CA1052994A

CA1052994A - Convection oven and method of drying solvents

Info

Publication number: CA1052994A
Application number: CA223,405A
Authority: CA
Inventors: Alan S. Whike; Kenneth Ellison
Original assignee: B&K Machinery International Ltd
Current assignee: B&K Machinery International Ltd
Priority date: 1976-10-13
Filing date: 1975-03-25
Publication date: 1979-04-24
Also published as: GB1556982A; GB1556981A

Abstract

ABSTRACT OF THE DISCLOSURE

An elongated workpiece carrying a coating, such as paint, containing an oxidizable solvent is dried or cured in an oven containing a plurality of zones. Oven gases are circulat-ed in each zone around the workpiece. To minimize the fuel re-quired for heating the oven and to reduce the volume of oven gases exhausted to the atmosphere, oven gases containing oxidiz-able solvent vapour are transferred from one oven zone to anoth-er where they are incinerated to provide additional heat input to that zone, such incineration also reducing the solvent vapour content of the oven gases and providing zone ventilation.

Oven gases are also incinerated to heat a radiant heater for radiant heating of the workpiece during its passage through the oven.

Description

105'~g94 The present invention relates to ovens for drying or curing coatings such as paints, adhesives containing oxidizable ; solvents and the like applied to a workpiece moving through such oven, such as for exa~ple sttip material.
BACKGROU~D OF THE INVENTION
: . .
The oven under consideration i8 generally known in the trade as a "recirculating convection oven".
` Such ovens are usually divided into oven zones. In each zone recirculating fans and ducts are provided to continuously 10 recirculate the zone atmosphere and produce gas flow around the workpiece. Such gases are heated du~ing recirculation to main-tain oven temperature, A proportion of such gases is continuously withdrawn as "effluent", and replaced with make up air or gases.
The curing of coatings containing solvents, such as those applied to strip sheet metal, presents a number of problems.
In the first place, the solvent fumes must be rendered harmless before venting to atmo~phere so as to avoid environmental -pollution. This can be done in some cases by solvent extraction, condensing the solvent vapours from the effluent from the oven for reuse or by use of a catalyst such as platinum. However, in the majority of cases the solvent vapours are si~ply oxidized by passing the effluent through an incinerator chamber which in most cases must be capable of operation at a solvent oxidation level of 98% to 99~ in order to meet prevailing standards for emissions from this type of equipment. Usually such incinerators are gas fired incinerators, and the fuel consumption required in order to operate at these levels of efficiency with the very large volumes of oven effluen~ iB a major consideration in the design o~ such an oven.
~ 30 Recovery of the heat generated by such incinerators .', - 1 --loS~994 for use in the oven, or for use elsewhere will somewhat reduce the operating cost of the incinerator, but in many cases it is not possible to use the heat recovered from the incinerator in an economical manner, or to its full extent.
It is therefore desirable where possible to reduce the volume of emissions to atmosphere, and thereby reduce the size of the incinerator for treating such emissions. Proposals have been made for continuously recycling oxidized gases from the exhaust incinerator, and returning them within the system, so as to reduce the volume of exhaust going to atmosphere, but this is of only limited value, and leaves large volumes of ox-idized gases which cannot be used in the oven due to tempera-ture control limitations required for individual zones in the oven. Since any exhaust volume must be replaced by fresh air, which must eventually be heated to incineration temperature, an unnecessary heat load is incurred.
A second major factor in the construction of such ovens is the manner in which the various zones in the oven are heated. Various different heating systems have been used, a common system being the use of gas burners heating the recir-culating gases in the various zones. Clearly, the fuel cost for heating such gases is a further major factor in the cost of operating the oven. Some systems have been proposed for reduc-ing the fuel requirement for heating the gases in the various -zones by recycling the oxidized gases exiting from the incin-erator back through the zones, and such systems have met with some degree of success. However, they introduce further problems.
In particular, the gases exiting from a typical incineratQ~r will be at about 1,400F. At these temperatures, conventional steel duct work, fans, dampers, and the like are no longer usable, and .

105'~994 special alloys must be employed to withstand such tem~eratures.
This of course greatly increases the construction costs of the oven and requires more frequent maintenance, and redu oes reli- ~' ability.
A further major factor in the design of such ovens is the ability to control the temperature of the gases in the var-ious zones, and to regulate the gas temperatures in the differ-ent zones progressively so that the coating on the strip is cured in the most advantageous manner, Such coatings may employ several different solvents having different boiling points so s that the co~ting dries progressively from ~he inside out to pro-duce the desired finish. Similarly, some types of paints have solvents with relatively high boiling points therefore requiring relatively high temperatures in the oven, and other forms of coatings, such as some adhesives use solvents with relatively low boiling points requiring lower temperatures.
Accordingly, in order to build an oven which is capable of handling a wide range of different paints, coatings, adhesives and the like over a relatively wide range of temperatures, it is essential that the gas temperatures in the various zones may be closely regulated and controlled. The controlling of gas temp-erature in the different zones of an oven, where the gases are heated even partially by means of recycled incinerator gases at high temperature~, becomes particularly difficult, since the , regulation of the temperature will depend upon the proportioning of a mixture of fresh air,and incinerator gases introduced into each zone, 80 as to produce the correct gas temperature ` within the zone. A~ mentioned above, the handling of inciner-ator gases at the high temperatures experienced, is both dif-ficult and relatively expensive in terms of the e~uipment required : .

lOSZ994 and these factors still furth~r mitigate against the use of recycled incinerated gases for maintaining the gas temperature in each o f the oven zones.
A further factor in the design of such curing ovens is that for safety reasons it is essential that the solvent vapour content of any effluent in the oven duct work shall be at or below a desired percentage of the lower explosive limit ( the so-called L.E.L.) for any particular solvent. Normally, this is achieved by ensuring that the make up gases entering the zones contain negligible amounts of solvent vapours, and maintain a sufficient level of ventilation in the zone. If an unusual situation should arise and excess solvent vapours ~ should become entrained with the gases and the solvent limit --~
i is exceeded, then emergency measures must be taken to vent the oven and reduce the solvent vapour content of the gases present ~ in the system to avoid the danger of an explosion. Obviously, ; if such emergency measures have to be taken at all freguently, ~
then the operation of the system is not commercially sound -since each time the system is shut down, there will be consid-erable wastage of product and machine down-time. `
It is however, desirable that in any such an oven system provision should be made for rapid venting and cooling of the system, with a minimum of disruption to the operation of the coating line, 80 as to permit rapid change-overs from one colour to another for example, and at the same time provid-ing for emergency venting of the system if the solvent limit is inadvertently exceeded~ Earlier oven systems did not qener-ally speaking have this flexibility combined with the safety features mentioned, and relatively lengthy proceedures were necessary to effect a change-over of colour for example.

