Lubricant for pressing 3/32" 420 SS roll pins in 17-4PH SS
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  1. #1
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    Default Lubricant for pressing 3/32" 420 SS roll pins in 17-4PH SS

    Hi group,

    We are installing 3/32" 420 SS roll pins through some various 17-4PH stainless parts. Quantity is low thousands per month. Press is a small 1 ton hand arbor press. There is custom tooling to hold the pins to be installed inline with the hole.

    About 9% of the initial test run has pins that jammed part way through. Maxing out the small press did not provide enough force to get them through.

    I am thinking that the pins are galling. Perhaps they are slightly off alignment and start to dig in. Does this seem like a reasonable possibility? The roll pins are passivated and the various 17-4PH pieces are off the machine and maybe washed in soap and water ... if it matters.

    I am considering dipping the random 17-4PH pieces or possibly the roll pin in some form of lubricant to prevent galling. The pressed together assemblies gets installed in anodized and powder coated aluminum parts. So I need something is relatively benign and/or easy to clean off under running water. I have seen WD40 stain and discolor anodize before, so I think it is out.

    Any recommendations?

    Thanks,

    -Jim

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    try soap, bar or liquid

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    IME Stainless on stainless is going to gall, (1 of the machinists cammandments) and will need a EP lubricant,..... I know it's not water soluble but I'd be looking at the nickle based antiseize.

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    You could also try a PTFE dip on the roll pins. Coat them in bulk then allow the volatiles to evaporate, which will leave a light film of lube.

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    Quote Originally Posted by HWooldridge View Post
    You could also try a PTFE dip on the roll pins. Coat them in bulk then allow the volatiles to evaporate, which will leave a light film of lube.
    I like this. Put the pins on a cookie sheet, spray with PTFE aerosol spray, roll around, and let dry. Lube should be pretty inert and not harm the powder coat or anodize ... and I get bonus lubrication of the press tooling at no additional charge. I see McMaster-Carr has 8710T13 which is a PTFE 14 oz aerosol for $10.

    Limy Sami - you recommended EP (extreme pressure?) lube? What do you think of the PTFE suggestion?

    Thanks!

    -Jim
    Last edited by kb0thn; 03-01-2011 at 07:12 AM. Reason: typo in Limy Sami's name

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    Quote Originally Posted by kb0thn View Post
    Hi group,

    We are installing 3/32" 420 SS roll pins through some various 17-4PH stainless parts. Quantity is low thousands per month. Press is a small 1 ton hand arbor press. There is custom tooling to hold the pins to be installed inline with the hole.

    About 9% of the initial test run has pins that jammed part way through. Maxing out the small press did not provide enough force to get them through.

    I am thinking that the pins are galling. Perhaps they are slightly off alignment and start to dig in. Does this seem like a reasonable possibility? The roll pins are passivated and the various 17-4PH pieces are off the machine and maybe washed in soap and water ... if it matters.

    I am considering dipping the random 17-4PH pieces or possibly the roll pin in some form of lubricant to prevent galling. The pressed together assemblies gets installed in anodized and powder coated aluminum parts. So I need something is relatively benign and/or easy to clean off under running water. I have seen WD40 stain and discolor anodize before, so I think it is out.

    Any recommendations?

    Thanks,

    -Jim
    ROLL Pins jamming???
    About 9% of the initial test run has pins that jammed part way through.
    Roll pins colapse a bunch.... and tollerate a lot of mis alignment...
    I'd bet a dollar to a donut hole that the holes are not lined up within a country mile..

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    Quote Originally Posted by kb0thn View Post
    Limy Sami - you recommended EP (extreme pressure?) lube? What do you think of the PTFE suggestion?

    Thanks!

    -Jim
    Never tried it Jim so I can't comment, but IME preventing stainless steel galling needs serious lubing.


    I also agree with gary E, check your hole alignment, if a drill bit of the same diameter used on each of the holes won't slip though a roll pin IS going to struggle.

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    Maxing out a 1 ton press sounds way too much force even if there is galling involved. I was told that order of 100 lb. or so push was typical for the usual run of smaller roll pin sizes. This link seems to agree Mechanical engineering other topics - Spring Pin Insertion Force.

    Time to check the hole sizes, roll pin sizes and supplier quality methinks. "Roll pin is so simple that low bid supplier is fine" may be the accounts department view but my quickie intro into roll pin engineering came when struggling with a batch of (very) cheap pins which, my educator proclaimed multiply expletive deleted substandard or words to that effect. Apparently its vital that the pin is not even the slightest amount bell mouthed and that the chamfer is at least even or, better, ever so slightly longer on the slit side reflecting the fact that a relaxed roll pin is slightly oval. As always even the tiniest inequality in things that push in rapidly leads to jamming if the presentation is anything less than perfect. (Some of my pins were so bad that the slit walls were visibly curved and some even had a tiny ridge at the end of the lead in taper.)

