GB2098881A - Improvements in or relating to the protection of metal products from corrosion - Google Patents

Abstract

There is disclosed a method of protecting a metal product, such as electrical trunking formed by cold- rolling pre-galvanised steel strip, in which, after cleaning, e.g. by high pressure steam to remove oil and grease a thin film of wax is applied preferably by directing a fine spray of the molten wax onto the surface of the trunking.

Description

SPECIFICATION Improvements in or relating to the protection of metal products from corrosion This invention relates to the protection of metal products from corrosion and is particularly, although not exclusively, applicable to such protection of elongate metal products, for example rolled sections, for example of galvanised steel.

In the manufacture of elongate metal products such as lengths of channel-section electrical trunking made from galvanised steel strip by cold rolling, the product, as delivered from the cold-rolling stage, normally has a slightly oily surface as a result of the application of a water soluble coolant applied during manufacture. However, such a product has disadvantages when used as lighting trunking in proximity to white or light-coloured wall or ceiling surfaces in rooms, particularly in installations in which access to electrical wiring, etc. necessitates handling of ceiling panels, ceiling tiles etc., as the slightly oily finish on the surface of the product can dirty the hands of personnel servicing or installing the electrical wiring etc. in question, with the risk of undesirable and unsightly marking of the white or light-coloured surfaces referred to.

Similarly, there are many other applications in which the film of oil on such a product may lead to undesirable soiling of material in the vicinity.

It is, of course, possible to clean off the film of oil from such products before use, but this leaves the exposed metal surface susceptible to corrosion. For example, if an article with a galvanised finish, otherwise unprotected, is exposed to the atmosphere for any length of time, the phenomenon known as "white rusting" will occur.

It is an object of the present invention, in one of its aspects, to provide a method of protecting a metal product from corrosion which is inexpensive and clean to handle.

According to this aspect of the invention there is provided a method of protecting a metal product from corrosion, comprising the steps of cleaning the surface of the product and subsequently applying to said surface a thin film of wax.

Preferably the metal product is cleaned by directing steam under high pressure on to the surface of the product from a plurality of nozzles to remove any traces of oil or grease and subsequently a thin film of wax is applied to the surface by directing molten wax, in the form of a fine spray, from a plurality of nozzles on to said surface.

According to another aspect of the invention there is provided apparatus for use in performing the method, and comprising means for passing an elongate metal product longitudinally along a predetermined path, a cleaning station and a waxing station disposed at successive positions along said path, with the waxing station being downstream of the cleaning station, the cleaning station having a plurality of nozzles directed towards said path and connectable with a source of steam under pressure and the waxing station having also a plurality of nozzles directed towards said path and connectable with a source of molten wax under pressure, the arrangement being such that, in operation, the nozzles in the waxing station, supplied with molten wax under pressure, will deliver molten wax in the form of a fine stray directed towards said path.

The invention also extends to a metal product protected from corrosion by the method of or using the apparatus of the invention.

By way of example, an embodiment of the invention is described in more detail below as applied to the production of lengths of electrical trunking.

In such production, electrical trunking, of substantially channel-section, is produced in a conventional manner by cold rolling pre-galvanised steel strip to provide 6m lengths of the trunking. The trunking is delivered longitudinally from the apparatus which rolls the pre-galvanised strip to the desired section. On emerging from the rolling apparatus, the trunking is covered by a thin film of coolant oil which is normally applied to the metal while going through the forming process. The trunking, emerging longitudinally from the rolling apparatus, passes longitudinally along a predetermined conveying path extending through a treatment box comprising two treatment chambers or stations disposed one after the other.In the first treatment chamber, an array of steam nozzles is disposed, directed towards the path along which the trunking passes, these nozzles being connected with a source of steam under pressure, so that pressurized steam is directed on to the surface of the trunking passing through the first treatment chamber, so that the trunking passing therethrough is steam cleaned and thus completely de-greased. In the second treatment chamber there is disposed an array of spray nozzles connected with a source of molten wax under pressure so that the last-noted nozzles direct a fine spray of molten wax on to the surface of the trunking which settles as a fine film over the whole of the pre-galvanised surface of the trunking. When the trunking cools, the wax forms a thin dry protective surface.The wax used is preferably a watersoluble wax, or a wax which is capable of "wetting" a surface already wetted by water and at the same time driving the water off so that there is no need to ensure that the trunking is dry before applying the wax. However, if desired the trunking may be deliberately dried after steam cleaning before application of the wax, in which case, of course, the wax need not have the last-mentioned properties. The trunking channel thus produced is clean and bright and coated with a thin protective film of wax which inhibits the phenomenon known as "white rusting" which occurs over a length of time when galvanised finishes are exposed to the humid atmosphere. The wax coated surface is perfectly clean to handle, by contrast with an oil-coated surface, or even a galvanised finish free from surface contamination, which finish, when rubbed with a hand, will transfer black marks from the galvanising. The presence of the wax film in the products produced by the method of the invention largely prevent this happening.

The wax utilised is preferably a commercially available wax which does not contain silicone.

Claims (8)

1. A method of protecting a metal product from corrosion, comprising the steps of cleaning the surface of the product and subsequently applying to said surface a thin film of wax.

2. A method according to claim 1 wherein the metal product is cleaned by directed steam under high pressure on to said surface from at least one nozzle.

3. A method according to claim 1 or claim 2 wherein the wax is applied in molten form as a fine spray over said surface.

4. A method according to any preceding claim,wherein the metal product is an elongate product and wherein the product is passed longitudinally along a path at successive positions along which are disposed, respectively, a cleaning station and a waxing station, the cleaning station having a plurality of nozzles directed towards said path and connected with a source of steam under pressure so as to direct jets of steam at the product as it passes through the cleaning station, the waxing station also having a plurality of nozzles directed towards said path and connected with a source of molten wax under pressure and arranged to direct molten wax in a fine spray over the surface of the product as it passes through the waxing station, the arrangement being such that the product, in proceeding along said path, passes first through the cleaning station and subsequently through the waxing station.

5. A method according to any preceding claim wherein said elongate metal product is of galvanised steel.

6. Apparatus for use in performing the method of claim 4 comprising means for passing an elongate metal product longitudinally along a predetermined path, a cleaning station and a waxing station disposed at successive positions along said path, with the waxing station being downstream of the cleaning station, the cleaning station having a plurality of nozzles directed towards said path and connectable with a source of steam under pressure and the waxing station having also a plurality of nozzles directed towards said path and connectable with a source of molten wax under pressure, the arrangement being such that, in operation, the nozzles in the waxing station, supplied with molten wax under pressure, will deliver molten wax in the form of a fine spray directed towards said path.

7. A metal product protected from corrosion by the method of any of claims 1 to 5 or using the apparatus of claim 6.

8. Any novel feature or combination of features described herein.