JPH0253481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application The present invention relates to a method and apparatus for manufacturing a hot working tool as set forth in the preamble of claim 1.

b. Prior art and its problems It is already known to produce porosity-free or nearly porosity-free raw molded parts by spraying a metal melt and immediately collecting the particles in a mold. .
Such a method is described, for example, in DE-A-2537103. The specific gravity of this original molded product is at least 90%, usually 95-99
%Must. This means that the pores that are still present no longer connect with each other. This means that the part in the heated state has to be further processed by forging, pressing or extrusion presses, and the ingress of oxygen into the pores causes undesirable internal oxidation, resulting in mechanical This is a serious problem because the characteristics of the

Furthermore, it is common practice to produce porous products or semi-finished products by powder metallurgy methods, which require heat treatment in a reactive gas or vacuum. This method requires at least the following steps: production of the powder, condensation of the powder, and sintering of the compact. Especially when manufacturing large products, high costs are required.

Furthermore, it is known to add reinforcing substances (for example Al ₂ O ₃ ) to the metal powder before pressing in order to produce wear-resistant molded bodies. In this case, it is often a disadvantage that the press tools are subject to severe wear.

c. Object The object of the invention is a simplified method with which it is possible to produce hot working tools made of atomized metal melt and having a specific gravity of 70-90%, and for carrying out this method. The goal is to provide equipment for

d. Means for solving the problem This object is achieved by the method recited in claim 1. Preferred embodiments of this method are set out in claims 2 to 8. An apparatus for carrying out the method according to the invention is defined in claim 9. Preferred embodiments of this device are set out in claims 10 to 12.

e Summary of the Invention According to the present invention, large porous hot working tools can be manufactured directly by spraying the metal melt and collecting the melt particles in a mold.
In that case, the process conditions, i.e. superheating of the melt, flow of melt per unit time (which is determined by the melt injection diameter), amount of atomizing gas, temperature,
The velocity and the distance from the spray nozzle to the mold are such that when the melt particles collide with the mold below the spray nozzle or melt particles already collected in the mold, the melt particles become like dough. It can be selected to be cooled to the extent that it has hardness. In this case, "dough-like" means a state in which the particles are still deformable by slight pressure, i.e. in this state the particles are fully solidified but still liquid. This nucleus is so small that the shell surrounding it will not break when it hits the mold. This is necessary in order for the produced tool to have a specific gravity of 70 to 90%, especially 80 to 85%. In addition, it is necessary to have sufficient thermal energy to weld (sinter) the melt particles together.

Adjustment of particle hardness is fundamental to the production of metal powders that require solid particle characteristics and require as little thermal energy as possible to prevent particles from adhering. differ in terms of

On the contrary, in the case of the method according to DE 25 37 103 A1, particularly soft particles are produced in order to set the specific gravity as high as possible, and the accumulation of particles collected in the mold is The depressions and irregularities created in the surface must be completely filled by subsequent particles so that no interconnected pores occur.

According to the invention, during the atomization of the melt, combinations of processing conditions are set, which in the prior art had to be avoided in each case.

An appropriate combination of conditions is, for example, in a test,
Others can be found under constant conditions by varying the distance between the mold and the spray nozzle.
In that case, the tendency is to a higher superheating of the melt,
An increase in the melt flow rate per unit time, an increase in the gas temperature, and a decrease in the amount of atomized gas supplied per unit time,
It is necessary to pay attention to softening the hardness of the particles or increasing the specific gravity under other conditions.

A specific gravity of up to 90%, in particular 80 to 85%, guarantees a porous shaped body in which the pores are interconnected. This makes it possible to perform a reactive annealing treatment on compacts that do not require a pressing step for shaping, in which the reactions carried out (e.g. decarburization, oxidation, reduction, nitridation, etc.) This is done not only in a limited surface area, but also in the entire area, or at least in a large volume area, due to the open pore structure. Therefore, the desired material properties (for example heat resistance) can be achieved through thorough depth effects. If the specific gravity of the tool exceeds 90%, there will be insufficient pores, and the reaction gas will not be able to penetrate deeply into the tool, so that the effect of the reactive annealing process will not be sufficiently achieved. On the other hand, the specific gravity of the tool is 70%
It has been found through experiments that if the strength is less than that, the strength necessary for the tool is insufficient.

