Choose the Right Process Heating Equipment To Cure Your Powder Coat
Powder coatings are increasingly used today to create finishes not only on metal parts, as was the primary application in the past, but also for MDF (medium density fiberboard) products such as furniture and kitchen cabinets. Metal parts are also being finished in innovative ways. Appliance boxes are coated in flat form and then bent into shape, which requires a very strong yet flexible bond so the finish doesn’t crack.
Preparing surfaces and curing powder coats for some of these newer applications (and even the older ones) can be tricky. Your process needs to be precisely controlled, and it’s important to choose equipment that’s designed to help you do that.
1. Advantages and challenges of using powder coatings
It’s no surprise that so many manufacturers are turning to powder coating finishes instead of using liquid water-based or solvent-based finishes. Powder coating offers some important financial, safety and product quality benefits:
- A tougher, stronger finish. Powder coatings are bonded to the surface material in a way that creates a longer-lasting finish. One example is in the automotive industry, where manufacturers use powder coatings on vehicle hoods and alloy wheels. The additional finish on top of the paint protects these parts from the impact of pebbles, sand and even salt from the road.
- Lower risk to health, safety and environment. Powder coatings don’t require the use of solvents, so there are no VOCs released into the atmosphere. Not only does this choice more environmentally-friendly, but it protects your workers and even consumers from the health and safety risks associated with exposure to VOCs.
- Reduced material waste. Paints and finishes in liquid form require overspray to ensure that edges and corners are sufficiently covered. This overspray produces a great deal of waste. Powder coating eliminates that waste and saves you money, since the oversprayed powder is captured and recycled.
However, powder coating does present certain challenges. Surface preparation and uniform heating are critical to a quality result.
2. The importance of surface preparation
Just like applying any other type of finish, surface preparation is key to achieving a strong and durable bond between your powder coating and the surface material.
- MDF: This material is challenging for two reasons: wood is not a very conductive material, and it absorbs moisture. If you coated MDF without getting rid of the moisture, the coating would not adhere well, and moisture would bubble up and cause pinholes in your coating. Pre-drying the MDF before applying the powder coat removes the moisture and improves the finish.
- Cast metal parts. All metal parts need to be cleaned before coating, but cast metal parts such as faucets and plumbing fixtures need an additional step. Gases are trapped during the casting process that, like moisture in MDF, can cause detects in your finished product. Removing these gases is accomplished by pre-heating the parts to a temperature higher than the curing temperature of the powder.
3. The curing process
Once your surface has been prepared and the powder coating applied, the powder is converted to a coating with a three-step process:
- Melting. First, the powder-coated surface is heated to the point where the powder melts.
- Gelling. Once the molten state is reached, a cross-linking process occurs where the finish components interact and form a smooth film.
- Curing. During this stage the coating is fully cured and actually bonds to the surface material that you are coating.
Each stage of the process has different heating requirements that make your oven design critically important to achieving a quality result.
4. The right equipment design ensures a good bond
Powder coating curing can be accomplished with a hot air oven, but the process can take upwards of 15 to 20 minutes. There’s also the issue of blowing air that needs to be minimized during the melting stage to avoid blowing the powder off the surface. Using IR heating is often a better choice, since there is no moving air and the job can be accomplished in 4 to 5 minutes… that makes that process 3 to 4 times faster.
In addition to choosing the right type of heat, you also need an oven with multiple heating zones that can be individually controlled. That’s because each stage of the powder coating curing process has different heating requirements.
For these reasons, a three-zone infrared oven is commonly used for curing powder coatings. Typically these ovens feature an overhead conveyor that moves hanging parts at a specified speed through each zone. A vertical tunnel of IR heaters applies heat on both sides.
Due to its intense energy, one of the challenges of using IR is getting uniform heating across all surfaces of the product, especially when you’re working with a 3-dimensional surface. It’s crucial to make sure the energy flux is designed so that some product surfaces don’t get overheated while others are under-cured. Look for a design that uses multiple zones in machine direction as well as vertically to get good, uniform heating and ensure a strong bond.
The most effective design will always be one that’s created for your specific product and process needs. That’s why it pays to choose a vendor with demonstrated process knowledge, and also one that takes the time to work through the details of your process to discover the best possible solution.
If you are new to powder coating, or not sure your current process heating equipment vendor has the process knowledge you need, you may need to seek out new suppliers. If you’re worried about the risk of using someone new, learn how to properly vet a new vendor to avoid mistakes by downloading a copy of our helpful guide