EP0979688A1 - Method of manufacturing copper tubes - Google Patents

Abstract

Copper pipes have an inner tin-plated surface of sufficient thickness to fulfill the requirements of the valid mandatory standard for drinking water installations. Production of copper pipes having an internal tin-plated surface comprises forming a pre-pipe having a length of up to 15 m with a constant wall thickness of 2-15 mm and a maximum outer diameter of up to 150 mm; galvanically coating the inside of the pipe with a tin layer of thickness of 20-500 mu m by the electrolytic decomposition of a tin salt solution; and deforming the pre-pipe in several stages into a finished pipe with a constant tin layer thickness of 2-50 mu m and producing finished pipes with a length of up to 200 times the starting length.

Description

The invention relates to a method for producing copper tubes with an internally tinned Surface.

Installation pipes, especially for drinking water installations, are made seamless drawn SF-Cu pipes. These pipes meet the requirements for wide areas Requirements of the German Drinking Water Ordinance, in which a guideline for copper of 3 mg / l is specified. In the course of harmonization in the European Community is according to an official guideline of the EC council over the quality demands limit on drinking water intended for human consumption of 2 mg Cu / l. The copper value in drinking water is determined over a fixed period of time and a sampling regime, which in the are still specified as draft DIN 5093.

Bare copper installation pipes manufactured according to the current state of the art meet the requirements of the EU directive for most water. In practice, however, water also occurs which, although fulfilling the requirements of the Drinking Water Ordinance, can, due to fluctuations in the water quality, lead to Cu emissions that exceed the permissible limit value. This particularly affects water supply areas in which the pH value is below the prescribed pH value of 6.5 and / or the proportion of free carbonic acid, KB _8.4 > 1 mol / 1, is exceeded. Due to these conditions, the use of copper pipes was generally prohibited in these areas or associated with a high warranty risk due to increased risk of pitting corrosion. In order to avoid direct contact between copper and water, various solutions for the inner coating of copper pipes, such as, for example, using tin, have already been proposed. A copper tube is known from WO 96/28 686, which consists of an alloy of Cu and at least one of the elements Zn and Mn, which are contained individually or together in a total amount of 0.02% by weight or more in a copper alloy to prevent an ε phase from growing. An Sn protective film with an average layer thickness of 0.2 to 4 μm is applied to the inner surface of such a copper tube.

DE 43 21 244 A1 describes a method for the inner coating of copper pipes known in which a coating of tin oxide and a diffusion intermediate layer is formed from copper / tin alpha monophase by chemical tinning the inner surface of the copper pipe, diffusion annealing of the copper pipe below inert atmosphere and an oxidizing thermal inner surface treatment. The layer thickness of the tin oxide layer is 0.05 to 0.5 µm and that of Diffusion intermediate layer 5 to 20 µm. The chemical tinning process exists from a degreasing stage, flushing the copper pipe with a chemical tinning solution and a subsequent hot water rinse final drying in hot air. The subsequent diffusion annealing takes place at temperatures of 450 to 700 ° C under an inert atmosphere. For oxidizing thermal interior surface treatment is a gas mixture at elevated Temperatures used, the exposure time is at least 5 min. This The process is very complex and leads to high costs for the inner coating produced in this way Copper pipes.

EP 0 723 037 A1 describes a simplified method for producing a Installation pipe made of copper with a tinned inner surface described. The inner surface of the copper pipe becomes chemical in a first step Finally, the cross-section of the tinned copper pipe is tinned deformed by at least 2% by a single finished train. The chemical Tin plating of the copper pipe is carried out essentially according to that in DE 43 21 244 A1 described procedure. It becomes a pure tin layer with a thickness of 0.5 up to 4 µm on the inner surface of the copper pipe. The deformation of the internally coated copper pipe is 5 to 40%. By the only one final deformation train, the tin layer is compressed. The main disadvantage of this method is as follows. The chemical Tinning the copper pipe requires several steps and is relatively time consuming. In addition, only a limited layer thickness can be achieved since Formation of a closed tin layer no more deposition takes place. The maximum upper limit of the achievable layer thickness is approx. 5 µm. The subsequent deformation is used only to densify the tin layer in order to close any pores still present in the tin layer. The one in practice Applicable degree of deformation is relatively low, since starting from the maximum achievable layer thickness of the tin layer by chemical tinning after Deformation must still have an adequate residual tin layer thickness, to prevent the release of copper ions into the drinking water.

