GB2123936A

GB2123936A - Paint curing apparatus

Info

Publication number: GB2123936A
Application number: GB08216787A
Authority: GB
Inventors: Robert Fulton
Original assignee: FLAKT Ltd
Current assignee: FLAKT Ltd
Priority date: 1982-06-09
Filing date: 1982-06-09
Publication date: 1984-02-08
Also published as: GB2123936B

Abstract

A method of operating a paint curing apparatus 1 in which there is an oven 2 through which painted articles 3 to be cured are conveyed in spaced apart relationship along the oven during curing of the paint, comprising supplying a diluent gas to the oven 2 to dilute solvent evaporated from the painted articles 3 during curing, monitoring the articles at 11 as they enter the oven, and regulating the supply of diluent gas in proportion to the number of articles 3 monitored entering the oven so that a lower volume of diluent gas is supplied when a lower number of articles are being cured in the oven. <IMAGE>

Description

SPECIFICATION Paint curing apparatus Technical field The invention relates to paint curing apparatusand in particulartoflow line paint curing ovens and to a method of operating them.

Background art Paint cu ring ovens are used for a variety of applications, particularly for curing vehicle bodies after the application of a finishing coat or coats of paint. Energy is used in such an oven in several ways, for example by heating up the mass of the painted article to tha required curing temperature, evaporation of solvents from the applied paint finish, heat loss through the casing of the oven to the surroundings, heating of conveyors on which the articles are being conveyed through the ovens, and heating of fresh air or inert gas applied to the ovens for dilution of the solvent evaporated from the paint finish to ensure that the atmosphere in the oven is below the standard 25% LEL (Lower Explosive Limit).

The supply of the fresh air or inert gas requires a large amount of energy, and this supply is at present constant no matter what the solvent production in the oven amounts to at any time.

Disclosure of invention It is an object of the invention to seek to mitigate this disadvantage of the prior art.

According to one aspect of the invention there is provided a method of operating a paint curing apparatus in which there is an oven through which painted articles to be cured are conveyed in spaced apart relationship along the oven during curing of the paint, comprising supplying a diluent gas to the oven to dilute solvent evaporated from the painted articles during curing, monitoring the articles as they enter the oven, and regulating the supply of diluent gas in proportion to the number of articles monitored entering the oven so that a lower volume of diluent gas is supplied when a lower number of articles are being cured in the oven.

According to a second aspect of the invention there is provided a paint curing apparatus, comprising an oven through which painted articles to be cured are conveyed in spaced apart relationship during curing of the paint, means to supply a diluent gas to the oven to dilute solvent evaporated from the oven during cu ring, and means to monitor the articles as they enter the oven and means to regulate the supply of diluent gas in proportion to the number of articles entering the oven so that a lower volume of diluent gas is supplied by the supply means when a lower number of articles are being cured in the oven.

Atechnological advantage obtained using the invention is a substantial energy saving during periods when reduced solvent quantities are released in a paint curing oven.

The monitoring step may comprise the step of counting the articles and the regulating step may comprise providing a control unit which controls dampers in a diluent gas flow line.

The step of supplying a diluent gas may comprise supplying fresh air as diluent.

The means to monitor and regulate the supply of diluent gas may comprise a numerical counter and the means to regulate may comprise a control unit connected to the counter and to the supply means so that the supply means may be regulated in dependence on the number of articles counted.

There may be an incinerator for the solvent in the gas leaving the oven.

The apparatus may include parallel flow heat exchangers, or series mounted heat exchangers for extracting heat from the gases leaving the oven.

Apparatus in the form of a paint curing oven for curing painted articles in the form of vehicle bodies is hereinafter described, by way of example, with reference to the accompanying drawing.

Brief description of drawing The drawing shows schematically the oven and a fresh air system for diluting solvent in it.

Referring to the drawing the paint curing apparatus 1 shown has an elongate paint curing oven 2 through which articles, in this case car bodies 3 are conveyed on a conveyor system (not shown). There are air seals 4 at the entry 5 and exit 6 of the oven 2, which is separated internally into zones A and.B each one with its own air supply line 7 and exhaust line 8 for gaseous solvent diluted with air. The respective lines 7 and 8 are connected in a common system 7 including a fan means 9 to supply fresh air, parallel flow heat exchangers 10 to utilise the heat from the gases leaving the oven 2 and the air seals 4.

There is at the entry 4 and exit 5 of the oven 2 means in the form of optical sensors 11 to monitor or count the number of bodies 3 passing through the oven 2. There is also a regulator or control means 12 in the form of an integrator or central controller which is connected electrically with the optical sensors 11 and with dampers 13 on the exhaust lines from the oven and to the fan means 9 for supplying fresh air. The integrator or central controller 12 receives and processes signals from the optical sensors 11 in order to control the dampers 13 and fan means 9 to reduce the flow of fresh air into the oven when fewer bodies 3 enter it. This is acceptable because with fewer bodies, there is less solvent evaporated from the paint and therefore less to be diluted to ensure that the predetermined LEL is not exceeded. Thus this saves energy.

