By J.W. GUANCI, III – PRECISION QUINCY CORP.
Virtually every manufactured product requires the introduction of heat at some point during the production process. Purchasing the
proper piece of thermal processing equipment is rarely an easy or a casual consideration. Reputable oven manufacturers share those
exact sentiments, in that they will consider a customer’s application, production needs and concerns seriously.
It is also understood that multiple issues become intertwined to create a series of details which must be resolved before trust is gained
and equipment is purchased. This text serves only as a general guide to heat processing equipment and the issues which must be
considered in order to select the proper oven, as well as the appropriate options and features. Of course, for an application specific
diagnosis, consultation with a member of your oven manufacturer’s sales team is always recommended.
The Fundamentals: What Are Ovens?
Ovens are insulated enclosures or tunnels which operate at temperatures from slightly above ambient to 250°F (676°C). Loading
configurations take two essential forms, batch or continuous with the more common sources of heat being electricity, gas (natural or
propane), steam, hot water and fuel oil. As for the means by which heated air is introduced into the work area, it is commonly
accomplished with forced convection.
Laboratory vs. Industrial Batch vs. Continuous Ovens
The three essential categories of ovens are laboratory, industrial batch and continuous process -- with the distinguishing
characteristics being construction, product handling functions and flexibility.
Laboratory units have a typical temperature range of slightly above ambient to 650°F (343 °C) and can range in size from 2 to 32 cubic
feet. Construction differs from industrial batch ovens in that lab ovens have positive latch doors, pressure release panels, stainless
steel interiors, solid state controllers & contactors, an epoxy/chemical resistant exterior coating and an extended multi-year warranty.
In terms of how a laboratory oven is utilized, its capacity lends itself towards test samples or light duty production of “smaller” parts
and product.
Industrial batch type units operate at temperatures from slightly above ambient to 1250°F (676 °C) and range in sizes from 3 cubic feet
and up. The two general categories of industrial batch ovens are shelf/cabinet and truck/walk-in. Typical features include aluminized
steel interior, fully adjustable duct work, scratch resistant enamel paint on the exterior, digital set-point controller, UL listed control
panel and a one year warranty. These units are suited for the processing of larger quantities of product in a single batch.
Conveyor units tend to be less flexible than batch ovens because they are usually designed for a specific product or production rate.
Temperature ranges are the same as the industrial batch, up to 1250°F (676°C), and operate on a continuous or on an indexing basis
through one or multiple heat zones. Conveyor units tend to be oriented toward automated production in greater quantities of small to medium sized product. The type of conveyance system depends on the product line, the volume of work to be produced as well as the temperature to be obtained.
Air Flow Patterns
The type of air flow is an important and essential component to successful oven selection and operation. If the wrong air flow is
coupled with the wrong product loading configuration, the results could be very undesirable. There are six basic types of airflow which
are commonly utilized:
- Horizontal/Vertical
- Vertical/Horizontal
- Vertical/Top Down
- Vertical/Bottom Up
- Full Horizontal
- Full Horizontal/Vertical
Horizontal/Vertical air flow is when the air is supplied from the side walls of the oven and is returned to a duct or opening on the
ceiling of the oven. It is most applicable in those production situations where the parts are larger in nature and are loaded into the
oven on a flatbed cart or skid.
Vertical/Horizontal is when the supply duct is located on the oven ceiling and the return ducts are located on each side wall and is
typically used when a vertical type air flow pattern is needed in a truck or walk-in oven.
Both vertical/top down and vertical/bottom up are suited for those production scenarios where the product is going to be hung or when the parts are smaller in size which are then placed on perforated shelves. It is important to remember that if shelves are to be used with this pattern that they be designed so as to let the air pass from the supply to the return duct with minimal obstruction.
A full horizontal air flow pattern is designed for those products which are loaded into the oven on shelves or if the product is to be
hung. This combination of loading configuration and air flow allows the recirculated air to pass above and below each shelf, encircling
the product with air.
