DE2742203A1 - Hollow compacts pressed from hard metal powders - where die core is removed by dissolving or melting after pressing - Google Patents

Abstract

The inner wall or core of the die is made of a solid material removed via heat or a liq. solvent after pressing the compact. The core pref. contains a hole or holes via which the molten core and/or the solvent can be removed. Core is pref. provided with a coating protecting the bore of the powder compact from the heated or dissolved core and/or the solvent. Used e.g. in pressing hollow cylinders from hard metal powders, where the arrangement prevents cracks in the bore of the compact.

Description

Process for the production of crack-free hollow bodies

from pressed Pu @ vermaterial The invention relates to a technological Process for the production of pressed powder bodies with crack-free cavities, how it z. B. in the production of hollow cylinders made of hard metal or hard metal powder can be applied.

It is known for the production of hollow cylinders from pressed powder insert solid mandrels and pull these mandrels out again after pressing the powder.

The insertion of solid thorns has the disadvantage that in the powder body Various cracks can occur when removing the mandrel. They arise on the one hand by a transverse to the axis and on the other hand in the axial direction Thorn movement.

1.) The mandrel is loosened or heweat in the direction transverse to the axis.

Cracks will certainly arise in the powder, namely in the axial direction, see picture 1 (1 = outer wall, 8 = norn) 2.) The mandrel is pulled vertically upwards.

Cracks can be transverse to the axis or tangential cracks develop.

In addition, due to the high contact pressure, the powder on the mandrel get stuck. The shear stress can be so great when pulling out the nornes be that the compacted powder tears close to the mandrel parallel to the mandrel surface.

Platelets or scales form, see Figure 2.

(1 = outer wall of the container, 2 = pressed powder cylinder, 6 = @ orn) It is still there known, the cavity of the pressed powder body by mechanical processing, z. B. Boring to manufacture.

In the case of mechanical processing, however, local ones also act Forces in the circumferential and axial direction that lead to cracks in the brittle powder body know lead.

When the pressed hard metal powder bodies are sintered, they disappear these cracks do occur without leaving any visible traces however, in the event of later tensile stress, especially in the case of pulsating stress, z. B. in compressors as expanding axial and transverse cracks and as flaky Lift-offs of the surface reappear and cause the failure of the Component or the compressor.

The invention is based on the object of a method for production of pressed hollow, crack-free powder bodies.

This object is achieved according to the invention in that a special (lost) core is prefabricated with sufficient strength around which the Powder is firmly pressed so that the core acts as a supporting or Pormwand during pressing serves, but after pressing the core through liquid or heat (e.g.

Ice, carbon dioxide snow, wax, etc.) is dissolved without the Dissolving powder particles are displaced from their place or

Tensile or shear stresses arise in the pressed powder body, which can lead to fine cracks, or that the core remains in the powder body and in the sintering chamber without the Damaging powder bodies, dissolves, see Rild 3).

The advantage achieved by the invention is that pressed Powder bodies with cavities can be produced without being in the powder body fine cracks arise, which may occur when the component is subjected to stress Operational use to failure of the component lead wild.

On the one hand, there are various ways of guiding the heat into the core Principles are applied (e.g. warm air, electric heating coil) and on the other hand Precautionary measures (e.g. drilling, see Fig. 3) for draining off the core material or the solvent may be necessary.

It can also protect the pressed powder body from the undesired Penetration of the solvent or the dissolved core material may be necessary to cover the dissolvable core with a protective layer.

An embodiment of the invention is shown in the drawing as a powder cylinder, see picture 3).

Part 1 shows schematically the outer mold wall in which part 2 / the compacted powder / is located.

The inner mold wall is formed by the solid core / part 4 1, which is covered with a thin protective layer, s.

Part 3, to protect against penetration of the solvent or the dissolved Core material into the compacted powder, part 2.

Part 5 represents a through hole in the core, which, if necessary, Depending on the material, it can be useful for introducing the solvent, the heat and for draining off the solvent and the dissolved core material.

Patents considered: su - 383-534 SU - 307-826 U.S. 363-2243

Claims (1)

PATENT CLAIM 1. Fin technological process for the production of pressed powder bodies with cavities, characterized in that the inner mold wall or the core consists of a solid material and by heat or liquid 2. Fin technological process according to claim 1.), characterized in that the core has cavities for discharging the dissolved core material and optionally the solvent. 3. Fin technological process according to claim 1.), characterized in that that the core surface is provided with a layer to protect against undesirable Penetration of the dissolved core material and possibly the solvent in the pressed powder and / or to protect against heat absorption or release during Pressing the powder or dissolving the core.