CN1034793Y - Method of making a multi-wall pipe - Google Patents

Abstract

The invention relates to a method for manufacturing a pipe, which comprises plating one side of a metal strip with a first layer of a weldable first metal, and plating the other side of the metal strip with the first layer of the first metal. A second layer of a second metal of a different metal, and after plating the aforementioned two layers, the tape is rolled into a tube having at least two double walls.

Description

Method of making a multi-wall pipe

The present invention relates to a method of making a multi-wall pipe, the method comprising: applying a first or a second layer of weldable metal to one side or the other of a metal strip, respectively, and applying these layers This tape is then rolled to form a tube having at least two double walls.

Such a method has been disclosed in patent application GB2241185. In this known method, a metal strip is coated with a copper layer as a first and a second layer. This tape is then rolled into a multi-wall tube. According to this prior method, the tape is rolled through two complete turns to form a double walled tube. The fact that such a pipe has double walls means that there is also a layer of copper between the double walls of the pipe. After the tape has been rolled, the tube thus formed is heated, thereby welding the two walls in contact with each other.

Applying a layer of copper or other weldable metal to one side or the other of a metal strip has the advantage of improving the technical quality of the tube formed, especially in terms of corrosion resistance, by applying a layer of nickel, which is suitable for Welding may protect the tube from the fluid circulating in it.

Metallizing the tapes described above does have its advantages, but it has been found that it also presents various problems. For example, when this type of pipe is used as a vehicle brake fluid pipe, the copper layer inside the pipe can have good stability against aggressive brake fluid, but the copper layer on the outside of the pipe cannot be significantly exposed to harsh conditions. This tube provides adequate erosion resistance in climates. In this case, the pipe must be protected by an additional coating such as a zinc layer. However, since the metal strip at this time is already plated with copper, the electrochemical coupling performance is not ideal, which limits the quality of the overall product in terms of corrosion resistance.

Another significant problem is that the copper plated onto the inner surface of the tube dissolves. Certain alcohols used in fuel additives, especially in unleaded gasoline, can attack or dissolve copper, eventually clogging the injectors of internal combustion engines.

The purpose of the present invention is to overcome the above-mentioned drawbacks.

For this purpose, the method of the present invention is characterized in that a first and a second metal are respectively plated as the aforementioned first and second layers, and the second metal is different from the first metal. The choice of two different layers of metal will allow the finished tube to be plated with the most appropriate layer of metal while protecting the inside and outside of the tube. Since both the first and second metals can be welded, the welding itself is not disturbed by the two different layers of material being plated. By selecting the metal of the second layer to be different from the metal used in the first layer, the same tape can be used for two different tubes simply by selecting the direction of rotation of the tape. This greater flexibility also allows such tubes to be used more appropriately for their end purpose without the need for additional tapes.

In this way, by plating two different metal layers, the problem of corrosion on the outside of the pipe and the problem of corrosion on the inside of the pipe by the liquid flowing therethrough can be solved, and the welding quality of the pipe will not be hindered.

A first preferred embodiment of the method according to the invention is characterized in that copper or correspondingly nickel is applied as the first or corresponding second metal. Nickel has good corrosion resistance and sufficient stability to alcohols or other fuel additives, while copper is perfectly suitable for welding purposes. This unifies the superior properties of weldability and corrosion resistance.

According to a further preferred embodiment of the method according to the invention, nickel or correspondingly tin is applied as the first or correspondingly second metal layer, or tin or correspondingly copper is applied as the first or correspondingly second metal layer The second metal layer. Tin has good antioxidant properties.

A second preferred embodiment of the method of the present invention is characterized in that after rolling the strip, a third layer of an alloy is plated on the outer surface of the formed tube. As a result, the protective performance of the pipe can be improved.

A third preferred embodiment of the method of the invention is characterized in that the above-mentioned layers are plated at high current densities. Such high current densities enable rapid deposition of the metal layer to be plated, thereby significantly reducing the likelihood that metals used in different layers will interfere with each other.

The invention is described in more detail below by means of embodiments given by way of example and illustrated by the accompanying drawings.

