EP1222038A1

EP1222038A1 - Device and method for mechanically removing surface coatings by means of coldness

Info

Publication number: EP1222038A1
Application number: EP00960649A
Authority: EP
Inventors: Wolfgang Volker; Thaddaeus Poloczek
Original assignee: Messer Griesheim GmbH
Current assignee: Messer Griesheim GmbH
Priority date: 1999-09-30
Filing date: 2000-09-12
Publication date: 2002-07-17
Also published as: WO2001023112A1; DE19946957C1

Abstract

In prior art, devices for treating surfaces are only useful for removing easily removable coatings, whereby dry ice jet appliances are used for instance, or only for treating hard substrates, whereby needle appliances are used for instance. The aim of the invention is to provide a possibility for treating surfaces, whereby said possibility can be used for hard as well as soft substrates. According to the invention, a surface treatment tool (2), such as a needle appliance, that acts upon the surface of a substrate (10) by means of mechanic pulse transmission engages with a cooling device (3) for projecting a cooling means onto the surface of the substrate (10). Said tool is provided with components (12) which are useful for treating sensitive substrates (10). Said components can be needles (4) consisting of synthetic material. In a preferred embodiment, the cooling means is CO2 which is transported to the cooling device (3) in a liquid, warm form and develops the coolness effect thereof by means of expansion.

Description

Device and method for cold-assisted mechanical removal of

surface coatings

The invention relates to a device and a method for removing a coating from a substrate.

Surface processing methods such as sandblasting, shot peening, vibrating needles or dry ice blasting are known, the purpose of which is to detach a coating from a substrate. For the treatment of easily removable layers, the dry ice blasting process is widely used today, which achieves its best effect on medium-hard and easily embrittled surfaces that are applied to a relatively firm and hard surface. This process, which is described, for example, in the article by S. Donath and F. Lürken: "ColdJet - environmentally friendly cleaning with dry ice pellets" gas aktuell 41, p.4 (1991), is used, for example, for the derusting of hulls. Here it is not important to create shiny metallic surfaces, but only to remove the poorly adhering rust particles, since firmly adhered, passivated components of the oxide layer already provide a certain rust protection for the underlying metal. Because of the relatively low hardness of the dry ice particles of 2 ( Mohs) dry ice blasting processes are also suitable for cleaning sensitive surfaces, but the process is only very ineffective in removing hard coatings or coatings that are firmly attached to the substrate, thanks to a special nozzle geometry, such as that described in DE 198 07 917 A1 indeed the jet speed and thus the areal power can be maximized based on the amount of dry ice and compressed gas used, but the jet speed has only a minor influence on the removability of hard layers or layers firmly attached to the substrate.

To remove hard surface coatings, on the other hand, devices are used in which the coating to be removed, such as in the needle hammer tool described in DE 44 27 910 A1, is operated mechanically. kung is eliminated. Air-operated needle tools are equipped with hard steel needles, which are periodically struck against the surface to be cleaned by the interaction of a flying piston driven by compressed air and a return spring, and in this way remove a coating abrasively.

A disadvantage of these devices according to the prior art, however, is that the treated surface heats up during use, which in some cases can result in the toughness of the surface covering to be removed increasing and thus the removal process being made more difficult; furthermore, the substrate surface may be damaged.

In the technical article by D. Rebhan: "Rubber molded parts deburred with liquid nitrogen as a means of supercooling," in: Maschinenmarkt Würzburg 91, p. 1884 (1985) describes a process in which rubber molded parts are subjected to cold treatment by deburring with liquid nitrogen before deburring Burrs adhering to the molded parts become brittle as a result of the cold effect and can then be removed more easily by using blasting media. This process is not suitable for removing firmly adhering surface coatings.

The object of the present invention is therefore to create a possibility for removing surface coatings which is gentle on the material and is suitable for removing both soft and hard coatings.

This object is achieved by a device with the features of patent claim 1.

When the invention is used as intended, the substrate is thus subjected to a cold treatment by irradiation with a refrigerant during the mechanical processing or with a time delay. The cold treatment leads to embrittlement of the coating, which complements and supports the abrasive cleaning effect of the processing tool. The mechanical-abrasive machining can thus be carried out with tool parts of lower hardness than with machining tools according to the prior art. Any substance that can cause the coating to become brittle is conceivable as a refrigerant. This includes, for example, carbon dioxide, which can be irradiated onto the substrate in the form of cold gas or solid particles. It is also conceivable to use CO ₂ pellets, the low hardness of which allows particularly gentle processing.

