Hardness testing advice?
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  1. #1
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    Default Hardness testing advice?

    Sorry for the world's dullest topic...
    Have to certify hardness on a casting that won't fit on a Rockwell tester. Weighs about 10 lbs. Only induction treated on one small appendage.
    I can cut off the treated part, but have to use a hand grinder without coolant, so the hunk might get hot. OK, cut slowly with lots of air or use a spray bottle and a raincoat.
    But then the chunk has no flat / parallel surfaces to set on the stage. Would have to take off 1/8 to 1/4 inch (don't know the depth of penetration). Maybe could use a small vise but not sure if that would affect the reading. OK, try that with a reference piece to find out...

    Mostly I was hoping to use a Leeb on the intact casting. So we bought the world's cheapest Leeb (literally eBay "sort by price") called DY-10 for $200. I know, didn't expect much. We don't have much budget for test equip. I could have convinced them to pay $5000 but would be buying a pig in a poke as we have no experience with Leeb. If it didn't do the job they would remember me for that. So the cheapie was just to get my feet wet.

    (We also have a cheap ultrasonic tester that is completely worthless. It will read HRC 20 to 70 totally at random. Our calibration service said to throw it out, but there is one job where it seems to work as a go-nogo check so I kept it. It has a diamond bigger than my wife's ring so maybe I'll pry it out for our anniversary.)

    Surprisingly the little Leeb seems to work pretty well. Consecutive readings have low variance (maybe twice that of the Wilson on an as-machined surface). Seems to correlate pretty well with Wilson (for my purposes +/- 2 is OK). But it is hard to compare, as the Leeb only works on heavy objects and the Wilson only works on small or cut-off pieces.

    Surface prep is necessary (on a rough casting) but I am hoping a Dremel sanding drum is good enough. We have a surface grinder but some of these odd-shaped castings would be difficult or impossible to hit the desired area. And that can overheat the surface very easily - 4140 can be hard to drill after surfacing (the way I do it anyway ).

    So far I haven't really asked a question other than putting my ignorance on display but that never stopped you guys from offering helpful advice!

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    I've only done a limited amount of hardness testing but sample prep is crucial if you want any kind of accurate or even consistent answer. I'd cut the sample out any way you can, keeping it cool. Then I'd mill the top and bottom so you have parallel surfaces and probably surface grind or lap the top one. Then use the Wilson. The design of the Wilson is very clever and takes compliance out of the measurement, but I still like to work on the rigid post inserts if at all possible. If the casting has any sort of hard skin or a lot of variation with depth, all bets are off. IMO, the customer should have a specific procedure for the hardness measurement when it's anything unusual. Do you have calibration disks for the Wilson?

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    There is a reason the standard hardness test for castings is Brinell.

    What traceability requirements do your hardness test specify? It sounds like a Teleweld Telebrineller would be useful. Any workpiece that has received any thermal treatment is questionable as to hardness results.

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    Do you have calibration disks for the Wilson?
    Sure, and the diamond is fine etc. It's a good unit, digital.
    Any workpiece that has received any thermal treatment is questionable as to hardness results.
    (Covers ears with hands) Laa laa laa laa...! (so at least it's not just me)
    They would love me if I made them EDM these every shipment.

    I don't have to publish any numbers, just OK the samples are "to print." So I'll probably keep chopping & grinding & Wilson-ing but if the Leeb pleases me in the long run I may just switch to a go-nogo check. After all, if it's always the same place on the same part with the same prep, and the Leeb correlates repeatably with a Wilson, I'm OK with that. The induction job doesn't heat an odd shape uniformly anyway so nobody is expecting hard numbers (hopefully...)

    If I had a million dollars I'd have a Brinnell and a Vickers and a Knoop and one of those polarized laser profilometers and a neutron thingy and oh, yeah, wanted a SEM since I was eight (found one on eBay, too).

    But at least I have a file!

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    I have a Leeb (200 dollars more or less) and a Wilson Junior with calibration coupons. I test cast iron castings several times per week.

