Curing and baking ovens are important equipment for developing the full performance of a coating film.

Heating coated products to dry and cure the paint develops properties such as adhesion, hardness, chemical resistance, and durability.

However, a curing oven does more than simply warm the products.

Solvents and volatile components are released from the coating film.
Depending on baking conditions, odor-producing components or decomposition products may also be generated.
Tar-like deposits and dust can accumulate inside the oven and exhaust ducts.

Curing oven exhaust is therefore more than just hot air.

It contains VOCs, odors, tar, dust, and heat, and is an important subject of management.

Poor management of curing oven exhaust can lead to odors, external complaints, duct deposits, fire risks, VOC issues, and energy losses.

1. Coating Films Release Volatile Components in the Curing Oven

A coating film may still contain solvents and volatile components immediately after application.

When it enters the curing oven, heating releases these components from the film.

In solvent-based paints, solvents in the coating film evaporate.
In baking paints, heating advances the reaction and may release volatile components.
Even powder coatings may generate small amounts of odor-producing components or decomposition products during baking.
Waterborne paints may release co-solvents and additives, as well as water.

Curing oven exhaust thus contains various components depending on the paint used.

Changing the paint may also change the properties of the exhaust.

Curing oven exhaust is therefore closely related to paint selection, as well as being an oven issue.

2. What Are VOCs?

VOC stands for volatile organic compounds.
Put simply, these include organic solvents in paint and thinner that evaporate into the air.

VOCs may be released from the applied coating film in the curing oven.

VOCs relate to odors, the working environment, fire risks, and exhaust treatment, as well as environmental performance.

When VOC levels are high, the following checks are needed.

• Is exhaust air volume sufficient?
• What is the concentration in the exhaust?
• Is exhaust leaking into the factory?
• Are odors being discharged outside?
• Is exhaust treatment equipment needed?
• Are deposits forming inside ducts?
• Is there scope for heat recovery or energy savings?

VOCs in curing oven exhaust may differ in character from those in coating booth exhaust.

The temperature is high.
The concentration fluctuates.
Tar may be present.
Odor-producing components may be present.

Curing oven exhaust therefore needs to be checked separately from coating booth exhaust.

3. Odors Affect the Working Environment and Can Lead to External Complaints

Odors commonly cause problems in curing oven exhaust.

Odors from a curing oven may differ from the thinner smell in a coating booth.

A burnt smell.
The smell of heated resin.
A mixed solvent smell.
A tar-like smell.
An irritating smell characteristic of the paint.

Such odors burden operators when they leak into the factory.
When discharged outside through an exhaust outlet, they may lead to complaints from neighboring factories or the industrial park.

Simply increasing exhaust volume is not enough for odor control.

Odor sources.
Exhaust paths.
Exhaust outlet location.
Wind direction.
Duct deposits.
Paint type.
Baking temperature.
Whether treatment equipment is installed.

These factors need to be checked together.

Odors are difficult to judge from numbers alone.
Operators’ observations, checks outside the factory, and conditions around exhaust outlets are therefore also important.

4. Tar Causes Duct Deposits and Fire Risks

Tar-like components can become a problem in curing oven exhaust.

Tar is easiest to understand as heated paint components and volatile components that cool and accumulate as sticky deposits.

Tar deposited inside the oven or exhaust ducts causes problems such as the following.

• Accumulated deposits inside ducts
• Increased exhaust resistance
• Reduced exhaust air volume
• Persistent odors
• Deposits inside the oven
• Dirt pickup
• Increased cleaning burden
• Fire risk
• Reduced exhaust treatment performance

Tar does not necessarily appear immediately as a major problem.

It gradually accumulates inside ducts and affects exhaust capacity and safety over time.

Regularly checking deposits inside ducts and on exhaust fans is important for curing oven exhaust.

5. Insufficient Exhaust Affects Both the Oven and the Factory

Insufficient curing oven exhaust allows volatile components and odors to linger inside the oven.

This may cause the following problems.

• Odors leak into the factory
• Volatile components remain inside the oven
• Coating film appearance is affected
• Deposits inside the oven increase
• Deposits inside ducts increase
• Safety risks increase

Curing ovens need adequate exhaust.

However, the solution is not simply to increase exhaust volume.

Excessive exhaust discards heat from inside the oven.
This increases energy losses and raises electricity and fuel costs.

