DE3115675A1 - Process for application and thermal bonding of metal powder alloys in a thick layer - Google Patents

Abstract

Published without abstract.

Description

Method of application and thermal bonding

of metal powder alloys in a thick layer = = The invention relates a method for applying and thermally bonding metal powder alloys in a thick layer according to the preamble of the main claim.

"Thick" layers are those with a thickness of at least 0.2 mm “Difficult” surfaces mean those that are difficult to access (narrow inner bores) and / or those that are present on the workpiece that the There is a risk of the application compound running off if the application layer is relatively should be thick.

Under the commonly used name "Thermal spraying with Subsequent melting "it is known to use on blank trimmed surfaces of Iderka pieces of powder particles with so-called flame spray burners to spray or to fling. Through the burner flame take the powder particles pasty liquid state and can therefore stick to the support surface. Since this, so to speak, "loose" adhesive connection is not sufficient, a thermal one Post-treatment required, with a burner flame or in a suitable one The furnace is carried out to make the powder particles actually melt with the Support surface, i.e. to connect in the metallurgical sense.

This well-known coating process (in addition to the also usual thermal spraying without post-heat treatment) satisfies the requirements that placed on the workpieces treated with it.

However, this procedure has the considerable disadvantage, caused by the spray hour to be observed in connection with the dimensions of the usual Flame spraying devices, that areas that are difficult to access, i.e. in the area of confined spaces Lying conditions, cannot be layered in this way. So are bapw. No surfacing on the inside of the bore with an inside diameter smaller than 70 mm possible.

In powder application technology, it is now also well known to use metal powder particles to mix with dissolved organic binders and spray this "foam" and then the order to be thermally treated in order to remove solids and Drive out the binder and at the same time the metallic compound of the metal powder particles to be metallurgically connected to the work piece surface to be coated.

This is done for reasons, e.g. to produce porous layers, to avoid oxidation or the like.

Thicker layers can be made with such powder-binder mixtures can be achieved, but only on condition that the application surfaces then are not difficult in the sense of the above definition.

The moment you get such well-known powder-binder mixtures in a thick layer, i.e. thicker than about 0.2 mm on strongly curved or vertical layers If you want to apply standing surfaces, which is usually the case, then this also helps Do not continue to use a powder slurry, as the applied is inevitable or sprayed slurry begins to run off the non-horizontal surfaces.

The existing need to meet such difficult surfaces Up to now, being able to coat thickly was only possible in a rather cumbersome and costly manner Way, namely by centrifugal processes or condenser discharge processes, whereby there are still limits to the downward centrifugal process are, as a rule, not even with very small inner diameter ratios the required centrifugal pressure can be achieved.

There is a need to apply thicker layers insofar as than once wear conditions can require such thick layers and for Others usually require follow-up treatments (grinding, honing or the like) that require thicker layers from the outset.

For example, you need wear-resistant coatings on extruder screw cylinders in thicknesses of 0.5 mm, which then have to be honed.

Incidentally, "difficult areas" can arise insofar as than, for example, in the case of mass production in the course of the further conveyance of the workpieces Surfaces to be coated are in a vertical position.

The invention is accordingly based on the object of providing a method create, with the on "difficult surfaces" thick wear protection layers in the sense of the above definition can be applied to the wear requirements and / or to be able to meet the post-processing requirements.

As it has been shown, this is after in a surprisingly simple manner of the invention by what is stated in the characterizing part of the main claim. An advantageous one Further education. this procedure results. according to the subclaim *; The for it essential measures do not extend to interventions in the order material nor on the application technique itself, but on a simple temperature control measure on the workpiece, which means that the applied material is practically immediately in solidified and in the desired order level on or on the difficult " Application surface remains and therefore cannot run.

That way it's bapw. possible to use even thin tubes with only 8 - lo mm, i.e. very strong curvature, to be provided with an inner coating, which practically so far has only been much more complicated with the capacitor discharge process Kind of feasible.

The essentials are therefore the requirements that the workpiece or the support surface is brought into a preheated state and when the evaporation temperature is reached the application takes place immediately, whereby after application or upon impact the metal particles coated with the binder burns the binder or is evaporated, whereby the combustion or evaporation residues of the binding agent ensure that the particles actually adhere, i.e. the application immediately solidifies, which, however, does not yet have a metallurgical connection with the carrier surface is given, which is only achieved by the subsequent melting.

