JPS5926653B2 - How to form cemented carbide - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for compacting cemented carbide powder.

The normal manufacturing process for cemented carbide consists of mixing metal carbide powder as a raw material and metal powder as its binder phase, adding a binder to the mixed powder and molding it using a hydraulic press, etc. It consists of a process of heating and sintering it in a vacuum furnace or the like.

In general, in powder metallurgy, it is desirable to mold cemented carbide, which is particularly hard and difficult to machine, into a shape as close as possible to the product.

However, the forming methods conventionally applied to the production of cemented carbide generally include uniaxial molding, hydrostatic molding, and extrusion molding, but these methods produce products with hollow or complex uneven shapes, such as type. It is extremely difficult to mold the material into a precise shape like the mother mold, and usually requires machining at a relatively high processing cost after intermediate sintering or after sintering.

Furthermore, cemented carbide is generally compression molded by mixing a few percent of paraffin, camphor, etc. into the powder as a molding binder, but these are used to prevent cracks and deformation after molding due to uneven pressure, etc. Yes, it is removed by evaporation during intermediate sintering.

However, since the binder phase metal of cemented carbide is liquid-phase sintered, in which it melts and liquefies during sintering, the required shrinkage rate from molding to sintering is low, which reduces the molding accuracy of the product. I'm letting you do it.

Furthermore, in the case of extrusion molding, grease, paraffin,
Since a large amount of resin etc. is added, the shrinkage rate increases further.

The present invention provides a molding method that can obtain a high-density green compact having a shrinkage rate as small as that of powder embossing, and that can be molded into complex shapes such as hollows using injection molds and flow molds. It is.

To explain the present invention in more detail, a carbide powder such as tungsten carbide and a metal powder such as cobalt are mixed at a mixing ratio of a normal cemented carbide, and this cemented carbide mixed powder is added with a polycarbonate powder based on the total weight of the powder. Vinyl butyl alcohol resin 2
% to 5% (same as below weight %), 2% to 5% of alkyl phthalate ester such as dibutyl phthalate or dioctyl phthalate, and 1% to 5% of stearic acid, and to this, butyl alcohol, trichlene , a resin consisting of an azeotropic solution of ethylene tetrachloride is added, and if necessary, a nonflammable or fire extinguishing solvent is added, and the mixture is thoroughly mixed using a sieve machine, a ball mill, etc.

After dispersing the powder in this way, it is dried to remove the solvent,
This material is used as a raw material to be molded using a matrix such as injection molding, flow molding, or extrusion molding.

Such a raw material has precise formability with respect to the matrix and also has a sintering shrinkage rate of 17% to 19%.

In the binder used in the molding according to the present invention, polyvinyl butyl alcohol resin (PUB) gives fluidity to the powder when heated, and is used as a binder to maintain the shape after molding. It decomposes inside the tank, and leaves as little decomposition residue as possible.

If the amount of PUB is less than 2%, the molded product will not have practical strength, and if it is more than 5%, the pores of the final product will increase, so 2 to 5% is appropriate.

In addition, plasticizers made of alkyl phthalate esters such as DBP or dioctyl phthalate function as plasticizers similar to those used in plastic molding, increasing fluidity during molding, and increasing the fluidity of polyvinyl butyl phthalate. It has the effect of lowering the softening point of alcohol resin.

Furthermore, this alkyl phthalate ester vaporizes and decomposes in a hydrogen stream during intermediate sintering at a temperature lower than that of the resin, and the minute pores created thereby facilitate the decomposition and removal of the resin.

If the amount of the alkyl phthalate ester is less than 1%, there will be no effect, and if it is more than 4%, the molded product will be easily deformed and the dimensional accuracy will deteriorate, so the appropriate amount is 1 to 4%.

Furthermore, stearic acid has excellent mold release properties and evaporates easily at low temperatures during intermediate sintering, so it has the function of promoting decomposition of the binder.

If the amount of stearic acid is less than 1%, it will not be effective.
Moreover, if it is 5% or more, undecomposed carbon will be produced in the product due to lack of oxygen, so 1 to 5% is the appropriate amount.

Resins such as butyl alcohol, tricrene, and ethylene tetrachloride are used as solvents to dissolve the above-mentioned solid PUB and stearic acid, and the viscosity of the molded product may vary depending on the amount. Since the amount changes, the amount should be adjusted so that the viscosity of the molded product has an accuracy of 100 centipoise.

Among the raw materials used in conventional extrusion molding,
Since the binder used to give the powder fluidity is mixed in a large amount, there is a large amount of decomposition residue, which has the disadvantage of affecting the carbon value of the cemented carbide.

However, the molded binder used in the present invention decomposes and removes in a relatively shorter time than conventional binders used for the same type of raw materials, and the binder is removed by the minute pores that are created after the stearic acid and phthalate esters decompose and escape. The decomposition of the decomposition and the removal of the resulting gas become easier, and no swelling or cracking occurs due to the decomposed gas being trapped.

Furthermore, the molded product formed by the method of the present invention has high strength and can be fixed to a chuck using a lathe or the like and processed, and has an extremely wide range of applications.

Three examples of the molding method of the present invention are shown below in Table 1, and the appropriate blending amount and shrinkage rate from the time of molding when sintered are shown together with the shrinkage rate in the case of conventional powder molding. Ta.

In both cases, the average particle size of the powder was 15% of 2.5M cobalt.

As described above, according to the present invention, cemented carbide can be manufactured by extrusion and acid forming by injection molding.

Claims (1)

[Claims] 1 Add polyvinyl butyl alcohol resin, phthalate ester such as dibutyl phthalate or dioctyl phthalate, and stearic acid to cemented carbide powder in weight percentages of 2% to 5%, 1% to 4%, and 1% to 1% of the powder, respectively.
Add a binder consisting of 5%, add resins such as butyl alcohol, tricrene, ethylene tetrachloride, etc., mix them, remove these solvents by drying, etc., and then injection mold, flomold, extrusion. A method for molding cemented carbide powder, which is characterized by molding with a matrix such as molding.