` 1052994 ;~ In addition to convection heating of the stri~ by recirculating hot gases, it is also desirable at some point in the curing line to provide for radiant heating of the strip so as to actually heat up the strip metal itself and thereby cure . 7 the paint or other coating material from the inside to the out-side of the coating layer. In the past, such radiant heating was usually effected, if at all, by means of gas radiants or by means of electrical radiants located within the oven. Such ~ radiant heating systems involved the use of still further fuel - 10 input adding still further to the cost of the operation of the system.
BRIEF SUMMARY OF THE INVENTION
It is therefore a general objective of the present inven-;~ tion to provide an oven and method of treating a workpiece of the type described in which the varioui disadvantages and inefficiencies of earlier oven systems are eliminated or at least reduced. A major proportion of the oven zone effluent containing solvent vapours is , .
recycled within the system and returned to the zones. Prior to being fed into the zones, the effluent is passed through individual zone incinerators located at the entrance to each of the oven zones, thereby heating such incoming effluent gases to a controlled elevated temperature for oxidation of the solvent vapour. Suf-~7 ficient oxidized gas volume is admitted to each zone to maintain a predetermined desired zone gas temperature. A further incin-erator is provided in the exhaust system for the oven, through -which a certain proportion of the oven effluent is passed, to permit venting of some of the oven effluent to atmosphere, the exhaust incinerator oxidizing the solvent vapour content to avoid environmental damage. A furt~er portion of the oven ef-fluent containing solvent vapours, passes through a bypass 7 _ 5 _ _ 105'~994 incinerator and the oxidized gases then enter a radiapt heating ~i system and provide heat input for the radiant heating system which is in turn transmitted as radiant heat directly to the strip. The oxidized gases are then discharged from the radiant heater into the oven, providing additional ventilation.
In an altermate form of the invention the exhaust in-cinerator discharges into separate radiant header ducts which displace the first convective zone of the oven, and the oxidized fumes are then discharged up the stack.
More particularly, it is an objective of the invention to provide a curing oven having the foregoing advantages in which the effluent from one or more low solvent release zones ~s re-introduced directly through a high solvent release zone, whereby "~
to increase the ventilation of ~uch zone.
More particularly, it is an objective of the invention to provide a curing oven having the foregoing advantages in which effluent from low solvent zones i8 reintroduced in cas-cade form progressively through other zones of higher solvent release whereby to atill further increase the ventilation of ¢ 20 these further zones.
~ More particularly, it is an objective of the invention s to provide an oven having the foregoing advantages in which the bypass incinerator discharges to a radiant duct system extend- -~- ing above and below the part of the workpiece, and having in-wardly directed radiant surfaces for radiating heat from aaid duct work onto both sides of said workpiece. The duct work pro-¢ vides an extended oxidation space thereby prolonging the dwell time and ensuring adequate oxidation of recycled oven effluent.
The solvent vapours thus provide a portion of the fuel for pro-viding the heat input for said radiant heating unit. The bypass : . : ..

`` 105Z994 incinerator incorporates means for varying the fuel i~put to the incinerator, and further control means for varying the input of recycled oven effluent to the incinerator, whereby to provide for oxidation of greater or lesser amounts of solvent vapours.
This provides a fully flexible system in which a fixed proportion of oven effluent is exhausted to atmosphere, and the balance ¦ of effluent is taken either by the zone incinerators, or by the bypass incinerator , depending on the volume of effluent re-quired by the zone incinerators to satisfy the heat input demand of the zones. In this way, the system avoids any variation in ~, the exhaust to atmosphere and fresh air intake.
,' More particularly, it is an objective of the invention to provide a curing oven having the foregoing advantages in which the individual oven zones are provided both with individual zone - -~
incinerators for oxidizing the recycled oven effluent prior to reintroduction into the zones, and in addition, are provided with supplementary heaters, for providing a rapid warm up of the various zones, and providing supple~entary heat if required.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure, For a better `
understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which - there are illustrated and described preferred embodiments of the invention.
IN THE DRAWINGS
Figure 1 i8 a schematic illustration showing the ~ layout of a curing oven system according to the invention in i 30 which provision is made for simultaneous curing of a strip _ 7 _ 105A~994 having a prime coat, and a further strip having a finish coat;
Figure 2 is an enlarged illustration showing one-half of the oven system shown in Figure 1, in greater detail;
Figure 3 is an enlarged illustration showing the other half of the oven system shown in Figure 1 in greater detail;
Figure 4 is an enlarged schematic elevational view ` showing the radiant heating means of the oven of Figure 2; and Figure 5 is a schematic plan view showing an alternate form of the radiant heating means.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to Figure 1, this illustration shows in ~ schematic form the layout of an oven installation suitable for i a strip coating plant, where strip sheet metal is painted, or ~ coated with a prime coat and a finish coat. Obviously, however, s oven installations of the same general type will be suitable for other purposes such as the curing of other forms of coatings, and the curing of adhesives, with only minor modifications as wiIl suggest themselve~ to persons skilled in the art.
$ As shown in Figure 1, the oven installation comprises a prime coat oven 10 and a finish coat oven 12, which are sepa-rate from one another, but are interconnected with the same ven-tilation and heating system, whereby they may be operated simul- ~
taneously, for curing two different strips at the same time. ~ -The prime coating oven 10 will be seen to be divided nominally into four zones, namely lOA, lOB, LOC and lOD. The finish coating oven will be seen to be nominally partitioned into five zones, namely 12A, 12B, 12C, 12D and 12E.
The organization and arrangement of the ovens 10 and 12 i8 essentially the same, and accordingiy detailed description will be given initially of oven 10, it being understood that the .. :

s - 8 -; ~A
..
~. `. . . . . .

~05'~994 finish coating oven 12 is provided with essentially the same equipment, which will be described somewhat more briefly herein- ;
after.
The four zones 10A, 10B, 10C and 10D of oven 10 are all constructed as a single continuous unit essentially in the form of a tunnel or elongated chamber of suitable dimensions to ac-cept passage of a strip of sheet metal or other strip workpiece moving therethrough. Each of the oven zones 10A, 10B, 10C and 10D are provided with oven zone gas recirculation chambers 14, 16, 18 and 20, through which the zone gas mixtures is continu-ously recirculated into the zone in a manner known per se, by any suitable circulating fans and duct work, not shown. s Effluent gas is extracted from each of the oven zones through respective exhaust conduits 22, 24, 26 and 28. In order to increase the ventilation through zone 10B, the exhaust con-duits 26 and 28 are united at conduit 30, which reintroduces the effluent from oven zones 10C and 10D back into oven zone 10B.
Oven zone 10A will receive fresh air input through , fresh air conduit 32 which in turn will receive fresh air through the fresh air supply system 34. This fresh air supply system 34 may be connected so as to receive fresh air from the atmosphere.
Alternatively, however, and in the preferred case, it will in fact be connected to the air ventilation and exhaust system for the coater rooms, where the strip is coated. In this way, the atmosphere of the coater rooms is kept fresh and breathable, and any solvent fumes which may evaporate within the coater room will be contained and used within the oven system, so that the heat available from the solvent vapours may be used in the ovens, and will not be simply vented to atmosphere from the coater rooms themselves. ~his system also avoids the requirement for attach-~.................................................................... .

