Portable holding oven for welding electrodes utilizing exhaust heat from welding machine

A portable oven for holding shielded metal arc welding electrodes prior to their use. The holding oven utilizes the heated exhaust gases of a welding machine engine to maintain welding electrodes at an elevated temperature to prevent the absorption of moisture, which would adversely affect the quality of welds. The holding oven includes an insulated outer housing, which is positioned on or near an engine-driven welding machine. An interior rack for the electrodes is mounted in the upper portion of the housing and is accessible through a hinged door. A heat exchanger in the lower part of the housing is coupled to the exhaust pipe of the welding machine and radiates the exhaust heat into the interior of the housing before transferring the exhaust gases to a directional exhaust port. The holding oven may include means for measuring and regulating the interior temperature of the housing to keep the electrodes within a predetermined temperature range. In an alternative embodiment, the holding oven is integral with the welding machine housing.

FIELD OF THE INVENTION 
The present invention relates generally to electrical arc welding, and more 
particularly to portable holding/drying ovens for arc welding electrodes, 
which ensure that welding electrodes are kept dry prior to use to prevent 
defective welds. 
BACKGROUND OF THE INVENTION 
Shielded-metal arc welding (SMAW) is a versatile welding process used for 
forming high quality welds. For example, in gas and chemical piping 
applications, the welds must be of the highest quality because a failed 
weld could be catastrophic. The quality or integrity of the welds are 
generally tested by X-rays or ultrasonic inspection equipment, which will 
reveal defects in the welds. 
Shielded-metal arc welding is also a simple process in principle requiring 
only a high current source, insulated electrical cables, and an electrode 
holder for holding a consumable electrode, which is used to supply 
additional metal to form a continuous weld. Welding electrodes are also 
called welding "rods" or "wires". The high current source is supplied by a 
welding machine, which is basically an engine-powered electric generator. 
A welding electrode for use in SMAW typically consists of a metal core 
surrounded by a flux covering. In the welding process, an electric arc is 
formed between the flux-covered metal electrode and the metal being 
welded. Particularly, the electric arc is generated by touching the tip of 
a coated electrode to the workpiece and withdrawing it an appropriate 
distance to maintain the arc. The heat generated melts a portion of the 
electrode tip, its coating, and the base metal in the immediate area. The 
electrode, as it moves down the length of the weld, is consumed. The 
molten electrode and the base metal must be shielded against the ambient 
atmosphere, which includes oxygen and nitrogen, which may interact with 
the molten metal and cause voids, porosity, and other weld defects. The 
shielding is supplied by the flux coating of the electrode. As the flux 
coating is consumed, it creates a gas shield which protects the weld from 
oxygen and nitrogen during the welding process and also forms a solid 
protective slag, which protects the weld during cooling, which must later 
be chipped away. 
It is clear from the above discussion that the welding electrode with its 
flux coating is the most important element of the SMAW process. The 
composition and condition of the welding electrodes contribute to the 
quality of the welds. For high quality welding work, welding electrodes 
are composed generally of a high tensile strength steel core and an outer 
coating of low-hydrogen material, which may include iron and carbon 
powder. These "low-hydrogen" electrodes avoid the problems associated with 
defective welds, such as voids, porosity, lack of fusion, and slag 
inclusions, which may cause a weld to fail an X-ray inspection, for 
example. The low-hydrogen electrodes are therefore preferable for 
high-quality welding work. Electrodes of this type are commonly available 
from welding supply companies such as Lincoln, Hobart, and Merriam-Graves. 
Low-hydrogen electrodes are identified as 70-series electrodes, and 
include different grades and tensile strengths, identified by American 
Welding Society classifications 7018 through 7024. 
