Quality Control Testing for Your Powder Coating Line

Understanding QC Testing

No matter what you are powder coating, the size of your line, or the type and color of powder, everyone aims to deliver exemplary coating jobs. We all strive to ensure our customers are happy and that their powder-coated products look impressive while performing well. Achieving a visually appealing finish is crucial, but how do you verify that your coated surfaces meet technical standards? Quality Control Testing, or QC testing, provides a variety of straightforward and easy-to-execute tests and performance criteria to ensure your powder-coated finish performs excellently. The great news is that these tests are cost-effective and simple to implement.

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You’re probably familiar with the process. You carefully apply the powder, ensuring the color matches the standard provided by the coating company – that’s what your customer desires. Aside from aesthetics, we need our coatings to deliver basic performance. Conducting simple QC tests will assure you that the powder will adhere, protect, and perform as needed when applied to the part. This promotes confidence in providing a high-quality and reliable service and ensures your customers receive a great coated piece along with an enjoyable experience, making them likely to return for future orders.

There are several straightforward QC tests that are quick and easy to conduct. Let’s delve into a few of these tests, their importance, and what to observe during the process.

Who Should Conduct QC Testing?

At IFS, we prioritize quality. As manufacturers and suppliers of top-tier industrial powder coatings, our production facilities and quality control systems are engineered with excellence in mind, utilizing advanced technologies alongside experienced staff to QC test our powders at the IFS facilities.

We perform QC testing before, during, and after the production of every product we create. However, the necessity of testing does not end there. When applying powder, testing remains equally essential. Anyone — regardless of the type of powder or operation — can carry out simple QC testing for peace of mind. It is also an excellent service attribute to offer your customers!

These basic QC procedures help assure that the product will conform to the specifications laid out in the Technical Data Sheet (TDS) that we provide. Each powder coating product includes a TDS, serving as a valuable tool to gauge expected performance. Make sure your finished coating aligns with the required standards so your customer receives the high-quality coating job they requested.

If you’re unfamiliar with TDS, let me provide some insight... at IFS Coatings, we generate a tech data sheet for every product we produce. This TDS contains a description of the product, typical physical properties (such as gloss level, hardness, flexibility, and adhesion expected from the powder when applied correctly), application tips, cure schedules, and storage requirements.

The TDS conveys a basic performance level, a quality specification that the powder can attain if applied correctly. These sheets offer ample useful information, but it’s critical not to assume the powder will automatically meet specifications — correct application is a significant factor in achieving desired performance. Below are some simple tests you may conduct and key factors to observe.

Essential QC Tests to Perform

Now that we've established who should conduct QC testing and its rationale, what exactly should we be testing for, and how can it be done? Several cost-effective and easily performed tests can significantly impact customer satisfaction. Nobody wants to dispatch a coated product that looks excellent but underperforms. Let’s delve into the tests you should consider:

Film Thickness Testing: Using a Film Thickness Meter

Image Credit: PosiTector

Ensuring uniform and appropriate film thickness is crucial. It impacts both the appearance of the coating (no one wants a patchy finish) and overall performance.

The simplest method to assess film thickness is with a Film Thickness Meter or Gauge.

Ideally used on flat surfaces, these meters are user-friendly. Typically, you press the meter against the surface, hold it for a few seconds, and receive a reading indicating the film thickness at that location. It’s advisable to repeat the test across various points on the part, as the readings may vary slightly. This practice provides an average to ensure compliance with the required film thickness range. In a brief explainer video, Dave Merritt, one of our technical service managers, illustrates this process and highlights what to look for.

Various gauge options exist; advanced models yield immediate thickness readings upon contact, while others may take longer. Some are magnetic and designed for steel or aluminum. Knowing your substrate is essential since certain meters only measure thickness for one material. Always validate compatibility to avoid miscalculations, particularly when measuring aluminum.

With film thickness gauges, you can find options at various price points. Basic, accurate models can start around $100, while more advanced gauges, which can be calibrated, typically range from $400 to $800. For those willing to invest heavily in equipment, advanced models can be priced around $2,000.

Film Thickness Testing Failures

It’s important to remember that film thickness measurements must fall within a specific range. Failure can occur due to excessive or insufficient thickness. Too little thickness leads to poor appearance, inadequate substrate coverage, and failure of related tests like corrosion resistance. Conversely, excessive thickness can result in adverse appearances and can cause failures in impact and flexibility tests.

Addressing Film Thickness Issues:

Fortunately, resolving film thickness challenges in powder coating is generally straightforward. Regular testing with your film thickness gauge will help you assess whether you have mastered the proper application technique and corrected any related issues.