ing an incinerator to the coater room ventilation system which might otherwise be necessary in certain ~urisdictions to avoid environmental pollution. A branch fresh air duct 32a may be connected to the entrance to the oven zone lOA so as to pass fresh air directly into the opening at the front of the oven zone lOA.
The exhaust conduit 22 i8 located at the main oven ex-haust section 22a in zone lOA and is connected to a central mix-ing chamber or plenum 36. From the plenum 36 a main supply duct 38 connects with branch supply ducts 40, 42 and 44 respectively.
The branch ducts 40, 42 and 44 in turn are connected with the zone recirculation chambers 16, 18 and 20 of the oven zones lOB, lOC and lOD.
The plenum 36 also connects with the exhaust duct 46, feeding the exhaust incinerator 48 which is then directed to the exhaust stack 50. A heat recovery system 52 may be provided on ~, the output to the incinerator 48, and the heat recovered may be ; used for any heating purpose around the plant, and may also be ~ used for preheating the incoming air on the air supply system 34 i 20 by means for example of the air preheater 54.
It will be understood that the plenum 36 will be re-ceiving oven effluents which are essentially the combined efflu-ent output of zones lOD, lOC, lOB and lOA.
In accordance with the invention, some of the vapours in the effluents going to the plenum 36 are utilized for heating the zones lOB, lOC and lOD. In order to achieve this purpose, each of the zones lOB, lOC and lOD respectively is provided with its own incinerator 56, 58 and 60 respectively. Each of the in-cinerators 56, 58 and 60 i9 supplied with oven effluent carrying solvent fumes, by means of the branch ducts 40, 42 and 44. ~he ~.,,~
.~, . .

lOS2994 incinerators function to oxidize the solvent vapours, and the high temperature oxidized gases are then mixed with the recircu-lating zone gases entering the oven zones through the respective zone recirculation chambers 16, 18 and 20 and at the same time reducing the percentage of solvent vapours in such recirculating zone gases. A branch input duct 62 communicates with air cur-tain at 20a of oven zone 10D to supply hot gases to the exit end of the zone lOD.
In order to control the temperature within each of the ', zones lOB, lOC and 10D, control dampers 64 are located in the ,' ducts 40, 42 and 44, and are controlled by suitable temperature controls 66, connected to suitable temperature sensors (not shown) located within the respective zones lOB, lOC and lOD.
Variation in the zone temperature due to varying heat load will produce variation in the volumes of oven effluent gas supplied to the incinerators, by operation of the dampers 64, thereby varying the flow of hot oxidized gases from the respective inci-nerators 56, 58 and 60. In this way, the temperature of each zone can be regulated to a desired preset level.
In accordance with well known practice in the art, the incinerators 56, 58 and 60 will be fired normally by natural gas or other sultable fuel, more or less being required dependent upon the percentage of solvent vapour content in the gas suppli-ed through the ducts 40, 42 and 44. In order to control the tem-perature of the oxidized gas from the incinerators 56, 58 and 60, suitable temperature controls 68 are provided and connected to sensors ~not shown) for sensing the temperature of the gases exit-j ing from the respective incinerators, thereby controlling the fuel input.
In order to provide for a rapid warmup of the oven ~!
~ .. . .

.

~05;~994 zones lOA, lOB, lOC and lOD, supplementary heaters 70 are pro-vided for the respective recirculation chambers. It will of course be appreciated that such supplementary heaters will be used mainly during the initial start-up phase of operation, and that in the great majority of cases, once the gases in the ducts 40, 42 and 44 are carrying their regular volumes of solvent va-pours, the operation of the individual incinerators 56, 58 and 60 will be sufficient to provide all the heat required for the zones lOB, lOC and lOD and the heaters 70 will remain on low fire or will be shut down. Such supplementary heaters will usual-ly be fired by natural gas for example although any other suit-able fuel, capable of providing adequate heat at the location may be substituted. Any suitable control may be provided, the details of which are omitted for sake of clarity.
~' A heater 72 is provided on the air conduit 32 for heating the combined incoming fresh air and effluent gases en-tering the zone lOA of the oven. Heater 72 is not an incinera-tor and does not oxidize the solvent vapours in the effluent gases at this point.
` 20 In order to regulate the flow of exhaust gases out of the zones lOC and lOD, dampers 74 are provided in the exhaust conduits 26 and 28, and pressure sensitive control means 76 are provided for sensing the pressure in the zones lOC and lOD, and ; varying the position of the dampers 74 accordingly~ Similarly, 3 the exhaust conduit 24 is also provided with a control damper 78, and pressure sensing means 80 for sensing the pressure in the zone lOB and varying the opening of the damper 78 accordingly.
A damper 74 is also provided in the conduit 30.
In order to provide for radiant heating of the strip, a radiant heating unit indicated generally as 82, and shown in - 12 - j 105;~994 greater detail in Figure 4, is located between zone lOA and zone lOB. As shown in Figure 4, the radiant heating unit 82 will be seen to comprise a generally U-shaped loop of duct work, hav-ing a lower portion 84 and an upper portion 86 and a return U-bend 88. The lower and upper portions are adapted to extend on the lower and upper sides of a strip or workpiece passing through the oven 10, and are spaced apart a suitable distance to accom-modate any variation in the position of the strip during opera-tion of the oven. The portions 84 and 86 of the duct work are provided with inwardly directed radiant surfaces 90, which are ; preferably formed, at least on the interior of the duct work, with any suitable heat exchange surface formation such as fins, ridges, or any other suitable formation. Insulation is provided elsewhere around the duct work, to retain heat therein.
Bypass supply duct 92 extends from the plenum 36 to by-pass incinerator 94 which in turn discharges into one end of the radiant heating unit 82, which end may be either that of the low-er portion 84 or the end of the upper portion g6. The other end ^` of the unit 82 dlscharges into zone lOA at exhaust section 22a and the gases then enter exhaust conduit 22 which communicates with the plenum 36 as described above. The bypass incinerator 94 is located in the bypass supply duct 92 for oxidizing the solvent vapours entrained in gases coming from the plenum 36. Such by-, pass incinerator will normally be fired by natural gas, or any ; other suitable fuel. The temperature of the oxidized gas from the bypass incinerator 94 is controlled by means of a temperature sensitive controller 96 sensing the temperature of the gases exiting from the incinerator.
The duct work portions 84, 86 and 88 provide;an elon-gated oxidation chamber ensuring a long dwell time for oxidation ~ 13 -105'~994 of solvent vapours. The bypass incinerator 94 can thus be opera-ted at a somewhat lower temperature while still achieving effi-cient oxidation.
Supply of gases to the bypass incinerator 94, from the plenum 36, is controlled by means of the damper 98 and pressure sensitive controller 99, sensinq the pressure in the interior of zone lOA of the oven.
In order to provide for rapid cooling, and rapid vent-ing in an emergency situation, a series of quick cooling fresh ~f air vents are provided throughout the oven system which will ad- ~ -mit fresh air to the oven at a number of different locations.
Such quick cool vents are indicated as 100 and consist essenti-ally of dampers which may be opened or closed either manually on command, or automatically by any suitable emergency control.
., Typically, such emergency controls will comprise gas analyzers located at various points within the oven, and operable to give 6 an alarm signal if the solvent vapour content should exceed thedesired percentage of the L.E.L. for that particular solvent.- ~ -An additional sealing damper 102 is provided to back-up the quick cool damper 100 so as to prevent any risk of a leak of the oven effluent gases from the conduit 26 to atmosphere at t .
this point in the system.
A pressure relief duct 104 extends from a point be~
tween the damper 100 and the sealing damper 102, back to the up-stream side of a fan F feeding gases from the conduit 26 to the conduit 30 so that any leakage through the damper 100 can be re--~ cycled back into the conduit 30.
Throughout the system numerous fans are provided which are shown schematically, the function of which will be apparent ' 30 to those skilled in the art, and essentially maintain flow of ."., ~

