Precision cleaning solvents
Published

Powder Coating Clinic: Avoiding Rust on Parts

Q. We apply lighter colors of powder to our ticket machines for parking lots.

Share

Q. We apply lighter colors of powder to our ticket machines for parking lots. Some go into covered garages, but many of them are exposed to the outdoor elements. We have some problems with rust around the base of the machines and also on corners. We currently run the steel parts through a five-stage iron phosphate washer, then apply a coat of TGIC polyester powder to a thickness of around 3 or 4 mils. What else should we be doing to prevent rust?

A. Outdoor performance is a bigger challenge for any steel part that is coated with an organic finish. The exposure to sunlight and rain creates a corrosive environment that can break down a finish at its weakest points and cause corrosion cells to break through the coating. The thinnest coating is often at the sharper edges or corners of the part. The problem is compounded when the base is fastened onto a surface and the corners and holes are exposed to standing water or corrosive elements present on the ground around the product. If you use the product in a northern climate, chances are that one of those elements is salt or another corrosive chemical used to melt winter ice. 

What can be done to protect steel in a harsh outdoor environment? The first thing to concentrate on is understanding that powder coating is an engineered process. The steps in the process need to be carefully planned to meet a specific outcome. A five-stage iron phosphate pretreatment followed by a single coat of powder is outstanding for indoor product but not adequate for harsh outdoor situations. 

There are different ways to achieve the performance needed for outdoor installations. It starts with the pretreatment process. Steel can be blasted to remove inorganic soils, leaving a relatively clean, rough surface. This creates a great anchor pattern for the coating because as it cures, it hardens. Blasting does not add additional corrosion protection, but does remove elements that would otherwise interfere with adhesion or create a nucleus for a corrosion cell under the film. If you blast and then add a primer coat before the topcoat, you will drastically improve your corrosion resistance. If you want to get the best possible corrosion on a blasted surface, use a zinc-rich powder primer. The zinc in the prime layer provides barrier protection against moisture penetration to the steel surface.

If you cannot blast or choose not to blast, you can increase the performance by improving the pretreatment. A zirconium oxide treatment or zinc phosphate will increase the corrosion resistance when compared to iron phosphate. Again, the addition of a primer coat will improve corrosion resistance a lot, used with any of the aforementioned pretreatment options. One of the reasons that the double coat (primer plus topcoat) is so effective is that it increases the coverage on the sharp edges where you are most vulnerable to corrosion. If you do not have a system that lends itself to the addition of a primer coat, you must enhance the pretreatment and make sure to get a thick coating on the edges. If you can, add a radius to the corners for better coverage with a single coat.  


Originally published in the November 2016 issue. 

Cleaning Technologies Group
vacuum vapor degreasers
high-performance systems for efficient parts cleaning
Cleaning questions ask Kyzen
Echoflex modular ultrasonic cleaning machines
Precision Cleaning Solvents
Pickelx one step metal prep
Metal Pretreatment Technology

Related Content

Top Shops

Products Finishing Reveals 2024 Qualifying Top Shops

PF reveals the qualifying shops in its annual Top Shops Benchmarking Survey — a program designed to offer shops insights into their overall performance in the industry. 

Read More
Electrocoating

An Altruistic Growth Strategy Puts People First

Professional Plating emphasizes investing in its team and fostering a supportive environment on the shop floor.

Read More
Powder Coating

Selecting the Right Outdoor-Durable Powder Coating

The powder coating industry offers an array of chemistries to provide an excellent match to the manufacturer’s expectations for outdoor durability. 

Read More
Powder Coating

Calculating the Cost of Powder Coating

How can you calculate the cost of powder coating a component if you only know its surface area? Powder coating expert Rodger Talbert has the answer.

Read More

Read Next

Pollution Control

Episode 45: An Interview with Chandler Mancuso, MacDermid Envio Solutions

Chandler Mancuso, technical director with MacDermid Envio discusses updating your wastewater treatment system and implementing materials recycling solutions to increase efficiencies, control costs and reduce environmental impact.

Read More
Parts Cleaning

A ‘Clean’ Agenda Offers Unique Presentations in Chicago

The 2024 Parts Cleaning Conference, co-located with the International Manufacturing Technology Show, includes presentations by several speakers who are new to the conference and topics that have not been covered in past editions of this event.   

Read More
Parts Cleaning

Education Bringing Cleaning to Machining

Debuting new speakers and cleaning technology content during this half-day workshop co-located with IMTS 2024.

Read More
Vacuum Degreasers and Aqueous Solutions