When considering coating line productivity, many operations first check equipment capacity.

How many coating booth stations are available?
How many meters long is the curing oven?
At what speed in m/min does the conveyor run?
How many pieces can pass through per hour?
How many automatic coating machines are installed?
How many operators are assigned?

Equipment capacity is, of course, important.
However, actual coating line productivity is not determined by equipment capacity alone.

Even if equipment capacity appears sufficient, production may not actually proceed according to plan.

The cause lies in the workflow routes.

Where are workpieces stopping?
Where are operators walking around?
How far do they go to fetch paint or fixtures?
How much downtime occurs for color changes and cleaning?
Where do inspection and drying queues occur?
Where do defective products and rework return?

If these workflow routes are poor, overall line productivity will not improve even when equipment capacity is available.

Coating line productivity is determined first by workflow routes, ahead of equipment capacity.

1. Equipment Capacity and Actual Productivity Are Not the Same

Coating equipment has capacities stated in its catalog.

Booth size.
Fan air volume.
Conveyor speed.
Curing oven temperature.
Effective curing oven length.
Automatic coating machine processing speed.
Pretreatment equipment capacity.

These allow a calculation of how many pieces the line can process per day.

In actual operations, however, flow often does not follow that calculation.

This is because coating lines involve many supporting tasks in addition to the time equipment operates.

Preparing workpieces.
Hanging them on fixtures.
Mixing paint.
Masking.
Changing coating conditions.
Changing colors.
Cleaning guns and piping.
Waiting for cooling after drying.
Inspecting.
Repairing defective products.
Returning rework.

If these tasks create bottlenecks, the line stops even with high equipment capacity.

In a coating line, what happens between pieces of equipment matters more than the capacity of each individual unit.

2. Places Where Workpieces Stop Reveal the Causes of Reduced Productivity

When improving a coating line, the first places to examine are those where workpieces stop.

They stop in untreated product staging.
They stop after pretreatment.
They stop before coating.
They stop before the curing oven.
They stop while waiting for cooling after drying.
They stop before inspection.
They stop in the defective product area.
They stop at the point where they return as rework.

There is always a reason why workpieces stop at a particular place.

Is the loading sequence from the preceding process poor?
Is pretreatment capacity insufficient?
Are there too many coating booth changeovers?
Is curing oven capacity the bottleneck?
Is cooling space insufficient?
Are there too few inspectors?
Are decisions on defective products delayed?
Is the rework route unclear?

To improve productivity, check where workpieces stop before increasing equipment capacity.

Workpiece accumulation is a signal from the line.
It provides a starting point for improvement.

3. Operator Walking Distance Is a Hidden Loss

Operator walking distance greatly affects coating line productivity.

Operators repeatedly fetch paint.
They travel far to fetch fixtures.
The cleaning area is distant.
They walk to the inspection area.
They transport defective products elsewhere.
They move to check work instructions.

The travel time for each trip may appear short.
However, dozens of trips per day create a substantial loss.

Long walking distances also increase operator fatigue.
Greater fatigue leads to work errors, missed checks, and quality variation.

It is important to observe where operators walk around on a coating line.

Frequent operator movement may have causes such as the following.

• Paint storage is far away
• Fixture storage is far away
• The cleaning area is far away
• Tool storage locations are not defined
• Work instruction displays are difficult to understand
• The defective product area is far away
• The inspection area and coating process are separated

Operator movements indicate which workflow routes need improvement.

4. Poor Supply of Paint, Fixtures, and Auxiliary Materials Stops the Line

Coating lines need paint, thinner, fixtures, tools, and auxiliary materials, as well as workpieces.

Poor supply of these items stops the line.

Paint has not been prepared.
Curing agents are not nearby.
Thinner is insufficient.
Fixtures are insufficient.
Masking materials are unavailable.
Cleaning tools cannot be found.
Replacement filters are unavailable.
Tools are not in their designated locations.

