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Патент USA US2412990

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Dec. 24, 1946.
0, Q, KRusE
.
2,412,990
DRYING OVEN CONTROL
Filed July 6, 1942
3 Sheets-Sheet l
INVENTOR.
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BYDLM 4% {02,1
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?TTOE/YEYS‘
Dec. 24, 1946.
Q_ Q, KRUSE
2,412,990
DRYING OVEN CONTROL
Filed July 6, 1942
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3 Sheets-Sheet 2
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Dec. 24, 1946.
o. o. KRUSE
2,412,990
DRYING OVEN CONTROL
Filed July 6, 1942
3 Sheets-Sheet 3
A?
,5Q.
?g. SQ
“Q
INVENTOR.
_'XYM
ATTOE/VEYS‘
Patented Dec. 24; 1946
12,412,990
UNITED STATES PATENT. OFFICE,
DRYING OVEN CONTROL
Orlln 0. Kruse, Oak Park, 111., assignor to Ameri
can Can Company, New York, N. Y., a corpora
tion of New Jersey
Application July‘6,.1942, Serial No. 449,939
5 Claims. (Cl. 158-28),
1.
'
The present invention relates to drying ovens
and the like which are heated by gas burners and
has particular reference to devices for controlling
the lighting of the burners and for purging the
Fig. 31s a view similar to Fig. 1 with parts
omitted and with other parts shown in section;
and
'
Fig.‘ 4 is a. wiring diagram of the electric appa
ratus used with the devices.
As a preferred embodiment of the invention the
drawi'ngsillustrate a portion of a sheet drying
oven of the general character disclosed in United
explosions.
In drying ovens used for baking coated and
lithographed metal sheets, such as tin plate and
the like from which container or can parts are
States'Patent 1,691,683, issued July 6, 1926, to
produced, the drying of the sheets usually is ef
fected by circulating heated air through the
ers.
.
stantially along the broken line 2-2 in Fig. 1;v
'
oven of unburned gases and other vapors prior to 6
lighting the burners to safeguard the oven against
ovens.
2
Fig. 2 is a transverse sectional view taken sub
- C. G. Preis.
In such an oven freshly coated or
lithographed sheets of tin plate or the like mate
rial are conveyed through a. drying chamber in
The air is heated by way of gas burn-.
In starting up such an oven and when re
lighting a burner, which for some reason has 16 an upright or "on-edge” position while heated
gone out, unburned gas sometimes collects in the
air is circulated through the chamber to dry'the
oven and results in a terri?c explosion if proper'
precautions are not taken.
coating on the sheets.
In_ the instant oven the air to be circulated
The instant invention contemplates the pre-‘ Q through the chamber is heated to a predetermined I
vention of such explosions by the provision of 20 temperature by a ring shaped main gas burner
prior to the lighting of the burners.
'
An object therefore of the invention is the pro- I
H (Fig. 1) which is located in a sheet metal duct
l2 formed on top of the oven. The duot com’
municates, by way of suitable entrance and re
vision in a drying oven which is heated by gas
tum openings, with the drying chamber in the
control devices which insure purging of the oven
burners, of control devices which operate to purge
even.
the'oven of unburned gases prior to the lighting 4
of the burners so that an explosion resulting from
ignition of such gases will be prevented.‘
.
pipe 13 which leads from any suitable supply of
The burner is supplied with gas by a
', gas outside the oven.
, The ?ow'of gas to the bumer H is controlled
by a main cut-on‘ or ‘service valve l5 and a regu
Another object is the provision of such oven
controldevices wherein‘ the heating burners are 30 lator valve 16 which are connected into the sup
ply pipe l3. The cut-oil? valve I5 is of ‘the nor
held inoperative, i. e., ignition is delayed,'fora
mally closed type and is formed witli'a manually
the
predetermined
purging operation
time cycle
so after
that the
the beginning
burners are
of .
operable opening lever l8.- The valve is provided
not lighted until the oven is cleared of explosive '
gases.
-
7
Another object is the provision of control de
1' with a locking electric solenoid I! which when
35
venergized permits of opening the valve by ma
nipulation of the lever I8 and holds it open re
vices of this character wherein electric instru- -~ ' gardless of any further manipulation of the lever.
mentalities and suitable electric circuits are in
Closing of the valve is effected ‘by the solenoid.
terconnected insuch manner as to interlock the .