1 is a cross-sectional view of a metal strip that has been plated with two layers of metal; FIG. 2 is a cross-sectional view of a tube made by applying the method of the present invention; and FIG. 3 is a metal strip capable of being plated with two layers of metal. Device example.

In the above figures, the same reference numerals refer to the same or similar parts.

To make the multi-wall pipe, a metal strip, such as a steel strip with a thickness of 0.355 mm, is used. Figure 1 is a cross-sectional view of a metal strip 1 that has been plated with two layers of metal. In the method of the invention, a first layer 2 of a first solderable metal is first plated onto the first side of the tape 1 . The other side of this tape 1 is then plated with a second layer 3 of a second solderable metal, this second metal being different from the first.

The first metal plated here is, for example, a 3 μ thick layer of copper, while a 3 μ thick layer of nickel is used as the second metal. The advantage of their combination is that nickel has good corrosion resistance and copper is quite suitable for welding purposes. Since the melting temperatures of copper and nickel are 1080°C and 1452°C, respectively, the fusion of these two metals is carried out at a temperature between 1200 and 1300°C, so that the tape equipped with the above two layers can be rolled and The formed tube is welded.

Additionally, it has been noted that copper and nickel are a good choice because at about 550°C diffusion of one metal to the other occurs.

In fact, in order to make a multi-wall pipe such as the one shown in cross-section in Figure 2, the relevant tape can be rolled two or more times to form two or more walls. During rolling, care should obviously be taken to ensure that successive wall ends contact each other. Once the tape has been rolled up, the welding operation can begin.

A coiling operation of the present invention using a tape with two different plating layers will result in a first metal layer in contact with a second metal layer between two successive layers. Therefore, it is very important to choose two metals that can be welded, and the welding temperature difference between them is not too large. Too large a temperature difference can actually cause problems in the soldering process. For example, it must be avoided that the first or corresponding second metal in combination has a melting temperature of approximately 200°C or correspondingly approximately 1000°C. However, it has been known that the higher the melting temperature of the two, the greater the acceptable temperature difference.

The metal of the inner layer 2 of the tube 4 produced by applying the method of the present invention is different from the metal of the outer layer. In addition, the tube is also provided with a protective layer on the inside and outside, but this is not the case if only one side of the tube has a plated layer.

The advantage of having the inner layer different from the outer layer of the tube is that the final finished tube has greater in-use value. Take, for example, a vehicle in which there are gasoline pipes and lubricating oil or brake fluid pipes. In order to increase the octane number, several additives are included in the relevant fuels, especially in unleaded gasoline. Alcohols that attack copper are used as such additives. Erosion of copper dust can clog the injector. As for gasoline pipes, it is necessary to use nickel-layer pipes with inner surfaces that are ideally resistant to alcohols or other additives. The outer layer of the pipe must then be formed, for example, from a copper layer that is sufficiently resistant to corrosion, in view of the fact that the fuel pipe does not have to be located in an excessively exposed location. The corrosion resistance can be further improved by coating with a layer of zinc-aluminum alloy after the tube is formed.

The problem with aggressive substances such as brake fluid is quite different. The best inner layer material for brake fluid resistance is copper. However, brake fluid lines are significantly exposed to harsh weather conditions and require good external erosion protection. Nickel can ideally meet these requirements. In fact, for later deposits such as zinc-nickel alloys, or zinc, or zinc-aluminum alloys, nickel is an excellent primer in terms of adhesion and corrosion resistance.

The inclusion of two different layers of tape allows the formation of two different tubes based on the same tape. In fact it is sufficient to allow the tape to roll in one direction or the other.

In addition to the selection of nickel and copper as the first and second layer materials plated onto the tape, other options are also available, such as nickel, tin and tin, copper.

When the coil is closed, a third layer of metal can also be plated on the outer wall of the coiled tube. Obviously, this third layer of metal must be different from the metal plated on the opposite side. The third layer material is most suitable for the following alloys: for example, copper-nickel alloy and zinc-nickel alloy are used for plating on the nickel layer; and copper-nickel alloy is used for plating on the copper layer. The advantage of plating on a third layer is that the corrosion resistance is thereby improved. It goes without saying that other material layers can be additionally plated on this third layer. As the third layer, an aluminum layer or a zinc-aluminum alloy layer and a lead-tin alloy or a zinc-nickel alloy layer can also be used here.