These small shortages and searches reduce coating line productivity.

In high-mix, low-volume production in particular, each product requires different paint, fixtures, and operating conditions.
Delays in preparing materials or auxiliary supplies therefore leave the entire line waiting.

Even high equipment capacity cannot improve productivity unless the necessary materials and fixtures arrive when needed.

Improving coating line workflow routes requires examining the flow of paint, fixtures, and auxiliary materials, as well as workpieces.

5. Color Changes and Cleaning Are Major Causes of Coating Line Downtime

Coating lines require color and paint changes.

These require cleaning spray guns, cups, hoses, piping, booth surroundings, and fixtures.
Inadequate cleaning leads to color contamination, dirt inclusions, cratering, and coating film defects.

However, cleaning takes time.
It also uses thinner.
It places a substantial burden on operators.

Color changes and cleaning are major causes of downtime, particularly in operations with many colors or frequent small production lots.

Check the following points.

• How many color changes occur?
• Is the color change sequence optimal?
• Is the cleaning area easy to work in?
• Is cleaning thinner consumption known?
• Is waste thinner storage nearby?
• Are cleaning completion criteria clear?
• Do defects occur after color changes?
• Is color change time established as a standard time?

Color changes and cleaning greatly affect coating line productivity.
Before increasing equipment capacity, review the workflow routes for color changes and cleaning.

6. Bottlenecks Commonly Occur Before and After the Curing Oven

One of the places where coating lines readily develop bottlenecks is around the curing oven.

A curing oven requires a certain time to dry and cure the coating film.
If line speed or oven length is unsuitable, the curing oven becomes a bottleneck.

The following problems also commonly occur before and after the curing oven.

• Coated workpieces accumulate before the curing oven
• Required flash-off time cannot be provided
• The loading sequence into the curing oven is disrupted
• Cooling space after drying is insufficient
• Products awaiting cooling are placed in aisles
• Inspection space is insufficient
• Finished products accumulate at the curing oven exit

Workflow routes before entry into and after exit from the curing oven matter, as well as the oven’s capacity itself.

Some paints can enter the curing oven immediately after application, while others require a defined flash-off time.
Touching products immediately after drying can also leave scratches or marks.

Areas before and after the curing oven need to be designed for the required waiting, cooling, and inspection times, and staging space.

7. Delayed Inspection Allows the Same Defects to Continue

Inspection is also important when considering coating line productivity.

Delayed inspection may reveal a large quantity of defective products later.
By then, many workpieces may already have been coated under the same conditions.

Examples include the following defects.

• Debris and dirt inclusions
• Sagging
• Uneven color
• Gloss defects
• Insufficient film thickness
• Excessive film thickness
• Insufficient drying
• Scratches
• Cratering

Prompt feedback of inspection results to the coating process allows conditions to be corrected early.
However, distant inspection areas, delayed records, or slow information sharing create a risk of continuing to produce the same defects.

This also has a major effect on productivity.

More defective products require repair, recoating, and reinspection.
They use additional paint, thinner, working time, and curing oven time.
Waste also increases.

Inspection does more than identify defects at the exit.
It returns information so the line can be corrected promptly.

Improving coating line productivity also requires designing inspection information flow.

8. Define Return Routes for Defective Products and Rework

Coating lines generate defective products and rework.

The issue is where to return them.

There is no defective product area.
Rework is not labeled.
Acceptable and defective products are placed close together.
The route for reinspection after repair is not defined.
Products requiring recoating interrupt the normal product flow.
It is unclear who decides on rework.

These conditions create confusion on the shop floor.

Rework follows a different path from normal products.
It therefore needs dedicated staging areas, labels, approval, return routes, and reinspection rules.

Actual productivity falls substantially on lines where defective product and rework flow is undefined.
This is because rework requires additional shop-floor decisions, transport, inspection, paint preparation, and drying time, as well as the work itself.