' The‘regulatorvalve I6 is' partially opened or
control devices so thatthey are dependent for
closed, ‘as the case may require, tocontrol the
operation upon the ?ow of air through the oven
'heat, output of the burner and to maintain the
with-the result thatthe latter 'will be purged " j air- circulated through the oven at a predeter
fully of unburned gases before" the burneris
made ready for lighting.
-
-
_
Numerous other objects and' advantages of the
invention will be apparent as it isbetter under
stood from the following description, which,
taken in connection with the accompanying
drawings, ~ discloses a preferred embodiment“
thereof.
mined constant temperature. Actuation of the
valve is e?ected preferably by a valve arm 2|
vwhich is connected by a link'22 to an actuating _
arm 23 mounted‘ on a gear shaft 24 carried in
suitable bearings formed in a bracket assembly
‘25 bolted ,or otherwise secured to the‘ burner. "
end of the duct l2.
The gear shaft 24 is part of a, speed reduction"
transmission which includes a pair of meshing
Figure 1 is a sectional view taken-through the 7 '. gearstl, 32 and a worm wheel 33. The worm
wheel is rotatable in either direction by a \worm
burner and air circulating portion of a drying
34 which is mounted on a rotor shaft 35 of a re
‘ oven embodying the instant invention,'with parts‘.
55 versible electric motor 36 bolted to the bracket
broken away;
Referring to the drawings: .
9,419,600 .
4
' poses. The holes communicate with cooperating
circumierentially spaced holes or apertures 88 in
assembly 25. The motor is operated by suitable
circuits which will be explained hereinarter in
connection with the wiring diagram in Fig. '4.
Air heated by the burner II is circulated
through the drying chamber of the oven by a
rapidly rotating fan'lla which is located within
the duct I2 and which is disposed in axial align
the outer end oi.’ the cylinder for this purpose.
At the end of the purging cycle, the rotary
damper 5'] is closed and a pilot 68 located adja
cent the burner II, is lighted. The pilot is
fan shaft is rotated in any suitable manner by
formed on the inner end of a gas supply tube 80
connected into the main gas pipe I 3 adjacent the
inlet side of the‘ service valve I5. A normally
closed valve 12 connected into the pilot supply
tube is opened at the end of the purging cycle by
fan ll. ' These de?ector elements are secured to
the solenoid ‘I8 of the pilot valve ‘I2 will be more
ment with the burner. The fan is mounted on '
a horizontal shaft 42 iournaled in bearing brack
ets 83 secured in place within the duct I2. The
a connecting solenoid ‘I3. This permits gas to
an electric motor 44, which is indicated in the
wiring diagram in Fig. 4. A pair of spaced and - _ ?ow to the pilot.
Lighting 01 the pilot 68 is effected by a spark
aligned sheet metal i'rusto-conical de?ector ele
ments ‘8 located around and adjacent the burner 15 from a spark plug 15 which is located adjacent
the pilot. The operation or this spark plug and
III direct the‘ heated air toward the circulating
fully explained hereinafter in connection with
the wiring diagram.
transverse support beams 41 secured in place
within the . duct I 2.
‘
Provision is made to safeguard the oven against
explosion when ?rst lighting the burner II or
when relighting the burner if for any reason it
goes out during operation of the oven. This is
brought about by purging the duct I2 and the
drying chamber for a predetermined time cycle oi.’ 25
After lighting the pilot 68, the burner II is ig
nited therefrom by the opening of the main serv
ice valve I5. This is brought about by energiz
ing the-valve solenoid I9 by suitable circuits here
inafter to be explained. These circuits are es
any unburned gases, fumes, or vapors which may
have collected in the oven and around the burner.
pilot 88.
tablished by ionized gas given o? by the lighted
'
Reference should now be had to the wiring dia
gram shown in Fig. 4. In this diagram the cir
It has been found that a time cycle of approxi
culating fan motor 44 is directly connected by
mately three minutes is su?lcient to clear the
three main lead lines 8|, 82, 83, to a suitable
average oven ofunburned gases.
' 30
source of power such as an electric generator
When the burner II goes out, the main gas
85. This constitutes a fan or main circuit A.
service valve I5 closes and cuts oil‘ the supply of
A service switch 86 is interposed in the line to
gas to the burner. Before the .burner' can be
start and stop the Ian motor. Closing of this
again ignited the circulating fan 4| must be in
switch sets the ‘fan in motion and starts the oven
operation or must be set in operation.‘ The set
purging cycle through a control circuit B and a
ting of the fan in operation at the starting of
time delay circuit C which'will now be explained.
the purging time cycle is accompanied by the
The control circuit B includes a conventional
opening of a rotary damper 5| (Figs. 1, 2 and 3)
?ame operated protecting relay unit 88 of the
which admits large quantities of fresh air into
character disclosed in United States Reissue Pat- \
the duct. This unheated air is circulated through
ent 20,210, issued December 22, 1936, to Dewey D.
the drying chamber and is discharged by way
Knowles, on Safety system. Such a unit picks
or a vent pipe.