The third layer described above is preferably plated on top of the nickel layer because nickel makes a good primer for plating other layers. The thickness of this third layer is generally significantly greater than that of the first and second layers. For example, the thickness of this third layer may be, for example, 12 μ or 25 μ, or even 100 μ, depending on the degree of protection required and the process used in the plating. This third layer is plated onto the outer tube wall to be protected after the tape is coiled. If this third layer were to be plated before the tape was rolled up, its thickness would likely cause considerable problems in welding after the tape was rolled up. For example, the third layer may begin to melt, with consequent melting of the first and second layers.

The aforementioned first or second layer constitutes a good base layer for the attachment of the third layer. It has been found that when a third layer of zinc is plated onto the nickel layer, it is perfectly possible to deposit a 7 to 8[mu] layer of zinc on top of the nickel layer in order to obtain very high protective properties. The degree of protection thus achieved is equivalent to a single layer of zinc plated with a thickness of 15 μ on a copper substrate. Thereby, the material consumption can be significantly reduced and the productivity of the manufacturing equipment can be greatly improved without reducing the corrosion resistance of the pipe.

Figure 3 illustrates, by way of example, an embodiment of an apparatus capable of plating two layers of different metals onto a metal strip. Figure 3 is only a schematic diagram showing only those parts necessary to understand the function of such a device. The metal strip 1 is introduced into the first tank 5 in which the first and second anodes are mounted, which are arranged on one side and the other side of the metal strip 1 . Tank 5 contains a known electrolyte for depositing a first layer of metal such as copper. Between the belt 1 and the first anode 8 is provided a screen 9 made of a non-conductive material such as plastic. This screen 9 acts as a mask for the anode 8 and thus prevents the deposition of a metal layer on this side of the strip 1 . Only the anode 6 is supplied with current in the cell 5 .

After the tape 1 passes through the first groove 5 , the tape plated with the first layer enters the second groove 7 . In the cell 7, the screen 9 shields the first anode 6 from metallization to this side of the strip. This second tank also contains a known electrolyte, such as that used to deposit nickel. In the cell 7 , no current is supplied to the anode 6 .

By locating anodes 6 and 8 on each side of the strip, while using different tanks, different layers can be plated on each side.

According to another example of an arrangement in which two different metal layers can be applied to a strip, each cell 5, 7 contains only a single anode, so that it is not necessary to mask one of the two anodes.

A high current density, eg, 250 A/dm2, is preferably used between the anode and the belt. Such high current densities facilitate rapid metal deposition, thereby avoiding contamination or electrodeposition effects on the opposite side of the treated surface. The shorter the transit time, the less risk there is for the metal to reach the other side of the belt and mix with the metal layer plated thereon.

Using a device operating at current densities as low as 10A/dm2, it is naturally also possible to plate two different metal layers onto the tape.

Claims (8)

1. A method of manufacturing a multi-wall pipe, comprising plating first and second layers of weldable metal on both sides of a metal strip, respectively, after plating the metal layer, rolling up the metal strip To form a pipe having at least two double walls, the method is characterized in that in the first and second metals plated as the first and second layers, respectively, the second metal and the first metal are different. 2. The manufacturing method according to claim 1, wherein copper or nickel is used as the first or second metal, respectively. 3. The manufacturing method according to claim 2, wherein nickel or tin is used as the first or second metal, respectively. 4. The manufacturing method according to claim 2, wherein tin or copper is used as the first or second metal, respectively. 5. The manufacturing method according to claim 2, wherein after rolling up the strip, the outer surface of the tube formed by the strip is plated with a third layer of alloy. 6. The manufacturing method according to claim 5, wherein the third layer is plated with a copper-nickel alloy. 7. The manufacturing method of claim 5, wherein the third layer is plated with a zinc-nickel alloy. 8. The manufacturing method according to any one of claims 1 to 7, wherein the aforementioned metal layer is plated with high current density.