Industrial Ovens Selection, Configuration, and Operations Best Practices Guide

This article discusses the key criteria to consider when selecting an industrial oven for your application.

It will serve as a guide for project engineers, operations managers and purchasing agents for understanding the processes, decisions, and tradeoffs that are required for delivering the best quality industrial oven at the best value for your capital investment.

Section 1: Define your Heat Processing Requirements

The first step in selecting a new industrial oven is to define the heat processing requirements and the application specifications such as floor space limitations, including ceiling height.

What is Heat Processing?

A combination of heating and cooling operations applied to a material to obtain desired conditions or properties.

The 3 Steps of Heat Processing:

1. Heating to a specified temperature
2. Holding at that temperature for the appropriate amount of time
3. Optionally, cooling according to prescribed methods
   

What is the difference between an industrial oven and a industrial furnace?

The heating temperature

• Oven <1,000°F
• Furnace >1,000°F
• Air flow management system in the heating chamber will differ between an oven and furnace
  

What type of ovens are available for industrial use?

Batch Ovens are used for a wide variety of heat processes including drying, curing, aging, annealing, stress relieving, bonding, tempering, preheating, and forming. Batch ovens process products one at a time or in groups (“batches”). The part(s) are brought into the oven in batches on racks, carts, or trucks, and can be loaded manually or via automated loading.

Continuous Conveyor Ovens offer labor savings and material handling efficiency over typical batch processes. The part(s) are brought into the oven manually or by a machine. Conveyors can be overhead, belt (steel or fabric), powered roller, chain or slat. Conveyor ovens perform the same processes as batch ovens, but deliver a continuous throughput. Continuous ovens can include multiple zones operating at different temperatures and may include a cooling zone.

Will the oven be customized for my application?
Industrial ovens and furnaces are available in standard or custom models.


What heat processes can be done in an Industrial Oven?

• Aging: Aging ovens are used to increase the strength of an alloy.
• Annealing: Annealing ovens soften parts by heating to and holding at suitable temperature followed by cooling at a controlled rate. Annealing is used to reduce hardness, increase ductility and help eliminate internal stresses.
• Baking: Baking ovens heat objects to a low temperature in order to remove entrained gases and moisture.
• Calcining: Calcining Ovens create phase change or remove moisture.
• Composite Curing: Composite curing ovens are used to cure high strength, low weight carbon composite materials.
• Curing: Curing ovens raise the product mass and coated material to a specified temperature and holds this temperature for a set time. Curing Ovens cure parts, coatings, and adhesives.
• Drying: Drying ovens remove water or other liquid from a material or object.
• Food Processing: Baking or curing to remove moisture from the product.
• Preheating: Preheat ovens are used in a variety of processes that require heating the product prior to a secondary process such as forming, coating, fitting or welding.
• Powder Coating: After application of the powder coating, the parts enter a curing oven where, with the addition of heat, the coating chemically reacts to produce a heavy duty finish.
• Stress Relieving: A heat treatment process used to reduce internal residual stresses in an object or material.
• Tempering: Tempering decreases the brittleness of the metal and is usually performed after hardening or quenching.
  
  
  

A best practice for ensuring durability of your industrial oven is to have a  discussion about the skills and expertise of the manufacturer’s build team to make sure that they have the experience to deliver a well-built industrial heat processing oven that will last for many years.

Section 2: Production Requirements - Batch Processing or Continuous Flow Processing

The second criteria to consider is whether continuous or batch processing is best suited for the application.

To determine if batch or conveyor processing is the best option, answer the following:

1. How many Parts Per Hour are required?
2. Will the oven be part an automated manufacturing line?
3. Are multiple heating/cooling zones needed?

Conveyor Ovens, in the simplest terms, are batch ovens that operate with product moving through it. Conveyor Ovens can utilize indexing or continuous motion, with horizontal, vertical, inclined, or spiral motion paths. Conveyor styles include roller, belt, chain-on-edge (COE), overhead monorail, or power and free.

