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Title:
A METHOD OF SUPPLYING HEAT TO A DRYING ROOM AND A DRYING ROOM FOR CARRYING OUT THE METHOD
Document Type and Number:
WIPO Patent Application WO/1981/000448
Kind Code:
A1
Abstract:
In a drying room, especially for painting cars, there is an endless piping system (25) through which a predetermined quantity of air is circulated and is kept heated by means of a preheater (19). The heated pipes give off heat to the room by means of convection and radiation for drying the paint in a first drying phase. In a second drying phase, hot air is led off at a plurality of places along the piping system to increase the drying temperature and for ventilating the room.

Inventors:
KARLSSON A (SE)
Application Number:
PCT/SE1980/000198
Publication Date:
February 19, 1981
Filing Date:
July 31, 1980
Export Citation:
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Assignee:
KARLSSON A
International Classes:
F26B3/28; F26B23/10; (IPC1-7): F26B21/04; A21B1/24; F27D7/00
Foreign References:
SE218153C
SE330673B1970-11-23
US1595928A1926-08-10
US3673703A1972-07-04
Download PDF:
Claims:
CLAIMS
1. A drying plant, especially for drying automobile pain or curing plastics, comprising a drying room and a closed ducting system for circulating hot air through an air pre¬ heater which preferably operates with electrical heating elements, whereby the duct walls in the ducting system are so adapted that on heating they give off heat to.the dryin room for drying an object placed therein, the walls of sai system also being provided with regulatable valves which a completely closable or are regulatably openable to provide a regulatable outflow of hot air from the ducting system t th drying.room, characterized in that inside the drying room (10) there is arranged along its walls a plurality of heating pipes (26,27,28) incorporated in the ducting syste (25) for circulating hot air, and which are heated up by t air for giving off heat to the room in turn, that the heati pipes are provided at a number of places along their lengt with blowingin valves (32,33,34) individually regulatable from closed to desired opened position for providing a loc ly regulated outflow of hot air to the drying room and the respective valve, and that an outlet from the room is open able in response to the valve openings for exhausting a pr determined quantity of hot air together with the gases obtained during drying.
2. A drying room for carrying out the method according t claim 1, for driving off inflammable gases from the object placed in the room for drying, characterized in that the place where the object is disposed in the drying room is a least partially surrounded by a plurality of pipes (26,28, comprising heatconductive material such as relatively thi sheet and which, form parts of an endless piping system (25) in which there are included an electric air preheater (19) and a fan (17) for circulating heating air in the piping system, while at the same time the heating air is heated during its passage through the preheater, that a closable ( inlet for fresh air is connected to the piping system J^Λj and that the piping system is provided with at least one, suitably a plurality, of discharge points situated in the drying room, in the form of openable valves (32,33,34) for blowing hot air into the drying room.
3. A drying room as claimed in claim 2, characterized in that the blowing—in valves are provided with nozzles which are adjustable with respect to the way they direct the respective hot air current.
4. A drying room as claimed in claim 3, characterized in that the nozzles of the valves include a telescopically extendable pipe, so. that the direction of the pipe can be adjusted at the same time as its length can be altered, so that the nozzle can be disposed at a short or longer distance from the object in the drying room. OMPI ".
Description:
A method of supplying heat to a drying room and a drying room for carrying out the method

The present invention relates to drying rooms such as are used for drying different objects and especially to such rooms used for drying a coating of paint or lacquer on an object such as an automobile. The room is provided with means for regulating the heating in the room and for regulatable ventilation thereof. In drying rooms known up to now, e.g» for painting automobiles, heating is customarily achieved by the use of electrical radiant heaters or by passing a hot air current through the roam, .The, electrical heaters cause heating which is too intense in some cases and can result, inter alia, in blisters in the paint and other deterioration of the quality, while the method using the hot air current signifies the risk of dust and other solid particles swirling up and depositing themselves in the paint coating. In both cases, large amounts of energy are consumed to generate the necessary heat. The object of the present invention is to provide a method of supplying heat to the drying room in question with the aid of simple and cheap apparatus making it possible to carry out heating of the air in the room and the object therein, so that heating takes place gently while at the same time the power requirement and energy consumption will be less than in drying rooms known up to now.

