Radiant airflow heat processing assembly

A radiant heater comprising a plurality of individual heating elements depending from a pair of spaced apart parallel dielectric members and electrically connected to bus bars that are secured along one longitudinal edge of the dielectric members. The individual heating elements are arranged in a side-by-side relationship along the dielectric members but spaced apart so that air blown downwardly towards the heating elements is heated thereby and passes between and around the heating elements towards a surface to be heated.

BACKGROUND OF THE INVENTION 
Radiant heaters have long been provided to dry manufactured articles that 
are carried below heating elements of the apparatus by a conveyor belt or 
as a web of material that is to be dried as in the case of printed 
textiles or paper. Such apparatus is also used to heat soften material 
which can then be vacuum formed to a desired shape or otherwise processed 
in the softened state. Heat transfer to the material being dried or heated 
is accomplished by radiation and also by convection as when a flow of air 
is directed over the radiant heating elements, where it is heated, and 
onto the material being processed. Quite often relatively high 
temperatures are employed to speed the flow of material beneath the 
heating elements and, as a consequence, the heating elements, and more 
particularly the electrical leads of the elements and the conductors 
connecting the elements to a power source, are subject to periodic 
failure. Such failure requires the apparatus to be shut down so that the 
damaged heating element can be replaced. The prior art (see, for example, 
U.S. Pat. No. 3,499,232) was cognizant of this problem and provided means 
to facilitate the replacement of radiant heating elements. 
SUMMARY OF THE INVENTION 
The present invention relates to an improved radiant heating apparatus that 
minimizes the frequency of failure requiring replacement of individual 
radiant heating elements, or other conductors within the heater enclosure, 
while at the same time enabling the convenient replacement of individual 
elements when such does become necessary. 
In carrying out the invention, a housing or enclosure preferably having 
insulated walls is provided with at least one pair of spaced apart 
parallel support members formed of a dielectric material extending the 
length of the enclosure. A plurality of radiant heating elements are 
spaced from each other along the length of the support members. Means for 
mounting each heating element on the support members permit an element to 
be readily removed and replaced when required. The electrical connection 
of each heating element to a power source is made by connecting one of the 
two leads from the heating element to a rigid non-insulated bus bar that 
is secured along the length of one support member and the other lead to a 
second similar bus bar secured to the other support member. In addition to 
their electrical function, the bus bars give structural rigidity to the 
support members which otherwise might sag or distort under the high 
temperatures generated in the heater. The bus bars extend out of the 
enclosure so that their connection to the flexible conductors of a power 
source is made away from the heat of the apparatus. 
Features and advantages of the invention may be gained from the foregoing 
and from the description of a preferred embodiment thereof which follows.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring to FIG. 1, the heating apparatus 10 of the present invention is 
shown supported above a conveyor belt 12 which may carry articles or 
material that are to be subjected to heat from apparatus 10. Instead of a 
conveyor belt carrying articles or material, the heating apparatus may be 
positioned above a web of material that is fed under the apparatus. 
Apparatus 10 includes an enclosure 14 that is essentially a double walled 
box open on top and bottom. The spacing between the walls 16 and 18 is 
preferably filled with a heat insulating material which, if the structure 
is large and fabricated in place, can be a fiberglass blown into the space 
or an expandable plastic foam injected between the walls. The bottom of 
enclosure 14 is open since the articles or material to be dried or heated 
pass immediately below the enclosure and are subjected to the radiant heat 
and convective air flow emanating from the heating elements located within 
the enclosure. The top opening of enclosure 14 is closed by a removable 
cover plate 20 which is shown in one piece but may, in a large or long 
heating apparatus, include several individually removable sections. A 
blower 22 for forcing air through the heating apparatus is shown mounted 
on cover plate 20. It may be preferred, if blower 22 is cumbersome or 
heavy, that the section of the cover plate to which blower 22 is attached 
be a non-removable section which remains secured to enclosure 14. It is 
only required that a sufficient portion of the cover plate be removable to 
give access to the interior of the enclosure 14 so that the heating 
elements can be replaced when necessary. 
Each end wall 24 and 26 of enclosure 14 is provided with a shelf 28 which 
may consist of an angle member bolted or otherwise secured to the wall. 
The shelves serve to support a pair of dielectric support members 30 and 
32 which are spaced apart in parallel alignment and extend the length of 
the enclosure. Members 30 and 32, which may be formed of monobestos, are 
secured in place by angle brackets 34 and 36, respectively, which are 
fastened to the members and the end walls 24 and 26 by screws 38. 