The method according to the invention also makes it possible to produce tools with desired different properties within the shaped body volume. This can be done, for example, by time-controlled feeding of reinforcing substances (e.g. carbides, nitrides, oxides, etc.) into the spray nozzle during the spraying process, and mixing them into the compact with the flow of melt particles. It becomes possible.

By doing so, it is possible to mix the reinforcing substance only within a predetermined range. For example, in the case of wear-resistant objects, to facilitate later machining,
Volumes which serve to accommodate the clamping element and which must be mechanically processed (for example screw holes) can be kept free of reinforcing substances. Also,
Of course, it is possible to uniformly mix the reinforcing substance into the entire molded body.

In many cases it is preferred to cause the reinforcing material to be generated during the spraying of the metal melt and/or during the reactive annealing process (ie within the shaped body itself). For this purpose, the melt must be sprayed before spraying.
One or more gases capable of reacting with the gases used during spraying and/or reactive annealing (e.g. nitrogen, carbon dioxide, oxygen components of air, etc.) and producing reinforcing substances (e.g. Al ₂ O ₃ ) in the process. metals (e.g. Al, Ti, Nb). In order to carry out the annealing treatment, the compact needs to have a specific gravity of about 80 to 85%.

For example, to prevent the metal melt from reacting with oxygen in the air, spraying the metal melt and accumulating it in the mold should be
It is preferable to carry out the reaction in a container isolated from the outside air.

Inert gases such as argon or nitrogen can be used as atomizing gas. The requirements for the purity of the inert atmosphere are not too great; it is possible, for example, to use nitrogen as the atomizing gas, in which case the atomization can also take place in an open container; teeth,
A complete shielding of the outside air is required during the spraying, with the exclusion of nitrogen which is continuously freshly supplied to the container.

Adjustment of different material properties inside the tool
This can be achieved by varying the distance from the spray nozzle to the mold over time, producing layers with different densities and porosity in the molded body. This also has an effect, for example, on the optional subsequent reactive annealing treatment. Generally, high density is desirable where it is necessary to attach a clamping member to a tool.

A uniform or deliberately non-uniform filling of the mold, possibly associated with a change in the distance from the nozzle to the mold, is carried out by moving the mold approximately horizontally under the nozzle. In principle, contrary to the above, it is also possible to change the injection direction of the nozzle so that the impact location of the melt particles falls within the desired range of the mold. In this way, tools are produced which have significantly different material properties inside the shaped body, possibly also in connection with the addition of reinforcing substances which are incorporated over time.

Tools produced by the method of the invention are generally used directly as products or require relatively simple machining (eg seats, holes).

The device for carrying out the method of the invention comprises a melt container, at the bottom of which a spout is attached, below which a ring-shaped spray nozzle is arranged coaxially with the spout.

This nozzle is equipped with a connection for the atomizing gas. It is often preferred to choose other cross-sectional shapes for the nozzle (eg rectangular), for example to produce a narrow but slightly longer spray radiation with a length approximately equal to the length or width of the mold. The mold for collecting the melt particles is convertible below the nozzle on a receiving device whose height is adjustable (for example by motor drive) so that the distance to the nozzle can be varied. In particular, it is preferred to design the receiving device below the nozzle to be pivotable or movable, so that the impingement area of the spray radiation inside the mold can be varied at will (for example by motor drive). Furthermore, it is preferred to provide the nozzle and the receiving device together with the mold in a spray container in close contact with the melt container, which is provided with an outlet for exhausting the atomization gas and is isolated from the outside atmosphere. Since the cooling of the melt particles generated by spraying up to condensation is carried out primarily by thermal radiation and to some extent by heat dissipation of the atomized gas, it is important to control the condensation conditions. For this purpose, the spray container is preferably provided with an auxiliary cooling device in or on its wall.

f Example Next, the method according to the present invention will be explained in more detail by way of example.