A needle device can be used as the preferred processing tool. In such a device, processing is carried out by means of needles which can be moved longitudinally in the needle device and which periodically act on the substrate and in this way bring about an abrasive removal of a coating lying on the substrate.

In order to enable the processing of particularly sensitive or soft substrates, the needles of the needle device are not made of steel, as is the case with commercially available needle devices, but of plastic. Tough-hard plastics are considered as the preferred material, for example polyamide, which is reinforced with Kevlar fibers or with aluminum powder; however, other materials with similar properties are also conceivable.

For easier maintenance of the processing tool, the needles are accommodated on their side opposite the intended use tip in sleeves made of a hard, for example metallic material, and are firmly but detachably connected to them. The needles can be easily replaced, for example if the needles wear out or if the needles are to be replaced by those with different processing properties, without impairing their mode of operation. In order to ensure high efficiency in the abrasive actuation of the machining tool, the machining tool can be operated pneumatically, for example with compressed air.

In a particularly advantageous development, the cooling device is pneumatically connected to the compressed air supply to the machining tool. Pneumatic devices are provided which, when the compressed air supply to the processing tool is opened, open the refrigerant supply simultaneously or with a time delay. If required, however, both compressed air supply lines can be disconnected from one another, for example, so that the tools can be used independently of one another.

It is advisable to arrange the refrigerant supply inside a compressed air supply, preferably coaxially. In this way, the refrigerant supply, such as a supply hose for liquid CO ₂ , is effectively protected against mechanical damage.

As an alternative or in addition to the pneumatic drive, the machining tool can also be operated electrically and / or hydraulically.

A low-cost refrigerant supply, which is particularly advantageous for small and very small applications, consists in a riser bottle filled with liquid carbon dioxide, in which carbon dioxide is in liquid form under pressure at room temperature. As a result of the pressure drop when exiting the cooling device, the carbon dioxide has a considerable cooling effect.

For larger and / or industrial applications of the device according to the invention, a medium-pressure tank system for cooling supply is recommended, in which the carbon dioxide is in liquid form. A jet funnel connected to the processing tool, into which the jet nozzle of the cooling device opens, ensures a further improved concentration of the

Effect of cold on the processing zone.

A further expedient embodiment of the invention is provided by a device with the features of claim 12: The tool part or the tool parts which act on the substrate are received in a guide device into which a jet nozzle of the cooling device opens at the same time. This not only effectively cools the machining zone, but also the tool part or parts during use.

The cooling device is advantageously detachably connected to the machining tool. This configuration facilitates the maintenance of the individual components and also allows the processing tool or the blasting device to be used separately.

The object of the invention is also achieved by a method having the features of claim 14. The cold treatment which takes place at the same time or with a delay in relation to the mechanical treatment leads to embrittlement of the coating and thus to an improved cleaning effect.

The cold treatment is expediently carried out by a radiation treatment in which the substrate is irradiated with gaseous and / or solid carbon dioxide. For this purpose, the carbon dioxide is introduced in liquid form and only expanded in the immediate vicinity with the formation of gaseous CO ₂ . In this way, costly insulation of the coolant supply lines is unnecessary and icing problems do not occur in the area of the cooling device or only to a very limited extent. An advantageous development of the method according to the invention provides, in addition to the cold treatment of the substrate, also the pulse-transmitting tool parts

To apply refrigerant.

Exemplary embodiments of the invention will be explained in more detail below with reference to the drawings. Schematic views show:

Fig. 1: A needle tool with CO ₂ cooling device in longitudinal section, Fig. 2: The needle tool from Fig. 1 in cross section along the section line AA Fig. 3: Various configurations of a needle device according to the invention with CO ₂ cooling device, Fig. 4: Various Embodiments of a needle for a needle tool, FIG. 5: in a block diagram, a refrigerant supply for a needle tool with CO ₂ cooling device and FIG. 6: different configurations of supply lines for compressed air and refrigerant in cross section.

The device 1 shown in FIGS. 1 and 2 comprises a compressed air-operated needle tool 2 and a cooling device 3.

