Wednesday, November 8, 2017

Putting Theory to Work

Sprayed with 4 thick layers of gelcoat

Up until now, all this has been a big theory and there have been some engineering obstacles to overcome.  Little by little, the sprayability of the Duratec and gelcoat has been perfected.  The pressures and flow rates have been perfected.  All that has been sprayed is a bunch of plastic sheets to see how things might appear in reality.





Sprayed with 'Guide Coat'
The idea is not to start with some grand piece of repair.  It's to start with something small in case it doesn't work out, the damage won't be too great nor the mess too big to clean up.  The first trial was to spray the television base which is made out of a piece of G10 epoxy board.  This worked well and I got an idea to what thickness the gelcoat needed to be applied.  This also helped the learning curve improve bit by bit.



Initial sanding of the guide coat with the mouse sander
Trying to make the black spots evenly distributed
The next level was to spray the cockpit storage locker lids.  They were in pretty bad shape with cracks and rotted core material which all needed to be repaired first.  Then the insides were all sprayed.  This a true test of the large scale repeat-ability of the spray system.  Since I was spraying the inside of the lockers, a screw up wouldn't be so dramatic here either.   

 
All went well and we geared up to spray the outsides.  Each lid took an hour to complete.  Basically 4 coats of gelcoat with 10 minutes between coats and 20 minutes wait time before moving the lid to a safe place to dry.  The lids also required much more hand sanding and detail work with the finishing than an entire side of the boat.  This also helped the learning curve.



Wet sanding with the 'Softie'
After the lids were sprayed and allowed to cure for a day, a "guide coat" thinned out Black Oxide primer was sprayed over all the new gelcoat.  The guide coat helps show where the orange peel has been sanded and where it hasn't.  It really helped keeping from over-sanding through the gelcoat and ending up having thin or no gelcoat.  The corners are particularly sensitive to over-sanding since the sanding disc can cut through at one place rapidly without any warning.  They must all be hand sanded with light block pressure and fingers. 

Progressively remove more gelcoat with finer sandpaper
Initial sanding was done with 80 grit on the mouse sander.  Then 120 grit on a Softie glue pad.  Next came 330 grit, then 800 grit, then compound on a buffing pad, then wax.  There is some hand sanding, especially on the corners but the beauty of what I am seeing is that 90% of the work can be done with machine sanding and polishing.  This should make quick work of the big areas when that time comes. 
Rough sanded, no guide coat remaining






















Final finish and polished














Sunday, November 5, 2017

Pressure Gauges and Regulators



I thought that once you set a pressure regulator to a certain position, the corresponding pressure would stay constant.  Turns out that's not the case. If you turn off the air and reapply it, the pressure will be completely different.
Gauges are accurate, regulators are imprecise.  Every time you reapply air to a regulator, it needs to be adjusted on the gauge to provide the pressure that you need. 

If you change the regulator input pressure, the output also changes, not much but it doesn't stay constant.  That doesn't seem too regulated to me.  I need very exact pressures to the pressure pots to provide a constant, measurable, flow of materials to the spray gun.  Plus or minus 10% is not good enough.  My solution was to regulate the regulators.  I regulate the air coming out of the compressor to 40 psi.  This is then regulated to 20 psi at the tank with another regulator. and then a 3rd and final stage is the only regulator that I have to actually adjust provides the pressure to the tanks.  This 3 stage regulation works very well and the pressure stays right where I need it, plus or minus 1%. 





From the picture on the right, when the outlet pressure equals the spring pressure on the diaphragm, the poppet valve closes.  It won't open again until the outlet pressure drops somewhere below the spring pressure.  This will cause fluctuations in the output pressure every time the poppet valve opens and closes.



Regulators are also not very accurate in the extremes.  Either very low of very high pressures don't allow the internal spring tension to work in a very linear manner. 












To solve both of these problems, I put a calibrated orifice on the tank.  Basically I drilled a hole in a fitting.  This always leaks air at a constant rate and keeps the poppet valve always slightly open and makes the spring tension operate more in the middle of it's range.  This would  be a stupid idea if I was trying to regulate the pressure of something like Propane, but it is just air and so what if it leaks.

