WO1994005517A1

WO1994005517A1 - Paint stripper

Info

Publication number: WO1994005517A1
Application number: PCT/EP1993/002228
Authority: WO
Inventors: Otmar Fahrion
Original assignee: Otmar Fahrion
Priority date: 1992-09-10
Filing date: 1993-08-20
Publication date: 1994-03-17
Also published as: EP0659123A1; DE4230026A1

Abstract

In order to strip paint from the skin (10) of an aircraft, the invention proposes a device with a work head (12) with a treatment chamber (34) which can be placed close (38) against the skin of the aircraft. Located in the treatment chamber is a heat-exchange unit (40) whose curved end surface (42) matches the curvature of the aircraft skin (10) and is brought into thermal contact with the paint layer on the skin directly or through a layer (52) of heat-conducting gas. Liquid nitrogen (48) is allowed to evaporate in the heat-exchange unit. The resulting coolant gas is led away from the work head (12) through a common main.

Description

Paint stripping device

The outer skin of an aircraft is usually painted in order to avoid signs of corrosion and to maintain an owner-specific appearance. As a result of wear and tear, this painting must be regularly repaired or completely renewed in accordance with the manufacturer's instructions. Repainting also takes place when the owner changes. The paints used to paint the outer skin of an aircraft must withstand extreme loads (temperatures between -55 ° C and 70 ° C, air and dust abrasion at speeds up to over 2000 km / h, chemical effects of oil, kerosene, sea air, mechanical Effects of hail, snow, rain, vibrations, stone chips, etc.) These high requirements can currently only be achieved with paints with high levels of pollutants (phenol).

Stripping is currently carried out mainly by manual stripping of the old paint using solvents. This means a danger to people and the environment; In particular, the disposal of the mixture of old paint and solvent that occurs during paint stripping is very expensive.

Stripping is now occasionally carried out using water jets if there is no risk of damage to seals, electronics, mechanics, hydraulics, rubber-like parts or glass. Grain blasting with plastic, stone or wood granulate is only used on military aircraft. With this method, there is a risk that the surface of the aircraft will be mechanically compacted and thus stresses and

REPLACEMENT LEAF Deformations arise.

It has also been proposed to dip degradable compact aircraft parts in liquid nitrogen for paint stripping.

The present invention is intended to provide a device for stripping paint from the outer skin of an aircraft, which also ensures brittleness and / or detachment of the paint layer on non-degradable parts of an aircraft economically by cooling to very low temperatures, particularly in terms of consumption evaporating liquid coolant.

This object is achieved according to the invention by a paint stripping device having the features specified in claim 1.

In the paint stripping device according to the invention, there is a treatment chamber which is only open to the outer skin of the aircraft and is placed essentially tightly on the outer skin, in which the coolant boiling at low temperatures, usually nitrogen, is evaporated and the very low temperatures there Temperatures generated. Because the treatment chamber is closed, on the one hand the amount of coolant to be used is kept small, and it is further ensured that there is no excessive precipitation of moisture from the ambient atmosphere in the treatment chamber and on the outer skin of the aircraft. The stripping device according to the invention can be easily automated and used for largely automatic stripping of an aircraft under numerical control of the movement of the working heads. The use of the paint stripping device according to the invention is harmless

REPLACEMENT LEAF for people and the environment. The detached old paint is obtained in the form of dry tinsel on its own.

Advantageous developments of the invention are specified in subclaims.

The development of the invention according to claim 2 allows the coolant to be guided through the working head in a closed path, but at the same time good heat transfer to the outer skin of the aircraft is ensured. A good heat transfer to the outer skin of the aircraft is advantageous because it allows the paint layer to cool down very quickly, so that large thermal stresses occur at the interface between the paint and outer skin, which promote the detachment of the paint layer. With slow cooling, however, the section of the outer skin to be processed and the lacquer layer cool down essentially at the same rate, so that the thermal stresses are reduced.

