Posted this on another forum(MTBR), no response, hoping someone here can help. What blast media and size is generally used to strip paint and clean any brazing residue prior to painting and/or powder coating? What is the typical nozzle size for blasting bike frames? I searched here and got general info on the interweb but no bike specific info.

thanks, Brian

stripping paint with a sand blasting is pretty miserable. For steel, I'm not sure any of that is particularly critical, but then again I'm not a painter

unterhausen: "stripping paint with a sand blasting is pretty miserable"

I assume you mean without a cabinet which I would never even consider. A friend gave me a large blasting cabinet, already have a compressor that meets requirements for blasting. Just looking for a recommendation from someone experienced with bike frames, if not I'll use alum/ox 80-100 grit, this ain't rocket science.

info regarding nozzle size:

Nozzle Specifications



[TABLE="class: chart tablepad, width: 510"]
[TR]
[TH="class: head htext, bgcolor: #072F7A, colspan: 9"]Air Consumption/Nozzle Size


(cubic feet per minute at pressures shown)[/TH]
[/TR]
[TR]
[TH="class: subhead shtext nozzlebore, bgcolor: #B2B2B2"]Nozzle
Bore Size
[/TH]
[TH="class: subhead shtext fifty, bgcolor: #B2B2B2"]50#
[/TH]
[TH="class: subhead shtext sixty, bgcolor: #B2B2B2"]60#
[/TH]
[TH="class: subhead shtext seventy, bgcolor: #B2B2B2"]70#
[/TH]
[TH="class: subhead shtext eighty, bgcolor: #B2B2B2"]80#
[/TH]
[TH="class: subhead shtext niney, bgcolor: #B2B2B2"]90#
[/TH]
[TH="class: subhead shtext onehundred, bgcolor: #B2B2B2"]100#
[/TH]
[TH="class: subhead shtext consumption, bgcolor: #B2B2B2"]Abrasive
Consumption

*
(pounds per hour)[/TH]
[TH="class: subhead shtext area, bgcolor: #B2B2B2"]Blast Area

