A moan – steel of mysterious composition

[charadamParticipant @charadam]

I volunteer with REMAP and was recently modifying a fully-adjustable bariatric bed.

The modification required drilling a couple of clearance holes for 10mm bolts in the 13mm trunnions for the bed actuators.

The holes had to be drilled with hand held tools as the bed is large and unwieldy.

The pilot holes at 5mm and 7mm went well using HSS bits.

When the 10.5 mm HSS drill was tried in the first hole it smeared and raised a large burr on the surface, as well as wandering off centre by a good 3mm.

A cobalt bit was tried next with no more success.

An end mill did not succeed.

I finally touched up a carbide tipped masonry drill on the green wheel and got through. Luckily the job did not require precision!

I talked to the bed manufacturers' representative who told me that the steel is notorious for unpredictable properties in his industry.

Must have been slag or stainless inclusions or what?

 

 

 

 

Edited By charadam on 29/06/2017 22:03:13

[charadamParticipant @charadam]

[HacksawParticipant @hacksaw]

Bed iron ! Arghh ! Try drilling really slow using a hand brace,a new drill bit and lots of pressure….It's hard..

[jason udallParticipant @jasonudall57142]

I find it very surprising that that every component isn’t documented down to the batch /cast of the steel.
But maybe the manufacturer didn’t feel like shareing with you.

That said more interesting might be the apparent variation of hardness across the section….

Work hardening would be my explanation.
I don’t expect any possible effect of radiation but repeated stress might be an intresting essay

Edited By jason udall on 30/06/2017 08:54:54

[larry PhelanParticipant @larryphelan54019]

I remember trying to drill bed irons many years ago and it nearly broke my heart,not to mention many drills. I thought it would be cheaper than buying angle iron [since there was plenty of it around ] Now I know why it was left around.I found too that the only way to get through it was with a hand brace and plenty of push. Take good advice and stay well away from it,no wonder it ends up in scrapheaps !

[S.D.L.Participant @s-d-l]

Posted by jason udall on 30/06/2017 08:52:18:
I find it very surprising that that every component isn't documented down to the batch /cast of the steel.
But maybe the manufacturer didn't feel like shareing with you.

That said more interesting might be the apparent variation of hardness across the section….

Work hardening would be my explanation.
I don't expect any possible effect of radiation but repeated stress might be an intresting essay

Edited By jason udall on 30/06/2017 08:54:54

Why would it be documented to that level?

Its an adjustable bed i would expect most of the parts to be mild steel, might be modern equivalent of EN3 or EN1

Steve

[KWILParticipant @kwil]

Maybe just "good commercial quality" which is the code for we do not know the grade nor care.

[SillyOldDufferModerator @sillyoldduffer]

Posted by larry Phelan on 30/06/2017 08:57:32:

I remember trying to drill bed irons many years ago and it nearly broke my heart,not to mention many drills.

…

I recall reading that a lot of bed-iron was made of recycled tram-line. Huge amounts of it were lifted as motor transport replaced trams and light railways in quarries and factories etc.

If true it certainly explains why bed-iron is notorious. Rail steel has always been carefully formulated to maximise durability, stiffness and strength. And unlike mild-steel, a slice of old railway line makes a decent anvil!

Probably not what Chardam's bed is made of though!  That might be some species of stainless.

Dave

Edited By SillyOldDuffer on 30/06/2017 11:53:00

[charadamParticipant @charadam]

This is a modern bed costing thousands.

The trunnion I was drilling is 13mm thick and I can't see any good reason for it to be anything other than bog standard MS.

I am told that the steel is manufactured in Poland, as is the bed.

Maybe there is a "special recipe" for bed steel but why go to what must be additional cost?

[HacksawParticipant @hacksaw]

The 1" angle that temporary road signs are made of…. that's similar stuff … !!

I don't bother nicking ones left behind anymore

Beds might well work harden. Kids use them as trampolines, grown ups give them a pounding every night and twice on Sundays…

[Howard LewisParticipant @howardlewis46836]

Many years ago, made a trailer from bed angle iron (he could get lot of it for free). The quality varied greatly, from good (in drilling terms) to appalling. The supposedly household names were often the worst!

Almost on a par with rebar!

Howard

[SillyOldDufferModerator @sillyoldduffer]

Posted by charadam on 30/06/2017 11:55:35:

This is a modern bed costing thousands.

The trunnion I was drilling is 13mm thick and I can't see any good reason for it to be anything other than bog standard MS.

I am told that the steel is manufactured in Poland, as is the bed.

Maybe there is a "special recipe" for bed steel but why go to what must be additional cost?

Just a guess Charadam but being a medical bed could explain why it might be made of stainless steel.

Your description reminds me of bad experiences with work-hardening stainless which I now avoid like the plague! First a sharp fast drill cuts OK. Then, moving up to a bigger drill, the cutting edge starts to rub and the stainless steel hardens. That blunts the drill and the steel gets even harder; hard enough to immediately blunt a new drill. As the horrible stuff only hardens around the edge of the hole you can get a sort of burr as the soft metal underneath deforms under tool pressure.

Dave

[larry PhelanParticipant @larryphelan54019]

I can see where this subject is heading !

I never knew bed irons were made from old tram tracks,you learn something new every day.

Stainless steel is something I seldom have to deal with,but I know most drills dont like it,neither do guillotines.