Finally, a full horizontal/vertical air flow pattern is best suited for those applications which require extremely tight temperature uniformity in a horizontal/vertical air flow pattern or when two shelf carts or hanging carts will be loaded into the unit side-by-side with a space between them, so the air may travel to a top return duct without obstruction.
All ovens have one common element in the realm of air flow: the air needs to pass, with minimal restrictions, from the supply duct to
the return duct. If properly adjusted, this will bring about good temperature uniformity, a topic of the next section.
Temperature Uniformity & Control Sensitivity
Uniform temperatures within the oven work area helps to ensure a uniform product, there are several issues which need to be
described and defined:
- Temperature Uniformity
- Control Sensitivity
Temperature uniformity is defined as the greatest spread of deviation, in °F and/or °C, between the highest and the lowest points
within a given work area. For example, it is important to note that ±5°F actually represents a difference of 10°F.
As for the factors which impact work area uniformity: controller calibration; thermocouple calibration/placement; oven temperature; air
circulation (CFM); air flow pattern/loading configuration; heat losses via walls; metal to metal contact; placement of the load within the
oven.
Also, as mentioned under the Air Flow Pattern portion of this text, the loading configuration has to be properly mated with the
appropriate air flow. If it is not, then the air may be cut off or reduced to such an extent that good uniformity within the unit may be
lacking. For example, if a process has product which is set upon flat/solid shelves, the vertical air flow pattern would be the most
inappropriate. In this case the air would be blocked and not allowed to follow the desired path to the return duct, and since ovens
transfer heat via the movement of air, the oven will not perform as desired. Continuing with the example, if flat solid shelves are
coupled with a full-horizontal air flow pattern, the oven will perform properly with the air flowing above and below each shelf.
At this point, let's assume the proper flow has been selected in relationship to the product and loading style at hand. Now it is
important to identify those other major oven characteristics which improve the oven’s uniformity and performance.
The first of these is the volume or cubic feet per minute (CFM) which passes through the work chamber. As a general statement, there
are some exceptions: the more CFM an oven produces, the better the uniformity and the resulting product.
The second point, which is closely linked to the first, is that the fan and motor must be sized properly and rated for the oven’s rated maximum temperature. As the air rises in temperature, it becomes thinner and lighter, consequently, a motor and fan are still required
to provide an appropriate amount of CFM. This is most easily accomplished with a fan that is rated to stand the higher temperatures of
the oven heat chamber.
The third major component is the interaction of the air, both fresh and recirculating, and the heat source. The return duct and fresh air
inlet must be strategically placed so that the recirculated air and the fresh air meet at a given point. This should be on the negative
side of the fan, prior to its continuing past the chosen source of heat. Upon exiting the supply duct, into the oven work area, some of
the air will pass to the return duct and the rest will be ventilated out of the exhaust port or forcefully exhausted out of the work area by
a powered exhaust system. Furthermore, by positioning the fresh air inlet and the ventilation/exhaust opening properly, a slight
positive pressure will develop, ensuring that fresh air is introduced into the unit at the fresh air inlet and not at possible leak spots (i.e. -
door seals).
The fourth overriding factor which will impact the uniformity and performance of an oven is the means by which it is balanced and
tested at the factory. A proper test is that which utilizes at least a 10 point thermocouple profile with 9 points placed in the work area,
at least 4 inches from all interior surfaces, and the 10th point being integrated with the controller/programmer. This allows a manufacturer to ensure that the oven’s actual temperature and the temperature which is registered by the controlling device to be
accurate. Also, the profile ought to be started at ambient to the oven’s rated maximum temperature. The benefit in this is being able to
trace the performance of the oven throughout the range of operation.
Note: Higher CFM, motor sizing, fan design, proper fresh air to exhaust ratios and placement all become increasingly critical
to the successful balance of an oven, especially at higher operating temperatures. With the proper equipment, design,
components and factory tests, consistently good result should be had over years and years of use.
