Bubbles in the outside wet lacquer after curing
Remedy 1 – Too much heat during the first part of the curing process:
- The tin flow has to to be only as wide as the width of the powder and / or lacquer stripe and not more (usually around 15 mm for food and aerosol cans)!
- This width covers also lateral shifting can bodies during the daily production.
- The internal powder must have a low melting point, starting from 180°C.
- Most commercially available and good powder coats are fulfilling this demand.
- For further information for recommended powders, contact Soudronic support.
- The conveyor speed in the oven is too high, therefore the curing time too short.
- Distances between the cans of more than 1/2 canbody height is a reduction in curing time of 25% (or from 5 sec. to only about 3,8 sec.!).
- The adjustment of the coil to the can bodies is wrong.
- The curing length is too short (before order a longer curing system, please follow first the Correctives 2 and 3!)
Remedy 2 – The wet lacquer application is not constant, too thick or too thin!
- Especially for induction curing system, with shorter curing time, a constant film thickness is required!
- Please note that a constant and a “as thin as possible” lacquer application is essential not only on the curing effect, but it also reduces the lacquer cost!
- The can body must be round – within standard tolerance -, overlap begin and end must be equal!
- Depending on the configuration, rubber roller or steel rollers must be used!
- The speed of the application roller is wrong, compared to the passing can bodies!
- Generally it can be said, that a too high application roll speed leads to worse results than a too slow one.
- Depending on steel or rubber rollers different speed than can body speed might be used, but must be controlled and monitored.
- The material and / or the form of the rubber/steel roller profile is wrong!
- For the use of a steel roll (longer lifetime) we urgently recommend to have a “supporting conveyor “under” can body (available from Soudronic)
Remedy 3 – Wrong wet lacquer type in use:
- Not every wet lacquer type is applicable for induction curing system due to the fact that the heat up ramps are much faster than with a gas curing system.
- For a list of recommended lacquers contact Soudronic
- The correct viscosity and therefore the proportion of solvent is most important for a non-porous side seam protection.