EP1916905B1 - Coating device for coating small parts - Google Patents

Description

Field of the invention

The invention relates to the coating of small parts, and in particular the coating of small parts in coating drums.

Background of the invention

Coatings are commonly used in today's technology to alter the physical and chemical and especially the electrical and optical surface properties of all kinds of workpieces.

To meet the specific requirements of each coating, the coating material - for example, paint - evenly on the workpiece to be coated be applied. Careful action is essential as any irregularities, interruptions or blisters that result from improper application to the coating will usually cause adverse effects. Nevertheless, especially for small parts, such as screws, pins, rivets, rings, buttons, buckles or seals, the manufacturing costs must be kept low.

A known effective coating process for small parts makes use of a rotating coating drum. Such a coating drum is approximately in the Internet appearance (www.walther-trowal.de) of the company Walther Trowal! GmbH & Co.KG presented as "Rotamat". It has a rotationally driven drum, which circulates the small parts to be coated by their rotational movements, so that a spray device mounted in the drum reaches the small parts from all sides with a coating jet. To dry the freshly coated small parts, a stream of hot air is passed through the drum. Such a coating drum holds, for example, 40 liters of workpieces which it coats and dries in a period of up to three hours.

However, drying with the help of the hot air flow often causes problems. Thus, the hot air first acts on the paint surface, which hardens faster than the paint layer underneath. The consequence is often entrapment of residual solvents with further delayed drying; possibly arise so-called "cooker" by strong outgassing of solvents at individual points. Furthermore, the stream of hot air can disturb the fine coating jet from the spraying device and thereby prevent a homogeneous application of the coating material. In addition, the relatively slow warm air drying limits the choice of coating material: since the circulating small parts in the moving drum are in constant contact, the warm air must dry the coating within a very short, defined time, at least to the extent that it does Contact with other small parts survives undamaged. Only coating materials with very good drying properties come into question for this.

The US 6,027,568 (ND Industries) provides for the drying of freshly coated screws with infrared radiation. Here, however, the screws are moved by a conveyor belt first through a spray station and then through a drying station in which the drying takes place with the IR radiation.

Also the EP 367 867 A1 (Classic Sanitary Products GmbH) describes a revolving conveyor, which transports small workpieces to dry in a equipped with infrared radiators drying oven after they were previously coated in a separate unit with paint.

Finally, the mentioned DD 268 284 A1 (VEB Lehrgeräte- und Reparaturwerk Mittenwalde) general UV lamps as a means of heat treatment or drying of surface-coated products.

The sake of completeness is still on the US 5,362,505 (The Procter & Gamble Company), which describes coating unbleached, raw edible nuts with polysaccharide in a rotary coater and then drying them by infrared heating.

Furthermore, the show FR 2 374 968 A1 as well as the EP 0 132 480 A1 Coating devices in which, for example, pills can be coated and dried by means of microwave radiation.

Summary of the invention

Against this technical background, the invention deals with the problem of coating small parts both high-quality and time and cost-saving.

The invention solves this problem by a device or a method according to the independent claims. The dependent claims relate to advantageous embodiments of the invention.

Brief description of the drawings

Fig. 1

einen Ausschnitt aus einer Ausführungsform einer erfindungsgemäßen Beschichtungsvorrichtung;

Fig. 2

eine weitere Ausführungsform einer erfindungsgemäßen Beschichtungsvorrichtung;

Fig. 3

einen Infrarotstrahler mit gesonderter Luftkühlung zum Einsatz in einer Ausführungsform der Erfindung;

Fig. 4

einen Ausschnitt aus einer weiteren Ausführungsform einer erfindungsgemäßen Beschichtungsvorrichtung;

Fig. 5

eine andere Ansicht des in Fig. 4 gezeigten Ausschnitts.

The invention will now be explained in more detail by means of embodiments together with the attached drawings. In the drawings show:

Fig. 1

a detail of an embodiment of a coating device according to the invention;

Fig. 2

a further embodiment of a coating device according to the invention;

Fig. 3

an infrared radiator with separate air cooling for use in an embodiment of the invention;

Fig. 4

a section of a further embodiment of a coating device according to the invention;

Fig. 5

another view of the in Fig. 4 shown detail.

Detailed description of the drawings

Before a more detailed description of FIG. 1 First, the idea of the invention is explained in more detail.

The invention provides a device for coating of small parts, which circulates the small parts in a coating drum, there sprayed by means of a spraying device with coating material and there also by means of a drying device using electromagnetic radiation dries. Furthermore, the invention proposes a corresponding method for coating small parts.

