By
Sarge
I have two means of cleaning paint/rust here and some thoughts that might help others about their use and mods to make them perform better . One is an old Snap On glass bead blast cabinet that lives in the basement shop , the other an older model Clarke sand blasting pot . The Snap On works ok , but it's gun was super expensive as well as replacement tips and especially the tempered glass window in the cabinet . Solved the gun issue with a TP Tools Scat gun with a carbide blast nozzle and their custom pickup tube design which helps to better mix air into the media stream since this cabinet is a suction type . The dumb glass window and it's associated gasket was replaced with some aluminum extrusions , gaskets and just common grade single strength glass from the Hardware store . Lasts just about as long as the tempered , much easier to change and I've only broken it once . I also opened up the cabinet's air intake with a larger hole and diversion baffle to help it flow air better . Still needs a proper dust extractor , will eventually get a Scat Hepa type as they have a nice design and far better pricing on filters and such . TP also has some pretty good rubber coated gloves at half the cost of Snap On - and they last longer .
The Clarke blast pot has been a pain in the keister for a very long time . I hated the dead man valve setup it used , the tips weren't easy to get nor cheap for their short life span and they only sell the dumb things in 3-packs that are 3 different sizes , if you need only the 1 size you're screwed with quite a few useless spares . A trip to the large Auction site and solved that problem by switching to a ball valve setup that a guy builds that uses the more common and far more durable 3-3/4" long by 5/8" tip by 1-1/8" base tapered ceramic venturi nozzles . Now - for the warning : this is not a dead man setup , if you drop it or something happens to you that setup will not shut itself off since it's just a common ball valve , so be wary with it . However , those tapered cone style nozzles last 50 times longer than the little junk design short ones that come with these common Chinese built blast pots . There is another dead man gun out there that might work better if you want to go that route and it will use the cone style nozzles , but it's quite cumbersome and hard to use in tight areas . To stop blasting , this one works by just shutting the ball valve off , quickly . Be aware that his included valve won't last long since it's brass - the thing wasn't even machined straight and the Black diamond media found it's way around the ball in short order , so it started to leak/bypass air pressure a bit . Once that gets started , in a short time of about 100lbs of coal slag it blew a hole in the side of the valve . Found an old heavy USA made steel valve rated for high pressure steam systems - this one should hold up for a long time .
First , let's start with a bit of lesson on media - it can be the biggest part of what you're trying to accomplish . Too heavy of a grit requires a much larger nozzle and far higher cfm compressor , which most people don't have . The profile left by that larger media or screen size can also damage lighter gauge sheet metal , aluminum and other soft metals - it will leave a very rough profile . Now , on heavier rusty , scaled steel such as 1/8" thickness - it's perfect but having enough cfm is the problem .
Here's a chart to help understand the media sizing :
http://www.blackdiamondabrasives.com/media/1060/usminerals-blackdiamond-nozzleconversionchart.pdf
The numbering system is the screening sizing - 2040 means grit size between 20 and 40 grit , which is pretty aggressive and works only with larger cfm/hole size tips , otherwise it will clog easily . At 3/16" nozzle sizing , that would require either a very high volume reciprocating 2-stage compressor over 30cfm or a engine driven rotary . Running 30/60 grit and using the smaller 1/8" nozzle allows the use of a good quality 2-stage compressor in the 23-28cfm range . Common size machine for most shops and finding a good used one is generally pretty easy . It must be a continuous run capable unit - not the cheap modern versions sold in the stores today but a commercial grade type with a heavy cast iron pump and at least 5hp . Anything smaller/lighter won't last long and can't keep up with the demand of the cfm required - you'll just burn it up and probably ruin the pump/motor in short order from heat . I use an old early 80's Speed Air 27cfm 2-stage unit with 5hp heavy series motor - this thing is north of 500lbs total with the 80 gallon tank and was a freebie - but needed repairs such as new legs and some work on it's pressure switch . It's ran here for nearly 20yrs now with barely a glitch , oil changed when it turns dark and new air filters when needed - will probably outlive me . Nice part of this one is the common Champion rebuild/gasket/reed kits will fit it as the pumps were made by Champion in my hometown of Princeton , Illinois . If you can find an older R-30 series equipped pump/ 80 gallon compressor used - buy it as they run forever . Prior to 1985 is best , but even later models are far better than other brands .
