JPH09201813A - Molding method of green body for sintered parts - Google Patents

Abstract

(57) [Abstract] [Problem] To provide a method for molding a green body that gives the same size to a final sintered part by using either a recycling compound containing molding waste or a virgin compound containing no molding scrap. [Solution] Regarding a compound a composed of fine particles of calcium titanate kneaded by a batch-type pressure kneader and a binder (mixture of synthetic resin and paraffin organic material), a function of plasticizing the binder by having a twin screw 1 with a continuous kneader 10 equipped with or an extruder, pelletizer, injection molding machine with similar plasticizing function
Compounds b, c, ..., e, f, which have been passed more than once
injection molding of the green body G using g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered part for sintering fine particles such as ceramics and metals,
The present invention relates to a method for forming a green body before sintering.

[0002]

2. Description of the Related Art Sintered parts manufactured by sintering fine particles such as ceramics and metals have many uses because they can be mass-produced and precise parts can be supplied at low cost.
Then, for the production, a compound consisting of fine particles of ceramics or metal and wax or synthetic resin as a binder is injection-molded to make a fine particle compact (called a green body). It is carried out by a method of heating to a temperature to remove the binder, and further heating to a high temperature to sinter the fine particles. That is, (1) selection of raw materials, (2) mixing of raw materials, (3)
Green body molding, (4) Binder removal, (5)
Firing for sintering is performed.

Conventionally, a batch type pressure kneader is generally used as a mixing device in the step (2).
The batch type pressure kneader 20 is shown in a vertical section in FIG. 5, and a pneumatic pressure lid 21 presses a predetermined amount of raw material,
Two rotors 22 having two blade-shaped blades rotate in opposite directions in the mixing tank 23 to knead the raw materials, and the degree of kneading is obtained by a kneading time determined in advance. From the relationship with the flow value during heating of the compound, it is controlled by the kneading time until the flow value rises and becomes almost constant.

In actual production, in addition to the above-mentioned fine particles of ceramics and metals and a binder, molding scraps such as sprues and runners generated at the time of injection molding are acceptable in quality for reuse in actual manufacturing. It is added within the range. However, for the final sintered parts that require particularly high dimensional accuracy, the finished dimensions differ between the recycled compound containing molding waste and the virgin compound containing no molding waste, and high dimensional accuracy is required. In order to maintain it, only virgin compound had to be used, and a large amount of molding waste was generated. Of course, by considering the injection molding conditions, binder type, molding scrap addition ratio, etc., it seems possible to use a recycling compound, but this requires a lot of work, so a simple solution is desired. ing.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to use the virgin compound and the recycle compound in the same manner for a sintered part that requires high dimensional accuracy, and therefore, to perform molding. It is an object of the present invention to provide a method for molding a green body for a sintered component, which enables reuse of scraps.

[0006]

The above object is a compound for producing a sintered part made of fine particles of ceramics, metal or the like, comprising the fine particles and a binder having a pour point lower than the sintering temperature of the fine particles. In the method for molding a green body before sintering by using the compound, the compound is used in which the fine particles and the binder are mixed and kneaded once or more with an apparatus having a function of plasticizing the binder. And a method of forming a green body for a sintered part. By this method,
Since the binder is plasticized when kneading the fine particles such as ceramics and metals with the binder, the kneading is sufficiently performed, and the flow value during heating is almost constant regardless of whether it is a virgin compound or a recycle compound. The dimensions of the final sintered part obtained are constant.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A method for molding a green body for a sintered part according to an embodiment of the present invention will be specifically described below.

Mean particle diameter of substantially spherical particles 1 μm
Although the binder can be selected within the range of 1 to 2.5 kg with respect to 10 kg of the calcium titanate fine particles in Example 1, 1.9 kg was used in this example. The composition of calcium titanate is TiO2 (titanium dioxide) 50-60 mol%, CaO
(Calcium oxide) can be selected in the range of 40 to 50 mol%, but in the present embodiment, TiO2 / CaO = 52/48
(Mol ratio), and MgO (magnesium oxide)
2.3wt%, ZrO2 (zirconium oxide) 0.4w
The one to which t% was added was used.

Acrylic resin 1 is used as the binder.
3-32wt%, polystyrene 9-27wt%, stearic acid 2-13wt%, paraffin wax 7-18w
Although it can be selected as a mixture having a composition range of 15% to 58% by weight of vinyl acetate copolymer, 22.2% by weight of acrylic resin, 17.8% by weight of polystyrene, 6.7% by weight of stearic acid, and 13.2% of paraffin wax in this embodiment. 3 wt
%, Vinyl acetate copolymer 40 wt%.

