EP0000369A1 - Thin - walled metal tube, method for manufacturing it, and its application - Google Patents

Abstract

In the case of a thin-walled metal tube made of a metal band (1) bent transversely to its longitudinal axis and wrapped with a helical wire or band (4), the connection between the edge regions of the bent metal band is made by a connecting means (3) which is in the gap ( 2) is arranged between the edge regions and which fills the gap as a result of the gap capillarity and which solidifies on cooling.

The connecting means, which melts under the influence of heat and can flow into the gap, can be applied to the bent metal strip together with the wire or tape coil before the edge areas are connected.

Description

The invention relates to a thin-walled metal pipe, in particular for condensers of refrigeration devices, for the brake fluid in motor vehicles, as a jacket pipe for electric tubular heaters and for air heaters with low-pressure steam, from a metal strip bent transversely to its longitudinal axis, the edge regions of which are connected to one another and with a wire or Band is wound in a spiral shape, as well as a process for its production.

Such metal pipes are known from DE-PS 524 552 and are produced by continuously running a metal strip through forming rolls which form a slotted pipe. Then the edges of the tape are welded together. Unless other technical reasons speak for a relatively large wall thickness of the tube and thus for a large material consumption, the wall thickness of the tube, that is to say the thickness of the metal strip used as the starting product, is matched to the radial pressure occurring in use. The axial load on the tube is generally not critical, ie the strength of the tube under internal pressure is in the longitudinal direction of the tube only half as large as in the tangential direction.

In the manufacture of the slotted tube, the longitudinal edges of the strip must be pressed against one another so strongly by shaping rolls that the contact is permanent, i.e. H. "Popping open" of the slotted tube is to be prevented. However, this is only possible if the tape is compressed. The band must therefore be wider than the circumference of the pipe to be manufactured in order to compensate for the reduction in circumference that occurs due to the compression. The degree of compression for strips made of unalloyed steel is about 5%. Despite the upsetting, changes in the soldering gap occur under the influence of heat during soldering, which impair the quality of the soldering. Without compression, a slot is created that is relatively wide, e.g. B. with a width of 0, 2 - 0, 3 mm with a strip with a thickness of 0.5 mm made of unalloyed steel. However, such a slot does not have the capillary action required to draw in a solder.

The use of seamless tubes is also known. Here, for example, a copper tube is produced using the extrusion process, which is then drawn to the desired diameter and the desired wall thickness. These pipes are relatively expensive. According to the method of the invention, with the same or superior properties, a saving of over 30% compared to this type of seamless tubes is achieved.

Furthermore, tubes manufactured by the so-called bundy method are known. In this process, an unalloyed steel strip, which is approximately twice as wide as the circumference of the pipe to be manufactured, is galvanically copper-plated. The steel band is then in Formed into a double spiral, ie the wall thickness of the finished pipe is twice the wall thickness of the starting strip. This is followed by soldering in a soldering furnace, the galvanically applied copper serving as the soldering material. In a next process step, the tube is then drawn cold in general and optionally soft annealed again. The advantage of the bundy pipes manufactured in this way compared to welded pipes is their absolute tightness and thus safety. However, these tubes are relatively expensive, due to the galvanic copper plating and the complex manufacturing process. In addition, there is the disadvantage that the wall thickness of the finished pipe is twice as large as the thickness of the steel strip serving as the starting material, so that pipes with very small wall thicknesses cannot be produced.

The invention is based on the object of proposing a new method for producing thin-walled metal pipes, in which a high degree of safety with regard to the tightness of the pipe and a higher load-bearing capacity of the pipe against radial stress can be achieved. Furthermore, depending on the intended use of the tube, special advantages can be achieved, as will be described below.

The characteristics of the new method result from the characteristic term of the main claim. Preferred embodiments are described in the subclaims.

Although it is known, the surface of a finished pipe to increase the heat output by edging on a pipe to enlarge wound ribs. An example of this is the finned tube radiator for space heating, in which a strip of unalloyed steel is wound upright on a seamless or welded tube made of unalloyed steel. In these cases, however, an improvement in the heat dissipation is only achieved if appropriate heat transfer from the tube to the wound tape is ensured, ie corresponding soldering or welding work is required.

