Drying system in a spraybooth

Details Drying system in a spraybooth Drying system in a spraybooth

1999-08-09

2001-02-27

Gravini, Stephen (Department: 3749)

Drying and gas or vapor contact with solids

Apparatus

Houses, kilns, and containers

C034S202000, C034S210000, C034S218000

Reexamination Certificate

active

06192604

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a paint drying system for painted bodies, especially automobiles and particularly, but not exclusively, a system for drying painted motor cars.
Conventional automobile spraybooths dry solvent-borne paints which have been applied onto the surfaces of an automobile by passing heated air over the painted surface. Typically, heated air is blown down through inlets in a ceiling of the booth and is evacuated through floor outlets. This process involves the release of polluting solvents into the atmosphere after the paint has dried. In an effort to conform with new legislation which regulates the use of solvent-borne paints, paint manufacturers have developed new paints, such as water-borne paints which are less damaging to the environment.
However, the conventional paint drying spraybooth has proved unsuitable for the drying of water-borne paints. This is because it relies on the volatility of the paint solvent to dry the paint quickly. As water is not volatile it takes substantially longer to evaporate under normal ambient conditions. The water in water-borne paints is thereby released more slowly, resulting in extended drying times when using conventional drying systems. The drying of water-borne paints is further hindered when ambient humidity levels rise. Experiments involving dehumidification techniques have proved impractical and expensive.
It is also known, as described in EP 0 690 279, to dry water-borne paints with directional air jets using re-circulated air from within the spraybooth. As described in this specification, the jets are directly optically aligned with individual painted surfaces to be dried. The specification states that the directional air jets, when used with heat lamps, reduce the drying times for one vehicle from 60 minutes to 8-14 minutes. This is still significantly longer than is required for the drying of solvent-borne paints. Furthermore, since the air jets are individually aimed directly at painted surfaces, water may be entrained in the paint resulting in subsequent blistering of the paint surface.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome or ameliorate the problems in drying water-borne paints by providing a paint drying system which can dry water-borne paint treated automobiles particularly, but not exclusively, motor cars efficiently, cost effectively and on a time scale comparable to the drying time of solvent-paints.
According to one aspect of the invention therefore there is provided a paint drying system for drying a painted body, the system comprising a spraybooth having a enclosure, an air inlet, an air outlet, pump means and a heater to supply air from the atmosphere externally of the booth to the air inlet to flow through the enclosure from the air inlet to the air outlet, characterised by the provision of at least one further air inlet which receives air from the atmosphere externally of the booth and directs this air into the enclosure transversely to said air flow, heating means being provided to heat such air.
Advantageously, the paint drying system may be used for drying a body painted with a water-borne paint. Preferably the body is an automobile, and particularly a motor car.
Many paints, including water borne paints, are usually applied as a series of layers or coats and the paint may require drying after each coat is applied. Accordingly, the system of the present invention may be used to dry water borne paint during what is known as the “flash-off period” or “flash-off cycle”. During this period the water or solvent in the paint is driven off, either after each individual coat is applied or after a number of coats have been applied. Where the paint must be dried in between coats of paint, the paint drying system of the present invention ensures thorough drying between coats so that water is not trapped within the paint film.
Certain paints are cured in a baking operation following flash-off cycle. During a baking operation, hot air (normally at a temperature of 80° C.) is re-circulated in the enclosure.
In accordance with convention, therefore, the enclosure may also be used for paint spraying, and baking operations.
With the system of the invention, a body painted with a water-borne paint can be efficiently dried in a period of time comparable with the time taken to dry solvent-borne paints using conventional drying systems and without surface film problems.
Air introduced via the further air inlets disrupts such air flow to cause turbulent air flow within the enclosure and this high air movement accelerates the drying of the painted body. The pump and\or the heater may be located in any suitable position, and may for instance be located on, adjacent or within the air inlet system.
It is preferable to avoid the flow of air directly onto, i.e. perpendicular to a painted surface (of the motor car). This may lead to the unwanted entrainment of water in the paint which can cause blistering thereof.
Accordingly, it is preferable that the further air inlet is operable to direct air obliquely at a painted surface (of the automobile).
This encourages high air movement in the form of vortices adjacent the painted surface which accelerates the drying thereof, but without the undesirable entrainment water in the paint.
The air inlet may be in the form of an air inlet system which includes an air inlet duct or ducting in which said heater may be located.
Preferably air entering the air inlet system is heated to a temperature of 35° C. by said heater, however it may be lower if required, for example, when the body is painted in the enclosure.
The air inlet system may include a plenum chamber located in between the air inlet duct/ducting and the enclosure, the plenum chamber having an inlet and an outlet so as to allow air to flow from the inlet duct/ducting to the enclosure.
Preferably the plenum chamber is above to withstand high air pressures.
The plenum chamber may be any suitable shape such as a box construction.
The plenum chamber may house said pump means which is operable to draw air from the inlet duct through the plenum chamber and into the enclosure.
Preferably air enters the enclosure via the plenum chamber filters at a speed of 0.2-1 ms
−1
, and preferably at 0.5 ms
−1
.
Preferably, the air is filtered prior to entering the enclosure, and this may be effected by any suitable means, such as synthetic filter.
Preferably the filter is operative to remove particles exceeding 10 microns in diameter.
The filtering of the inlet air reduces contamination of the painted surfaces over which the air flows, which would otherwise lead to particles of dust, etc. being entrained in the painted surface which can cause spoiling of the surface, an effect known as peppering.
The further air inlet may receive air via air supply means which may include a duct or ducting and may include one or more fans operable to draw air through the further air inlet and into the enclosure.
The further air inlet may receive said air from the air inlet system and accordingly the air inlet system may be connected to the further air inlet by means of a duct or ducting.
Preferably said means for heating the air which is directed into the enclosure by the further air inlet is said heater. Alternatively or additionally said means may comprise one or more further heaters which may be located on, adjacent or within the further air inlet.
The further air inlet may incorporate one or more further pumps or fans.
Preferably the further air inlet is operable to direct air into the enclosure at 2-40 ms
−1
and particularly preferably at 25 ms
−1
.
Preferably, the further air inlet includes one or more air jets to affect direction of the air into the enclosure. The or each air jet may simply comprise an opening through which air may flow or alternatively the or each air jet may be a nozzle/spray jet structure of any suitable form.
The air jets may comprise any suitable material but preferably the material has anti-static properties. One preferred material is alumi

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