EP0167088B1 - Method and plant for coating the interiors of hollow bodies - Google Patents

Abstract

A method and an apparatus for interior coating of hollow bodies comprising a mandrel introducible into at least one tubular body, a coating arrangement on the mandrel for applying a coating medium to an interior of the tubular body and a heating mechanism on the mandrel and arranged so as to predominantly deliver heat directly from the mandrel into a surrounding area toward the tublular body. The heat-applying efficiency of burning in a coating medium can be improved by applying the heat from the interior at least predominantly directly to one of an interior area of the tubular body just before being coated and an interior area of the body already coated to burn in the coating according to the disclosed method.

Description

The present invention relates to a method of the type defined in the preamble of claim 1 and an installation of the type defined in the preamble of claim 3.

The problems that arise, for example with regard to corrosion, with connected as well as soldered or welded edges of hollow bodies, such as sheet metal frames for the production of cylindrical containers, such as can bodies, have long been known. To solve it is, for. B. from CH-PS-444 632 known to subsequently carry out a soldering for welding the frame edges, such that the solder flowing over the weld seam causes corrosion protection. It is also envisaged there to spray the connection seam combined in this way by means of a spray nozzle in order to achieve further improved corrosion protection. The sheet to be covered with solder after welding is preferably warmed up to provide a good solder flow by providing an unspecified heating source, especially if the welding process and the soldering process do not immediately follow one another in terms of location or time.

DE-PS-714 669, in turn, proposes to apply a varnish to the frame edges that are not yet connected, and then to solder the edges, the varnish being selected such that the soldering temperature leads to baking of the varnish.

This last-mentioned method, in which an energy used for connecting the edges is simultaneously used to burn in the pre-applied lacquer, cannot be used in particular when welding the edges, since the heat of welding does not burn the lacquer, but would burn it and also a clean welding by the Paint disturbance layer would be affected.

Methods are known from DE-PS-750 056 and EP-A-0 120 810, in which a protective layer is applied from the inside after connecting the frame edges. This protective layer is then baked in accordance with EP-A-0 120 810, by providing a heat source which acts on the finished cylindrical body from the outside.

Inductive sources, gas heaters or infrared heaters can be used as the heat source. This brings the entire cylindrical body to the stoving temperature and keeps it at this temperature for a certain time. Particularly when using such a method on cylindrical bodies made of bare sheet metal, there is a high level of heat reflection and the efficiency of such heat sources acting from the outside is correspondingly poor, measured in terms of the stoving effect to be achieved.

The same applies if, for an inner powder coating, the body to be coated is preheated from the outside in order to improve the adhesion of the powder sprayed on from the inside. If this is realized, body warming from the outside heats up the entire body, the heat capacity of which entails transferring too much heat into the area of a proposed coating arrangement, which in turn can lead to the coating arrangement and in particular the spray nozzles being too strong be heated, which can lead to the packaging of such outlets.

From US-A-3 077 171 a method or a plant of the type specified above has now become known. For the internal coating of a hollow body, it is moved with respect to an internal working arm. A pressurized, viscous coating medium is dispensed through this working arm. At the end of the coating arm there is a heat source, which mainly acts inside the working arm, on the medium to be dispensed, in order to keep its viscosity low enough for printing. Thus, here under the influence of this heat supplied to the coating medium, a medium layer is formed on the hollow body by its application and moved on.

The medium layer applied in this way on the inside is then heat-treated by heat sources provided outside the hollow body.

Since, on the one hand, the heat source provided inside the hollow body, apart from scattered radiation, has to act inside the working arm in order to act on the coating medium before it is dispensed, on the other hand and with regard to the effect of the heat source, which is also external here, for heat treatment of the applied medium layer, the above, for example in Connection with the disadvantages listed in EP-A-0120 810.

Starting from the technique proposed in US Pat. No. 3,077,171, the aim of the present invention is to use the heat necessary for the heat treatment of the inner coating in a targeted manner where it is also needed. This is solved in the method of the type mentioned by execution according to the characterizing part of claim 1, or, in the creation of the type mentioned, by training according to the characterizing part of claim 3.

Looking back at the aforementioned US-A-3 077 171, heat generated within the hollow body is used according to the invention for the heat treatment of the applied medium layer, i.e. the heat used for this is applied directly to the inside of the body, coated or still uncoated.

Another significant advantage of the proposed method or the proposed system is the fact that the thermal stress on the immediate outer body environment is significantly lower than in conventional methods with warming up from the outside, which in addition to the verb mentioned above Efficiency further leads to the fact that a continuous conveyor belt arrangement can now be provided at least between the coating arrangement and the stoving heat source arrangement in the region of the coating, with at least one conveyor belt for moving the body between the mentioned arrangements.