A second major issue is control sensitivity, which is the ability of a control instrument to not only measure, but to react to, temperature
fluctuations at a given set point. This issue is important for one simple reason: if an oven’s instrumentation is not reading accurately,
then it cannot respond accurately.
For example, an oven may have a uniformity reading of +2°F and a set point of 300°F, yet, the control sensitivity may be poor, with
temperature "swings" over and below the set-point of 25 degrees. The result: the oven will perform poorly, even with a tight
temperature uniformity reading, due to the lack of control sensitivity and being able to hold the oven at a given set-point.
Sources of Heat
Naturally, one of the most important decisions to make when selecting thermal processing equipment is choosing the proper heat
source for your process. The following list represents the six more commonly used sources:
- Electric Heated
- Direct Gas Fired
- Indirect Gas Fired
- Steam Heated
- Hot Water Heated
- Oil Fired
Electric-heated. These units are the most prevalent, are powered by Incoloy sheathed heating elements, expressed in terms of KW, which are
manufactured to provide long life and quick heat-up times. Also, electric ovens, when in a Class “B” configuration, are not as costly to
purchase, are clean/non-polluting and are more appropriate for those applications where a direct gas fired heat source cannot be
applied successfully. An example of just such a process is the aesthetic production of aluminum, which would be “yellowed” or
marred by the products of combustion produced by a direct gas fired unit. In this case an electric heated oven would be the most
appropriate.
Direct-gas-fired. The ovens are another very common source of heat, expressed in BTUs/Hr., and can be equipped to handle either natural
gas or propane. These ovens can be more expensive than electric units to purchase due to the fact that they are Class “A”
automatically due to the products of combustion. In that sense, gas ovens offer more flexibility due to the presence of the required
NFPA safeties (to be discussed later). Finally, to offset the initial purchase price, the cost of operating a direct gas fired unit is only 25-30% of their electric heated counterparts, which can pay big dividends in the long run.
Indirect-gas-fired. These ovens fire into a stainless steel heat exchanger which is then vented to atmosphere, allowing for a clean process by
keeping the products of combustion from the work area. As compared to direct gas fired ovens, the initial purchase cost is greater and
their efficiencies are rated at approximately 70 percent, yet, they are still twice as efficient as an electric heated equivalent and cost
less to operate.
Steam-heated. These ovens present a viable alternative when the appropriate circumstances present themselves. The first component is
when a facility already has steam in sufficient quantities, measured in PSI, to obtain the desired temperature. Furthermore, the
application must be in the lower temperature ranges of approximately 300°F or below the process cannot accept a “red hot” source of
heat (heater elements or a burner); quick time-to-temperature is not of critical importance. In this scenario, steam would be not only
very cost efficient, but would also be a very clean means of processing product.
Hot-water-heated. This a source of heat, is similar to the steam heated unit mentioned above except that the temperature range tends to be
more constricted, approximately 160°F and below. Essentially the hot water will travel through “radiator coils” in sufficient quantities,
it will emit heat and the recirculating air will be warmed and carried into the work area. In terms of efficiency, cleanliness and
compatibility with certain processes, hot water heated ovens provide a very viable alternative in lower temperature ranges when a
quick heat up is not critical.
Oil-fired. Fuel oil is typically used when natural gas is unavailable and electricity is too costly to operate, however, as a source of heat, it has
several drawbacks. First, the initial purchase price tends to be higher than the gas fired or electric heated units. The byproduct of
burning fuel oil is soot, which will eventually recirculate through the oven work area if the oven is not cleaned or maintained on a
regimented basis. Also, it is a dirty process from the standpoint of what is exhausted into the atmosphere and the environment. An
increasingly popular alternative to fuel oil is propane, which costs less to purchase, is more cost efficient to use and the maintenance
costs are lower.
NFPA 86 Classifications & Oven Safety Features
All oven manufacturers are required to follow the guidelines as specified in the NFPA 86 Code Book. Essentially there are two oven
classifications and definitions which need to be considered and defined:
Class B. A Class “B” unit is that which is not intended or manufactured for the processing of solvents or volatile materials. A possible process
which would be Class “B” would be the annealing of plastics which produce no off-gassing or the stress relieving clean metal parts.
