Note: Descriptions are shown in the official language in which they were submitted.
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PAIIq'r DRYING OVEN WITH RADIANr ENERGY FLOOR
BACKGROUND OF THE INVENTION
The present invention relates to a paint drying oven for a vehicle which uses
a radiant energy floor and to a method of drying paint on a vehicle using a
radiant
energy floor.
Paint drying ovens are used on vehicle production lines. A vehicle body is
initially transported through a paint spray booth where paint is applied to
the body.
The vehicle body is then transported into a paint drying oven. During the
curing
or drying process, the vehicle body is transported through the paint drying
oven
while drying energy is applied to the vehicle body to dry the wet paint. For
the
purpose of this invention, the term "drying" is used synonymously with
"curing."
Various factors influence the selection, operation and design of paint drying
ovens. The oven must apply drying or heat energy to the vehicle body, while at
the
same time not disturbing the wet paint finish on the vehicle body. Also, it is
desirable to maintain the vehicle body in its entirety at a single target
temperature
during drying. Thus, while convection heaters, which blow heated air onto the
vehicle, have many desirable attributes in maintaining a relatively constant
vehicle
temperature, they have undesirable characteristics due to the volume of air
being
directed onto the wet paint. However, the other major type of drying ovens,
radiant
ovens, have not always been able to uniformly apply drying energy to the
vehicle.
The prior art radiant ovens have used radiant generators on the side walls or
ceiling
of the oven. In most vehicle bodies, more heat needs to be directed towards
the
lower part of the body compared to the upper part of the vehicle body. The
upper
vehicle body, such as the vehicle roof, etc., is typically formed of thinner
metal,
and thus requires less heat.
A typical paint drying oven for a vehicle is divided into two sections. The
first section, a so-called "heat-up" section, initially heats the vehicle body
to a
relatively hot target temperature. The particular target temperature depends
upon
the type of paint being applied, however, it is usually above 200 F. In
particular
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examples, for a primer paint oven target, temperatures of between 280 F and
330 F
are achieved in the oven. For a color paint oven, target temperatures of
between
250 F and 290 F are achieved. For an electro-coat oven, target temperatures of
between 320 F and 400 F are achieved. Once the heat-up section has achieved
this
initial heating of the vehicle body, the vehicle body moves into a second
portion
typically known as a "hold" portion. In the hold portion, the vehicle is
maintained
at the target temperature achieved by the heat-up portion for a period
sufficient to
dry the paint surface.
In the prior art, the heat-up section has often been provided by radiant
ovens.
However, radiant ovens have typically not been believed to be capable of
providing
the hold function. As such, the hold function has almost always been
accompanied
by large air movement. For that reason, hold zones have typically used
convection
heating. This belief was due to the difficulty of maintaining a constant
temperature
across the vehicle with the conventional radiant energy ovens. Radiant ovens
that
were used in a hold zone were used with large air flow volumes to create
turbulent
air flow. This defeats the benefit of radiant ovens as described above.
SUMIVIARY OF THE INVENTION
A disclosed radiant energy paint drying oven emits radiant energy for drying
a painted vehicle body from the oven floor. The oven comprises a housing with
side walls, an oven ceiling and an oven floor defining a heating chamber
through
which a freshly-painted vehicle is transported. The oven contains a radiant
energy
generating means in the oven floor. The oven floor includes a thin inner wall
adjacent the heating chamber and an outer wall spaced below the inner wall. In
a
more preferred embodiment, an inventive insulation layer is disposed adjacent
and
in contact with the outer wall and remote from the inner wall. The inner and
outer
walls define a heating passage. Heated air is supplied to the heating passage,
and
heats the inner wall of the floor to a temperature sufficient to emit radiant
energy
therefrom. Wall temperatures of up to 800 F may be expected. The radiant
energy
is emitted to the heating chamber, and dries a freshly painted vehicle body.
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The inventive paint drying oven is most preferably utilized in a "hold"
section of a drying oven. Even so, it should be understood that the invention
has
benefits in all areas of the oven. The radiant energy floor has provided a
relatively
constant temperature throughout the vehicle body. This is an unexpected
result, and
also solves problems that have been experienced in this area. As described
above,
in the prior art it has been difficult to achieve a relatively constant
temperature in
the hold section without convection heating. As also described, convection
heating
has undesirable characteristics with regard to disturbing the paint finish. As
such,
the use of the radiant oven floor as the sole supplier of radiant energy to
the vehicle
provides unexpected benefits.
