JPH0832410B2 - Method for forming ceramic coil spring - Google Patents

Description

The present invention relates to a method for forming a ceramic coil spring.

[Conventional technology]

Coil springs are used as important parts for various machines. Although such coil springs have been manufactured from metal materials, since metal coil springs are inferior in properties such as heat resistance, corrosion resistance, and wear resistance, in recent years, it has been possible to manufacture ceramic coil springs that can improve these properties. Being tried.

As a method of manufacturing a ceramic coil spring, an organic material imparting moldability to a ceramic powder raw material and a solvent thereof are kneaded, and a coil spring having a desired coil shape is formed using a ceramic wire obtained by extruding the kneaded material. The method of obtaining is performed.

When a coil spring is manufactured by using water as the organic material that imparts moldability and water as the solvent,
The following problems occur.

When the wire contains a large amount of water (a wire having a high water content) The coiling itself is easy, but when wound around a core rod for coiling, the inside (inner diameter) is easily crushed during coiling. In addition, if drying is performed in this state, wire breakage due to drying shrinkage due to evaporation of water and further collapse of the inner diameter of the coil occur. In the case of coiling using a wire rod having a high water content, if the molded body is removed from the core rod immediately after coiling, there is no shape retention and the coil shape is not maintained.

On the contrary, if the water content in the wire is low: reduce the amount of water added when kneading the ceramic extrusion raw material, or dry the extruded wire to reduce the water content, and try to minimize the drying shrinkage after coiling, The wire becomes hard and the subsequent coiling work is difficult, causing wire breakage during coiling. Further, since the coiling state is greatly affected by the atmosphere (temperature, humidity, etc.), the conditions under which coiling is possible are limited. In addition, there is a large variation in shape after drying due to a slight change in the amount of water. Therefore, it is difficult to coil small wires with a wire diameter of 1 mm or less and coil with a small D / d (D: coil average diameter, d: wire diameter). is there.

Therefore, for example, the following method is known as a generally considered method for manufacturing a ceramic coil spring.

The ceramic powder raw material, methyl cellulose, surfactant, polyhydric alcohol and water are kneaded, extruded to obtain a wire, coiled on a core rod, pre-sintered as it is, and then the core rod is removed. Main sintering method
-7659).

In order to improve the above method and obtain a coil spring with an equal pitch, moisture is adjusted in an extruded wire rod whose main raw material is ceramic powder, and a core rod having heat shrinkage characteristics similar to that of the wire rod is held at a distance. A method in which the wire is wound together with a coil material for embedding, embedded in alumina powder for temporary sintering, and the temporarily sintered wire is removed from the core rod and then main sintered (JP-A-62-2501).
No. 3 bulletin).

A block diagram of these methods is shown in FIG. As shown in FIG. 2, in these methods, a kneaded material of raw materials is extrusion-molded to obtain a wire, and then the wire is dried to a predetermined moisture content, generally about 3% or less. The plasticity of the wire is adjusted so that the ceramic coil spring can be molded. Note that a large amount of surfactant and polyhydric alcohol are added so that the plasticity of the wire can be advantageously maintained even after drying (after water content adjustment).

[Problems to be solved by the invention]

 However, the conventional method has the following problems.

In order to obtain a wire that does not cause wire breakage after coiling, delicate control is required for moisture adjustment by drying.

Since the plasticity of the wire can be advantageously maintained even after drying, the shape retention after coiling is poor. Therefore, it is necessary to perform sintering while being wound on a core rod having the same heat shrinkage characteristic as the wire.

Since a core rod having the same heat shrinkage characteristics as the wire rod is used, it is possible to prevent wire breakage and inner deformation of the coil to some extent, but it cannot be reused because it is pre-sintered. The cost required for the core rod increases.

As described above, the conventional method has poor mass productivity from the viewpoint of cost, yield, and the like.