Further disadvantages of this method are the low cost-effectiveness and their Limited to a few assortments of finished pipes.

The invention was based on the object of a method for producing copper pipes with an internally tinned surface that is characterized by an effective Mode of operation, with which all marketable products within a technological line Assortments for installation pipes can be produced and with the on the finished pipe a sufficiently thick and dense layer of tin can be achieved that meets the requirements the applicable standards for copper migration.

According to the invention the object is achieved by the features specified in claim 1 solved. Suitable design variants are in claims 2 to 13 specified.

According to the proposed procedure, pre-pipes made of copper or Copper alloys of relatively large dimensions in a defined length, such as e.g. Copper pipes with an outer diameter of 85 mm and an inner diameter of 57 mm, preferably in a length of 3 to 6 m. The front pipes can have a length of up to 15 m and by extrusion, cross rolling, Casting, welding, mushrooming or drawing can be made. If necessary these manufacturing processes can also be used in combination, e.g. Extrusion a pipe blank, which is then cold pilgrimed to be coated Fore tube is formed. If necessary, this can not yet be coated Copper pipe at a temperature above the recrystallization temperature of the Copper are annealed. In terms of the quality of the front pipes, there are no special ones Requirements. The inner surface of the front pipes is in a separate Coating plant by electrolytic decomposition of a tin salt solution with a Tin layer electroplated. The coating system can be within a Production line can be integrated or located externally at a separate location are located. The galvanic coating known per se has the advantage that by means of this relatively large layer thickness can be applied, e.g. up to 500 µm. Based on the procedural parameters of the galvanic Depending on the requirements, the coating can have any layer thickness achieve. A front pipe of the dimensions mentioned has after Coating with a tin layer with a thickness of 300 µm a piece weight each 150 kg. Such a front pipe is subsequently known by itself Forming processes such as cold pilgrimage and pulling with flying, semi-flying and / or with a fixed mandrel within several reduction stages to Final dimension of the finished tube formed. Depending on the respective reduction stages can make different assortments of finished pipes from a downpipe getting produced. From a front pipe with a length of 5 m, an outer diameter of 85 mm and a wall thickness of 14 mm (85 x 14) as well as an internal tinning with a layer thickness of 300 µm, 370 m finished pipe (15 x 1) with a Tin layer thickness of 18 microns can be produced. Starting from the inside coated Downstream tubes can be subjected to overall forming degrees of up to 99.5% reduction in cross-section realize.

The proposed method is particularly economical and flexibility. Due to the relatively low cost of galvanic Coating the front pipes and the quantities of finished pipes that can be produced from them the internally tinned finished pipes can be manufactured particularly cost-effectively. in the A comparison to this leads to chemical tinning according to the known state of the art Technology with a final forming in a finished train at essential low degrees of deformation at significantly higher costs.

Ready-made pipes with a grooved inner surface can also be made from the tinned downpipes produce, the longitudinal grooves formed during the last forming train become.

The internally tinned finished pipes can also be used to manufacture fittings such as Sleeves, T-pieces, reducers or pipe bends can be used.

Due to the high Sn layer thickness of the tin layer of the front pipes and their subsequent ones multiple densifications through the individual reduction stages of the forming processes becomes a relatively relative on the inner surface of the prefabricated pipe high layer thickness achieved with a closed and dense layer. Investigations in the migration test, only very low Cu concentrations were found. There is a solid between the base metal and the tin layer on the finished tube Binding without formation of alloy phases. The new process does not require any special technical equipment and can by means of a known galvanic coating system and conventional forming technology become.

The process is used to make soft, semi-hard and hard tinned Suitable for copper pipes.

By applying a relatively thick layer of tin to the inner surface of the Front pipes and their subsequent forming processes are particularly economical Manufacturing enables. For example, for the production of 370 m finished pipe 15 x 1 only 5 m front tube can be tinned. The throughput times and drawing speeds for the subsequent forming operations correspond to those during manufacture of copper pipes.

