JPH04323305A - Production of iron-based large-sized sintered member - Google Patents

Abstract

PURPOSE:To stably produce an iron-based large-sized sintered member without cracking and deformation by providing a relaxation region consisting of a deformation absorbing material on the side face of a forming die, packing an iron-based powder into the region by vibration, sintering the powder and impregnating the sintered body with a copper-based impregnant. CONSTITUTION:An iron-based powder is packed into a heat-resistant forming die 1 by vibration to form a packed bed 2, the relaxation regions 3 and 4 of a deformation absorbing material are placed between the side face of the die 1 and the side face of the bed 2. The bed 2 and the die 1 are heated in a nonoxidizing atmosphere to sinter the powder. The sintered body is then impregnated with a copper-based impregnant to increase the strength of the sintered body. According to this constitution, the difference between the expansion and contraction of the die 1 and the sintered body is absorbed by the regions 3 and 4, hence the die 1 and sintered body are not cracked or deformed, and this powder metallurgical product being an iron-based large-sized sintered member is produced at a high yield.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing large sintered members such as molds, and more particularly to a method for preventing cracks in sintered members.

0002

2. Description of the Related Art Large sintered members such as molds are manufactured by applying powder metallurgy. The present inventors have demonstrated that this method allows production of complex-shaped parts in a short period of time.
JP-A-1-165704 and JP-A-1-1657
It was disclosed in Publication No. 06. These methods involve filling a mold with iron-based powder without pressure and sintering it together with the mold to obtain a large component. This method uses infiltration material to fill the voids.

[0003] At this time, a ceramic material is usually used as the mold. The iron-based powder filled inside the mold is usually vibrated to increase the packing density, and then heated and sintered together with the mold. At that time, according to the method disclosed by the present inventors in Japanese Patent Application Laid-Open No. 2-270932 and Japanese Patent Application No. 1-150383, cracks caused by sintering shrinkage caused by the iron powder filled layer being restrained by the ceramic mold. The occurrence can be effectively prevented.

[0004] However, as sintered members become larger, deformation and cracking of molds and sintered bodies due to increases in the absolute values of expansion and contraction during sintering and infiltration have become a problem. In other words, when the size is increased, stress is generated on the ceramic mold due to thermal expansion and contraction of the iron-based powder packed bed due to heating, causing cracks and rough deformation of the mold, resulting in cracks and deformation of the sintered body. A problem arose in that defects occurred and the product yield significantly decreased.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a technique for stably manufacturing large-sized sintered members using iron-based powder. without using special equipment,
By using conventional general atmosphere furnaces and vacuum furnaces,
The purpose is to reduce cracking and deformation of molds and sintered bodies during heating without increasing costs, and to prevent a decrease in product yield.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention vibrates and fills iron-based powder into a mold, heats and sinters it together with the mold, and then injects copper-based infiltration material into the mold. The method for producing a powder metallurgy product by infiltration is characterized in that a relaxation zone using a deformation absorbing material is interposed between the side surface of the mold and the side surface of the iron-based powder packed bed.

[0007]

[Function] The present invention prevents deformation and cracking of a molded product obtained by filling a mold with iron-based powder using the above-described structure. The iron-based raw material powder used in the present invention is basically not subject to any limitations. However, in order to make the effects described later more effective, the expansion due to heating and the sintering contraction must be ±3 based on the standard of the filled compact.
．． A raw material powder with low expansion and contraction within 0% is desirable. This is because the above-mentioned problems mainly occur in the characteristic range of the powder. ±3.0 based on filled molded body
In order to obtain a raw material powder with low shrinkage and low expansion within %, the particle size structure, particle shape, etc. may be selected. It is also possible to add and mix powdered lubricants and graphite powder.

[0008] The above iron-based powder is filled into a mold prepared in advance. The mold may be any mold as long as it does not cause a significant reaction with the powder and does not impair the transfer of the mold. Usually, a ceramic mold is used. The shape of the mold is such that the sintered body can function as a mold or the like after the sintering process, either as it is or without significant processing. The production method may be by machining, or by the production method of ceramic molds used in precision casting.In short, any production method may be used as long as the roughness of the transfer surface is small and the material is strong. .

