WO2012005599A1

WO2012005599A1 - Method and equipment for the production of tubes and other extended products

Info

Publication number: WO2012005599A1
Application number: PCT/NO2011/000197
Authority: WO
Inventors: Bjørn Andor RUSTAD
Original assignee: Norsk Hydro Asa
Priority date: 2010-07-09
Filing date: 2011-07-08
Publication date: 2012-01-12

Abstract

A method for production of tubes with small dimensons, in particular capillary tubes and other closed and open profiles of various sizes. The tubes are produced from an extruded multiport extrusion product, MPE (1 ) comprising a number of ports or tubes (2) provided side by side and each being interconnected by means of a step or fin (3). Initially the MPE product (1 ) is produced by extrusion, where after the tubes (2) of the MPE product is split such that individual tubes (2) are provided by separating them from one another through cutting of the steps or fins (3) in the longitudinal direction of the MPE product.

Description

Method and equipment for the production of tubes and other extended products

The present invention relates to a production concept or method for the production of various profiles and tubes with small diameters, in particular capillary tubes and micro fin tubes such as for applications in the HVAC&R industry. Of particular interest are geometries where subsequent drawing and other manipulating processes must be avoided in order to maintain certain geometrical and/or mechanical properties of the extruded profile. The invention further includes equipment for the production of such profiles and tubes.

Capillary tubes, for instance of aluminium, may be used as pressure and temperature gauge lines or as expansion devices in refrigerators and other systems. While capillary tubes for pressure- and temperature gauges may have quite wide internal tolerances, this is not the case when capillary tubes which are used as expansion devices. Due to the need for tight control of the pressure drop in the cooling cycle, the geometrical tolerances as well as the internal surface roughness need to be well defined and uniform.

Production of drawn tubes is commonly done by means of cold drawing processes. By this method the tube is drawn through a die, either with or without internal support. If further reductions are required, the tube must be annealed to bring it back to ductile strength. There are two basic methods of cold drawing; one method is sink drawing and the other is plug drawing.

Production of capillary tubes, i.e. tubes with very small diameter, as it has been carried out so far, involves many drawing processes in order to transform the base tube to a drawn tube with the desired reduced dimensions. For example a capillary tube of aluminium may involve 7 successive draws in order to achieve an internal diameter of 1 ,7 mm. Further, it has proved difficult to conduct plug draws in the last drawing steps due to the very small internal diameters of the end product.

Sink drawing has two major influences on the end product; 1 ) the geometrical ID tolerance is less accurate in sink drawn tubes than for plug drawn tubes and 2) excessive sink drawing creates an undefined surface roughness which affects the pressure drop in the tube in an uncontrollable manner.

Plug drawing is usually conducted with lubricants which represent a risk of oil remnants in the end product. The use of the internal tool also means that internal cleanness may be affected by particles from the tube material itself. Both factors may affect the tube's pressure drop characteristics uncontrollably.

Consequently, due to the many process steps and the limitations of the internal flow properties of today's capillary tubes, the tubes are costly to produce, and they are not suitable for applications where high precision is required, such as expansion devices, due to the lack of control of tolerances and the poor internal surface.

With the present invention is provided a method of producing capillary tubes which represents a more productive production of capillary tubes than existing drawing processes and where the tubes have higher tolerances and improved internal cleanness and surface quality which for instance offers better control of pressure drop than existing drawn capillary tubes and may be used precision applications such as for expansion devices. The capillary tube according to the invention further is much cheaper to produce than the existing drawn capillary tubes.

The invention is characterized by the features as defined in the attached independent claims 1 and 6.

Preferred embodiments of the invention are defined in the sub-ordinate claims 2 - 5 and 7 - 9.

