[R-390] Front Panel Restoration soda blasting trials

[Glenn Scott via R-390]

Strange..I use the HF blaster with their coarse media and it took me half an hour or more...a full bag of media ( maybe two..can't remember) and I killed the grass in a 20x20 area in the yard even after a good flushing with the hose. Humidity is a big deal with these things and during the summer her you can plan on 90% most days.I had frequent clogs and had to purge the system often..between those problems stripping was slow and used way more media than I had hoped.  That was my first try though...will have to have another go at it.  The glass bead blasting was very quick...wiped away the paint, primer, corrosion and cleaned out the engravings quickly...it was in a blast cabinet though and nicely contained.


Cecil and anyone interested,


When you are using soda, hopefully Armex, you want the flow to be very lean. You should be able to do at least 2 panels from and back with ~40 pounds of media. You MUST have enough volume from your compressor or you will be starting and stopping constantly waiting for air and this may be causing some of the clogging problems.  I blast at a pressure of ~90psi but some shops use lower pressure but they have even more volume with larger compressors. My Quincy compressor delivers 15.4cfm @90PSI which is decent but NOT like the big shops have. My smaller compressor would only deliver about 9cfm and I had problems similar to what you described.


If the supply line to the media tank is too small, this will compromise the flow and pressure at the spray nozzle. I had a cheap Harbor freight ~$100 blasting unit 5 or 6 years ago to start with and constantly had clogging problems but some of that may have been being new at dialing in volume and pressure properly. I still have that unit and have planned to see if I could do better with it now.


When I learned to set the flow for less volume is when things started to work much better. I used less media and got faster and better results. Dialed in wrong, I was just pumping a thick spray of powder that worked very slow to not at all and wasted a huge amount of media.


**ALSO** Sodium Bicarbonates has a hardness of 2.5 on the Mohs scale. Aluminum  4 - 5 . Glass-bead is 5.5, Silica sand is 6-7, lead free glass 7... Which is my primary reason for using Sodium Bicarbonate; it will NOT burrow into the aluminum.


http://www.reade.com/Particle_Briefings/mohs_hardness_abrasive_grit.html


I am not an expert in this area and have learned by a lot of trial and error. One thing I have learned is when the process is working properly the tone of the air through the nozzle is pitched differently and the almost invisible spray of Armex cuts through paint like crazy. There may be a name for this effect, It was as if you dialed into a resonant point where performance took off. ( maybe a poor analogy)  I simply don't know. What I do know is out of the medias I have tried Soda was best by far.


Not to insult your work but I ASSUME, you know that you must use a SODA  nozzle for soda blasting. It is different than those used for sand, glass, hulls etc.


Eastwood sells a nozzle kit that can be used for abrasive units.


http://www.eastwood.com/abrasive-blast-media-vs-soda-blast-media-removing-rust-and-paint-with-media


Our summer time humidity here in SC is high as well but that does not affect what is coming out of my nozzle. I use 2 stages of water filtering and all hoses are as short as possible..


I am glad you are happy using glass and you know the inherent safety issues with silicone getting in your lungs. Soda blasting is probably as dangerous especially if you are blasting zinc chromate primers off that are often found on R390(A) panels. I have done enough of these with Soda that I am convinced this is that way I need to proceed. Though, I did go through a lot of media initially trying to get the results I had hoped for. Good luck!


73,
Glenn Scott WA4AOS
DSM Labs
glenn at dsmlabs.com



-----Original Message-----
From: Cecil <chacuff at cableone.net>
To: Glenn Scott <wa4aos at aol.com>
Cc: r-390 <r-390 at mailman.qth.net>
Sent: Sun, Jul 19, 2015 10:26 am
Subject: Re: [R-390] Front Panel Restoration Knobs Rock Tumbler


 
  
 
 
  
On Jul 18, 2015, at 9:45 PM, Glenn Scott via R-390 <  r-390 at mailman.qth.net>   
 
 
  
      
      
   Once the flow and pressure are dialed in, I can do one side of a panel in about 5 minutes or less with no subsequent picking of paint and primer from the engraves. The Armex powder pellets are small and get deep into into the engraves much better than anything else I have tried.  
 
 
  
 
 
 
  
   Strange..I use the HF blaster with their coarse media and it took me half an hour or more...a full bag of media ( maybe two..can't remember) and I killed the grass in a 20x20 area in the yard even after a good flushing with the hose. Humidity is a big deal with these things and during the summer her you can plan on 90% most days.I had frequent clogs and had to purge the system often..between those problems stripping was slow and used way more media than I had hoped.  That was my first try though...will have to have another go at it.  The glass bead blasting was very quick...wiped away the paint, primer, corrosion and cleaned out the engravings quickly...it was in a blast cabinet though and nicely contained.  
 
 
 
Cecil