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To maintain the reproducibility of the coating quality at your enameling plant, it is important to monitor and control all major process parameters.
With regard to the electrostatic powder enamel application department, it is necessary to keep your ambient conditions, equipment settings and powder properties within strict tolerances.
This web page focus on testing the properties of powder porcelain enamels, which may be characterized by the following parameters :
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 = ( powder weight after impact / powder weight before impact ) x 100 %
According to the theory, there are two different methods :
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)
|Test result||Conclusion according to DEV|
|STPA > 75 %||Very safe for the enamelling shop|
|75 % > STPA > 65 %||With risk for the enameling shop|
|STPA < 65 %||Insufficient for the enameling shop|
However, please note that in order to get reproducible results, it is necessary to keep the following test parameters constant :
The application rate of powder is generally used to determine the rate of material transfer.
It may be measured by determining the gun output per unit of time and then using that value as a denominator for the amount of powder applied to a standard target at a given time.
Application rate = ( grams on target / grams output from gun ) x 100 %
|Fluidity||Outflow in gr/sec|
|Very good||4.0 - 3.5|
|Good||3.5 - 3.0|
|Fair||3.0 - 2.0|
|Insufficient||2.0 - 0.0|
However, please note that in order to get reproducible results with this test, it is necessary to keep the following test parameters constant :
The gain size spectrum has a considerable influence on its electrostatic charging and aerodynamic characteristics.
The share of coarse particles in a powder enamel can be determined by means of the Bayer
test sieve with for example a screen aperture of 0.04 mm. (= 40 mu = 16900 mesh/cm2)
The residue of powder (RP) in percentage by weight is a measure for the frequency of coarse particles.
Since the powder particle size distribution is a "normal" distribution, the one point check is usually satisfactory for determining the acceptability of a powder.
However, please note that the gain size distribution may be altered if the powder recovery at the application system is defective.
Resisitivity is determined by applying high voltage on a compressed powder enamel sample and measuring the resulting current.
Ditmer Trading & Consulting BV is a family owned company, which was founded by Ronald Ditmer in 2007.
We are specialized in providing worldwide professional services & supplies to the porcelain (vitreous) enameling & powdercoating industry.
Our Managing Director & Owner has been personally involved in 50+ industrial porcelain enameling projects since 1984, while working respectively for Ferro (Holland) BV, Smit Ovens BV, Smit Sinus Enameling BV, Nordson Corporation and/or Ditmer Trading & Consulting BV.