The method according to the invention differs from such manufacturing methods in that a wire or a coil is wound in a spiral shape on the semi-finished product. ie before the edge areas of the strip serving as the starting product are connected to one another. A defined seam gap can be achieved by the helical winding with a certain pre-tensioning of the band or wire, without the band being compressed by the forming rollers. The seam gap has the capillary action required for soldering. In the case of strips made of unalloyed steel, a thin copper foil, for example 3 mm wide and 0.1 mm thick, can now be put on before winding up the wire helix. The copper foil serving as solder is held by the wire helix. If the semi-finished product thus produced is heated in a soldering oven until the copper foil melts, then the molten copper is drawn into the gap under the capillary action, so that the tube is closed cleanly and durable after cooling. The main advantages of this manufacturing process lie in the achievement of an exact capillary gap, in the exact metering of the solder material and in the fact that the solder material is held firmly at the desired location by the wire helix. It is also guaranteed that there are no undesirable changes in the soldering gap due to the heat in the soldering furnace.

If thin-walled tubes are to be produced which are not exposed to any particular internal pressure, the helix can be unwound after the gap has been closed and rewound onto a new tube section. The prerequisite for this is the use of a spiral wire that does not bind with the appropriate solder, e.g. B. a spiral made of stainless steel is used in the manufacture of an unalloyed steel pipe with copper as solder. In many applications, however, it will be beneficial to leave the wound coil on the tube. In the latter cases, care will generally also be taken to ensure that the coil is also soldered onto the tube when the gap is closed when heated in the soldering furnace. Pipes manufactured in this way have the appropriate dimensions, i. H. with appropriate selection of the diameter and the pitch of the coiled wire, a strength `in the radial direction that is twice as high as the strength in the axial direction. Accordingly, with the same material weight per unit length, the radial pressure load of a pipe manufactured in this way is significantly higher than that of a conventional pipe.

However, there are also a number of advantages for special areas of application.

If the tube is used as a jacket tube for a tubular heating element, then the heat-emitting surface can easily be doubled with a corresponding slope of the coil. This means that with a comparable nominal load, the tubular heater can be shortened by at least a third. Apart from the significant reduction in price, this is too take into account that the space available for the tubular heater is limited in most household appliances. If the space is fully used, the device can be operated with higher nominal powers, so that heating times are shorter.

The attachment of pipes or tubular heaters to holding plates, water flow pipes or other shaped bodies was previously problematic. Due to the relatively low price and excellent thermal conductivity, aluminum or aluminum alloys are often used. Soldering is usually not possible with these materials. In electric welding, very strong currents are required, since the entire length of the tube should lie against the holding plate, for example. In addition, since the tubular jacket is traversed by the welding current, there is a risk that the tubular jacket will be damaged, e.g. H. is welded on. In the case of the tubes produced by the method according to the invention, the coiled wire coil forms a large number of welding points arranged at a distance from one another, so that, so to speak, a spot weld is achieved automatically. The welding current mainly flows through the coil, so that damage to the jacket tube is excluded.

Another possibility of fastening the pipes is that the pipe is pressed onto the holding plate or onto the shaped body in a press. The adjacent spiral sections penetrate vertically into the material of the holding plate. The material must move sideways, ie in the axial direction of the tube, and is pressed in behind the largest cross-section of the adjacent wire spiral section. In this way there is an anchoring effect achieved. The pressed-on pipes cannot be detached from the holding plate even when large forces are applied.

The soldered helix can also be used for fastening in another way, since it is practically a tube with a soldered thread. Should such a tube z. B. are attached to a container wall, then only two special nuts are required, which have a matching internal thread to the soldered coil. If at least one of these nuts is conical, then a rubber ring can be inserted into the cone, which is enclosed by the cone, the tube and the container wall and enables a sealed passage. If two such pipes are to be connected to one another, this can be done with the aid of a sleeve with a continuous thread. The pipes to be connected must be turned against each other. If this is not possible, then a pipe with a right-handed helix must be connected to a pipe with a left-handed helix by means of a sleeve with left-hand and right-hand threads.

The following examples serve to further explain the method according to the invention.

example 1

A band of oxygen-free copper with a thickness of 0.5 mm is bent by means of forming rolls to form a slotted tube with an 8 mm diameter. A copper wire with a 1 mm diameter is wound helically onto the slotted tube, the pitch being 2 mm. Simultaneously with the winding, a band of copper solder 3 mm wide and 0.1 mm thick is inserted between the helix and the slotted tube. The pipe is then optionally in the continuous pass heated in a soldering furnace, the melting copper solder flowing into the gap of the slotted tube and closing it due to the capillary action. In addition, the coil is soldered to the tube.

Without the wire helix, the tube would have a surface area of 250 mm ² per cm length. The surface of the wound wire is 450 mm ² per cm of tube length. Assuming a solder width of 0.2 mm, 60 mm ^{2 are} to be subtracted from this for the soldering point. The surface of the tube is thus increased from 250 mm ² per cm to 640 mm 2 by the coil.