Now , to the pot -
This old Clarke used a crappy cast tee and brass ball valve to regulate the media at the bottom of the tank . This results in a less than consistent media flow and the tee's won't last long due to the media having to make that 90* turn when it's mixing into the air stream . I found some mods others have done on the net and ordered a malleable iron wye fitting in 1/2"NPT . Not easy to find , but they are out there -
https://www.amazon.com/FNPT-Malleable-Iron-Wye/dp/B0078S2P4Q/ref=sr_1_3?ie=UTF8&qid=1504186031&sr=8-3&keywords=1%2F2"+wye
This fitting mod allows a much smoother transition and far better/more consistent mixing of the media and air as well as provides better overall air flow/volume . Much less clogging at the valve as well . It took some adapters and such to get it fitted but sure made a difference how well the unit works .
I'll have to get some better pics but you can pick the wye out in this photo of yesterday - trying to clean out a batch of wet media from the pot (no , not fun) .
Blasting this irritating 6.5'x12' US Cargo utility trailer and it's heavy mill scale/rust/paint . They evidently used imported steel and the mill scale layer is tough to get off - not to mention they painted right over the top of it , which allows it to rust from inside out easily . The heavy rust/mill scale where the decking was sitting had to first be removed with the needle scaler - otherwise you'll spend a lot of extra time blasting it off as the stuff creates a cushion to the media stream . Needle scaler is the Ingersoll Rand attachment version that fits the common air hammers threaded heads - scaler runs on a simple medium barrel one and works great for the $40 cost at TSC .
This all started when the trailer was loaded , the big D180's hydro coupling failed and I had to put the trailer on the jack loaded . The original tongue was only built with 1/8" thick 2x3 angle iron - not a good idea in my opinion but I'm no engineer . Needless to say - the tongue failed when the trailer tried to roll against the wheel chocks when it was on the jack - just a slight depression in the driveway did the damage as the tongue just twisted into a pretzel as I was trying to hook it up to the truck . Watching it slowly go sideways to the ground in the truck's rear view camera is a sight no one wants to see , trust me .
New tongue is 2x3x3/16" wall rectangular tubing , US Steel specifically . All welded with 7018 rod with beveled joints in 2 passes for proper strength . This will also help stiffen the nose of this thing - the angle iron allowed far too much flex in the front half of their design - it had cracked 4 welds in the main frame already - all of which have been properly repaired .
Between the heavy mill scale and rust in the main frame areas I've had to switch from the lighter 80/100 grit from Menard's https://www.menards.com/main/building-materials/concrete-cement-masonry/bagged-concrete-cement-mortar/black-blast-blasting-sand/p-1444445322601.htm
to the more coarse 2040 Black Diamond from TSC . The only nozzle size I had here was the 1/8" tapered cones so I'm waiting on UPS this morning to bring the 5/32" size nozzles from McMaster in Chicago - I love how they can get me stuff overnight .
I'll try to get some better pics today of the blast profiles , Clarke pot tank mods and the nozzle setups I'm using . Maybe it will help others determine what to get and how to use it when cleaning their tractors/equipment/trailers for restoration work or otherwise . So far this mill scale issue has cost me 14-50lb bags of coal slag . I should have used the heavier grit size to start with , but the finer grit should have done the job . I will say this - the Black Blast brand from Menard's might be cheaper at $6.99/bag , but the amount of dust and extra fine media isn't worth the savings unless you're doing very light work . The Black Diamond brand is far more consistent and nearly no dust or fines , but it also costs more at $7.99/bag . If the trailer hadn't been so bad to start with I'd have used a large tarp to catch the media and recycle it into the pot with a sifting screen to keep out the junk . It's more work , but does save money in the long term .
Hope this all helps - figured I'd give back to the forum a bit while I'm waiting on the brown guy to show up with my nozzles ...lol .
Sarge
By DennisThornton