Class A. The second grouping, Class “A”, includes those units which are equipped to handle and process solvents, volatile materials or
combustible materials. Specifically, this rating is determined by calculating the volatile type, gallons per hour, and operating
temperature. An example of a Class “A” application would be the curing of a solvent based paint or the curing of a rubber by-product.
Another area which needs to be examined is the way in which your oven’s manufacturer complies and meets with the appropriate
NFPA 86 Codes. Typically, all Class “B” ovens are either electric, steam or hot water heated - not gas or oil fired. Essentially, a Class “B” unit will
include the following safeties: an air flow safety switch on the recirculation fan, a manual reset excess temperature control and the
necessary quantity of back up contactors.
Conversely, all gas (natural or propane) and oil-fired units are Class “A” as standard and include the following safety features: powered
exhaust system (sized to the unit, the burner & the volatile quantities); three air flow safety switches (one on the recirculation fan, one
on the exhaust fan & one on the burner fan) two manual reset excess temperature controls; Hi/Lo gas pressure switches; purge timer;
flame safety; spark ignition.
In terms of electric heated Class “A” ovens; they are equipped with the following safety equipment: a powered exhaust system (sized
to the unit & the volatile quantities); two air flow safety switches (one on the recirculation fan & one on the exhaust fan); two manual
reset excess temperature controls; extra back-up contactors; extra KW (to compensate for powered exhaust system losses); and a purge
timer.
Note: volatile ratings are never to be exceeded. Physical injury or death may arise if the volatile ratings are not strictly followed.
Additional Codes & Specifications
The five specifications which insurance companies and government agencies may want businesses to meet are the following:
- NFPA 70
- Underwriters Laboratories (UL)
- Factory Mutual (FM)
- Industrial Risk Insurance (IRI)
- Occupational Safety and Health Administration (OSHA)
NFPA 70. The counterpart to NFPA 86, addresses in its National Electrical code book the required safeties, standards and rules which
manufacturers must obtain or surpass. As relates to electrical components and installations in the workplace.
UL. This is a group founded to test for and analyze the results of product manufactured and sold in the United
States. As it pertains to the oven industry, UL is primarily interested in the use and integration of electrical components and controls.
FM. This is an association of mutual insurance companies which are dedicated to loss prevention. Many of its efforts are
made through investigations, analyzing and determining those means by which fire, and other losses, can be greatly reduced.
IRI. Formerly the Factory Insurance Association (FIA), IRI comprises member stock insurance companies concerned with all phases of fire
protection and other perils. It constantly reviews and studies methods of making the industrial workplace safer.
OSHA. This federal agency concerns itself with a variety of different issues; examples of this are motor guards,
exterior skin surface temperatures, insulating materials and general oven construction.
A quality manufacturer will not only have some of the above specifications (that is: OSHA & NFPA 70) as a standard feature, but also
the capacity to completely build to the additional specifications mentioned.
Hazardous Environments
An additional oven category which needs to be considered is that of explosion-proof. Such an oven is manufactured with specialty
rated electrical components, gas train, control panel, as well as with other rated equipment. Other features include spark resistant
fans & motors, explosion-proof wiring/conduit and control equipment.
An example of a work situation which requires an explosion proof oven is when the oven is near an open paint spraying application
that is within “...20 feet (6.10 m) horizontally and 10 feet (3.05 m) vertically...” Naturally, these rules change from year to year and
edition to edition, therefore, it is critical that you either refer to the NFPA 70 Code book, or contact the factory and let them analyze
your situation and determine if the oven must carry an explosion-proof rating.
Product Loading Options
Section One: Batch Ovens
Batch ovens have multiple means by which to load product, the most popular of these are:
Shelves are available in a couple of configurations; typically they rest on rails which are attached to the side of the oven via keyhole
slots. As a variation on this theme, roller shelves can be an important feature when a load has to be moved out of the oven with
minimal effort or when product has to be picked up with an overhead hoist or crane.
