JP2558748B2 - 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 molded from metal materials, metal coil springs are inferior in properties such as heat resistance, corrosion resistance, and wear resistance, so in recent years, it has been possible to manufacture ceramic coil springs that can improve these properties. Being tried.

As a method for manufacturing a ceramic coil spring, a coil spring having a desired coil shape is obtained by using a ceramic wire rod obtained by kneading an organic material which imparts formability to a ceramic powder raw material and a solvent thereof and extruding the kneaded product. Is being done.

When a water-soluble organic material that imparts moldability is used to manufacture a coil spring using 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, variation in the shape after drying is large due to a slight change in the amount of water. Therefore, it is difficult to coil a fine wire having a wire diameter of 1 mm or less and a coil having a small D / d (D: average coil diameter, d: wire diameter).

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 publication).

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-62-250).
No. 13).

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-mentioned problems, and particularly when the wire diameter of the wire is large, it is possible to prevent wire breakage, deformation, etc. of the wire, and to reduce the variation in shape. The purpose is to provide.

[Means and actions for solving the problems]

A method of molding a ceramic coil spring according to the present invention comprises a ceramic powder, a first and a second binder having different solubilities, a plasticizer, and a first binder which dissolves the first binder.
And kneading the solvent to form a wire, then drying the wire, immersing the wire in a second solvent that dissolves the second binder to impart plasticity, and coiling the wire. And a process.

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 non-oxide ceramics are used, the surface treatment may be performed with a silane coupling agent, an aluminum coupling agent, a titanium coupling agent or the like in order to improve the wettability.

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 compact, the plasticizer functions to impart plasticity and flexibility, and the dispersant controls the uniform dispersion when the ceramic powder and the organic material are kneaded and the amount of the organic material solvent added. Has a function to reduce.

In the present invention, the first binder is a water-soluble binder,
A combination in which the first solvent is water, for example, methyl cellulose and the like, and the second binder is a binder that dissolves in an organic solvent, such as polyvinyl butyral, polyacrylic acid ester, polymethacrylic acid ester, and the second solvent is organic solvent. Can be considered. As the plasticizer, those having solubility in both water and organic solvent, that is, amphipathic ones are preferable, and examples thereof include polyethylene glycol, and one or both ends of polyethylene glycol are substituted with various hydrophilic groups. It may be one. Further, a polycarboxylic acid salt or the like may be added as a dispersant.

In the method of the present invention, when the wire material that has been dried and shrunk by removing the first solvent (for example, water) is immersed in the second solvent, the second binder in the wire material absorbs the second solvent, and the coiling is performed. It gives the required plasticity. And, after the wire is dried, shape retention is obtained. Therefore, even with a wire material having a large wire diameter, coiling can be performed in a short time without causing wire breakage or deformation inside the coil, and shape variation can be extremely reduced. Further, the wire rod can be stored and optionally coiled as necessary, which is suitable for high-mix low-volume production.

〔Example〕

Hereinafter, the method of the present invention will be described in more detail based on examples.

Example 1 A ceramic coil spring was manufactured as follows according to the method shown in FIG. First, the raw materials (other than polyvinyl butyral) shown in Table 1 were mixed and adjusted at the compounding ratio shown in the same table, and further 3 parts by weight of fine particles of polyvinyl butyral were added and kneaded to uniformly disperse. Next, this raw material was extruded to prepare a wire rod, and this wire rod was dried until it was sufficiently dried and shrunk to obtain a wire rod having a wire diameter of 5 mm. Subsequently, the dried wire rod was immersed in trichlorethylene. In this case, since the wire diameter of the wire is as large as 5 mm, ultrasonic waves may be applied to accelerate the dissolution of polyvinyl butyral. At this time, when the added polyvinyl butyral had a large particle size, the wire swelled, but when the polyvinyl butyral had a small particle size, the wire did not swell. The wire rod thus imparted with plasticity was coiled around the core rod. When dried after coiling, the coil-shaped molded product had sufficient shape retention. After that, remove from the core rod, remove the binder, sinter in air at 1450 ° C, wire diameter 3.8mm, coil diameter 25m
A ceramic coil spring with m and 5 effective turns was manufactured. The properties of the resulting ceramic coil spring, sintered density d = 6.09g / cm ^2, the spring constant k = 2.40kgf / mm ^2, was shear strength τ = 46kgf / mm ² (average value).

Example 2 A ceramic coil having a wire diameter of 3.0 mm, a coil diameter of 20 mm, and an effective number of turns of 6 in the same manner as in Example 1 except that polymethacrylic acid ester was used as the second binder as shown in Table 2. The spring could be manufactured. The characteristics of the obtained ceramic coil spring are as follows: Density of sintered body d = 6.09g / c
m ² , spring constant k = 1.52 kgf / mm ² , shear strength τ = 39 kgf / m
It was m ² (average value).

Example 3 A coil-shaped formed body was obtained in the same manner as in Example 1 except that the raw materials shown in Table 3 were used. By sintering at 1850 ° C. in N ₂ gas, a wire diameter of 3.8 mm, A ceramic coil spring with a coil diameter of 30 mm and an effective winding number of 5 could be manufactured. The characteristics of the obtained ceramic coil spring were a sintered body density d = 3.23 g / cm ² , a spring constant k = 1.93 kgf / mm ² , and a shear strength τ = 43 kgf / mm ² (average value).

[Advantages of the Invention] According to the method of the present invention, it is possible to obtain a ceramic coil spring that can perform coiling in a short time without causing wire breakage or deformation inside the coil even with a wire having a large wire diameter, and that has a very small shape variation. it can. Also, store the wire rod,
Since it can be coiled arbitrarily, it is suitable for high-mix low-volume production.

[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, and FIG. 2 is a block diagram showing a method for forming a conventional ceramic coil spring.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideshi Umura, No. 1 Shinisogo-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Central Research Institute, Nikka Group (72) Ryusuke Adachi 1 Isogo-cho, Isogo-ku, Yokohama-shi, Kanagawa Address: Central Research Institute of Nikka Group

Claims (2)

(57) [Claims] 1. A wire rod is formed by kneading a ceramic powder, a first binder and a second binder having different solubilities, a plasticizer, and a first solvent dissolving the first binder, and molding the wire. A ceramic coil, comprising: a step of drying, a step of imparting plasticity by immersing the wire in a second solvent that dissolves the second binder, and a step of coiling the wire. Spring forming method. 2. The first binder is a water-soluble binder, the first solvent is water, the second binder is a binder soluble in an organic solvent, and the second solvent is an organic solvent. A method of forming a ceramic coil spring according to claim 1.