'
up low voltage current set in motion by ionized
The rotary damper 5| includes a stationary
gas from the burner I I and from the pilot 88 and
hollow cylinder 52 which surrounds the burner‘
this current is ampli?ed‘ to operate certain
supply pipe I3 and which is or may be bolted to
switches in the unit. This unit is supplied with
the burner end of the duct I2. The inner end
electric energy from the generator 85 by way oi
of the cylinder is open and communicates with
a pair of wires 9 I, 92 which connect with the main
the interior of the duct by way or an opening 58
lead wires 8|, 82.
,
formed in the end wall of the duct. The cylin
Hence when the main line service switch 86 is
drical wall or the cylinder is formed with a plu
closed the unit 88 is immediately ‘actuated and
rality of elongated periperally spaced slots 55.
sets a normally closed switch having contacts
The stationary cylinder 52 carries a surround
84, 95 which are included in-the time delay cir
ing sleeve 56 which is formed with a plurality of
cuit C. Contact 94 is connected by a wire 96 to
_ elongated slots 51. Normally these slots are held
the main lead wire 82. Contact 95 is connected by
out of register with the slots 55 in the cylinder
a wire 91 to one side of a solenoid relay 98 having
so that no air passes through them. The sleeve
a movable core 98. The other side of the solenoid
is held in this position by a weight 58 which is
coil is connected by a wire IOI to the main lead
connected to the sleeve by an arm 58. The weight
wire 8|.‘ Electric energy passing along this cir
is ?xed to a plurality of vertical rods 5| which
are connected to a vertically movable member of 60 cuit energizes the solenoid relay 98 and closes a
switch I05 which is actuated by the core 90 of
what may be termed an “oil gear'thrustor unit”
the solenoid. _
which includes an electric solenoid 82. The
' Closing of the switch I05 establishes a motor
“thruster unit” usually is actuated by a motor
circuit ‘D and a damper circuit E. The motor cir
through a solenoid. In order to make the expla
nation‘briei it is su?lcient at this time to show in 65 cuit D is part of the time delay circuit C and in
a
the wiring diagram the solenoid directly connect
ed to the damper.
when the. solenoid 82 is energized the weight
58 and'its arm 58 are raised and this rotates the
cludes a motor I08 and a timing cam I08 that is
rotated by the motor in any suitable manner.
Electric energy for the motor ?ows from the main
lead wire 8I along aconnectlng wire I I I, through
sleeve 58 onthe cylinder and-thus brings theslots; 70. the closed switch I05, a wire II2, motor I08, a
wire “8, a normally closed cam actuated switch
55, 51 into register so. that fresh air will enter‘
I“, and a connecting wire II5 backto the main
the duct I2. An adjustable end plate 88 having
lead wire 82.
circumferentially spaced holes or apertures 85 is
Electric energy passing along this motor cir
clamped on the rotary damper and is provided to
cuit
drives the motor I08 which rotates the cam
75
0 permit air to enter the duct for combustion pur
2,412,090
the spark circuit H and electric energy passes
‘through the-transformer I43 and is induced into
the spark plug ‘I5 to create a spark adjacent the
I99 through one revolution. It is this cam, that
holds the threeminute purging cyclehereinbefore
_mentioned.,- At the completion of said revolution
of the cam, the cam switch ‘I I4 is opened and this
breaks the circuit D.
pilot 58. It is this spark that ignites the pilot..
‘
When the pilot 58 is lighted, ionized gas from
The cam switch motor
thereupon ceases. operation.
V thepilot impinges against a detector element or '
.
electrode I53 which ‘is located adjacent thereto.
The damper circuit E includes the solenoid52
that opens the rotary damper 5|. This solenoid is‘
connected by a wire I ii to one side oi’ the switch
I85 and by a wire II8 to ‘one side of the switch
I I4, as shown in the wiring diagram. Thus when
the switch I85 closes, electric energy passes from
.This electrode is connected by a wire I54 to the
in
ground I48 and by a wire I55 to the ?ame oper- _
ated relay unit 88 hereinbefore mentioned. This
unit is also connected by a wire I55 to the ground.