By comparison, a batch oven only allows for product to be placed in a static position for thermal processing. Depending on how the oven is used, product may be positioned consistently and uniformly inside of the chamber on a cart or shelves. Because conveyor ovens incorporate motion, inherently they are a more expensive solution than a batch oven, however there are a number of reasons to consider using a conveyor oven:

High Production Volumes - If a customer has enough product volume, at some point a batch oven may no longer be a viable solution for them. There may not be enough time to load, heat up, cool down (if required), and unload the amount of product that must be processed in a given time.

Production Automation - A conveyor oven can often easily be incorporated into a production line, eliminating or minimizing human intervention with the equipment. This can in turn, lead to a more consistent product or product placement with fewer variances/defects.

Process Flexibility - Oven conveyor drive systems can be fit with a variable frequency drive (VFD) in order to change the speed of the conveyor. This can be useful in changing the residence time of product in a heated zone/s. Additionally, a change in the oven (temperature) set point, combined with that of a third parameter, e.g. air velocity, can completely alter a temperature profile. Conveyor ovens can be zoned based on a required temperature profile -- up to a zone for every profile segment. Further, a customer process may often dictate that their product must be cooled. With a conveyorized system, product can be moved to or through a designated cooling zone. Conversely, in a batch oven process, heating and cooling will generally occur within the same zone. Energy is expended not only in cooling the product, but also in cooling the internal components of the oven which in turn has to be reheated for the next batch process.

Section 3: Application Specifications - Custom Engineered or Standard Unit

Most industrial oven manufacturers offer both standard and custom engineered models. The next step is to determine if a custom engineered or a standard sized oven is the best option based on your specifications. To determine, consider the following:

The Top 10 criteria to consider when deciding between a standard or a custom oven

1. Part Loading - Standard ovens are an optimal choice when the parts can be manually or automatically loaded onto the standard size entrance stand and no special belt or pallet/part holders are required. If the part does not fit within the standard size range, then a custom oven may be required.
2. Part Size and Weight - An oven can be built to accommodate any part size or weight, but if your part fits within the standard sizing, mark one up for a standard oven!
3. Controls - Each manufacturer will offer a standard controls package with basic functions. If your process requires additional controls (e.g. ramp and soak, multiple set points, data acquisition, PLC, etc.) not offered in the standard control package, a custom control package can be designed to meet your application.
4. Temperature - Standard ovens are designed with a maximum operating temperature. If this falls within your requirements, then a standard oven may be right for you. A custom oven offers the option to be designed with multiple temperatures, multiple zones and cooling capabilities.
5. Heat Source - A standard oven is typically gas or electric, while a custom oven can be designed around any heating medium. (e.g. gas, electric, oil, steam).
6. Load Height - Standard ovens are offered with load heights with small adjustments predetermined by the manufacturer. Custom ovens can be designed to your process requirements.
7. Exhaust - Standard ovens are specified with pre-designed exhaust rates. Custom ovens are designed to your requirements (e.g. no exhaust, gravity exhaust, power and non-power exhaust).
8. Air Flow - Standard ovens are offered with pre-designed air flow arrangements while custom conveyor ovens are designed to specific requirements (e.g. vertical, horizontal, combination, direction, volume, high/low velocity).
9. Materials of Construction - Standard ovens are typically manufactured from steel or aluminized steel and custom ovens can be designed with many material options based on the application (e.g. stainless steel, exotic metals, etc.).
10. Certifications - Standard ovens are based on manufacturer’s standard design. Custom ovens are designed to meet your requirement (e.g. Underwriters Laboratory, CE, CSA, etc.).

Section 4: Oven Construction Materials

When it comes to the design of industrial ovens and furnaces, the selection of construction materials is of the utmost importance. The two most important decisions to make are what metal to use for interior and exterior construction, and what insulation materials to use in the walls, roof and floor when applicable.