Curing oven exhaust requires a balance between properly discharging volatile components and avoiding excessive heat loss.

6. Excessive Exhaust Reduces Energy Efficiency

Curing ovens are among the largest energy users in coating equipment.

Electricity or gas is used to heat the oven and maintain its temperature.
Discharging too much exhaust then discards air that has already been heated.

This is a significant heat loss.

Increasing exhaust can have some effect on odor and VOC control.
However, excessive exhaust volume raises energy costs.

Check the following items.

• Current exhaust air volume
• Stability of oven temperature
• Exhaust temperature
• Odor generation conditions
• VOC concentration
• The need for exhaust treatment
• The potential for heat recovery
• Operating adjustments according to production volume

Curing oven exhaust requires considering environmental performance and energy savings together.

7. Cooling in Ducts Can Increase Deposits

Exhaust leaving a curing oven is hot.

However, its temperature falls as it passes through exhaust ducts.
As the temperature drops, some volatile components may condense inside the ducts and form deposits.

This may result in tar-like contamination and sticky deposits.

Particular care is needed when ducts are long, have many bends, cool easily in outdoor air, or are inadequately insulated.

Increasing deposits inside ducts raises exhaust resistance.
Exhaust capacity declines.
Odors remain.
Cleaning becomes difficult.

Curing oven exhaust duct design needs to consider temperature drops, deposits, and ease of cleaning, as well as exhaust volume.

8. Deposits Also Accumulate on Exhaust Fans

Components in curing oven exhaust also affect exhaust fans.

Tar and dust deposited on fan blades upset the fan’s balance.
This may cause vibration and unusual noises.

Increased deposits on blades may also reduce exhaust capacity.

Check the following items.

• Deposits on fan blades
• Unusual noises
• Vibration
• Motor load
• Exhaust air volume
• Cleaning intervals
• Whether inspection openings are provided
• Deposits inside ducts

A rotating exhaust fan does not necessarily mean normal operation.

For curing oven exhaust, check whether the fan is maintaining its intended capacity.

9. Check Exhaust Properties Before Installing Treatment Equipment

When VOCs or odors in curing oven exhaust cause problems, exhaust treatment equipment may be considered.

Combustion treatment.
Regenerative thermal oxidation.
Catalytic treatment.
Activated carbon adsorption.
Scrubbers.

Each of these methods has its own characteristics.

However, exhaust properties need to be checked before selecting treatment equipment.

• Exhaust air volume
• Exhaust temperature
• VOC concentration
• VOC composition
• Odor intensity
• Whether tar is present
• Whether dust is present
• Whether moisture is present
• Variation with production volume
• Operating hours
• Standards after exhaust treatment

Selecting equipment without checking exhaust properties may fail to deliver the expected results.

Pretreatment may be necessary, particularly for exhaust containing large amounts of tar or dust.

10. Pay Attention to Tar and High-Temperature Exhaust in Activated Carbon Adsorption

Activated carbon adsorption may be considered for odor and VOC control.

Activated carbon is a material that adsorbs VOCs and odor-producing components.
However, care is needed when using it for curing oven exhaust.

Curing oven exhaust may be hot.
It may also contain tar and dust.

If these enter the activated carbon, the following problems may occur.

• Reduced adsorption performance
• Early replacement of activated carbon
• Clogging
• Odor breakthrough
• Fire risk
• Increased operating costs

When using activated carbon adsorption, check exhaust temperature, dust, tar, pretreatment, and replacement intervals.

Treatment equipment should be selected to match exhaust composition, rather than by the method’s name alone.

11. Consider Heat Recovery Methods Such as RTO Together with Energy Savings

A method known as RTO is sometimes used for VOC treatment.

RTO stands for regenerative thermal oxidizer.
It treats VOCs by combustion while recovering heat to save energy.

Curing oven exhaust is often hot, providing scope to consider exhaust treatment and heat recovery together.

However, RTO is not a universal solution.

Exhaust air volume.
VOC concentration.
Operating hours.
Exhaust temperature.
Tar.
Dust.
Capital cost.
Fuel costs.
Maintenance costs.
Installation space.

These points need to be checked.

The decision to introduce RTO should consider exhaust conditions and long-term operating costs, rather than simply the need for VOC treatment.

12. Paint Changes Also Change Curing Oven Exhaust

Changing paint may also change curing oven exhaust.