The -.?ow of ionized gas between theyelectrode
I53 and the ground I 48 sets up a ?ow of low volt
the lead wire 8i, along wire III, closed switch I85, '
age electric energy in the ?ame operated relay
wire II‘LsOlenoid 52, wire II8, closed switch II4,
andwire I I5 back to the lead wire 82. This flow 15 unit 88 and this is ampli?ed sufficiently to‘ open
the normally closed switch bridging the contacts
of energy energizes the solenoid 52 and thus opens
94, 95. It also closes a normally open switch in
- eluding a pair of contacts I5I, I52 located within
' the damper.
The damper 5I remains open for the duration
or the purging cycle. At the completion of this ’ the unit. Contact I5I .is connected by a short
cycle, at which time the switch I I4 opens to break 20 jump wire-to the 'contact 94. Contact I52 is con
the motor circuit D, the damper circuit E is ' nected by a wire I53 to a pivotally mounted nor
mally open conventionalmercury switch I54
broken also and thus the solenoid becomes de
I which is rocked or. its pivot‘into closed position
energized. This closes the damper and it re
by. a vane I55 secured to theswitch. Vane’ I55 is
mains closed until a subsequent purging cycle is
initiated.
I
_
' located adjacent the fan 4| and is disposed in
'
.the path of travel of the air set in motion thereby.
The mercury, switch I55 is connected by a wire
brings the movable element of the switch into '
‘I51 to one side of a solenoid I58 of a relay
. closing engagement with two'normally open‘ con
switch I59 which forms a part of a burner circuit
.tacts I2I, I22 of a holding circuit‘ F which cuts
J. The opposite side of the solenoid coil is con
out the cam motor I88. Contact I2! is connected
nectedby a wire ill 'to the main lead wire 8i.
by a wire I24 to the switch I85 of the motor cir
Hence with the circulating fan M in operation
cuit D. Contact I22 is connected to one side of a ,_
and the vane switch I54 closed, electric energy
solenoid relay I25 which surrounds a movable core
from the main lead wire 82 ?ows along the wire
I25 connecting with the switch element I I4. The ‘
Opening ‘of the cam switch II4 by the cam I89
95, contacts 94, I5I, I52, wire I53, closed vane
switch I54,_.wire_ I51, solenoid-I58, and wire I'IIv
other side of the solenoid is connected by a wire
I2‘! to ‘the main lead wire 82.‘ Electric energy
' passing along this holding circuit energizes the
back to the main lead wire 8I. This electric en
ergy energizes the solenoid I58 and thus closes
the relay switch. I59 for the burner circuit J.
solenoid I25 and thus holds the switch. element
II4 closed against the contacts I2I, I22. This '
maintains the motor circuit D and the damper
circuit E in open condition;
'
' The burner circuit J includes the main gas
valve solenoid I9.‘ One side of the solenoid coil is
'
Connecting the two‘contacts I2I, I22 by the
v I connected by a1wireJI'I5 to the main lead wire 82
switch element I I4 also establishes a pilot circuit U
while the opposite side is connected by a wire I18
to-the relay switch I59. This switch is connected '
G which includes the pilot- gas valve solenoid 1-3
and an auxiliary solenoid relay I3I. Contact I22. 45 bya wire I" to the main lead wire 8|.
Hence closing of the relay switch I69 estab
is connected by a wire I32 to one side of the auxil
lishes the burner'circuit J and permits electric
iary solenoid relay I3I and to a wire I33 which
connects with one side of the pilot valve solenoid ' '
energy toenergize the main gas valve solenoid I9.
13.‘ The opposite sides of these solenoids are con- -
As hereinbefore mentioned the energizing of this ‘
nected by a wire I34 and this wire is connected
solenoid permits opening of the main gas valve
I5 by way of the lever I8 and thus-allows gas to
flow into the burner II. .This gas is immediately
by a wire _I35 to the main lead wire 82.- ,
j
,
Hence when the switch element II4 connects
ignited by the previously lighted pilot 58.
the contacts I2 i, I22 electric energy from thewire
As mentioned above, the switch bridging the
I II passes along the holding circuit F and the
pilot circuit G and thus energizes the two sole 55. normally closed contacts 94, 95 opens simultane
ously with the closing of the switch that bridges
noids ‘I3, I3I. Energizing 0f the pilot gas valve
the normally open contacts I5I, I52. Opening‘
‘solenoid ‘I3 opens the pilot gas valve 1-2 and per
mits gas to ?ow to the pilot 58. Energizing-of the ' v of the switch contacts 94, 95 breaks the time ‘de
lay circuit C and thus deenergizes the solenoid 98
auxiliary‘solenoid‘relay I3I establishes a spark
circuit H which is associated with the spark plug 60 of this circuit. The de-energizing of solenoid 98
opens the switch I85 and thus breaks the motor
‘I15.