Because the primary application of adhesive in relation to the otherwise in build-up welding The temperatures used are "cold", so to speak, so no burner flame is required is, the application distance can be kept very small, which means that apparatus the possibility arises with the spray nozzle, which under the given circumstances in their outer dimensions can be kept correspondingly small, very close to be able to approach the support surface. Apart from that, an order after the In accordance with the invention, the method can also be carried out in a vortex chamber.

The layers applied according to the invention, i.e. not yet are metallurgically firmly connected to the support surface, withstand easily light bumps and do not fall off the support surface, as has been shown. However, they can easily be removed by mechanical stripping, which is advantageous means that, if necessary, it is possible to apply the actually desired application area to be very sharply defined by, for example, the particular when spraying or Defeat the resulting transition areas before the thermal aftertreatment simply takes off again. A spray application with the interposition of a stencil is thus also possible, so that if necessary application surfaces with a very specific shape can be produced.

The binding agent is usually an average of 20% by weight of the total mix, but ultimately depends on the required Viscosity of the binder and can accordingly be set higher or lower.

The actual melting of the applied metal powder is either in a suitable Furnace (possibly under protective gas or in Vacuum) or by induction or resistance heating, if necessary

carried out under protective gas.

For less demanding surfaces, which may be relatively porous and can be oxidized, the melting can also be carried out in a normal atmosphere will. It should be noted, however, that the required heat energy is indirect is introduced into the workpiece, i.e. there must be a heat transfer from the supporting surface to the applied metal powder particles to ensure a continuous oxidation to avoid.

The application method according to the invention is for all metallic Suitable for support surfaces whose melting point is higher than approx. 900 ° C.

High-pressure and low-pressure polymers, in particular, are, for example, used as binders Polyethylene and propane and xthane diols as solvents in question.

Known metal powders are particularly suitable as metal powder alloys based on Ni, B. Si for use (so-called self-fluxing alloys).

Exemplary embodiment: A hydraulic cylinder with an inner diameter was used 15 mm with a wall thickness of 5 mm and a length of 300 mm with a preventive coating namely the entire inner surface of the cylinder.

A nickel-chromium-boron-silicon alloy was used as a wear protection alloy with a hardness of approx.

8o HRC used, which had the following composition: Cr-% G-% Si % Fe-% C-% Ni 15 3.5 3, o 3.0 o, 7 remainder The metal powder alloy was with a organic binders mixed. The proportion of the binder was 20% by weight. A mixture of 90% by weight propanediol and 10% by weight ethanediol was used as the binder used.

The cylinder was pressure sanded with a ceramic bond Bricks the stone in the coating area to a shiny metallic state. Thereafter the cylinder was preheated to 1800 C and placed in the transport device of a commercially available Rotary painting machine was used, with which the powder-binder mixture was applied.

The speed of rotation of the part was 120 min 1. After The layer thickness of the application was 0.6 mm.

The cylinder was then initially flooded in an argon protective gas furnace brought to 350 ° C. in order to remove remaining residues of the binder.

The temperature of 350 ° C. was maintained for 15 minutes.

This was followed by rapid heating to the melting temperature of 1o5o0 C. This temperature was 5 min.

held. Then the cooling to BooOC took place under an argon atmosphere. After the temperature fell below 8000C, the part was removed from the furnace and cooled in the air. The layer thickness after melting was 0.4 mm and was already so precise that during the final post-processing by honing only a few loo-atel mm had to be removed in order to achieve the required final dimension.

Claims (2)

Petitioner's claims: 1. Application and thermal bonding process of metal powder alloys in a thick layer on and with bare metal, difficult Surfaces of workpieces, the metal powder to be applied with an in Solvents are mixed with dissolved organic binders and after application are metallurgically bonded to the surface by thermal post-treatment, d u r c h e k e n n n z e i c h n e t that this is the surface to be coated exhibiting workpiece before the powder application to the evaporation temperature of the solvent heated and immediately after reaching the evaporation temperature and at their Maintaining the powder-binder mixture is applied. 2. The method according to claim 1, d a d u r c h g e k e n n z e i c h n e t that in the case of thermal aftertreatment of the workpiece in the form of externally supplied Heat the melting of the coating layer in an inert gas atmosphere and at Heat generation in the workpiece, the single melting is carried out in normal atmosphere.