A further increase in the surface area can be achieved if the wound wire is rolled flat while rotating the tube.

Example 2

Condensers, i.e. capacitors of refrigerators, consist of an unalloyed steel tube, which is bent in a meandering shape and to which wires or sheet metal ribs made of unalloyed steel, spaced apart to enlarge the surface, are attached in a heat-conducting manner across the meandering windings. To protect against corrosion, the entire structure is hot-dip galvanized and then painted. Inside there is an operating pressure of max. about 16 atü and accordingly the tube must be dimensioned.

According to the invention, a strip of unalloyed steel with a thickness of 0.5 mm is bent in forming rolls to form a slotted tube with an outer diameter of 6 mm. A wire made of copper-plated, unalloyed steel with a diameter of 1.2 mm is wound helically with a pitch of 2.2 mm onto the slotted tube. At the same time it becomes a copper tape of 7 mm width and 0.1 mm thickness inserted between the helix and the slotted tube. The tube is then optionally heated in a continuous pass in a soldering furnace, the melted copper flowing out of the copper strip into the gap in the slot tube due to the capillary action and closing it. In addition, the coil is soldered to the tube and, due to the excess solder, coppering is achieved, which serves as protection against corrosion. In this case, it is particularly advantageous to use a galvanically copper-plated steel wire, ie a so-called staple wire, instead of bare, unalloyed steel wire for the wound coil.

The pipe thus produced is e.g. bent in a meandering shape and the evaporator is finished. Apart from the much simpler production, the tube length is reduced by about a quarter due to the particularly favorable heat-emitting surface with the same effect, which is associated with a substantial saving in material. A further saving results from the fact that the tube wall thickness can be kept smaller, since the tube is more resistant to the internal overpressure in the tangential direction due to the wound coil.

Example 3

A spiral tube, which is produced exactly as described in Example 2, but with a spiral wire diameter of 0.8 mm, is used as the jacket tube of an electric tubular heater. After centering the heating coil, the remaining space inside the tube is filled with magnesium oxide under vibration. For pre-compression, the tube is then pressed flat and bent into an annular shape. The pipe bent in this way is inserted into a die sets and pressed against the bottom of a fat baking device made of aluminum with a pressure of 5 t per cm ² . The adjacent spiral sections penetrate vertically into the aluminum floor panel; the aluminum flows in the axial direction of the tubular heater and is pressed in behind the largest cross-section of the adjacent wire coil section. In this way, an anchoring effect is achieved, so that the pressed-on tubular heating element cannot be detached from the aluminum floor even when large forces are applied.

In the selected example, the bottom of the fat baking device has an outer diameter of 220 mm, the tubular tubular heater has an average diameter of 180 mm and a total length of 450 mm. The tube jacket is made of unalloyed steel with a wall thickness of 0.5 mm, the helix wire is also made of unalloyed steel with a diameter of 0.6 mm, the helix pitch is 2 mm. The outer diameter of the tube, without taking the helix into account, is 8 mm.

Is pressed flat to a thickness of 6.5 mm; the pressing tool has a semicircular profile. After pressing on with a pressure of 220 t, the surface in contact with the aluminum floor is flat, the tube has a width of 9 mm there.

Temperature cycling tests in the range between 150 and 250 C have shown that up to a load in the contact area of 80 W / cm ^2, the temperature difference between the tubular heater and the aluminum floor remains constant. This provides sufficient security, because in practice the maximum load at the connection level is around 30 W / cm ² .

Example 4

Panel radiators for electrical space heating are in most cases equipped with heating elements in the form of U-shaped tubular heating elements. These lie between two sheet metal plates forming the housing and give off the heat to them by radiation. Unalloyed steel is used as the pipe material for cost reasons. However, this is only possible up to an output of approximately 500 W per tubular heating element, because at higher outputs the AC humming noise becomes so strong that this disturbs. Tubular radiators with non-magnetic austenitic chrome-nickel steel sheaths must be used for higher outputs, which are more expensive.

For this purpose, a slot tube with an outer diameter of 8 mm is now produced from an unalloyed steel strip with a thickness of 0.4 mm in form rollers. A wire made of chromium steel with 18% chromium with a diameter of 0.3 mm is wound helically with a pitch of 4 mm onto the slotted tube. At the same time, a copper strip 2 mm wide and 0.1 mm thick is inserted between the helix and the slotted tube. The tube is then optionally heated in a continuous pass in a soldering furnace, the melted copper flowing out of the copper strip into the gap in the slot tube due to the capillary action and closing it.

