a sintered product, which comprises subjecting the binder-removed molded body to a sintering treatment after the binder-removing treatment by heating at 1. 5. The method for producing a sintered product according to claim 4, wherein after the injection molding, the sintering raw material composition remaining in the spool runner of the mold is reused. A method of manufacturing a product.