*
(feet per minute)[/TH]
[/TR]
[TR]
[TD="class: subhead shtext, bgcolor: #B2B2B2, colspan: 2"](general blasting
pressures)[/TD]
[/TR]
[TR]
[TD="class: bwhite nozzlebore"][SUP]3[/SUP]/32"[/TD]
[TD="class: bwhite fifty"]8[/TD]
[TD="class: bwhite sixty"]9[/TD]
[TD="class: bwhite seventy"]11[/TD]
[TD="class: bwhite eighty"]12[/TD]
[TD="class: bwhite ninety"]13[/TD]
[TD="class: bwhite onehundred"]15[/TD]
[TD="class: bwhite consumption"]70-100[/TD]
[TD="class: bwhite area"]0.5[/TD]
[/TR]
[TR]
[TD="class: bgray nozzlebore, bgcolor: #D0D0D0"][SUP]1[/SUP]/8"[/TD]
[TD="class: bgray fifty, bgcolor: #D0D0D0"]15[/TD]
[TD="class: bgray sixty, bgcolor: #D0D0D0"]17[/TD]
[TD="class: bgray seventy, bgcolor: #D0D0D0"]19[/TD]
[TD="class: bgray eighty, bgcolor: #D0D0D0"]21[/TD]
[TD="class: bgray ninety, bgcolor: #D0D0D0"]24[/TD]
[TD="class: bgray onehundred, bgcolor: #D0D0D0"]26[/TD]
[TD="class: bgray consumption, bgcolor: #D0D0D0"]125-175[/TD]
[TD="class: bgray area, bgcolor: #D0D0D0"]1-1.5[/TD]
[/TR]
[TR]
[TD="class: bwhite nozzlebore"][SUP]5[/SUP]/32"[/TD]
[TD="class: bwhite fifty"]26[/TD]
[TD="class: bwhite sixty"]30[/TD]
[TD="class: bwhite seventy"]34[/TD]
[TD="class: bwhite eighty"]38[/TD]
[TD="class: bwhite ninety"]43[/TD]
[TD="class: bwhite onehundred"]47[/TD]
[TD="class: bwhite consumption"]175-250[/TD]
[TD="class: bwhite area"]2-2.5[/TD]
[/TR]
[TR]
[TD="class: bgray nozzlebore, bgcolor: #D0D0D0"][SUP]3[/SUP]/16"[/TD]
[TD="class: bgray fifty, bgcolor: #D0D0D0"]33[/TD]
[TD="class: bgray sixty, bgcolor: #D0D0D0"]38[/TD]
[TD="class: bgray seventy, bgcolor: #D0D0D0"]43[/TD]
[TD="class: bgray eighty, bgcolor: #D0D0D0"]48[/TD]
[TD="class: bgray ninety, bgcolor: #D0D0D0"]53[/TD]
[TD="class: bgray onehundred, bgcolor: #D0D0D0"]58[/TD]
[TD="class: bgray consumption, bgcolor: #D0D0D0"]275-400[/TD]
[TD="class: bgray area, bgcolor: #D0D0D0"]3-3.5[/TD]
[/TR]
[TR]
[TD="class: bwhite nozzlebore"][SUP]1[/SUP]/4"[/TD]
[TD="class: bwhite fifty"]58[/TD]
[TD="class: bwhite sixty"]67[/TD]
[TD="class: bwhite seventy"]76[/TD]
[TD="class: bwhite eighty"]85[/TD]
[TD="class: bwhite ninety"]94[/TD]
[TD="class: bwhite onehundred"]103[/TD]
[TD="class: bwhite consumption"]500-700[/TD]
[TD="class: bwhite area"]4-4.5[/TD]
[/TR]
[TR]
[TD="class: bgray nozzlebore, bgcolor: #D0D0D0"][SUP]5[/SUP]/16"[/TD]
[TD="class: bgray fifty, bgcolor: #D0D0D0"]91[/TD]
[TD="class: bgray sixty, bgcolor: #D0D0D0"]105[/TD]
[TD="class: bgray seventy, bgcolor: #D0D0D0"]119[/TD]
[TD="class: bgray eighty, bgcolor: #D0D0D0"]133[/TD]
[TD="class: bgray ninety, bgcolor: #D0D0D0"]146[/TD]
[TD="class: bgray onehundred, bgcolor: #D0D0D0"]161[/TD]
[TD="class: bgray consumption, bgcolor: #D0D0D0"]800-1100[/TD]
[TD="class: bgray area, bgcolor: #D0D0D0"]5-5.5[/TD]
[/TR]
[TR]
[TD="class: bwhite nozzlebore"][SUP]3[/SUP]/8"[/TD]
[TD="class: bwhite fifty"]130[/TD]
[TD="class: bwhite sixty"]151[/TD]
[TD="class: bwhite seventy"]171[/TD]
[TD="class: bwhite eighty"]191[/TD]
[TD="class: bwhite ninety"]211[/TD]
[TD="class: bwhite onehundred"]232[/TD]
[TD="class: bwhite consumption"]1200-1600[/TD]
[TD="class: bwhite area"]6-6.5[/TD]
[/TR]
[TR]
[TD="class: bgray nozzlebore, bgcolor: #D0D0D0"][SUP]7[/SUP]/16"[/TD]
[TD="class: bgray fifty, bgcolor: #D0D0D0"]178[/TD]
[TD="class: bgray sixty, bgcolor: #D0D0D0"]206[/TD]
[TD="class: bgray seventy, bgcolor: #D0D0D0"]233[/TD]
[TD="class: bgray eighty, bgcolor: #D0D0D0"]260[/TD]
[TD="class: bgray ninety, bgcolor: #D0D0D0"]286[/TD]
[TD="class: bgray onehundred, bgcolor: #D0D0D0"]315[/TD]
[TD="class: bgray consumption, bgcolor: #D0D0D0"]1700-2200[/TD]
[TD="class: bgray area, bgcolor: #D0D0D0"]7-7.5[/TD]
[/TR]
[TR]
[TD="class: bwhite nozzlebore"][SUP]1[/SUP]/2"[/TD]
[TD="class: bwhite fifty"]232[/TD]
[TD="class: bwhite sixty"]268[/TD]
[TD="class: bwhite seventy"]304[/TD]
[TD="class: bwhite eighty"]340[/TD]
[TD="class: bwhite ninety"]376[/TD]
[TD="class: bwhite onehundred"]412[/TD]
[TD="class: bwhite consumption"]2300-2800[/TD]
[TD="class: bwhite area"]8-8.5[/TD]
[/TR]
[/TABLE]
* Note: Blast area coverage per/minute and abrasive consumption are approximate guidelines. Abrasive material used and surface blasted may alter coverage and consumption.


and media info:

Media

Many types of finish may be obtained by the selection of abrasive and by the adjustment of air pressure in the blasting unit. The more commonly used abrasives are

• aluminum oxide,
  
• white aluminum oxide,
  
• urea and other plastic abrasives,
  
• corn cob grit,
  
• walnut shell grit,
  
• glass beads,
  
• pumice,
  
• crushed glass grit,
  
• silicon carbide,
  
• steel grit and
  
• steel shot.