For truck-in or walk-in style units, carts typically come in three configurations -- shelf, hanging or flatbed. Either style of cart can be
rated to different weights and for varying processes. Each style of cart tends to be more compatible with a particular airflow, as
mentioned earlier in the airflow pattern section of this text.
Section Two: Conveyor Ovens
As briefly touched upon at the onset of this guide, continuous ovens have a variety of material handling means at their disposal. The
means of conveying product through such a unit are as follows:
- Belt conveyors
- Monorail conveyors
- Pusher conveyors
- Drag chains
- Screw conveyors
- Powered roller conveyors
- Walking beam conveyors
The type of conveyance system depends almost entirely on the type of product and the physical form of that product at the time of
processing, product weight, temperature and loading/unloading methods.
Cycle Dynamics
One of the more critical considerations, cycle dynamics, refers to the following four sub-issues:
- Proper Capacity
- Heat-Up
- Ramp/Soak
- Cool Down
Section One: Proper Capacity
Several factors must be considered and calculated to determine the necessary amount of
heating capacity for a specific material during a given time frame: mass & mean specific heat of the product; powered exhaust system
losses; wall losses; and heating the oven itself. Let’s assume we are curing hard rubber, which has a mean specific heat of 0.33, in 1,000
pound loads at 350°F (177°C) for one hour. Following are the formulas to determine the proper capacity for this example:
Formula #1 - Product Load
In order to raise the temperature of the load to 350°F, it is important to apply the following equation:
Product Wt. x (Operating Temperature °F - Ambient Air °F) x Mean Specific Heat ÷ Cycle Time = Btu/Hr.
That is: 1,000 pounds x (350°F - 70°F) x 0.33 Btu ÷ 1 hour = 92,400 Btu/hr.
Formula #2 - Powered Exhaust System Losses
Let's assume we need 100 cfm of powered exhaust in order to comply with NFPA 86 Codes and remove the appropriate amount of
fumes from the cycle, the following equation would be applied:
Exhaust system cfm x (Operating Temperature °F - Ambient Air °F) x Correction Factor = Btu/hr.
That is – 100 cfm x (350°F - 70°F) x 1.08 Btu/Hr. = 30,240 Btu/Hr.
Formula #3 - Wall Losses
Let’s assume we are using a standard walk-in oven (72” x 72” x 72”) with a four inch insulated wall and four pound density
Rockwool insulation, the total wall losses for one hour would be as follows:
Total Sq. Ft. of Oven Exterior x Btu/Hr. Loss Per Sq. Ft. of Oven Exterior = Total Btu/Hr. Wall Losses Per Hour
That is – 277 Square Feet x 70 Btu/Hr. per square foot = 19,390 Btu/Hr.
By adding the above totals, we're able to determine the minimum amount of Btu/Hr. needed in this application:
92,400 Btu/Hr. (Product Load)
30,240 Btu/Hr. (Exhaust System Losses)
+ 19,390 Btu/Hr. (Wall Losses)
142,030 Btu/Hr. (Minimum Total)
If a person wants to think in terms of kilowatts, simply divide the total number of BTU/Hr. (i.e., 142,030) by 3,412 and arrive at the
minimum number of kW necessary. In our rubber curing example, the minimum number of kW needed would be 42.
Section Two: Heat-Up
Once the appropriate amount of Btu/hr. or kW has been determined, it's important to assess how the set-point
(350°F) should be reached.
A desired temperature can be obtained in two ways: 1) Use a set-point controller to get the specified temperature as quickly as possible.
This method of reaching set-point is the most straightforward of the two methods. Load the product into the oven, turn the unit on, set the
temperature and allow the unit to run at full capacity until the set-point is reached. With this type of control device, the oven and the
product will not obtain temperature in a linear fashion.
2) Control the rate of increase with a ramp/soak programmer, which establishes multiple set-points and plateaus. This type of device allows for the gradual and linear increase in temperature of both the oven and the product,
ensuring that the oven interior area is a precisely controlled environment.
