Undercar: The Science Behind Traction And Braking
A best practice to follow before any repair work begins is to get the color dialed in.
Article courtesy BodyShop Business.
Collision repair facilities today face many challenges with paint. Here are some common problems and how to overcome them.
Contaminants and Color
Meeting customer expectations at the time of delivery often boils down to the appearance of the vehicle repair. Nothing stands out more than a poor color match or contaminants in the finish. The best way to manage these issues is to create standard operating procedures and make sure your team follows them.
The worst time to discover you have a color variation is when the vehicle is in the booth ready to be painted. A best practice to follow before any repair work begins is to get the color dialed in. The painter should check the paint code, mix the color and create a sprayout card to confirm an acceptable match. A portable spectrophotometer is always helpful, but a keen eye is usually all you need. All of this will help you avoid bottlenecks and not delay other time-sensitive repairs.
It’s easy to understand how contaminants can get in the booth and become an unexpected accessory to a paint finish. Good housekeeping will save a lot of time and headaches. SprayMax suggests the best practices include:
- Thoroughly blowing sanding dust from under the hood and door jambs, ducts and crevices.
- Keeping hoses and booth floors well-maintained and free from materials that could be picked up and transferred during the painting operation.
Don’t forget that personal protective equipment like paint suits, air masks, hoods and work boots are magnets for particles (big and small). Follow the simple actions above and you can significantly reduce the need for wet sanding and polishing vehicles before customer pickup.
Dieback and Solvent Pop
Dieback, or loss of gloss in a clearcoat finish, and solvent pop are common problems that can result from a variety of scenarios:
- Too long of a period between coats, which allows the first coat to partially skin over, leading to trapped solvent in the underlying coat.
- Topcoating waterborne basecoats before they are flashed
- correctly, trapping moisture.
- Improper mixing of hardener into the clear.
- Insufficient air flow after clearcoat is applied, such as turning the booth off too quickly.
- Clearcoats are over-reduced with urethane reducers. Many clearcoats are “viscosity correct” without reduction. Reducing them can lead to solvent “boil” as the solvent evaporates.
- Adding reducer, as once again excessive solvents become trapped and cannot escape from the underlying film.
- Using too fast of a hardener for the temperature conditions.
- Using a low-quality clearcoat that does not have adequate resin technology.
To avoid these problems, U-POL states that one of the most important things to do is use a premium, two-component clearcoat with high-quality resins and UV inhibitors to prevent loss of gloss.
Next, it is critical to follow the application instructions outlined in the manufacturer’s technical data sheets regarding flash-time between coats as well as reducing/not reducing.
There are two ways to get rid of dieback, depending on the exact cause, severity and size of the repair. In less severe cases where the dieback is in the top layer of clear, it may be possible to sand the affected area with 2000/3000 grit abrasives and polish the affected area to bring back the gloss. In more severe instances, it is recommended to re-sand the repair area exhibiting dieback and reapply the clearcoat according to the manufacturer’s technical data sheet. However, depending on the loss of gloss, it may be necessary to re-sand the repair area and reapply both the basecoat and clearcoat according to the manufacturer’s instructions.
Some painters expect a perfect color match without color verification. While it may not be the most common issue in the refinish department, it has one of the most significant impacts on the refinish department’s cycle times and paint and material profitability.
Sherwin-Williams emphasizes that the color verification process must be done early in the repair process to reduce or eliminate color match issues in the spraybooth. The paint applied to the vehicle is a “part” of the repair process. Just as replacement parts are verified for correctness before assembling, the color must also be verified before application. Color verification is critical for every car; just because the last three vehicles with the same paint code were painted using variant-1, you can’t assume it will match the fourth car with the same color code.
The color verification process should include:
- A review of the repair order with the production manager. Is there enough area for a successful blend? Can the customer’s expectations be achieved?
- Reading the vehicle with a photo-spectrometer.
- Reviewing the available formulas and color chip location in the color retrieval program.
- Checking to see if you have an existing sprayout card that is an acceptable match.
- Creating a sprayout card in the same environment, using the same equipment and air pressure that is going to be used to refinish the vehicle.
- Evaluating the color in natural sunlight or with a full-spectrum light source.
Speed, Speed, Speed
Collision repair facilities face many challenges with paint, everything from proper mixing to achieving an acceptable final appearance for the customer.
However, Industrial Finishes identified that one of the biggest paint challenges facing today’s body shop is getting more jobs out the door to achieve higher profitability. The speed of cure of auto refinish paint chemistry (2K polyurethane), along with multi-step painting processes (body repair, primer, basecoat, clearcoat), limit many shops’ productivity. Typically, the use of a spraybooth with a convection heat bake oven is used to try to accelerate the paint curing process when using standard refinish paint products, but this approach can only go so far.