The development of the invention according to claim 3 enables good heat transfer to the outer skin of the aircraft even with a very irregularly shaped surface of the outer skin, e.g. small bumps or the like. In addition, the density or pressure of the heat exchanger gas makes it very easy to continuously set the thermal resistance of the thermal transmission path between the heat exchanger and the outer skin within wide limits.

The further development of the invention according to claim 4 is also advantageous with regard to improved thermal contact with the outer skin of the aircraft, since the free surface of the heat exchanger does not usually have an exact shape adaptation to the outer skin of the paint to be stripped

REPLACEMENT LEAF Airplane or its sections can have.

With the development of the invention according to claim 5 adjustment movements of the heat exchanger with a larger stroke are possible.

In the case of a working head designed according to claim 6, a scratching effect can be exerted on the lacquer layer while it is cooling.

A working head directs jets of coolant directly against the outer skin of the aircraft, where the evaporation then takes place. You have a very abrupt and intensive cooling of the outer skin. Such a working head can also cope particularly well with irregularly shaped surfaces.

A working head designed according to claim 8 can cover a large section of the outer skin, since the edge of the treatment chamber is designed in accordance with the main curvature of the outer skin. This is advantageous with regard to the rapid stripping of paint from large aircraft.

Sealing the edge of the treatment chamber, as specified in claim 9, works reliably even at low temperatures and has a long service life.

With the development of the invention according to claim 10, a further improvement in the tightness of the treatment chamber is achieved, the elastic seal being exposed to only low negative temperatures.

The development of the invention according to claim 11 is advantageous in terms of further savings in coolant. That occurs when the liquid coolant evaporates

REPLACEMENT LEAF standing cold gas can be used in another working head for pre-cooling another part of the outer skin to be stripped. This has the further advantage that the total gas used is obtained at a higher temperature, so that less heat is withdrawn from the room to which this gas is supplied and less moisture condensation takes place in this room.

The development of the invention also serves to remove residual cold from the gas obtained from the coolant. This residual cold can e.g. be used in an air conditioning system of the building complex in which the paint stripping device is installed.

In a stripping device according to claim 13, temporary differences in the consumption of liquid coolant and in the consumption of cold cooling gas can be compensated.

In a device according to claim 14, it is possible to quickly heat the working head to room temperature or higher temperature if necessary, e.g. then when the work is to be stopped and moisture condensation inside the working head is to be avoided.

The development of the invention according to claim 15 also serves to reduce the consumption of coolant and to reduce the condensation of moisture on the working head.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing. In this show:

REPLACEMENT LEAF FIG. 1: a plan view of the bow section of an aircraft and two working platforms which are provided with leaching work heads;

FIG. 2: a front view of another aircraft section which is processed with two stripping work heads carried by an industrial vehicle;

FIG. 3: a schematic transverse section through a first paint stripping working head together with the outer skin of an aircraft;

FIG. 4: a view similar to FIG. 3, in which a modified paint stripping working head is shown;

FIG. 5: a view similar to FIG. 3, in which a further modified paint stripping work head is shown; and

6 shows a block diagram of a coolant supply device for paint stripping working heads, as shown in FIGS. 1-5.

In FIGS. 1 and 2, the outer skin of a commercial aircraft is shown schematically at 10, which skin is to be freed of the lacquer layer applied to it. For this purpose, a total of 12 paint stripping heads are used, the inclination of which can be adjusted via two vertically spaced hydraulic cylinders 14, 16 (see FIG. 2, to be thought analogously in FIG. 1). The hydraulic cylinders 14, 16 are carried by working platforms 18, which in turn are attached to two double scissor linkages 20, 22. The latter are attached to sled 24

REPLACEMENT LEAF Makes that are adjustable in height on vertical frames 26.

The frames 26 are in turn guided on horizontal supports 28 so as to be displaceable in the horizontal direction, with these supports being part of a dock, not shown, surrounding the aircraft. However, the frames 26 can also be carried by an industrial vehicle 30, as shown in FIG. 2.