The invention will now be further described by way of examples and with reference to the drawings where: Fig. 1 shows in perspective a schematic view of a multi port extruded product

(MPE) prior to splitting in accordance with the present invention,

Fig. 2 in end view a) and perspective b) example of an MPE product with a different cross sectional design,

Fig. 3 shows a side view a) and end view b) of a cutting equipment according to the invention with an MPE as shown in Fig. 1 being cut,

Fig. 4 shows a side a) and end view b) of another cutting equipment according to the invention,

Fig. 5 shows an example of a third cutting equipment, as well in side a) and end b) view, Fig. 6 shows the same MPE as is seen in Fig. 1 being split by an alternative splitting equipment according to the invention, where the upper part of the figure a) shows cross sectional views (A-A, B-B, C-C, D-D, E-E, F-F) along splitting line as shown in figure part b) below. The initial starting point for the method according to the present invention is, as shown in Fig. 1 , a so called multi port extruded product 1 , often denoted MPE. The MPE product 1 is extruded though a die and consisting of a number of round tubes 2 provided side by side. In the example shown in the figure the MPE includes four ports or tubes. The tubes of the MPE are interconnected with intermediate steps or fins 3. Each MPE 1 may, as an example have a width of 18 mm and a fin thickness of 0,15-0,20 mm.

Up to 8 such dies can typically be mounted at each extrusion press, which implies that it would be possible to extrude up to 56 capillary tubes simultaneously if each MPE is extruded with 7 ports.

Tests have shown that even a small MPE consisting as shown in Fig. 1of 4 capillary tubes of 2/0.85 mm (OD/ID) could easily be extruded with good productivity and material flow.

After extrusion, each of the 8 produced MPEs are split inline and coiled as a finished product or coiled on a suitable roll for transport and intermediate storing before being split in a subsequent process..

The method according to the invention is based on the principle that the MPE product, either provided directly from the extrusion press or de-coiled from a coil, is split into separate capillary tubes by means of especially developed splitting equipment which is provided with some kind of separating device.

Thus, the method according to the present invention is characterized in that a multi port extrusion, a MPE profile is extruded and then split in the longitudinal direction such that individual tubes or products with desired cross sectional design are provided by separating said tubes or products of the MPE from one another. The splitting and separation can be accomplished in many different ways by mechanical splitting apparatus or heating means (cutting torch, blow pipe, water jet laser etc.).

As to the term MPE, it should be stressed that it is not restricted to a port or tube as shown in Fig. 1 but may include any shape of an extruded and extended product such as the example of a multi u-channel shape 4 with ribs 5 as is shown in Fig. 2. The MPE may also consist of capillary tubes or other shapes connected without fins or steps 3. In such designs the slit area represents a relatively larger fraction of the capillary tube's or profile's outer surface which may have some kind of functional purposes included the end product. The method according to the invention is based on the principle that the MPE 1 may be split into individual products or tubes by splitting along premade weakening lines or by cutting all through the steps 3 between the products 2. Thus the weakening lines may be made mechanically or with heat, or they may be made during extrusion. The attached figure 3 - 6 show different types of cutting equipment according to the invention. Hence, Fig. 2 shows a cutting equipment in the form of a roller cutter 6 and a support roll 7 with elevated support rims 8 designed to fit between each port or port or tube 2 of the MPE (see Fig. 1 for details). The roller cutter 6 has a twin cutting edge 9 enabling cutting of a longitudinal cut on each side the step 3 between the tubes 2.

Depending on the thickness of the step 3, the cut may be accomplished partly or fully through the step. Being cut only partly through, the step 3 is provided with a longitudinal weakening line (not shown) and may easily be removed in a later process step as is explained in a later paragraph of the description in conjunction with the attached Fig. 6 if cut fully through. The split tubes are each stored on suitable coils or other storing means, while the cut off steps 3 are led to a collection container for cut off material (not further shown).

Fig. 4 shows another cutting equipment with the same rotary cutter 6 and support roller 7 as shown in Fig, 3, but where an additional cutter 6 and support roller is provided after the first. Such double cutter and support roller arrangement may be used to cut thicker steps 3 of the MPE or to create weakening lines on both sides of the step which may improve the burr characteristics after splitting.

