EP0934497B1 - Method and device for drying thin coatings - Google Patents

Abstract

The invention relates to a method for drying coated workpieces, and a device to carry out such a method, whereby workpieces are exposed to dry air i.e. air with an absolute humidity of 0-10 grammes moisture charge per cubic centimeter.

Description

The invention relates to a method for drying thin layers based on water, solvent or alcohol, which were applied to objects by spraying, dipping or brushing, and an apparatus for carrying out the method.
The materials described are used for coating a wide variety of objects, for example for coating and painting auto parts, machine components, metal sheets and the like.

According to the state of the art, the coatings applied and then dried.

Drying takes place according to the state of the art either by infrared radiation or by warm Air is passed over the coated objects, so that drying is done by heat convection. After this There are also combined methods in the prior art, wherein the coated objects simultaneously warm air and be exposed to additional infrared radiation. The workpieces are heated to 60 ° C to 120 ° C, to the moisture contained in the thin layer evaporate. This causes considerable temperature loads on the components and partly thermal chemical Implementations on.

The methods belonging to the prior art the disadvantage that they are very energy and time consuming, the latter in particular by heating the workpiece which the thin layer is applied so that the drying requires several hours. In addition, the workpieces after drying from their heating temperature, the means from 60 ° C to 120 ° C, again cooled down to about 30 ° C so that further processing of these parts can be done and these parts are manageable.

Another major disadvantage is skin formation over still damp base layers when painting over warm air and the heating of the workpieces to high temperatures.

Will the workpieces during the drying process transported on a conveyor belt, for example in the case of the processes belonging to the prior art, the danger overheating during a conveyor belt stoppage.

Other disadvantages of the prior art Drying processes are heat, moisture and odorants can escape into the environment, and that a Insulation of the hot air-carrying components is necessary, on the one hand to keep energy consumption within limits and on the other hand, to protect working people.

In the drying processes belonging to the state of the art can affect the heat on the surface of a Thin layer for sealing and for the formation of bubbles to lead. This means that the layer is completely dry the base material is not secured.

In addition, the state of the art associated drying processes often shifts in color that are not wanted. Furthermore occurs at the State of the art drying process in the Paint an "orange peel", that is, the paint is after slightly wavy after drying.

According to the prior art (DE 295 04 040 U1) is a Industrial dryer with improved efficiency known.

Disadvantage of this is part of the prior art Industrial dryer is that the temperature of the dehumidified Air is not adjustable because of the dehumidifier (2) is structurally predetermined by the heat exchanger (15), the air cooler (16), the heat exchanger (17) and the Air heater (18). With these to the state of the art belonging industrial dryers is no energy from the System dissipated so that the temperature automatically adjusts and thus during the drying process continuously increased.

The prior art (DE 37 34 994 A1) also belongs a method and a device for fully automatic Drying cleaned items. According to this method works with drying air, which has a temperature range of 40 ° C to 80 ° C. As already stated several times, this high temperature range of considerable disadvantage.

It also belongs to the state of the art (US-A-4,365,480) an apparatus for condensing out Water from a gas. With this device, however drying of layers of paint on workpieces is not possible.

The technical problem underlying the invention consists of a drying process as well as a device to carry out the procedure whereby the Drying time is significantly reduced, which is a significant there is less energy consumption, and that is also applicable to heat sensitive parts.

This technical problem is caused by the characteristics of the Claim 1 and the features of claim 8 solved.

By using air to dry the has a relative humidity between 0% and 30%, preferably a relative humidity of approx. 10% (dry Air), and in that the dry air over and / or around the workpiece to be dried is taken, the dry air the moisture of the applied on the workpiece Thin film on. Because the workpiece is constantly dry air is supplied, is always approximate maintain equal vapor pressure difference, whereby the evaporation of moisture on the workpiece surface is accelerated. The moisture coming out in vapor form is immediately absorbed by the ambient air. According to the The inventive method is the temperature of the air by means of an additional cooling device with an in Circulating refrigerant and through a subsequent Warming at a low temperature level kept from 15 ° C to 60 ° C.

According to the method of the invention dry air by cooling so-called "moist air", that is air with a relative humidity of more than 40%, in a dry air unit obtained by condensation. To After dewatering, the air is warmed up again Moisture absorption fed to the paint.

The dry air takes away the moisture of the thin layer on the workpieces. The workpieces are themselves in one housing. The housing can be used as a cabinet Recording of the workpieces can be formed, for example large workpieces, such as lower parts of buses or the like, to be ordered. After the air is over drying workpieces has been passed, leaves the Air the housing and in turn becomes the dry air unit fed so that the air is dehumidified again. The Air is then heated again and the one to be dried Workpieces fed again.

