Certain expressions are commonly used when checking coating-line capacity.

“How many units can it coat per day?”
“How many units can run through per hour?”
“What monthly unit output can it handle?”

Thinking about production capacity through unit count is easy to understand.
It is a clear indicator for management, factory managers, production control, purchasing, and sales.

However, judging coating-line capacity from unit count alone is risky.

One hundred small parts and one hundred large covers create entirely different coating loads.
Even for a single unit, a product coated on one side and one coated on all internal and external surfaces require different application times and paint quantities.
Even with the same geometry, doubling film thickness changes paint consumption and drying load.

Coating-line capacity must be assessed through coating area and process load, rather than simple unit count.

Area density is a particularly important concept.
Here, area density means the amount of surface area to be coated that is loaded onto the line.

A coating line processes more than units.
It actually handles coating area, film thickness, paint quantity, and drying load.

1. Unit Count Alone Does Not Reveal Coating Load

Hearing that a line can coat 500 units per day may seem to define its capacity.

However, what those 500 units are makes a major difference.

Five hundred small brackets.
Five hundred large covers.
Five hundred flat sheets.
Five hundred complex frames.
Five hundred box-shaped parts coated internally as well.

All are 500 units, but their coating loads differ entirely.

Coating requires the following work.

• Deposit paint over the entire coating surface
• Achieve the required film thickness
• Coat edges and recesses
• Coat rear and internal surfaces
• Dry and cure the film
• Inspect
• Touch up where necessary

Unit count alone does not show these requirements.

Unit count is needed for production control.
However, assessing coating-line capacity accurately requires examining the coating area and process load behind that count.

2. Greater Coating Area Requires More Application Time

Products with greater coating area naturally have more surface to coat.

Greater coating area also increases the following.

• Application time
• Paint consumption
• Overspray quantity
• Booth load
• Drying-oven load
• Inspection time
• Touch-up risk

For example, a 2 m² part creates 20 times the coating-area load of a 0.1 m² part, even though each is one unit.

Unit count alone still treats both as one.

When considering coating-line capacity, check coating area per unit.

Then examine how much coating area flows through the line per day or per hour.

3. Greater Film Thickness Increases Paint Quantity and Drying Load

Film thickness matters as well as coating area.

Film thickness is the thickness of the coating film.

Even over the same area, thin and thick film requirements use different paint quantities.
Thicker application consumes more paint.
A greater paint quantity may also increase the load required for drying and curing.

For example, a product requiring a thick film for rust protection may need more than one coat.
Two coats, or a primer and topcoat, may be necessary.

Greater film thickness makes the following problems more likely.

• Sagging
• Insufficient drying
• Pinholes
• Foaming
• Retained solvent
• Underbaking
• Increased paint consumption
• Insufficient drying-oven capacity

Coating-line capacity must therefore be assessed with film-thickness requirements as well as area.

4. Area Density Is the Coating Area Loaded onto the Line

The term area density may sound somewhat difficult.

It can be understood as follows.

How much coating area travels through a given line length or time interval?

For example, hanging workpieces on a conveyor involves a hanger pitch.
Hanger pitch is the interval at which workpieces are hung.

Hanging a small part every 1 m and hanging a large cover every 1 m produce different coating areas on the line.

Higher area density increases the following loads.

• Application workload
• Mist quantity in the booth
• Paint supply quantity
• Thermal load in the drying oven
• Inspection workload
• Contact risk during conveying

Area density may be more important than unit count on a coating line.

5. Hanger Pitch Changes Line Capacity

Workpiece hanging intervals are important on conveyor coating lines.

Reducing hanger pitch allows more workpieces through in the same time.
At first glance, production capacity appears to increase.

However, excessively narrow pitch causes the following problems.

• Closely spaced workpieces are difficult to coat
• The required gun angle is difficult to achieve
• Mist affects adjacent workpieces
• Operators cannot keep up
• Robot paths are difficult to create
• Hot air has difficulty passing through the oven load
• Workpieces contact one another
• Inspection becomes difficult

Hanger pitch should not be determined by productivity alone.
Consider coating quality, workability, drying, and conveying stability together.