If the heat is supplied from the outside, then a common conveyor belt arrangement, as provided in EP-A 0 120 810, provided between the coating arrangement and the stoving heat source arrangement, must be arranged on the side opposite the heat source and thus the coating, in order to reduce its thermal impairment by the heat source to prevent and in order not to have to use complex, thermally resistant conveyor belt material.

Because of the targeted supply of heat, the conveyor belt provided can now, as mentioned, easily in the coating area, i.e. in the area of the seam, which act on the body, the design freedom of the overall system is thus significantly increased.

The heat source arrangement preferably has at least one infrared radiation source. The fact that a temperature measurement is carried out in the arm area in one embodiment variant makes it possible to monitor the temperature conditions during body processing.

Preferably, the result of this temperature measurement is passed as an ACTUAL value output signal to an ACTUAL value input of a temperature control circuit, with the heat source arrangement as an actuator, with which, then, of course, a TARGET value specification unit can be entered, and the actual temperature value is regulated to this.

To further increase the targeted supply of energy or heat, it is now further proposed that at least one reflector arrangement be provided on the arm, in order to concentrate the source radiation on predetermined areas of the body.

In this case, the heat source arrangement is preferably extended axially and arranged in this regard at a radial distance, and the reflector arrangement comprises an axial reflector channel arranged on the arm side of the source arrangement, which is preferably incorporated into the arm and has a reflective surface.

Taking into account that the production of cans as hollow bodies works at production speeds of up to 650 cans / min, it can be seen that a reduction in the amount of heat required for the inner coating leads to the intended use of this heat, leading to enormous energy savings, both if the heat to increase the medium adhesion as well as when it is used to burn in the applied medium layer or for both. The directional heat application, in particular with the provision of the above-mentioned reflector arrangement, also considerably alleviates a construction problem, namely that all feeds for the coating arrangement, as well as for the intended heat sources, such as electrical supply cables, have to run through the arm, and specific heat application prevents this an impermissible thermal load on the arm, which also insignificantly stresses the feeds mentioned.

The invention is subsequently explained, for example, using figures.

• Fig. 1 eine prinzipielle Anordnung einer Dosenherstellungs- und Beschichtungsstrasse, mit Wärmeapplikation bekannter Art und Weise,
• Fig. 2 geschnitten,die Ausbildung einer erfindungsgemässen Anlage, zur Ausführung des erfindungsgemässen Verfahrens, mit Beschichtungsanordnung und Wärmequellenanordnung am Arm,
• Fig. 3 einen Querschnitt durch die Anordnung gemäss Fig. 2, entlang Linie 111 -III,
• Fig. 4 eine weitere erfindungsgemässe Anordnung im Längsschnitt, mit erfindungsgemässen Wärmequellen für das Einbrennen und die Körpervorerwärmung.

Show it:

• 1 shows a basic arrangement of a can manufacturing and coating line, with heat application in a known manner,
• 2 cut, the formation of a system according to the invention, for carrying out the method according to the invention, with a coating arrangement and heat source arrangement on the arm,
• 3 shows a cross section through the arrangement according to FIG. 2, along line 111-III,
• Fig. 4 shows another arrangement according to the invention in longitudinal section, with heat sources according to the invention for stoving and preheating the body.

FIG. 1 shows the general arrangement of a can welding and seam coating system, as is usually built today, without the features according to the invention. The can welding and coating arrangement 1 is fed with flat sheets 2, which are formed in the system in a known manner to round cylinder frames, the opposite longitudinal edges of which are then welded to a welding station 3. The shaping of the frames and the welding are not the subject of the present invention and are therefore not described in more detail. A conveyor belt 4 takes over the hollow body, i.e. the can bodies, which are moved astride an arm 6, the latter comprising a coating station with a medium supply line 5 for the coating medium, corresponding nozzles and usually a suction station 7. The can bodies 11 are then placed on a further conveyor belt 9, with the aid of which they are moved through a stoving station 8, where they are generally heated from the outside by means of burners, induction heating elements, and heat sources 10. The temperature is maintained for a certain time by this indirect heating of the coated seam over a prescribed passage of the body 11.

Then the cans are transferred to the next conveyor belt (not shown).

2 and 3, the features according to the invention are shown on an arm 6 according to FIG. 1. The arm 6, usually also referred to as a welding arm, here has an extension 6a, viewed in the direction of movement of the body 11, directed downstream. The coating of the can bodies, which is supported electrostatically in a known manner, takes place via the medium supply line 5 for powder or lacquer, with the aid of a high-voltage generator 12, with the aid of which a high electrostatic field is applied between the can body and electrodes 5a provided for this purpose. The high-voltage generator 12 emits a DC voltage of approximately 60 kV. Following the coating arrangement, infrared rod radiators 14 are arranged in the extension 6a of the arm. These are fed via cables 13 which are guided through the entire arm 6, 6a. This is facilitated in particular by the fact that the medium film, powder or lacquer film 17, is heated directly, especially since such systems also coat cylindrical bodies down to a diameter of approximately 40 to 60 mm.