In general, the invention enables the coating of small parts of any shape with a diameter between a few millimeters and about 15 cm, which consist of any material, for example metal, rubber or plastic. Examples are rings, buttons, mobile phone shells, screws, gaskets, rivets, pins or golf balls.

For the coating, the small parts are filled into a barrel-shaped drum. The - normally closable - drum is usually equipped with a drive which ensures a rotation of the drum. The rotational movement of the drum moves the small parts in motion. Preferably, the inner wall of the drum is provided with lamellae known from mixing drums ago, which take the small parts and thus cause a good circulation and mixing of the same.

Furthermore, the coating device comprises a device which applies the coating material in the interior of the drum, for example with the aid of a spray gun to the small parts. Since the small parts are in constant motion due to the rotation of the drum, the spray of the coating material reliably reaches every point of every single small part with sufficient spraying time. The duration, strength, repetition rate and area of the spray jet are adapted to the small parts to be coated and the coating material. As a coating material come - to name just a few examples - paints of all kinds and insulation, corrosion protection, lubricants and adhesives, adhesion promoters, Nanocoatings or special solutions in question.

The drying device of the coating device according to the invention heats, dries and / or hardens the freshly applied coating material still inside the drum. For this purpose, a radiator belonging to the drying device is directed, for example, on or directly next to the point at which the spray jet strikes the small parts. So there is a targeted, selective drying of the freshly sprayed small parts instead.

In order to prevent - potentially dangerous - excessive heating of the radiator, the drying device may comprise a cooling device. This directs, for example, an air flow to the drying device or passes water or other liquid along it. Particularly when using coating materials which emit harmful or explosive vapors during their processing, an independent cooling circuit separate from the drum interior proves to be advantageous for this purpose: the defined supply and discharge of the cooling medium to the radiator facilitates monitoring of the cooling, and the separation from the interior of the drum makes leakage of contaminated air through the cooling device impossible.

According to the individual embodiment of the coating device, an arrangement of the drying device in each part of the coating device is conceivable as long as the radiator can reach the small parts in the interior and dry or harden. However, the drying device (possibly together with the cooling device) is usually either arranged inside the coating drum or integrated in a cover for the coating drum. The cover may for example be a multi-part door, which closes the coating drum during operation and thus allows the generation of a negative pressure inside the drum and / or prevents falling out of the small parts to be coated.

Depending on the properties of the small parts and the coating material, the drying / curing can alternatively simultaneously with the spraying or (immediately) afterwards. For example, spraying and drying can be provided alternately, but this necessitates a relatively slow circulation of the small parts; a simultaneous with the spraying drying allows due to the good drying properties of electromagnetic radiation a much higher rotational frequency of the drum or the application of a thicker coating material layer per drum rotation, which leads to faster completion of the overall coating.

The radiation used according to the invention for drying preferably originates either from the infrared (about 750-1000 nm) or the ultraviolet (about 5 to 400 nm) wavelength range. The use of radiation from both wavelength ranges in a coating drum is also possible.

UV radiation is used, for example, for the drying of UV-curable or UV lacquers. UV coatings usually have a high surface hardness and scratch resistance. This type of paints needs no heat for drying; Rather, the UV radiation in the UV coating contained photoinitiators, which form radicals on UV exposure and induce polymerization.

In contrast, the IR radiation in the entire coating layer generates heat evenly and thus causes their rapid and direct drying. Therefore, IR radiation is suitable for drying all heat-responsive coating materials. An adaptation of the infrared frequency to the coating and / or small parts material used further accelerates the drying process.

Drying with radiation from both wavelength ranges is particularly advantageous when coating the small parts with hybrid lacquer. The IR radiation heats up first coat the hybrid paint and then dry it before the UV radiation finally hardens the paint to achieve good surface hardness.

Now back to FIG. 1 showing a section of an embodiment of a coating device according to the invention, namely a drum 1 with a spray device 4, 5 and a drying device 6, 7, 8.

In the drum 1 to be coated small parts 3 are filled. The drum 1 is rotatably mounted; a drive device, not shown, can put the drum about an imaginary axis through the center M of the drum 1 in rotation, as indicated in the drawing by the arrow P. The rotation speed of the drum is adjusted to the spray and drying speed.