Problem

Potential Cause

Recommended Solution

Uneven film thickness

Excessive proximity between the gun and the part

Relocate the gun further away from the part.

Inconsistent powder delivery

Optimize equipment/air settings.

Variable voltage

Examine the entire setup (from voltage source to electrode) to ensure continuous electrical charge.

The Solvent Rub Test

Another valuable testing method is the solvent rub test, which measures the degree of cure of a coating. Ensuring your coating is fully cured is vital as it directly impacts performance. This is assessed by evaluating the coating's resistance to solvents.

The two primary solvents used for this test are acetone and the more common Methyl Ethyl Ketone (MEK).

The MEK test adheres to ASTM standard protocols, making it both simple and efficient. The procedure involves wetting a cotton swab with acetone or MEK and firmly rubbing it over the coated surface. Generally, you should conduct 25 double rubs, where pressing down and lifting counts as one double rub. The coating's performance can vary based on product type or resin system used; for instance, some powders like epoxies can endure up to 50 double rubs.

Upon completing the 25 double rubs, you might notice slight de-glossing of the coating. Minor de-glossing can still signify a passing grade; however, significant material transfer onto the Q-Tip indicates insufficient curing.

It’s essential to understand that certain resin systems might underperform on solvent resistance tests, misleading you to believe that an uncured state exists when, in fact, it may just be a characteristic of that particular resin type. Always consult with your manufacturer regarding new products to clarify expectations.

The solvent rub test is quick, cost-effective, and easy to conduct! Watch this short video where Dave Merritt demonstrates the process and highlights what to observe.

If you encounter a test failure, check your oven temperature and dwell time. Ensure parts have enough time to reach operating temperatures before being subjected to curing. Reheating and sustaining temperature levels throughout the curing process is crucial. It is sometimes possible to reintroduce parts to the oven for additional curing, while other times, recoating and recuring may be necessary. For persistent issues, reach out to IFS for technical advice.

Common Causes of Solvent Rub Test Failures

If your solvent rub test results indicate failure, various factors may be responsible, but temperature and curing time are typically the most critical. Refer to the technical data sheet for the recommended oven temperature and curing duration. If a powder fails a QC test, consider adjusting the oven temperature upward by 10 or 15 degrees to see if it resolves the issue, or verify if the component spent enough time in the oven.

Don’t overlook the thickness of metals used; thicker metals naturally require longer periods to reach curing temperatures.

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In case of a failure, check oven performance, ensuring sufficient temperature and time for curing.

Experience Matters

It’s noteworthy that the solvent testing process often requires practical experience. Some minor discrepancies can be accepted, while others need more attention depending on the product's known performance characteristics. Over time and repeated testing, you will develop an understanding of what is acceptable and what is not.

The Pencil Hardness Test

Once you have established good curing protocols, the pencil hardness test provides an effective means to evaluate scratch resistance and overall coating hardness. The ASTM D method allows for the use of known hardness pencils, which are drawn across the coating surface at a consistent angle and pressure.

Pencils vary in hardness; “B” pencils signify the softest category, while “H” pencils indicate the hardest. Additional numerical ratings (such as 2H or 6H) represent variations in hardness within that category. As numbers rise, so does hardness, making 4H stronger than an H pencil.

High-quality powder coatings usually fall within the H range, so if your TDS or customer specification demands a 2H pencil hardness, that’s the standard to follow.

To perform the test, ensure your pencil is sharp, creating a flat tip using sandpaper. Position the pencil at a 45-degree angle to the coated surface and apply pressure while pushing it across. A penetration down to the metal indicates failure; absence of scratches denotes a passing result. In this brief video, Dave walks you through conducting the pencil hardness test and the criteria for assessment.

This test is simple, affordable, and effectively demonstrates the quality of your application. However, ensure you maintain a reliable set of pencils. Low-quality, worn-out, or generic-brand pencils can yield inconsistent results. When using the pencil test, we recommend investing in a trusted brand, available at most art supply stores, to ensure consistent performance across the hardness range. Testing an additional coated piece until it fails could reveal that your offered hardness rating exceeds requirements, a valuable selling point!

Additionally, note that varying individuals and pencils may yield different results due to the manual nature of the process. Maintaining consistency in the pencils and applied pressure will lead to fairer results. Regularly executing the test will help familiarize you with your scales and strengths.

Pencil Hardness Testing Failures

The pencil hardness test typically fails due to two primary issues: under-cure or over-cure. Always consult the technical data sheet to verify curing guidelines, specifically time and temperature.