Prior to use in the welding process, low-hydrogen electrodes must be 
properly stored and handled to prevent the absorption of atmospheric 
moisture which would degrade the low-hydrogen coating on the rods and 
result in poor quality welds. Moisture is eliminated by keeping the 
welding electrodes at an elevated temperature within a specified 
temperature range immediately prior to their use. Welding electrodes are 
typically sold in boxes that have a moisture proof packaging. These sealed 
boxes are often carried separately to the work-site, where the welding 
process will be performed. When the packaging is opened, the 
moisture-proofing is breached, and the welding electrodes must be 
transferred to a holding oven as soon as possible, to avoid moisture 
absorption by the welding electrode coating. 
The problem is compounded because high quality welding work often occurs at 
remote locations, which is particularly true for gas and chemical piping 
work, for example. Because welding occurs in remote locations, welding 
machines include gasoline, diesel, or propane powered engines to generate 
electricity used in the arc welding process. 
Portable electrical holding ovens are known for the storage of a small 
number of welding electrodes at the job site. These holding ovens operate 
exclusively on electric current. A number of companies manufacture 
electrode ovens such as Henkel Incorporated of Hammond, La. 
There are two drawbacks to the presently available holding ovens. First, 
the known holding ovens do not hold a large number of electrodes, partly 
because the electric power requirements for heating a large quantity of 
welding electrodes would be excessive. Secondly, all known holding ovens 
are electrically-powered. At a remote welding site in particular, electric 
power outlets are generally not available. Welding machines typically 
include a plurality of electrical outlets for providing power to operate 
power tools, for example. However, portable electric holding ovens are 
often plugged into the welding machine outlets as the only available 
source of electricity at the remote site. A portable electric holding 
oven, when powered from the welding machine, puts a high electrical load 
on the welding machine, causing the welding machine engine to operate 
constantly at fast idle. This causes a greatly increased ambient noise 
level for the welding operator and excessive fuel consumption for the 
welding machine. 
The present invention overcomes the disadvantages of the prior portable 
holding ovens, such as the requirement for electric power at remote 
locations. 
SUMMARY OF THE INVENTION 
A solution to the problems of prior electrode ovens is provided in the 
present invention, which furnishes the needed elevated temperatures and 
drying effects for welding electrodes in a portable holding oven, which 
operates without electricity. The present invention thereby avoids the 
problems of prior art ovens, which place a significant electrical load on 
the welding machine engine, causing it to fast idle. 
The present invention is a portable holding oven for welding electrodes 
which utilizes the exhaust heat of the welding machine engine to keep a 
large quantity of electrodes at an elevated temperature for extended 
periods of time. 
The holding oven includes an insulated, weatherproof outer housing of 
sufficient size to hold up to 50 pounds of welding electrodes. The 
interior of the housing includes a box-shaped electrode rack mounted in 
the upper portion of the housing for holding various types of electrodes 
on perforated shelving. A heat exchanger, in the lower part of the 
housing, receives heated exhaust gases from the welding machine exhaust 
and transfers the heat to the interior of the housing. The heat rises 
upwardly into the electrode rack, passing through the perforated shelves 
and elevating the temperature of the welding rods being held therein. The 
welding machine exhaust continues through the welding machine and exits 
the housing by means of an exhaust pipe. The housing includes an access 
door to provide the user with access to the electrode rack, for inserting 
and removing the electrodes, as needed. The door is gasketed and includes 
a tension latch to provide a tight seal. The door includes a thermometer 
to provide temperature readings inside the housing. 
In use, the oven is placed on top of the welding machine. The exhaust from 
the welding machine is piped directly into the back of the oven through a 
connecting pipe which is custom contoured to fit the engine exhaust 
location of each make and model of welding machine. The connecting pipe is 
fitted with an insulated waterproof sleeve to prevent contact burns. This 
connecting pipe is attached with clamps so the oven is easily removed, yet 
stable enough for travel. 
