Testing powder enamel adhesion

Introduction

Adhesion checks are most probably the best indicator of the condition of the powder.

The adhesion of a powder is usually tested by applying a normal coating on a panel at standard settings.

After a certain time interval, the panel is subjected to an impact of a controlled force, which is reproducible.

Adhesion formula

The adhesion strength may be calculated by means of the following formula :

Adhesion = ( powder weight after impact / powder weight before impact ) x 100 %

Test methodes

According to the theory, there are two different methods :

• STPA - Short Time Powder Adhesion
• LTPA - Long Time Powder Adhesion

The only difference between the STPA and LTPA method is the duration of the time interval between powder application and impact. (1 minute versus 15 minutes)

Important aspects

However, please note that in order to get reproducible results, it is necessary to keep the following test parameters constant :

• Film thickness of applied powder
• Gun settings like tension, flow rate and atomizing air
• Pressure, temperature and humidity of compressed air
• Ambient conditions between application and impact
• Force of impact