BACKGROUND OF THE INVENTION

1_ Field of the Invention

This invention relates to paint baking ovens. More particularly, the invention relates to a method and apparatus for ventilating paint baking ovens.

2_ Description of Related Art

Paint baking ovens are used throughout the manufacturing industry to bake the paint or coating applied to various articles such as automobile components. Such paint baking ovens often have conveyors or similar devices for bringing the component to be baked into the paint baking oven and then carrying the component through the various sections or zones of the paint baking oven. While the component is within the paint baking oven, ventilation air is. introduced for a variety of reasons. Heated ventilation air mixed with recirculation air is often blown over the surface of the component passing through the paint baking oven to achieve an even temperature over the surface of the component. Obtaining an even temperature over the surface of the component helps insure a consistent baking which in turn results in a more desirable finish.

Ventilation air is also useful to carry the evaporated solvents and/or resins which are driven from the component during the paint baking process out of the paint baking oven.

Designers of paint baking ovens have traditionally attempted to deal with improving the final appearance of the paint or finish applied to the component by providing a ventilation system which helps prevent impurities, such as solvents and resins, from settling or condensing within the paint baking oven.

None of the art known to applicants suggests introducing all of the heated fresh ventilation air into

the paint baking oven at the air inlet seals to reduce the occurrence of solvent condensation in the vicinity of those seals within the paint baking oven.

Additionally, none of the art presently known to the applicants suggests introducing heated fresh ventilation air above the oven zone equilibrium point in a camel-back paint baking oven such that the heated fresh ventilation air draft naturally will move upwardly to a succeeding oven zone carrying evaporated solvents and resins toward an exhaust system.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a paint baking oven having an outer ceiling and a floor interconnected by two side walls to define a tunnel with air sealed. entrance and exit ends, with articles to be baked moving longitudinally along and through the tunnel from the entrance end to the exit end. Air inlets for introducing air into the paint baking oven are provided at the air seals. Air exhausts extend from the paint baking oven at a preselected location along the tunnel between the entrance and exit ends and is operative to withdraw solvent and/or resin laden air from the paint baking oven.

It is a feature of this invention to provide heated fresh ventilation air into the paint baking oven at the air seals to prevent condensation of solvents and/or resins within the paint baking oven.

It is a further feature of this invention to provide heated fresh ventilation air to accommodate for the decrease in oven temperature which occurs as a result of heat exchange with the component and internal oven parts.

It is a further feature of the present invention to. provide cool ventilation air into a first radiant bring up zone so that infrared lamps may be utilize . Another further feature of this invention is to provide an exhaust element between a last bring up zone and a first convection air holding .zone such that the maximum

solvent concentration occurs at points in the oven furthest from the entrance and exit ends.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of the invention will become apparent from a reading of the detailed description taken in conjunction with the drawings, in which:

FIG. 1 is a cross-sectional side view of a paint baking oven of the camel-back design having exhaust means located between a first bring up zone and a convection air holding zone.

FIG. 2 is an expanded cross-sectional side view of the camel-back paint baking oven of Fig. 1.

FIG. 3 is a cross-sectional side view of a paint baking oven of the straight through design having exhaust means located between a first bring up zone and a convection air holding zone.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT With reference to Figs. 1 & 2, a camel-back paint ^* baking oven 10 in the form of an elongated tunnel having first and second end sections separated by an extending hump 11 located above the two end sections is shown in cross section. Beginning at the sealed entrance end 12, the articles to be baked move upon a conveyor (not shown) longitudinally along a path of travel parallel to the longitudinal axis of the zone or section through which the component is passing. The camel-back paint baking oven 10 of Figs. 1 & 2 includes a first radiant bring up zone 20 located proximate to the entrance end 12, an inclined transition area 28 leading to an elevated convection bring up zone 30, an elevated first convection air holding zone 40 located within the oven hump portion 11 within which the components are baked by a chemical reaction and a declining transition zone leading to the exit end 14 of the oven. Also included on the camel-back paint baking oven 10 are a plurality of air inlets 17, 22 and 44 for introducing

