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This article takes an in-depth look at curing ovens and their uses.
You will learn more about topics such as:
Curing Ovens and How They Work
How Curing Ovens are Made
Types of Industrial Curing Ovens
Applications of Curing Ovens
Benefits of Curing Ovens
Considerations and Maintenance of Curing Ovens
And Much More…
Chapter 1: Curing Ovens and How They Work
This chapter will discuss what a curing oven is and how heat treating ovens work.
What is a Curing Oven?
A curing oven is thermal processing equipment used by thermal specialists to improve or enhance the strength and durability of materials. Many factory processes such as baking, drying, heating, cooking, and curing require industrial ovens to make a specific product. To achieve this, the material is heated to accelerate a desirable chemical reaction. An example of a curing oven is shown below.
How Heat Treating Ovens Work
Curing ovens are a type of heat treating oven. The heat treating is accomplished by increasing the temperature of a material sample to a value that is within or slightly above a specific limit. There are physico-chemical linkages inside a material that bind it together, and once these are increased the mechanical characteristics of the material or product are improved. One of the common practices that specialists use to produce a stronger and more durable product is to add catalyzing agents in the curing process.
It is well known that time is money meaning the faster a thing can be done the more money it can produce. Catalysts play a vital role in curing ovens because they make the chemical reactions go faster. Catalysts are substances that are used to increase the rate of a chemical reaction and are not consumed by the reaction. Catalysts differ depending on the type of reactants, and they have operating temperatures where they are activated.
Common examples of catalyzing agents that can be used in curing processes include the Isocyanate groups.
The Principle of Hot Air Circulation
The principle of operation of a curing oven is based on two main things which are:
Air circulation patterns
Heat plays an important role in curing ovens. The main sources of power for the heat required are electricity, steam, direct gas, indirect gas, ultraviolet light, oil, and hot water. These sources have brought about another way these ovens can be classified.
1. Electric Heat Treating Ovens
Electric heat ovens use electricity as their main source of power. This electricity is used to heat the elements which then produce the required temperatures for the chemical reactions to take place. These kinds of ovens that use electricity are a standard choice for many applications because they are a common source of power. Many oven manufacturers use electricity as their source of power. They are widely used because of their fast heat-up times, they are relatively cheap, they give precise temperature values, they are robust and easy to work with. When working with combustible products like aluminum, electric heat ovens are ideal.
2. Direct Gas Heat Treating Ovens
In direct gas ovens, the gas flames are produced directly onto the material to be processed. Although this is an effective heat source it is not ideal for working with products that are delicate because the flames produced tend to have a negative physical impact on the product. They are complicated in the sense that they have pumps of high precision dosage. Their heating elements are made of nozzles which could be sophisticated in design. They may be unwanted burns and distorted when working with the direct gas ovens. Heat may be excessive in other instances. Direct gas ovens are relatively easy to maintain when compared to electric gas ovens, but they are generally more expensive to purchase.
3. Indirect Gas Heat Treating Ovens
The main difference between the direct and indirect gas ovens is that the gas fire produced does not come directly in contact with the material being processed. In these ovens, the heat produced by the gas is concentrated by heating the heat exchanger, which is usually made of stainless steel. Although the heat comes from the gas, usually the rest of the controls use electricity as their source of power. Once the fan has been heated the fan blows this heat into the heating chamber. The heating chamber allows for the heat to travel to the material without damage by the heat flame. The indirect ovens produce better results than direct ones, but they are more complicated and require more maintenance routines. Their cost is even higher than both electrical and direct gas ovens.
4. Industrial Steam Heat Treating Ovens
Steam is generally one of the best sources of heat mainly because it's environmentally friendly, clean, cost-efficient, and can reach very high temperatures, especially when used in industrial ovens. One of the drawbacks of these kinds of ovens is their slow heat-up times and some of them cannot work with pressurized steam. These ovens cannot be used when working with materials that are susceptible to rusting and corrosion such as iron.
5. Hot Water Heat Treating Ovens
In hot water ovens, there are radiator coils where hot water flows in them, emitting heat to the outside environment, which is used to heat the material. It’s a clean source of environmentally friendly heat and has a simple design. These ovens are however not ideal to use where high temperatures are needed because the temperatures do not exceed 70°C.
6. Oil Fired Heat Treating Ovens
The oil-fired ovens are mainly used as an alternative when the other methods are not available and are rarely used in industries. This is because of the disadvantages that are way more than the advantages. They are more expensive to buy, expensive to maintain, complicated, and most of them are not user-friendly.
