Heating apparatus for a coating process

Abstract: A heating apparatus for a coating process for radiation heating of the workpiece W coated with an aqueous coating material, comprises radiation heaters (10) controlled by power units (11). It has been found that solvent flash-off is improved by tailoring the heat applied to the colour of the workpiece. The coating colour of the workpiece is specified or detected, and solvent flash-off operation is performed by automatically regulating the radiated heat intensity according to the detected colour. A control system may store data providing the optimum radiated heat intensity for predetermined colours.

Description: In coating processes using organic solvent based coating materials there have been strong demands in recent years for complete separation and recovery of the volatile organic solvents without discharging them to outside of the process, ie. out of the coating facilities, to prevent pollution, particularly because of problems of photochemical smogs. In coating processes for large workpieces such as car bodies, aqueous (water based or water-soluble) coating materials are now used, which utilise solvents based on water instead of organic solvents because coplete separation and recovery of solvents not only means a high economic burden and an increase in the size of the coating facility, but also does not provide a complete solution to the problem. Such aqueous coating materials cause some drawbacks in the subsequent processes because water is evaporated much more slowly than organic solvents. Namely, when coating is performed on a wet-on-wet basis, dripping occurs, while, when placed into an oven, bubbling occurs. Accordingly, it is necessary to provide an evaporation process to evaporate water to a certain extent before proceeding to the subsequent processes (hereinafter referred as the "flash-off process"). However, when this flash-off process is of the spontaneous evaporation type, a long time is required for flash-off because the evaporation speed of water is slow. For this reason, the flash-off zone must be extended and so larger facilities are required. In this respect, it has been proposed to shorten the flash-off time by positively heating the workpiece during the flash-off process. A radiation heating system using a radiation heater is suitable for initial heating, as described in Japanese Patent Publication No. 52-30170, because this system is free of the disadvantages of convection heating systems, such as suspended dust, or of induction heating systems, such as complicated facilities and the restriction on the workpieces, and because quick heating can be accomplished. GB-A-2091858 (=FR-A-2 495 964) also discloses a radiative heating system used in a booth for repairing damaged vehicles. The radiating elements are controlled to apply a required amount of heat only to the car body parts needing treatment. However, when this heating apparatus is adopted, and a wide variety of workpieces is transported to the flash-off zone one after another, then, some of the workpieces may be dried up, and the quality of the coating may be impaired. An object of the present invention is to offer a heating apparatus for a coating process, which can achieve optimal flash-off by automatically regulating the radiation heat ray intensity based on the coating colour of the workpieces. Specifically, from the studies of the present application, it is thought that the quantity of heat absorbed, ie. the temperature rise, differs according to the coating colour of the workpieces. It has been found from practical experience in the coating process that the influence of the difference in coating colour is surprisingly strong. The present invention provides heating apparatus for a coating process, comprising heating means for radiative heating of a workpiece coated with an aqueous colour coating, and control means for controlling the amount of heat radiated by said heating means, characterized by means for specifying the colour of the coating and means for controlling the amount of heat radiated towards the workpiece in accordance with the colour of the coating. The coating colour of the workpiece to be coated with the aqueous coating material is specified in advance by the coating colour specifying means. When the workpiece is carried towards the front of the radiation heater, the control means controls the power unit to obtain a radiation heat ray suitable for the specific colour. Thus, without being worried by complicated procedures such as changing the speed of transport and without decreasing the productivity, quick and satisfactory flash-off operation can be performed, and coatings of high quality can be achieved. By providing a coating colour specifying means and control means, and regulating automatically the intensity of radiation to an optimal value for each coating colour of the workpiece, complicated and careful adjustment is not required, and adequate and satisfactory flash-off operation can be achieved without decreasing productivity, regardless of the coating colour of the workpiece. Other preferred features and advantages of the invention will be apparent from the following description and the accompanying claims. The invention will be further described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a diagram illustrating first and second embodiments of the invention; and Fig. 2 is a flow chart for explaining the operation of the embodiments of Fig. 1. A first embodiment of the invention will be described by reference to Fig. 1 in which a flash-off zone 1 comprises an air supply chamber 2, a radiation heating chamber 3, and an exhaust air processing chamber 4. A workpiece W coated with aqueous coating material is transported by transport means 5 (along a line perpendicular to the plane of the drawing) and is automatically transported to subsequent processes through the spontaneous evaporation region. A pair of these radiation heaters 10 are furnished, positioned one on each side of the workpiece W transported to the flash-off zone 1. Power units 11 supply power to the radiation heaters 10. A control means 20 controls the entire coating apparatus in this embodiment, and comprises CPU 21, ROM 22, RAM 23, keyboard 24, I/O port 25, etc. connected by a bus. A coating colour specifying means consists of the CPU 21, ROM 22, RAM 23, etc., and the control means consists of CPU 21, etc. According to previous systems when the workpiece W is transported in front of the radiation heaters 10 by the transport means 5, the control means 20 turns on the power units 11 through I/O port 25 and then turns them off. In the present invention, the coating colour of the workpiece W is specified in advance, and the intensity of the radiated heat is regulated automatically according to the specified colour. For this purpose, data for coating colour and radiated heat intensity, ie. the data corresponding to the coating colour and radiated heat intensity, are stored in ROM 22, which constitutes the coating colour specifying means. CPU 21 specifies the coating colour of the workpiece to be transported to the radiation heating chamber 3 by the transport program of the workpiece W, stored in ROM 22, and this is stored temporarily in RAM 23. At the same time, the radiated heat intensity, corresponding to said specified colour, is read from ROM22, and this is stored temporarily in RAM 23. This coating colour specifying program (steps 10, 12 and 14 in Fig. 2) is stored in ROM 22. CPU 21, constituting the control means, performs drive control of the power units 11 for a predertermined time according to the value of the radiated heat intensity temporarily stored in RAM 23. CPU 21 executes the control program (the steps 16, 18 and 20), which is terminated after a predetermined time. The coating colour and radiated heat intensity are reloadable on ROM 22. In this embodiment, the data are inputted on the keyboard 24 before starting the operation and are stored in RAM 23, such as how many workpieces are to be produced, in which colour and in what kind of sequence. The radiation heater 10 is in this embodiment is an infrared (eg. near infrared - medium infrared) radiation heating system. Accordingly, the response speed is quick, and the radiation intensity is easily controlled. In the present embodiment, the CPU 21 reads from RAM 23 and specifies the coating colour of the workpiece W to be transported to the radiation heat chamber 3 while commanding the predetermined operation of the transport means 5 (steps 10 and 12 in Fig. 2). Then, the required radiated heat intensity is read out from ROM 22 and is stored in RAM 23 (step 14). Thereafter, CPU 21, as the control means, performs drive control of the power units 11 for a predetermined time in order to obtain the required radiated heat intensity (steps 16 and 18). Therefore, the workpiece W as it is transported at a constant speed is heated to the preset temperature while it passes between the radiation heaters 10, and a flash-off operation optimised to the specified colour is performed. The power units 11 are then turned off at step 20. In this embodiment 1, the coating colour specifying means (21, 22, and 23) and the control means (21) are provided, the coating colour of the workpiece W to be transported to the radiation heating chamber 3 is specified, and the drive control of the power units 11 is performed to obtain the optimal radiation heat ray intensity for the specified coating colour. Thus, it is possible to adequately and quickly dry the workpiece W coated with the aqueous coating material, and a coating of high quality can be achieved. Moreover, because the workpiece can be dried as desired within a predetermined time, even when the coating colour is changed, diversified requirements are satisfied and productivity is increased. In a second embodiment of the invention, the coating colour is specified automatically by providing a colour detector 30, which is shown by two-dot chain line in Fig. 1. Specifically, the specified coating colour is detected by the colour detector 30 when the workpiece W is transported to the radiation heating chamber 3, CPU 21 temporarily memorizes this detected coating colour as the specific colour in RAM 23. The required radiated heat intensity is read out from ROM 22 and stored in RAM 23. The control means, CPU 21, functions in the same manner as in the embodiment 1. Consequently, the same operational effect as in the first embodiment can be obtained in the second embodiment with adequate and quick flash-off operation. Further, there is no need to input the coating colour and the number of workpieces to be produced on the keyboard before starting the operation, and so productivity can be extensively increased. In the above embodiments, the coating colours of the workpiece W are indirectly or directly specified. Other methods are possible. For example the car number may be inputted before the operation is started. Instead of colour detector 30, a detector for detecting car number of other indicator may be provided, and the coating colour may be determined from the car number or other indicator.