Metals
Temperature and corrosion resistance are the top two factors to consider when choosing interior and exterior metal construction. Aluminized steel is the metal of choice for oven manufacturers in the temperature range up to approximately 1100°F. The aluminized steel coating offers excellent protection from temperature and allows for ease of welding during fabrication as opposed to galvanized. Manufacturers typically utilize aluminized steel on the exterior as well for additional corrosion resistance and ease of painting.
At temperatures above 1000°F, the design changes to a different construction type commonly referred to as “furnace construction”. Exterior construction is typically 3/16” hot rolled carbon plate with sufficient buck stays to contain an explosion. Per NFPA 86 this allows for the elimination of explosion relief panels. It also is a more robust construction typically necessary in an industrial heat treat environment. For superior corrosion resistance in ovens and furnaces up to 1500°F, 316 stainless steel is the most often selected material.

Insulations
The insulation of choice for oven applications up to 1000°F is mineral wool. Besides being economical, mineral wool offers excellent insulation and sound proofing characteristics while being very easy to install. It comes in various densities up to 10#/cu.ft. and typically has a thickness from 2” to 10” when installed. Its fire resistance is yet another feature of this type on insulation.
Above 1000°F, different types of insulations start to become necessary. The most common choice is ceramic fiber boards, blankets and modules. The standard ratings for these ceramic fiber materials are 1800, 2300, 2600 and 3000°F. In addition, firebricks and cast refractory are widely used in temperatures to 3300°F and above. There also various lightweight insulating boards available up to 3300°F.

Section 5: The Importance of Air Flow Design

The 4 Keys to Successful Industrial Air Flow Design

Key 1: Uniformity
Process time at temperature, heat up rates and uniformity are all variables that need to be taken into account to help determine the most efficient design of a system. Process time and heat up rates will determine the size of the oven along with the BTU output of the heat source. Uniformity is the next major element to consider.
A basic batch oven usually will operate at an oven air temperature of +/- 10°F chamber uniformity. Oven manufactures can lower the tolerance down as far as +/-1°F if needed. To achieve tighter chamber uniformity we need to increase the volume of air. Higher rates of recirculation require larger horse power motors and/or bigger fans which can increase the cost of the oven.
Not every process will require tight uniformity tolerances so it is important to let your supplier know what temperature variance is acceptable for your process. The engineer will design a system that not only meets the needs of your process, but is energy and cost efficient. Remember, the tighter temperature tolerance required will increase the price of the equipment.

Key 2: Air Flow Patterns
Industrial ovens are much more than heated boxes. ITS utilizes precise engineered air flow design to deliver the air to the product. There are various air flow patterns that are commonly used in the industry including top down, bottom up, horizontal, or combination. Each of these air flow patterns are an important component in oven design. Typically, certain products favor certain air flow design. Conveyor ovens very often have vertical air flow, while batch ovens favor horizontal.

Key 3: Nozzle Design
After an air flow pattern is determined the next step to consider is called impingement. Impingement increases the surface to volume ratio and heats up the product faster. Usually this is accomplished with the use of some type of slot nozzle, cone or louver. The velocity and type of nozzle is best determined by the application. The shape, texture and material type all are instrumental and contribute to the type of nozzle that will work best for the application. The impingement works best when the air hits the product perpendicular to the surface of the material to be heated.

Key: 4 Manufacturer Experience
Now that you have defined your process, it’s time to partner with a manufacturer who can meet your needs and stay within your budget. ITS has successfully designed and installed industrial ovens with our classic HVN air flow, the ITS patented Turbo Flow, or the newly introduced Three5 and Acu-flow system. ITS has a proven track record of meeting tight temperature uniformity requirements in applications across a wide variety of industries. ITS can also use Computational Fluid Dynamics (CFD) software to provide visual representation showing the airflow and uniformity characteristics of the proposed system. ITS also offers an onsite test facility where we can demonstrate real time testing on your parts under conditions similar to the actual application.

As described, there are many different variables that need to be considered when designing the air flow pattern for your industrial oven, connecting with a partner that understands thermal processing is vital to a successful project.

Section 6: Heating Systems

There are primarily 3 different types of heating sources used in industrial processing ovens. These are most often referred to as direct gas fired, indirect gas fired and electric coil heaters. Direct fired heaters are generally more efficient and less expensive as there are fewer components in these systems. Although this is true, there are instances when an indirect gas fired heater or an electric heater is a better choice. Understanding the advantages of each system will aid you in understanding which system to use.

