The present invention relates toward an inventive oven for curing coatings applied to an object. More specifically, the present invention relates to a convection combustion oven having a simplified design for curing coatings applied to an object.
Various types of ovens are used to cure coatings, such as, for example, paint and sealers, that are applied to articles in a production setting. One example is decorative and protective paint that is applied to automotive vehicle bodies in a high volume paint shop known to process vehicle bodies at rates exceeding one per minute.
A typical oven uses combustion fuel to provide the necessary amount of heat to cure paint applied to a vehicle body. Generally two types of ovens are presently used, a convection oven and a radiant heat oven. Occasionally, a combination of convection and radiant heat is used in a single oven to meet paint curing specifications. A convection heat oven makes use of a heat source such as natural gas flame that heats pressurized air prior to delivering the heated air to an oven housing. A first type of convection heating applies combustion heat directly to pressurized air prior to delivery to the oven housing mixing combustion gases with the pressurized air. A second type of convection heating uses an indirect heating process where combustion heat is directed into a heat exchanger that heats the pressurized air without mixing the combustion gases with the pressurized air.
An alternative source of heat is provided inside the oven housing by a radiant heater that transfers heat to the vehicle body by way of proximity to the vehicle body. As known to those of skill in the art, a radiant heater is generally a metal panel that is heated by circulating hot air into a space located behind a radiator.
The conventional convection and radiant ovens have proven to be exceedingly expensive to construct and do not provide energy efficiencies desirable in today's high-cost energy market. A conventional oven design is generally shown at 10 in
A typical oven zone of about eighty feet in length of a conventional oven requires an actual air volume of about 30,000 cfm when using a heater box. This high air volume is required to transfer the necessary heat to the vehicle body to cure the applied coating. The air temperature at the nozzle 22 in a conventional oven is generally 444° F. requiring an air velocity at the nozzle 22 of 4,930 fpm to transfer the desired amount of heat energy. The operating parameter set forth above generally provides 1,595,000 BTU/hr at a momentum of 4.9×106 ft-lb/sec2. Because hot air is recirculated by the fan located in the heater box 12, and because the recirculated air is often reheated prior to being pressurized by the fan, the fan requires an overlying robust design adding to operation and installation costs.
The volumes and flow rates presently used in conventional ovens require heavy duty fans and heater systems that are not believed necessary to obtain the required heat transfer. This is in part due to the recirculation of hot air through the fan and back into the oven housing 12. Furthermore, due to the recirculation, a substantial amount of insulation 24 is required around the heater box 12 and the hot air duct 16 to reduce heat loss and protect workers from physical contact. Therefore, it would be desirable to design a simplified oven assembly that does not require extensive insulation and complex apparatus associated with conventional heater boxes.
The present invention discloses an oven assembly for curing a coating applied to an article being conveyed through the oven assembly. A transporter extends through an oven housing for conveying the article through the oven assembly. A fan provides pressurized air into the oven housing drawn substantially from outside the oven housing. A duct includes a first element extending into the oven housing and a second element interconnected with the fan for transporting pressurized air from the fan into the oven housing. A burner is disposed generally between the first element and the second element for heating the pressurized air being transported into the oven housing. The first element defines a plurality of air outlets spaced throughout the oven housing for directing heated air toward the article. The first element is substantially insulated inside the oven housing reducing the escape of heat generated by the burner from the duct except through the air outlet. The burner heats the pressurized air being directed into the oven housing to a temperature of about three times the curing temperature of the coating that is applied to the article.
The inventive oven assembly solves the problems associated with the prior art, or conventional oven assembly. Particularly, the size of the ventilator or fan used to provide pressurized air to the oven housing for transferring heat to the article being baked is significantly reduced for two reasons. First, the fan primarily draws ambient temperature air as the present design does not circulate heated air back into the oven housing and, therefore, does not need to be heat resistant. Furthermore, the heater or burner used to heat the ambient temperature air prior to the introduction to the first element of the duct is configured to heat the air to about two to four times the curing temperature of the coating applied to the vehicle body adjacent the oven housing. This temperature air, when introduced to the oven interior at a high nozzle velocity, reduces the air volume of a conventional 80 foot long oven zone from about 30,000 acfm to about 2,000 scfm. At this combination of air volume, air temperature, and air velocity, a substantially similar amount of BTUs per hour is delivered to the oven as a conventional oven while using less energy to drive the ventilator and having a significantly simplified ventilation and heating apparatus. Specifically, the complex heater box presently used in conventional ovens is no longer necessary and is, therefore, completely eliminated substantially simplifying the construction and design of a production oven.
Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
Referring to
In a production paint shop, a coating is applied to the vehicle body 34 providing decorative and protective paint finish to the vehicle body 34. Different coatings have different baking or curing requirements that, along with vehicle body type and production volume, dictate the length and thermal requirements of the inventive oven assembly 30. For example, electrodeposition primers typically cure at about 340° F. for about twenty minutes and decorative top coat and clear coats cure at about 285° F. also for about twenty minutes. For simplicity, the explanation of the inventive concepts of the present oven assembly 30 will assume a typical eighty foot long oven zone requiring a delivery of heat of about 1,595,000 British thermal minutes per hour (BTU/hr).
Pressurized air is delivered into the oven housing 32 through a duct 40 by a ventilator 42. Preferably, the ventilator 42 is a conventional fan capable of providing the transfer of ambient air at a volume of about 2,000 scfm. The duct 40 includes a first element 44 generally extending inside the oven housing 32 and a second element 46 generally extending from the ventilator 42 to the first element 44. A heater 48 is disposed between the first element 44 and the second element 46 to provide heat to the pressurized air passing through the duct 40 as delivered by the ventilator 42. Preferably, the heater 48 is a gas fired burner sized to provide the desired amount of heat to the pressurized air passing through the duct 40 to adequately cure the coating applied to the vehicle body 34. However, it should be understood by those of skill in the art, that alternative heaters may also be used to provide heat to the pressurized air as set forth above.
As will be explained further below, the heater increases the temperature of the pressurized air to about 1,100° F. or hotter. One range contemplated is between about 700° and 1,100° F. The desired temperature is selected to be between about two and four times the curing temperature of the coating as will be explained further below. The heater is located, preferably, adjacent to or nearly adjacent to the oven housing 32 so that the heated, pressurized air travels only through the interior of the oven housing 32. This reduces the need to insulate the duct 40, or more specifically, the second element 46 of the duct 40 further reducing assembly costs. However, insulation 50 covers the first element 44 of the duct 40 inside the oven housing 32 to prevent the escape of heat through the first element 44 into the oven housing 32 except where desired.
The oven assembly 30 represented in
Each first element 44 defines an upper header 52 and a lower header 54 that extend in a generally horizontal direction. Nozzles 56 are spaced along each of the upper header 52 and lower header 54 through which pressurized, heated air is projected toward predetermined locations on the vehicle body 34.
Referring again to
Referring to
An alternative nozzle in the form of an eductor or venturi nozzle is shown at 82 in
A further embodiment nozzle is shown as an air amplifier 96 at
The embodiments set forth above are desirable to heat heavy metal areas of the vehicle body 34, which have higher heat requirements than thin or sheet metal areas of the vehicle body 34. In these embodiments, the eductor 84 and the air amplifier 96 are each directed at a predetermined location of the vehicle body drawing heated air from inside the oven housing 32 maximizing the amount of heat energy directed toward the heavy metal area of the vehicle body 34. As explained above, pressurized air passes through the header 52, 54 through air inlet 88 and into the venturi chamber 90 prior to exiting through the nozzle 92. Hot air is drawn into venturi inlet 94 via the venturi effect increasing the volumetric flow rate of hot air being directed toward the vehicle body 34.
Table 1 shows the operational parameters of the inventive oven assembly 30 that provides the benefits set forth above.
The data shown in Table 1 is based upon a typical 80 foot long oven section (i.e., heat up zone) at a typical vehicle body 34 production rate. In each example, the required heat delivery is about 1,595,000 BTU/hr. The first column shows the various operating requirements to produce the heat required in a conventional oven design and the following columns indicate the inventive oven nominal design, with a lower limit velocity and an upper limit velocity establishing the general operating range.
Most notably, a significant reduction in the standard delivery volume is realized in standard cubic feet per minute (ambient temperature). Those of skill in the art will understand that delivery volume in a conventional oven is generally 30,000 acfm because hot air is recirculated through the oven by the heater box 12 shown in
Further operating parameters proven to achieve desired heat and momentum requirements include providing the volume of air to the oven housing at less than about 25 scfm per foot of oven housing. An alternate embodiment provides a volume of air to the oven housing of less than about 50 scfm per foot of oven housing. A still further alternate embodiment provides a volume of air to the oven housing at a rate of about 75 scfm per foot of oven housing. This is significantly less than a conventional oven design which requires about 220 scfm per foot oven length, requiring higher energy usage than the inventive oven assembly 30.
An additional benefit of heating the pressurized air to about 1,100° F. is the ability to clean the oven 30 by combustion of coating byproducts known to coat oven walls. This eliminates the need to manually wash oven walls, which is labor intensive.
The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.
Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.
This application claims priority to Provisional Application Nos. 60/814,632, filed Jun. 16, 2006, 60/807,875, filed Jul. 20, 2006, and 60/839,082, filed Aug. 21, 2006.
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