In an alternative embodiment, the holding oven is built into the housing of 
a welding machine and is integral with it. The electrode heating process 
is the same as in the portable unit except that heat is utilized directly 
from the welding machine's exhaust system, before the exhaust exits the 
welding machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning initially to FIG. 1, a portable holding oven 10 in accordance with 
the present invention is shown installed for use on an arc welding machine 
12. In the figure, the holding oven 10 is shown supported on the welding 
machine housing 14. The portable holding oven 10 of the present invention 
is used in conjunction with the welding machine 12; therefore, the basic 
structure and operation of a typical welding machine 12 will be discussed 
in detail in what follows. 
The welding machine 12 functions as an engine-powered electrical generator 
to provide a regulated source of electric current for the welding process. 
Welding machines are available in different sizes and configurations. 
The welding machine 12 would be used by a single operator in performing the 
arc welding process. Welding machines are typically powered by gasoline, 
diesel, or propane fueled engines. The welding machine 12 may be, for 
example, a Bobcat Model 225NT welding machine manufactured by Miller 
Electric Manufacturing Company of Appleton, Wis. In the preferred 
embodiment, the welding machine 12 in FIG. 1 includes a gasoline-fueled 
engine generally located within the rear portion 16 of the welding machine 
housing 14. The gasoline fuel tank is located in the base 18 of the 
welding machine 12. 
A welding machine 12 such as the one shown in FIG. 1 might typically be 
transported in the back of a pickup truck to a construction site, where 
the arc welding process is being performed. Less commonly, the welding 
machine 12 may also be installed on a trailer which would then be towed by 
truck to the work site. The welding machine 12 weighs approximately 
six-hundred pounds. The welding machine housing 14 is approximately 36 
inches in height, 18.75 inches in width and 48 inches in depth. These 
physical dimensions are sufficient to provide a platform-like area on the 
top of the welding machine housing 14 to support the holding oven 10 of 
the present invention. 
The welding machine 12 incorporates a front panel 20, which includes a 
number of operator controls. In the upper right of the front panel 20, 
engine controls include an electric starter switch 22, an engine idling 
adjustment control 24, and an elapsed hours meter 26. In the upper left of 
the front panel 20, a range selector switch 28 provides selection of 
overlapping output AC & DC current ranges (for example, 50-100 amperes; 
70-150 amperes; 85-225 amperes). A rotary switch 30 controls fine current 
selection within each range selected by the range selector switch 28. 
Various electrode sizes and compositions require different current 
settings for the welding process. A process selector switch 32 provides 
the selection of output options to support various types of arc welding 
processes, such as SMAW (shielded metal arc welding), FCAW (flux-cored arc 
welding), and GMAW (gas metal arc welding) processes. The present 
invention relates to the proper conditioning and handling of welding 
electrodes for high-quality SMAW welding processes, which is also known as 
manual metal arc (MMA) or stick welding. 
The front panel 20 includes terminals 34 and 36 for the attachment of two 
heavily-insulated welding electrode cables. As previously stated, in the 
SMAW process, the welding machine 12 generates a high current source of 
electricity sufficient to melt a coated welding electrode. One cable is 
the negative ground cable, which terminates in a brass spring-loaded clamp 
that securely clamps to the workpiece. The other cable terminates in an 
electrode holder, which accommodates various-sized welding electrodes and 
includes a tightening means for firmly clamping a welding electrode in 
place; the electrode holder also acts as a handle for the operator and is 
designed to insulate the operator from the high electric currents used 
during welding. 
The front panel 20 includes one 240-volt outlet 38 and two double 120-volt 
outlets 40 and 42 for powering auxiliary equipment--such as grinders, 
drills and other tools--as may be needed at the welding site. A 
conventional electric-powered holding oven would use one of these power 
outlets. 