lOSZ994 gases through the system. t The finish coat oven 12 is provided with essentially the same system of zone incinerators and recycling of zone ex-~; haust, the respective zone recirculating chambers being shown as 114, 116, 118, 120 and 122, for zones 12A to 12E respectively.
Similarly, branch supply ducts 124, 128, 130 and 132 communicate from the main supply duct 38 with the respective zone recircula-ting chambers 12B to 12E. Individual zone incinerators 134, 136, 138 and 140 provide for oxidation of the solvent vapours suppli-ed to them through the branch ducts, and provide heat input for gas recirculating in their respective zones.
Controls similar to those shown in the case of oven 10 will of course be incorporated, the details being omitted for the sake of clarity.
Similar supplementary heaters 142 are provided for ;
. zones 12A to 12E. A heater 150 is provided on the inlet duct 152 for heating the combined incoming fresh air and effluent gases entering the zone 12A of the oven 12. Heater 150 is not an incinerator and does not oxidize the solvent vapours in the effluent at this point.
i A radiant heating unit 154 is provided in the main exhaust section of zone 12A, similar to the radiant heating unit 82 and provided with a bypass incinerator 156 controlled in the same manner as bypasis incinerator 94 of the radiant heating unit 82.
t Similar quick cool ventilation is provided by means of ventilators 158. Effluent from the zones 12C, 12D and 12E ex-hausts through respective exhaust ducts 160, 162 and 164 all of which are controlled by dampers, as described in connection with zones lOC and lOD. A common return duct 166 feeds the effluent . ~ , .
,;

lOS;~994 s of zones 12C, 12D and 12E back into zone 12B.
The effluent exhaust from zone 12B is removed through duct 168, uniting with fresh air duct 152, for supplying a mix-- ture of fresh air and oven effluent directly into zone 12A.
t Effluent from the main oven section in zone 12A is removed r through duct 170 and flows back into the common plenum 36.
A similar sealing damper 172 i8 provided to back-up the quick cool vent 158 on duct 166.
STATEMENT OF OPERATION
. , ~
During normal operation, i.e. when a steady state has been achieved, the plenum 36 and duct 38 will normally contain oven effluent containing solvent vapours at or close to the desired lower explosive limit. These gases flow down the duct 38 ;~ and up the branch ducts 40, 42 and 44. It will of course be understood that similar gases will also flow up the branch supply ducts 124, 128, 130 and 132. However, the operation of the oven 12 will not be described in detail for the sake of simplicity since it is essentially the same as the operation of oven 10, and takes place simultaneously. -~
As the effluent gases flow down the branch ducts, they ~; pass through the incinerators 56, 58 and 60 where the solvent`^ vapours are oxidized in known manner. The combustion of the sol-vent vapours, together with the heat input from the incinerator ~ -burners, raises the temperature of the exiting oxidized gases sufficiently so as to maintain the desired temperature level in ~,~
the gases recirculating within the zones 10B, 10C and 10D. It j~ will of course be borne in mind that the temperatures in the zones - will in the preferred case be maintained at different levels and ~ consequently different heat inputs will normally be required.¦ 30 ~he temperatures of the zones, as described above, are controlled .

I
, ' ~ , .

through the operation of the dampers 64 in the branch ducts 40, 42 and 44, which are in turn controlled by the temperature sen-sitive controls 66. In order to reduce the temperature in a particular zone, its respective damper i~ closed down thereby ; shutting off some of the supply of effluent gases containing . solvent fumes to the incinerator for that zone.
In this way, the temperature of each zone can be con-. trolled accurately.
. A proportion of the recirculating gases is removed as oven effluent from the zones lOC and lOD, continuously through their respective exhaust conduits 26 and 28, and is returned i .
through the conduit 30 and reintroduced back into the zone lOB.
At the same time, zone lOB is also receiving oxidized incinera-tor gases from its incinerator 56, as described above, and zone lOB will therefore normally be subjected to approximately three times the ventilation passing through zone lOC or lOD. This is desirable since there will be a greater volume of solvent vapours evaporated and removed in zone lOB, than in zones lOC and lOD.
The exhaust from zone lOB is removed through the ex-haust conduit 24, and reintroduced into the gases recirculating ~.
in zone lOA. A certain proportion of fresh incoming air re- ~ `
quired by the system is introduced here so that the temperature ~. input to the gases in zone lOA can be controlled and at the samei time the overall percentaqe of solvent vapours in the gas mix-ture circulating in zone lOA is somewhat diluted, by the mixture of fresh air, without incinerating the gases passing into zone s lOA. It will be understood that the heater 72 does not function .i as an incinerator but simply operates to maintain a desired stable temperature within the gases circulating in zone lOA.
This is desirable since in the majority of cases zone lOA should , j~

be operated at a somewhat lower temperature than zones lOB, lOC
and lOD. The ventilation passing through zone lOA will be the sum of the entire exhaust from zone lOB together with the fresh air input.
The entire exhaust from zone lOA is removed at the main oven exhaust 22a through conduit 22 and passes into the plenum 36 where it is again available for recycling down the supply duct 38. ~;
Throughout this operation, a varying proportion of the gases in the-plenum 36 is continuously withdrawn through the by- ' pass duct 92 and passed through the bypass incinerator 94. The oxidized gases are fed into the radiant heating unit 82. The gases will circulate through the duct portions 84, 88 and 86, and ~ ~
give up some of their heat to the heat exchange surfaces 90, -which will then radiate heat directly onto the strip passing be- -tween them, from both sides.
Gases exiting from the radiant heating unit 82 will t discharge into the main oven exhaust section 22a and mix with cooler gases entering the exhaust duct 22 and be returned to the plenum 36.
Throughout this operation a continuous fixed portion of gases is removed from the plenum 36 through the exhaust duct 46 and fed through the incinerator 48, and the heat recovery sys-tem 52 and out through the stack 50.
Preferably, the percentage of gases passed through the ~ incinerator 48 and up the stack 50 will be kept as low as possi- t `, ble consistent with the volume of fresh air enterinq the system, and the volumes of solvent vapours and products of combustion evolved during operation.
It will be noted that the very high temperature incine-rator gases, i.e, gases at about 1,400F, will occur only after iOS;~994 ; passage through the incinerators 56, 58 and 60, and incinerators 94 and 48. In the zones lOB, lOC and lOD, as soon as the gases pass through the incinerators, they will enter their respective zones, mix with the recirculating gases and lose their excess heat. Consequently, when they are again drawn into the duct work, they will be at a considerably lower temperature. In the case of the gases discharged from the radiant heating unit 82, -the gases will immediately be mixing with gases at a lower tem-perature in the oven exhaust section. Consequently, the problem of handling gases flowing through the system and duct work at very high temperatures is eliminated. In fact, the maximum nor-mal operating temperature experienced throughout the main portions of the duct work, fans and the like, will not exceed 900F. At these temperatures, conventional duct work materials and fan ma-terials can be used without suf fering damage.
During the steady state operation of the oven unit, the volumes of gases entering the individual zones lOB, lOC and lOD will be more or less stable, or subject only to quite minor variations in response to operation of the various temperature controls. ~ ~-Similarly, the volume of gases exiting to atmosphere, i, through the incinerator 48 and stack 50 will also be maintained at a stable percentage of the total oven effluent. This percen-tage may vary somewhat depending on the nature of the solvents and the oxygen requirements of the system. If the system can operate with a lower percentage of oxygen while still maintaining ~ effective oxidation of the solvent vapours, then less fresh air 7 iS required and less exhaust gases will be vente~ to atmosphere.
As mentioned above, the oven is highly flexible in its operation, and can accept different typeæ of materials and dif-- . , ~ .