Example 1 - Production of a semi-hard 15 x 1 tinned copper tube

On a conventional extrusion press, copper pipes with a wall thickness of 14 mm and an outer diameter of 85 mm (85 x 14) in lengths of 5 m. These so-called front pipes are galvanized in a coating system tinned internally by electrolytic decomposition of a tin salt solution, with a Layer thickness of 300 µm. The inner tinned front pipes have a unit weight of approx. 130 kg / tube.

Tinning of the tube blanks with a galvanically deposited tin layer thickness of up to 500 µm is no problem in practice. A pre-made internally tinned tube blank 85 x 14 as a preliminary tube is in a first reduction stage reshaped to a pilgrim size of 53 x 2.7 on a cold pilger mill. The Length of the rolled front pipe is 37 m, starting from the pipe blank 85 x 14 the degree of deformation is 86%. The rolled front tube is pulled using a flying mandrel within a drawing line in five further reduction or Drawing stages at drawing speeds of 80 to 130 m / min to a dimension of 17.5 x 0.9 drawn. During the drawing process takes place in a manner known per se internal and external lubrication of the front pipe. The drawn front tube 17.5 x 0.9 has a length of 330 m. The degree of forming, starting from the rolled tube 53 x 2.7 is 89%. The drawn front pipe 17.5 x 0.9 is then with a Gas mixture consisting of 3% hydrogen and the rest nitrogen, purged and at a temperature above the recrystallization temperature of copper, at 450 ° C, annealed and on a finishing machine in a final reduction stage to the final finished size 15 x 0.93 with a drawing speed of 130 m / min drawn. The degree of deformation in the last drawing stage is 12%. During the drawing process the front pipe is lubricated on the outside.

It becomes an internally tinned semi-hard prefabricated pipe (15 x 1) with a length of 370 m obtained with a consistently constant tin layer thickness of 18 µm. The scored Total degree of deformation, starting from the 85 x 14 front tube, is 99.5%. The The tin layer thickness was determined by chemical detachment of the tin layer.

Example 2 - Production of a hard-drawn internally tinned copper tube 64 x 2

Extrusion is used to make copper pipes with a wall thickness of 5 mm and one Outside diameter made of 89 mm, in lengths of 5 m each. In a galvanic coating system, the front pipes 89 x 5 are analogous to those in Example 1 tinned internally, with a tin layer thickness of 50 μm. The piece weight an inner tinned down tube is approx. 60 kg. The inner tinned downpipes are on a conventional drawing machine by pulling on chain benches fixed mandrel in four reduction or drawing stages to the finished dimension 64 x 2 drawn. The drawing speeds are 20 to 80 m / min. The degree of deformation of the individual reduction or forming stages averages 25% per train. Starting from a front pipe 89 x 5, a finished pipe 64 x 2 with a length of 17 m obtained with a constant, constant tin layer thickness of 20 µm. The total degree of deformation based on the internally tinned front tube is 89 x 5 70.5%.

The thickness of the tin layer was determined analogously to that in Example 1.

Example 3 - Production of a hard (F 96) tinned copper tube 10 x 1

Extrusion of copper turns tube blanks with the dimensions 85 x 14 manufactured, which then on a cold pilger mill to copper pipes Dimension 53 x 2.7 processed and cut to pipe lengths of 5 m. For To achieve an adjusted strength, the piled copper tube is 53 x 2.7 above the recrystallization temperature of the copper, at 410 ° C, soft annealed. Analogously to example 1, these preliminary tubes are tin-plated with a tin layer thickness of 50 µm. The unit weight of the tinned downpipe is approx. 19 kg. The inner tinned tubes 53 x 2.7 are used on a conventional drawing system flying mandrel in seven reduction or drawing stages at drawing speeds drawn from 80 to 130 m / min to the finished size 10 x 1. The degree of deformation per train is 35% on average. Copper pipes are made from an internally tinned downpipe 10 x 1 in a length of 75 m with a constant, constant tin layer thickness obtained from 18 µm. Starting from the inner tinned downpipe 53 x 2.7, the total degree of forming of the finished pipes is 93%.

The thickness of the tin layer was determined analogously to that in Example 1.