Claims: Heating apparatus for a coating process, comprising heating means (10, 11) for radiative heating of a workpiece (W) coated with an aqueous colour coating, and control means (21) for controlling the amount of heat radiated by said heating means (10, 11), characterized by means (24, 30) for specifying the colour of the coating and means (22, 23, 24, 30) for controlling the amount of heat radiated towards the workpiece (W) in accordance with the colour of the coating. Heating apparatus as claimed in claim 1, characterized by means (22) for storing data relating the required radiated heat intensity to the coating colour. Heating apparatus as claimed in claim 1 or 2, characterized by means (23, 24) for storing a predetermined sequence of workpiece numbers and their respective coating colour, and control means (21) controlling the radiated heat in accordance with the arrival of workpieces in a heating chamber (3) containing the heating means (10, 11) according to said sequence. Heating apparatus according to claim 3, wherein said control means consists of a CPU (21), which drives a power unit (11) of said heating means for a predetermined time based on the value of the radiated heat intensity which is temporarily stored in a RAM (23). Heating apparatus according to any one of claims 1 to 4, characterised is that said coating colour specifying means (24, 30) comprises a colour detector (30) for detecting directly the colour of a workpiece transported to the heating means (10, 11).

Inventors: ASAOKA YUKIO, WATANABE TOUICHI, YANO HITOSHI, ASAOKA, YUKIO, WATANABE, TOUICHI, YANO, HITOSHI
Applicants: TRINITY IND CORP, TRINITY INDUSTRIAL CORPORATION
Application year: 1990
Main classification: B05B12
IPC codes: A45C15, B05C9, A45C3, F26B23, F26B3