, lOSZ9~4 ferent types of coatings and solvents. In the case of some ma-terials and solvents, the operation of the individual zone in-cinerators 56, 58 and 60, will consume a larger proportion of effluent and thus reduce the volume required to be handled by the bypass incinerator to a minimum.
In other cases the demand of the zone incinerators 56, 58 and 60 will be lower, and in these cases the bypass incinera-tor 94 will be regulated to consume a proportionally increased ~ -volume of the effluent so as to reduce the solvent vapour percen-~ .
tage and thus maintain the desired level throughout the system.
Thus, once a steady state operation is achieved in the zones lOB, lOC and lOD, the volume of gases passing through the ~ bypass incinerator g4 will be regulated to whatever level is -~ necessary to consume the balance of the solvent vapours in the system. In this way, the bypass incinerator provides a wide range of flexibility in the overall operation of the entire oven system without the necessity for increasing the volumes of gases which are exhausted to atmosphere in a wasteful manner.
In some cases, it may be desirable to provide an alter-nate form of radiant heating unit, as is shown in Figure 5.
O
In this embodiment, the zone lOA of the oven is modi-fied to eliminate the convection heating of the workpiece, and the recirculating fans and duct work, and this is replaced by s~ more extensive radiant heating throughout the zone lOA. Thus ~` zone lOA is shown having a fresh air branch air duct 32a which , receives fresh air from any source such as a coater room, fresh air or the like. The plenum 36 is connected with the zone lOA
through a gas input duct 200. The duct 200 supplies solvent t : laden gases from the plenum 36 to an incinerator 202 and gases $' from such incinerator 202 are supplied through radiant duct work $' ;;`

; - 20 -; ~,, .

lOS'~994 204 consisting essentially of upper and lower pa~sages extending lengthwise along the zone lOA above and below the path of a strip or workpiece passing through the zone lOA. A return duct 206 communicates with the other end of the radiant duct work 204, and connects with the fresh air preheater 54 and then to the stack S0.
An effluent gas duct 210 receives effluent gases from zone lOB (not shown) and connects with the branch air duct 32a s and provides a joint gas input 212 entering the zone lOA, to 10 provide a gas mixture consisting of combined hot effluent gases, and cooler fresh air for ventilation of the oven lOA. This pro-.~ .
vides ventilating gas flow parallel to the workpiece having only a minimal heating effect.
Exhaust from the oven lOA is withdrawn through the ~ ~ -: exhaust conduit 22 and returned to the plenum 36.
Additional fresh air if required for the purposes of cooling the radiant duct work 204 may be introduced through a `i secondary fresh air intake 216.
As will be seen, the gases exiting from the incinera-tor 202 are first of all employed for radiant heating of the strip itself, through the radiant duct work 204, and are there-after passed to the exhaust duct 206 and stack 50. Thus the in-cinerator 202 replaces the exhaust incinerator 48 of the embodi-ment of Figure 1 producing further economies in heat recovery.
` The bypass incinerator 94 and radiant heating unit 82 remain unaffected and function as before.
During the start up condition of the oven, since there will be only a small percentage of solvent vapours in the incom-ing fresh air, or possibly none at all, the supplementary burners 70 will be turned up to a point where sufficient heat input i8 .;.~ ~ , . .

lOSZ994 ~ provided for each of the zones to provide a satisfactory cure or r': treatnlent of the workpiece and coating thereon.As the effluent content of the gases circulating in the zones builds up, then the heat input from the zone incinerators will become greater, and it will then be possible to turn the supplementary heaters down to their low fire condition.
In the event that the line is shut down for some rea- -son either for a changeover from one colour or coating to another or for some other reason, then the quick cool venting system 100 will be put into operation whereby to admit fresh air direct-,~j ly into the system at the various points where the quick cool dampers are provided, thereby rapidly reducing the temperature of the gases in the various zones.
In this way, it is possible to effect a relatively rapid colour change for example by shutting down the line, opera~
ting the quick cool damper system, and then when the line is - -,: . ;
started up again the supplementary burners are put into action to rapidly increase the heat in the zones to their working temp-erature.
~aving described what is believed to be the best mode by which the invention may be performed, it will be seen that the invention may be particularly defined as follows: -A heat treatment oven apparatus for treating a work-piece carrying a coating containing a vapourizable solvent, said -solvent being oxidizable to provide at least part of the heat ;
input requirement for said oven, said apparatus comprising:
an oven having a plurality of oven zones, said work-piece being movable through said zones in sequence;
gas circulation means in said zones for circulating gases therein continuously around such a workpiece h,'.7~2 ~.~,... ..... . . .
;, - ~ ' . i ~1 '' ' .':''':' ' '- ~: .-105~994 within said zones;
a gas input at each said zone for continuou~ly intro-ducing gases into such zone;
a gas exhaust at each said zone for continuously re-moving a portion of the gaseous atmosphere from such zone;
a gas -transferring means connected between said gas exhaust of one of said zones and said gas input of a ~ different one of said zones for transferring gases `:; 10 exhausted from said one of said zones and introducing them into said different one of said zones; and an incinerator disposed essentially at said different one of said zones for oxidizing solvent vapour contain-ed within said gases exhau~ted from said one of said zones on introduction into said different one of said zonesJ
The invention further comprises such a heat treatment oven apparatus in which said gas -transferring means is adapted to transfer gas exhausted from an upstream said one of said zones of said oven to a said different one of said zones disposed downstream with respect thereto with reference to the direction of movement of a workpiece passing through said oven apparatus.
Th~ invention further comprises such a heat treatment oven apparatu~ and whloh addltlonally comprises an upstream gas-transferring means connected between said gas exhaust of one of said zones and said gas input of an upstream one of said zones.
The invention further comprises a method for the heat treatment of a workpiece carrying a co~ting containing a `-; :. . ~ .. .
.-. . j ~ .
, ~.
.

` ~05Z994 ~ -a vapourizable solvent, said solvent being oxidizable to provide at least part of the heat required for such heat treat-ment, and said method comprising the steps of:
moving said workpiece sequentially through aplurali-~ ty of zones of an oven;
Y circulating gases in said oven zones;
removing gases from one of said zones;
transferring said gases as removed from said one of said zones to an incinerator disposed essentially at a different one of said zones;
incinerating said gases in said incinerator; and .~ , ~ discharging said gases after incineration into said `~ different one of said zones.
~-~ The invention further comprises such a method in `-~ whioh said gases are transferred from one of said zones to said different one of said zones~ in a downstream direction with respect to the direction of movement of a workpiece through the oven.
- The invention further comprises such a method ~- which additionally compri8e~ transferring gases from a downst~eam one of said zones to an upetream one of s~id zones.

i.............................. . .
The foregoing de8cription of the invention is given ~,; hereby way of example only with reference to the drawing~ here-in. It is not intended that the invention shall be limited to -any of the specific features as desoribed or shown, but compre-hens all such variation8 as come within the scope of the - appended claims.

~ 30 . ~ , i - 24 -, 3C~ .
...... .. . . . .

, . .