In the embodiment shown, the gas flow in the gas lines is measured with means such as orifice meters 14 or the like which operate with the control dampers 13 at the fans to deliver the required air volumes. The fresh air at the air seals 4 remains constant. Each zone A or B, or each zone recirculation ducting may or does include a LEL detector (not shown) coupled to the fresh air supply fan means 9 and to the exhaust fans from the oven so that should LEL exceed the predetermined level all the dampers 13 would open and the oven 2 would be fully ventilated.

The following examples show how cost savings are obtained using variable fresh air system (VFA) according to the invention.

Example 1 Assume an oven designed to dry 41 car bodies an hour Average production during working hours - 40 bodieslhr.

Pattern of work is 20 hrs 5 days per week. Of these 20 hours 15 produce bodies, the other 5 hours are made up from start up, breaks such as lunch and shift change periods.

Energy consumption per working hour - 41 bodies/hr Plain integrated integrated with VFA (Variable fresh air) 1,115,902 Kcal/hr 1,115,902 kcal/hr The following is based on constant 3000kg/hr FA (fresh air) through air seals. FA is varied in proportion to (13,700-3,000) Actual Bodies 3,000 41 Energy consumption per working hour - 40 bodies /hr Plain integrated Integrated with VFA 1,086,690 Kcal/hr 1,049,300 Kcal/hr Energy consumption per working hour - 0 bodies/hr Plain integrated Integrated with VFA 845,300 Kcal/hr 394,740 Kcal/hr Total Energy consumption Plain integrated Integrated with VFA 15 hrs x 5 days &commat;40bodieslhr 40 bodies/hr 81.5 x106Kcal/hr 78.7 x 106Kcal/hr 5 hrs x 5 days &commat; ; Obodies/hr 21.13x lO6Kcallhr 9.87x lO6Kcallhr 102.63x 106Kcal/hr 88,57x 106Kcallhr 46 Wks. Prod = 4,720 x 106 Kcal/hr 4,074 x 106 Kcal/hr Cost &commat; 30p/therm 56,6401year = 48,488 Saving for 1 oven per year = 7,750 The energy costs calculated are approximate but as equal rules were applied to both types of systems the comparison is valid.

Example 2 It should be noted too that with the VFA system if the oven works for long periods at a production load much below its design the savings in energy would increase - i.e. assume 20 cars/hour for 15 hours per day.

Plain integrated Integrated with VFA 962,440 714,440 Total Energy Consumption 15 hrs x 5 days 20 bodies/hr 72.18 x 106 53.6 x 106 5 hrs x 5 days 0 bodies/hr 21.13 x 106 9.87 x 106 93.31 x 106 63.47 x 106 46Wks.Prod 4,292 x 106 2,920 x 106 Cost &commat; 30p/therm 51,500 35,000 Saving for 1 oven per year = 16,500 It will be understood that although the invention has been described with respect to air as the diluent gas, it is equally applicable if an inert gas is used as diluent. Also, although an oven for curing painted car bodies has been described, the invention is equally applicable to an oven for curing other painted articles.

Claims

1. A method of operating a paint curing apparatus in which there is an oven through which painted articles to be cured are conveyed in spaced apart relationship along the oven during curing of the paint, comprising supplying a diluent gas to the oven to dilute solvent evaporated from the painted articles during curing, monitoring the articles as they enter the oven, and regulating the supply of diluent gas in proportion to the number of articles monitored entering the oven so that a lower volume of diluent gas is supplied when a lower number of articles are being cured in the oven.

2. A method according to Claim 1, in which the monitoring step comprises the step of counting the articles and in which the regulating step comprises providing a control unit which controls dampers in a diluent gas flow line for gases from the oven.

3. A method according to Claim 2, in which the step of supplying a diluent gas cocmprises supplying fresh air as diluent.

4. A paint curing apparatus, comprising an oven through which painted articles to be cured are conveyed in spaced apart relationship during curing of the paint - means to supply a diluent gas to the oven to dilute solvent evaporated from the oven during curing, and means to monitor the articles as they enter the oven and means to regulate the supply of diluent gas in proportion to the number of articles entering the oven so that a lower volume of diluent gas is supplied by the supply means when a lower number of articles are being cured in the oven.

5. A paint curing oven according to Claim 4, the means to monitor and to regulate the supply of diluent gas comprising a numerical counter and the means to regulate comprises a control unit connected to the counter and to the supply means so that the supply means is regulated in dependence on the number of articles counted.

6. A paint curing oven according to Claim 4 or Claim 5, including an incinerator for the solvent in the gas leaving the elongate oven.

7. A paint curing oven according to any of Claims 4 to 6, including parallel flow heat exchangers.

8. A paint curing oven according to any of Claims 4to 6, including series mounted heat exchangers.

9. - A method of operating a paint curing oven, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

10. A paint curing oven, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.