On samples of the tin-plated copper tubes produced according to Examples 1 to 3 the following material tests were carried out in accordance with the test specification of the quality association Copper pipe e.V. carried out.

Determination of the Sn layer thickness by chemical detachment of the Sn layer, determination of the migration and determination of the purity of the tin layer. The results are shown in the table below. Examples 1 2nd 3rd Tube 15 x 1 Tube 64 x 2 10 x 1 tube Layer thickness in µm 18th 20th 18th Migration in µg / mm ² <1 (0.03) <1 (0.05) <1 (0.03) Purity of the Sn layer 99.9% Sn 99.9% Sn 99.9% Sn

Furthermore, the tightness and the adhesion of the Sn layers were assessed Checking the adhesion of the pipe samples were subjected to a 90 ° bend. Furthermore, the tightness, adhesive strength and formation of Intermediate alloy layers on the basis of cross sections, which are carried out using a scanning electron microscope and microsensor were evaluated.

The test results of the samples showed that the finished pipes over the have a closed, dense Sn layer over the entire length. On the pipe samples no cracks or tinsel were found after the bend. On the examined Samples were free of pores, cracks and inclusions of foreign elements detect. The dividing line between copper and tin is very sharp, i.e. it there were no diffusion zones and / or intermetallic phases with the copper Matrix formed.

The present test results show that the internally tinned copper pipes meet the requirements of the Gütegemeinschaft Kupferrohr eV with regard to the tightness of the Sn layer, the layer thickness and the purity of the Sn layer and that the pipes produced according to the invention in water supply areas with a pH value of the water <6, 5 and / or proportion of free carbonic acid, KB _8.4 > 1 mol / l can be used without hesitation.

Claims (13)

A process for the production of copper pipes with an internally tinned surface, wherein first the inner surface of the pipe is tinned and then the tinned pipe is formed into a finished pipe, characterized in that a) a straight forward pipe with a length of up to 15 m and an essentially constant wall thickness of 2 to 15 mm and a maximum outer diameter of up to 150 mm is produced, b) the inside of the front tube is then electroplated by electrolytic disassembly of a tin salt solution with a tin layer thickness of 20 to 500 µm and c) finally, the internally tinned down tube is formed in several reduction stages to finished tubes with an essentially constant tin layer thickness of 2 to 50 microns, and finished tubes with a length up to 200 times larger are produced based on the initial length of the down tube. A method according to claim 1, characterized in that the front pipes a Have a length of 3 to 6 m. Method according to one of claims 1 or 2, characterized in that the Vorrohre by extrusion, cross rolling, casting, welding, pilgrimage or Pull are made. Method according to one of claims 1 to 3, characterized in that the tubes above the recrystallization temperature during the manufacture of the preliminary tubes of the copper are soft annealed. Method according to one of claims 1 to 4, characterized in that the pre-pipes a tin layer thickness of 50 to 300 µm is applied. Method according to one of claims 1 to 5, characterized in that at the forming of the tinned inner tubes, degrees of deformation from 60 to 99.5% can be achieved. Method according to one of claims 1 to 6, characterized in that the internally tinned downpipes in several successive process stages by cold pilgrims and / or pulling with flying, semi-flying and / or with fixed mandrel are formed. Method according to one of claims 1 to 7, characterized in that an inner tinned downpipe finished pipes of different diameters and Wall thicknesses are produced. Method according to one of claims 1 to 8, characterized in that the Tinned downpipe before one of the subsequent forming stages above the Recrystallization temperature of copper in a temperature range from 350 to 550 ° C is heat treated. A method according to claim 9, characterized in that the front pipe before the Heat treatment with nitrogen or a gas mixture of nitrogen and Hydrogen, with a hydrogen content of 1 to 4 vol .-% is flushed. Method according to one of claims 9 or 10, characterized in that the heat-treated front pipe finally in one step to a finished pipe is reshaped, starting from the heat-treated downpipe degrees of reshaping from 2 to 30% are observed. Method according to one of claims 1 to 11, characterized in that the inner tinned pre-pipes finished pipes with a longitudinally grooved Inner surface are made. Use of a tin-coated prefabricated pipe according to at least one of the preceding claims for the production of fittings.