.
>
circuit D, the holding circuit F, the pilot circuit
The spark circuit H includes a normally open
switch I38 which» constitutes a part of' thesole-_ . G and the spark circuit H.’ This restores all of
noid relay I3 I. One side of the switch is con-l , . thesecircuits to original open condition in- readi
nessfor subsequent establishment by the same
' JIBOIZEd by a wire Hi to the lead wire 82. The op
posite side of the switchvis connected by a‘ wire. . procedure as just explained, in case the burner I I
I42 to the primary side of a step-uptransformerv ' ' is, extinguished for any reason after it ‘is once
‘I43.
The primary side of the transformer also, ,
' lighted.
-In order to permit of su?icient- time for the
connects by a wire I44 to the'main lead wire 8|.
Thesecondary side of the transformer -is.con, 70 lighting'of the burner II after-the burner cir
cuit J is established, a time delay dash pot I8I
nected toa ground I48 (which may be the oven
may be secured to the movable core of the control
frame) and to one-wire I49 of the'spark: plug ‘I5.
The other wire of the plug is connected to they
ground I48.
-
‘circuit-solenoid 98.'_This dash pot prever’s too
‘rapid an opening of the switch I85 following the
Hence closing of the'relay switch I38 completes‘ 75 opening of the switch that bridges the ?ame op
. 2,412,990
,
erated relay unit contacts 88 and 88. This allows
su?icient time for the burner valve I! to open and
for the burner to be lighted, before the circuits
controlling the pilot 88, act to extinguish the
8
I
.
‘determined period or time to admit fresh air into
the oven for purging it of unburned gases prior
to the lighting of the burner to safeguard the
oven against explosion, said time delay means
pilot. ~
after a‘predetermined period being operative to
If the .fan II is not in operation when an
attempt is made to light the burner or if for any
ignite said main gas burner, and means energized
close said damper and light said pilot burner. to
by a ?ow of ionized gas issuing from the lighted
reason the. fan should stop operating, the gravity
controlled vane switch I84 would be opened and
pilot burner for controlling the actuation or said
.
the circuit leading to the solenoid I88 of the 10 burner control valve.
2. In an oven for drying coated metallic sheets
relay' switch I69 would be broken. The solenoid
and the like, the combination of a gas burner de
I68 would be deenergized and thus the relay
signed for issuing ionized gas for heating the
switch is open. The burner circuit J being bro
oven, a normally closed and locked shut-oil.’ burner
ken under such circumstances, the valve solenoid
l9 would be deenergized. A deenergizing of the 15 valve controlling the ?ow of gas to said burner,
a gas pilot for lighting said burner, a normally
solenoid I9 immediately closes the burner valve
closed pilot valve controlling the ?ow of gas to
I5 and locks it against'opening until the valve
said pilot, electric means for lighting said pilot,
solenoid is again energized.
a fan for circulating air heated by said burner
Opening of the main switch 88 as by manual
actuation disconnects the generator 85 from all 20 through said oven, time delay means connecting
with said pilot valve and with said electric means
for delaying the opening or said pilot valve for
.a predetermined interval of time to insure purg
ing of the oven of unburned gases by said Ian be
of the circuits. All solenoids are deenergized
when their respective circuits are open and the
entire apparatus remains inoperative since all
motors are idle.
After the burner II is lighted its heat output 25 fore the lighting of said pilot, said time delay
means being further operative to commence and
is controlled by a thermo-couple I82 which is
to terminate the purging operation for said pre- I
located within the duct I2 and which is disposed
adjacent the circulating fan II von its discharge
determined time interval, and electric instru-‘
mentalities disposed adjacent said pilot and con
side. The thermo-couple is connected by wires
I83, I88 to a conventional temperature control 30 necting with said burner valve and operable by
electric relay panel I85 which in turn is con
‘ ionized gas issuing from the lighted pilot for un
locking said burner valve to permit the burner
nected by wires I88. I 81. I88, I89 to the reversible
electric motor 36. v This motor it will be recalled
valve to be opened to light said burner by said
opens and closes the regulator valve I6 as it op
pilot after the purging of the oven, thereby safe
erates in forward or reverse.