The welding machine 12 shown in FIG. 1 typically operates for 12 hours at 
slow idle on a single tank of gasoline fuel. Slow idle is a relatively low 
noise, low fuel consumption operating state. To perform the welding 
process, the operator increases engine speed by selecting fast idle with 
the idling adjustment control 24. In contrast, fast idle is a high noise, 
high fuel consumption operating state. When the welding machine 12 is 
being used continuously in the welding process, the fuel usage increases 
and the welding machine 12 typically operates for eight hours on the same 
quantity of fuel. When the welding machine 12 is not being used in the 
welding process, other electrical loads as provided through the outlets 
38, 40 and 42 will cause the welding machine 12 to switch to fast idle, 
and the noise level will be much greater and fuel consumption will 
increase. It is therefore advantageous to limit the load on the engine 
exclusive of the power used in the welding process. As stated, prior 
electrically-powered holding ovens, designed to be used at a work site, 
have the disadvantage of causing the welding machine engine to operate at 
fast idle at all times while in use, thereby causing high noise pollution 
levels and excessive fuel consumption rates. The holding oven 10 of the 
present invention avoids these disadvantages by utilizing the exhaust heat 
discharged from the welding machine engine, as will be described. 
The welding machine 12 includes an engine exhaust pipe 44, which protrudes 
through an aperture in the top rear of the welding machine housing 14. 
Some welding machine designs have the engine exhaust pipe 44 exit through 
the side of the welding machine housing 14, but the same principles of the 
invention apply. 
The engine exhaust pipe 44 expels heated exhaust gases from the engine of 
the welding machine 12 in a typical manner. The holding oven 10 includes 
an intake pipe 46. In FIG. 1, the engine exhaust pipe 44 of the welding 
machine 12 is shown coupled to the intake pipe 46 by means of an 
intermediate pipe section 48, custom-shaped for the particular application 
and rigidly connected by conventional muffler clamps. 
As shown in FIG. 1, the holding oven 10 is conveniently supported on the 
top surface of the housing 14. However, it is anticipated that the holding 
oven 10 of the present invention may be used with all types of welding 
machines including those of considerably smaller size. For smaller sized 
welding machines, the holding oven 10 may be positioned alongside the 
welding machine 10 instead of on top of it, provided that the engine 
exhaust pipe 44 may be coupled by intermediate piping connections 48 to 
the intake pipe 46 of the holding oven 10. 
Turning now to FIG. 2 and FIG. 3, the major exterior and interior features 
of the holding oven 10 are shown. The present invention is a portable 
holding oven for drying metal arc welding electrodes, which is to be used 
at the site where the welding process is being performed. Such locations 
may be remote from electrical power sources, except for the power 
receptacles 40, 42 provided by the welding machine 12 itself, which are 
used to power conventional portable holding ovens. As stated, the holding 
oven 10 of the present invention is used at the site where the welding 
process is being performed, and has the advantage of not requiring 
electrical power, which would adversely affect the welding machine, 
causing it to run at high idle, as electrical holding ovens do. 
The exterior of the holding oven 10 is shown in FIG. 2. The holding oven 10 
includes the main features of a housing 50 which has a faceplate 52 and 
backplate 54, an access door 56 for inserting and removing welding 
electrodes, an intake pipe 58 for receiving exhaust gases from the welding 
machine 12; an exhaust pipe 60 for expelling the exhaust gases from the 
holding oven 10, including a swivel head 61; and carry handle 62. 
The internal components of the housing are shown in FIG. 3, which is a 
front view illustration of the holding oven 10 with the faceplate 52 
removed from the housing 50, so that the interior may be viewed. The 
interior of the housing 50 includes an electrode rack 64 for supporting 
the electrodes within the housing 50 and a heat exchanger 66 for radiating 
heat into the interior of the housing 50. 
The housing 50 is fabricated from corrosion-resistant galvanized steel. The 
housing 50 is roughly ten inches wide by fifteen inches high by sixteen 
inches deep. The dimensions are somewhat determined by the size of welding 
electrodes to be heated within the housing. With the dimensions of the 
preferred embodiment, all common welding electrode types can be 
accommodated. It is anticipated that once the holding oven 10 is filled 
with electrodes, the electrodes will be kept in the holding oven 10 until 
they are used up. In the preferred embodiment, the welding oven 10 is 
designed to hold up to 50 pounds of welding electrodes. It follows that 
situations may arise where the user may need to carry or otherwise 
transport the oven with up to 50 pounds of welding electrodes inside. 
