Solutions to incorrect Chopper gun use


Potential quality problems resulting from substandard workmanship

Potential Quality Problems Resulting from Substandard Workmanship and Inconsistent Maintenance of MVP Machines

Please be aware that the following problems (affecting quality) are a potential result due to FRP machine operators using poorly maintained equipment or exercising substandard workmanship.

These problems most often take weeks, months or even years to show up as faults in fiberglass products.

Blister Formation Behind gel coats
Highly possible with "external mix" gel coaters / spray equipment when operators do not pay attention. Especially with high viscosity filled systems such as barrier coats or gel coats. The blister size can range from 0.5 mm up to the size of a R 5,00 coin. This can happen if the catalyst spray tip is partly blocked and not atomising correctly. Splattering of catalyst on to the gelcoat exciting the nozzle is not mixed in to the gelcoat at all!

The catalyst is "splattered" (not dispersed adequately) on top of the gelcoat instead of being mixed in. This happens due to poor vapour pressure or blockage of the catalyst spray tip. Thus liquid catalyst drops - which are not easily visible to the eye - fall onto the mould or newly sprayed gelcoat surface, and do not actually mix in properly. Make sure that spray tips are cleaned after use and free from dripping gelcoat.

When resin or barrier coat is sprayed on top of the gelcoat (with the small liquid catalyst drops now on the gelcoat) the following scenario will take place; the high concentration of catalyst drops are trapped between the gelcoat and barrier coat layer. It will not be absorbed or mixed with the resin. The resin forms a "skin" around the drop - sealing it in. Later, that drop will form a gas if exposed to the sun - appearing as a blister, and in a marine environment will, due to an osmotic effect also form a blister. This blister may eventually rupture and exude a pungent vinegar like smell.

The same can happen with damaged turbulent or incorrect turbulent mixers in internal mix machines where the catalyst is not dispersed correctly.

Struggling to Achieve Adequate Spray Pattern
Note that in the small external mix, Pro Rider gel coaters - which one struggles to spray higher viscosity gel coats - the atomisation pressure needs to be increased even higher on the catalyst spray tip, than the normal 10-15 PSI. This is to improve the "mixing in" (blending) of catalyst in to the gelcoat. (Operators do not like this because it increases the level of catalyst vapour in the air.) You need to ensure ventilation and safety equipment is in place. 

If you are not achieving a good spray fan (the projection of product from the nozzle) you cannot achieve adequate catalyst dispersion with external mix machines. Blisters and other problems may arise including poor UV stability, poor gloss retention, colour instability and tackiness.

Poor Curing Due to Excessive or Under Catalisation
We often fail to realise or link the following problems to poor maintenance of machines which result in either poor catalyst dispersion, over catalisation or under catalisation. Poor maintenance includes faults such as:

a. Damaged or improper turbulent mixers (there are different types for filled and unfilled resin systems).
b. Incorrect catalyst slave arm settings (0.5% is sufficient for filled resins but not for unfilled systems).
c. Blocked catalyst up - take valves, resulting in less catalyst usage than the machine settings, damaged hoses, incorrect catalyst being used LPT on gelcoat instead of Butanox M50.
d. Damaged catalyst fluid pumps.

The following problems can occur:

  • Product distortion or warping a few weeks after production.
  • Excessive print through in undercatalised gelcoat.
  • Poor gloss and colour retention in under catalysed gel coats.
  • Wet spots that "dry" instead of cure resulting in a dull finish that attract dust and dirt more than normal.
  • Over catalisation can also result in increased yellowing and reduced UV stability of gel coats.
  • Poorly catalysed laminates will not demonstrate good corrosion resistance in VE resins.
  • Poorly catalysed laminates will not meet the required mechanical properties.

 


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