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Patent Searching and Data


Title:
PROCESS FOR REMOVING A PLASTIC COATING FROM METAL PRODUCTS
Document Type and Number:
WIPO Patent Application WO/1999/019087
Kind Code:
A1
Abstract:
A process for removing a plastic coating from metal products coated with said plastic, wherein a water-jet is directed to the location from which the coating must be removed without damaging the metal. A water pressure between 2500 and 3500 bar is preferred and as the water-jet may be directed under an angle between 40° and 50° with respect to the surface from which the plastic must be removed.

Inventors:
HEDEDAM OVE (DK)
BRAEUNER HANS (DK)
Application Number:
PCT/EP1997/005710
Publication Date:
April 22, 1999
Filing Date:
October 10, 1997
Export Citation:
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Assignee:
NORSK HYDRO AS (NO)
HEDEDAM OVE (DK)
BRAEUNER HANS (DK)
International Classes:
B08B3/02; B08B9/02; B08B9/053; B29C63/00; (IPC1-7): B08B3/02; B08B9/02
Foreign References:
DE4020034A11991-01-03
FR2630667A11989-11-03
US5220935A1993-06-22
EP0436421A11991-07-10
Other References:
PATENT ABSTRACTS OF JAPAN vol. 18, no. 636 (M - 1715) 5 December 1994 (1994-12-05)
Attorney, Agent or Firm:
Bleukx, Luc (Avenue Marcel Thiry 83, Brussels, BE)
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Claims:
CLAIMS
1. A process for partly removing a plastic coating from metal products coated with said plastic, characterised in that a waterjet is directed to the location from which the coating must be removed, said waterjets having a sufficient force to remove the coating without damaging the metal.
2. A process according to claim 1, characterised in that the metal is aluminium.
3. A process according to claims 1 or 2, characterised in that the product is a tube.
4. A process according to any one of the claim 13, characterised in that the coating is made of polyamide.
5. A process according to any one of the claims 14, characterised in that the water pressure is between 2500 and 3500 bar, preferably between 2,800 and 3,000 bar.
6. A process according to any one of the claims 15, characterised in that the outlet opening of the nozzle for directing the water jet has a diameter between 0.15 and 0.2 1mm, preferably between 0.17 and 0.19 mm.
7. A process according to any one of the claims 16, characterised in that the nozzle has a conical shape.
8. A process according to any one of the claims 17, characterised in that the nozzle. is directed under an angle between 40° and 50° with respect to the surface from which the plastic has to be removed.
Description:
Process for removing a plastic coating from metal products The invention relates to a process for partly removing a plastic coating from metal products coated with said plastic.

It is common to coat metal product with plastic material for different reasons. In a number of applications the plastic coating is intended as a protection against corrosion, shock impact, as a decorative element, or as an isolation for heat and/or electricity.

As the plastic coating is generally applied by means of a submersion process, i. e. a process in which the metal product is temporarily completely submersed into a bath containing molten plastic material, the coating is not selective, i. e. the complete surface of the metal product is coated with plastic material. The application methods, such as spraying the plastic coating on the surface of the metal product, are mostly not very selective, which means that it is difficult to clearly define the transition between the coated and the uncoated area.

In a number of applications of metal products coated with plastic material it is desirable to have certain parts of the surface of the metal product in an uncoated condition. This is especially applicable in situations in which the metal product has to be connected to other metal products. Otherwise it is desirable to have the non-coated area of the metal product as small as possible in order to not reduce too much the effect of the plastic coating.

It is possible to remove the plastic coating by means of traditional processes such as scrubbing, scraping, milling, abrasing, grinding, etc., but all these methods show the disadvantage that they effect also the underlying metal surface of the product. This generally results in a raising of the internal stress at that location in the metal product and mayh weaken locally the product.

It is therefore an object of the invention to provide a process for removing a plastic coating from a metal product which does not have the above mentioned disadvantages.

This object is achieved in that a water jet is directed to the location from which the coating must be removed, said water jet having a sufficient force to remove the coating without damaging the metal.

Water jet cleaning of surfaces is generally known in the art. However up till now it was not used to remove plastic coatings from metal products. This can advantageously be done in such a way that only a defined area of the plastic coating is removed without damaging the underlying metal surface. This is possible with a water jet system because a water jet can be highly focused on defined area without influencing neighbouring area's and because the force of the water jet can be controlled in such a way that only the plastic coating is removed without deteriorating the underlying metal surface. In this way a very effective and reliable removal of the plastic can be obtained.

