EP1524333A1 - Process for applying a coating - Google Patents

Abstract

A surface of the cast iron portion (10') is decarburized to an effective depth before it is coated with finely powdered wear resistant alloy. The coating (12) is fused by heating cast iron part together with the coating to a temperature below the melting point of the cast iron portion but sufficient to cause alloy of coating to fuse.

Description

The invention relates to a method for applying a preferably feinpudrige, wear and / or corrosion resistant alloy coating a surface of a casting to an area of increased To obtain wear and / or corrosion resistance.

Machine parts or components, in particular those of Vehicles and equipment of agriculture, forestry and construction and of mining, are prone to general wear and tear, as well as by corrosion and mainly by cooperative effects of erosion and corrosion wear out. Although different processes available stand to the surface of such machine parts so Change that reduces wear is often a Sinter coating preferred, if the appearance as well as the Fine tolerances no big demands are made. This is because such a coating quickly and can be carried out inexpensively and a good Wear and corrosion resistance as well as a high Has impact resistance and a very good metallurgical Can form a connection with the steel support material. Such Process is exemplified by US-A-5,879,732 described. Although such methods are in use with different Gussträgermaterialien, such as gray cast iron and Spheroidal graphite, described, can still cause problems in occur in such a way that during fusion or Sintering the coating at temperatures around 1085-1100 ° C to a leakage of liquid metal in a borderline or transition region between the carrier material and the Coating can come. In this boundary area becomes liquid Metal formed while the upper region or the upper layer the coating is sintered or fused. During the Fusion process keeps the top layer the same Composition like the original powder or substrate and stays firm or semi-solid while the location on the Transition area tends to leave the transition area in uncoated areas of the substrate to flow in which she is not wanted. This leads to a component, which in the area to be coated an undesirable Having uneven coating, and to a component, which out of tolerance. Are the required tolerances Critically, the component must be scrapped.

The problem underlying the invention is seen therein that known method for coating castings can produce uneven coatings.

This problem is inventively achieved by the teaching of the claim 1, wherein in the other claims the Solution advantageously developing features are listed.

It is a method for applying a preferably fine powder, wear and / or corrosion resistant Alloy coating on a surface of a Casting proposed. The method creates an area increased wear and / or corrosion resistance. According to the Procedure is first a surface area of the casting up decarburized to an effective depth. This decarburization, the for example, by suitable heat treatment of the Casting can be achieved takes place before the Coating or a final coating preparatory substrate is applied to the casting. at This coating is, for example, a Mud or even a powder or any other suitable Material comprising the alloy. The coating can In addition, other ingredients, such as in the Art fluxes, etc. included. The coating will be on the decarburized surface area by means of a method or Applied process that causes the coating to adheres to the component. The process can be any suitable coating methods, for example a Method of chrome plating, act.

In particular, during or through the process that the fine powder, wear-resistant alloy coating on at least one surface area of the casting applied and the coating by heating the Casting and the coating to a temperature below fused to the melting point of the casting, but the it is sufficient to fuse the alloy. Such a Process is for example by a method for sintering represents.

The coating may be in any suitable manner be applied to the area or the surface. In particular, however, for example, an aqueous sludge applied, which contains the alloy or by the Alloy and possibly other constituents is formed.

The coating can also be achieved by a thermal spraying or spray method are applied.

Due to trials, an effective depth of about 0.25 mm proved to be particularly advantageous. Using a modified method and / or other or also modified support materials or coatings, the effective depth deviate from this preferred depth. The effective depth can then be determined by suitable experiments become.

Preferably, however, the effective depth is between about 0.25 and 0.5 mm.

Fig. 1

eine schematische, den Stand der Technik repräsentierende Darstellung eines Gussbauteils mit einer eine Legierung umfassenden Beschichtung vor einem Verschmelzen bzw. - sintern,

Fig. 2

der Gussteil aus Figur 1, wobei verdeutlicht wird, dass der relativ hohe Kohlenstoffgehalt des Gussteils in dem Übergangsbereich zwischen der Beschichtung und dem Trägermaterial das Verschmelzen beeinflusst,

Fig. 3

die unregelmäßigen, endgültigen Abmessungen eines Gussteils gemäß den Figuren 1 und 2 nach dem Verschmelzen bzw. Versintern und

Fig. 4

eine Ansicht ähnlich Figur 2, wobei der Gussteil vor dem Beschichten einem Entkohlungsvorgangs unterzogen wurde.

In the drawing, an embodiment of the invention described in more detail below is shown. It shows:

Fig. 1

FIG. 2 is a schematic prior art representation of a cast component having a coating comprising an alloy prior to fusing; FIG.

Fig. 2

the casting of Figure 1, illustrating that the relatively high carbon content of the casting in the transition region between the coating and the substrate affects fusion;

Fig. 3

the irregular, final dimensions of a casting according to Figures 1 and 2 after the fusing and

Fig. 4

a view similar to Figure 2, wherein the casting was subjected to a decarburization before coating.