For the most efficient performance, when the abrasive in the machine has broken down too much, the entire load should be replaced. Adding new material to the old load greatly reduces the performance of the abrasive and increases the amount of dust.
If you are getting a sporadic flow of abrasive, it is being caused by fine material not flowing down to the pick-up area or too much pressure. Banging on the side of the cabinet hopper can test this. If the flow is good after this, your material is too fine or may be moist.

Media Hints

• Glass beads can be used to texturize, descale, or remove light burrs and die-cast flash leaving a smooth bright satin finish. Used at 40 to 80 PSI.
  
• Abrasive grits can be used for more aggressive work leaving a dull satin finish and are useful for creating a good surface for bonding. Use up to 120 PSI.
  
• Walnut shell grit can be used for deflashing thermoset plastics without destroying the original polish. Use 30 to 80 PSI.

and technique/method info:

Abrasive blasting is supposed to be a scrubbing action, not a peening process. Therefore, the gun should always be aimed at a 60° to 45° angle to the surface being cleaned. When the gun is aimed at 90°, peening occurs and, due to the abrasive particles colliding with the abrasive bouncing off the surface, a very high rate of media wear occurs

All above info from: https://www.kramerindustriesonline.co...ing-guides.htm

and their ShopTalk Forum: https://www.kramerindustriesonline.co.../blasting.html


Brian

I find stripping paint with a blast cabinet to be slow and frustrating work. I know people that blast outside, and prefer that to a cabinet if the weather permits. When I started at Trek we were still blasting every tube, they later moved to processing them chemically so we didn't have to do that. The best part of using a blast cabinet in Wisconsin in the winter was constantly getting shocked. My favorite was getting my face too close to the window and getting shocked on the lips

Thanks for the info. The chemical processing was probably done in dip tanks, right? I don't think that would be practical in a home shop, at least for mine. I've used various strippers for frames but dont like the time/process involved, nor do I like their toxicity.

Regarding the shocking(getting shocked on the lips, ouch!) here's info from the Krammer site;

Grounding
Blasting machines occasionally cause shocks from static electricity. If the operator stands on a mat grounded to the machine and the gun is grounded to the cabinet, this will be eliminated. The cabinet can also be grounded to any conduit for insurance.

The only blasting I've done is with a very funky cabinet at a friends auto shop for cleaning/striping a couple of large vise's and a few forks, and it was as you stated kinda frustrating(forks were pretty easy). The cabinet I now have is way better than that one, I'm going to give it try and see how it goes.

Brian

grounding is an inexact science. There was actually a copper wire on that blast cabinet that you would hook to yourself. Didn't do much, but it was better than nothing. 15 minutes on that machine was like torture.

Yikes. I have a big cabinet waiting in NY for me to pick up. I do my blasting outside currently and get sand from glass blowers. They discard a lot of sand. I have some in several grades from "fine as flour" on up to fish tank filler.

Never used it for brazing slag removal...so don't know if that would work well or not.

Have used soda and walnut shell for paint removal. I have always outsourced that task and the local companies are low cost and are well versed in removing what is specified and nothing more.

For example, if requested they can remove just the top coats and leave the original primer while cleaning a specific marked area needing a repair down to the bare metal.

/K

Soda. Always, always soda. It is astoundingly forgiving, and the residue washes away wonderfully :-)

Calstar,

I and a few other painters I know, use Star Blast by Dupont. Cant think of the size though. You could try emailing Toby at Hot Tubes or Chris and Brian at Circle A. A walk in cabinate with a fresh air pack and and a pot style blaster is the best setup for stripping. Cabinets are great for bare metal prep as all you need to do is give the frame/metal some tooth.

Slag, nothing takes it off. It has to be removed prior to blasting (soaking, scraping, etc). A thin burnt layer will come off but an actual glassy chunk, no way. That stuff is hard.

Paint, burn it or do something else prior to blasting. Stripping paint with a blaster sucks. For powder coat, send it out to be dipped/stripped first.

Hope this helps-Chris