The present invention solves the above problems, and performs coiling of fine lines and D /
Coiling with a small d is possible, it is possible to prevent wire breakage and deformation of the wire rod, and to reduce the shape variation.
An object of the present invention is to provide a method for forming a ceramic coil spring which has mass productivity.

[Means and Actions for Solving Problems]

The method for forming a ceramic coil spring according to the present invention comprises a step of drying an organic material which imparts formability to a ceramic powder and water which is a solvent for the organic material and kneading the mixture to form a wire, and then drying the wire. It is characterized by further comprising a step of immersing the wire rod in a solvent to impart plasticity and improving shape retention after molding and drying, and a step of coiling the wire rod.

In the present invention, the ceramic powder as a raw material may be oxide-based ceramics or non-oxide-based ceramics. Examples of the oxide ceramics include alumina, mullite, partially stabilized zirconia, and the like. Examples of the non-oxide ceramics include silicon nitride, silicon carbide, sialon and the like. When using non-oxide ceramics, the surface of the powder is treated with a silane coupling agent, an aluminum coupling agent, a titanium coupling agent, etc. in order to improve the wettability with water. Is desirable.

In the present invention, the organic material to be added (also generally called a binder) imparts plasticity and shape-retaining property to the molding of a non-plastic material such as ceramic powder, and is decomposed and scattered by sintering to form a sintered body. It has the feature of leaving no residue such as impurities.

Organic materials used include binders, plasticizers, dispersants and the like. It is generally known that these have the following functions.

The binder functions to maintain the strength of the green molded body. If the amount of the binder is too small, the obtained kneaded material becomes brittle, and it becomes difficult to perform extrusion molding or processing into a coil shape. Further, if the blending amount is too large, problems such as difficulty in extrusion molding from a die (nozzle) occur.

The plasticizer has a function of imparting plasticity and flexibility, and imparts good flexibility to the extrusion molding and the wire rod obtained by the extrusion molding. If the blending amount is too small, the viscosity of the kneaded product will be high, and there will be a problem that extrusion will be difficult.If the blending amount is too large, the strength of the kneaded product will decrease and the shape retention of the coil shape will be reduced. It causes problems such as loss of nature.

The dispersant has a function of uniformly dispersing the ceramic powder and the organic material when kneaded and reducing the amount of the organic material solvent added.

In the present invention, a binder that is water-soluble but is difficult to dissolve in the solvent during coiling, such as methyl cellulose, is used. As the plasticizer, a water-soluble one that is easily dissolved in the solvent during coiling (an amphipathic one) is selected. Such plasticizers include
CH ₂ CH ₂ O _n (where n is 1 or more) as the molecular structure
Are preferred, and examples thereof include polyethylene glycol. Also, one or both ends of the polyethylene _{glycol, -OCH 3, -COCH 3, -COOH} , -NH 2, -CN,
It may be substituted with a hydrophilic group such as —NHCONH ₂ . In addition,
n may be 1 or more, but is more preferably 4 or more. As the plasticizer, glycerin or the like may be used. Further, in order to improve the dispersion state of the ceramic powder and the organic material, a polycarboxylic acid salt or the like may be added as a dispersant.

Each of the above raw materials is mixed and kneaded at an appropriate mixing ratio. Each raw material is based on 100 parts by weight of ceramic powder,
Binder 1 to 20 parts by weight (preferably 3 to 10 parts by weight, plasticizer 1 to 25 parts by weight (preferably 5 to 20 parts by weight), dispersant 0 to
The compounding ratio is 10 parts by weight (preferably 0.01 to 3 parts by weight) and an appropriate amount of water. These kneaded products, after being formed into a wire, are dried to a state in which most of the water is removed and the product is sufficiently dried and shrunk. In this state there is not enough plasticity required for coiling. Any method may be used to form the kneaded product into a wire rod, and an appropriate method is, for example, extrusion molding.