The motor is con
35 guarding the oven against explosion.
nected by wires I9I, I92 to the main lead wires
82., 83.
-
,
3. In an oven for drying coated metallic sheets
' and the like, the combination of a gas burner de
Thus the thermo-couple I82 detects‘ a tem
signed for issuing ionized gas for heating the
perature higher than a predetermined desired
oven, a normally closed and locked shut-on‘ burner
amount and then acts through the control panel, 40 valve controlling the ?ow of gas to said burner,
to set the motor 38 in operation in one direction
a gas pilot for lighting said burner, a normally
to close the gas regulator valve I8 an amount
closed pilot valve controlling the ?ow of gas to
in accordance with the actual temperature. This
said pilot, electric means for lighting said pilot,
reduces the ?ow of gas and thus reduces the heat
> a fan for circulating air heated by said burner
output of the burner.
45 through said oven, time delay means connecting
When the temperature falls below the prede
with said pilot valve and with said electric means
termined set value, the thermo-couple acts _ for delaying the opening of said pilot valve for
through the control panel to rotate the motor in
a predetermined interval of time to insure purg
the opposite direction to open the valve and thus
ing of the oven of unburned gases by said fan
increase the heat output ofthe burner as re 50 before the lighting of said pilot, said time delay
quired. ‘In this manner the thermo-couple main
means being further operative to commence and
tains the temperature of the air heated by the
to terminate the purging operation for said prede
burner at a constant predetermined value.
termined time interval, electric instrur'nentalities
It is thought that the invention and many of
disposed-adjacent said pilot and connecting with
its attendant advantages will be understood from 55 said burner valve and operable by ionized gas
the foregoing description, and it will be apparent
issuing from the lighted pilot for unlocking said
that various changes may be made in the form,
burner valve to permit the burner valve to
construction and arrangement of the parts with
v be opened to‘ light said burner by said pilot
out departing from the spirit and scope of the
after the purging of the oven, whereby to
invention or sacri?cing all of its material advan
tages, the form hereinbefore described being
merely a preferred embodiment thereof.
I claim:
I
60 safeguard
the oven against explosion, and
means operable by air circulated by said fan
for closing said burner valve when the air fan
'
1. In an oven for drying coated metallic sheets
and the like, the combination of a main gas
burner for heating'the oven, a valve for control
ling the admission of gas to said burner, electric
devices including a pilot burner for lighting said
gas burner, a fan for circulating air heated by '
said burner through said oven, a damper opening 70
into said oven, damper actuating instrumental
ities, time delay=meansoperatively connected to
said damper actuating instrumentalities and also
operatively connected with said burner lighting
' devices for ?rst opening said damper for a pre
stops operating, thereby extinguishing said
burner.
4. In an oven for drying coated metallic sheets
and the like, the combination of a gas burner for
heating the oven, a valve-for controlling the ad
mission of gas to said burner, means for light- '
ing said burner, purging means for exhausting
unburned gases from the oven, time delay means
'‘ interconnected with said burner lighting means
and with ,said purging'meansv for delaying the
.lighting of the burner fora predetermined time
interval after the beginning of the oven purg- ‘
75 ing operation to safeguard the oven against ex
2,412,990»
'
plosion, said time delay means being further op
erative to commence and to terminate the purg—
ing operation for said predetermined time inter
val, a regulator valve disposed between said burner
and said burner control valve for regulating the
?ow of gas to said burner, and means for. actu
ating said valve in accordance with the heat out
put of said burner, thereby maintaining said oven
at a predetermined constant temperature.
5. In an oven for drying coated metallic sheets
and the like, the combination of a gas burner for
heating the oven, a valve for controlling the ad
mission of gas to said burner, means for light
ing said‘ burner, purging means for exhausting
(a4
10
and with said purging means for delaying the
lighting of the burner for a predetermined time
interval ‘after the beginning of the oven purging
operation to safeguard the oven against explosion,
said time delay means being further operative
to commence and to terminate the purging opera
tion for said predetermined time interval, a reguw
lator valve disposed between said ‘burner and
said burner control valve for regulating the ?ow
of gas to said burner, a reversible electric motor
for actuating said valve, and means disposed in
said oven for controllingthe operation of said
motor in accordance with the heat output of said
‘burner, thereby maintaining said oven at a pre
unburned gases from the oven, time delay means 15, determined constant temperature.
interconnected with said burner lighting means
'
ORLIN o. KaUsEQ
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