The Intech Insider is designed to help readers stay in touch with the latest information & developments in the industrial coating industry. Stay connected with the Intech Insider!

Thursday, October 7, 2010

Adhesion Tips for Teflon* Coatings

One of the most critical aspects of applying a Teflon® coating is achieving proper adhesion to the metal as well as proper intercoat adhesion in multiple coat systems. 

While there are many variables that can affect substrate and intercoat adhesion of a Teflon® coating, the following information outlines the primary culprits of adhesion failures.

Substrate Adhesion

1) Clean Surface – it is critical to make sure surface is clean of all grease, grit, and other contaminants. Many coaters prebake parts and use chemical cleaners to ensure the metal surface is very clean. 

TIP: Be sure to use latex or nitrile gloves when handling parts to avoid getting dirt and grease on the clean parts

2) Roughened Surface Profile – A roughened metal surface is critical for coating adhesion. It increases the surface area and creates an anchor profile that dramatically increasing adhesion. Typically, grit-blasting the surface with aluminum oxide is the best way to roughen the surface. In situations where the metal cannot be blasted, phosphating, anodizing, and other conversion coatings can be utilized. 

3) Proper Blast Techniques – In addition to using the appropriate type blast media, it is also critical to use the proper media size and air pressure to create the optimum surface profile.    Depending on the type of metal and final coating thickness, the media size, air pressure, and recommended blast depth will vary. 

We will explore this topic in more detail in a future Intech Insider. 

4) Proper Cure – This is perhaps the most common problem area. Having control over the part temperature (not oven temperature) as well as the dwell time of the part once it reaches the goal temperature is one of the most critical aspects of processing a coating. 

TIP: We always recommend using a thermocouple to verify part temperature.

5) Special Considerations for Metal Types
a. Carbon steel - may flash rust when using water based products or when in areas of high humidity. 
            Solution: Preheat parts and spray when still warm to reduce water formation.

b. Copper, Brass - exposure to high temperatures will cause oxidization to form on the metal surface. This oxide can then loosen and cause premature peeling and ultimate adhesion failure of the coating from the substrate.
 TIP: Use some of our low cure products to avoid the formation of oxide with copper or brass
Intercoat Adhesion

1) Correct primer thickness – Primers are designed to be sprayed very thin relative to topcoats. For example, 420-703 primer should be applied at .4 - .6 mil dry film thickness (DFT). If primer is too thick, it will cause delamination of the topcoat from the primer. 

TIP: With new sprayers, spray a test panel and measure the (DFT) to demonstrate the proper amount of wet spray that should be applied to a part. Most new sprayers are not used to applying thin coatings and will over apply primer.

2) Proper cure schedule – A proper cure of the topcoat is paramount to ensure excellent intercoat adhesion. Be sure to make sure the part temperature and time are consistent with DuPont recommendations.   

TIP: Be sure to always confirm the parts cure time and temperature with a thermocouple

Testing Adhesion
There are several techniques for testing the bond strength between the coating and the metal surface. The most common test is a cross hatch test. Since this is a destructive test, it is typically performed on a test panel that is processed along with actual parts. Contact Intech for more information about this test.   

No comments:

Post a Comment