View Full Version : Has anyone used smaller than #80 grit for blasting before park?
September 01, 2001, 16:21
I am currently using #80 brown aluminum oxide for blasting before park. I wanted to experiment with other grits/combinations.
I was wondering, what is the smallest grit that can be used with decent park results? I am afraid that #220 will only polish and not leave a rough enough surface for the park to stick on.
Also, has anyone used some kind of combo, such as 50/50 mixture of #180 aluminum oxide and fine (100-200) or extra fine (170-325) glass beads? What were your results?
Remember, this is prep for park not blueing.
September 01, 2001, 17:20
For whatever it's worth ...just about any surface-finish will "take" parkerization, as long as it is cleaned down to bare (white) metal. The Park does not actually stick to the metal ... it convets the top layer to a chemical compostion of phophate, iron, zinc/manganese, depending on the type of park solution. Typicall, it will produce a grainy copy of the orginal finish before Parking. Before I rigged up my "poor-boy" blasting cabinet, I just hand-polished the parts with fine grit paper. The finish ended up very smooth and satisfactory - almost like a sort of "blued" finish, but dark black. I have seen receivers done with very coarse grit to clean to bare metal, then a very fine grit (or glass beads)to polish. They ended up with a beautiful,extremely fine grain, velvety finish. Experiment on some bits of metal and try to develop a process that gives you consistant results that you like. And then share it with the rest of us...
September 01, 2001, 19:58
We use a 50/50 mix of 120 grit carbide and aluminum oxide media to blast all parts before parkerizing. It wears out normal blaster jets and nozzles fairly qwik, so we use Boron Carbide jets and nozzles. Rotate both of them after each 4 hrs of use to keep from wearing a groove in the blaster parts.
September 01, 2001, 20:09
What is this "toy box sand" we have seen in many posts? I understand it can be purchased at hardware stores, which franchise? Thanks :D
September 01, 2001, 21:21
Toy box sand is exactly what it sounds like. You can get it at any Wal-Mart and Home Depot. It literally is the sand that you use to fill sand boxes with.
That being said, I understand that toy box sand is too coarse and will leave a very rough surface on your parts. If you use a silica type sand you should use "fine" construction sand.
I use aluminum oxide since I recycle my media in a table top blast cabinet.
September 01, 2001, 21:40
I've been using #220 glass beads with good results. Just make sure everything is super clean. To my way of thinking, aluminum oxide is just too abrasive.
September 01, 2001, 22:00
I hear that glass beads break down rather rapidly above 55 psi. Have you found this the case?
I want to try glass beads, but I don't want to buy a 50lb pail and find out that I made a mistake.
September 01, 2001, 22:47
I use 120 grit silica sand at 50psi. Bought it at local lumber yard for about 5 bucks for a 50lb bag. Best results and finish I have found. I have tried the others.
September 02, 2001, 18:20
I have used a #220 Aluminum Oxide grit with very good results. It puts a smaller tooth than the large grit. The end finish after Parkerizing is all but the same as the original finish. The #80 grit some folks are using leaves the surface much rougher than it was intended to be. However, it does cover up a lot of minor dings better. I spend a reasonable bit of time with a file to take off all the burrs and dings. When done you might believe that the parts are new. Often find that you need to put attention to the receiver covers, lowers, and rear sight block to get things really right. If the weather is anything but dry, add some corn starch to the mix to keep the grit from sticking. Hope this helps.
sam i am
September 03, 2001, 07:09
I have been thinking about what to use and can not seem to make up my mind. Everyone has a different opinion and tast. I was going to go with gunplumber's advice and use #80 al.oxide but now am second guesing. So, how about posting some pictures to show what #80 al. oxide looks like versus 220 glass bead versus 120 sand etc.
September 03, 2001, 08:49
I was thinking about doing that with a bunch of old receiver stubs. Doing the following:
1) #80 Aluminum oxide
2) #220 Aluminum oxide
3) #220 Glass beads
4) 50/50 mix of #80 aluminum oxide and #220 glass beads
5) 50/50 mix of #220 Aluminum oxide and #220 glass beads
6) Potentially the same combo's with #120 Aluminum oxide and glass beads.
The only problem is that I cannot find the beads and aluminum oxide in small quantities. I can only find 50lb pails, plus the shipping costs are brutal.
If I can find small quantities available and I actually get around to doing this test I will post result.
September 03, 2001, 12:08
Originally posted by DontTouchMyGuns:
I hear that glass beads break down rather rapidly above 55 psi. Have you found this the case?