The drying process according to the invention is a closed one System in which there is no exhaust air. This has the advantage that no odorants, no moisture and no heat is transported outside.

The heat generated when the air is dehumidified is used for reheating the air after dehumidifying used.

This ensures that the invention Process has very low energy consumption because a closed system is in place.

a) Der Energieverbrauch ist sehr gering.

b) Es ist keine Abkühlstrecke für die Werkstücke erforderlich, da die Werkstücke sich lediglich auf circa 20 °C bis 25 °C erwärmen.

c) Die mit einer Dünnschicht belegten Teile werden keinen thermischen Belastungen ausgesetzt, da die im Kreisprozeß erhitzte Luft zu keiner wesentlichen Aufheizung des zu belegenden Gutes führt, da durch die Verdunstungskühlung die Oberfläche kalt bleibt.

d) Es ist keine Überhitzung der Werkstücke möglich.

e) Es ist ein einfacher Anlagenaufbau möglich, da keine Wärmeisolierung notwendig ist.

The dehumidified air is heated to a temperature of approximately 15 ° C to 60 ° C. This is sufficient for drying with dry air. As a result, the method according to the invention has the following advantages:

a) The energy consumption is very low.

b) No cooling section is required for the workpieces, since the workpieces only heat up to approximately 20 ° C to 25 ° C.

c) The parts covered with a thin layer are not exposed to any thermal loads, since the air heated in the cycle does not lead to any significant heating of the material to be covered, since the surface remains cold due to the evaporative cooling.

d) The workpieces cannot overheat.

e) A simple system structure is possible since no thermal insulation is necessary.

Because the workpieces have no thermal loads are suspended in the method according to the invention, it is also possible to dry heat sensitive parts. This means that, for example, plastic parts are dried that can not be heated above 50 ° C to 60 ° C may be. It is also possible to dry parts already with rubber seals or oil fillings, for example are provided. Due to the relatively low temperatures take no harm.

Due to the low temperatures is beyond that No isolation of the device necessary, because according to safety regulations the working temperatures only up to 20 ° C may be above room temperature.

The housings intended for drying are the Adjusted conditions of the individual case. For example Vehicle underbodies are dried by buses an appropriate dryer tunnel is required through which the entire underbody of a bus can be driven through can. For drying railway and car models can be provided a kind of drawer system in which each model is arranged individually. The dry air is here through the individual drawers of the Drawer system directed.

The inventive method has the advantage that much less time is required for drying is as with the methods belonging to the prior art. With the method according to the invention, the Drying process, depending on the material and surface, between three and ten minutes. For very jagged parts the time spent can range from twelve to fifteen minutes increase. This is because the dry air is cracked and recesses can not penetrate so well, so that in These cracks and recesses are exposed to air that is filled with liquid is saturated, so that the drying process stagnates. Here you can use a blower or nozzles Air circulation guaranteed in all gaps and recesses become.

With flat sheets, the time for air drying is at about three to four minutes. The time for that Air drying depends on the type of coating liquid used.

Another advantage of the method according to the invention is that only 10% to 25% of the energy required for the stand the method belonging to the technology is required.

Further details of the invention can be found in the subclaims be removed.

Fig. 1

eine Trocknungsvorrichtung;

Fig. 2

eine Trocknungsvorrichtung mit einer zusätzlichen Kühlvorrichtung.

The invention is explained below with reference to a drawing. Here show:

Fig. 1

a drying device;

Fig. 2

a drying device with an additional cooling device.

The embodiment shown in Fig. 1 is for the invention is not claimed, but it is for the in Fig. 2 shown device relevant.

Fig. 1 shows a device (1) with a drainage device (2) for a water-based paint layer, through the humid air (3). The humid air (3) is in the dewatering device (2) Condensation drains so that the air has a vapor partial pressure from 0 to 16 mbar. The condensate (12) is collected in a basin (4). The condensed Air (5) is passed through a heater (17) and by means of a fan (7) in the direction of arrow (A) in an area (8) of the device (1) directed. The dry one Air sweeps through circulation over workpieces (9), which are coated and should be dried. The dry air takes the moisture out of the paint on, so that the air in area (10) in turn a higher has relative humidity.

The moist air will turn in the direction of arrow (B) fed to the drainage device (2) where the air (3) the water is withdrawn again.

The air has a temperature of 15 ° C. in area (8) up to 60 ° C. The workpieces (9) are painted over not with the dry air heated to 15 ° C to 60 ° C significantly heated because the evaporative cooling Surface of the workpieces (9) remains cold. The device (1) forms a closed cycle for the circulating air.

