WO1991014024A1

WO1991014024A1 - Method and device for surface treatment of elongated, metallic articles

Info

Publication number: WO1991014024A1
Application number: PCT/NO1991/000040
Authority: WO
Inventors: Morten Syslak; Leiv Ådne FOLKEDAL
Original assignee: Norsk Hydro A.S
Priority date: 1990-03-16
Filing date: 1991-03-13
Publication date: 1991-09-19
Also published as: NO901250D0; NO901250L

Abstract

Continuous surface treatment of elongated metallic articles (5) is performed by means of coiling the articles on one or more rotating devices fitted in containers (2) filled with treatment media (3). The rotating devices are drums (1) fitted horizontally or vertically within the container, said drums having perforated surfaces for effective contact between the article and the treatment medium.

Description

METHOD AND DEVICE FOR SURFACE TREATMENT OF ELONGATED, METALLIC ARTICLES.

The present invention relates to a method for surface treatment of elongated metallic articles, and more particularly continuous surface treatment of tubes, shapes or the like, and a device for carrying out the method.

Surface treatment of e.g. extruded and/or drawn metallic tubes and shapes often comprises a number of steps, such as degreasing, pickling, anodising, coating, etc., either to obtain a better (nicer) surface on the product or to change the properties, such as corrosion resistance, surface hardness, etc. , of the product more profoundly.

The conventional treatment takes place in a series of containers filled with active liquids, such as lyes, acids, electrolytic baths, etc. with intermediate rinsing between each step of processing of ready cut lengths. The treatment time can vary from 20-30 seconds up to several minutes, depending on the type of treatment and the equipment used, something which makes it difficult to perform treatment continuously in-line with the production of articles.

In order to improve the economy of the process and to increase the flexibility in terms of the length of the finished products, continuous treatment of "continuous" articles is desirable, e.g. from large coils or directly linked to the extrusion or drawing of tubes. The devices and processes known for this hitherto are largely based on the use of long containers and/or moving the articles back and forth repeatedly by means of a number of belts submerged in the container. In practice there are clear limits on how long a treatment vessel can be, the space available and how complicated the feed device can be, in light of that the equipment must withstand the aggressive environments and elevated tempera¬ tures which are often characteristic of such processes.

It is therefore an object of the present invention to provide a new method which avoids the aforementioned difficulties and limitations of known equipment and processes, and which permits continuous, in¬ line treatment of long articles with high productivity and low investment and maintenance costs, and a device which ensures a flexible treatment time for the articles which is adapted to the relevant steps of treatment in the process.

According to the invention a method for surface treatment of elongated articles has been provided where the articles are fed into a container at a tangent to the surface of one or more rotating devices fitted in the container, the articles being exposed to a treatment medium and held in contact with the medium by means of coiling during lateral movement along the axis of rotation of the devices.

In the following the invention will be explained in greater detail by means of preferred embodiments and with reference to the attached drawings, Figs. 1-3, in which

Fig. 1 shows a schematic perspective drawing of a device to carry out the method,

Fig. 2 illustrates a fragment of a detailed embodiment of the surface and control of article introduc¬ tion to the device, Fig. 3 shows in a vertical cross-section an alternative embodiment of the device.

Figure 1 shows a device comprising a drum 1 fitted horizontally in a container 2 containing a treatment medium, e.g. a bath of chemicals 3, in such a way that the drum is in all essentials submerged in the bath. An article 5, which is to be treated, is introduced onto the surface of the rotating drum 1, follows its circumference, is coiled and during successive lateral movement of the coiled article in an axial direction, the treated article leaves the bath on the opposite side of the drum after a predeter¬ mined contact time in the bath. The articles, such as aluminium tubes, shapes or the like, are supplied to the device either directly in-line with production equipment (extrusion press, drawing machine) or from coils (not shown in the figure) and transferred after treatment to the next step of treatment, possibly coiling or final cutting of the product.