Reference is first made to FIGS. 1 to 3, in which a schematic cross section of a casting 10 made of cast iron which forms a carrier material is shown on the one sludge coating 12 was applied. The Coating 12 is preferably an aqueous solution a polyvinyl alcohol (PVA) used as a binder of a aqueous sludge of an alloy without a flux is used as disclosed in US-B-5,879,743 and which in the present application by this reference is included. The casting 10 is here as a Sphärogussteil described, the free graphite or carbon in the form of beads 15, which in the casting 10th are distributed, with some of the beads 14 at a Interface 16 between the casting 10 and the coating 12 are arranged. It should be noted here that the Principle of the invention as described below equally on a casting 10 made of a cast iron can be applied, in which the graphite or the carbon in the form of flakes / lamellae.

The casting 10 has a melting point between 1150 ° and 1260 ° C on. The fusion or sintering temperature of Coating 12 is between 1085 ° and 1100 ° C, ie below the melting point of the casting 10, but still relatively high. It was found out in this Melting temperature range of beads 14 made of carbon at the Interface 16 in a contact surface or an inner layer 20th the coating 12 diffuse and thus the composition the inner layer 20 change so that they have a higher Having a carbon content which is one generally has lower melting point than the alloy in the outer layer 22 of the coating 12. When the melting or Sintered temperature is reached, the outer layer 22 of the Coating 12 thus begin in a solid or semi-solid Material to sinter, while the inner layer 20 of the Coating 12 becomes liquid and from the boundary layer flows out, as shown at 24 in Figure 3, and Make laugh and globules. Suppose the desired Dimension of the casting 10 with coating 12 is in the Figures 1 and 2 Shown, it can be seen that the Leakage of the liquefied coating 12, as shown in FIG 3 results in that the outer limits 26 of the coating 12 below the original limits "Schrupfen", while the boundaries of the casting 10 under the originally applied coating 12 based on the original dimensions "grow". Accordingly, the go desired dimension of the component lost and the component must, if the measurements are critical, they will be scrapped.

However, it was found that this undesirable result can be avoided or greatly reduced if the amount of free carbon or graphite in the casting surface by a Decarburizing heat treatment process before coating and sintering is removed. Reference is now made to FIG taken, which shows a casting 10 ', which before the Applying the coating 12 from mud to a depth d was decarburized. Since no or little free carbon or Graphite exists in the boundary region 16 becomes little or no Carbon absorbed by the coating 12, and consequently remains the composition and therefore the melting point of inner layer of the coating 12 adjacent to the Boundary region 16 with respect to the remaining coating 12 unchanged. If this is the case, the whole will Coating 12 without melting and leakage of the Coating 12 at the interface 16 between the casting and the coating merge or sinter.

In an attempt that led to this result, some Ductile castings a decarburizing heat treatment cycle exposed. The cycle involved heating the castings at 982.2 ° C (1800 ° F) for two hours, and a subsequent air cooling of the castings. The cycle generated a decarburized area of 0.5 mm depth. These decarburized Castings and also a set of corresponding castings, the were not decarburized, were with a muddy coating Mistake. The castings were then placed on the fusion or Heated sintering temperature of the coating. In the result showed none of the decarburized castings an occurrence of leakage liquid metal at the interfaces between the casting and the coating. In contrast, all castings, which had not been decarburized, that was liquid metal the interface between the casting and the coating had formed and flowed into areas that were not should be coated.

Further experiments revealed that the depth in which one Decarburization of castings covered with a coating of should be coated, about 0.25 mm so as to act to cause formation of liquid metal during sintering or Merging step is prevented. In any case, the Professional the effective decarburization depth for each appropriate Simply find out the composition of the coating by asking the coating on a casting with different Decarburization depths melts or sintered and the components checked to see if, during the merge or Internally the coating has leaked. There the coatings of similar composition also by means thermal spraying or spraying be applied It is thought that a decarburizing of too coating areas of a casting also in this Job type will be similarly beneficial.

The above suggests that a decarburization process is the Adhesion of other types of coating, such as a Chrome plating, can support. The coatings can, but do not necessarily have a fusion of the coating lock in.

After the preferred embodiment has been described is it becomes clear that various changes are being made can be without departing from the scope of the invention as he is determined by the following claims.

Claims (6)

Method for applying a coating (12) having a preferably fine powdered, wear and / or corrosion-resistant alloy onto a surface of a casting (10) in order to obtain a region of increased wear and / or corrosion resistance, comprising at least the following process steps: a) decarburizing at least one surface area of the casting (10) to an effective depth b) applying the coating to this surface area by means of a process that causes the coating (12) to adhere to the component (10). A method according to claim 1, characterized in that the process according to the method step b) comprises the following method steps: c) applying the coating (12) comprising the fine-powder, wear-resistant alloy to at least one surface region of the casting (10) d) fusing the coating by heating the casting (10) and the coating (12) to a temperature below the melting point of the casting (10) sufficient to fuse the alloy. Method according to one or more of the preceding claims, characterized in that the coating (12) is applied by applying a slurry. Method according to one or more of the preceding claims, characterized in that the coating (12) is applied by a thermal spraying or spraying process. A method according to claim 1 or 2, characterized in that the effective depth (d) is about 0.25 mm. Method according to one or more of the preceding claims, characterized in that the effective depth (d) is between about 0.25 and 0.5 mm.

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