    Stainless on stainless galling is in part related to inter-part pressure. I'd be surprised if pushing a pin into a correctly sized hole would generate enough wall pressure to totally seize things up. According to this site Spring Pins technical specs your 3/32 pins should be compressed between 2 and 8 thou on diameter for design radial retention force. Over compression into a too small hole will send installation forces through the roof, as taking stainless past its elastic limit always does, but once its in retention will probably be poor. Its supposed to be a spring not a compression fitting after all.

    Of course, given the chance, smart man puts a slow taper on the installation fixture so the pin is right sized as it enters the hole and maybe an oil wetted felt washer for that piquant hint of lubrication.

    Clive

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    Quote Originally Posted by Clive603 View Post
    Maxing out a 1 ton press sounds way too much force even if there is galling involved. I was told that order of 100 lb. or so push was typical for the usual run of smaller roll pin sizes. This link seems to agree Mechanical engineering other topics - Spring Pin Insertion Force.

    Time to check the hole sizes, roll pin sizes and supplier quality methinks. "Roll pin is so simple that low bid supplier is fine" may be the accounts department view but my quickie intro into roll pin engineering came when struggling with a batch of (very) cheap pins which, my educator proclaimed multiply expletive deleted substandard or words to that effect. Apparently its vital that the pin is not even the slightest amount bell mouthed and that the chamfer is at least even or, better, ever so slightly longer on the slit side reflecting the fact that a relaxed roll pin is slightly oval. As always even the tiniest inequality in things that push in rapidly leads to jamming if the presentation is anything less than perfect. (Some of my pins were so bad that the slit walls were visibly curved and some even had a tiny ridge at the end of the lead in taper.)

    Stainless on stainless galling is in part related to inter-part pressure. I'd be surprised if pushing a pin into a correctly sized hole would generate enough wall pressure to totally seize things up. According to this site Spring Pins technical specs your 3/32 pins should be compressed between 2 and 8 thou on diameter for design radial retention force. Over compression into a too small hole will send installation forces through the roof, as taking stainless past its elastic limit always does, but once its in retention will probably be poor. Its supposed to be a spring not a compression fitting after all.

    Of course, given the chance, smart man puts a slow taper on the installation fixture so the pin is right sized as it enters the hole and maybe an oil wetted felt washer for that piquant hint of lubrication.

    Clive
    I love to see an Englishman using English - piquant is a great word... reminds me of New Orleans and Oysters Rockefeller. Reckon it's time for a road trip.

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    i've had small diameter 420 stainless roll pin insertion into 304 problems in the past. holes were close to lower limit for size. thought galling was the culprit and used lubricants to overcome to no avail. discovered that all roll pins are not the same; the closed diameter of certain roll pins were larger than hole diameter and installing them was impossible since interference fit wouldn't allow it.

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    I am thinking of a dry graphite lubricant that may be similar to ammunition reloading neck sizing lube.
    Another lube could be a stainless tapping fluid. If it prevents a tap from seizing, it may go a long way to prevent galling.
    Of course the prime lube would be white lead grease, but I don't know how well that would wash off, and we can't get that anymore in Kalifornia.

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    Quote Originally Posted by MJR7 View Post
    the closed diameter of certain roll pins were larger than hole diameter and installing them was impossible since interference fit wouldn't allow it.
    Eeek! That shouldn't even begin to happen. When properly fitted the slot only closes by a few thou, as I understand it order of 20 thou per inch of diameter is typical. Principle of a roll pin is that when made they are supposed to be slightly oval in the relaxed state, long on the back to slot diameter and short on the side to side diameter. When pushed into the hole the thing should be sprung into a circle giving even contact pressure all round except where the slot is. This gives maximum grip. Over compression into an undersize hole makes it much, much harder to get the thing in and actually reduces the total grip due to uneven pressure.

    Just occurred to me that the OP may be being given 2.5 mm pins instead of 3/32, 0.0984" (nominal) diameter as opposed to 0.0938" (nominal) is going to eat up pretty much all your tolerance on oversize. Actual measured relaxed state diameters being + 5 to +10 thou (ish) over nominal. Minimum pin into maximum hole is just about OK as being pretty much equivalent to maximum pin into minimum hole for right size pins but everything else will need excessive compression. Which fits the reported needs too much force and some jam up scenario quite well as maximum pin in minimum hole will need something like 3 times as much squeeze as it should have.

    Clive

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    Swagelock, High Purity Goop.

    Says right on the tube "Prevents galling in any material" Pretty big talk in the industrial world. So far as long as I have known about it (25 years) I have yet to prove them wrong. I guess thats why its $20 a tube. Its takes just a microscopic amount to do the job.

    Tom Lipton


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