A compound obtained by thoroughly kneading the above-mentioned fine particles of calcium titanate and a binder with a batch-type pressure kneader 20 for a predetermined period of time has a diameter of 3 mm by a pelletizer.
The virgin compound made into pellets is called compound a, and it has two screws for it.
A compound with different kneading degree was sampled three times through a continuous kneader (manufactured by Toshiba Kikai) equipped with the function of plasticizing the binder, and injection molding was repeated twice, and the number of recycles collected each time Different compounds,
Various compounds shown in Table 1 were prepared, and the flow value during heating was measured for these compounds.

[0011]

[Table 1]

The continuous kneading machine has a partially omitted transverse sectional view of FIG. 4A and [B] -in FIG. 4A.
[B] Referring to FIG. 4B showing the cross section in the direction of the line, the main part of the continuous kneading machine 10 is provided with two screws 12 arranged side by side in the barrel 11, and the respective peaks and troughs are meshed with each other. The drive unit 13 at the base causes both shafts to rotate coaxially. By changing the gears, they can rotate in opposite directions. Then, the compound a is introduced from above into the supply unit 14 shown by the alternate long and short dash line on the root side, and while being kneaded, is sent to the left in A of FIG.
It is adapted to be extruded like a string from the die 15 at the tip. The kneading conditions of the continuous kneader 10 were a screw rotation speed of 60 rpm and a cylinder temperature of 100 ° C., and the amount of the compound a was adjusted so that the torque of the screw 12 was 45% of the full scale of the instrument. The injection molding was carried out at a compound temperature of 170 ° C., which will be described later in detail.

Table 2 shows the measurement results of the flow value of each compound of Table 1. The flow value was measured with a Shimadzu flow tester CFT500. Measuring conditions are: plunger area 1 cm2, die length 2 mm, die diameter 1 mm,
Load 20 kg, heat time 300 sec. And 14
It measured at 0 degreeC, 150 degreeC, 160 degreeC, 170 degreeC. In particular, at 150 ° C., the average value was obtained by measuring three times in order to see the tendency of variation, and a value 3 times as large as the standard deviation of the population, 3σ (n-1) was shown. Further, the relationship between the temperature and the flow value, that is, the flow characteristic, for each compound in Table 2 is shown in FIG.

[0014]

[Table 2]

Next, for each of the compounds e, f, and g shown in Table 1, ten green bodies G shown in the perspective view of FIG. 2 were molded by an injection molding machine. As shown in FIG. 2, the green body G comprises a leg 1 and a flat plate 2 having an opening 3 and a protrusion 4
have. The injection molding is equipped with a uniaxial screw kneading part. Injection molding conditions are VP switching position 9
mm, mold temperature 24 ° C., compound temperature 170 ° C., injection speed 40%, injection pressure 30%, holding pressure after injection 30%. All percentages are for the full scale of the instrument. Then, the mixture was placed in a binder removal furnace, heated to 500 ° C. at a binder removal rate of 20 ° C./Hour, held for 1 hour, and then naturally cooled. Then, it was put into a firing furnace, heated to 1300 ° C. at a firing rate of 120 ° C./Hour, and then naturally cooled. The sintered component S obtained in this manner is wholly contracted from the green body G, but FIG. 3A is a plan view of the sintered component S, and FIG. 3B is a rear view of the same. The parts corresponding to the respective parts shown in 2 are denoted by the same reference numerals with ('). The dimension measurement points 1., 2., 3., 4. and 5. shown in A of FIG. 3 and B of FIG.
Table 3 shows the average value of the results of measurement with a 0-times optical microscope and 3 times the standard deviation 3σn of the samples.

[0016]

[Table 3]

The mold used for the above-mentioned injection molding is for examination, and since it is made of a material that easily wears out, it is currently in a state where measurement error is likely to occur, but the dimension measurement point 3 has an edge. Since it was confirmed that it was easy to see and had no errors, the evaluation was mainly performed on the dimension-side fixed points 3. The other dimension-side fixed points were used as reference data.

From the results shown in Table 2 and FIG. 1, the compound a, which has been sufficiently kneaded by the batch type pressure kneader 20 for a predetermined time, is also kneaded by the continuous type kneading machine 10 to greatly increase the flow value like the compound b. Fluidity is increased by the continuous kneading machine 10, and then the compound e, d, the compound e through the pelletizer, the compound e through the injection molding machine, and the compounds f, g through the injection molding machine. Eventually, as shown in the flow value of h, it becomes a constant value or slightly decreases, but Table 3
As shown in (3), as the flow approaches a certain value, the standard deviation of the dimension, 3σn, decreases, and the variation in the dimension decreases. This means that the entire surface of the fine powder of calcium titanate is substantially covered with the binder by the kneading for plasticizing the binder, and the dimensional accuracy of the sintered part S is improved regardless of the virgin compound or the recycling compound. , It indicates that there is no problem in dimensional accuracy even if the molding waste is recycled.