Airflow patterns refer to how effective the air distribution inside the oven is. The flow of air in curing ovens plays a vital role because the generated heat needs to be controlled lest it leads to distorted material or explosions. Before purchasing an oven, one needs to consider the flow pattern which suits best the process that they want to achieve. There are 3 main types of flow namely horizontal/vertical, vertical, and full horizontal flow. The image below shows these types of flow patterns.
1. Vertical/Horizontal Flow
In this flow, the air gets into the oven by the sidewall and is returned through the ceiling of the oven. This flow is effective when the parts are large.
2. Full Horizontal Flow
It is mainly used when the material to be processed is hung and when the parts are small and put on perforated shelves. In this flow, the air passes both the shelves above and below horizontally from sidewall to sidewall.
3. Vertical Flow
In the vertical airflow, the part or material to be processed is put in shelves but there must be an allowance for the air to flow from the sidewall below to the sidewall above as shown in the diagram above. This flow pattern is used for small parts that are hung.
Chapter 2: How Curing Ovens are Made
Industrial curing ovens are made up of 5 main components, which are listed below.
Supply air system
Recirculated air system
Exhaust air system
The Oven Enclosure
The enclosure refers to the environment that promotes the curing process. This is the space inside the mechanical structure and is supposed to be closed to ensure that heat flow can be controlled according to the parts/material-specific requirements. In designing an oven there are factors to be considered, which are:
Electrical Components – Examples include motors, switches, overall circuit diagrams, power supplies.
Supply of Fuel and the Ancillary Systems – Usually to be considered when working with liquid fuels like diesel or liquid pressure gas (LPG).
Explosion Relief Systems – Part of the design should involve how the system will respond to explosions since these ovens use high-power energy sources.
Mechanical Components – Quite a large fraction of ovens is mechanical designing and knowledge in parts such as conveyors, transmission belts, jetting systems, air blowers, gears, extraction systems should be known as these parts will make up the system.
Heat Recovery Systems – In the process of generating heat to use for curing, it is not all of the heat that will be used. A fraction of the heat does not directly come into contact with the material and an effective system should have ways of capturing this heat for use. Saving this waste heat is directly linked to saving money as this has been generated from a power source that is constantly equal to a certain amount of money.
Thermal Components – These are parts such as the heat exchanger, insulation materials, steam generators, steam damping equipment, and ribbon burners.
Instrumentation and Control Devices – Part and parcel of the industrial ovens have to do with the controlling aspect of things. Ovens are delicate systems and should have proper control and instrumentation systems such that accidents can be prevented, risks minimized, efficiency enhanced yet friendly to operate and understand.
Electronics and Automation Systems – Nowadays there are advanced systems that are programmable for example the Programmable Logic Controller (PLC) based and which are user friendly. If a proper design is made, the system’s operation can be more efficient.
The above image shows a picture of an oven enclosure with numbers indicating the parts of the design.
Steel structured framework comprising of lifted eyes
Double doors of full width with an internal release handle and sprung door seals
Represents a marked CE, and compliant that has a Machinery directive
An advanced electronic control unit that has a PID temperature control
Explosion relief which all of the roof area
Exhaust fan with independent interlock system
Air circulation fans with a powerful motor
Represents temperature uniformity
Four sided duct
Dampers for volume control
Dampers for air distribution and control
Insulated panels for thermal efficiency
The Heater Unit
One of the prerequisites for the curing process to occur is the generation of heat, so this unit should be properly designed. Supply fans, burners, filters, insulation material are vital parts that should be taken into consideration. To properly determine the heater equipment, the heat load and the heat losses of the system must be calculated and used for the burner control. In most cases, the fan motor size is made for cold starts to prevent overloading.
Construction and Structure Components – After material research parts of the systems such as equipment walls and hoods can be incorporated into the design for strength, insulation, size of the building, etc. The filters are responsible for letting clean air into the systems that can be burned by the burner to produce heat.
The Air Supply System – For heat to be produced air is required in the burner and the greater the proportion of air present in the burner the more efficient the system is. The air supply system usually is in the walls of the oven to allow even distribution of the heated air.
Air Recirculation System
The recirculation system allows the conservation of air and heat, by reinjecting them back into the system. This allows adequate air to be present in the burner. A poor design of the air recirculation system may result in poorly made products.
The Exhaust Air System
The exhaust air system ensures a clean environment for the oven by eliminating unwanted gasses and fumes.
Leading Manufacturers and Suppliers
Chapter 3: Types of Industrial Curing Ovens
There are two main types of industrial curing ovens namely:
Continuous process ovens (also known as constant process ovens).
Batch Process Ovens
The batch process ovens operate by placing parts in the oven over a period. There are many designs of ovens, and some allow the parts to rotate inside for even distribution of heat whereas in others, the parts will be stagnant. Parts are loaded and unloaded into the oven with transportation carts, and the doors are closed thereafter. One of the disadvantages of the batch process over the continuous is that it takes a lot of material handling as well as involving many workers to set up the process. Part of the limitations of the batch ovens is that there may be an uneven distribution of heat inside the system.