Therefore, in the preferred embodiment, the housing 50 is rigid and sturdy 
enough to survive normal use and transport while being fully loaded with 
welding electrodes. The carry handle 62 is bolted to the top of the 
housing 50. Likewise, the carry handle 62 and its connection to the 
housing 50 must be strong enough to support the weight of the holding oven 
10, including a full load of welding electrodes. 
The housing 50 along with the faceplate 52 and the backplate 54 are sealed 
to form an airtight enclosure. The faceplate 52, covers the front of the 
housing 50, and the backplate 54 covers the rear of the housing 50. The 
faceplate 52 and backplate 54 are welded to the housing 50 to form an 
airtight seal, to prevent leakage of moisture into the housing 50. The 
faceplate 52 includes cutouts for the access door 56 and for the exhaust 
pipe 60. The backplate 54 includes a cutout for the intake pipe 58. 
The access door 56 door includes a hinge 68, a tension latch control 70, 
and a thermometer 72. The access door has a sandwich structure including a 
layer of insulation so that heat is not conducted from the interior of the 
housing 50 to the exterior of the access door 56. This prevents heat loss 
through the access door 50 and also provides a safety function to prevent 
burns to the hands of an operator using the holding oven 10. During a 
typical working day, as the welding process is being performed, the access 
door 56 will be opened and closed numerous times as the welding electrodes 
are removed, generally in small bunches, as needed. 
The access door 56 pivots outwardly and downwardly to provide convenient 
access to the electrode rack 64 for inserting or removing welding 
electrodes. The door is supported for movement by a piano-type hinge 68, 
running the length of the lower edge of the access door 56. The access 
door 56 includes a gasket 74 around its edge to provide a moisture-proof 
seal. The access door 56 closes with a tension-latch control 70, which is 
pushed inwardly and rotated to squeeze and lock the access door 56 tightly 
against the faceplate 52 to ensure a watertight seal. Alternatively, the 
access door 56 could be spring-biased so that it would tend to close when 
released by the operator. Any other type of latch may be used to perform 
the same function as long as the access door 56 is held tightly closed and 
the seal is maintained to isolate the interior of the housing 50 from 
atmospheric moisture which could contaminate the welding electrodes. 
The access door 56 also includes a small thermometer 72, mounted 
externally, to provide the operator with an indication of the temperature 
in the interior of the housing 50 in the proximity of the electrode rack 
64. Alternatively, the thermometer 72 could be mounted inside the access 
door 56 or on the electrode rack 64 itself. 
The interior of the housing 50 includes a layer of insulation 76 as shown 
in FIG. 3. The electrode rack 64 is separately insulated by a layer of 
insulation 78 on its top and sides but not on its bottom. In the preferred 
embodiment a dense heat-resistant, fiberglassbased insulation is used. The 
insulation layer 76 extends to the lower part of the housing under the 
heat exchanger 66 itself. The function of the insulation layer 78 is to 
keep the heat in the electrode rack 64. The function of the insulation 
layer 76 is to ensure that the heat radiated from the heat exchanger 66 is 
contained within the housing 50, and that the heat is not conducted to the 
external surface of the housing 50. Once again, the purpose of the 
insulation layer 78 is to prevent heat loss and burns to the hands of an 
operator using the holding oven 10. 