Also important for an optimized function of such an arrangement is the provision of a reflector 18, which is preferably integrated in the arm 6, 6a, as can be seen in FIG. 3, as a reflective groove incorporated therein. With appropriate geometric training, the heat radiation of the radiator 14 can be made to the necessary width B, e.g. B. between about 5 and about 25 mm. Since the rod radiator 14 emits up to 3 kW of thermal radiation with a length of, for example, only about 800 mm, a very high thermal output per unit area can thus be achieved on the inner surface of the body 11.

In order to further optimize the curing of the coating during baking, a temperature measurement is generally carried out on or in the arm in the area of the arm. This takes place either indirectly using fever optics or directly using a pyrometer 20. The result of the temperature measurement, a signal F ('.beta.Jsr) as a function of the measured actual temperature, is sent to a comparison unit 22 with a corresponding signal F (which can be input to a specification unit 24). _' Ös _OLL ) compared and the supply voltage of the radiator via the leads 13 as a controlled variable with the difference F (Δ / ð). A controller 26, such as a known thyristor controller, is also provided in order to set the infrared radiators 14 as actuators. The design of controller 26, specification unit 24 and comparison unit 22 are known and will not be explained further.

This arrangement enables exact temperature control on the coated seam, the powder or lacquer layer. The number of IR radiators 14 and their length depend on the transport speed of the bodies 11 and the hardening property of the coating medium on the layer 17.

Another embodiment variant is shown in FIG. 4. Here, one or more IR radiators 19 are installed before the spray arrangement with the feed line 5. Here too, as already explained with reference to FIG. 3, the heat radiation is specifically focused on a strip of the inner wall of the can body 11 by means of a reflector 18 '. As a result, the can body is preheated in the seam area and in the subsequent coating process, and in particular during powder coating, a significantly improved deposition or. Accumulation efficiency achieved without such a lot of heat in the area of the coating arrangement that the nozzles could paper. The powder output per unit of time can thus be significantly reduced, and thus also the load on the powder recovery system, such as the suction system 7 and its pumps.

Claims (10)

1. Method for applying an internal coating to hollow bodies, in particular to welds of longitudinally welded can bodies, whereby the hollow bodies are moved relative to an internal operating arm, by means of which a medium layer is formed on one moving hollow body respectively under the influence of internally applied heat, through the application of a coating medium, and the applied medium layer is heat-treated, characterised in that the medium layer is heat-treated by admitting heat to the inside of the hollow body and/or the coated hollow body prior to and/or after the application in order to achieve desired layer properties.

2. Method according to claim 1 for baking the coating, characterised in that, following the application of the coating, the baking heat is admitted to the body directly from inside.

3. Apparatus for implementing the method according to claim 1 comprising an operating arm (6) and means (4) for moving the hollow bodies (11) relative to and along the operating arm (6), whereby a coating arrangement (5) and a heat source (14) for influencing the coating process are provided on the operating arm (6), and whereby further a heat source (14) for heat-treating the applied layer is provided, characterised in that the heat source (14) for heat-treating the applied layer is the heat source (14) provided for influencing the coating process and is arranged in front of and/or behind the coating arrangement (5) on the operating arm (6).

4. Apparatus according to claim 3, characterised in that a baking heat source arrangement (14) is arranged behind the coating arrangement (5), in order to bake the layer applied by means of the coating arrangement (5, 7, 12).

5. Arrangement according to claim 4, characterised in that a continuous conveyer belt arrangement (4) is provided at least between coating arrangement and the baking heat source arrangement (14) in the coating area, comprising at least one conveyer belt for moving the bodies (11) between the coating and heat source arrangements (5, 7, 12; 14).

6. Apparatus according to one of claims 3 to 5, characterised in that the heat source arrangement (14, 19) comprises at least one IR radiation source.

7. Apparatus according to one of claims 3 to 6, characterised in that at least one temperature measurement is carried out in the area of the arm (6, 6a), e.g. by means of a temperature sensor (20).

8. Apparatus according to claim 7, characterised in that the result of the temperature measurement is supplied as an actual value output signal to an actual value input of a temperature regulating circuit using the heat source arrangement (14) as final control element.

9. Apparatus according to one of claim 3 to 8, characterised in that at least one reflector arrangement (18) is provided on the arm (6, 6a) for concentrating the source radiation to cover specific body areas.

10. Apparatus according to claim 9, characterised in that the heat source arrangement extends in axial direction of the arm and at a radial distance from same and the reflector arrangement (18) comprises an axial reflector trough arranged on the side of the arm opposite the source arrangement and preferably worked into the arm.

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