Continuous Process Ovens
Continuous process ovens operate by using a transport method that is powered such as a conveyer to expose parts, or the materials to heat at a predetermined rate. Continuous processes usually require one operator to monitor and carry out the process. Calculations are made as to how much the material is going to be exposed to the heat inside the oven. The parts are moved in and out of the oven through a conveyor system.
Parts of most continuous process ovens include pumps, insulated panels, nozzles, chains, pipe fittings, pressure switches, fans, blowers, burners, flame rods, drives, transmissions, air kits, tooling, regulators, fixtures, controllers, conveyors, fuses, etc.
Ovens can be classified according to size, functionality, type of fuel/heat used, manufacturer specifications, etc. However, for the sake of learning and having a basic understanding of the oven, they have been classified according to the two main types.
Comparison between the Batch and Continuous Process Ovens
Batch Process Ovens
Continuous Process Ovens
Size (Space Occupied)
Relatively small and portable
More than one worker
Usually, one operator
More material handling involved
Less material handling involved
Transportation and Loading
Can take unusually shapes and sizes
Have specific shapes and sizes
Chapter 4: Applications of Curing Ovens
Curing ovens have many uses, which include but are not limited to:
Curing paints and coatings
Preheating metal for coating
Adhesives are commonly used in industries such as electronics, aerospace, electrical, automotive, transport, clean energy, etc. Depending on the bond strength, adhesives are cured at room temperature, while some require heat (curing oven). Examples of adhesives are white glue, yellow wood glue, super glue, hot glue, spray adhesives, fabric adhesives, epoxy, etc. The figure below shows adhesives that were made using curing ovens.
Curing Paints and Coatings
After painting, curing can be used to heat the painted surface, making the water in the paint mix evaporate. This curing will also strengthen the bonds between the paint molecules, making the surface stronger.
Techniques like convection and infrared are used to enhance paint curing. Convection curing involves circulating a heated fluid, like heated air, oil, or water or simply leaving the material in heated air. Infrared curing involves exposing the material to infrared panels in an oven such that the energy source will work on the material.
The techniques used in such a curing process include:
Convection Technique for Curing
This is also referred to as the radiation curing method. Convection is a method of transferring heat energy using a heated fluid like air, oil, or water. Most curing ovens use air as the method of transfer. For this technique to be effective a fan to blow the hot air is implemented together with an exhaust system.
Infrared (IR) Technique
Infrared radiation refers to waves from the electromagnetic spectrum which have longer wavelengths than visible light. In this technique, infrared rays are used for the curing of materials. Infrared ovens are faster than convection ovens. This technique is more efficient than convection because it targets heat points, unlike convection, where heat is distributed everywhere.
Ultraviolet (UV) Light Technique
The UV technique for curing involves the initiation of a photochemical reaction by UV light that forms a network of polymers. This technique is used in the printing, coating, stereolithography as well as in the assembly of materials. It is also known to be a low temperature and high-speed type of process. The UV technique is widely used in the automation industry.
Polymerization is the process where small molecules known as monomers combine and form long chains of molecules known as a polymer. Curing polymers is when liquid low-weight polymers are irreversibly changed to solid and infusible 3-dimensional polymers. The process requires heat (ovens) or high-energy radiation and catalyzing agents. Common chemical processes of these polymers include curing polyester resins and phenol-formaldehyde resins.
Curing ovens are made to operate at specific ranges of temperatures. When a product or part is exposed to these temperatures the water/moisture inside the material evaporates, leaving a strong and hardened material. Drying is very important in many products because if the moisture does not leave the material, there is a high probability of another reaction that is not wanted to occur. Chemical bonds present have a higher chance of getting distorted or wiped out, like in the case of paints.
Pre-Heating Material for Coating
Curing ovens can be used for preheating materials before they can be coated. In this case, the ovens are being used to eliminate unnecessary moisture that may affect the next process coating.
Finishing is a term that describes the process by which these curing ovens protect materials and parts from corrosion and rusting. Once they get stronger and hardened, they resist corrosion, and their durability is prolonged. Curing ovens often have other applications like drying, dehydrating, and backing, which play an important role in finishing the processes of beautifying and coloring. This can be done by applying heat at different temperatures, using various techniques/methods of curing, etc.
Chapter 5: Benefits of Curing Ovens
Benefits of using curing ovens include:
Small and Portable
Unlike the traditional ovens, curing ovens are small and portable, meaning they can be easily transported in relatively small trucks. Nowadays technological advancement in many electronic devices is highly rated when the size is reducing and the functionality increasing. This is the case with ovens nowadays. Decades ago, they used to be very big, and many people could not afford to cater for the transport, maintenance, and material handling costs involved.