Figure 2 shows a more detailed embodiment of the surface of the drum. In order to ensure that the relevant contact time with the treatment medium for the entire surface of the objects is approxi¬ mately equal to the time spent in the bath during coiling, the drum 1 has a perforated surface. The surface is divided into annular segments 11 comprising apertures (windows) 12 which are staggered in relation to the apertures in adjoining annular segments. During the successive lateral movement of coiled articles, this will ensure as the drum turns that even those parts of the articles which are touching the partitions 13 between the apertures in one segment come into contact with the treatment medium when they pass the next segment. The size of the apertures and their configuration can also be varied to ensure periodic exposure of the entire surface. The drum is also equipped with an auxiliary device (cam) 15 which ensures that the elongated article 5, e.g. a tube, which has been introduced at a tangent is coiled and moved laterally towards the opposite end of the drum without any danger of the articles piling up during introduction to the drum.

By means of the device described above, it is possible by varying the speed of rotation (rpm) , drum diameter and number of coils on the drum to operate at very high line speeds adjusted to the speed of production (in-line) , even if the relevant surface treatment time is long. The length of the line and space required is also much less than that for existing installations.

Example

The actual line speed is 300 m/min. and the provided tube has an outside diameter of 6 mm. The surface treatment time required is 1 minute. If a drum with a diameter of 1 m is chosen, the circum¬ ference will be equal to 3.14 m. The speed of rotation required will be 300/3.14 = 96 revolutions per minute and the resulting number of coils on the drum 96.

Provided that the coils touch each other, the width of the drum will be 96 x 6 = 576 mm, i.e. the device will be of moderate dimensions.

Figure 3 shows another preferred embodiment of the device for surface treatment of elongated articles according to the present invention. In this case two, and possibly more, drums 1 are fitted in all essentials vertically in a container 2 partly submerged in the bath 3. The article (tube) 5 is once more introduced at a tangent onto the surface of the first drum, coiled around the circumference of the drum, and, during successive lateral movement downwards in an axial direction, reaches the bottom of the drum and is introduced by means of guide rollers 6 at a tangent onto the surface of the other rotating drum. The lateral movement of the article during rotation is reversed to an upwards direction, and the treated article leaves the drum and the container 2 by means of another guide roller 6' above or below the level of the bath 3. The operation of the two drums is synchronised, and this embodiment of the device will produce a simpler structure in that there does not have to be a shaft gland through the container.

The present invention is not limited to the embodiments of the devices described above. The horizontal drum could for example have a longitudinally conical cross-section with or without perforation of the surface, so that the treated, coiled articles would at the same time be continuously displaced around the perimeter of the drum during lateral movement along the axis of rotation. This would result in further alternating exposure of shielded areas of the surface of the articles. Other possible ways of exposing the articles to the medium than the above disclosed dipping/submerging are also feasible, e.g. spraying, splashing etc.

Claims

1. A method for surface treatment of elongated, metallic articles such as tubes, shapes or the like by means of a treatment medium in a con¬ tainer, c h a r a c t e r i z e d i n t h a t the articles are introduced into the container at a tangent onto the surface of one or more rotating devices situated in the container, and exposed to the medium for a predetermined period of time by means of coiling of articles during controlled lateral movement along the axis of rotation of the devices.

2. A method according to claim 1, c h a r a c t e r i z e d i n t h a t the rotating device comprises a drum (1) fitted horizontally in which the coiled articles are displaced continuously during their lateral move¬ ment along the axis of rotation.

3. A method according to claim 1, c h a r a c t e r i z e d i n t h a t the coiling of the articles takes place by means of two or more drums fitted in series and in all essentials vertically in the container and where the controlled lateral movement is reversed during successive transfer of the articles between the drums.

4. A method according to 2 or 3 of the above claims, c h a r a c t e r i z e d i n t h a t the surface treatment is a continuous process based on in-line feeding of continuous articles such as extruded or drawn aluminium piping.

5. A device for surface treatment of elongated metallic articles comprising a container (2) and a retardation device (1) for holding the articles back in the container in contact with the treat¬ ment medium for a predetermined period of time, c h a r a c t e r i z e d i n t h a t the retardation device (1) comprises one or more rotating drums with the introduction of articles onto the surface of the drums at a tangent.

6. A device according to claim 5, c h a r a c t e r i z e d i n t h a t the surface of the drums has a number of apertures (12) arranged in a staggered manner.