The device (1) can also have an open circuit be driven. For example, the device (1) be designed as a continuous system with open passage openings for the parts to be dried.

The device (1) has a housing (11) in which the process of dehydrating the air, heating the dry Air, drying the workpieces and returning the moist air to the drainage device (2) in a closed Cycle is carried out.

The device works in the same way for the Drying of any kind of thin layers, be it on water, Alcohol or other solvent based, but also when using grease or glue and the like.

2, the drying device (1) in a preferred embodiment of the invention an additional Cooling device (13). In the additional cooling device (13) becomes a circulating refrigerant, with which the drainage device (2) operated is cooled. This is necessary to get a low one To maintain the temperature level of the drainage device (2).

The moist air (3) is in the drainage device (2) dewatered by condensation, so this will the refrigerant with which the drainage device (2) is operated, heated. The warmed refrigerant arrives from the dewatering device (2) into a compressor (14). The refrigerant is in the compressor (14) compresses, causing the refrigerant to heat up. This further heating is based essentially on the heat of compression. The compressed comes out of the compressor (14) Refrigerant in the refrigerant condenser (6). With help of the heated refrigerant is in the refrigerant condenser (6) the dry air (5) to a predetermined temperature heated to this heated air then in area (8) to dry the workpieces (9). Through the Delivery of thermal energy by the heated refrigerant the dry air (5) in the refrigerant condenser (6) the refrigerant is pre-cooled. The pre-cooled refrigerant then passes into another refrigerant condenser (15). The pre-cooled is in the refrigerant condenser (15) Refrigerant with the help of circulating air, which by means of a Fan (16) from the vicinity of the drying device (1) is removed, cooled further. The air circulation has essentially room temperature.

With the help of the additional cooling device (13) the refrigerant used in the refrigeration cycle is always cooled, such that a drainage of the circulating air in the drainage device (2) is optimally executable.

As the temperature of the dry air (5), which leads to Drying of the workpieces (9) in the area (8) is used, is approximately 15 ° C to 60 ° C, the housing (11) Drying device (1) as a non-thermally insulated housing be trained.

reference numerals

1

contraption

2

dehydrator

3

moist air

4

pool

5

dry air

6

Refrigerant condenser

7

fan

8th

Area

9

workpiece

10

Area

11

casing

12

condensate

13

cooler

14

compressor

15

Refrigerant condenser

16

Fan in the cooling device 13

17

heater

A, B

arrows

Claims (12)

1. A method of drying thin coatings applied to a workpiece, wherein air with a moisture of between 0 and 10 g of vapour charge per cubic metre (dry air) is conveyed over and/or around the workpiece (9) to be dried, wherein the air for the drying is at a temperature of between 15°C and 60°C, and wherein the temperature of the air is kept at this low level by cooling by means of an additional cooling device (13) with a refrigerant circulating in the circuit and by a subsequent heating.
2. A method according to Claim 1, characterized in that the thin coatings are coatings of grease, adhesive or the like, in particular coatings of paint or lacquer or the like which are water-, alcohol- or solvent- based.
3. A method according to Claim 1, characterized in that the moisture of the dry air has a partial vapour pressure of from 0 to 16 mbar.
4. A method according to Claim 1, characterized in that the dry air is produced by cooling the air and condensing out the moisture.
5. A method according to Claim 1, characterized in that heat which occurs during the production of the dry air by condensation is used for the following re-heating of the under-cooled dry air to from 15°C to 60°C.
6. A method according to Claim 1, characterized in that the air is circulated in a closed or an open circuit, in such a way that the cooling of the air takes place in a refrigeration evaporator.
7. A method according to Claim 6, characterized in that condensing out the vaporized liquids of the coatings to be dried takes place on under-cooled tubes at from 0°C to -20°C.
8. A device for drying thin coatings applied to a workpiece, in accordance with the method according to Claim 1, characterized in that

   a) the device (1) comprises a cooling device (2) with a refrigerant circulating in the circuit for condensation and a heating device (17) for re-heating for the circulating air,

   b) a housing (11) is provided for receiving the workpieces (9) to be dried, wherein the housing (11) is designed in the form of a housing which is not thermally insulated, and

   c) at least one fan (7) is provided for the circulation of the air in the device (1).
9. A device according to Claim 8, characterized in that the housing (11) is of closed or open form.
10. A device according to Claim 8, characterized in that the housing (11) is in the form of a tunnel.
11. A device according to Claim 8, characterized in that the housing is in the form of a drawer system.
12. A device according to Claim 8, characterized in that the device (1) is in the form of a device containing the air in the closed circuit.

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