In the present invention, the solvent used for imparting plasticity before coiling the dried wire (hereinafter referred to as coiling solvent) easily penetrates between the ceramic powder particles and softens the organic material to improve plasticity. What is given is used. That is, a material is used that softens methyl cellulose, which is a water-soluble binder, but is difficult to dissolve it, and has a function of dissolving a plastic component. Examples of such coiling solvents include alcohols, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, alicyclic hydrocarbons, single solvents selected from the group of chlorinated hydrocarbons, or mixed solvents of two or more types, Alternatively, a mixed solvent of alcohol and a small amount of water may be used. In particular, a mixed solvent of ester, ketone or chlorinated hydrocarbon, a mixed solvent of alcohol and chlorinated hydrocarbon and the like are preferable. Since the organic coiling solvent as described above has a small surface tension and easily enters between the ceramic powder particles from the pores or the like on the surface of the wire, the plasticizing effect is imparted by the plasticizing effect and the softening of the organic material. Is advantageous to. When a mixed solvent is used as the coiling solvent, the softening degree of the organic material (solubility of the binder and plasticizer) can be adjusted by the composition ratio, and the evaporation rate of the solvent during drying can be adjusted. Wider choice.

In the present invention, in order to coil the wire, a core rod of a lathe type coiling machine may be coiled or an automatic coiling machine may be used. In order to continuously form the ceramic coil spring according to the present invention, a solvent tank containing a coiling solvent may be provided in front of the coiling machine, and the dried wire may be immersed in the solvent tank. Further, an extrusion molding machine and a drying furnace for drying the molded wire may be provided in the preceding stage of the solvent tank.

The coil-shaped molded body thus obtained is dried, removed from the core rod, and then debindered and sintered to produce a ceramic coil spring.

In the method of the present invention, when the wire rod which has been dried and shrunk by removing water is immersed in the coiling solvent, the coiling solvent is absorbed between the ceramic powder particles and the organic material from the pores or the like on the surface of the wire rod to coil the wire rod. It gives the required plasticity. After the wire is dried, the coiling solvent elutes the plastic component (polyethylene glycol, etc.),
In addition, the water-soluble binder (methyl cellulose) is only softened by the coiling solvent and is hardly dissolved or swollen, so that good shape retention can be obtained after drying the coiling solvent. Therefore, unlike the conventional case where the water content and the organic material (binder, plasticizer, etc.) contained in the wire give the plasticity necessary for coiling the wire,
A coiling machine can be used like a conventional metal spring, which does not require water content adjustment, has good shape retention, and does not need to be sintered while being wound on a core rod having a heat shrinkage property similar to a wire rod. It has the effect of being mass-producible. Further, coiling of thin wires and coiling with a small D / d are possible, it is possible to prevent wire breakage of wire rods, etc., and it is possible to reduce variations in the shape of the molded body.

〔Example〕

Hereinafter, the method of the present invention will be described in more detail based on examples. In the following examples, each operation was performed according to the steps shown in the block diagram of FIG.

Example 1 The raw materials shown in Table 1 were blended at the blending ratio shown in the same table to prepare the raw materials, which were then kneaded and then extruded using a die having a diameter of 2.9 mm to prepare a wire rod. Dry until shrinkage. Next, the dried wire rod was immersed in the coiling solvent shown in Table 1.

First, FIG. 3 shows the results of examining the drying behavior after the wire was immersed in the coiling solvent for 5 minutes. The increase in weight immediately after the wire rod is taken out in FIG. 3 is due to the coiling solvent absorbed in the wire rod, and thereby the plasticity necessary for coiling is imparted. The decrease in weight of the wire after drying is due to the elution of the plastic component. Since the coiling solvent used is a poor solvent for methylcellulose, which is a water-soluble binder,
Methylcellulose softens but hardly dissolves. From this, the shape retention after drying of the coil-shaped molded body is improved.