In addition, since the radiant energy creating structures that have typically
been required on the sidewalls are eliminated with this invention, the width
of the
drying oven may also be significantly reduced. The reduction of required space
in
any vehicle assembly environment is a valuable benefit.
The radiant energy oven preferably contains air supply ducts located in the
upper lateral corners of the oven housing for delivering air to the heating
chamber.
The air supply ducts include inlet and outlet ducts which deliver and then
exhaust
a small amount of air to remove paint solvents from the air in the heating
chamber.
In a method of drying paint according to this invention, radiant energy is
produced in the floor of a radiant energy oven. A car having wet paint is
transported along the longitudinal direction of the radiant energy oven.
Radiant
energy is produced by a radiant energy means as disclosed above, i. e. , a
pair of thin
walls defining a passage through which heated air is passed. The inner wall of
the
radiant energy means is heated to a temperature wherein the inner wall emits
radiant
energy thereby supplying radiant energy to the heating chamber of the oven.
In a more detailed method according to the present invention, a vehicle
having wet paint is initially passed into a drying oven and brought up to a
target
temperature, which is at least above 200 F. Once the vehicle has been brought
up
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to this target temperature, it moves into a "hold" portion of the drying oven.
The
hold portion of the drying oven includes a radiant energy generating oven
floor as
described above. The radiant energy generating floor generates radiant energy
to
continue to heat the vehicle, and maintain it at the ta:rget temperature.
These and other features of the present invention will be best understood
from the following specification and drawings, of which the following is a
brief
description.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of an inventive oven.
Figure 2 is a cross-sectional view of a radiant energy paint drying oven of
the invention herein.
Figure 3 is plan view of a radiant energy means comprising the floor of the
radiant energy oven shown in Figure 2 taken along section line 3-3.
Figure 4 is a view of an alternative floor air flow embodiment.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a vehicle paint drying oven 10 incorporating a heat-up
portion 15 which would include heating elements, which may be radiant energy
generating elements, that initially heat a vehicle 18 to a target temperature.
As
discussed above, the target temperature differs with the type of paint applied
on the
vehicle, but is typically above 200 F. The vehicle 18 moves along a conveyor
16
through the heat-up section and into a second "hold" section 20. The goal of
the
"hold" section 20 is to maintain the vehicle at the target temperature
achieved in the
heat-up section 15. The hold section 20 incorporates an inventive radiant
energy
generating floor which maintains a vehicle 18 at the target temperature.
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The floor may be heated as high as 800 F, depending upon the particular
application and particular target temperature. A worker of ordinary skill in
the art
would be able to determine the required temperature for the floor to maintain
the
desired target temperature at the vehicle body 18.
Figure 2 shows hold portion 20 having a radiant energy source in accordance
with the invention, as will be described below. Although the inventive floor
is
shown in the hold zone, it should be understood that the invention has
benefits at
all oven locations. Portion 20 has a housing with opposed longitudinally
extending
side walls 22 and 24, a ceiling 26, and a floor 28. The opposed side walls 22
and
24 define a heating chamber of the oven through which a series of freshly
painted
vehicles are transported for drying. The materials for construction of the
sidewalls
and oven ceiling, are well known in the art and are not critical to the
present
invention.
Freshly painted vehicle 18 is shown mounted on a conveyor 16 which moves
a series of such vehicles longitudinally through the length of the oven, above
the
oven floor 28. Conveyor 16 transports vehicles along a central corridor, at a
lateral
center between sidewalls 22 and 24.
Optional air supply ducts 41a and 41b are also shown in the upper lateral
corners of the oven housing extending along the length of the oven. Inlet
ducts 42
and 43 deliver a small amount of air to the heating chamber, and air outlet
ducts 44
and 45 quickly exhaust that air. These air supply ducts provide circulation of
a
small amount of air to remove solvents in the air. The ducts could be
incorporated
into the walls or floor in alternative embodiments. The air supply ducts can
be
connected to any apparatus that can provide relatively clean, dust-free, and
dry
re-circulation of air. Blowers and fans of the type required herein are well-
known
in the art.