On the inside of the drum 1 slats 2 can be seen. They take the small parts 3 in part with a rotation of the drum 1 and thus ensure their good circulation and mixing. Preferably, the slats 2 are bent from sheet metal and welded into the drum. So there are no joints, etc., in which solvent residues could settle. The shape of the lamellae 2 is preferably adapted in the manufacture of the coating device to the type and shape of the small parts 3, which are to be coated in the device. Alternatively, the blades 2 are mounted interchangeably in the drum 1. In this way, when providing differently shaped slats 2 an optimal match between the lamellar shape and shape of the small parts 3 - and thus an optimal entrainment effect - to improve the circulation / mixing of the small parts 3 can be achieved.

At a predetermined location, a pivotable and height-adjustable spray gun 4 sprays a jet of coating material onto the moving hardware 3. The coating material is passed through the spray gun 4 Supply hoses fed, which extend within a fastening device 5. From the cited prior art, the person skilled in the art further details, for example, on the structure and function of the sprayer 4, 5 and the drive device known, which therefore need not be discussed here.

The drying device 6, 7, 8 includes an IR radiant heater 6. This is like the spray gun 4, mounted pivotably and height adjustable so that it can irradiate arbitrary locations of the small amount. It is fastened by means of a fastening device 7 on the drum 1, which contains the necessary supply lines (eg power lines).

For measuring the small parts temperature, a sensor 8 is attached directly to the IR radiator 6. Its measured values are used to regulate the irradiance and duration.

FIG. 2 shows an embodiment of a coating device 20 according to the invention.

The - already in Fig. 1 shown drum 1 is rotatably mounted in a receiving device 14 between two vertical columns 13. The drive, which sets the drum 1 in rotation, is provided in the interior of the receiving device 14. Preferably, the coating device 20 in one of the uprights 13 or the receiving device 14 in addition to a pivoting device, which can change the inclination angle of the receiving device 14 and thus the drum 1 as indicated by the arrow P relative to the vertical columns. The optimum angle of inclination is determined as a function of the amount of small parts with which the drum 1 is filled.

The present embodiment has mounted on the receiving device 14 doors 9, which close the drum 1 in operation and thereby the structure a - later explained - allow negative pressure. Openings in one of the doors 9 allow the fastening devices 5, 7 and thus the supply lines for the spray gun 4 or the electromagnetic radiator 6, which are inside the drum 1, to pass through the fastening devices 5, 7. The continuation of the lines is not shown.

A viewing window 10 in one of the doors 9 allows an operator to observe the coating progress in the drum 1. About controls 11, which include, for example, a display and various buttons, the operator can intervene in the coating process, which is preferably fully automatic.

Depending on the coating material used, vapors or gas mixtures may form in the drum 1 during operation of the coating device 18. In order to avoid the danger of explosion or poisoning or odor nuisance, a ventilation is provided in the present embodiment: a valve located in the right-hand upright 13 , Not visible in the figure extraction sucks through the exhaust duct 12, the gas mixture from the drum 1 and at the same time through an air supply port 18 fresh air into the drum 1. This method also causes a slight negative pressure in the drum 1, the leakage of vapors or odors effectively prevented. If there is no danger of explosion or poisoning, fresh air injection is conceivable for other embodiments of a coating device according to the invention instead of the exhaust air extraction.

Since new vapors are constantly generated during the coating operation, the drum is never completely free of possibly harmful gas mixtures. For example, in the case of solvent-containing vapors that release some types of paint during the coating process, despite aeration in the Extremely explosive atmosphere arise. Under certain circumstances, this danger is further increased by the use according to the invention of electromagnetic radiation for drying the coating: since a (very effectively drying) radiation source can heat up to high temperatures within a short time, it may under certain circumstances trigger an explosion in a corresponding atmosphere.

In order to prevent such a hazard and to make the invention fully usable for all coating materials, some embodiments of the invention provide for cooling the radiation source contained in the drying device.

For example, it is possible to direct the exhaust air flow or to place the radiation source in such a way that the exhaust air flow cools the radiation source.

Another possibility is a separate air cooling of the radiator.

Fig. 3 shows an infrared radiator 6 with separate air cooling for use in an embodiment of the invention.

Three radiation sources 15, for example IR lamps, are arranged in a housing 17. Decisive for a risk of explosion is the temperature of the housing exterior 17. In order to prevent the temperatures there from becoming too great, the ventilation connections 16 allow air to be blown through the housing 17 when corresponding lines are connected, for example in the direction of the arrows for this cooled air.

An embodiment of the invention directs the heated air flow after passing through the housing 17 as an additional heating in the drum interior and on the small parts that he can not penetrate into the area of the spray, but hits small parts outside the spray area.

Another embodiment uses the in Fig. 3 shown housing in conjunction with a separate from the coating chamber inside the drum cooling circuit. Then, for example, a fan sucks in a defined amount of air from the environment of the drum and directs it via an air duct into the housing 17. There, the air stream heats up before it is discharged via the air control system back into the environment of the drum 1.

