Drying and baking ovens are among the major energy-consuming equipment in coating processes.

Drying ovens remove solvent or moisture from applied films and stabilize them.
Baking ovens use heat to advance resin reactions and develop film performance.

Both are important equipment directly linked to coating quality.

However, shop floors sometimes treat them simply as equipment for raising temperature.

Oven temperature has reached the setting.
The conveyor is running.
Products are passing through.
The film appears to have dried.

Being satisfied with these alone may leave substantial hidden losses.

Examine more than the setting.
The important questions are where heat is used, where it escapes, and how much it contributes to film performance.

Before lowering temperatures to improve drying or baking ovens, first make energy losses visible.

1. Drying and Baking Ovens Develop Film Performance

Drying and baking ovens are more than heating equipment.

They develop coating-film performance.

Each paint has appropriate drying or baking conditions.
The finish varies with temperature, time, thickness, substrate, oven air velocity, and workpiece heat capacity.

Insufficient temperature may cause the following defects.

• Insufficient drying
• Insufficient curing
• Poor adhesion
• Inadequate chemical resistance
• Inadequate water resistance
• Inadequate abrasion resistance
• Blocking
• Scratches or marks in subsequent processes
• Premature deterioration after shipment

Excessively high temperature also causes problems.

• Film yellowing
• Gloss changes
• Discoloration
• Substrate deformation
• Damage to plastic components
• Excessive energy consumption
• Higher workplace temperatures
• Increased equipment load

Higher temperatures or longer times are not necessarily better.
These ovens should consistently develop the required film performance with sufficient, appropriate thermal conditions.

2. Set Temperature and Workpiece Temperature Are Not the Same

A common misconception is to assume conditions are correct based on the oven setting.

However, the setting and actual workpiece temperature differ.

For example, setting the oven to 180°C does not immediately bring the workpiece surface to 180°C.
Heating rate varies with material, thickness, geometry, weight, fixture condition, and conveyor speed.

The following cases require particular attention.

• Thick workpieces
• Heavy workpieces
• Metal with high heat capacity
• Heavy fixtures
• Densely arranged workpieces
• Limited oven airflow exposure
• High conveyor speed
• Heat escaping at oven entrances or exits

In these cases, the workpiece itself may not heat sufficiently even when oven temperature matches the setting.

Film performance depends on more than the displayed temperature.
It depends on the temperature actually reached by the workpiece and how long it remains there.

Manage ovens with attention to workpiece temperature as well as oven temperature.

3. Energy Losses Extend Beyond Heat Escaping from the Oven

Oven energy loss may bring to mind heat escaping through the oven body.

Poor insulation or door gaps certainly cause major losses.
However, losses extend beyond them.

Drying and baking ovens have the following losses.

• Heat dissipated through the oven body
• Heat leakage through doors or openings
• Heat discharged with exhaust
• Heat used to warm up the oven
• Heat used during empty operation
• Heat used to warm heavy fixtures or carts
• Drying longer than necessary
• Temperature settings higher than necessary
• Excessive settings to compensate for uneven oven temperature
• Operation with few workpieces
• Losses from repeated stopping and restarting

Oven losses therefore involve equipment structure, operating methods, workpiece conditions, fixtures, and work planning.

For energy saving, isolate where heat is wasted rather than simply lowering oven temperature.

4. Check Heat Leakage from the Oven Body

Heat leakage from the oven body is a first point to check.

The exterior is abnormally hot.
Areas around doors or inspection openings are hot.
Large amounts of hot air escape from entrances or exits.
Operators feel intense heat near the oven.
Air-conditioning load around the oven is high.

These conditions suggest heat is escaping into the workplace rather than remaining in the oven.

Heat leakage affects more than fuel or electricity costs.
It also affects working conditions.

Heat spreading into the workplace increases operator fatigue.
Heat may reduce concentration and increase work errors.
Air-conditioning load also rises.
In some cases, paint or thinner storage conditions may be affected.

Heat-leakage prevention therefore addresses both energy saving and working-condition improvement.

Check the following items.