Productivity improvement must also consider routes for handling defective products as part of workflow routing.

9. In High-Mix, Low-Volume Production, Setup Capability Matters More Than Equipment Capacity

High-mix, low-volume production is common on coating lines.

There are many colors.
Product shapes differ.
Paint types differ.
Film thickness requirements differ.
Drying conditions differ.
Masking requirements differ.
Inspection criteria differ.

In such operations, productivity cannot be discussed in terms of equipment capacity alone.

Setup and changeover capability becomes important.

In what order should products be coated?
Which color should come first?
Which fixtures should be used?
Where should masking be performed?
When should paint be mixed?
When should cleaning be performed?
How should urgent insertions be handled?
Who should check operating conditions?

Poor setup and preparation stop the line in high-mix, low-volume production.
Conversely, good preparation may improve productivity without adding equipment.

Before increasing equipment capacity, review changeover time, the number of color changes, cleaning time, and work sequence.

10. Review Flow Before Adding Equipment

When production cannot keep up, additional equipment may be considered.

Add booths.
Add curing ovens.
Add operators.
Introduce automatic coating machines.
Extend conveyors.

Additional equipment is, of course, sometimes necessary.

However, flow should be reviewed first, before equipment is added.

Is the equipment really the bottleneck?
Or is the loading sequence poor?
Are there too many color changes?
Does cleaning take too long?
Is workpiece staging space insufficient?
Are products waiting for inspection?
Are operators walking around?
Is there excessive rework of defective products?

Adding equipment without checking these points may simply create a bottleneck elsewhere.

For example, adding booths will not improve productivity if the curing oven is congested.
Adding curing ovens will not deliver finished products if inspection cannot keep up.
Introducing an automatic coating machine will not prevent stoppages if fixture preparation or color changes are slow.

Review flow before investing in equipment.
This is also important for improving the return on investment.

11. How CoatureVietnam Assesses Coating Line Productivity

CoatureVietnam does not judge coating line productivity by equipment capacity alone.

It checks from perspectives such as the following.

Workpiece flow

Where workpieces stop, backtrack, or become mixed along the route from untreated products to finished products.

Operator movements

Where operators walk, wait, or perform overly demanding work.

Paint and fixture supply

Whether paint, thinner, fixtures, tools, and masking materials are supplied when needed.

Color changes and cleaning

Whether color change time, cleaning time, waste thinner volume, and cleaning completion criteria are managed.

Before and after the curing oven

Whether the flow of flash-off, drying, cooling, and inspection has bottlenecks.

Inspection feedback

Whether defect information returns promptly to the coating process and a system prevents continued production of the same defects.

Rework returns

Whether staging areas and return routes for defective, repaired, and recoated products are clear.

Coating line productivity is assessed by considering equipment capacity, workflow routes, setup and preparation, information, and quality together.

Summary

Coating line productivity is not determined by equipment capacity alone.

Even high coating booth capacity cannot improve productivity if workpieces stop before the booth.
Even sufficient curing oven capacity cannot deliver finished products if cooling or inspection creates bottlenecks.
Even an automatic coating machine cannot prevent line stoppages if color changes or fixture preparation are slow.
Operators walking around increase hidden losses.
Without feedback of inspection results, the same defects continue to be produced.

When assessing a coating line, it is important to examine flow before equipment.

Where are workpieces stopping?
Where are people walking?
Where are paint or fixtures insufficient?
How much downtime occurs for color changes or cleaning?
How quickly do inspection results return to the process?
Where do defective products and rework flow?

These questions provide clues for productivity improvement.

CoatureVietnam examines coating lines through workflow routes and connections between processes, rather than isolated equipment.
It organizes the flow of workpieces, people, materials, inspection, and rework to make the most of equipment capacity.

Coating the Future with Science and Care.
Organizing coating line workflow routes improves productivity and also reduces the burden on people working on the shop floor.