Heat Processing applications commonly use direct gas fired, indirect gas fired or electric coil heaters to heat the oven.

Direct Gas Fired Heaters

A direct fired heater uses natural gas, propane, butane or other gas mixtures to create an open flame for heating. The gas burners are designed to operate in a fresh flowing airstream. Gas is fed directly to the burner and the fresh airstream provides the needed oxygen for combustion.

Direct Gas Fired Heater Advantages

• Efficient- since it is firing an open flame; almost all of the fuel is converted to heat in the chamber. These types of burners are rated at 92% efficiency.
• Smaller footprint – since these burners do not use heat exchangers, they are able to produce more heat in a smaller footprint.
  Flexibility – Direct fire burners have a higher turn down ratio. This allows for better temperature control and a larger temperature range than indirect burners.

Direct Gas Fired Heater Disadvantages

• Combustion – combustion byproducts are introduced into the air stream. In certain applications, these byproducts could affect the users product.
• Explosion Panels – since the byproducts are introduced into the work stream of the oven/furnace, extra cost and design input is needed to design explosion relief into the product equipment or specific explosion relief panels in the equipment.
• Exhaust – a powered exhaust is needed in the oven/furnace to remove byproducts and water from the combustion process.
• Purge time – Before starting or re-firing a direct gas burner, there is a wait time (purge time) where a specific volume of air in the system needs to be purged.
  
  

Indirect Gas Fired Heaters

An indirect heater used in industrial ovens and furnaces is a gas burner that fires directly into a heat exchanger. When using indirect heaters, the process air is heated by passing over the heat exchanger. For gas burners, the combustion byproducts remain in the heat exchanger and are expelled out the flue which eliminates them from the process air stream.

Indirect Gas Fired Heater Benefits

• Product of Combustion – Products of combustion are eliminated from the process air stream
• Exhaust – Powered exhausts are no longer needed required to expel combustion byproducts
• Explosion Proof – as the combustion is not happening inside the oven or furnace, there is not a need to design the system with explosion panels, the tube or exchanger would typically be built of an explosion proof construction.

Indirect Gas Burner Disadvantages

• Low Efficiency – The heat loss from the flue and inefficiencies in the heat exchanger result in efficiencies of 65% to 80% depending on the type of burner and heat exchanger.
• Higher Cost ¬– Utilizing heat exchangers increases the cost over direct fired burners as the build materials can get costly at higher temperatures.
• Space – Indirect systems are physically larger as a result of packaging a heat exchanger into the equipment.
• Temperature control – The heat exchanger tends to make holding a tight temperature range harder as it tends to overshoot or undershoot a couple of degrees, due the lag of heat transfer in the heat exchanger.

Electric Heaters

An electric heater converts electrical energy into heat through resistance. This heat spreads out in every direction. Electric heaters are typically placed in the ductwork so that the air moving over them can be controlled. The air can either be recirculated or fresh. Recirculated air is more commonly used to reduce power consumption and the heater size. Fresh air is used when ventilation of the process is necessary.

Electric Heater Benefits

• Simple - Electric heaters are simple to install, control and have the least number of components.
• No Exhaust - Powered exhaust and introduction of fresh air are eliminated. Other than what may be required to remove process gasses or to balance the equipment.
• Product of Combustion - Eliminates the worry of products of combustion affecting the end user’s product.
• Turn Down - Can turn to zero percent out, allows running at very low temperatures.

Electric Coil Disadvantages

• Operating cost - Electricity costs in most parts of the world are higher than that of propane or natural gas heating
• Large heaters - Larger heating requirements increase the upfront costs to the end user as a result of providing a larger electrical service to the machine as well as the increased costs of the electrical cable and circuit costs.
• Footprint - Packaging heaters throughout the oven and furnace can increase its size compared to gas fired. Watt density of the coils can also drive a larger physical size.
  