Following this, the helix wire made of chrome steel is unwound again and can now be used. Chrome steel does not solder to the unalloyed steel when using copper solder. Product is a jacket pipe for a tubular heater, in which a significantly smaller AC humming noise occurs due to the interruption of the magnetic flux, so that you can practically all Panel radiators can produce occurring services in this way.

Example 5

A spiral tube, which is produced in the same way as described in Example 2, but with a spiral wire diameter of 0.5 mm and a pitch of 3 mm and a copper bandwidth of 5 mm, serves as a delivery tube for the brake fluid of motor vehicles. In such a braking system, steel pipes alternate with hoses made of rubber, plastic or the like. At the connection point of the pipe with the hose, the hose end is pushed onto the pipe end and fastened with a hose tie. As practical tests have shown, this transition point is absolutely tight despite the soldered-on helix, and it has the advantage even over a smooth tube that it is not possible to pull the hose off the tube because of the anchoring effect of the helix as long as the hose tie is tightened.

• Figur 1 schaubildlich ein Schlitzrohr mit Drahtwendel vor dem Verlöten;
• Figur 2 einen Querschnitt einer abgewandelten Ausführungsform eines Schlitzrohres;
• Figur 3 einen Querschnitt einer weiterhin abgewandelten Ausführungsform und
• Figur 4 einen Querschnitt einer dritten abgewandelten Ausführungsform.

The drawings show:

• Figure 1 shows a slotted tube with a wire coil before soldering;
• Figure 2 shows a cross section of a modified embodiment of a slotted tube;
• Figure 3 shows a cross section of a further modified embodiment and
• Figure 4 shows a cross section of a third modified embodiment.

In the embodiment shown in Fig. 1, a metal strip 1, z. B. made of unalloyed steel, bent to form a slotted tube by form rolling. A copper strip 3 is placed on the slotted tube in the vicinity of the gap 2. Furthermore, a wire made of copper-plated unalloyed steel is wound helically under prestress, so that a wire coil 4 is formed.

Special dimensions, calculated on an internal pressure of approximately 50 atm, are as follows:

The gap 2 is a capillary gap. For reasons of clarity, it is wider in the drawing than is shown in reality.

When such a prepared tube is continuously heated in a soldering furnace, the copper strip 3 melts. The molten copper flows into the gap 2, due to the capillary action thereof, and closes it. The coil is also soldered to the tube. Due to the excess solder, coppering of the coil is achieved, which serves as corrosion protection.

In the embodiment shown in Fig. 2, the edges areas 5 of the metal strip 1 angled vertically. The mutually opposite surfaces of the edge areas 5 are pressed together by the wire helix 4, not shown. This creates a deeper gap 2 with a correspondingly increased strength of the seam connection.

If an improvement in heat transfer, e.g. from a medium flowing in the interior of the tube onto the outer surface of the tube, then, as shown in FIG. 3, a metal strip can be used which is considerably wider than the diameter of the tube to be produced. The edge regions of the tube are angled twice at 6 and 7, so that on the one hand a gap 2 of the desired depth is formed, but on the other hand lobes 8 are formed which extend far into the interior of the tube. The lobes 8 cause the medium to flow through in a laminar flow kept and accordingly turbulence avoided. The heat transfer to the outer surface of the tube is significantly increased.

The embodiment shown in FIG. 3 is also particularly advantageous in fields of application in which heat is to be transferred inwards from the outer surface of the tube, e.g. B. if a poorly heat-conducting liquid is conveyed inside the tube, which is to be heated. For temperature measuring or control devices, e.g. B. in liquid thermostats, the response speed can be significantly improved by the protruding into the tube lugs 8. Of course, the cooling of flowing media is also significantly improved.

In the embodiment shown in Fig. 4, the metal band bent so that an overlap point is formed at 9. The inner edge area still strives to bend slightly. The outer edge area is pressed onto the inner edge area by the helix 4, not shown. A defined capillary gap is also formed in this way.

With the method according to the invention, therefore, pipes of a high quality are achieved. The wire or ribbon helix ensures that no changes can occur under the action of heat when soldering - not even in the range of far below 1/10 mm - so that an extremely exact, uniform seam is achieved.