, 30
Oven floor 28 extends between sidewalls 22 and 24, and includes thin radiant
inner wall 30, outer wall 32, and insulation layer 34. The thin radiant inner
wall 30
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is adjacent the heating chamber of the oven and stretches the length of the
oven
along a longitudinal direction. The outer wal132 is spaced from the inner wall
30
and is adjacent and below the insulation layer 34. The inner wall preferably
has a
thickness between about 1/16 and 1/4 inches and comprises a thermally
conductive
material which radiates heat well. Because the outer wall carries an
insulation
layer, it may comprise the same material as the inner wall, which may be an
appropriate steel. The thickness, however, of the outer wall may be greater
than
that of the inner wall. The insulation layer consists of known insulative
material.
Because of insulation layer 34 adjacent and above outer wall 32, only inner
wall 30 will radiate heat. Energy will not radiate from outer wall 32.
As shown in Figures 2 and 3, the space 60 between the inner wall 30 and the
insulation layer 34 includes a plurality of spacers, here three, which define
a flow
path for heated air. As shown, outer channels 64 carried heated air in a first
direction along the oven to an end 66 of the outer spacers 55. The air then
bends
and returns along an inner channel 68. A conduit 62 carries the heated air to
the
channels 64, and a conduit 70 returns the air from outlet channels 68 to a
heater 72.
In this way, the air is heated to the desired temperature, and the floor is
evenly
heated to, in turn, apply a relatively uniform heat to the vehicle 18.
Preferably, the space 60 extends for a vertical extent between the insulation
layer 34 and the inner wall 30 that is two to eight inches. Most preferably,
the
space is three to five inches.
As shown in Figure 4 in an alternative embodiment, the spaced inner and
outer walls, 30 and 32 define a heating passage through which heated air is
directed.
Heated air supplied by heater 36 passes through the heating passage, heating
inner
wall 30. The air is then recirculated to the heater. The inner wall 30 is
heated to
temperatures up to 800 F and emits radiant energy to the heating chamber of
the
oven. The heating passage contains a passage inlet 46, passage outlet 48, a
left
channel 52 and a right channel 54. The channels are defined by a single spacer
55.
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Heated air enters passage inlet 46, travels down left channel 52 running down
the
left side of the oven floor the length of the drying oven, makes a turn at the
closed
end of the oven floor 50, and travels back through the right channel the
length of
the drying oven and out heating passage outlet 48.
Heater 36 supplies heated air to the heating passage through heating passage
inlet 46. After circulating through the heating passage, the air exits the
heating
passage through heating passage outlet 48 and recirculates through the heater
36
Heater 36 may be of a type well known in the art.
The heated air, as it travels through either embodiment heating passage,
transfers heat energy to the thin inner radiant wall 30. Since inner wall 30
is
relatively thin, it is easily heated to high temperatures. The hot inner wall
emits
radiant energy into the heating chamber.
The painted vehicle 18 travels on conveyor 16 through the heating chamber
of the oven defined by the space between opposed sidewalls 22 and 24. The
radiant
energy in the heating chamber holds the vehicle at the target temperature,
drying the
paint on the vehicle to the extent that at the end of the oven, vehicle 18 has
a dry
paint coat.
In an inventive method of drying paint, radiant energy is emitted from a
radiant energy means in the floor to the heating chamber of the oven. A
vehicle
having wet paint is moved through the heating chamber along the longitudinal
direction of the oven.
The heating passage may comprise other configurations so long as it provides
for the circulation of heated air from the heating means into a passage inlet
through
the heating passage configuration, out a passage exit, and back to the heating
means.
For example, the heating passage may be a single open-ended channel running
between the inner and outer walls the length of the oven floor. The heating
passage
as illustrated in Figure 3 could also be easily reversed with the heated air
traveling
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along the laterally inner channels and returning in the laterally outer
channels. The
passage inlet would be at one end of the channel and the passage outlet would
be at
the other end, with the inlet and outlet are connected to a heating means in a
recirculating fashion.
A preferred description of this invention has been disclosed; however, a
worker of ordinary skill in the art would recognize that certain modifications
would
come within the scope of this invention. For that reason, the following claims
should be studied in order to determine the true scope and content of this
invention.
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