Next, the wire rod which had been imparted with plasticity by being immersed in a coiling solvent was coiled on a core rod having a diameter of 25 mm and dried, and then the coil-shaped molded body was removed from the core rod. As for this molded product, there was almost no drying shrinkage after coiling, and there were broken lines,
There was little deformation inside the coil, and there was little variation in shape even when a large number of molded bodies were compared. Next, the coil-shaped molded body was debindered and then sintered in air at 1450 ° C. to manufacture a ceramic coil spring. The ceramic coil spring thus obtained has a wire diameter of 2.2 mm, a coil diameter of 20 mm, an effective winding number of 6, a sintered body density of 6.09 g / cm ³ , and a spring constant k = 0.43 k.
It was gf / mm and shear strength τ = 45 kgf / mm ² (average value).

To compare with this, using the same ingredients as above,
A ceramic coil spring was manufactured by a conventional method of kneading and extruding a wire, adjusting the amount of water in the wire, coiling the core, and then removing the binder and sintering. As a result, the coil-shaped molded body after coiling is dried and shrinks, resulting in the occurrence of line breakage, shape variation, etc.
The yield was about 70% lower than that in Example 1 above. Further, the shear strength of the ceramic coil spring after sintering varied more than in the case of Example 1 due to the variation in shape, and the average value of the shear strength was 42 kgf / mm ² which was slightly small.

Example 2 The raw materials shown in Table 2 were blended at the blending ratio shown in the same table to prepare the raw materials, which were kneaded and then extrusion-molded to produce a wire, which was dried until it was sufficiently dried and shrunk. Next, the dried wire rod was immersed in the coiling solvent shown in Table 2.

First, FIG. 4 shows the results of examining the drying behavior after the wire was immersed in the coiling solvent for 5 minutes. FIG. 4 also shows the same drying behavior as in the case of FIG. 3, and the same discussion as above is possible. It should be noted that the increase in weight immediately after taking out the wire from the coiling solvent is larger in FIG. 4 than in the case of FIG. 3, and the coiling solvent used in Example 2 gives plasticity to the wire. It is advantageous.

Next, the wire rod which has been imparted with plasticity by being immersed in a coiling solvent was coiled on the core rod. In this case, since the wire rod has good plasticity, a coil-shaped molded body having a shape of D / d = 5 could be easily obtained.

To compare with this, using the same ingredients as above,
After kneading and extruding the wire rod, the amount of water in the wire rod was adjusted, and the wire rod was coiled. In this case, when trying to form a coil shape with D / d = 5, line breakage occurred. Therefore, when polyethylene glycol and glycerin, which are plasticizers, were increased more than in the case of Table 2, it was possible to mold into a coil shape with D / d = 5. However, this molded product had poor shape retention when removed from the core rod. Therefore, upon sintering, it was necessary to coil and sinter a core rod having the same heat shrinkage characteristics as the wire rod.

Example 3 The raw materials shown in Table 3 were blended in the blending ratio shown in the same table to prepare the raw materials, which were then kneaded. The silicon nitride powder was surface-treated with a silane coupling agent CH ₃ O (CH ₂ CH ₂ O) nCH ₂ CH ₂ Si (OMe) ₃ (n≈8) to enhance hydrophilicity. Thereafter, a wire rod was produced by extrusion molding using a die having a diameter of 3.1 mm, and the wire rod was dried until it was sufficiently dried and shrunk. Next, the dried wire rod was immersed in a coiling solvent shown in Table 3 to impart plasticity thereto, coiled on a core rod and dried, and then the coil-shaped molded body was removed from the core rod. Next, after removing the binder from the coil-shaped molded body, the temperature was 1850 ° C. in N ₂ gas.
To produce a ceramic coil spring. The ceramic coil spring thus obtained has a wire diameter of 2.2 mm, a coil diameter of 20 mm, an effective winding number of 6, a sintered body density of 3.23 g / cm ³ , a spring constant k = 0.7 kgf / mm, and a shear strength τ = 48 kgf / mm ^2. (Average value).