1~)5'~994 SUPPLEMENTARY DISCLOSURE
.
In the original disclosure of this patent application, ; we have described and claimed certain heat treatment oven appara-tus as well as a method for the heat treatment of a workpiece carrying a coating containing a vapourizable and oxidizable sol-vent. The apparatus and method of the original disclosure pre-sent the important advantage that they permit a very significant reduction in the volume of waste gases discharged into the at-mosphere from such an oven apparatus compared to those previous-ly known. As explained in the original disclosure, such reduc-tion in exhaust gas volume leads to a considerable saving in the amount of fuel required for operating such an oven apparatus.
The heat treatment oven apparatus described in the original disclosure can broadly be defined as comprising a plu- ;~
rality of oven zones, a workpiece being movable through such zones in sequence; gas circulation means in those zones for cir-culating gases therein qontinuously around such a workpiece within the zones; a gas input at each such zone for continuously introducing gases into such zone; a gas exhaust at each such zonè for continuously removing a portion of the gaseous atmos-phere from such zone; a gas-transferring means connected between the gas exhaust of one of the zones and the,gas input of a dif-ferent one of the zones for transferring gases exhausted from such one of the zones and introducing them into the different one of the zones; and an incinerator disposed essentially at the different one of the zones for oxidizing solvent vapour contain-ed within the gases exhausted from the one of the zones on intro-duction into the different one of the zones.
The method described in the original disclosure can r; ~s~

~. ' ., .
- . . - ~ .

lOSZ994 broadly be defined as comprising the following steps of moving a workpiece carrying a coating containing a vapourizable solvent, oxidizable to provide at least part of the heat required for t such heat treatment, sequentially through a plurality of zones of an oven; circulating gases in the oven zones; removing gases from one of the zones, transferring the gases as removed from -~
such one of the zones to an incinerator disposed essentially at a different one of the zones; incinerating such gases in that in- ;
cinerator; and discharging such gases after incineration into such different one of the zones.
In the preferred embodiment specifically described in ¦~
the original disclosure, solvent-rich vapours are transferred .;~ .
from an upstream zone of an oven apparatus into one or more down-stream zones thereof where they are incinerated to provide both additional heat input to those zones and ventilation of those zones. The transfer of gases from a downstream zone to an up-stream zone to ventilate such upstream zone was also described in the original disclosure.
It has now been found that additional benefits can be -~
obtained by incinerating at such an upstream zone of such an oven the gases transferred to such an upstream zone from one or more ` downstream zones. Such additional incineration will frequently ' further reduce fuel requirements and will often lessen the risk of the solvent vapour concentration within such an upstream zone exceeding the lower explosive limit.
Further advantages in the way of more uniform zone tem-peratures are presented by providing the incinerators already considered so that they discharge generally into the intakes of respective ones of zone gas recirculating fans.
Heat losses are further reduced by disposing the means ",-~.v ~

~. . .
.,.. :

105;~994 such as ducts for transferring gases from oven zone to another within the oven apparatus itself.
Other features of these further developments and the advantages presented thereby will become apparent as the descrip-tion proceeds with reference to Figures 6 to 9 of the accompany-ing drawings in which:
Figure 6 is a top plan view partly in section of a strip treatment oven in accordance here-with;
Figure 7 is a side elevation partly in section of the oven of Figure 6;
Figure 8 is a partially sectioned view along the line ~`
8-8 of Figure 7; and ;~ Figure 9 is a schematic perspective illustration par-... . .
tially cut away of an alternate embodiment.
Referring to Figures 6, 7 and 8, the invention is thçre shown in the form of an oven for curing coatings applied to strip sheet metal. The oven comprises three oven zones indicated as 300, 302 and 304, respectively.
An inlet end 306 and an outlet end 308 form the two ends of the oven.
The oven zones are not separated from one another but, in fact, are all contained within a single integral housing which is continuous from one end of the oven to the other.
The zone 300 comprises the lower temperature high sol-vent release zone, and the zones 302 and 304 will be respective-ly at somewhat higher temperatures, with the volume of solvent release progressively decreasing. Within each of the zones 300, 302 and 304 a separate fan and duct recirculating system is pro-vided for continuously recirculating the atmosphere within that ~.. ~,~. ' .
... . .

~OSZ994 zone and redirecting it onto the strip shown as S in Figure 7 Each of the zones is thus provided with a fan 310 having an in~
take 312 and an outlet duct 314. The outlet duct 314 in turn . j .
' supplies upper and lower discharge ducts 316 and 318. These ducts 316 and 318 run lengthwise along the zones 300, 302 and 304 , respectively, thereby to provide continuous discharge of zone ;~ atmosphere onto both the upper and lower surfaces of the strip S
~' simultaneously along substantially its entire length as it passes ~,. through each of the zones. Fans 310 are driven by separate power sources such as electric motors or the like. The upper and lower discharge ducts 316 and 318 will usually be provided with suit-able dampers or the like. Preferably, the fan 310 and the outlet . ducts 314 are all located in a small chamber indicated as 320 formed at one side of each of the zones 300, 302 and 304 respec-tively. An air flow baffle 322 is disposed between the intake of each fan 310 and the interior of a respective one of the zones 300, 302 and 304 to avoid undesirable air flow patterns within ~; the zones. Each of the zones 300, 302 and 304 respectively are ', provided with incinerator flame tubes 324, 326 and 328 respect-'~ 20 ively. The flame tubes are in turn supplied internally with in-,~ cinerator burners 330 which a,re typically fired by natural gas, : or other suitable fuel.
Fans 332a, 332b and 332c are provided for forcing por-tions of zone atmosphere through the flame tubes 324, 326 and 328 s respectively.
,, In order to supply zone atmosphere to the incinerator tube 324, a zone atmosphere transfer duct 334 is provided extend-ing down the length of the interior of the oven from the upstream ., .
end of the tube 324, in zone 300, and having its free open end at the downstream end of the zone 304. In this way, the fan 332a ., `~ ? ~ ~ ;

~ t i .~ . .

.

105;~994 supplying the tube 324 will draw zone atmosphere from the down-stream end of the zone 304, and will pass it all of the way up the oven through zones 302 and 300 and supply it to the flame tube 324.
Supply for the flame tube 328 is provided by the oven atmosphere transfer duct 336, communicating between the fan 332c and a point midway between zones 300 and 302. In this way, zone atmosphere will be drawn from the transition between zone 300 and 302 and supplied to the flame tube 328.
The flame tube 326 of the zone 302 is supplied through port 338j communicating with the fan 332b. The port 338 draws zone atmosphere from about the same point as the transfer duct 336. In this way, zone atmosphere is withdrawn simultaneously by both the fans 332b and 332c from about the same point, i.e.
the transition between zone 300 and 302.
. The outlets of the respective incinerator flame tubes 324, 326 and 328 are located more or less adjacent the intakes ~; 312 of the fans 310 in the zones 300, 302 and 304 respectively.
In this way, incinerator gases exiting from the tubes 324, 326 ~ 20 and 328 respectively will mix with oven atmosphere gases before .~ being drawn into the intakes 312 of the fans 310 thereby modify~
ing the temperature of both gases, and achieving the two desir- -able objectives, namely, raising the temperature of the oven at-~ mosphere as a whole, while redu~ing the temperature of the in-; cinerator gases themselves, thereby overcoming problems caused by the handling of high-temperature incinerator gases.
This significant advantage is achieved at least in part ~ .
by the location of the flame tubes 324, 326 and 328 essentially within the zones 300~ 302 and 304 respectively where they are surrounded by the zone atmosphere which is already at an elevated " ~3 ~9 ~. `
, .