Section Three: Soak Times
We know that the recirculating air within an oven will reach temperature faster than the product load. Therefore, soaks can be viewed
as a technique which allows the product temperature to catch-up to the recirculating air temperature.
For example, the oven air reaches 350° F and the product is only at 280°F. At this point, a thermocouple attached to the product or
placed within the work area senses the discrepancy in temperature and stops the oven from rising in temperature until the controller
detects that the product has obtained 350° F, as well. At that point, the timer begins to count until a predesignated time has been reached, thus providing for an assured soak. As mentioned above, programmers allow for ramps & soaks, which allow for the
coordinated and controlled increase in product temperature as it relates to the recirculated air temperature.
Section Four: Cool Down
Cool down is categorized as the removal of recirculating and residual heat from the oven work area. Normally this is accomplished by
the exhausting of the hot air and the introduction of ambient air. If this rate in decline does not have to be controlled, then the opening
of the adjustable dampers on the ventilation/exhaust system and the fresh air inlet ports will suffice. However, if the cool-down has to
be controlled then there are two basic options:
1) Manually open the ventilation/exhaust port and the fresh air inlet port a proper amount, allowing the heater(s) to run or the burner to
modulate at the appropriate level. This controls the rate of decrease and allows for a “soft landing” when reaching lower
temperatures.
2) Couple a programmer with a modulating damper arrangement to allow for an automatic cool down. First, the
programmer will automatically open, sense and manipulate the ventilation/exhaust damper and the fresh air inlet damper so as to
allow the correct mixture of air. Secondly, the heater bank(s) or gas burner will be controlled in coordination with the modulating
damper arrangement - assuring the desired rate of decrease in oven temperatures (2°F per minute).
When calculating oven capacity, heat-up time, soak parameters or cool-down segments, remember that
much depends on the product configuration and loading pattern as it relates to the selected airflow type and the way in which the air
interacts with the product.
Space Conservation: Heat Chambers & Doors
Space conservation is a significant issue. Selecting the proper heat chamber location (walk-in ovens), door type (walk-in and
cabinet ovens), or both can prove critical.
First, heat chambers are available on the back or the top of walk-in ovens. The advantage of a back-mounted heat chamber is that
it usually doesn't have to be reattached to the oven. A top mounted heat chamber is usually shipped separately and
will have to be reinstalled at the customer's plant. A top mounted walk-in oven allows the maximum amount of work area, while taking
up a minimum of plant floor space.
Second, doors are available in two general configurations: bi-parting horizontal swing and vertical lift. The first style is the most
common, is the least costly to purchase and is widely found throughout industry. However, when allowing for the physical size of the
oven, a person must take into consideration the swing of each door. This can represent a significant amount of space which must be
kept free or empty in order for the door to travel unobstructed.
The alternate door style: vertical lift, all but eliminates this type of
scenario. With the door traveling straight up, there is no “swing” to contend with, which means the area to the front/side of the oven
may be used for other functions. This also applies to cabinet style
ovens; that is, door swing is eliminated and the area can be used more advantageously.
Oven Floors & Cart Guide Tracks
As stipulated by NFPA 86, section 2-1.5, ovens which operate at temperatures over 300°F do require an insulated floor. At this point, it
is important to discuss the multiple floor options available as well as cart guide tracks:
- Multi-inch Insulated Oven Floor
- Plate Floor Over Insulating Cement
- No Oven Floor, Insulating Cement Only
Multi-inch insulated oven floor. These floors come in different intervals and are rated for certain temperature ranges: 2.5 inches (rated at slightly above ambient to 750°F/399°C); 3 inches (rated at 850°F/454°C to 1,000°F/538°C); 6 inches (rated at 1250°F/676°C). Insulated oven
floora represents the utmost in flexibility due to the fact that if the oven has to be moved, the insulated floor automatically moves with
it.