The invention can be applied with special good results if the metal product is made of aluminium. Aluminium means here aluminium and aluminium alloys. This special advantage is especially the result of the inherent characteristics of aluminium, which on the one hand is an excellent material for a number of applications, but on the other hand is very susceptible to damages if not treated in the right way. Especially the use of external forces can easily result in internal stresses in the aluminium and deterioration of the surface.

Although the invention is not restricted to any special shape of the metal product, it is preferably used with metal tubes coated with plastic material, more specifically with aluminium tubes coated with polyamide.

Aluminium tubes coated with plastic material such as polyamide are widely used in a number of applications, especially in the automobile industry. In order to connect the tubes to other implements it is required to remove part of the plastic coating. This is especially the case of the end portions of the tubes, which must be able to be connected to nipples or valves, which connection is commonly made by means of brazing, requiring the removal of the plastic coating in order to obtain a reliable fluid tight connection. Otherwise also hose-connections to the end portions of the tubes require some further machining of the tube end. Especially in case of crimped hose

connections one or more O-ring grooves must be fitted so the tube ends. Such groove cannot be made within the plastic coating, but must be arranged completely in the metal surfaces in order to have a fluid-tight connection between the hose and the tube.

In practice the process is done with a water pressure between 2500 and 350 bar. It has been founed that with this water pressure most of the conventional plastic materials can be removed in an efficient and clean way without affecting the underlying metal surface. In case of aluminium products coated with polyamide it has been founed that an optimal water pressure lies between 2800 and 3000 bar, thereby leaving a clean aluminium surfaces and a sharp transition between the coated and uncoated area.

In the process according to the invention a nozzle is used in order to generate the water jet removing the plastic coating from the metal surface. Such a nozzle has an outlet diameter between 0.15 and 0.21 mm, preferably between 0.17 and 0.195 mm.

Such outlet diameters guarantees that a sufficient high pressure can be generated with a water jet which is sufficiently well focused in order to obtain a clean transition between coated and uncoated surfaces of the metal product. The distance with respect to the metal product from which the plastic coating must be removed must be maintained between 20-40mm, dependent on nozzle-design.

The output channel of the nozzle is conical resulting in an outlet channel with decreasing cross-section towards its outlet end.

An optimal effect of the water jet system according to the invention can be obtained if the nozzle generating the water jet is directed under an angle of 40-50° with respect to the surface from which the plastic coating must be removed. In this way the water jet helps in the discharge of the plastic material removed from the metal product.

Simultaneously a shearing force is used to remove the plastic material from a metal surface thereby decreasing the risk of deteriorating the metal surface.

The invention will now be further explained by means of a practical test performed in accordance with this invention, without being specifically restricted to this example.

An aluminium tube having an outlet diameter of 10 mm has been coated with polyamide PA-12 in a continuous process wherein the tube was submersed in a coating bath containing molten PA-12. After coating the tube was cut into pieces of 700mm each.

In order to make the tube sections, susceptible for connection with other parts in their final application as gasoline supply tube in a passenger car the two end portions of each section must be free from the polyamide coating over a distance of 55mm.

For that purpose a nozzle having a fluid outlet diameter of 0.18 mm was installed and connected to a water source supplying water under a pressure of 2900 bar. The tube section was clamped in a movable and rotatable clamping head in such a way that the end portion of the tube section can be moved under the nozzle which was installed under an angle of 45° with respect to the longitudinal axis of the tube section.

After clamping the tube section in the clamping head and supplying the water to the nozzle, the clamping head was started rotating at 900 r. p. m. whereupon the tube section was moved in longitudinal direction at a speed of 160 mm/min. with respect to the nozzle. The end portion of the tube section was in this way exposed to the removal force of the water jet, and this was done during a time sufficient to remove the plastic coating over the desired length from the end portion. As soon as this length has been reached, the longitudinal movement of the tube section was reversed, and the water supply interrupted. The water and PA-12 contained therein was recovered, the PA-12 pieces removed by filtering or centrifuging and the cleaned water recycled to the nozzle.

Inspection of the tube section ends revealed that the PA-12 was completely removed from the end portions envisaged, that the aluminium tube itself was not visibly damaged, and there was a clear and sharp transition between the coated and uncoated part of the tubes.