~ ~05'~994 ;
temperature and in a state of considerable turbulence caused by the rapid high volume circulation of the oven atmosphere induced by the fans 310. In this way, as soon as the high temperature incinerator gases are discharged from the incinerator flame tubes they are immediately mixed with the surrounding oven atmosphere which is at a considerably lower temperature without the need for providing costly high temperature ductwork and control dampers.
In order to admit oxygen for combustion, and control the L.E.L. of the oven atmosphere, a certain volume of the oven atmosphere must be withdrawn and a certain volume of fresh air introduced into the oven continuously. An exhaust stack 340 is therefore provided, which will communicate with a further inci-nerator 342, where the exhaust gases are incinerated to oxidize the solvent vapour content prior to venting such incinerated exhaust gases to the surrounding ambient atmosphere. If desired, some form of heat recovery can be incorporated in the exhaust stack, downstream of the incinerator 342, to recover some of the ~-heat. Possibly, such heat recovery system may be used to preheat incoming fresh air, although in the majority of cases this will not be necessary and the heat recovery system will merely pro-3~ vide, for example, steam for heating the building.
Admission of fresh air in volumes essentially equal to the volume of oven atmosphere exhausted through the stack 340 may be provided in various ways. Where only limited volumes of fresh air are required, then it can enter simply through either end of the oven, i.e. through the strip entry 306 and the strip exit 308. In this way, the air flow pattern within the oven will always be inward with respect to either end thereby substantially 3 completely preventing the escape of oven atmosphere through the ~ 30 open end of the oven with consequent pollution of the atmosphere ,~1 ' ~.~i . ~
~ .... .

i~S'~994 within the buildings surrounding the oven.
However, where larger volumes of fresh air are requir-ed, due to larger volumes of exhaust gases being exhausted up the stack, then fresh air inlets (not shown) may be provided.
Adjacent the strip exit 308, there may be provided an additional circulating fan 310a, and ductwork 312a, 316a and 318a, for maintaining continuous circulation of the zone atmos-phere at the exit end. In the majority of cases, the zone atmos-phere at this point will not require the provision of a further zone incinerator, and consequently none is illustrated in the embodiment of Figures 6 and 7. r~
In some circumstances, it may be desirable to provide 1-for additional direct heat input to the strip. This may be achieved by radiant heating by means of the additional radiant heater as shown in Figure 9. Figure 9 illustrates a radiant heating unit in the form of a generally square box-like duct 344 having a rectangular opening 346 therethrough for passage of the ; strip S therethrough.
The box-like duct 344 is connected to, for example, ,~
the incinerator flame tube 328 for receiving the high tempera-ture incinerator gases directly therefrom through suitable high ` temperature ductwork (not shown).
The high temperature incinerator gases will flow through the duct 344.
Within the duct 344, four rectangular wall members 348 are provided, providing an open-ended passageway extending through the duct 344, communicating with the openings 346 through which the strip S passes.
In the upper and lower walls 348, gas outlet holes 350 may be provided, through which jets of high temperature incinera-.,-~ _ 3 ~1 .
.

~05Z994 - tor gases may pass downwardly and upwardly and impinge directly on the upper and lower surfaces of the strip S.
In addition, the four wall surfaces 348 will be heat-ed to an elevated temperature by the high temperature incinera-tor gases, and will thus subject the strip S to radiant heat as well as heating by the action of the impingement of the gases themselves.
The radiant heater duct may be provided with or with-,~ out the holes 350, depending on its location in the oven. Where no such holes 350 are provided, then the only heating effect will be a radiant heating effect. In this case, it will usual-ly be located in the first, high-solvent release zone 300, and will heat the strip sheet metal itself without heating the coating to the same extent. The coating will then tend to cure from the inside outwardly.
Where additional heat input is required in, for exam-ple, zone 302, having a higher temperature and lower solvent re-lease, then the provision of holes 350 is acceptable since the coating is already partially cured and can withstand the impinge-ment of the high temperature gases.
In accordance with the invention, a novel form of fuel ~ .-contr~l is provided for the incinerators 330. Each of them is provided with a separate fuel control 352 which will typically be an electrical type control, possibly in the form of a synchro-nous motor operating a fuel supply valve 354.
The motor 352 is in turn operated by a relay 356. The relay 356 is in turn connected with two temperature-responsive signal generators 358 and 360.
Signal generator 358 is connected with a temperature sensor 362, and signal generator 360 is connected with a tempera-105'~994 ture sensor 3~4. The signal generators 358 and 360 are respon-ive to predetermined high and low temperatures to operate the ' motor 352 so as to supply either less or more fuel to the burn- --s er 330-The burners 330 are thus re~ponsive to (a) variations in the temperature of their own output and to (b) variations in the temperature of the oven atmosphere.
In this way, each of the burners 330 is solely respon-sible for maintaining a predetermined temperature level in ~ts respective zone of the oven.
It will be appreciated that, while only one such sys-tem of temperature control is illustrated for one of the burners 330, the same system of controls is provided in fact for each of the burners.
` Air doors 366 and 368 are provided at the entry and exit respectively to the oven chamber and prevent the escape of oven atmosphere at these points.
Numerous variations and modifications in the structure hereinbefore specifically described are of course possible.
From the foregoing supplementary disclosure it will , be seen that the invention further comprises a heat treat~Sent oven apparatus in which said gas-~ transferring means is adapted to transfer gas~s exhausted from t~ a downstream said one of ~aid zones of said oven to a said different one of said zone~ disposed upstream with respect thereto with reference to the direction of movement of a work-piece passing through said oven apparatus.
The invention further compri~es such a heat treatment apparatus and which additionally comprises a downstream gas trans-ferring means connected between said gas exhaust of one of said ~ ~05'~994 `' zones and said gas imput of a downstream one of said zon~s.
The invention further comprises such a heat treatment ~' oven apparatus and which also comprises an incinerator at said downstream one of said zones OL incinerating gases transferred thercto by said downstream gas-transferring means.
~, The foregoing is a description of a preferred embodiment ` of the invention which is given here by way of example only. The : invention is not to be taken as limited to any of the specific ., , features as described, but comprehend all such variations thereof as come within the scope to the appended claims. -~

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,:.......... . . ~ , .
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A heat treatment oven apparatus for treating a work-piece carrying a coating containing a vapourizable solvent, said solvent being oxidizable to provide at least part of the heat input requirement for said oven, said apparatus comprising:
an oven having a plurality of oven zones, said work-piece being movable through said zones in sequence;
gas circulation means in said zones for circulating gases therein continuously around such a workpiece within said zones;
a gas input at each said zone for continuously intro-ducing gases into such zone;
a gas exhaust at each said zone for continuously re-moving a portion of the gaseous atmosphere from such zone;
a gas-transferring means connected between said gas exhaust of one of said zones and said gas input of a different one of said zones for transferring gases exhausted from said one of said zones and introducing them into said different one of said zones; and an incinerator disposed essentially at said different one of said zones for oxidizing solvent vapour contain-ed within said gases exhausted from said one of said zones on introduction into said different one of said zones.

2. A heat treatment oven apparatus as claimed in Claim 1 and in which said gas-transferring means is adapted to transfer gas exhausted from an upstream said one of said zones of said oven to a said different one of said zones disposed downstream with respect thereto with reference to the direction of movement of a workpiece passing through said oven apparatus.

3. A heat treatment oven apparatus as claimed in Claim 2 and which additionally comprises an upstream gas-transferring means connected between said gas exhaust of one of said zones and said gas input of an upstream one of said zones.