ventilation air into the camel-back paint baking oven 10 and exhaust means 35 located between the bring up zone 30 and the convection air holding zone 40 which provides a passageway to an incinerator. Initially, the component enters the camel-back paint baking oven 10 on a conveyor through an air sealed silhouette (not shown) located at the entrance end 12 of the camel-back paint baking oven 10. Once inside the camel-back paint baking oven 10, the component passes into and through a first oven section referred to herein as the first radiant bring up zone 20. In the camel-back type paint baking oven 10, the upper surface or ceiling 71 of first radiant bring up zone 20 is situated at least 0.5 meters below the lower surface of floor 72 of the elevated convection air bring up zone 30. This height differential of at least 0.5 meters provides the camel-back paint baking oven 10 with a thermal lock which helps reduce leakage out of hot air and leakage in of cold air, thereby reducing the occurrence of undesirable condensation of solvents and/or resins at the air seals 17, 22 and 44.

Within first radiant bring up zone 20, radiation is applied to a painted component (not shown) to quickly raise the component temperature to a desired level in preparation for the paint baking which occurs by chemical reaction within the convection air holding zone 40. The source of radiation within first radiant bring up zone 20 may, in general, be either dark radiation panels or infrared lamps. When infrared lamps 24 are utilized, ventilation air must be introduced into the first radiant bring up zone 20 to cool the infrared lamps which cannot operate under standard paint baking oven conditions. Therefore, cool fresh ventilation air is introduced as shown by arrows 16 behind quartz glass walls 50a and 50b which isolate the infrared lamps 24 from hot air in the bring-up zone 20. The cooling air sweeps through and cools the infrared lamps 24. Typically, fresh ventilation air is injected through the air inlet seals 17 at a velocity of

between 0.5-1.5 meters per second (m/s) to avoid the creation of turbulence within the radiant bring up zone 20. As the component temperature is raised within first radiant bring up zone 20, solvents and/or resins tend to evaporate from the component and pass into the ventilation air stream. The ventilation air stream then carries the evaporated solvents and/or resins further within the camel-back paint baking oven 10 toward the middle thereof. The ventilation air passes completely through the first radiant bring up zone 20 and flows into the inclined transition zone 28 where the component is raised up into the elevated hump portion 11 of the camel-back paint baking oven 10. Additional air seals 22 are provided at approximately the halfway point on transition zone 28 for introducing additional heated ventilation air into the camel-back paint baking oven 10. This additional heated ventilation air which enters the camel-back paint baking oven 10 through air seals 22 typically has a temperature significantly higher than the temperature of the air already contained in the camel-back paint baking oven 10 to compensate for the heat exchange which occurs between the oven air and the component and infiltrating cooler air entering from lower portions of the camel-back oven. For example, if the camel-back paint baking oven temperature is required to be 150°C to sufficiently bake the component, the heated fresh ventilation air will typically be between

200-250 ^β C to compensate for any heat exchange which occurs.

The heated fresh ventilation air which is introduced at air seals 22 is introduced above the oven zone equilibrium point which is the point within the oven where the ventilation air draft naturally moves upwardly from the transition zone 28 to the succeeding oven zones when contacted by the cooler air from the first radiant bring up zone 20. Extending above the camel-back paint baking oven

10 between the trailing end of the bring up zone 30 and the convection air holding zone 40 are exhaust means 35 through

which the solvent and/or resin laden air leaves the camel-back paint baking oven 10. The exhaust means 35 generally include a single horseshoe or U-shaped exhaust duct through which the air from the camel-back paint baking oven 10 is withdrawn and sent to an incinerator (not shown) where the solvents and/or resins are burned off prior to releasing the exhausted air into the atmosphere. It will be understood by those skilled in the art that the exhaust means may be of varying designs. Heated fresh ventilation air is also introduced through seal 44 located approximately at the halfway point on a second inclined transition zone 48 above an oven equibrium point near exit end, 1 .

The heated fresh ventilation air, which is introduced through air seal 44, rises to the top of the transition zone 48 and into the convection air holding zone 40 toward the middle of the paint baking oven 10.

Again, this fresh ventilation air introduced through air inlet 44 near the exit end 14 of the camel-back paint baking oven 10 has a temperature which is greater than the oven temperature to accommodate for heat loss resulting from contact with the component and the internal oven parts. This heated fresh ventilation air introduced near the exit end 14 of the camel-back paint baking oven 10 is provided so that no condensation of solvents or resins will occur in this area of the oven.