The problem of spray jet deflection or other disturbances of the coating process does not occur in this separate from the coating chamber cooling device, since the cooling air flow flows only in the leads and in the radiator housing 17, but does not escape from them. Because no exchange of air between the air handling system and the coating space is possible, also z. B. in case of failure of the cooling (possibly contaminated by solvent) air on the air control system from the coating room in the environment of the drum 1 or directly to the radiator 6.

An embodiment of the invention provides monitoring of the refrigeration cycle. In the case of the defined supply and discharge of cooling air as described above, a measurement of the volumetric flow at one point of the air-handling system is suitable for this purpose, for example. Particularly advantageous is a measurement of the volume flow in the exhaust duct, because there the amount of cooling air can be detected, which has actually passed the radiator housing 17. Alternatively or additionally, a temperature sensor can be used, which receives the temperature of the radiation sources 15 or the radiator housing 17.

On the basis of the measured values determined, a control unit then detects occurring standard deviations and, if so, triggers an alarm or turns off the spotlight 6. Other reactions of the control unit are also conceivable and known to the person skilled in the art.

After the in Fig. 3 illustrated principle, some embodiments of the invention perform a water cooling of the radiation source in the drying device. Again, the radiation source (or the radiation sources) in a housing, for example made of glass. Instead of air, cool water is passed through the housing with the help of two water connections, which dissipates a considerable amount (up to 50%) of the heat introduced into the housing itself. The passing water heats up only a few degrees. The radiation source (or its power connection) preferably comprises a radiation-permeable cover as protection against the water flowing through the housing. A monitor could include, besides a temperature measurement, for example, a flow measurement.

FIG. 4 shows as a detail of another embodiment of the coating device according to the invention, the inside of a door 9, which forms part of a cover 9 for the drum 1. Here, the "inside" of the closed door 9 of the drum 1 faces, their "outside" is visible and accessible to the operator of the coating system.

In the illustrated embodiment, the radiation device 6 is integrated in the door 9. The spotlight housing 17 has a quartz glass pane, through which the radiation source 15 (not visible in this figure) emits its electromagnetic radiation to the small parts in the interior of the drum 1. Opposite the inner surface of the door 9, the spotlight housing 17 protrudes slightly.

In Fig. 5 is the outside of the door 9 off Fig. 4 shown. Normally, the "inner life" of the door is 9 hidden by a removable service cover (not shown).

Visible thereby is the radiator 6 with the radiation sources 15 and the housing 17. The opening into the housing 17 air hoses 32 belong to a closed relative to the drum interior cooling device and conduct air through the radiator housing 17. For the most part, the hoses 32 extend invisibly behind a panel 34; they are with the in Fig. 4 shown inlet and outlet openings 36 connected.

In this embodiment are in the receiving device 14 of the coating system the supply and exhaust ports 36 corresponding openings, which are connected to a suitable air control system inside the receiving device. If the door 9 is closed, the openings of the receiving device preferably snap into the inlet and outlet openings 36 of the door 9, so that an air-tight connection is formed. A fan of the air duct system then sucks cool air from the environment of the system and passes it through lines in the receiving device 14, the supply air opening 36 and one of the hoses 32 in the housing 17. When passing through the radiator housing 17, the air heats up before the Air control system over the other of the hoses 32, the exhaust port 36 and lines in the receiving device back into the environment.

A preferred alternative to this embodiment of the air duct system is a coupling or connection of the supply or exhaust air openings 36 with the corresponding openings of the receiving device 14, which also remains when opening the door 9. This ensures even with the door open 9 a conclusion of the air duct system against possibly emerging from the drum interior, with solvent residues offset air. For the realization, for example, offer flexible hoses on the Opening the door 9 are partially pulled out of the receiving device 14.

In another alternative, the entire air handling system including fan etc. is integrated in the door 9; in the receiving device 14 is then no part of the cooling air control system. In this case, the inlet and outlet openings 36 are arranged so that they are exposed when the door 9 is closed. During operation of the radiator, for example, a ventilator of the air control system integrated in the door 9 sucks in air from the environment through the inlet air opening 36 and, after passing through the radiator housing 17 through the exhaust air opening 36, discharges it back into the environment.

The described integration of the radiator 6 in the door 9 saves space and also proves to be advantageous for the arrangement of a cooling device: the cooling medium need not be passed through the interior of the drum; rather, the cooling control system runs completely outside the coating space. In addition, simplified access to the spotlight 6 facilitates maintenance work.