4. A heat treatment oven apparatus as claimed in Claim 2 which comprises at least three said oven zones and in which said gas-transferring means is adapted to transfer gases exhausted from said one of said zones to a plurality of downstream ones of said zones.

5. A heat treatment oven apparatus as claimed in Claim 4 and in which a said incinerator is provided at each of said downstream ones of said zones for incinerating solvent vapour transferred to said zones by said gas-transferring means.

6. A heat treatment oven apparatus as claimed in Claim 5 and which additionally comprises an upstream gas-transferring means connected between said gas exhaust of at least one of said zones and said gas input of an upstream one of said zones.

7. A heat treatment oven apparatus as claimed in Claim 2 and which additionally comprises air intake means on a first up-stream one of said zones.

8. A heat treatment oven apparatus as claimed in Claim 1 and in which said incinerator has associated therewith a damper for controlling the flow of gases thereto automatically in res-ponse to the temperature of an associated one of said zones.

9. A heat treatment oven apparatus as claimed in Claim 8 and in which said incinerator comprises a fuel supply controller automatically operable in response to the temperatures of the exhaust from said incinerator and the gaseous atmosphere within a respective one of said zones.

10. A heat treatment oven apparatus as claimed in Claim 1 and which additionally comprises an auxiliary heater for each of said zones and operable to heat the gases in respective ones of said zones.

11. A heat treatment oven apparatus as claimed in Claim 1 and including air inlets for each of said zones and normally closed dampers controlling said air inlets and being operable to admit air to said zones for rapid ventilation thereof.

12. A heat treatment oven apparatus as claimed in Claim 1 and which additionally comprises a gas discharge system for re-moving, incinerating and discharging a portion of the gases from said oven apparatus.

13. A heat treatment oven apparatus as claimed in Claim 12 and in which said gas discharge system is adapted to receive gases from a first upstream one of said zones.

14. A heat treatment oven apparatus as claimed in Claim 1 and which additionally comprises a heat exchanger disposed with-in one of said oven zones and an incinerator for receiving and oxidizing gases containing solvent vapour from one of said zones for discharging such gases after oxidation thereof into said heat exhanger comprising surfaces disposed for radiating heat onto a workpiece passing through said oven apparatus.

15. A heat treatment oven apparatus as claimed in Claim 14 and in which said heat exchanger is disposed in a first upstream one of said zones, receives gases containing solvent vapour from that same zone after incineration and discharges such gases into that same zone.

16. A heat treatment oven apparatus as claimed in Claim 1 and in which said incinerator disposed essentially at said dif-ferent one or ones of said zones is disposed so as to discharge incinerated gases into a respective one of said gas circulation means.

17. A method for the heat treatment of a workpiece carry-ing a coating containing a vapourizable solvent, said solvent being oxidizable to provide at least part of the heat required for such heat treatment, and said method comprising the steps of:
moving said workpiece sequentially through a plurali-ty of zones of an oven;
circulating gases in said oven zones;
removing gases from one of said zones;
transferring said gases as removed from said one of said zones to an incinerator disposed essentially at a different one of said zones;
incinerating said gases in said incinerator; and discharging said gases after incineration into said different one of said zones.

18. A method as claimed in Claim 17 and in which said gases are transferred from said one of said zones to said dif-ferent one of said zones in a downstream direction with respect to the direction of movement of a workpiece through the oven.

19. A method as claimed in Claim 18 and which additionally comprises transferring gases from a downstream one of said zones to an upstream one of said zones.

20. A method as claimed in Claim 18 and which comprises transferring said gases from said one of said zones to a plurali-ty of zones disposed downstream relative thereto for incineration and discharge into those zones.

21. A method as claimed in Claim 20 and which comprises transferring gases from a plurality of said oven zones to an up-stream one of said zones.

22. A method as claimed in Claim 21 and in which the gases transferred into said upstream one of said zones have a lower solvent vapour content than the gases circulating in that zone, such discharge thereby reducing the solvent vapour level in that zone.

23. A method as claimed in Claim 17 and which additionally comprises exhausting a portion of the gases from an upstream one of said zones.

24. A method as claimed in Claim 23 and which additionally comprises introducing air into said upstream one of said zones.

25. A method as claimed in Claim 24 and which comprises the additional step of incinerating the gases exhausted from said upstream one of said zones.

26. A method as claimed in Claim 25 and which comprises passing gases as exhausted from said upstream one of said zones, after incineration, through a heat exchanger adapted to radiate heat into a workpiece passing through said oven.

Claims supported by the Supplementary Disclosure

27. A heat treatment oven apparatus as claimed in Claim 1 and in which said gas-transferring means is adapted to transfer gases exhausted from a downstream said one of said zones of said oven to a said different one of said zones disposed upstream with respect thereto with reference to the direction of movement of a workpiece passing through said oven apparatus.

28. A heat treatment oven apparatus as claimed in Claim 27 and which additionally comprises a downstream gas-transferring means connected between said gas exhaust of one of said zones and said gas input of a downstream one of said zones.

29. A heat treatment oven apparatus as claimed in Claim 28 and which also comprises an incinerator at said downstream one of said zones of incinerating gases transferred thereto by said downstream gas-transferring means.

30. A heat treatment oven apparatus as claimed in Claim 29, which comprises first, second and third said oven zones for the sequential movement of a workpiece therethrough, in which said gas-transferring means for transferring gases from a downstream said one of said zones to a said different one of said zones is disposed for the transfer of gases from said third zone into a said incinerator discharging into said first zone, and in which said downstream gas-transferring means is disposed for the transfer of gases from said second zone into a said incinerator discharging into said third zone.

31. A heat treatment oven apparatus as claimed in Claim 30 and which additionally comprises a second zone incinerator disposed so as to receive gases from said second zone and to discharge said gases, after incineration, into said same second zone.

32. A heat treatment oven apparatus as claimed in Claim 30, in which each said gas circulation means has a gas inlet for receiving gases from a respective one of said zones and a gas outlet for discharging gases into said same zone.

33. A heat treatment oven apparatus as claimed in Claim 32 and in which each said incinerator is disposed so as to discharge incinerated gases generally at the gas inlet of the gas circulation means of a respective one of said zones.

34. A heat treatment oven apparatus as claimed in Claim 28 and in which each gas-transferring means is disposed within said oven.

35. A heat treatment oven apparatus as claimed in Claim 27 and which additionally comprises a heat exchanger having at least one radiating surface for radiating heat onto a workpiece passing through said oven, such heat exchanger receiving high temperature incinerated gases from one of said incinerators.

36. A heat treatment oven apparatus as claimed in Claim 35 and in which openings are provided in said radiating surface of said heat exchanger for the discharge therethrough of high temperature gases for impingement heating of a workpiece passing through said oven apparatus.

37. A method as claimed in Claim 18 and in which said gases are transferred from said one of said zones to said different one of said zones in an upstream direction with respect to the direction of movement of a workpiece through said oven .

38. A method as claimed in Claim 37 and which additionally comprises transferring gases from an upstream one of said zones to a downstream one of said zones.

39. A method as claimed in Claim 38 and which additionally comprises incinerating at said downstream zone gas transferred thereto from said upstream one of said zones.

40. A method as claimed in Claim 39 and which comprises mixing said gases after said incineration with gases circulating in respective ones of said zones immediately prior to entry of said gases into a zone gas-circulating means.