Most curing ovens present are capable of being used for other applications such as drying, backing, dehydration, etc. This is because of the advancement in controls which can allow for a variety of products, range of temperatures, different part sizes, etc. Depending on the part to be processed alterations can always be made such as the number of shelves to be used, insulation material, etc.
Oven Economic Impact
Since they are small in size, the cost of manufacturing them is lower compared to their counterparts. They are easy to clean, maintain, operate, store, and accommodate. They are becoming popular in many industries because of their affordability.
Accessible and Available
Curing ovens are not difficult to find and they are gaining popularity. Many manufacturing companies are manufacturing them at affordable prices.
Chapter 6: Curing Oven Considerations and Maintenance
This chapter will discuss considerations when selecting curing ovens and the maintainability of curing ovens.
Considerations When Selecting Curing Ovens
Some of the considerations when selecting a curing oven include:
Applications for Curing Ovens
Before one can purchase a curing oven, it should be clear in their mind as to why they want the oven. This question should be answered by stating facts that come from a specialist who would have done enough research and explored if there are other methods cheaper that can replace the oven or not. It is wise to purchase these machines when they are the best method to use to process the product.
Curing Oven Price
Price is one of the most important factors to consider when looking for a curing oven. The quality of the product the oven produces should be a priority than seeking a lower price. It is better to buy a high-quality producing machine at a higher price than getting a low-quality producing oven at a lower price. Of course, the goal for any businessperson
is to purchase a low-priced good of the highest quality, which should be the first option even in this case.
It is vital to ensure that the oven supplier meets the certification required for the electrical/electronic device they are selling. It is important to check if the supplier can design/maintain the system in-house. This will be helpful in the case that the oven experiences some faults or when troubleshooting is required.
One should ask themselves the following questions:
What are the kinds of control systems in the oven?.
What is the pattern of the system and how effective is the airflow system?.
What are the methods of heating involved and how much power do they consume?.
What rate of curing does the machine have?.
How effective are the gas or electric heat sources?.
Factory Acceptance Testing
Factory acceptance testing is when you enquire from the supplier on whether they can test or run the product for you before transporting it to you. This can be verified in case the product has faults or not working properly.
The best type of maintenance one can get for their product is one that comes from the manufacturers of that product. It is necessary to inquire from the company you are purchasing the product on whether they provide after-sale services like maintenance or installing? This will help in planning for the future and prevent unexpected costs. This also involves answering the question of durability and expected life service. Is the curing oven going to last for a long time?
Curing Oven Maintenance
Maintenance of curing ovens is important because the failure of some parts to perform may yield unwanted results. Depending on the operations carried out and the manual guide, maintenance routines should be carried out frequently and the recommended for many industrial curing ovens is weekly maintenance. Below is a list of some of the parts which need to be checked regularly if they are part of the oven.
Flame Failure Detector
A flame detector is designed to detect fuel leakages inside an oven. If the fuel is highly flammable, like gas or diesel, frequent checks on the sensor/detector should be practiced as failure to do so may cause an explosion. Such a detector should be replaced on fixed time bases and not wait for it to stop working.
Checks on the Burner
Regular checks on the burner are important because it is the one that creates a spark for burning the fuel. If the spark is not strong enough the fuel might not get burned, causing a fault or incomplete combustion.
Burner Air Filter
The air filter should be checked and cleaned if there are any contaminations. The burner is supposed to be supplied with clean air for complete combustion to take place.
Burner Motor and Blower Impeller
Maintenance of the motor and the blower impellers required them to be cleaned to avoid dirt between the fins of the impeller and the housing of the motor. When they are dirty, the system is prone to overheating because of inadequate circulation of air. At the end of everything, these parts affect the material results to be processed because they reduce efficiency.
The fan allows air to be distributed inside the oven. If the fan is not operating efficiently, some parts of the oven may not receive enough heat. If this occurs, the material inside the oven may come out with uneven appearances. Some parts may be harder than others or some parts may be weaker, resulting in cracking or burns. The fun should be well oiled for it to rotate at the designed speed for the process.
Some parts may fall or get trapped inside the oven. Maintenance should involve picking up these, and putting or remounting them onto their respective positions.
A curing oven can be used by thermal specialists to improve or enhance the strength and durability of materials. Many factory processes such as baking, drying, heating, cooking, and curing require industrial ovens to make a specific product. To achieve this, the material is heated to accelerate a desirable chemical reaction. It is critical to consider various aspects discussed in this article before deciding on the appropriate curing oven for a specific use.
Leading Manufacturers and Suppliers
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