• Oven-body surface temperature
• Insulation deterioration
• Sealing of doors and inspection openings
• Opening size
• Hot-air leakage at entrances and exits
• Working temperature around the oven
• How waste heat is discharged
• Operators’ perception of heat

A drying oven should heat coating films rather than the workplace.
Keep this perspective in mind.

5. Examine Heat Loss Through Exhaust

Exhaust is important in drying and baking ovens.

Solvent-borne paints release solvent during drying.
Exhaust is therefore necessary to maintain oven safety and working conditions.

Excessive exhaust, however, discards large quantities of heated air outside.
This creates substantial heat loss.

Reducing exhaust too far risks leaving solvent vapor or odors in the oven or workplace.
It also creates safety problems.

Oven exhaust therefore requires balancing energy saving with safety.

Check the following items.

• Is exhaust volume appropriate?
• Does the exhaust fan always run at full capacity?
• Can exhaust be adjusted according to production volume?
• What is the exhaust temperature?
• Does exhaust contain VOCs or odors?
• Could exhaust heat be reused?
• Is there unnecessary resistance along the exhaust route?
• Is the ventilation volume required for safety provided?

Exhaust should not simply be stopped.
Maintain the necessary exhaust while reducing excess.

6. Heavy Fixtures and Carts Also Consume Thermal Energy

Workpieces are not the only objects heated in drying or baking ovens.

Fixtures, hangers, carts, and conveyor components heat up too.

Heavy fixtures or carts require additional heat.
This loss is easily overlooked.

For example, a light workpiece may be carried on a very heavy fixture.
Some oven energy then heats the fixture rather than the product.

Thick paint accumulation on dirty fixtures can increase weight and impair heat transfer.
Insufficient fixture maintenance affects energy saving as well as quality.

Check the following items.

• Fixture weight
• Cart weight
• Heat capacity of conveyor components
• Fixture contamination or paint accumulation
• Workpiece loading efficiency
• Standardization of fixtures
• Fixture weight reduction
• Thermal balance between workpiece and fixture

Oven energy saving requires examining what enters the oven as well as the oven itself.

7. Examine the Relationship Between Line Speed and Drying Time

Coating lines may request higher conveyor speed to improve productivity.

Higher speed appears to allow more products through in the same time.
However, it requires care in the drying oven.

Higher conveyor speed shortens workpiece residence time.
Required drying or baking time may then be insufficient.

Maintaining drying time requires greater oven length.
However, building space is limited.

Examine the following relationships.

• Drying temperature required by the paint
• Drying time required by the paint
• Actual workpiece temperature
• Conveyor speed
• Effective oven length
• Oven temperature variations
• Workpiece loading quantity
• Overall line takt time

Increasing line speed for productivity is ineffective if insufficient drying increases defects.

Assess speed and quality together in the drying oven.

8. Review Empty and Standby Operation

Drying and baking ovens take time to start up.

Shop floors may therefore hesitate to stop an already heated oven.
It may continue running even when no production is taking place.

Frequent stopping and restarting can of course reduce efficiency.
Some preheating or temperature maintenance may also be needed for stable quality.

However, the following conditions need review.

• High-temperature operation during breaks
• Normal operating conditions during changeovers
• Long periods without workpieces
• Full operation of a large oven for small production quantities
• Unlinked production and oven-operation plans
• Long standby periods because start-up time was not considered

Oven energy saving requires managing operating time as well as temperature.

When should the oven operate, stand by, or stop?
Clear operating rules may reduce wasteful energy use.

9. Potential of Low-Temperature or Short-Time Drying Paints

Paint-side improvements are one way to reduce oven energy consumption.

Examples are low-temperature drying paints or short-time drying paints.

Lower required temperature.
Shorter drying time.
Shorter oven residence time.
Potentially higher line speed.
Potential application to heat-sensitive substrates.

These are possible benefits.

However, a low-temperature or short-time drying paint is not necessarily better in every case.

The following items must be checked.

• Adhesion
• Hardness
• Chemical resistance
• Water resistance
• Weather resistance
• Abrasion resistance
• Appearance
• Suitable film-thickness range
• Workability
• Pot life
• Oven compatibility
• Compatibility with workpiece material
• Compliance with customer specifications

Changing paint may be an energy-saving measure.
However, it must be considered together with quality assurance.