The needle tool 2 designed as a hand-held device has a number of needles 4 which are movably received in the longitudinal direction and are operatively connected to a piston 7 received in a guide cylinder 6. The piston 7 can perform periodic movements parallel to the longitudinal axis of the guide cylinder 6 by means of a drive 8 and in this way transmits a mechanical impulse to the needle heads 5, due to which the needles 4 with their active tips 12 against through an outlet opening 11 of the guide cylinder 6 Substrate 10 are thrown and in turn transmit a pulse to the substrate 10. In cooperation with the needle heads 5, a perforated plate 9 prevents the needles 4 from slipping out of the guide cylinder 6. Due to the restoring effect of springs (not shown in the figures), the needles 4 become in again their respective starting positions withdrawn. For better guidance of the needles 4, the guide cylinder 6 tapers at its front section in the direction of the outlet opening 11.

In the exemplary embodiment, the needle tool 2 is driven by means of compressed air, which is supplied via a feed line 14 from a compressed air supply (not shown here). A valve 15, which can be actuated by means of a control lever 16, enables the compressed air supply to the drive 8 to be regulated. For easier handling, the needle tool 2 is equipped with a handle 17, in which the compressed air supply 14 and the valve 15 are also arranged.

The cooling device 3, which in the exemplary embodiment according to FIG. 1 is mounted on the guide cylinder 6 of the needle tool 2, is a device in which carbon dioxide in the form of cold gas or particles is applied to a substrate to be treated from one or more jet nozzles 18 10 is blasted, whereby the surface of the substrate 10 is at least locally strongly cooled. Because of the different expansion coefficients of the substrate 10 and a coating 21 resting on its surface, the coating 21 becomes brittle, which can subsequently be easily removed from the substrate surface with the aid of the needle tool 2.

The carbon dioxide used for the irradiation is introduced in the cooling device 3 in liquid or supercritical form through a CO ₂ feed line 19 and exits at the jet nozzle 18. As a result of the sudden relaxation at the jet nozzle 18, the liquid or supercritical carbon dioxide evaporates and hits the surface in the form of cold gas and / or snow. The jet nozzle 18 is fluidly connected to the compressed air supply 14 via a flow divider 20 and a compressed air line 22 in such a way that when the compressed air supply is opened at the valve 15, the coolant supply into the jet nozzle 18 is opened at the same time. The cooling of the substrate 10 therefore takes place only when the mechanical processing begins. Of course, an embodiment is also conceivable in which the operation of the needle Tool from which the cooling device can be decoupled, for example by means of a two-stage switch, which first opens the refrigerant supply and only allows the supply of compressed air after a predeterminable period of time. In the latter variant, cooling starts before mechanical processing, which is particularly advantageous for short-term, selective processing.

The cooling device 3 is mounted on the guide cylinder 6 of the needle tool 2 in such a way that the refrigerant jet emerging from the steel nozzle 18 hits the surface area of the substrate 10 when the device 1 is used as intended, which is also affected by the action of the needles 4.

3 shows various embodiments of the device according to the invention in the region of the respective outlet opening of the needles or the jet nozzle, which are essentially determined by the position of the jet nozzle 18, 18 ', 18 "on the respective device 1, 1', 1 "from each other. Otherwise, however, the structure of the device 1 ′, 1 ″ corresponds to the structure of the device 1 shown in FIG. 1.

3a shows the device 1 described in FIGS. 1 and 2. The jet nozzle 18 of the cooling device 3 is mounted on the guide cylinder 6 of the needle tool 2. The irradiation takes place directly on the substrate surface to be treated. This embodiment is particularly easy to maintain, since the cooling device 3 can optionally be easily removed from or placed on the guide cylinder 6. After removal of the cooling device 3, the needle tool 2 can be used separately.

The device 1 'in FIG. 3b differs from the device 1 from FIG. 3a in that a jet funnel 24 is placed on the guide cylinder 6'. The jet nozzle 18 'of the cooling device 3' is passed through a bore 26 in the jet funnel 24 with a front section , The cooling effect of the refrigerant emerging from the jet nozzle 18 'on the one through the Concentrated area of the funnel opening 27 substantially limited area of the surface of a substrate 10 to be treated.