6. Increasing Conveyor Speed Shortens Drying Time

Increasing conveyor speed is one way to raise production capacity.

Higher speed increases workpieces per hour.
However, it shortens passage time through the drying oven.

For the same oven length, higher speed means shorter residence time.

This can cause the following problems.

• Insufficient temperature reached by the workpiece
• Insufficient curing
• Poor adhesion
• Insufficient hardness
• Coating-film defects after shipment
• Blocking in subsequent processes

When increasing line capacity, check drying-oven capacity as well as the application process.

Conveyor speed determines both productivity and drying quality.

7. Area Density Also Affects Booth Capacity

Higher area density also increases booth load.

Greater coating area increases the quantity sprayed.
More paint means more overspray.
This increases mist in the booth.

Insufficient booth capacity causes the following problems.

• Mist returning to the workpiece
• Mist flowing toward operators
• Dirt nibs
• Rough finish
• Increased booth contamination
• Filter clogging
• Increased odors
• Particle or mist emissions

Line-capacity assessment therefore requires checking whether the booth can handle the coating quantity, as well as conveyor and operator capacity.

8. Assess Drying-Oven Capacity Through Thermal Load Rather Than Unit Count Alone

Drying-oven capacity also cannot be judged by unit count alone.

The oven heats workpieces and dries and cures their coating films.

Its load varies with the following factors.

• Workpiece weight
• Workpiece material
• Workpiece thickness
• Coating area
• Film thickness
• Paint type
• Required baking temperature
• Oven residence time
• Hanging arrangement
• Loading density on the line

One hundred thin small parts and one hundred heavy metal parts require different heat quantities.

Assess oven capacity through whether workpieces reach the required temperature rather than simply how many fit inside.

Check workpiece temperature, oven temperature distribution, and holding time for this purpose.

9. Operator Capacity Also Varies with Area Density

Operator capacity is important in manual spraying.

It is sometimes assessed through units coated per hour.
However, unit count alone is again insufficient.

Operators actually coat surface area rather than merely process units.

Greater coating area requires longer application time per unit.
Complex shapes require changing angles while spraying.
Rear or internal surfaces take additional time.

Excessively high area density prevents operators from keeping up.

This causes the following problems.

• Rushed application
• Insufficient film thickness
• Missed areas
• Variations in gun distance
• Sagging
• Operator fatigue
• Quality variations

When increasing output, check that the workload allows operators to achieve quality without undue strain.

10. Area Density Also Matters When Introducing Robots

Robot coating is less dependent on human working speed.

However, area density still matters.

Greater coating area increases robot operating time.
Complex geometry requires more paths.
High film-thickness requirements require adjustment of output or overlap.

Excessively high line speed may also prevent the robot from completing the necessary coating path.

Check the following items.

• Application time per workpiece
• Robot’s effective working envelope
• Gun travel speed
• Output
• Required film thickness
• Workpiece spacing
• Conveyor speed
• Part-number changeover time
• Number of robots

Even with robots, assess capacity through coating area and application time rather than unit count alone.

11. Examine Line Load Through Paint Consumption

Paint consumption is also useful in assessing coating-line capacity.

Higher consumption increases the following loads.

• Paint supply load
• Pressure-feed tank or pump load
• Gun-cleaning load
• Booth-filter load
• Sludge generation
• VOC generation
• Drying-oven exhaust load
• Waste-treatment load

Paint consumption depends on coating area, film thickness, and transfer efficiency.

High paint consumption should prompt the following checks rather than simply being attributed to high output.

• Is coating area large?
• Is the film thick?
• Is transfer efficiency poor?
• Is overspray excessive?
• Is touch-up frequent?
• Is recoating of defects frequent?

Paint consumption is an important indicator of line load and improvement opportunities.

12. Excessive Area Density Increases Defects

Packing too many workpieces onto the line may appear to increase capacity.

However, excessive area density can increase quality defects.

Examples include the following.