Prior to filling the raw material powder, relaxation zones are provided on the sides of the ceramic mold. Generally, heat-resistant ceramic molds have smaller expansion and contraction than iron's thermal expansion and sintering contraction, so in ceramic molds filled with iron-based powder, there is a dimensional difference between the iron-based powder filled layer and the ceramic mold. Various defects such as deformation and cracking are likely to occur. When the shape becomes larger, the stress generated in the ceramic or iron-based powder filling layer increases because the absolute value of the difference increases, and the problem becomes more obvious. The relaxation zone relieves stress on the mold caused by expansion and contraction of these iron-based powders, and has the effect of preventing cracking or deformation of the mold and cracking of the sintered body during heating.

FIG. 1 shows a cavity type ceramic mold 1. As shown in FIG. (a) is a longitudinal sectional view, and (b) is a plan view. Relaxation zones 3 and 4 are provided in the packed bed 2 of iron-based powder. The relaxation zone 3 shown in FIG. 1 relieves the stress on the mold that occurs when the iron powder expands, thereby preventing deformation and cracking of the mold. On the other hand, the relaxation zone 4 relieves the stress generated in the iron-based powder due to contraction, thereby suppressing cracks and deformation occurring in the sintered body. The relaxation material maintains the relaxation region up to the temperature T1 at which the shape retention effect of the molded body occurs, and
Any material may be used as long as the relaxation material itself has the ability to absorb the expansion/contraction force of the powder. It may be one that self-combusts at a temperature T1 or higher. For example, a heat-resistant ceramic fiberboard (for example, Kao Wool (manufactured by Isolite Industries)) may be used, and paper or the like is effective as a self-combusting material. Those that do not cause excessive reaction with the sintered body during sintering infiltration, which will be described later, or those that have coarse pores due to generated gas, etc.
Any material that does not cause obvious defects in use as a product may be used. The temperature T1 varies depending on the type of iron-based powder used, but is usually about 600°C. Although these materials can be attached to the side surface of the mold after the mold is manufactured to form the relaxation region, it is of course also possible to manufacture the relaxation region by integrating the material at the time of manufacturing the mold. The thickness t of the relaxation material depends on the physical properties of the ceramic mold used, such as high-temperature strength, coefficient of thermal expansion, ceramic sintering shrinkage, and the composition of the iron-based powder.
Although it cannot be determined unconditionally because it largely depends on the density of the filling layer and the shape to be transferred, one method for determining the thickness t is preferably a range that satisfies the following relationship.

t≦{(L1×ΔL1/100)−(L2×
ΔL2 /100)} However, L1: Dimensions of the filling area (long side) L2: Dimensions inside the ceramic mold (long side) ΔL1: Coefficient of thermal expansion between T1 and T2 of the iron-based filled layer (%) ΔL2: T1 of the ceramic -T2 Coefficient of thermal expansion (%) T2: Temperature during sintering and infiltration When using a relaxing material that remains after sintering, such as ceramic fiberboard, the upper limit of the thickness t is It is sufficient that the difference in thermal expansion between the iron-based packed layer and the ceramic is within the temperature range from the temperature at which shape retention is achieved to the time of sintering and infiltration.

[0012] Filling is carried out in a dry manner, and the packing density can be improved by adding vibration. The method of vibration may be any method such as electromagnetic vibration or mechanical vibration. Further, by applying extremely lower pressure during vibration than in conventional pressure molding methods, filling properties can be further improved. This pressure may normally be 1 kg/cm2 or less, and the pressure not only improves the filling property but also has the advantage of improving the transferability of the edge portion of the mold. By using such a filling method, large-sized products can be formed inexpensively and easily without using expensive presses used in normal powder metallurgy, so injection molding molds as large as 1 m x 1 m can be formed. It is very suitable for mold manufacturing.

Next, the mold filled with powder is placed in a furnace and heated to perform sintering. Heating and sintering in a reducing atmosphere,
Sintering is performed in an inert atmosphere or in a vacuum, and the mold is removed after sintering. The obtained sintered body alone does not have sufficient strength as a mold, so the pores remaining in the sintered body are removed by, for example, F.
e: 3.9%, Mn: 2.8%, Zn: 2.0%, Al
: 0.06%, Si: 0.6%, Cu: balance (product name: FIPA-3 (manufactured by Fukuda Metal Foil Powder)) and Fe: 4.3%
, Cr: 4.9%, Zn: 2%, and Cu: the balance is infiltrated to increase the strength. Infiltration can be carried out in a reducing atmosphere, inert atmosphere or vacuum.