This is achieved by the heating being carried out in the manner disclosed in the following claims, and with a drying room executed in accordance with the patent claims. According to the invention, heating and drying takes place in two phases. During the first phase, a substantially definite quantity of air is circulated in a closed and endless system of pipes ,which consist of heat-conductive material, such as relatively thin metal sheet. The pipes are disposed along the walls in the room and possibly also in the ceiling thereof. A preheater for the air, e.g. one working with electrical heating elements, and a fan are coupled into the piping system. In this first pha.se, the outsides of the

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pipes are kept heated at a predetermined temperature thereb providing relatively uniformly distributed heating by conve tion and radiation in the drying room. Since the heating ai circulating in the piping is recirculated during the whole of this first drying phase, the power requirement and energ consumption will be considerably lower than what has so far been possible in drying rooms of the kind in question. Duri this phase, drying takes place relatively slowly- in a relatively low temperature in comparison to known methods. This is however an advantage, since a slower evaporation of the solvent from the paint or lacquer coating at the beginn of drying gives a better final result, inter alia with less risk of blister formation.

During the first drying phase, ventilation of the dryi room is minimal, which signifies that the air in the drying room is quiet and only flows slowly due to convection curre and thus does not swirl up dust and other particles which could adhere to the paint coating before it has dried and obtained some degree of solidity. When sufficient solvent has evaporated, the second. drying phase is coupled in to provide the recommended dryin temperature for the paint or lacquer coating, this temperatu being usually considerably higher than the temperature pre¬ vailing during the first drying phase. This second phase is equal to the first phase but with the addition that the heating air in the piping system is led off and blown out into the room at one or more places along the piping system For this purpose the piping system is provided with openabl valves and adjustable nozzles, so that the respective hot a current can be directed towards a desired area of the objec For example, if the object is repainted at one place only, it is sufficient to release hot air towards this place, e.g the front wing of a car. In this case, the amount of hot ai led off is thus relatively small. Taking place in step with blowing out hot air into the room, fresh air is supplied to the piping system, whereby a corresponding ventilation of th drying room takes place.

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In practical tests which have been made, maintaining the ventilation at as low as about 15% of the airflow circulating through the fan has been enabled without drawbacks. The heat losses will thus be comparatively small. If the air preheater works with electrical heating elements, the heater is heat-insulated on all sides apart from its upper side. By allowing the incoming fresh air to flow over the hot upper side of the heater, preheating of the fresh air is obtained which further improves the heating economy of the drying room.

The fan is usually driven by an electric motor which is aircooled, and by leading this cooling air through the electric motor and•subsequently into the piping system at . the fan on its suction side, further preheated fresh air is supplied which improves heating economy.

With regard to working environment, this has been improved considerably in relation to the working environment obtained when using radiant heaters for drying the paint in painting cars. It is namely practically impossible for a person to be in the room when radiant heaters are used,- since severe breathing difficulties are rapidly experienced. This disadvantage is practically entirely eliminated in the drying room in accordance with the invention, and especially in the second drying phase. The drying room is otherwise provided, in a manner known per se, with an inlet in the ceiling for blowing in fresh air into the chamber during paint spraying, and an outlet at the floor for exhausting this air so that a downwardly directed air current is obtained in the room during spraying. The method in accordance with the invention is explained in more detail while referring to the attached drawings, which schematically illustrate a drying room in accordance with the invention.

Fig. 1 is a section along the line 1-1 in Fig. 2 and illustrates the drying room in accordance with the invention. Fig. 2 is a section along the line 2-2 in Fig. 1, and Fig. 3 is a side view of the air preheater and the fan seen according to the view 3-3 in Fig. 1.

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The drying room has a floor 10, four walls 11,12,13,14 and a ceiling 15. The wall 13 has a door 13a as indicated by chain-dotted lines.

Up against the ceiling there is a unit 16 with a fan known per se and a filter for blowing a current of fresh a through an inlet in the ceiling into the drying room and providing a downwardly directed air current to an outlet 16 at the floor of the room. This air current is conventional coupled in during spraying paint or lacquer on the object which is placed on the floor or on some other substructure in the room.

There is a fan 17 outside the room which is driven by an electric motor 18 and blows air through a conventional . preheater 19 ' with, electrical heating elements. The preheate is heat-insulated on all sides apart from its upper side 19 which will thus be hot during operation and give off heat t the space under a fresh air inlet in the form of * a hopper¬ like induction cowl 20 the lower edge of which is free fro the upper side of the preheater to obtain an induction gap The cowl 20 is connected to the suction side of the fa 17 via an inlet pipe 22 containing a flap valve 23. nd a filter ' 24. The fresh air supplied to the fan will thus be considerably preheated due to the flow over the heated uppe side of the preheater. The pipe 22 is connected to a closed and endless syste 25 of pipes comprising relatively thin and heat-conductive sheet piping. As is apparent from Figs. 1 and 2, the fan 17 and air preheater 19. are a part of this closed piping syste so that when the flap valve 23 is closed, a predetermined quantity of air will be circulated round in the piping syst and be heated by the preheater to the desired temperature, which is regulated by a conventional thermostat controlling the preheater.