Further, the flow value of the compound b kneaded once by the continuous kneading machine 10 is more than doubled as compared with the flow value of the compound a sufficiently kneaded by the batch type pressure kneader 20 for a predetermined time. The continuous kneader 10 applies a large shearing force to the binder by the twin screw 12 and its barrel 11 to plasticize and knead the binder, whereas the rotor 22 of the batch type pressure kneader 20 does not have sufficient shearing force, and the fine particles are fine particles. It is understood that the kneading in which the entire surface of the above is covered with the binder is not achieved.

Furthermore, when kneading with a batch-type pressure kneader 20, a virgin compound and a recycle
The reason why the final sintered part S has a dimensional difference due to the compound is that since the batch type pressure kneader 20 does not perform complete kneading, the virgin compound and the injection molding machine having the kneading part are passed through once. The kneading degree was different from that of the recycling compound to which scraps were added, and it is considered that they were injection-molded as they were.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made based on the technical idea of the present invention.

For example, in the embodiment of the present invention, the compound a in which the fine particles of calcium titanate and the binder are kneaded in the batch type pressure kneader 20 for a predetermined time, that is, the compound a preliminarily kneaded has a function of plasticizing the binder. Kneading was carried out with the continuous kneader 10 provided,
Instead of passing through the batch type pressure kneader 20, the pressure may be directly supplied to the continuous kneading machine 10.

Further, in the embodiment of the present invention, the continuous kneading machine 10 having the two screws which rotate in opposite directions is used as the device having the function of plasticizing the binder, but it rotates in the same direction. A twin screw may be used, or a continuous kneader having a single screw may be used. In addition, the same kneading effect can be obtained by passing the material through an extruder, a pelletizer, or an injection molding machine equipped with a kneading part using a twin screw or a single screw once or more, even if it is not a kneading machine.

Further, in the embodiment of the present invention, calcium titanate is used for the fine particles, and the mixture of the limited synthetic resin and the paraffinic organic material is also used for the fine particles, but the fine particles can be sintered. As long as it is, the material may be a metal other than ceramics, or the like, and the binder can also be formed into a green body,
In addition, the type is not limited as long as it can be removed from the binder.

[0025]

As described above, according to the method for molding a green body for a sintered part of the present invention, since the fine particles and the binder are sufficiently kneaded, it is a virgin compound or a recycle compound. It is possible to maintain high dimensional accuracy of the final sintered part regardless. Therefore, the molding waste can be reused without being discharged to the outside, and the raw material cost of the sintered part is significantly reduced.

Further, since the fine particles are almost completely covered with the binder, even if the fine particles have a high hardness, the abrasion due to the direct contact of the fine particles with the mold is reduced, and the length of the injection molding mold is reduced. Life expectancy is expected.

Furthermore, since the continuous kneader requires several minutes for one pass, which is much shorter than that of the batch type kneader, the production efficiency is greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing flow characteristics of compounds having different kneading degrees.

FIG. 2 is a perspective view of a green body injection-molded in the first embodiment.

FIG. 3A is a plan view of a sintered component obtained by firing a green body, and B is a rear view of the same.

FIG. 4A is a partially omitted transverse sectional view of a continuous kneading machine,
B is a cross-sectional view taken along the line [B]-[B] in A.

FIG. 5 is a vertical sectional view of a batch type pressure kneader.

[Explanation of symbols]

10 ... Continuous kneader with twin screw, 12 ...
… Screw, 13… Driving part, 20… Batch type pressure kneader, G… Green body, S… Sintered parts.

Claims (4)

[Claims] 1. A green body before sintering is molded by a compound comprising fine particles and a binder having a pour point lower than the sintering temperature of the fine particles for producing a sintered part made of fine particles such as ceramics and metals. Forming a green body for a sintered part, characterized in that the compound is used in which the fine particles and the binder are mixed, and the compound is kneaded once or more with an apparatus having a function of plasticizing the binder. Method. 2. The method for molding a green body for a sintered component according to claim 1, wherein the fine particles and the binder are preliminarily mixed and preliminarily kneaded and then kneaded by an apparatus having a function of plasticizing the binder. 3. The apparatus according to claim 1, wherein the apparatus having a function of plasticizing the binder is a continuous kneader having a twin screw or a single screw, an extruder, a pelletizer, or an injection molding machine. Method for forming green body for sintered parts of. 4. The method for molding a green body for a sintered part according to claim 1, wherein the binder contains at least a synthetic resin and a paraffinic organic material.