Example 4 The raw materials shown in Table 4 were blended at the blending ratio shown in the same table to prepare the raw materials, which were then kneaded. The silicon nitride powder was surface-treated with a silane coupling agent CH ₃ O (CH ₂ CH ₂ O) nCH ₂ CH ₂ Si (OM) ₃ (n≈8) to enhance hydrophilicity. Thereafter, a wire having a diameter of 4.76 mm was extrusion-molded to prepare a wire, and the wire was dried until it was sufficiently dried and shrunk. Next, the dried wire rod was immersed in a coiling solvent shown in Table 4 to impart plasticity, and coiled on a core rod.

When coiling a wire with a wire diameter of 4 mm or more,
It is a poor solvent that has a high permeation rate into the wire (small surface tension) and is very difficult to dissolve methylcellulose, which is a water-soluble binder. The coiling solvents of Table 4 were suitable.

Examples 5 to 8 When the ceramic coil springs were molded in the same manner as in Examples 1 to 4 using the raw materials and coiling solvents shown in Tables 5 to 8, the same results as in Examples 1 to 4 were obtained. was gotten.

[Effect of the Invention] According to the method of the present invention, the wire material that has been dried and shrunk by removing water is immersed in a coiling solvent, and the wire material is given the plasticity necessary for coiling by absorbing the coiling solvent. After drying, the coiling solvent elutes plastic components (such as polyethylene glycol) to improve shape retention, and the water-soluble binder (methyl cellulose) is softened by the coiling solvent but hardly dissolves and swells less. It is possible to obtain the effect like.

1. Since the evaporation rate of the coiling solvent from the wire can be adjusted and the plasticity of the wire required for coiling can be maintained, coiling of thin wires and coiling with a small D / d are possible. In this case, the plasticity of the wire can be adjusted by the composition of the coiling solvent and the molecular structure of the plasticizer, and the coiling conditions can be selected according to the spring characteristics.

2. Since the drying shrinkage after coiling is small, it is possible to prevent wire breakage and deformation inside the coil. Moreover, the wire is not required to have a large elongation, the addition amount of the organic material and water as its solvent is smaller than before, and when it is immersed in the coiling solvent, the plastic component is partially eluted, so that it is dried. Even if it is removed from the rear core rod, good shape retention is exhibited, and variation in shape can be reduced. Furthermore, since the addition amount of the organic material may be small, it is possible to form a ceramic coil spring having a high green density, and as a result, it is expected that the density of the sintered body will be improved. Therefore, the yield and the performance of the spring can be significantly improved.

3. It is not necessary to adjust the water content of the wire and it is enough to dry and shrink the wire, so you can work continuously from extrusion of the wire to coiling, and in the same way as a metal spring using a coiling machine. Can be coiled. As a result, work efficiency is significantly improved. It should be noted that it is not necessary to use a core rod for coiling, which has the same heat shrinkage characteristic as that of the wire rod, as in the conventional case. On the contrary, since the dried wire can be stored and coiled at any time as needed, a variety of small quantities of ceramic coil springs can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a method for forming a ceramic coil spring according to an embodiment of the present invention, FIG. 2 is a block diagram showing a method for forming a conventional ceramic coil spring, and FIGS. It is a characteristic view which shows the drying behavior of the wire rod after being immersed in the coiling solvent in and.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toyoyuki Higashi, Toyoyuki Higashi, No. 1 Shinisogo-cho, Isogo-ku, Yokohama, Kanagawa No. 1 in the Town, Central Research Laboratory of the Nissha Group (72) Inventor Ryusuke Adachi No. 1 in Shinisogo-cho, Isogo-ku, Yokohama-shi, Kanagawa Within the Central Research Laboratory of the Nissha Group

Claims (1)

[Claims] 1. A step of drying an organic material which imparts moldability to a ceramic powder and water and kneading the mixture to form a wire, and then drying the wire, and immersing the dried wire in a solvent for plasticity. A method of forming a ceramic coil spring, comprising: a step of applying and a step of coiling the wire.