10. Oven Energy Saving Also Improves Working Conditions

Oven energy losses affect more than fuel or electricity costs.

Leaked heat enters the workplace.
Poor waste-heat discharge traps heat inside the factory.
High temperatures near the oven increase operators’ burden.

Heat around ovens is particularly significant in hot environments such as Vietnam.

Working in hot areas increases fatigue.
Concentration declines.
Hydration and breaks are needed.
Work errors and safety risks also increase.

Oven heat control therefore addresses working conditions as well as energy saving.

Oven-body insulation.
Discharging waste heat outdoors.
Partitioning oven areas.
Reviewing operator positions.
Separating heat sources from work areas.
Reducing air-conditioning load.

These improve energy use while showing consideration for shop-floor staff.

11. Drying- and Baking-Oven Checkpoints

The following perspectives are useful when checking ovens.

Temperature Conditions

• Is the setting appropriate?
• Is actual workpiece temperature checked?
• Is oven temperature uniform?
• Is heating-up time known?
• Is holding time sufficient?

Operating Conditions

• Is conveyor speed appropriate?
• Is oven operation excessive for the production volume?
• Are operating rules defined for breaks and changeovers?
• Is empty-operation time known?

Heat Loss

• Is the oven-body surface excessively hot?
• Is heat leaking through doors or openings?
• Is exhaust temperature excessively high?
• Is waste heat being dispersed into the workplace?
• Is insulation free from deterioration?

Conveying and Fixtures

• Are fixtures or carts excessively heavy?
• Has paint accumulation increased fixture weight?
• Is workpiece loading efficiency appropriate?
• Are workpieces too densely arranged in the oven?

Quality

• Is there a history of insufficient curing?
• Are there discoloration or gloss changes?
• Is the relationship between thickness and drying conditions checked?
• Are testing criteria established for drying-condition changes?

Working Environment

• Is the oven area excessively hot?
• Do operators feel hot air?
• Has air-conditioning load increased?
• Do operators work near the oven for long periods?

Assess drying ovens through quality, work, environment, and cost, as well as equipment.

12. CoatureVietnam’s Approach to Oven Improvement

CoatureVietnam does not treat oven improvement simply as introducing energy-saving equipment.

First, we check current conditions.

What is the oven temperature?
What is actual workpiece temperature?
How many minutes is drying time?
Is oven temperature uniform?
Is exhaust excessive?
Where does heat escape?
Do fixtures or carts waste heat?
Do operators feel excessive heat?
Is film performance stable?

We then consider the following improvements.

• Optimizing temperature conditions
• Reviewing conveyor speed
• Checking oven temperature distribution
• Improving insulation
• Preventing heat leakage through doors or openings
• Optimizing exhaust volume
• Reviewing waste-heat management
• Reducing fixture weight
• Considering low-temperature drying paints
• Reviewing operating schedules
• Reducing operators’ heat burden

Protecting quality is the first priority in oven improvement.
We then aim to reduce wasted heat, improve working conditions, and lower costs.

Conclusion

Drying and baking ovens consume substantial energy in coating factories.
However, they are more than heating equipment.

They develop coating-film performance.

Simply lowering oven temperature for energy saving is therefore risky.
First make visible where heat is used and where it escapes.

Check more than the setting.

Actual workpiece temperature.
Drying time.
Oven temperature variations.
Exhaust volume.
Insulation condition.
Heat leakage from openings.
Fixture or cart weight.
Conveyor speed.
Empty-operation time.
Heat experienced by operators.

These checks reveal actual improvement opportunities in drying and baking ovens.

Oven improvement goes beyond energy saving.
It stabilizes film quality, improves working conditions, reduces fuel costs, and lowers equipment load.

CoatureVietnam scientifically reviews coating processes through heat, airflow, materials, equipment, and staff movement.
We support improvements that reduce wasted heat and shop-floor burdens while protecting required film performance.

Coating the Future with Science and Care
Reviewing drying and baking ovens is one important starting point.