Also shown in FIG. 3 are rubber feet 80. The four rubber feet 80, mounted 
to the underside of the housing 50 near its corners, prevent slipping of 
the holding oven 10 when positioned on top of the welding machine 12 
during operation of the welding machine 1 2. This is necessary because the 
welding machine 12 vibrates slightly during operation. Without the rubber 
feet 80, the direct contact of the oven housing 50 with the welding 
machine housing 14 would cause scratches and marring to the welding 
machine housing 14. Generally, there is no concern with the holding oven 
10 moving significantly or falling off the edge of the welding machine 
housing 14 because it is held in operating position by the weight of the 
holding oven 10 and by the rigid pipe connection 48 to the welding machine 
exhaust 44. 
Turning now to FIG. 4, the electrode rack 64 is shown in more detail. The 
electrode rack 64 holds the welding electrodes in the housing 50. The 
electrode rack 64 is a welded box like structure, opened at the front, 
fabricated from stainless steel. The electrode rack 64 is designed to hold 
50 pounds of electrode electrodes. On a typical day, an operator will 
typically use ten to twelve pounds of welding electrodes. The size of the 
electrode rack 64 is somewhat determined by the dimensions and quantity of 
the welding rods it will hold. The length of an electrode is typically 
fourteen inches long. These include 70-Series rods, which are the type 
most commonly requiring heating in a holding oven. In the preferred 
embodiment, the electrode rack 64 has a depth dimension 82 of 
approximately sixteen inches to provide sufficient tolerance for loading 
and unloading the rods when the access door 56 is open. 
In the preferred embodiment, the electrode rack 64 has two shelves, 84 and 
86. The shelves 84 and 86 are fabricated from thin stainless steel and 
includes perforations 88 and 89. The perforations 88 and 89 allow the heat 
radiated from the heat exchanger to rise through the shelves 84 and 86 to 
reach the welding electrodes stored on both shelves 84 and 86. Stainless 
steel was chosen for the preferred embodiment because it is light weight 
but strong enough to support the maximum weight capacity of welding 
electrodes. It is also contemplated that the electrode rack could be 
manufactured from other galvanized corrosion resistant material with 
perforations punched therein, to reduce manufacturing cost. The more 
perforations 88 and 89 included in the shelves 84 and 86, the more 
effectively the heat will pass through the shelves 84 and 86, providing 
even heat distribution around the welding electrodes and efficient 
operation of the holding oven 10. 
Alternatively, the electrode rack 64 could have three shelves for handling 
a greater quantity of welding electrodes, or a single shelf for holding a 
smaller quantity of welding electrodes. Also, the shelves 84 and 86 could 
be partitioned into multiple sections, each for holding a different type 
of welding electrode. All these variations are within the scope of the 
present invention, and the principles of the present invention still 
apply. 
The heat exchanger 66 will now be described in connection with FIG. 5, FIG. 
6, and FIG. 1. As stated, the welding machine exhaust pipe 44 provides 
sufficient heat for the drying of the welding electrodes. The purpose of 
the heat exchanger 66 is to transfer this heat from the exhaust pipe 44 of 
the welding machine 12, without allowing the exhaust gases to come into 
direct contact with welding electrodes in the welding oven 10. 
Furthermore, the heat exchanger 66 performs its function without 
restricting the exhaust flow from the welding machine 12. Restricting the 
exhaust flow of the welding machine 12 would interfere with smooth 
operation of the welding machine 12. 
The heat exchanger 66 includes an intake pipe 46, two heat transfer 
sections 90 and 92, two radiator sections 94 and 96, and an exhaust pipe 
60. The intake pipe 46 is constructed of steel tubing having an inside 
diameter of 1.5 inches, the same as the exhaust pipe 44 from the welding 
machine 12. The connection from the exhaust pipe 44 to the intake pipe 46 
is by means of a hard-piped, rigid intermediate pipe section 48 connected 
by conventional muffler clamps. A rigid intermediate pipe 48 was chosen 
because flexible piping absorbs and radiates excessive amount of the 
exhaust heat; therefore, the heat loss would be excessive before the 
exhaust gases reach the heat exchanger 66 inside the oven housing 50. The 
purpose of the intermediate pipe section 48 is to conduct maximum heat 
through the intake pipe 46 to the heat enchanger 66. 