Arranged along the outside edges of members 30 and 32 are bus bars 40 and 
42 which are in the form of elongated angle strips that are fitted over 
the edges of the dielectric members. The bus bars may be in the form of 
elongated channel members or simply elongated bars that are secured to the 
eielectric members. The ends of the bus bars terminate well short of the 
end walls of enclosure 14 to insure that there is no electrical contact 
between the bus bars and enclosure 14. In addition to their function as 
electrical conductors, bus bars 40 and 42 provide structural support to 
members 30 and 32 which otherwise might sag or distort when subjected to 
the heat developed in the apparatus. 
Rigid bus bar extensions 44 and 46 are electrically connected to bus bars 
40 and 42, respectively, and they extend outwardly of enclosure 14 through 
an opening 48 in end wall 26. An insulated bushing 50 is provided in 
opening 48 to prevent bus bar extensions 44 and 46 making electrical 
contact with any metal parts of enclosure 14. The bus bar extensions 
terminate within a junction box 52 secured to the outside of end wall 26, 
and there they are connected by flexible insulated conductors 54 and 56 to 
a source of electric power. Box 52 is provided with a removable cover 58 
which permits access to the interior of box 52 and thereby facilitates the 
connection of conductors 54 and 56 to the bus bar extensions. 
Attention is now directed to the individual heating elements 60 and the 
means by which they are physically mounted within enclosure 14 and 
electrically connected to the source of electric power. The heating 
elements 60 may, for example, be GTE Sylvania 220/230 volt Elstein FSR 150 
watt radiant heaters in which the electrical resistance wires 62 are 
embedded in a ceramic body. The heating element is a rectangular member 
having a curved cross section, as shown, with an elongated boss 64 being 
formed at the center of the upper convex surface of the element 60. The 
periphery of boss 64 is undercut, as seet in FIGS. 2 and 3, for a purpose 
soon to be described. The external leads 66, 68 of resistance wire 62 are 
insulated with vertebra-like ceramic beads 70 and are provided with 
electrical connectors 72 and 74 which facilitate connection of the heating 
element to bus bars 40 and 42. 
The dielectric support members 30 and 32 are provided with a series of 
transverse notches 76 which determine the location and spacing of heating 
elements 60 within enclosure 14. Into each notch is placed a 
channel-shaped member 78 having a central aperture 80 through which boss 
64 of heating element 60 can extend when the heating element is placed 
against the underside of support members 30 and 32. To hold heating 
element 60 in position with its boss 64 extending through aperture 80, a 
pair of spring clips 82 are slipped into position beneath the overhanging 
top portion of the boss. Thus, heating elements 60 are securely held along 
the length of dielectric support members 30 and 32. Instead of notching 
members 30 and 32, a notched strip could be secured to the inner edges of 
members 30 and 32. The notches of such a strip could abut the inner sides 
of the members or they could be located higher than the top surfaces of 
the members. 
The heating elements 60 are electrically connected to bus bars 40 and 42 by 
placing a connector 72 over a screw 84 and tightening a nut 86 over the 
connector. A screw 84 and nut 86 may be provided on each bus bar for each 
heating element or for two (or more) heating elements as shown in FIGS. 1 
and 4. The screws and nuts may also serve the purpose of securing the bus 
bars to the dielectric support members and to the bus bar extensions, 
although separate securing means may be provided for these latter 
purposes. A stud 88 may be provided in dielectric support member 30 so 
that two adjacent heating elements may be connected in series when a 
higher voltage power source, e.g., a 440 volt source, is connected to bus 
bars 40 and 42, see FIG. 5. A particular heating apparatus would be 
configured either for connecting each heating element 60 directly across 
the bus bars or for connecting the heating elements in series across the 
bus bars, depending on the voltage rating of the heating elements and the 
voltage of the power source. FIG. 1, for illustrative purposes, shows both 
wiring arrangements. FIG. 8 schematically shows one arrangement for 
connecting heating elements to a three phase power source. 
FIG. 6 discloses another embodiment for mounting heating elements 60 on 
support members 30 and 32. Here, instead of channel-shaped members 78 and 
spring clips 82, a single wire clip 90 is used. The base 92 of the clip 
fits into notch 76 while the side arms 94 and 96 are positioned under the 
overhanging portion of boss 64. Arm 96 crosses in front of boss 64 and 
terminates in free end 98 of the clip. Similarly, arm 94 crosses in front 
of the boss and terminates in free end 100. The arrangement is such that 
by pressing the upstanding legs 102 and 104 of free ends 98 and 100, 
respectively, towards each other, the side arms 94 and 96 move apart to 
allow the overhanging top portion of boss 64 to pass between them. Thus, 
heating element 60 can be placed in position to be held by wire clip 90 or 
removed from that position for replacement by another heating element. 
