GB2210064A

GB2210064A - Alloy coating post-treatment

Info

Publication number: GB2210064A
Application number: GB8822305A
Authority: GB
Inventors: Hans-Theo Steine; Christopher Wasserman
Original assignee: Castolin SA
Current assignee: ECG Immobilier SA
Priority date: 1987-09-23
Filing date: 1988-09-22
Publication date: 1989-06-01
Anticipated expiration: 2008-09-22
Also published as: GB2210064B; NO884215L; GB8822305D0; IT8822035A0; NO884215D0; IT1229922B

Abstract

A process for coating a substrate comprises applying on to the substrate a layer of a self-flowing metal-base alloy by thermal spraying, and subjecting at least a zone of the layer to inductive heating, by means of an inductor, at a frequency of from 0.5 to 100 kHz and a power of from 1 to 150 kW, whereby the layer is fused or sintered into the surface of the substrate, and the depth of penetration of heating of the substrate is controlled according to the strength of the induced field and/or the size of the inductor and/or relative movement between the inductor and the layer being treated. The frequency may be varied within the range specified by hand or automatically. The size of the inductor may be such as to heat an area of 5 to 200 cm<2>. The frequency of the relative movement between the inductor and the layer being treated may be controlled by the use of a thermocouple element. In the specific example a pressure roller is spray coated with an alloy of Ni-Cr-B-Si admixed with tungsten carbide. The parameters in respect of frequency and power were established on a test portion. The substrate may be a coating roll of the type used in the paper industry.

Description

CASTOLIN ALLOY COATING POST-TREATMENT The invention relates to a process for post-treatment of metal-base alloy layers, which are applied by thermal spraying on to a substrate.

For the purpose of fusing metal-base alloys on to substrates, processes are known which have considerable effect on the substrate material. For example, fusion in a furnace has a particularly adverse effect, as the whole of the coated member is heated to the fusion temperature.

In contrast, when fusing with a flame, the time for heating up the material and fusing the alloy layer into the substrate material is reduced, and the effect on the substrate material is therefore reduced. Attempts to perform the fusing operation with induction heating have not previously given useful improvements; the constant frequency means that it is necessary to provide for each member which is to be subjected to post-treatment, an inductor which has a specifically adapted cross-section.

For thatZreason, the fusion has previously been conducted using an inductor only when long runs of components of the same shape have to be processed; it is only in that way that the costs involved in manufacture of the induction apparatus can be kept within limits. Even when the inductors used are precisely matched to the members in question, control of the depth of penetration of the heating effect, such depth being dependent on the frequency and the power of the magnetic field produced, is possible only in relation to components of predetermined size, shape and mass.

According to the present invention, the layer is of a self-flowing alloy (the "layer" may comprise one or more applied coatings) and the inductor for post-treatment of the layer is energised with a controllable frequency of from 0.5 to 100 kHz, in particular from 1 to 70 kHz, and a power of from 1 to 150 kW, preferably from 5 to 80 kW, whereby the layer is fused or sintered into the surface of the substrate, and the depth of penetration of heating of the substrate material is controlled according to the strength of the magnetic field and the size of the inductor.

In accordance with a preferred aspect of the invention, an induction loop is moved relative to a surface of the substrate, and its oscillating circuit is tuned in that respect. Suitable inductors are flat-type, strip-type or ring-type inductors with a heat-influencing 2 2 area of from 200 to 5 cm , preferably 100 to 10 cm , more preferably 50 to 20 cm . It has been found to be advantageous to use the inductor to heat a surface zone of from 200 to 5 cm ; the zone, by virtue of the relative movement of the substrate and the inductor, is passed over the whole of the surface to be fused or sintered, in dependence on the melting or sintering temperature of the alloy.

The frequency of the relative movement may be automatically adapted to the parameters of the inductor and the substrate respectively; for example, a thermocouple element can be used for this purpose, as a control aid.

It has surprisingly been found that the problems described above are reduced, even without matching the inductor to the shape, size and mass of the substrate, by processing flowable alloys with induction in an apparatus with a variable frequency in the ranges specified above.

The frequency for the inductor (which can be of a simple design) can be varied/controlled by hand or automatically.

The depth of penetration of the heating effect can be controlled by means of the variable frequency or field strength and the speed of movement, which is regulated by a temperature control, between the portion which is to be fused into the substrate material on the one hand and the inductor on the other hand.

It is thought to be particularly advantageous that, even when there are substantial variations in size, shape and mass and also in cross-section of the portions involved, it is possible to use the same inductors, that is to say, adaptation to the layer to be fused into the substrate material is effected only by way of modulation of the magnetic field.

The process of the invention may be used on an suitable workpiece or other substrate. The process is particularly suitable for coating rolls and cylinders in the paper industry, but also for components in general mechanical engineering for the production of wear-resistant surface layers.

In regard to additional features and, in particular, alloy composition, attention is directed to the claims.

The following is an illustrative example of the novel process: A pressure roller 300 mm in diameter and 1000 mm long was coated in the middle with a wear-resistant layer, 200 mm in width, consisting of a self-flowing alloy of Ni-Cr-B-Si with 50% fused tungsten carbide. As the roller is to be subjected to heavy loading, it is important that, when fusing the layer intp the substrate material, only the outer layer reaches its melting temperature of about 11000C, to a depth of about 10 mm.