Examples include the following cases.

• Switching from solvent-based to waterborne paint
• Switching to low-VOC paint
• Changing the baking temperature
• Switching to powder coating
• Switching to a locally sourced alternative paint
• Switching to a high-performance paint
• Changing curing agents or additives

Checking only coating film performance and appearance can overlook effects on curing oven exhaust.

A new paint produces stronger odors.
Deposits inside the oven increase.
Tar increases.
The load on exhaust treatment equipment changes.
A higher drying temperature increases energy costs.

These outcomes are possible.

When changing paint, check curing oven exhaust as well as drying conditions.

13. Common Curing Oven Exhaust Challenges in Vietnamese Factories

Vietnamese factories are prone to the following curing oven exhaust challenges.

Curing oven exhaust is regarded as simply hot air.
VOCs and odors are not measured.
Deposits inside exhaust ducts are not checked.
Duct cleaning intervals are not defined.
Exhaust fan deposits and vibration are not monitored.
Action is taken only after odors arise.
Exhaust outlet locations and effects on neighbors are not checked.
Excessive exhaust causes significant energy losses.
Exhaust properties are not checked when paints change.
Exhaust treatment equipment operating costs are overlooked.

Curing oven exhaust is difficult to see.
However, leaving it unmanaged affects quality, the environment, safety, and cost.

14. Basic Items to Check in Curing Oven Exhaust

The following checks provide a practical approach to managing curing oven exhaust.

1. Exhaust air volume

Check that the required exhaust volume is available.

2. Exhaust temperature

Check whether exhaust temperature is too high and whether there is scope for heat recovery.

3. VOC

Check VOC concentration, the processes generating VOCs, and the relationship to paint type.

4. Odors

Check effects inside the factory, around exhaust outlets, and outside the factory.

5. Tar

Check deposits inside the oven and on ducts and fans.

6. Dust

Check the discharge and accumulation of paint residue and dust.

7. Duct condition

Check deposits, blockages, cleaning openings, insulation, and temperature drops.

8. Exhaust fans

Check deposits on blades, vibration, unusual noises, and reduced capacity.

9. Exhaust treatment equipment

Check the need for treatment, method, pretreatment, and operating costs.

10. Effects of paint changes

Check whether exhaust properties have changed when the paint changes.

15. The Value of Curing Oven Exhaust Management According to CoatureVietnam

CoatureVietnam does not regard curing oven exhaust as merely hot air.

Curing oven exhaust provides important information about the condition of the coating process.

Which paint is being used?
At what temperature is baking performed?
How much VOC is generated?
Where do odors flow?
Is tar accumulating in the ducts?
Is too much heat being discarded through exhaust?
Is exhaust treatment equipment really needed?

Checking these points can improve quality, environmental performance, safety, and energy efficiency together.

CoatureVietnam examines curing oven exhaust from the following perspectives.

• Compatibility between paint and drying conditions
• VOC and odor generation conditions
• Deposits in ducts and on fans
• The need for exhaust treatment
• Heat recovery and energy savings
• Risk of external complaints
• Operator safety and the factory environment

This puts CoatureVietnam’s valued principle, “Coating the Future with Science and Care”, into practice.

Science means measuring and checking exhaust air volume, exhaust temperature, VOCs, odors, and duct deposits, then identifying the causes.
Care means creating conditions where the factory can operate with confidence without burdening operators or the neighboring environment.

Summary

Curing oven exhaust is more than just hot air.

It may contain VOCs, odors, tar, dust, and thermal energy.

Leaving curing oven exhaust unmanaged leads to the following problems.

Odors.
External complaints.
Duct deposits.
Reduced exhaust air volume.
Fire risks.
VOC issues.
Load on exhaust treatment equipment.
Energy losses.

Curing oven exhaust therefore needs to be managed as an important subject connecting quality, environmental performance, safety, and energy savings.

Exhaust air volume is not the only item to check.

Exhaust temperature.
VOCs.
Odors.
Tar.
Dust.
Duct condition.
Exhaust fans.
Exhaust outlet locations.
Exhaust treatment equipment.
Effects of paint changes.

It is important to consider these factors together.

CoatureVietnam regards curing oven exhaust as an opportunity to improve the overall coating process and proposes environmental, energy-saving, and safety measures suited to Vietnamese factories.