In the device 1 "in FIG. 3c, not only is the surface of a substrate 10 to be treated irradiated with refrigerant, but also the active tips 12" of the needles 4 ". For this purpose, a bore 29 is provided in the guide funnel 6" through which the Jet nozzle 18 "is passed through with a front section. During operation of the device 1", the needles 4 "are continuously, in particular also supplied with refrigerant when the needles 4" are not in contact with a substrate surface. The refrigerant emerging from the jet nozzle 18 ″ passes the needles 4 ″ to the outlet opening 11 ″ of the guide cylinder 6 ″ and from there to the surface of the substrate 10 during normal operation.

FIG. 4 shows two different embodiments of needles which can be used in the device 1, 1 ', 1 ". FIG. 4a shows a needle 30 in the usual form with an elongated needle body 31 and a bead-like needle head 32 which is used during use of the needle tool, in cooperation with a perforated plate 9, prevents the needle from being thrown out of the needle tool The hardness of such plastic needles 30 is roughly comparable to that of dry ice pellets, and it is also possible in this way to treat surfaces on which the use of dry ice pellets would be too complex or too cumbersome, such as for the derusting of hulls.

In the variant shown in Fig. 4b, the needle 34 consists of a plastic pin 35 which is received with a rear portion in a - preferably metallic - sleeve 36. In the intended installation state, the sleeve 36 faces the piston 7. This variant has the particular advantage that the Plastic pins easily removed from the sleeve after their wear and by new ones

Plastic pens can be replaced.

5 shows a possibility for the supply of refrigerant into the device 1. The device 1 is in this case via corresponding feed lines 39, 40, 41 both with a riser bottle 43 and with a medium-pressure tank system 44, each of which contains carbon dioxide in liquid form , connected. The device 1 can optionally be connected to one of the refrigerant supplies 43, 44 via valves 45, 46. When supplying liquid carbon dioxide from the ascending tube bottle 43, temperatures of approximately -80 ° C. to -95 ° C. can be reached in the cold gas jet emerging from the jet nozzle 18, 18 ', 18 ", whereby a considerable embrittlement effect can already be achieved.

Combined supply hoses 50, 51 are shown in FIG. 6, which enable a simultaneous transport of refrigerant and compressed air. The supply hose 50 shown in FIG. 6 a is suitable for the transport of liquid carbon dioxide, which is present at a temperature of approximately 10 ° C. to 30 ° C. and was removed from a riser tube bottle 43, for example. It is one of the advantages of carbon dioxide as a coolant that such transport temperatures are possible and that there is no need for costly insulation of the refrigerant supply. The supply hose 50 is constructed concentrically, the coolant line 52 intended for guiding coolant, for example liquid carbon dioxide, being arranged inside a compressed air hose 53.

In contrast, FIG. 6b shows a supply hose 51 which is intended for the transport of low-temperature refrigerants, such as cold liquid carbon dioxide. Here, the refrigerant line 54 is arranged separately from the compressed air hose 55, the refrigerant line 54 being additionally surrounded by a protective hose 56, and there is an insulating gap between the outer border of the refrigerant supply line and the inner wall of the protective hose 56 for thermal insulation. The supply hoses 50, 51 ensure that the

Devices 1,1 ', 1 ". If necessary, the supply hose 50,51 can be detached from the device 1, 1', 1" and replaced accordingly.

When used as intended, the devices 1, 1 ', 1 "ensure that a coating 21 lying on a substrate 10 is removed gently and effectively. Even at high needle speeds, they work on substrates such as sheet steel, aluminum molds or hard metal tools with almost no damage. Instead of the needle tool 2, In the method according to the invention, another tool can also be used, for example a drilling tool or a hammer, which, as an alternative to the pneumatic drive described, can also be equipped with an electric or hydraulic drive.