Claims (24)

1. A thin-walled metal tube made of a metal band bent transversely to its longitudinal axis, the edge regions of which are connected to one another and which is wound with a wire or a band in a spiral shape, characterized in that
that the edge regions of the bent metal strip (1) are connected by a connecting means which fills up between the edge regions and solidifies on cooling as a result of gap capillarity. 2. Metal pipe according to claim 1, in which the wire coil or the band coil is dimensioned with respect to its pitch and its diameter so that the limit load of the tube against radial pressure is approximately doubled by the action of the coil and / or in which the heat-emitting surface of the tube at least is doubled. 3. Metal pipe according to claim 1 or 2, in which one or both side regions of the metal strip (1) are angled so that protruding edge strips (5, 8) are formed in the pipe interior. 4. Metal pipe according to claim 3, wherein the side regions are angled twice, so that the edge strips (8) extend over more than the radius of the tube into the interior of the tube. 5. Metal pipe according to one of claims 1 to 4, in which the side edges of the metal strip (1) are chamfered, so that an oblique to the diameter of the tube soldering gap is formed, the length of which is greater than the thickness of the metal strip. 6. Metal pipe according to one of claims 1 to 5, wherein the wire or ribbon coil (4) consists of a material which has a smaller coefficient of thermal expansion than the material of the bent metal strip (1), so that the coil is larger with increasing temperature counterforce in the radial direction exerted on the tube. 7. Metal pipe according to one of claims 1 to 6, wherein the coil (4) has a coating of a solder material. 8. Metal pipe according to one of claims 1 to 7, in which at least the surface of the metal band (1) forming the outside of the pipe is provided with a coating of a solder material. 9. Metal pipe according to one of claims 1 to 8, wherein the solder material is copper or a copper alloy, preferably in the form of a narrow thin foil strip. 10. A process for the production of thin-walled metal pipes, in particular pipes for condensers of refrigeration equipment, pipes for the brake fluid of motor vehicles, jacket pipes for electric tubular heaters and pipes for air heaters with low-pressure steam, in which a metal strip in a continuous pass through suitable molding tools its longitudinal axis is bent and in which the edge regions of the band are connected to one another, characterized in that that in order to achieve a defined gap, the tube is wrapped in a helical form or wire before connecting the edge regions, and that the closing of the gap at the longitudinal edges or overlap points of the metal strip is effected automatically by the action of heat on a corresponding section of the wrapped tubular structure, a connector which solidifies during cooling using the gap capillary action to fill the gap. 11. The method according to claim 10, in which together with the wire or the coil a film strip or a wire is applied to the outside of the semi-finished tubular structure, which melts under the action of heat and flows into the gap. 12. The method according to claim 10 or 11, in which, under the action of heat, the wire helix or the tape helix is simultaneously soldered onto the tubular jacket. 13. The method according to any one of claims 10 to 12, wherein the helical wire applied in a flat wire with the narrow cross-section is deformed in the axial direction and the wide cross-section in the radial direction of the tube. 14. The method according to any one of claims 10 to 13, in which a non-magnetic solder is used to close the gap, so that AC noise is reduced in tubular electric radiators with a tubular jacket made of ferromagnetic materials due to interruption of the magnetic flux. 15. The method according to any one of claims 10 to 14, in which the tube with the soldered coil is fastened to a holding plate, to another tube or to a shaped body by means of spot welding, the parts of the coil which lie at a point at the pitch distance act as welding bosses and the Helix keeps the welding current away from the pipe jacket. 16. The method according to any one of claims 10 to 15, wherein the coil soldered onto the tube is pressed into a softer holding plate or another shaped body, the material of the holding plate or the shaped body behind the largest diameter of the by the support on the adjacent coil winding Helix wire is pressed in and anchoring is achieved. 17. The method according to any one of claims 10 to 16, wherein the tube with the helically soldered helix is screwed into a container wall opening, a connecting sleeve with an internal thread or into a holding plate. 18. The method according to claim 10, wherein the coil is unwound from the pipe after the gap has been closed and is wound up again on a pipe section which has not yet been closed. 19. The method according to any one of claims 10 to 18, in which the edge regions of the metal strip are brought into overlap and a defined overlap region is set by the pretensioning of the wound wire or strip helix. 20. The method according to any one of claims 10 to 19, wherein the heating of the slotted tube in a continuous pass takes place in two stages, first using high-frequency heating and then using radiant heating under protective gas. 21. The method according to any one of claims 10 to 20, in which the end of a tube made of a plastic or elastic material is pushed over the end of the tube provided with a wire helix or ribbon helix and the plastic or elastic material preferably by means of a tube binder in the wire or coil is pushed in. 22. Use of a metal tube according to one of claims 1 to 21 in hydraulic fluid systems, preferably of motor vehicles. 23. Use of a metal pipe according to one of claims 1 to 21 in the manufacture of liquefiers of refrigeration devices. 24. Use of a metal tube according to one of claims 1 to 21 in the manufacture of tubular heater assemblies and devices with tubular heaters. 25. Use of a metal pipe according to one of claims 1 to 21 in air heater devices and devices.

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