The single intake pipe 58 pipe brances out into two parallel heat transfer 
sections 90 and 92. The heat transfer sections 90 and 92 include radiator 
sections 94 and 96. The radiator sections 94 and 96 are constructed from 
stainless steel bellowed piping. The bellowed piping is basically 
flexible-connection tubing which absorbs and radiates the heat passing 
through the heat exchanger 66. Flexible-connection tubing is thin walled 
and has been found to heat up and radiate heat very quickly. The bellowed 
piping has an inside diameter of 1.5 inches; maintaining the same diameter 
piping throughout ensures that the exhaust flow will not be restricted. 
The two radiator sections 94 and 96 increase the heat transfer of the heat 
exchanger, while not restricting the exhaust flow, which would negatively 
affect the performance of the welding machine 12, as stated. After the 
heat transfer operation, the radiator sections 94 and 96 recombine and 
exit the heat exchanger 66. 
The heat exchanger is anchored in the lower interior of housing 50 by 
clamps. In the preferred embodiment, a single intake pipe 46 branches out 
into two heat transfer sections 90 and 92. It is contemplated, however, 
that three or more heat transfer sections may be used. 
In operation, the exhaust gases from the welding machine 12 pass through 
the heat exchanger 66 but do not directly enter the housing 50 where the 
welding electrodes are being held. Exhaust gases contain chemical 
contaminants which would have an adverse affect on the welding rod 
coating. The heat exchanger 66 radiates the heat into the housing 50 but 
isolates the exhaust. Therefore, it is cautioned that perforated piping 
can not be used as a heat exchanger material. Alternatively, the heat 
exchanger 66 could be fabricated from aluminum, or with aluminum radiator 
sections 94 and 96. Aluminum is a better conductor of heat than steel; 
however, the connections would need to be dry connections made with 
muffler-type clamps, because steel can not be welded to aluminum. Also, 
alternatively, the heat radiator sections 94 and 96 could include 
radiating vanes which would increase the surface area of the radiator 
sections 94 and 96 to increase the efficiency of heat transfer, much like 
a conventional radiator. As another alternative, copper could be used for 
improved heat transfer in the heat exchanger 66. 
The heat transfer sections 90 and 92 converge into a single exhaust pipe 60 
which exits through the front of the holding oven 10. 
In FIG. 6, the heat flow within the holding oven is diagrammatically shown. 
Exhaust gases leave the exhaust pipe 44 of the welding machine 12, and are 
conducted through the intermediate pipe 48 into the intake pipe 46 of the 
heat exchanger 66. This transfer of exhaust gases takes place with very 
little heat loss. Alternatively, a waterproof insulating sleeve 98 may be 
used to cover the entire exposed connection from the exhaust pipe 44 
through and including the intake pipe 46. The insulating sleeve 98 ensures 
that the heat loss would be minimal. Besides making the holding oven 10 
more efficient by minimizing heat loss, the insulating sleeve 98 protects 
the user from burns to the hand, which could result from coming into 
contact with exposed steel piping. The exhaust gases enter the heat 
exchanger 66, passing into heat transfer sections 90 and 92. The radiator 
sections 94 and 96 rapidly heat up, raising the temperature of the air in 
contact with the exterior of the radiator sections 94 and 96. The heated 
air rises upwardly to the electrode rack 64 and passes through the 
perforated shelve 86, heating the welding electrodes 100 stored on the 
perforated shelf 86. The heated air continues to rise upwardly through the 
perforated shelf 84 to heat the welding electrodes 102 stored on 
perforated shelf 86. In the heat go exchanger 66, the exhaust gases 
continue to flow and exit the heat exchanger 66 at the exhaust pipe 60. 
The exhaust pipe 60 passes through the faceplate 52 and terminates in a 
swivel head 61 to divert the exhaust in a user-chosen safe direction. The 
swivel head 61 is necessary because the exhaust gases exit the holding 
oven 10 at high temperature. 