The bottom line is that you must adjust the regulator pressure to read on the gauge exactly what you want every time you set up the system.  Trust the gauge, not the regulator.

Saturday, November 4, 2017

The Pressure Pots



Gelcoat Pressure Pot. -  5 Liters
I bought a nice 5 Liter pressure pot online and had it shipped to Malaysia.  It can hold a gallon container and actually has a pneumatic mixer that stirs the material without having to open the pot.  I thought that was a silly thing but it turned out to be very useful.  The biggest problem was the 100 psi pressure gauge.  I need 6 psi to push the gelcoat to the gun.  It was hard to get any type of exact reproducible reading at the low end of the scale so I got a 1 Bar (14.7 psi) gauge locally which has worked great. 



This is the Catalyst Pot that didn't work
For the catalyst pot, I initially planned to use a 1 Liter HVLP pressure pot from a Harbor Freight spray gun.  I adapted it and got it hosed it to the gun.  The big problem with it was that air always leaked from around the seal and that MEKP is a highly corrosive oxidizer.  The MEKP turned the aluminum and brass parts into chunks of scale which kept clogging the catalyst orifice on the spray gun.  I even installed a motor bike fuel filter in the line as a band-aid fix but that didn't keep the catalyst turn grey because it was eating the aluminum.  In the end, a new solution needed to be found.  Either plastic or stainless steel seemed to like a good idea.   





The Catalyst Pot Version 2
When we were home last summer, I fabricated one almost entirely out of 316 stainless steel.  I was fortunate enough to find a 100% 316 stainless 1 bar gauge and a nice 316 chemical reactor vessel.  I had to drill and tap 2 holes in the top.  One for the air supply and one for the pickup tube.  The brass pieces below and to the left of the gauge make up the calibrated orifice.  The double regulation gives a much more stable pressure at such a low pressure (2 psi).





Tuesday, October 31, 2017

Binks Mach 1 PCX Spray Gun



Robot Spray Gun

The next piece of the puzzle goes a long way toward being able to spray without mixing pre-catalyzed batches of material.  Factory and robotic production of fiberglass resin products have been using external catalyzation.  This is where the resin and catalyst are mixed in the airstream after leaving the sprayer.







Binks 2100GW
Binks makes a few external catalyzing hand spray guns.  I initially considered using the 2100GW.  This gun has a small catalyst bottle attached to the side of the gun.  It seemed to be fine for small repairs but one thing you don't want to do is run out of catalyst while spraying.  This would cause under or no catalyzation at all.  I also felt that it doesn't allow using the gun in all positions since the catalyst could be sloshing around in the bottle and the pickup tube may become uncovered and suck up air.




Binks Mach 1 PCX
Fortunately, Binks  also makes the Mach 1 PCX.  It is a very specialty product and since only a few are sold, the price is quite expensive.  Much more than I ever thought I would spend on a spray gun.  It is an HVLP (High Volume, Low Pressure) system.  The resin is routed to the gun by a hose from a pressure pot.  The catalyst is also routed to the gun through a second hose from it's pressure pot.  The air comes through a third hose to provide atomization.  This allows for spraying in any position and the catalyst quantity is only limited by the size of you tank.

 

The orifice size is 2.4 mm which is sufficiently large enough to spray high viscosity material like gelcoat.  Car paint orifices are half that size which is why those guns will not work unless the gelcoat is really thinned out.

Sunday, October 29, 2017

Catalyzation and Curing



Gelcoat is mixed with MEKP (Methyl Ethyl Ketone Peroxide) catalyst.  The MEKP bonds with the resin molecules and forms a hard polyester plastic.  The chemical reaction gives off some heat and in theory, all the MEKP is bonded and used up in the reaction.


The ratio of MEKP to resin is between 1 and 4% depending on the temperature.  The more MEKP, or the higher the temperature, the faster the resin will cure.
A fast cure is also not a good cure.  The reaction takes time and if the resin 'kicks' too fast, there will be unused catalyst in the polyester matrix. A 20-30 minute cure time is a good reasonable time to have.  As can be seen from this chart, 4% catalyzation at 5C will cure in 2 hours while at 20C it will cure in 5 minutes.