The radiation drying in a coating drum according to the invention offers a number of advantages.

Thus, in the case of radiation drying, the initially mentioned problem of spray jet deflection does not occur, because the air flow which is necessary at conventional hot air drying is absent at the spray point. Also, the coating material dries faster, which allows a variety of paint selection, in which only little attention must be paid to the drying properties of the coating materials. Because of the better heating and faster drying of the coating, higher drum speeds or thicker coating application per rotation are possible; the process time is significantly reduced (by about one third) compared to conventional hot-air drying. The Shortening the process time also leads to a reduction in the "overspray", ie the unnecessarily used coating material. In addition, the application of thicker layers of coating material and their rapid drying or hardening results in particularly brilliant, brilliant surfaces. Furthermore, the preheating time of the drum (especially when using infrared radiation) is significantly shortened because the radiation heats the small parts very quickly to the ideal temperature for coating. Since the radiation can act on the small parts in a targeted manner, it is not necessary to heat the entire drum. As a result, noticeable power savings of in some cases 20 kW and more are achieved compared to conventional air drying.

Claims (23)

1. Device for coating small parts (3), comprising:

   a drum (1) which can be set into rotation, for receiving and rotating the small parts (3);

   a means (4, 5) for applying coating material onto the small parts (3) inside the drum (1); and

   a drying means (6, 7, 8) comprising a radiator (6) which emits electromagnetic radiation, for heating, drying and/or curing the coating material applied onto the small parts (3), inside the drum (1),

   the heating, drying and/or curing procedures taking place inside the drum (1),

   characterised in that the radiator (6) has an independent cooling means (16, 17).
2. Coating device according to claim 1, which comprises a cover (9) for closing the interior of the drum.
3. Coating device according to claim 2, wherein the cover (9) comprises a plurality of parts.
4. Coating device according to claim 2 or claim 3, wherein the cover (9) can be opened and closed to allow the drum (1) to be filled and emptied.
5. Coating device according to any one of the preceding claims, wherein the drying means (6, 7, 8) is arranged inside the drum (1).
6. Coating device according to any one of claims 2 to 4, wherein the drying means (6, 7, 8) is integrated into the cover (9).
7. Coating device according to claim 6, wherein the drying means (6, 7, 8) is integrated into the cover (9) such that it is accessible from outside for maintenance purposes.
8. Coating device according to any one of the preceding claims, comprising a ventilation means for removing vapours, resulting during the coating procedure, from the interior of the drum (1).
9. Coating device according to claim 8, wherein the ventilation means also directs a flow of air onto the electromagnetic radiator (6).
10. Coating device according to any one of the preceding claims, wherein the cooling means (16, 17) is a supply air cooling means.
11. Coating device according to claim 10, wherein the supply air cooling means (16, 17) comprises a cooling circuit separated from the interior of the drum.
12. Coating device according to any one of the preceding claims, wherein the cooling means (16, 17) is a water cooling means.
13. Coating device according to any one of the preceding claims, wherein the cooling means (16, 17) comprises a monitoring means.
14. Coating device according to claim 6 or claim 7, wherein the cooling means (16, 17) is integrated into the cover (9).
15. Coating device according to any one of the preceding claims, wherein the radiator (6) is configured to emit infrared and/or ultraviolet radiation.
16. Coating device according to any one of the preceding claims, which is configured for the simultaneous operation of the rotating drum (1), of the spraying means (4, 5) and of the drying means (6, 7, 8).
17. Method for coating small parts (3), which comprises:

    rotating the small parts (3) in a rotating drum (1);

    applying coating material onto the small parts (3) inside the drum (1); and

    heating, drying and/or curing the coating material, applied onto the small parts (3), in the drum (1) using electromagnetic radiation,

    characterised in that a radiation source (15) emitting the radiation is air-cooled and/or water-cooled by means of an independent cooling means (16, 17).
18. Method according to claim 17, wherein the small parts (3) are sprayed and dried in the same working step.
19. Method according to claim 17, wherein the small parts (3) are dried immediately after being sprayed.
20. Method according to claim 17, wherein the small parts (3) are spray-coated with a plurality of coats and are dried in each case after each layer has been applied.
21. Method according to any one of claims 17 to 20, wherein the electromagnetic radiation is infrared radiation and/or ultraviolet radiation.
22. Method according to any one of claims 17 to 21, wherein the radiation source (15) is air-cooled by a cooling circuit separated from the interior of the drum.
23. Method according to any one of claims 17 to 22, wherein the cooling of the radiation source (15) is monitored.

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