The Crosshatch Adhesion Test

The Cross Hatch Adhesion Test is a popular method for assessing coating adhesion and provides a visual evaluation of the bond quality with the substrate. This test is straightforward and should be incorporated when checking powder coating adhesion!

The procedure entails creating a series of intersecting cuts through the coating. Use specialized kits containing preferred blade devices for each film type. Usually, five cuts are made in one direction using five sharp blades placed close together, followed by cuts in the perpendicular direction, creating a tic-tac-toe pattern.

After creating this grid, apply pressure-sensitive adhesive tape over it, press firmly, and then remove the tape. Inspect the area to see if any paint was pulled off along the cuts. A test that shows no coating removal is deemed a pass. Minimal breaches in one or two corners might still qualify as acceptable. In the attached video, Dave demonstrates the crosshatch adhesion test method.

An ASTM rating scale helps determine performance — a 5B result is typically ideal.

To ensure you conduct the test correctly, invest in a quality crosshatch adhesion test kit and routinely maintain it to guarantee precise and consistent testing. Kits usually range from $30 to $100.

Remember, this test is fast, simple, and cost-effective, and we highly recommend obtaining a comprehensive adhesion testing kit as part of your QC process.

Reasons for Crosshatch Adhesion Failures

Coating failures during the crosshatch adhesion test usually result from one of two scenarios: inadequate pre-treatment or poor substrate preparation, which can lead to adhesion problems. Thus, verifying your pretreatment process and the substrate’s cleanliness should be your first step.

Alternatively, under-cured paint can also contribute to a test failure. Refer to methods discussed in the solvent rub testing section for checks.

Visual Inspections

Thus far, we’ve discussed QC tests that include hands-on tools and movement, but simple visual inspections can also yield significant insights. While this may seem straightforward and obvious, various factors must be considered during visual checks. Where should you conduct these inspections? On the floor? Indoors? Outdoors? Here are important considerations...

It remains crucial to conduct visual tests in conditions mirroring how your customers will inspect and utilize the coated product. If customers are likely to assess the product in a specific light, you should conduct your tests under the same conditions.

For more controlled testing compared to indoor or outdoor spaces, many job shops use light boxes to regulate light conditions, although they require a substantial investment. The distance from which you examine the surface also matters, particularly when identifying surface defects. Observing at a 90-degree angle from a distance will yield different results compared to inspecting from a 45-degree angle up close. Our recommendation is to conduct visual tests using various light sources — in office settings, on the shop floor, and outdoors — to ensure comprehensive assessments.

Mica metallics can appear different under varying light conditions, potentially leading to disputes over color, making consensus on test measurement conditions paramount. Be mindful not only of lighting but also of the angles from which you evaluate or compare the coating.

While presenting too many variables may complicate visual inspections, remember that customers will instinctively conduct this check upon receiving the coated part, so aligning expectations in advance is vital.

Visual Inspection Failures

Visual assessments can reveal a range of defects, including craters, orange peel effect, and window framing; each can stem from changes or issues in the application process. We cover these topics in greater detail within our dedicated articles on appearance-related issues. For now, let’s focus on the basics: color and gloss.

Depending on the color used, results may vary. Generally, if a coating darkens, yellows, or exhibits de-glossing, there’s a strong chance of over-curing. If it appears lighter or more bluish than expected, coupled with excessively high gloss, under-curing might be the issue.

Discoloration could suggest film thickness variations, overheating, or even issues with oven exhaust. While challenges like these exist, they are often straightforward to address.

Conclusion

These tests represent just a fraction of the array of Quality Control procedures that are not only inexpensive but also easy to implement. Consistent execution should be a part of your standard practice to ensure high-quality processes, products, and satisfied customers. Ultimately, they afford you peace of mind that the coated parts leaving your operation are up to standard. Moreover, the more you conduct these tests, the more proficient you will become at delivering consistent evaluations and interpreting results.

While you may not wish to conduct every test or find all applicable to each project, performing the solvent rub test and crosshatch adhesion test serves as foundational practices that yield excellent results. Visually, confirm color and gloss alignment; otherwise, the customer will likely voice concerns. Maintain your reputation as a premier coater by thoroughly inspecting each job before dispatch.

None of the tests described above are particularly complex, and they are generally affordable to carry out. Like many procedures, consistency is crucial. Ensure uniform testing conditions across your operations — whether among you, your customers, or staff — to sustain reliable outcomes. Finally, remember that experience amplifies the quality of your testing; the more you practice, the more confident and efficient you’ll become in evaluating and resolving any ambiguous results.

For further inquiries or detailed information, feel free to get in touch with our team.