FIG. 7 illustrates another construction for the end wall 24 of enclosure 
14. In this embodiment, the inner wall 16 is a shaped member having an 
elongated channel 106 into which one end of dielectric support member 30 
is fitted and secured in place by a screw 108. The space between inner 
wall 16 and outer wall 18 is filled with and insulating material as 
previously indicated. 
In the three phase system schematically illustrated in FIG. 8, the heating 
elements 60 are shown connected as a balanced Y load. The dielectric 
support members are arranged in three support pairs, 110 and 112, 114 and 
116, and 118 and 120, each pair supporting a plurality of heating elements 
60. As in the single phase system of FIG. 1, the dielectric support 
members are each provided with a bus bar 122, 124, 126, 128, 130, and 132 
to which the heating elements are connected as shown. Bus bars 122, 126, 
and 130 will be provided with rigid bus bar extensions (similar to 
extensions 44 and 46) that extend outside the heater enclosure so that 
electrical connection to the three phase power supply can be made external 
to the heating apparatus. The connection between bus bars 124, 128, and 
130 preferably will be in the form of a rigid uninsulated cross bar 
similar to the bus bar extensions and may be made within the heating 
apparatus enclosure. Of course, the heating elements could be connected as 
a delta load and, for high voltage installations, two adjoining heating 
elements in a row of elements could be connected in series as shown in 
FIG. 5. 
The heating apparatus 10 according to the present invention is particularly 
efficient in drying or heating articles carried by belt 12 when it is 
noted (see FIG. 9) that the radiant heat directed at the belt is 
supplemented by the flow of air which is directed over the heating 
elements 60, where it is heated, and then freely between and around 
elements 60 to belt 12. The spacing between heating elements 60 and the 
downwardly curved shape of the elements contribute to the effectiveness of 
the supplemental convective heat transfer. 
It should be noted that the air which contributes to the heating of 
articles on belt 12 is being heated by passing over heating elements 60 
and the exposed current carrying parts, e.g., bus bars 40 and 42 and 
heating element leads 66, 68, of the apparatus. Thus, the air provided by 
blower 22 is extracting heat from those parts and thereby minimizing the 
heat build-up and consequent temperature rise in those parts. This is 
particularly important with respect to heating elements 60 since the 
external leads 66, 68 are an especially vulnerable part of the heating 
element and subject to failure when overheated. The arrangement of heating 
elements disclosed tends to minimize heating element failures and 
consequent shut down of the apparatus when heating elements have to be 
replaced. However, should a heating element 60 fail, its replacement can 
readily be accomplished. Cover plate 20 or, if the cover plate comprises a 
plurality of individually removable sections, the section thereof located 
over the defective heating element is removed. The leads 66, 68 are 
disconnected from the bus bars 40 and 42, and clips 82 slipped from under 
the overhanging portion of boss 64, thereby allowing element 60 to be 
lowered away from channel member 78. A new heating element is then 
positioned with its boss 64 projecting through aperture 80 of channel 
member 78 and clips 82 (or wire clip 90) are snapped into position below 
the overhanging portion of boss 64. After leads 66, 68 are connected to 
bus bars 40 and 42 and cover plate 12 replaced, the apparatus is again 
ready for service. It is to be noted that the heating element fastening 
means, i.e., clips 82 or 90, and the electrical connecting means 84, 86 
are locted facing the removable cover plate 12 thus facilitating 
replacement of a heating element when such is required. 
By relatively spacing the heating elements on the dielectric support 
members 30 and 32, which themselves are relatively spaced apart, 
relatively large air spaces are provided around and between the heating 
elements and the supports. These spaces permit the passage of a large 
volume of air moving from the blower 22 above to pass unimpeded through 
the spaces. When the heaters 60 are curved, the flow of air is diverted 
fully about the heaters as shown in FIG. 9 in the direction of the arrows 
140 and aided by the shapes of the heaters. This enables the heat to be 
focused directly on an object on the conveyer belt 12 to result in a more 
efficient transfer of heat from the heating elements to the object on the 
conveyer belt. 
Having thus described the invention, it is to be understood that many 
variations or embodiments thereof could be provided without departing from 
the spirit and scope thereof. For example, while an apparatus having one 
row of heating elements 60 is disclosed for a single phase system, such an 
apparatus having two or more rows of heating elements could be provided 
for heating a wider area. In such case, connections between bus bar 
extensions could be made by rigid cross bars outside of enclosure 14 in 
junction box 52. Thus, the foregoing specification and the accompanying 
drawing are to be interpreted as illustrative rather than in a limiting 
sense.