Once heated ventilation air reaches the leading end 41 of the convection air holding zone 40, it is exhausted via duct 35 and incinerated prior to being released into the atmosphere.

To maintain an even flow of ventilation air supplied to the paint baking oven 10, the total volume of air introduced into the paint baking oven 10 through the various air seals 17, 22 and 44 can be monitored and controlled by attaching apparatus such as a venturi tube to the exhaust means 35.

With reference to Fig. 3, a straight through paint baking oven 110 in the form an elongated tunnel having first and second end sections 112 and 114, respectively, and a middle section comprising a bring up zone 130 and a convection air holding zone 140 is shown in cross section. Beginning at the entrance end 112, the articles to be baked move upon a conveyor (not shown) longitudinally along a path of travel parallel to the longitudinal axis of the paint baking oven 110. The straight through paint baking oven 110 of Fig. 3 includes first and second air seals 117 and 118, located proximate to the entrance end 112 of the straight through paint baking oven 100, a bring up zone 130, a convection air holding zone 140, and third and fourth air seals 144 and 146 located proximate to the exit end 114 of the paint baking oven 110. Also included as part of the straight through paint baking oven 110 are exhaust means 135 located between the first bring up zone 130 and the convection air holding zone 140 which provide a passageway to an incinerator (not shown) .

Initially, the component enters the straight through paint baking oven 110 on a conveyor through an air sealed silhouette (not shown) located at the entrance end 112 of the straight through paint baking oven 110. Once inside the straight through paint baking 110, the component passes into and through a first oven section, referred to herein as bring up zone 120. Within first bring up zone 120, radiant heat is applied to the component through dark radiation panels to raise the component temperature to the desired level in preparation for the more intensive paint baking which occurs by chemical reaction within the convection air holding zone 140.

Solvents and/or resins generally evaporate from the component during the paint baking process. To prevent condensation of any evaporated solvents and/or resins heated fresh ventilation air is introduced into the paint baking oven 110 through air seals 117 and 118. While a

single air seal, such as 117, is believed satisfactory, it has been found that a pair of air seals 117 and 118 is preferable. This ventilation air sweeps the evaporated solvents and/or resins toward the exhaust means 135 provided at the center of the paint baking oven 110. Typically, this heated fresh ventilation air has a temperature which is approximately 50*C higher than the temperature of the air already contained in the paint baking oven to compensate for the heat exchange which occurs between the oven air and the component and internal oven parts.

Extending from the straight through paint baking oven 110 between the trailing end 138 of the bring up zone 130 and the leading end 141 of the convection air holding zone 140 are exhaust means 135 through which the solvent and/or resin laden air leaves the straight through paint baking oven 110. The exhaust means 135 generally include a single horseshoe or U-shaped exhaust duct through which the ventilation air is withdrawn and sent via the air exhaust duct to an incinerator (not shown) where the solvents and/or resins are burned off prior to being released into the atmosphere. It will be understood by those skilled in the art that the exhaust means 135 may be of varying designs. Heated fresh ventilation air is also introduced at the exit end 114 of the straight through paint baking oven 110 through air seals 144 and 146. Again, a pair of air seals is preferable, but not necessary. This fresh ventilation air also has a temperature which is greater than the oven temperature to accommodate for the heat loss which continually occurs throughout the straight through paint baking oven 110 as a result of heat exchange with the component and outside air which may infiltrate the oven at its entrance and exit ends. The heated fresh ventilation air is provided to avoid condensation of solvents or resins in the vicinity of air seals 144 and 146. Once this heated ventilation air, which has entered through air inlets 144

and 146, reaches the leading end 141 of the convection air holding zone 140, it too is exhausted via exhaust means 135 and incinerated prior to being released into the atmosphere. To maintain a total volume of air introduced into the straight through paint baking oven 110 which is equal to the amount of air simultaneously being exhausted, a venturi tube can be incorporated at the exhaust means 135 to monitor and control the rate at which the air is exhausted from the straight through paint baking oven 110.