The daytime temperature here in Malaysia is around 32C (90F).  This does not give a lot of time for catalyzed resin to be applied.  If you mixed a batch, put it in a spray gun and started applying, it would probably turn into a hard chunk of plastic before you were done spraying.  This would ruin the gun and obviously this would make it very difficult to do a large area like an entire boat. 

Even if you were to apply early on the cool morning with 1% MEKP, you have to thoroughly clean the gun spray gun between each batch or the residue will still harden in the gun even though more material is added.


There are spray guns for small projects that use disposable cups. Even using a gun like this, the material sprayed in the beginning could have a cure time of 20 minutes while the material at the end may only have a few minutes, if that.  These guns are also more like spatter guns than spray guns.  There is not a fine misting orifice nor a controlled airflow pattern like you would find on a proper spray gun.



Friday, October 27, 2017

Duratec 904-001 Hi-Gloss Additive



Gelcoat will not harden if exposed to air.  When it is sprayed into a mold, the mold itself keeps the air away from that side and allows it to cure.  When the fiberglass cloth and resin is layed up on top of the gelcoat, it keeps the air away from that side.   

If you are using gelcoat in a layup like the picture above, you actually do not want the surface of the gelcoat to cure hard because the subsequent cloth layers will not have a molecular bond and stick very well, and delamination could occur.

To get gelcoat to harden when it is exposed to air such as an external repair of spray job, liquid wax is added or a mold release agent is sprayed over it to keep the air away.  While curing, the wax rises to the surface and forms a barrier to the air.  The key to getting this to work out well is to not add too much wax, which causes porosity, and not have the gelcoat cure too fast, giving enough time for the wax to rise.  It's a tough balancing act and if it fails, the gelcoat will be sticky and gum up the sandpaper.

A California company, Dura Technologies has created an additive that you mix 1:1 with gelcoat.  It slightly thins the mixture but best of all, it allows the gelcoat to air cure and not be sticky.  Since we will be spraying multiple layers to build up a sandable thickness, a layer of wax does not form on the surface between coats preventing adhesion of multiple layers.  They also claim that it allows a Hi-Gloss super hard surface and it makes spraying gelcoat like spraying paint.   

We'll see.

http://duratec1.com/pdf/DS 904-001.pdf

Thursday, October 26, 2017

Gelcoat vs. Paint




Gelcoat is the usually white layer that covers a fiberglass boat.  It's kind of like paint but much thicker.  It is actually just pigmented fiberglass resin. The same thing that the boat is made of.   Normally it is the first thing sprayed into the boat's mold and becomes the outer surface when the hull is removed from the mold.










Over time, gelcoat get oxidized and pitted from UV and the elements.  Sanding to deoxidize, compounding, and waxing only go so far.  Dirt and stuff sits in the porosity and the color just becomes dingy.   


One solution is to paint the entire boat with car paint.  Quite a few older boats have this done and it looks good for a few years but scratches easily, is hard to repair, and needs to be done again every 5 years.  The going price in the Caribbean and Mexico for a monohull was around $6,000 USD.  
$20K Paint Job
  
There is a catamaran here that was just painted for $20,000 and the guy thinks he got a pretty good deal.  Once you paint a boat, you can never go back to gelcoat unless you sand off all the paint.  




 In my opinion, the only reason to paint a boat is if it is constructed out of Epoxy or if you are selling it and don't care much about the future owner. To me, painting a boat is not something that you want to build into a continual maintenance schedule.  There's enough of that already.  My goal is to do it once and have it last for 15-20 years.

The Preval can cover about 2 square feet
I have done quite a few gelcoat repairs in the past.  Both gelcoat and paint surface preparation is extensive. Gelcoat, however, can bury small scratches whereas paint is so thin that the surface needs to be perfect before spraying.  With small repairs, a disposable spray bottle like the Preval is used.  The gelcoat is thinned down with styrene, extra wax additive, the material is catalyzed, and is sprayed like spray paint out of a can.  The real work comes after it dries.  Since gelcoat is thick, the surface has an orange peel texture that needs to be sanded to get to a smooth surface and then sanded with finer and finer grit sandpaper and compounded until it has a brilliant shine.

So my real challenge is to scale up what I have done on small areas with the Preval and make it work in the 90 degree heat of Malaysia.   No worries.