Plate floor over insulating cement. This type of floor is a viable option when a multi-inch insulated floor and cart guide tracks are not an option (often
due to varying cart track centers). Plate floors are available on all units, even those rated at 1250°F/676°C. The benefit of the plate is
the oven chamber becomes an enclosed area which is not as susceptible to concrete dusting or powdering. A possible drawback to
this type of technique is if the oven has to be moved, insulating concrete must be poured again at the new oven location.
No floor and insulating cement only. This is acceptable when a process isn't sensitive to the possible effects of
powdering. It also proves to be advantageous when there is little or no chance of the oven being moved. If the oven
is moved, high temperature concrete has to be poured again.
In terms of loading product, cart guide tracks, a flat channel or v-groove configuration is most common and available on all walk-in
styles, except those operating at 1250°F. Tracks aren't available because of the extremely high operating temperatures and the
corresponding need to protect a normal plant floor. Such a high temperature unit will have its batch loaded via a forklift and a high
temperature stainless steel pallet. In the eventuality that guide tracks are not desirable, a ramp and an insulated oven floor reinforced
to the appropriate weight are viable alternatives.
Oven Construction
Numerous elements need to be considered in oven construction, more than could possibly be listed here. The following topics represent the more significant elements:
- Exterior
- Interior
- Duct Work
- Insulation and Wall-Panel Construction
- Control Panel
Exterior. An oven exterior should be constructed of heavy gauge cold rolled steel and primered and painted with a chip/scratch resistant
enamel paint. Under non-corrosive circumstances, this will provide for many years of corrosion resistance. In the eventuality that an
operating environment has corrosive fumes, a stainless steel exterior is recommended.
Interior. An oven interior ought to be of aluminized steel, not cold rolled steel with aluminized paint. Simply put, aluminized steel is
manufactured to resist the corrosive effects of moisture and heat, as well as other materials. In addition, aluminized steel doesn't
require the maintenance, and doesn't flake, peel or contaminate a given process, like aluminized paint may. Naturally, if a process
contain acids or corrosive materials, a stainless steel interior should be selected.
Duct work. The duct work of an oven, in terms of materials, follows the same guidelines as the oven interior prescriptions made previously. The style of quality duct work can be described as louvered or as slotted. Both are fully adjustable (without removal of the duct work)
and allow for the fine-tuning of air flow and temperature uniformities within the oven work area. In addition, an impinging style of duct
work may be necessary. Available in all of the air flow patterns mentioned previously, impinging air is applied to those applications where
a part has grooves or crevices that must receive a very high rate of airflow and wouldn't be properly served with a more ‘typical”
style of duct work.
Insulation and oven wall-panel construction. These are the two key elements which allow an oven, which is running at 1250°F, to remain cool
to the touch on the oven’s exterior. Quality insulation should be the proper density, oversized and compressed into the panel to avoid
sagging. Some companies use a heavier pound of insulation and make the oven wall thinner; this produces a unit which has poorer
structural rigidity or integrity compared with the thicker oven wall. The physical strength of an oven
is found in the wall panel construction and the overall frame. Finally, the wall panel should allow for minimal transfer of heat to the
outer skin.
Control panel. The control panel is of significant concern because it's the primary component with which the operator will interact.
Consequently, a high quality control panel must possess the following characteristics:
- Large push-button operation
- Legible legend
plates
- Clear readouts on the controller(s), timer(s) and recorder(s)
- UL-listed
We hope this primer has provided some insight and useful information about industrial process ovens.
J.W. Guanci, III is President of Precision Quincy Corp., 1625 W. Lake Shore Dr., Woodstock, IL 60098. For more information about the company's direct-gas-fired and electrically heated ovens, contact Precision Quincy at 815-338-2675 or pqsales@precisionquincy.com.
Precision Quincy Corp.
1625 W. Lake Shore Dr.
Woodstock, IL 60098
P: 815-338-2675
F: 815-338-2960
T: 800-338-0079
pqsales@precisionquincy.com
www.precisionquincy.com |