• Insufficient film thickness
• Uneven film thickness
• Missed areas
• Sagging
• Returning mist
• Dirt deposition
• Insufficient drying
• Workpiece contact
• Missed inspections
• Variations caused by operator fatigue

Overloading the line to increase unit output leads to more touch-up or recoating later.

Apparent capacity may rise while actual good-product capacity falls.

A coating line needs stable good-product output more than simply a high number of units passing through.

13. Bottlenecks Determine Line Capacity

The weakest process determines coating-line capacity.

The booth can apply paint, but the oven cannot keep up.
The oven has spare capacity, but manual sprayers cannot keep up.
Application is possible, but loading and unloading are slow.
Application is possible, but inspection becomes congested.
Robots are fast, but color changes stop the line.
The booth is large, but paint supply cannot keep up.

Line capacity therefore does not depend on one piece of equipment alone.

Identify which process becomes constrained first when area density increases.

Increasing output without identifying bottlenecks increases defects or delays.

14. Common Line-Capacity Assessment Issues in Factories in Vietnam

The following line-capacity issues commonly arise in factories in Vietnam.

Assessing capacity through unit count alone.
Not knowing coating area by product.
Omitting film-thickness requirements from capacity calculations.
Increasing conveyor speed and leaving insufficient drying time.
Reducing hanger pitch too far and impairing workability.
Applying more paint than booth capacity can handle.
Not checking workpiece temperature in the oven.
Increasing output without examining operator load.
Not linking paint consumption with area and thickness.
Unclear bottleneck processes.

These conditions prevent accurate line-capacity assessment.

Assess coating-line capacity through area density and process load, as well as unit count.

15. Basic Coating-Line Capacity Checklist

The following checks provide a practical approach to line capacity.

1. Coating Area by Product

Check how many square meters are coated per unit.

2. Film-Thickness Requirements

Check target thickness, tolerance range, and number of coats.

3. Area Density

Check how much coating area is loaded onto the line.

4. Hanger Pitch

Check whether workpiece spacing suits workability and quality.

5. Conveyor Speed

Check whether speed suits application, drying, and inspection times.

6. Booth Capacity

Check whether exhaust, collection, and cleaning can keep up with the coating quantity.

7. Drying-Oven Capacity

Check workpiece temperature, oven residence time, and thermal load.

8. Operator Workload

Check manual spraying, loading and unloading, inspection, and cleaning loads.

9. Paint Consumption

Check its relationship to area, thickness, and transfer efficiency.

10. Bottlenecks

Identify the process that most limits overall line capacity.

16. The Value CoatureVietnam Sees in Line-Capacity Diagnosis

CoatureVietnam does not assess coating-line capacity through unit count alone.

The important point is how much coating area and process load the line can handle consistently.

How many units can pass through per day?
That information is necessary.

However, it is insufficient by itself.

How many square meters per unit?
What film thickness is required?
Is paint consumption appropriate?
Can the booth handle the mist?
Can the oven handle the thermal load?
Can operators coat without strain?
Are products passing through as acceptable goods?

These perspectives are needed.

CoatureVietnam examines coating lines as follows.

• Examine area as well as unit count
• Examine thickness as well as area
• Examine drying load as well as thickness
• Examine operator workload as well as equipment
• Examine good-product capacity as well as production count

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

Science means organizing coating area, film thickness, paint consumption, drying conditions, and line speed numerically to understand true capacity.
Care means creating a stable coating line without excessive operator loads or constant touch-up and recoating.

Conclusion

Do not assess coating-line capacity through unit count alone.

Even for the same 100 units, different coating areas, thicknesses, shapes, and drying conditions create entirely different loads.

Examine the following items.

Coating area.
Film thickness.
Area density.
Hanger pitch.
Conveyor speed.
Booth capacity.
Drying-oven capacity.
Operator workload.
Paint consumption.
Bottleneck processes.

A coating line handles coating area, film thickness, paint quantity, drying load, and workload, as well as units.

Increased production count is not a true capacity improvement if defects or touch-up increase.

CoatureVietnam makes coating-line capacity visible through area density and process load and provides improvement proposals that stabilize quality, increase productivity, and reduce operators’ burden in factories in Vietnam.