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Brake Master Cylinder surface finish
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Source：Internet Author：Unknow Pubdate：2010-06-15
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quadracer12 (Mechanical)
1 Jun 10 18:10
So I found some roughness inside the cylinder of a brake master cylinder that we are producing in China. I know I cannot accept the roughness, but I am trying to find information on an acceptable surface finish inside of the cylinder. I am having very little luck.
I believe somewhere around Ra 24-32 or 0.6-0.8 micrometers would be acceptable, but I'm hoping to get some opinions from the fine engineers in this forum.
This is for vintage cars so no ABS or other electronic factors, simply the hydraulic cylinder. Thanks for the help!
swall (Materials)
2 Jun 10 7:41
Are the cylinders cast iron, bare aluminum or anodized aluminum?
GregLocock (Automotive)
2 Jun 10 8:25
The supplier of the seals will have a relevant opinion. Cheers 字串4
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
TVP (Materials)
2 Jun 10 9:39
My opinion: definitely no higher than Ra 0.6-0.8 micrometers. This range is not really that smooth, and most seal manufacturers recommend lower surface roughness.
quadracer12 (Mechanical)
2 Jun 10 11:26
The cylinders are cast iron, but we also have bare aluminum cylinders that we are playing with. Would it be different for each material?
Thanks TVP, I was thinking that 0.6-0.8 was the upper limit, I will probably hold them to a higher standard (lower roughness).
Any additional info would be great!
IRstuff (Aerospace)
2 Jun 10 11:54
字串6
Seems to be plenty of info on the web:
http://pdf.directindustry.com/pdf/james-walker/o-ring-guide/28272-15628-_24.html
http://www.allorings.com/oring_groove_design.htm
http://www.usseals.com/hydraulic_seals.htm
Note the caveats against too fine a finish.
http://www.allsealsinc.com/parker/dynamic-oring-sealing.pdf TTFN
FAQ731-376: Eng-Tips.com Forum Policies
swall (Materials)
2 Jun 10 13:25
What I was getting at was that if you are working with aluminum master cylinders, you have to take into account the roughening that will occur if you anodize the bores and start with a smoother finish than would be the case if running in bare aluminum bores.
dgallup (Automotive)
3 Jun 10 17:49
In general, 0,8 Ra (in microns) is considered the upper limit for sealing applications. That being said, there are a lot of different production processes that will produce a 0,8 Ra with very different roughness profiles and sealing properties. We regularly allow 1,2 Ra on turned parts with static o-ring seals because the direction of lay matches the seal. If the direction of lay is across the seal, a better finish is required. Dynamic seals, with their lower compression, need a somewhat better finish. However, it can't be too smooth or it won't hold any lubricant. 字串9
In any case, for a safety critical item like a brake cylinder, I would hope you are doing some serious leak testing at extremes of fit and finish and at high and low temperatures. There are too many variables involved to just take a stab in the dark.
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