    I routinely cut samples with an an angle grinder. You will not change cast iron hardness readings by abrasive wheeling them unless they are very very small on the order of less than ounce and the part turns distinctly red. Otherwise the wheel cut surface works well for either Wilson or Leeb testing. I have made plenty of comparison tests on the Leeb and Wilson so that I have trust in properly done Leeb tests. I also tested my Leeb against a old-style bench hydraulic tester requiring magnified visual measurement of the impression whose brand name I forget.

    Light parts can be accurately tested on a Leeb if coupled to the anvil that comes with the test unit using grease. I would have to look at the documentation, but i think the minimum uncoupled Leeb weight is about 5 Pounds. It works fine on a 8 pound casting I commonly check for instance.

    Since the Leeb uses the rebound velocity of the impactor compared to its striking velocity weight alone of the item is not the only criterion for testing. For instance a 1/4” thin-walled 10” diameter by 1 foot 20 pound cylinder would not accurately test So, some common sense is required.

    Overall, I will say I was somewhat skeptical of the Leeb unit when I bought it. But having owned and used it for a few months, I find it to be a useful and reliable tool. It allows me to conveniently test casting that are too large to wrestle and fixture onto the bench tester. I would love to comparison test my unit to a 5K Starrett. But the build quality on mine is very reasonable. It came with a calibrated anvil which serves as a reference to check the instrument. It is uncannily consistent when so checked.

    One user’s experience. If you have more questions contact me and we could chat.

    Denis

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    Quote Originally Posted by dgfoster View Post
    I have a Leeb (200 dollars more or less) and a Wilson Junior with calibration coupons. I test cast iron castings several times per week. ...
    Overall, I will say I was somewhat skeptical of the Leeb unit when I bought it. But having owned and used it for a few months, I find it to be a useful and reliable tool. It allows me to conveniently test casting that are too large to wrestle and fixture onto the bench tester. I would love to comparison test my unit to a 5K Starrett. But the build quality on mine is very reasonable. It came with a calibrated anvil which serves as a reference to check the instrument. It is uncannily consistent when so checked.
    Denis
    Thank you ! I would vote this up but don't think this forum has that crap (thankfully!)
    I was scared of Leeb after bad experience with ultrasonic. Starting to come around.
    Didn't know about the grease-on-anvil trick, anvil alone is not magic. I'll try that.
    Reminds me of that blue ketchup they spread on my wife for ultrasound.
    Thanks again, may I quote you to my boss ? Inspires confidence.

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    There's also the Ames style tester in several sizes. I have one with a 12" throat, it seems to match my Wilson bench tester when compared on test blocks.
    I had a NewAge hand held tester for a while, it was fiddly to use, plus spares like penetrators were unobtanium.
    111.jpg
    Last edited by Mud; 01-11-2021 at 02:47 PM.

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    Sure you can quote me... for all that is worth. ;-)

    Denis

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    I have an Ames in a stand right here on my desk. Works as well as Wilson minus one decimal place. Mine only goes up to R45N but that converts nicely to HRC. Highly recommended.
    The only fiddling is when that little pin gets on the wrong side of the finger - you probably know what I mean! Unless they fixed that.

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    Quote Originally Posted by rabtrfld View Post
    Sure, and the diamond is fine etc. It's a good unit, digital.

    (Covers ears with hands) Laa laa laa laa...! (so at least it's not just me)
    They would love me if I made them EDM these every shipment.

    I don't have to publish any numbers, just OK the samples are "to print." So I'll probably keep chopping & grinding & Wilson-ing but if the Leeb pleases me in the long run I may just switch to a go-nogo check. After all, if it's always the same place on the same part with the same prep, and the Leeb correlates repeatably with a Wilson, I'm OK with that. The induction job doesn't heat an odd shape uniformly anyway so nobody is expecting hard numbers (hopefully...)

    If I had a million dollars I'd have a Brinnell and a Vickers and a Knoop and one of those polarized laser profilometers and a neutron thingy and oh, yeah, wanted a SEM since I was eight (found one on eBay, too).