Note that even if the sintering and infiltration steps are performed in one step, that is, in one heat cycle, the effect obtained remains the same. By using one step, there is an advantage that the manufacturing process can be shortened. As described above, the present invention solves the problems of cracking and deformation without increasing costs by using conventional general atmosphere furnaces and vacuum furnaces without using special equipment, and enables large-scale firing using iron-based powder. A technique for stably manufacturing a connecting member can be provided.

[0015]

[Example] Examples will be described below. As iron-based powder, the average particle size is 490 μm (particle size range 250 μm to 1000 μm).
48% by weight of atomized pure iron powder (μm), average particle size 66
40% by weight of atomized pure iron powder of μm (particle size range 15 to 150 μm), average particle size 4.8 μm (particle size range 10 μm)
A mixed powder was used in which 12% by weight of carbonyl iron powder (below) was mixed in a V-type mixer to adjust the particle size structure. The filling rate of the mixed powder was 75%, and the dimensional shrinkage after sintering and infiltration was 1.0% based on the packed bed.

[0016] A mold for filling was manufactured by a method using a precision casting mold manufacturing method in which silicone rubber transferred from a wooden mold was further transferred using a ceramic slurry. The structure of the mold was a commonly used backup type. The backup material used was a molding material with a particle size structure of mullite and chamotte mixed with water glass, molded, and solidified with CO2. Two types of molds were manufactured: a cavity type and a core type. The shape of the mold is external dimensions 1300mm (vertical) x 900mm (horizontal) x 550m.
m (height) and the filled part is 1100 mm (vertical) 600 mm (horizontal) x 260 mm. An 8 mm ceramic fiber board (product name: Kao Wool (manufactured by Isolite Industries)) was attached to the sides of the cavity mold and the core mold to form a relaxation area. As comparison materials, molds without ceramic fiberboard attached were prepared.

These molds were filled with the above-mentioned mixed iron powder by vibration, and a Cu infiltration material (Cu-Mn-Fe system) was placed on the top of the packed bed.
was placed in a furnace together with a ceramic mold and heated in a nitrogen gas atmosphere at a temperature of 1010°C for 70 minutes to sinter the packed bed, and then heated to 1130°C over 5 hours.
The temperature was raised to melt the infiltrant material and infiltration proceeded. 113
The holding time at 0°C was 100 minutes, and then the furnace was cooled.

After cooling, cracks and deformation of the ceramic mold before it was removed from the ceramic mold and cracks and deformation of the infiltrated sintered body after it was removed were visually observed. Table 1 summarizes cracking and deformation. From this, it was found that by providing a relaxation zone, a large sintered member without cracking or deformation could be obtained. In the above embodiment, a case was explained in which a ceramic fiber board was used as the relaxation material, but the present invention is not limited to this, and the same effect can be obtained by using paper, hollow ceramic fiber board, etc. as the deformation absorbing material in the relaxation area. It is.

[0019]

[Table 1]

[0020]

[Effects of the Invention] The present invention prevents cracking and deformation by providing a relaxation zone between the mold side surface and the iron powder filled layer to relieve stress caused by expansion and contraction during sintering, and reduces product yield due to cracking and deformation. It has become possible to prevent In addition, by using conventional general atmosphere furnaces and vacuum furnaces without using special equipment, it has become possible to stably manufacture large sintered parts at low cost.

[Brief explanation of drawings]

FIG. 1 shows the mold of the example, and (a) of the cavity mold.
They are a vertical sectional view and (b) a plan view.

FIG. 2 is a longitudinal cross-sectional view of a core mold of another embodiment.

[Explanation of symbols]

1 Molding mold 2　Filled bed 3, 4, 5 Relaxation area

Claims (1)

[Claims] Claim 1: In a manufacturing method for producing a powder metallurgy product by vibratingly filling a mold with iron-based powder, heating and sintering it together with the mold, and then infiltrating it with a copper-based infiltrant, the side surface of the mold is A method for manufacturing a large iron-based sintered member, characterized in that a relaxation region using a deformation absorbing material is interposed between the side surface of the iron-based powder-filled bed and the side surface of the iron-based powder packed bed.