Method for manufacturing internally coated copper or copper alloy pipes

Description

[0001] The present invention relates to a method according to claim 1 for coating the inside of a copper or copper alloy pipe by a protective coating, particularly a tin coating.

[0002] In the prior art, the dissolution of copper for instance to household water has been effectively restricted and prevented by coating the inside wall of the copper pipe. The employed coating material has been for example tin. For a man skilled in the art, it is obvious that in order to succeed, the surface to be coated must first be carefully pretreated. The purpose of the pretreatment is to remove any grease and carbon films as well as oxidized spots created during earlier manufacturing steps. Therefore it has been almost without exception necessary to use acids or other strong solutions together with rinses in the pretreatment step. A tin-coated pipe and its manufacturing process, including the chemical pretreatment step, is illustrated in the patent publication CA2225464. Hence a remarkable drawback in known pretreatment processes used in connection with copper pipes or copper alloy pipes has been the use of strong chemicals, as well as the rinses required by said chemicals.

[0003] The object of the present invention is to realize a more viable pretreatment method to be applied in the internal coating of copper pipes, particularly in tin coating.

[0004] The invention is characterized by what is specified in the appended claims.
The method according to the invention is characterized in that prior to the coating treatment, the inside of the pipe is mechanically pretreated. In that way the use of dissolvents and rinses can be avoided. A preferred embodiment of the method is characterized in that the inside of the pipe is pretreated by grain blasting, such as sand blasting. Grain blasting is an extremely viable method for the mechanical pretreatment of the inside of a pipe. It can be carried out by connecting the pipe to a grain blasting device, or else the nozzle of the grain blasting device and/or the pipe under treatment can be moved with respect to each other.

[0005] According to another preferred embodiment of the invention, the inside of the pipe is pretreated by treating the surface with hard-spiked brush elements, such as steel wire brushes. In that case the brush element can be arranged in a rotating apparatus, so that said rotating brush element can be passed through the pipe, and consequently the whole interior surface thereof is treated.

[0006] According to a preferred embodiment of the invention, the pipe is cleaned after the pretreatment by blasting with gas, such as pressurized air. According to another preferred embodiment, the inside of the pipe is cleaned by using a cleaning element, such as a felt plug that fills the cross-section of the pipe.

[0007] As was already maintained above, it is advantageous that during the pretreatment, the pretreatment device and the pipe are moved with respect to each other.

[0008] The method according to the invention has several remarkable advantages. By applying the method of to the invention, the use of dissolvents and rinses prior to the coating treatment can be amazingly avoided. Thus the arrangement according to the invention can replace all solvent-based pretreatment steps. For example, a grain blasted inner surface of a pipe is active and absolutely clear of all impurities that could weaken the coating result. Thus for instance semi-hard copper pipes can as such be internally coated with tin. Also the quality of the obtained tin coating is excellent. The pretreatment according to the invention can be applied in connection with various different tin coating methods, operated according to different principles. By means of the pretreatment method according to the invention, there are achieved remarkable savings both in costs and otherwise, as regards the process materials, needs for investments and production times. By means of the pretreatment method according to the invention, there also are achieved ecological advantages and advantages related to the safety at work.

[0009] The invention is explained in more detail below, with reference to the appended example.

Example

[0010] A short length of a recently produced semi-hard copper pipe, internally grain blasted with corundum (Al₂O₃) and cleaned with pure pressurized air, was subjected to a laboratory-scale coating experiment. In order to pretreat the outer surface, the pipe was compactly plugged at both ends and immersed first in a degreasing solution and then in a warm water rinsing tank, and thereafter in a pickling solution and successive warm water rinsing tanks; after this, the outer surface of the pipe was dried by blowing with hot air. Thus the pretreatment of the outer surface of the pipe followed the conventional pretreatment by pickling, and the pretreatment of the inner surface of the pipe followed the pretreatment according to the invention. Next the plugs were removed from the pipe sample, and the pipe was immersed in a regular tin coating solution in order to coat the inner and outer surfaces thereof. Finally the pipe was rinsed in warm water rinsing tanks and dried by blowing with hot air. The properties of the tin coating on the inner wall of the pipe - layer thickness, porosity and even quality (even coloring) - were at least as good and even more homogeneous than the qualities of the tin coating on the outer wall of the pipe. Thus the advantages achieved by means of the fairly simple method according to the invention in order to internally pretreat copper and copper alloy pipes for coating were obvious. Similar results were obtained by using semi-hard copper pipe with an inner wall that was abrasively cleaned by a rapidly rotating steel wire brush passing through the pipe, and by successively blowing with pure pressurized air.

[0011] In the method according to the invention for internally coating copper or copper alloy pipes by a protective coating, particularly tin coating, the inner wall of the pipe is mechanically pretreated prior to the coating treatment. The inner wall of the pipe is abrasively pretreated by grain blasting, such as sand blasting. A known method is specified in the patent publication EP0335999 A1.

[0012] As an alternative, the inner wall of the pipe can also be pretreated by treating the wall surface with hard-spiked brush elements, such as steel wire brushes. After the pretreatment, the pipe is internally cleaned by blowing with gas, such as pressurized air. After the pretreatment, the pipe can also be internally cleaned by using a cleaning element. During this process, the pretreatment device and the pipe are moved with respect to each other. This can be realized so that only one or both of said elements are moved during the treatment. Before the pretreatment, the pipe to be coated is in a recrystallized state, and suitably the pipe is a so-called semi-hard pipe.

[0013] For a man skilled in the art, it is obvious that the invention is not restricted to the above described embodiments only, but several modifications can be made within the scope of the appended claims.

Claims

1. A method for internally coating a copper or copper alloy pipe with a protective coating, particularly a tin coating, characterized in that prior to the coating treatment, the inner wall of the pipe is mechanically pretreated.

2. A method according to claim 1, characterized in that the inner wall of the pipe is abrasively pretreated by grain blasting, such as sand blasting.

3. A method according to claim 1 or 2, characterized in that the inner wall of the pipe is pretreated by treating the surface with hard-spiked brush elements, such as steel wire brushes.

4. A method according to any of the claims 1 - 3, characterized in that after the pretreatment, the inside of the pipe is cleaned by blowing with gas, such as pressurized air.

5. A method according to any of the claims 1 - 4, characterized in that after the pretreatment, the inside of the pipe is cleaned by using a cleaning element.

6. A method according to any of the claims 1 - 5, characterized in that during the treatment, the pretreatment elements and the pipe are moved with respect to each other.

7. A method according to any of the claims 1 - 6, characterized in that the pipe to be coated is in a recrystallized state, and it is preferably a so-called semi-hard pipe.