The work platforms 18 can thus be moved in the longitudinal direction of the aircraft, adjusted in height, adjusted in the direction perpendicular to the aircraft axis and adjusted in their angle of attack to the aircraft axis. In addition, since the inclination of the working heads 12 can be adjusted, the different sections of the outer skin 10 can be machined equally. The corresponding adjustment movements for the work platforms and work heads can be handled under numerical control.

As can be seen from FIG. 3, a working head 12 has a housing 32 which delimits a treatment chamber 34 which has a rectangular cross section which is open to the outer skin of the aircraft. The rear of the housing 32 carries two tabs 36 on which the hydraulic cylinders 14, 16 engage. The free edge of the peripheral walls of the treatment chamber 43 carries a circumferential seal 38.

Arranged in the interior of the housing 32 is a heat exchanger part 40 which has a front end face 42 which is opposite the outer skin 10 and curved in accordance with the outer skin. A shoulder 44 of the heat exchanger part 40 extends into the rear section of the treatment chamber 34, which is charged with liquid nitrogen 48 via an inlet 46. To reduce weight and dimensions

REPLACEMENT LEAF In practice, in order to save material and to increase the effective surface area, the attachment 44 can consist of a large number of rods or have a larger number of blind holes. A suitable material for the heat exchanger part 40 is aluminum or copper.

The gaseous nitrogen formed when the heat exchanger part 40 cools is drawn off via an outlet 50.

In the exemplary embodiment considered here, the heat exchanger part 40 is fastened in the treatment chamber 34 in such a way that a narrow gap 52 exists between its end face 42 and the outer skin 10. A heat exchanger gas, which has a lower boiling point than the boiling point of the liquid nitrogen, e.g. a rare gas. By adjusting the pressure prevailing in the gap 52, the heat transfer to the outer skin 10 can then be varied within wide limits in a simple manner.

If this variation option is not used, dry nitrogen can also be used as the heat exchange gas. Furthermore, the heat exchanger part 40 can then also be designed to be adjustable in the depth direction of the treatment chamber 34 and then be pushed as close as possible against the outer skin 10 before the cold treatment.

An outer insulating housing surrounding the housing 32 is only indicated by dashed lines at 56 in FIG. This can be a vacuum jacket made of metal, a jacket made of thermally very poorly conductive plastic material (foam material or many layers of super insulation film) or a combination of vacuum jacket and plastic insulating jacket.

REPLACEMENT LEAF In the modified exemplary embodiment according to FIG. 4, the heat exchanger part 40 consists of an exchanger plate 58 which is bent according to the curvature of the outer skin 10 and onto which a heat exchanger coil 60 is firmly attached

Thermal contact applied, e.g. is soldered on. The end face of the curved exchanger plate 58 facing the outer skin in FIG. 4 bears a metal felt 62 which is made of copper wires or bronze wires or wires made of an aluminum alloy and preferably resiliently springs at least at room temperature. The metal felt 62 thus adapts to the contour of the outer skin 10 under the pretension of helical compression springs 64. This shape adaptation takes place when the metal felt 62 is already relatively hard at the temperature of the liquid nitrogen, at room temperature.

The heat exchanger coil 60 is connected via a control valve 66 to a feed line 68 for liquid nitrogen. A control valve 70 provided at the outlet of the heat exchanger coil 60 is connected on the outlet side to a manifold 72 for evaporated but still very cold coolant. The feed line 68 and the collecting line 72 are surrounded by insulating jackets 74, 76.

To seal the treatment chamber 34 from the environment, sealing strips 78, 80 are slidably inserted into the upper and lower chamber walls, which are made of a poorly heat-conducting material, e.g. Stainless steel. The sealing strips 78, 80 are held in contact with the outer skin 10 by springs 82. Correspondingly, sealing strips 84 are guided in the lateral boundary walls of the treatment chamber 34, the edge of which is curved in accordance with the diameter of the outer skin 10. The sealing strips 84 are opened again by springs (not shown)

REPLACEMENT LEAF the outer skin 10 biased.