The piping system extends from the air preheater with an upper pipe part 26 into the drying room and along the walls 11,12 to a union box 27 and from this box with a lowe pipe part 28 back again along the walls 12,11,14 to a union box 29 and with an upper pipe part 30 from this box back ____

again along the wall 14 and out through the wall 14 at a place in the vicinity of the fan 17 for being connected to the suction side of the fan via a pipe part 31. The pipe 22 is connected to this part 31 of the piping system, as is illustrated in Fig. 1.

The cooling air ducts in the electric motor 18 are connected to the suction side of the fan 17, resulting in that after the cooling air has been heated in the electric motor, this air will be sucked into the fan and supply a certain quantity of heat to the circulating heating air in the piping system.

After the application of lacquer or paint to the object -" placed -in- the drying room, e.g... a car,, the .fresh,air fan is switched o f in the unit 16. Since the drying room is now practically entirely closed off by the door 13a being closed, the air in the drying room and thereby the paint coating will be heated up "with the aid of the heated piping system which gives off heat via convec¬ tion and radiation. When painting cars, the temperature in the chamber will be in the order of magnitude of about 30 C. The paint coat will now be dried in this way in a first drying phase for driving off the greater part of the solvent in the paint. This drying takes place more slowly than it has done so far with electrical radiation heaters or hot air currents.

As a result of this .slower drying in the first phase, * the paint is subjected to a gentle heat treatment which gives substantial improvement of the final result, since heating is distributed relatively evenly in the drying room by the air which is only slowly self-circulating, its movement being so slow tϋafc there is obtained a considerably decreased risk of dust particles and other particles swirling up which could adhere to the paint before it has dried and hardened sufficiently. Furthermore, the slower drying results in less risk of blister formation in the paint.

When the paint has subsequently dried sufficiently for being able to withstand a given air current without dra ba^^-

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the second drying phase is coupled in to increase the dryi temperature to the recommended temperature for the paint o lacquer being used. This temperature is ' in the area of abo 60 C for certain automobile paints. This second drying phase is carried out with the help of a plurality of openable valves with nozzles 32,33,34 distributed along the pipe sections in the piping system 25 as is illustrated in Figs. 1 and 2. If the piping system a comprises pipe sections in the ceiling of the drying room, these sections are also provided with valves and nozzles f blowing down hot air against the object in the drying room. The schematically indicated nozzles 32,33,34 are suit- ably adjustable for directing the hot air currents. They ar moreover suitably provided with telescopically extendable pipes, so that the nozzles can be placed at a desired distance from the surface of the object worked on.

In most cases the whole object is painted, "and in such a case all the valves are opened, but in certain cases only a certain portion of the object is painted, and in such a case only the valve with nozzle situated nearest is opene enabling the possibility of not requiring the use of more hot air than is necessary.

There is thus provided during the second drying phase a controlled supply of hot air to raise the drying temperat to the recommended temperature, and to provide a controlled ventilation of the drying room by venting air- and evaporate solvent through a special outlet from the room or through the unit 16 in the ceiling of the room.

It was found from measurements taken in a trial that the ventilation was as little as about 15% of the airflow circulating through the fan. The heating effect in the air preheater was 10 kW as opposed to the 30 kW previously required with conventional electrical radiant heaters in the same room. The trial plant was used to paint cars, and the quality of the paint surface was considerably improved in relation to the result previously obtained with radiant heaters.

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The drying room in accordance with the invention can to advantage be incorporated in a production line, where the object passes into the room at one end and out of it at the other end, in which case the room can be divided into two zones, the first zone being adapted for carrying out the first drying phase, and the second zone adapted for carrying out the second drying phase.

The invention has been described above in connection with drying paints and lacquers, the principle being that drying is first carried out at a relatively low temperature in a relatively undisturbed atmosphere, thereafter increasing the temperature substantially by continuing drying with the aid of hot air currents. To advantage, this method can also be utilized within other areas, e.g. for curing plastics in the plastics industry.