  

Section 7:  Conveyor Belt Options

The 4 Best Conveyor Belt Types for Heat Processing

As more and more companies seek to automate their processes and facilities, a conveyor oven is a small, yet important cog in the wheel of product manufacturing. While batch processing will always have its place, continuous process conveyor ovens are in high demand as manufacturers strive to maximize efficiencies in their production processes.

There are a wide variety of conveyor types to choose from:

• Belt conveyors
• Chain conveyors
• Roller conveyors (powered, gravity)
• Screw/Auger
• Elevators/Elevating conveyors
• Feed systems (vibratory, centrifugal, etc.)
• Pneumatic conveyors
• Vacuum conveyors

However, many of these conveyor types are not viable solutions in the presence of heat. High process temperatures limit conveyance material options and eventually force drive components (ie: bearings, drive chain and motors) outside the heated zone completely.

There are four types of conveyors that are commonly used in heat processing applications; flat wire, woven belt, chain and roller.

1. Flat Wire Belt Conveyors

Of the four types described above, flat wire mesh belts are the most popular. Flat wire belts can be used for a wide range of process temperatures and applications, and offer the following advantages:

• High strength-to-weight ratio
• Wide range of belt widths for a wide variety of product sizes
• Easy to clean
• Vibration and shock absorbent
• High open area – preferred in convection applications
• Configurable with attachments (flights, lane dividers, edge guards, etc.)
• Inexpensive

With an appropriate material selection, flat wire belt conveyors are operable to 1,000°F and beyond.

2. Woven Wire Belt Conveyors

A woven wire belt offers many of the same advantages as a flat wire belt, but woven wire belts are able to handle higher load capacities than flat wire, are available in more configurations (mesh shapes and sizes), are customizeable, and offer increased surface area for conveyance of smaller parts.

Disadvantages include:

• Higher cost
• Lower open area reduces airflow
• Sometimes requires belt tracking

Woven wire belts are commonly used to move small parts including nuts, bolts, nails and even granular material.

3. Chain Conveyors

Chain conveyors are typically employed in heavy load applications. Chain conveyors can be designed as a rolling or sliding chain configuration. Chain type selection is highly dependent on temperature, connection type, material selection and lubrication.
There are hundreds of chain styles, many designed specifically for a single industry or application. Attachment-style chains allow for attachment of customized part fixtures.

Advantages of chain conveyors include:

• Ease of maintenance and replacement
• Durability
• Many available styles
• Customizeable

Chain conveyors are a good choice for heavy loads and specialty part sizes.

4. Roller Conveyors

Depending on processing temperature, roller conveyors will often be designed with shaft bearings mounted on the outside of the oven/furnace to protect power transmission components (chain, bearings, motors). Roller conveyors are used in heavy loading applications, and offer flexibility in motion, and accumulation of product. Products are often loaded on a pallet or frame when roller conveyors are utilized.

Section 8:  Putting it all together - Customer Support Services

You made it!

The oven has been manufactured and is ready to be checked and verified by Quality Control. The manufacturer will invite you to the facility to be a part of the final equipment check. You will have the opportunity to see the oven working and make any adjustments that may be needed. After verifying everything is working correctly, the oven will cleaned, prepped and packed for shipment. Next, installation, training and service become very important.

Once the oven is delivered to your facility, the customer support team will be on-site for installation and start-up (if this was part of the original quotation). Trusting the expertise of the support team is important; an experienced team is needed to install and start-up the oven. Operator training is available and is a worthwhile investment.

Industrial ovens are built to last and if maintained properly, will be a key workhorse of the manufacturing line for many years. When selecting a manufacturer to build the oven it is very important to consider the services they offer and how quickly they typically respond to service and parts requests. To maintain maximum efficiency and performance levels of the industrial oven, a maintenance schedule should be established. Manufacturers also offer equipment audits and preventative maintenance programs for ongoing support. Replacement parts should be readily available as well.

The ITS Industrial Heat Processing Oven Solution

In industries ranging from aerospace to food and beverage, ITS has been delivering industrial heat processing solutions for more than 50 years. Our designs include batch and continuous processing  and a wide variety of oven sizes for all applications. 

For more details and specifications, visit our industrial ovens page and learn more about the capabilities of International Thermal Systems.