External inflatable seals 86 are provided on the insulating housing 56 and are connected in series to the sealing strips 78, 80, 84 in terms of leakage. They are connected via line 88 to a suitable compressed air source.

In the working head according to FIG. 5, a plurality of nozzle heads 90 are connected to the feed line 68 via control valves 92. They direct coolant jets 94 against the outer skin of the aircraft. The coolant jets 94 can be very cold nitrogen gas or liquid nitrogen, as will be described in more detail later with reference to FIG. 6. The used coolant is withdrawn directly from the treatment chamber 34 via the manifold 72.

A working head 12 is only shown schematically in FIG. It is connected to the working connections of a 5/3 servo valve 96 via the assigned feed line 68 and manifold 72. On the input side, this is connected to a supply line 98 for liquid nitrogen, a collecting line 100 for cold nitrogen gas, a supply line 102 for cold nitrogen gas and to a collecting line 104 for used, warmer nitrogen gas.

The supply line 98 plunges into a storage container 106 for liquid nitrogen, in which a predetermined desired pressure is set by a control valve 108. The supply line 98 and, with the corresponding position of the servo valve 96, also the working head 12 are thus pressurized with liquid nitrogen of a predetermined pressure. Allow the individual control valves 66

REPLACEMENT LEAF dosing of the cooling capacity appropriate to the respective local need.

The manifold 100 is connected to the suction side of a pump 110, the delivery side of which is connected to the cold gas supply line 102 via a pressure regulator 112. Furthermore, a cold gas buffer 114 is connected to the delivery side of the pump 110.

The collecting line 104 is connected to the suction side of a further pump 116, the delivery side of which is connected via a heat exchanger 118 to an outlet line 120, which is preferably led over the roof. In the heat exchanger 118, residual cold is withdrawn from the liquid nitrogen, which is no longer usable for paint stripping purposes, e.g. can be used in a schematically indicated refrigerant circuit 122 of an air conditioning system of the building complex. The nitrogen gas thus leaves the paint stripping device at a temperature which no longer differs greatly from the ambient temperature, so that moisture is precipitated to a small extent only when mixed with the ambient atmosphere.

The paint stripping device described above preferably contains an even number of working heads, half of which are used for pre-cooling an outer skin area using cold nitrogen gas which is used by the other half of the working heads for the outer skin. Final cooling is generated using liquid nitrogen. Switching a working head from pre-cooling with gaseous nitrogen to full cooling using liquid nitrogen is done simply by changing the corresponding servo valve 96 accordingly. Differences in consumption of liquid nitrogen and gaseous nitrogen

REPLACEMENT LEAF The cold gas buffer store 114 can compensate for material and differences in the number of working heads that have just been switched on.

In a further modified embodiment of the stripping device, the servo valve 96 can be connected on the inlet side to two further connections which are connected to a hot air supply line or a collecting line for used hot air. The servo valve 96 then has a fourth working position, in which its two working openings are connected to the hot gas supply line or the corresponding manifold. In this way it is possible to quickly heat the working head to ambient temperature, so that no moisture condensation occurs in the treatment chamber 34 even when the working head is lifted off the outer skin 10.

Furthermore, it is possible to form the metal layer 62, which ensures good thermal contact, like a brush and to arrange it on a rotatable core, the jacket of which forms the heat exchanger plate 40 and on the inside carries the heat exchanger coil 60, which is connected to the supply line 68 or the collecting line 72 via rotary couplings - is closed. One can then carry out together with the cooling, a slight mechanical scraping effect layer to be stripped PVC¬ by turning the ^'cooled metal brush roll.

The invention has been described above with reference to liquid nitrogen as a coolant. It is understood that other low boiling point coolants can be used instead, e.g. liquid oxygen or liquid noble gases if the higher costs associated with this coolant result

REPLACEMENT LEAF other reasons are justified, for example with regard to chemical interactions with the paint or the surface of the outer skin.

