Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1985-10-24
1987-05-19
Makay, Albert J.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 4, 34 39, 34 62, F26B 1500
Patent
active
046656260
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for drying coated workpieces by infrared radiation and to an apparatus for carrying out this process.
The present invention can be used with special advantage for gelatinizing off (drying) powder-coated castings, particularly gray-iron castings including those of irregular shape. However, the present invention can also be applied with special advantage to thin-walled workpieces of complex configuration, as for example, sheet metal workpieces. The coating of the workpieces can be carried out by means of an electro-dipping varnish, a water-soluble varnish or a solvent-containing varnish. Coated workpieces of ceramics or glass can also be dried.
A furnacc in whose casing infrared emitters having reflectors are arranged so as to be spaced from the casing walls are disclosed in U.S. Pat. No. 2,419,643. The infrared emitters enclose an irradiation space. The casing has inlet and outlet openings as well as a means for conveying the workpieces through the casing. On entering the casing the workpieces pass into a zone in which the infrared emitters are disposed closely to each other so that the workpieces can be rapidly heated to the desired drying temperature by the intensive direct irradiation. As the workpieces pass further through the furnace it is only required to maintain the attained drying temperature and for this purpose a lower number of emitters is adequate so that the furnace has a second zone with infrared emitters spaced apart more widely than is the case in the first heating zone.
Means are also provided for producing an air flow through the casing or to draw off air from the central casing portion by a suction device, which can also be used for removing vapour generated during the drying operation.
However, coated castings of irregular shape cannot be dried or treated in this type of furnace since on the one hand burning of the coatings on projecting portions can be observed and on the other hand insufficient drying and treatment results on undercuts and on portions lying in the shadow of the infrared rays can be observed. The convective heat component is thus passed to the atmosphere completely unutilized.
The present invention provides a process by means of which workpieces, particularly workpieces coated with powder or even with liquid varnishes including those of irregular shape and with undercuts can be dried by infrared radiation. The present invention also provides an economical apparatus for carrying out the process.
According to the present invention there is provided in a process for drying coated workpieces by infrared radiation in which the workpieces are dried in several zones at a selected temperature, an air flow being provided in the zones and the air being drawn off from one zone, the improvement in which the workpieces are preheated in the first preheating zone, the infrared radiation is interrupted in the second rest zone so that the temperature of the workpieces slightly decreases and the workpieces are completely dried in the third reheating zone by subjecting them once more to infrared radiation while the air is circulated and additionally gives off heat to the workpieces by convection.
In the first zone and in the third zone the workpieces are heated by the radiation while projecting portions are cooled by the circulated air, excluding overheating. Portions which are irradiated to a lesser degree and can thus absorb less radiation energy are moderately heated. In the rest zone without infrared radiation the heat is equalized within the workpieces. This equalization of heat is enhanced by the air flow circumcirculating about the workpieces in this zone. Because of the equalization of heat in the workpieces the thermal energy required for drying is also supplied to the portions lying in the shadow of the radiation which absorb less radiation energy and the energy applied is thus more economically utilized. Because of the air circulation the reflectors of the emitters and the casing walls can be cooled and the heat absorbed by them can b
REFERENCES:
patent: 2388917 (1945-11-01), Hormel
patent: 2419643 (1947-04-01), Hudson
patent: 4197657 (1980-04-01), Leino et al.
patent: 4416068 (1983-11-01), Nilsson et al.
patent: 4535548 (1985-08-01), Hyde
patent: 4546553 (1985-10-01), Best
Berkmann Adolf
Veyhle Walter
Makay Albert J.
Westphal David W.
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