In terms of process speed, it is possible to significantly shorten drying and/or cure schedules of auto refinish coatings by using modern technology such as infrared curing equipment. Usually, this approach is most effective with clearcoats, but can also be used with basecoats and/or primers. Infrared curing equipment has been available for a long time, but recent developments in monitoring and automation have enabled entire spraybooths to be converted into extremely effective application and curing stations. Properly employed, infrared curing can decrease paint cure cycle times by up to 70%.
In terms of clearcoat chemistry, it is also possible to develop fast-drying 2K polyurethane clearcoats for use on smaller repair areas (one to three panels). These “speed clears” can significantly increase productivity on certain jobs without the need for curing or baking equipment. The chemistry utilizes special high-molecular weight polymers in the “A” component, which provide a “lacquer-dry” effect yet include the durability and appearance of a 2K polyurethane. They are especially useful in body shops that do not have heated spraybooths.
One of the most common paint issues in collision repair facilities is not properly cleaning a surface and painting over contaminants, which can cause problems such as low gloss, cratering and poor adhesion. Ten of the 28 common errors discussed in AkzoNobel’s “Solving Application Errors” class come from poor surface cleaning.
Proper surface cleaning is critical. It is the foundation of a shop’s work, and good surface cleaning actually saves paint and materials. Here are some recommended steps:
- Start with two types of cleaner – waterborne followed by solventborne, ensuring the use of proper cleaner for the substrate and contamination (cleaners can differ between metal and plastic prep, for example).
- Use clean, white, lint-free rags during the cleaning process.
- Use a two-rag method of wiping and cleaning – one rag to wet and clean the surface, the other to remove contaminants and thoroughly dry the surface.
- Change rags frequently.
- Thoroughly dry surface before the cleaner evaporates.
- Remember that plastic parts must be thoroughly cleaned to remove mold release agents with proper surface cleaners; following good processes helps prevent costly redos.
- Be sure to use manufacturer-recommended PPE when handling any cleaning products.
Quick Color Matching
Many collision repair facilities find it challenging to achieve a high-quality color match quickly. Factors such as dynamic consumer color preferences, increased demand for additional color choices and emerging paint technologies that produce unique effects such as increased sparkle and high saturation challenge high-quality color matching.
New variations of existing colors are frequently created in automotive assembly plants to keep up with demand and the ever-evolving market. These variations require that paint manufacturers develop variant formulas to provide quality color matches, which adds complexity to the job.
Axalta recommends that collision repair facilities optimize their color match performance by utilizing the correct tools and providing employees with ongoing training. When it comes to finding the closest color match, spectrophotometers and variant fan decks are the most effective tools on the market.
Color blending is an advantageous technique to achieve a quality color match since application equipment and style can impact the final color position. Using these tools and offering easy access to training, collision repair facilities can ensure their employees are always set up for success and prepared to use the latest methods for achieving the right color match.
Runs and Sags
Occasionally, the clearcoat is applied and develops runs or sags. A run or sag resembles a drip or a curtain in the film. PPG identified that some of the causes could be:
- Air pressure of the spray equipment is too low.
- The spray gun is held too close to the item being painted.
- Not enough flash-time in between coats.
- Too much material being applied.
- Too slow of a reducer or hardener for the spray environment.
Possible ways to prevent runs or sags include:
- Making sure air pressure is adjusted and fluid per any technical data sheet or gun chart.
- Choose the proper solvent or hardener.
- Adjust spray technique for speed and path.
- Allow proper flash-times in between coats.
Once there is a run or sag in the clearcoat, the way to correct it is to allow the paint to fully cure and sand smooth and polish.
Pinching/Loss of Gloss
The most common paint issue tends to be dieback, says BASF. Dieback can also be referred to as pinching, or loss of gloss. This problem can be caused by several different things, which makes it one of the more difficult paint issues to solve. And while it can be immediately apparent, it often shows up days or even weeks later. It can be intermittent as well, due to different environmental conditions.
The major cause of dieback is trapped solvent in the paint process. The key to solving dieback is determining which layer is causing the issue and address it. Different layers can require different remedies:
- Body filler can cause it, due to lack of curing, which could be caused by improper mixing of the filler, insufficient curing time or too low of curing temperatures.
- Primer can also be the source of dieback. Proper hardener/reducer selection for the environment is important; if the temperature in your shop changes throughout the year, so should your hardener/reducer. Proper curing times are needed, as well as curing temperature.
- Sealers, just like primers, need a proper hardener/reducer selection. The most common way that sealers cause dieback is from too much film build and too little flash-time. Respect the flash-times indicated on the TDS.
- Dieback in waterborne shops is frequently caused by the basecoat. In high-humidity conditions, waterborne basecoat can be very difficult to dry. Most paint manufacturers have special processes and products to help the basecoat dry properly even in extreme conditions. It’s important to know those processes and change those processes when those extreme conditions are present.
- Clearcoat hardener and reducer selection is important, and booth airflow can cause issues with clearcoat as well. Excessive airflow in the spraybooth can cause clearcoats to dry too fast on the surface, trapping solvent.