Turning now to FIG. 7, a temperature regulation mechanism 103 is shown 
which may be used with or as part of the present invention to keep the 
temperature internal to the housing 50 within a chosen temperature range, 
generally between 100 and 150 degrees Fahrenheit. The temperature 
regulation mechanism 103 includes an intermediate pipe 104 for connection 
between the exhaust pipe 44 of the welding machine 12 and the intake pipe 
46 of the welding oven 10. If the thermometer 72 indicates that the 
interior temperature of the holding oven 10 has exceeded the prescribed 
range, the user would open a first manually-operated knife valve 106 which 
would allow the exhaust gases to exit through a bypass pipe 108. The end 
of the bypass pipe 108 includes a swivel head 110, so that the exhaust 
flow may be directed in any user-selected direction, as desired. In 
addition, the user engages a second manually-operated knife valve 112, 
which closes off the exhaust flow to the holding oven 10. When the 
thermometer 72 indicates that the internal temperature of the holding oven 
10 has dropped within the specified heat range, the process is reversed. 
The second manually-operated knife valve 112 is opened, allowing the 
exhaust flow to re-enter the holding oven 10, and the first 
manually-operated knife valve 106 is engaged, shutting off the bypass pipe 
108. 
It is contemplated that the regulation mechanism 103 may be separate from 
the holding oven 10 or be integral with it. For example, the first and 
second manually-operated knife valves 106 and 112 could be permanently and 
conveniently mounted in the backplate 54 where the intake pipe 46 enters 
the housing. 
The holding oven 10 according to the present invention will generally 
operate within an acceptable temperature range without the regulation 
mechanism 103, as welding electrodes can not be harmed by highly elevated 
temperatures. For example, some drying ovens for welding electrodes are 
known that heat the welding electrodes up to 500 degrees Fahrenheit. The 
present invention does not require extremely high temperatures to be 
effective. 
Turning now to FIG. 8, an alternative embodiment is shown, in which a 
welding machine incorporates an intergral holding oven. The welding 
machine 114 includes an upper housing 118, and a holding oven compartment 
120. The holding oven compartment 120 is located over the exhaust pipe 
area of the welding machine 114. The holding oven compartment 120 includes 
an access door 122, an electrode tray 124 made of perforated stainless 
steel, and an exhaust pipe 126. Functionally, the exhaust piping from the 
welding machine engine is routed under the holding oven compartment 120. 
The exhaust piping may include a heat exchanger. Heat from the exhaust 
piping rises through the perforations in the electrode tray to heat the 
welding electrodes stored thereon. The exhaust piping then continues out 
the exhaust pipe 126. The integral holding oven compartment 120 is 
conveniently manufactured to be part of the welding machine 114. 
Alternatively, existing welding machines may be retrofitted to include the 
holding oven compartment 120 by replacing the conventional upper housing 
118 with a replacement that includes the holding oven compartment 120. The 
holding oven compartment 120 includes all the housing insulation and 
moisture-proofing as described in connection with the portable holding 
oven 10 of the present invention, and any or all of its other described 
features. 
The description of the invention has been directed to certain exemplary 
embodiments. Various modifications of these embodiments, as well as 
alternative embodiments, will become readily apparent to those skilled in 
the art. For example, various economies of construction may be obtained by 
manufacturing the housing 50 out of heat-resistant plastic. Also, the 
housing 50 may include means for venting moisture to the exterior 
atmosphere. Further, various electrically-operated thermostatic valves 
could provide a more precise regulation of the interior temperature of the 
oven housing. These and other modifications are certainly within the scope 
of the present invention. Accordingly, the description is to be considered 
in all respects only as illustrative and not restrictive. The scope of the 
invention is indicated by the appended claims rather than by the foregoing 
description, and all changes which come within the meaning and range of 
equivalency of the claims are to be embraced within their scope.