    But at least I have a file!
    I suppose it's not a requirement, but "case depth", or the hardness profile is checked using a microhardness tester. Cut a sample specimen (by whatever means to prevent changing the hardness) mount sample in polymer of choice (phenolic/epoxy/coldmount), grind, polish, etch sample, take measurements at appropriate depth intervals. Microhardness testers use a diamond indentor with a low load, combined with a microscope (the etching helps visually see the microstructure change with the case depth), and measure the physical dimensions of the indentation to convert to hardness.

    (I had an electron microscope years ago, bought used from DuPont. To temper your enthusiasm, when something goes wrong with them it's big bucks (or you have to be knowledgeable enough to fix them), and they're not overly useful without certain bells and whistles like backscatter detectors, and EDX detectors and software which allow elemental analysis and imaging (easily much more $$ than the price of the microscope and more stuff to go wrong), older detectors require continuous liquid nitrogen cooling, and of course working with vacuum systems and their attendant issues. Most everyone using SEM's has costly maintenance/repair contracts. In principle, a basic one to look at bugs and things (a carbon/gold coater is needed for non-conductive specimens) at low magnification (<10000x) is no more complex than an old TV, but guess there's never been a demand for a "consumer SEM".)

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    I know nothing about hardness testing.
    But using low-melt alloys you could quickly and easily make a bed that supports your part.
    It could even be 2 part, a 80C+ base and a thin 50C skim coat to hold the current part.
    Maybe use hot water or olive oil to wash the top skin off and recast it.

    Details, details !!?! .. like always..

    A 20 mm "hole" is one thing, 1€ for a motorcycle mount.
    A 20 mm cylindrical bore for an air spindle of -.001 mm -0.00 30 mm deep is quite another thing.
    Maybe 300$.

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    Where in Wisconsin? I have a big portable Rockwell hardness Tester and a Brinell tester.

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    Ok, stupid question time...

    What hardness/scale are you checking for? Could this be as simple as using a set of hardness files (with hardness standards)?

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    Quote Originally Posted by TeachMePlease View Post
    What hardness/scale are you checking for? Could this be as simple as using a set of hardness files (with hardness standards)?
    I always avoided hardness files because I wouldn't know when they are worn out. But I have used a generic file to check. Our drawing says HRC but I only want to check yes/no to see if our supplier skipped a process - which has happened. In this case I have caught errors using a file.

    Bought a kg of low-melt alloy a long time ago and there it sits... maybe time to try it. It's a pretty big hunk for cheap. I was afraid after we melted the pretty ingot we'd forget what it is and somebody would throw out the ugly blob. It would be great for first-article exams where we really want to map out the hardness profile. Our supplier doesn't seem too sure what they are getting from their induction coil. They aren't using a dedicated service, just glowing it up in their foundry with a lick and a promise. Offshore source - gotta watch them like a hawk. There are serious hidden costs when you outsource like that, an awful lot of rework. You can't afford the time or cost to reject anything. We had a lady professor in here a few years ago to set up an "AQL" program but she left after one month. And the rework is never an engineered process. I have guys come to me every week needing tooling designed and built the same day for emergency rework. Can't do quality work like that. Sure, we're all good improvisers but you're not investing in your own plant when all that work is for temporary use.

    Saw a U-tuber make a SEM, heroic effort but mediocre results at best. I have heard they are high maintenance. Not for looking at bugs! But any bug caught in my lab is going on scotch tape under the Micro-Vu for sure. 270x is cool enough. Seems to me almost any digital video microscope is way better than my natural vision at the same magnification. I never had a student-grade microscope look anywhere near that good at 270x.

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    Ok... So you can get a set of hardness files, and you can get calibrated hardness file standards so you can check your files.

    File set is $114. Each standard is $75. (Both prices from McMaster, possibly available cheaper elsewhere) You probably need 3 standards, and you can check your files each time before you use them.

    If it's simply a "Is it hard, or soft" check... I think that's the cheapest, fastest, easiest solution, and the hardness standards ensure you won't get bitten by a worn out file.

    Just my $.02.

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    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    0aac537d-522f-42de-b36b-fb1ba7fec16b.jpg


    This is the unit I bought. Incidentally, you can orient the impactor vertically, at 45, 90, 135, and 180 degrees and get accurate readings. It is selectable to read out Rc, Hb, Leeb, among other scales.

    Denis


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