To produce a molded body that undergoes significant wear as a hot working tool. This product has dimensions of approximately 420mm x 120mm x 40mm. A mold with appropriate internal dimensions is
It is mounted movably below the atomizing nozzle in a closed container sealed from air. The distance from the ring nozzle (diameter 80mm) to the mold is 600mm
It is.

Tests have shown that the density of the compact is approximately 6.3 g/cm, which corresponds to a specific gravity of approximately 80% for the CrNi steel used. Simultaneously with the injection of molten steel heated to approximately 1540°C, an amount of fine grain oxide (Al ₂ O ₃ ) corresponding to approximately 5% of the molten steel is continuously supplied as a reinforcing material to the suction part of the nozzle. Ru. This melt flows through the nozzle at a rate of approximately 0.5 Kg/sec. Room temperature nitrogen is used as the atomizing gas. During spraying, the mold is moved under the jet of melt particles so that the mold is evenly filled. Approximately 30 molded objects
When a height of mm is reached, the supply of reinforcing material is interrupted and the distance from the nozzle is reduced. In this way, a suitable size density of about 90% is created in the upper part of the molded body. The injection of melt is also stopped after the mold is filled (molding weight approximately 12.7 kg). The molded body is
It is maintained at a temperature below approximately 400°C with oxygen cut off.
Next, this compact is transferred to a closed furnace, where it is first annealed under vacuum and then under low nitrogen pressure (less than 1 bar) to form a heat-resistant structure.
is nitrided. Subsequently, machining of the upper layer surface, which is not coated with reinforcing material, e.g. facing, boring,
Thread cutting is performed.

Claims (1)

[Claims] 1. A method for manufacturing a hot working tool in which a melt of steel or a special alloy based on Ni or Co is sprayed using a gas as a medium and the melt particles are collected in a mold. , when the melt particles produced during spraying collide with the mold or the melt particles already collected in the mold, in order to bring the specific gravity of the tool to 70 to 90%.
The spray conditions (superheating of the melt, flow rate of the melt per unit time, amount of gas,
A method characterized by adjusting the gas velocity, gas temperature, distance of the mold from the spray nozzle), additionally feeding the spray nozzle with reinforcing material during the spraying process, and subjecting the tool to a reactive annealing. 2. The method according to claim 1, characterized in that the flow rate of the reinforcing substance to be added is varied over time. 3. Process according to claim 1, characterized in that the melt is doped with at least one metal, which forms a gas and a reinforcing substance during reactive annealing, before spraying. 4. The melt is characterized in that at least one metal which reacts with the atomizing gas and thereby forms a reinforcing substance is added to the melt before the atomizing.
The method described in any one of Items 1 to 3. 5. The method according to any one of claims 1 to 4, wherein the spraying is performed in a sealed container. 6. The method according to claim 5, characterized in that rougon or nitrogen is used as the atomizing gas. 7. Any one of claims 1 to 6, characterized in that the distance between the spray nozzle and the receiving mold is changed during spraying in order to make the inside of the tool have a different density depending on the location. The method described in. 8. The method according to any one of claims 1 to 7, characterized in that the collision location of the melt particles within the mold is changed over time. 9. An adjustable hot-working tool manufacturing device in which a melt of steel or a special alloy based on Ni or Co is sprayed using a gas as a medium, and the melt particles are collected in a mold. a spray nozzle connected to a gas conduit and mounted below the spout of the melt container, and a mold replaceably provided below this nozzle, for increasing the specific gravity of the tool from 70 to 90%. Spraying conditions (superheating of the melt, In an apparatus for adjusting the melt flow rate, gas amount, gas velocity, gas temperature, distance of the mold from the spray nozzle) and additionally supplying reinforcing material to the spray nozzle during the spraying process, said mold and said A device characterized by comprising a device that changes the distance between the nozzle and the nozzle. 10. Device according to claim 9, characterized in that the mold is mounted on a support device movable below the nozzle. 11. The device according to claim 9 or 10, wherein the nozzle and mold are provided in a container that is shielded from outside air. 12. The device according to claim 11, characterized in that a cooling device is provided on the wall of the container.