Understanding Striping in Automated Finishing Systems

Common Finishing Problems

Part 1 of 7: Striping

Coating defects can slow production, increase rework, and affect the quality of your finished products. Whether you're coating cabinet doors, furniture components, millwork, flooring, or other wood products, understanding what causes common finishing defects is the first step toward preventing them.

In this series, we'll explore seven of the most common defects found in automated finishing systems, explaining what they look like, what causes them, and how to troubleshoot them before they become costly production problems.

Our first topic is striping, one of the easiest finishing defects to recognize and one of the most preventable when your equipment is properly set up.

What Is Striping?

Striping is a finishing defect that appears as visible lines, bands, or differences in color, sheen, or coating thickness across a finished surface. In automated finishing systems, striping is most commonly caused by clogged spray tips, improper spray overlap, incorrect synchronization of the X and Y axes, or spray gun alignment issues.

Striping is one of the most common coating defects seen in automated spray finishing

operations. Sometimes the stripes appear as differences in color, while other times they show up as changes in gloss or sheen.

One of the challenges with striping is that it isn't always visible right away. A part may look acceptable as it leaves the spray machine, only for the stripes to become much more noticeable after the coating dries.

Because striping affects the appearance of the finished product, it is often one of the first defects noticed by operators, quality inspectors, or customers.

How to Identify Striping

Striping doesn't always look the same from one application to the next, but there are several common signs to watch for.

You may be dealing with striping if you notice:

• Light and dark bands across the surface

• Changes in gloss or sheen

• Visible spray pattern lines

• An uneven appearance after the coating dries

• Areas that appear to have more or less coating than surrounding surfaces

When checking for striping, don't focus only on the center of the part.

In many cases, striping is easier to spot along the edges of a door, panel, or component. Changes in light reflection near the edges often make uneven coating application more noticeable than it appears across the center of the surface.

Taking a few extra seconds to inspect the edges can help catch striping before parts move further down the production line.

What Causes Striping?

Unlike some finishing defects that are caused by contamination or substrate conditions, striping is usually an application issue. While there are several possible causes, they all lead to the same result: the coating isn't being applied evenly across the surface.

The most common causes include:

• Partially clogged, worn, or damaged spray tips

• Improper synchronization of the X and Y axes

• Spray guns that are out of alignment

• Air caps that are installed at different angles

• Inconsistent spray patterns from one gun to another

Clogged, Worn, or Damaged Spray Tips

One of the first things to check is the condition of the spray tips. If a tip becomes partially clogged, worn, or damaged, it can change the spray pattern and cause one gun to apply more or less material than the others.

Even a small restriction in one tip can create visible stripes across the finished part, making clogged tips one of the most common and easiest causes to identify.

X and Y Axis Synchronization

Another common cause is improper synchronization between the machine's X and Y axes.

In simple terms, the X axis is the movement of the part through the machine on the conveyor, while the Y axis controls the movement of the spray guns across the width of the conveyor.

These two movements have to work together. If the reciprocator is not moving at the correct speed for the conveyor speed, the spray pattern won't overlap evenly.

Some areas receive more coating than others, resulting in visible striping.

In many automated finishing applications, the reciprocator is programmed to achieve approximately a 50% overlap between spray passes. This helps ensure the coating is applied evenly across the entire surface.

Spray Gun Alignment

Spray guns should be positioned consistently across the reciprocator. If one gun is slightly out of alignment, it can apply a different amount of coating or direct the spray pattern differently than the others, creating visible stripes in the finish.

Air Cap Alignment

Air caps also need to be installed and aligned correctly. Even a slight change in air cap orientation can alter the shape or direction of the spray pattern, resulting in uneven coating application.

Inconsistent Spray Patterns

Every spray gun on the machine should produce a uniform spray pattern. If one gun is producing a pattern that differs from the others because of wear, contamination, or improper setup, the finish may develop visible striping.

The good news is that striping is usually one of the easier finishing defects to diagnose and correct once the source is identified.

Why Striping Matters

At first glance, striping may seem like only a cosmetic issue.