References

1, 1 ', 1 "device 29 hole in the guide cylinder

2 needle tool 30 needle

3 cooling device 31 needle body

4.4 "needle 32 needle head

5 needle heads 33 -

6.6 ', 6 "guide cylinder 34 needle

7 pistons 35 plastic pin

8 drive 36 sleeve

9 perforated plate 37 -

10 substrate 38 -

11, 11 ', 11 "outlet opening 39 supply line

12, 12 ', 12 "active tips 40 feed line

13 - 41 supply line

14 Supply line for compressed air 42 -

15 valve 43 ascending tube bottle

16 control lever 44 medium pressure tank system

17 handle 45 valve

18, 18 ', 18 "' jet nozzle 46 valve

19 CO ₂ feed line 47 -

20 flow dividers 48 -

21 coating 49 -

22 Compressed air line 50 Supply hose

23 - 51 Supply hose

24 - 52 refrigerant line

25 jet funnel 53 compressed air hose

26 Hole in the jet funnel 54 Refrigerant line

27 Funnel opening 55 compressed air hose

28 _ 56 protective hose

Claims

claims

1. Device for removing a coating (21) from a substrate (10) with a processing tool (2), which has a tool part (12, 12 ', 12 "intended for applying a mechanical impulse to the substrate (10) in the area of a processing zone. ), characterized in that the processing tool (2) is assigned a cooling device (3) which can be connected to a refrigerant supply (43, 44) and which has at least one jet nozzle (18, 18 ', 18 ") by means of which the substrate (10), for the purpose of embrittlement of the coating (21), at least in the area of the processing zone, with a refrigerant, such as carbon dioxide, which can be irradiated.

2. Apparatus according to claim 1, characterized in that a needle device (2) is provided as the machining tool with needles (4, 4 ', 4 ", 30, 34) which are accommodated in a longitudinally movable manner.

3. Apparatus according to claim 2, characterized in that the needle device (2) needles (4,4 ', 4 ", 30,34) made of plastic with preferably tough material inherent shadows, such as Kevlar or aluminum powder reinforced polyamide, are provided ,

4. The device according to claim 3, characterized in that the needles (35) on their intended use the substrate (10) facing away from the side in a - preferably metallic - sleeve (36) received and fixed, but detachably connected to this ,

5. Device according to one of the preceding claims, characterized in that the machining tool (2) is driven pneumatically, for example by means of compressed air.

6. The device according to claim 5, characterized in that the cooling device

(3) comprises a pneumatic device which is connected to the flow with a compressed air supply (14, 53, 55) of the processing tool (2) and by means of which the supply of refrigerant into the cooling device (3) can be coupled to the supply of compressed air into the processing tool (2).

7. The device according to claim 5 or 6, characterized in that for connecting the cooling device (3) to the refrigerant supply (43,44) a refrigerant supply line (52,54) is provided, which - preferably coaxially - inside a compressed air supply (14, 22) is arranged.

8. Device according to one of the preceding claims, characterized in that the machining tool (2) is provided with an electrical and / or hydraulic drive.

9. Device according to one of the preceding claims, characterized in that the refrigerant supply comprises a riser bottle (43) for supplying the cooling device (3) with liquid carbon dioxide.

10.Device according to one of the preceding claims, characterized in that the refrigerant supply comprises a medium-pressure tank system (44) for supplying the cooling device (3) with liquid carbon dioxide.

11.Device according to one of the preceding claims, characterized in that the processing tool (2) is provided on its side facing the substrate (10) when used as intended with a jet funnel (25) into which the jet nozzle (18, 18 ' , 18 ") of the cooling device (3) opens.

12. Device according to one of the preceding claims, characterized in that the jet nozzle (18, 18 ', 18 ") of the cooling device (3) in a guide aufnähme (6) for guiding the machining tool part (12, 12 ', 12 ") at

Insert flows.

13. Device according to one of the preceding claims, characterized in that the cooling device (3) is detachably connected to the processing tool (2).

14. A method for removing a coating (21) from a substrate (10), in which a processing tool (2) with a tool part (12, 12 ', 12 ") by mechanical impulse transmission in the region of a processing zone of the substrate (10) on the Coating (21) acts, characterized in that the substrate (10) is cold-treated by means of a cooling device (3), for example a jet device, at the same time and / or with a time delay for mechanical impulse transmission.

15. The method according to claim 14, characterized in that carbon dioxide is used as the means for performing the cold treatment, which is brought in liquid form from a refrigerant supply (43,44), relaxed in the immediate vicinity of the substrate (10) and in gaseous and / or solid form is blasted towards the substrate (10).

16. The method according to claim 14 or 15, characterized in that the pulse-transmitting tool part (12, 12 ', 12 ") of the machining tool is cooled during use by means of the cooling device (3).