Fig. 5 shows a third cutting equipment including two roller cutters 10, one abutting the other. This cutting arrangement may as well enable deeper cuts through thicker steps 3. Figures 3-6 shows, as described above, different simple solutions for cutting or forming longitudinal weakening lines in MPE product as part of a process for making extended product such as capillary tubes by splitting. Fig. 6 shows an example of a mechanical splitting apparatus including crack initiators 1 1 in the form of knives (cutting blades or rolling knives), crack fatigue initiators 12 in the form of rollers 13, 14 and slitting means 15 in the form of slitting rollers 16, 17.

The splitting equipment works as follows: The multi port tube 1 is led (from an extrusion press or roll store (not shown) to the cutting knives 11 to initiate a crack in the step 3 of the MPE (see Fig. 1 ) between each tube or port 2 of the product. Then the MPE product is further advanced to a number of crack initiators 12 where each step or fin 3 of the MPE is bent by the cams 18 of the upper and lower rollers 13 against oppositely provided rollers 14 in four different steps between the pair of rollers 13, 14. Finally the MPE is led to the slitting means where the ports are separated by the separating rollers 16, 17 being provided with groves 19 and cams 20, respectively such that the steps 3 of the MPE are removed . Each separated tube 2 may then be stored on a suitable coil or other storing means (not shown) while the removed step 3 is forwarded to a suitable collection container (neither not shown).

The invention as defined in the claims is not restricted to the examples as shown in the figures and described above. Thus, the invention may be used for producing tubes of different types of materials such as steel, copper and polymers. Even though the present invention in particular is applicable for capillary tubes and other small profiles, the invention is not limited to such dimensions, but may also be used for larger profiles.

Claims

A method for the production of tubes or other extended products with small dimensions, in particular capillary tubes (2) or other open or solid profile designs of various sizes,

characterised in that the products or tubes (2 ) are produced from an extruded multiport extrusion product profile, MPE (1), by initially extruding the MPE profile (1) comprising a number of tubes or other profiles (2) provided side by side or in a flat or curved configuration and each being interconnected by means of a step or fin (3), and thereafter splitting the products or tubes (2) such that individual products or tubes (2) are provided by separating them from one another along a weakening line or through cutting or slitting of the steps or fins (3) in the longitudinal direction of the MPE profile.

A method according to claim 1 ,

characterised in that

the steps (3) are provided with a longitudinal weakening line under extrusion of the MPE profile.

A method according to claim 1 ,

characterised in that

the steps (3) of the MPE are provided with a weakening line by cutting or is cut all the way through by a cutting means (6, 7, 10, 11 )..

A method according to claim 1 ,

characterised in that

the steps (3) of the MPE are cut by the use of heat.

A method according to claim 1 -4,

characterised in that

the MPE is made of aluminium.

6. Equipment for the production of products or tubes (2) with small diameter, in particular capillary tubes, where the products or tubes are produced from an extruded multiport extrusion profile, MPE (1), by initially extruding the MPE profile (1 ) comprising a number of products, ports or tubes (2) provided side by side and each being interconnected by means of a step or fin (3),

characterised in

means (6, 7, 8, 9, 10, 11, 12, 14, 15) for splitting the MPE product by separating the products or tubes (2) from one another along a weakening line or through cutting of the steps or fins (3) in the longitudinal direction of the MPE profile (1 ).

Equipment for the production of tubes according to claim 5,

characterised in that

the means for splitting includes a mechanical cutting device in the form of a rotary or stationary knife (5, 7, 10, 11 ) cutting partly or fully through the step (3).

Equipment for the production of tubes according to claim 6,

characterised in that

the means for splitting further includes in a next step a fatigue crack initiation device in the form of rollers (13,14) and in a final step a pair of slitting rollers (116, 17).

Equipment for the production of tubes according to claim 5,

characterised in that

the means for splitting includes a cutter in the form of a high temperature cutting means.