However, it can also indicate that the coating isn't being applied evenly across the entire part. Areas receiving less material may not provide the same level of protection as areas receiving the proper amount of coating.

Depending on the product and coating system, this can affect:

• Wear resistance

• Chemical resistance

• Moisture protection

• Overall coating life

Maintaining a consistent film build helps ensure the finished product not only looks good but also performs as intended.

Why Automation Helps Prevent Striping

One of the biggest advantages of automated finishing is consistency.

Once an automated finishing system has been properly developed and programmed, it repeats the same process every cycle. Spray guns remain in the correct position, reciprocators follow the same programmed path, and conveyor speeds stay consistent.

This repeatability greatly reduces the application variations that often lead to striping.

Of course, every finishing application is different. The ideal settings for one coating or product may not be the right settings for another. Factors such as part size, part geometry, coating chemistry, and production speed all influence how the finish should be applied.

That's why proper process development is so important.

Getting the Process Right Before Production

The best time to prevent striping is before production begins.

Every finishing application has its own requirements, which is why application testing plays an important role in implementing an automated finishing system.

During testing, technicians determine the best settings for:

• Conveyor speed

• Reciprocator speed

• Spray gun positioning

• Spray pattern overlap

• Material flow rates

The goal is simple: apply a consistent amount of coating across every part.

At Superfici America, application testing is used to develop and validate these settings before a system goes into production. This helps manufacturers start with a process that is optimized for their products, coatings, and production goals while reducing the risk of striping and other application-related defects.

How to Troubleshoot Striping

If striping begins to appear during production, start by inspecting the application equipment before looking at the coating or substrate.

Ask yourself:

• Are any spray tips clogged, worn, or damaged?

• Is every gun producing a consistent spray pattern?

• Are the X and Y axes properly synchronized?

• Is the reciprocator moving at the correct speed for the conveyor speed?

• Are the spray patterns overlapping consistently?

• Are all spray guns aligned correctly?

• Are the air caps installed and aligned properly?

A clogged spray tip can quickly create an uneven spray pattern, making it one of the first things worth checking when striping appears unexpectedly.

Likewise, if the reciprocator movement and conveyor movement are not properly synchronized, the spray overlap will become inconsistent even if the rest of the system is functioning correctly.

If the spray tips and spray patterns look good, continue checking the synchronization of the X and Y axes, spray overlap, gun alignment, and air cap orientation.

Because striping is typically an application issue, these checks will often lead you to the source of the problem.

Frequently Asked Questions

What causes striping in automated finishing systems?

Striping is most commonly caused by clogged spray tips, improper spray overlap, incorrect synchronization of the X and Y axes, or misaligned spray guns.

Is striping a coating defect or a substrate defect?

In most automated finishing systems, striping is considered an application defect rather than a substrate defect.

Can striping affect coating durability?

Yes. If striping results in uneven coating thickness, some areas may have reduced protection against wear, moisture, or chemicals.

How do you prevent striping?

Striping can often be prevented through routine inspection of spray tips, proper equipment setup, application testing, regular maintenance, and consistent process control.

Is striping easier to see on the edges of a part?

Often, yes. The edges of doors and panels tend to reflect light differently, making changes in coating thickness or gloss easier to spot than in the center of the surface.

This article is part of Superfici America's Common Finishing Problems Series, where we explore the causes, prevention, and troubleshooting of the most common coating defects found in automated finishing operations.

Looking Ahead

Striping is a great example of how small changes in application settings or spray equipment can create noticeable quality issues. Fortunately, it's also one of the most preventable defects in an automated finishing operation when equipment is properly maintained, application parameters are validated, and the process is monitored consistently.

In Part 2 of this series, we'll examine Orange Peel, another common finishing defect that creates a textured surface resembling the skin of an orange. Unlike striping, Orange Peel is often influenced by factors such as atomization, viscosity, and coating flow, making it a very different troubleshooting process.

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Read: Orange Peel in Automated Finishing Systems (Coming Soon.)

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