I want to try glass beads, but I don't want to buy a 50lb pail and find out that I made a mistake.</STRONG>
I'm not sure. I blast at 50 psi. I prefer glass beads as they don't abrade the metal, just frost the finish. Glass beads can be used fairly aggresively on rust or hard grease without removing steel.\
September 03, 2001, 16:03
I am unable to post any comparison photos of different blasting material. I have been out of that business for some time now. So let me go over the differences in the what they do to the metal.
Glass beads are used to peen the metal. They do not take ANY material away. Think of them as very small hammers which close the pores of the metal. In most cases they will give a finish that will not hold oil as the pores are all closed. Glass beads when they become broken end up as a dust which does little to change the finish. They will however cause the bead blaster to clog, especially if there is any water vapor about. Classically, this process is used to raise the surface hardness of the metal and to blend out machining or tool marks. Some degree of deburing can also be done but it really comes to rolling over the burr. Air pressure is purposely kept low so that beads do not shatter and become useless.
Aluminum oxide on the other hand is used to remove metal. It is considerably harder than the metal it is striking. Thus it will take rough bites out. Clasically, this is used to remove burrs and leave the surface suitable for holding a lubricant or binding surface for paint. Air pressure is quite a bit higher than for glass as the grit does not easilly break down.
So what does the grit size have to do with the end finish? For the glass beads, the smaller size will put an almost light fog on the surface of the metal. The larger the bead the more pronounced will be the cratering or peening from impact. For aluminum oxide, the smaller grit cuts slower and has a small grain finish. Very good at holding a film of oil. As the grit gets bigger, the cutting speed increases quickly but so does the size of the grain or roughness. I don't think the larger pore or grain size does much to improve the oil film capacity of the surface. Rather it is done as a path of expediency and lower cost, ie. less time doing the blasting.
Given that you are finishing oiled steel and not all of the oil crud will have been cleaned off, the larger grit is less sensitive to becoming oil coated and clumping. The small grit is very sensitive to this exposure, so it would be wise to carefully clean the parts before blasting if you want that small pore surface finish. This holds for both glass and aluminum oxide.
Bead blasting cabinets come in several flavors: open bucket exterior operation (typically using sand), closed recycle without broken bead separation, and lastly closed recycle with broken bead and dust separation. In the case between the later two options, the difference in finish becomes pronounced with aluminum oxide grit as recycled crud is jammed back into the newly opened pores. If you have choices, choose the last option as the finish will be best and frustration will be the lowest. However, this takes a big compressor, 5-10HP, and large reservoir tank to function well.
Just so you have some idea of where I come from on this info. I worked for two years doing vibratory and bead blasting process development for a sales company in that business. Spent many hours working out process finish solutions for customers as well as doing considerable small job work.
Hope this will answer many of your questions.
September 03, 2001, 18:17
Fred, that was very good information.
September 03, 2001, 18:38
Ditto, very useful!
September 03, 2001, 20:41
I have tested the difference between glass bead and silica sand using mild steel plates.
I was never happy with the finish (satin and light grey) after parking using Amerilene Zinc park and glass beads, so I went to Mang. park thinking this was the answer. Nope, same shade of finish, but now can reuse park which was a plus.
The refinish guy (gunthings) had a great post awhile back about the final finish when using glass bead. He mentioned the satin like finish and that they only used sand to achieve the more military matt finish.
Okay worth a try. Picked up a bag of 120 grit ss and proceded to test a series of mild steel plates (3 by 3).
30psi would hardly remove the scale.
60psi was slightly rough but barely.
45 to 50 seemed about right.
Also blasted a set of plates using glass bead at the same psi's.
All plates stamped with gb or ss and psi #
The ss plates starting gassing as soon as they hit the sauce. The gb after several seconds. Looks like the gb leaves a silver like finish on the metal and inhibits the park process.
The resulting finishes were as follows
The ss plates were at least 3 shades darker and matt in appearance.
The glass bead plates was again satin and medium grey.
At 45psi (ss)the finish was smooth to the touch. No where rough at all. Dark grey to light charcoal.
btw I reparked the new imbel receiver/stg barrel assembly and the receiver came out the same exact shade and texture as factory. Wonder if they are using sand?
I always wear a respirator when blasting or grinding anything that makes dust.
[ September 03, 2001: Message edited by: Ape ]
September 03, 2001, 21:16
After reading all the posts, I think I'll stick with my aluminum oxide. I may get #220 glass beads for cleaning the stock.
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