In the exemplary embodiments described above, the working head was each pivotably attached to a working platform that could be adjusted in four coordinates. It goes without saying that a working head can also be positioned on suitable areas of the outer skin of an aircraft with suitable lifting equipment, cranes, etc.

For reworking in difficult areas, e.g. Row of rivets, or for work on very difficult to access or extremely curved areas of the outer skin, it is also possible to realize small-sized working heads with the structure described above, which can then be moved by hand.

Finally, the free edge of the treatment chamber can also be designed to be deformable (for example by a plurality of wall segments which can be moved relative to one another in the direction perpendicular to the outer skin or by means of flexible wall end regions) or with exchangeable wall pieces, in order to adapt the sealing line ad hoc to widely differing curves To allow areas of the outer skin.

REPLACEMENT LEAF

Claims

1. Device for stripping the outer skin of an aircraft, characterized by a source (106) for a very low temperature coolant, in particular liquid nitrogen, by at least one working head (12) in which a treatment chamber open on one side ( 34), which can be placed tightly (38; 74-86) on the outer skin (10), by means of a cooling generator (40) arranged in the treatment chamber (34) with an inlet (46) for fresh coolant and an outlet (50) for used coolant, through a feed line (68, 98) for supplying the fresh coolant from the coolant source (106) to the working head (12) and through a collecting line (72, 100) for removing the used coolant from the working head ( 12).

2. Device according to claim 1, characterized in that the cooling generator comprises a heat exchanger part (40), one side of which is charged with the coolant (48) and the second side of which is in heat-conducting contact with the outer skin (10).

3. Device according to claim 2, characterized in that the second side of the heat exchanger (40) is in contact with the outer skin (10) via a highly heat-conducting layer (52) of gas condensing at very low temperatures.

4. Device according to claim 2, characterized in that the second side of the heat exchanger (40) via a deformable, preferably elastic material layer

REPLACEMENT LEAF (62) made of a good heat-conducting material, for example a metal fleece or a metal felt, is in contact with the outer skin (10).

5. Device according to claim 4, characterized by springs (64) for biasing the heat exchanger (40) and the deformable material layer (62) against the outer skin (10).

6. Device according to claim 4 or 5, characterized gekenn¬ characterized in that the heat exchanger (40) is designed as a roller core and carries on its outer surface the deformable material layer (62), which is preferably formed brush-like.

7. Device according to claim 1, characterized in that the cooling generator takes nozzles (90) u, which direct coolant against the outer skin (10).

8. Device according to one of claims 1-7, characterized in that the free edge of the treatment chamber (34) is curved in accordance with the curvature of the outer skin (10) to be treated or can be adapted thereto.

9. Device according to one of claims 1-8, characterized in that the edge wall of the treatment chamber (34) carries resilient (82) prestressed sealing strips (78, 80, 84).

10. The device according to claim 9, characterized by the sealing strips (78, 80, 84) associated elastic, preferably inflatable secondary seals (86) outside the sealing strips (78, 80, 84), preferably also outside of the Treatment chamber (34) surrounding the insulating housing (56) are arranged.

REPLACEMENT LEAF

11. Device according to one of claims 1-10, marked by a switching valve (96), via which the working head (12) either with a liquid coolant supply line (98) or with a cold coolant supply line ( 102) can be connected, and by means of a pump (110), the suction side of which is connected to a first manifold (100) for cold coolant gas and the pressure side of which is connected to the supply line (102) for cold coolant gas.

12. The device according to claim 11, characterized gekennzeich¬ net that a second manifold (104) for used coolant gas is connected to a further heat exchanger (118).

13. Device according to claim 11 or 12, gekennzeich¬ net by an intermediate storage (114) connected to the delivery side of the pump (110) for cold coolant gas.

14. Device according to one of claims 1-13, characterized in that the working heads (12) via a switch valve (96) with a further supply line for heating gas and a further manifold for used heating gas can be connected.

15. Device according to one of claims 1-14, characterized in that the treatment chamber (34) is surrounded by an insulating outer housing (56).

REPLACEMENT LEAF