The temperature of the core of the material should not exceed 6000C as, at an excessively high temperature, the strength of the roller is reduced, e.g. to the extent of bending.

The surface to be coated was prepared by rough-turning and subsequent blasting with corundum having a particle size of from 0.5 to 1.0 mm. The alloy, in powder form, was sprayed on to the prepared surface of the roller on a turning apparatus with automatic feed, using an automatic flame spray device, at a thickness of 0.1 mm per coating, to a total thickness of 1.5 mm.

The flame spray device mounted on the feed device was then removed and replaced by a flat-type inductor measuring 50 x 50 mm. The parameters in respect of frequency and power, which were established on a test piece, were set within the terms of the invention, and the layer was fused into the substrate material while that rotated, in a zone-wise pattern over a fusion area 2 of 20 cm . The speed of the feed movement was regulated by way of a temperature control means provided with an optical fibre. The measurement point for the control means was arranged in the middle of the inductor. The temperature monitoring of the substrate material was monitored; the maximum temperature was 5800C.

The coated roller and also a corresponding uncoated roller were each tested in a machine. After a running time of half a year, the degree of wear on the coated roller was found to be ten times less than that on the uncoated roller. The coated roller was monitored, e.g.

for bending, but it was not possible to find any adverse effects caused by the fusion process.

Claims

1. A process for coating a substrate, which comprises applying on to the substrate a layer of a self-flowing metal-base alloy by thermal spraying, and subjecting at least a zone of the layer to inductive heating, by means of an inductor, at a frequency of from 0.5 to 100 kHz and a power of from 1 to 150 kW, whereby the layer is fused or sintered into the surface of the substrate, and the depth of penetration of heating of the substrate is controlled according to the strength of the induced field and/or the size of the inductor and/or relative movement between the inductor and the layer being treated.

2. A process according to claim 1, in which the frequency is controlled in dependence on the inductor and the substrate.

3. A process according to claim 1 or claim 2, in which the frequency is from 1 to 70 kHz.

4. A process according to any preceding claim, in which the power is from 5 to 80 kW.

5. A process according to any preceding claim, in 2 which a surface zone having an area of from 5 to 200 cm is heated by means of the inductor, and the surface zone is moved relative to the inductor over the entire area which is to be fused or sintered into the substrate.

6. A process according to claim 5, in which the area is from 10 to 100 cm .

7. A process according to claim 5, in which the area is from 20 to 50 cm .

8. A process according to any preceding claim, in which the alloy is sprayed in powder form or in the form of a filling wire.

9. A process according to claim 8, in which the alloy is sprayed as a wire composed of metal powder and plastics material.

10. A process according to any preceding claim, in which the alloy is Ni- or Ni-Cr-based and contains B and Si.

11. A process according to claim 10, in which the alloy additionally contains Fe or C.

12. A process according to any of claims 1 to 9, in which the alloy is Co-based and contains B and Si.

13. A process according to claim 12, in which the alloy additionally contains Cr, C, W, Ni and/or Mo.

14. A process according to any of claims 1 to 9, in which the alloy is Fe-based and contains B and Si.

15. A process according to claim 14, in which the alloy additionally contains Cr, Ni and/or C.

16. A process according to any preceding claim, in which the alloy is mixed, prior to the spraying, with from 10 to 90% of a hard substance.

17. A process according to claim 16, in which the hard substance is a carbide of W, Cr, Mo, Nb, V, Ti and/or Ta.

18. A process according to claim 17, in which the hard substance is a tungsten carbide.

19. A process according to claim 18, in which from 2 to 30% Co is added to the tungsten carbide.

20. A process according to claim 18 or claim 19, in which the tungsten carbide is sheathed with Ni or Co.

21. A process according to claim 16, in which the hard substance is a boride of W, Cr, Mo, V, Nb, Ti and/or Ta.

22. A process according to claim 16,in which the hard substance is a nitride of W, Cr, Mo, V, Nb, Ti and/or Ta.

23. A process according to claim 16, in which the hard substance is a silicide of W, Cr, Mo, V, Nb, Ti and/or Ta.

24. A process according to any of claims 16 to 23, in which the alloy is mixed with from 20 to 80% of the hard substance.

25. A process according to any preceding claim, in which the heated zone is in a strip form.

26. A process according to any of claims 1 to 24, in which the heated zone is rectangular.

27. A process according to any of claims 1 to 24, in which the heated zone is annular, around the substrate.

28. A process according to any preceding claim, in which the inductor is adapted to the surface profile of the substrate.

29. A process according to any preceding claim, in which the surface temperature is controlled by relative movement of the inductor and the substrate.

30. A process according to any preceding claim, in which the surface temperature is controlled by the power of the inductor.

31., A process according to any preceding claim, in which the temperature is controlled by means of an optical system.

32. A process according to any of claims 1 to 30, in which the temperature is controlled by means of a regulating system provided with optical fibres.

33. A process according to any preceding claim, in which the layer is applied by means of an autogenous flame spray device or a plasma spray apparatus.

34. A process according to any preceding claim, in which the inductor has an induction loop.

35. A process according to any preceding claim, in which the substrate is a coating roll or cylinders of the type used in the paper industry.

36. A process according to claim 1, substantially as exemplified herein.