Must look closer at the beds next time I,m at my local hospital,will help to pass the time if nothing else.

[charadamParticipant @charadam]

Dave,

I think you've cracked it.

I never considered that it might be stainless, but the symptoms were as you describe.

But why would the choose stainless with all the added cost, special welding, etc. And then powder coat it.

I suppose it helps justify the price!

[Martin CargillParticipant @martincargill50290]

The angle iron used in the manufacture of beds (in the old days) was a form of spring steel. Those of us familiar with the stuff will recollect how thin it was, given its purpose. It was good for repair / strengthening brackets because it was considerably thinner and it tended to have a tighter angle internal than the round corner of angle iron.

Martin

[Ian Skeldon 2Participant @ianskeldon2]

Hi Charadam,

The reason they make em out of stainless is because of the exposure to bodily fluids which have a very corrosive effect, especially if left on the metal surface for a few hours, also the bed needs to be cleaned very stringently again using chlorine based cleaning products which are also corrosive.

The finish coating, which as well as being more estheticaly pleasing is also much easier for NHS staff to keep clean.

If the finished coating were to becomes porus, the stainless frame will not fail and end up in a law suite, the mild steel one probably would.

Edited By Ian Skeldon 2 on 30/06/2017 19:36:51

[Neil WyattModerator @neilwyatt]

Tell then young people of today that your bed was made of iron girders with steel springs and they just won't believe you.

Having dealt with the results of modern youngsters using a bed as a trampoline…

Neil

[duncan webster 1Participant @duncanwebster1]

Posted by Martin Cargill on 30/06/2017 18:50:22:

The angle iron used in the manufacture of beds (in the old days) was a form of spring steel. Those of us familiar with the stuff will recollect how thin it was, given its purpose. It was good for repair / strengthening brackets because it was considerably thinner and it tended to have a tighter angle internal than the round corner of angle iron.

Martin

Not a good idea to weld this stuff, the heat affected zone can be very brittle. Weld gives way spectacularly just when you don't want it to.

[vintagengineerParticipant @vintagengineer]

It is probably low grade cheap and nasty mild steel. When they recycle cars now they shred the whole car and this goes off to be made into new non structural steel and it contains boron,nickel, chrome and all sorts of exotic material!

Some of the steel I get cannot be drilled after it has been forged and can even shatter. Unless you buy structural grade mild steel now, you can end up with any old crap in it!

 

Ordinary hospital beds are made from mild steel then plastic coated. They are made to a price not a quality.

Edited By vintagengineer on 30/06/2017 21:31:10

[Rick Kirkland 1Participant @rickkirkland1]

Posted by vintagengineer on 30/06/2017 21:28:24:

It is probably low grade cheap and nasty mild steel. When they recycle cars now they shred the whole car and this goes off to be made into new non structural steel and it contains boron,nickel, chrome and all sorts of exotic material!

Some of the steel I get cannot be drilled after it has been forged and can even shatter. Unless you buy structural grade mild steel now, you can end up with any old crap in it!

Ordinary hospital beds are made from mild steel then plastic coated. They are made to a price not a quality.

Edited By vintagengineer on 30/06/2017 21:31:10 You possibly haven't read the bit on the first line at the top of the page stating "Fully adjustable Bariatric bed". In addition you possibly missed the post stating "This is a modern bed costing thousands". I refer you to the post by Ian Skelden2. It contains a factual account. I shall add that I have experienced these problems whilst doing trial mods to these beds several years ago. Keep the term "Bariatric" in mind when considering the bed construction.

[Antony PowellParticipant @antonypowell28169]

I come from family of steel makers…….modern steel unless a "special steel" has a very high recycled content which can be any metal or mix of metals contained within the scrap used therefore unless a "special steel" no record is kept of its content and can be made up of just about anything…….

Tony

[CirclipParticipant @circlip]

But what constitutes "Non Special"? ALL should be to some sort of Spec. unless we're working to ROC mixes?

Regards Ian

[vintagengineerParticipant @vintagengineer]

Mild steel is very low carbon steel less than 0.25% contains all manner of recycled crap. Special steels are normally alloy steel for structural and engineering work.

Bariatric beds are no different from ordinary hospital beds other than being stronger to take the weight of grossly obese patients.

Posted by Circlip on 01/07/2017 12:26:48:

But what constitutes "Non Special"? ALL should be to some sort of Spec. unless we're working to ROC mixes?

Regards Ian

[damianParticipant @damiannoble34800]

Posted by Circlip on 01/07/2017 12:26:48:

But what constitutes "Non Special"? ALL should be to some sort of Spec. unless we're working to ROC mixes?

Regards Ian

Agreed

Any quality steel producer will sample the scap going into the mix and alter the mix to suit,also sampling during the melting process to refine the steel. I doubt this is the case with most mild steel that enters the country from china.

All steel should have a data sheet which gives composition info

[Graham SwalesParticipant @grahamswales]

Working for a company which manufactures equipment for petrochemical and medical applications, the quality of material we use is generally proscribed by the end user, and we have to supply a detailed material record book which defines exactly what is used in manufacture.

For every ferrous and non ferrous material we utilise, we request from the supplier a certificate (see en 10204 on Google for details) which clearly determines the material through a series of traceability checks. In addition we also (for some clients) have to complete local PMI checks (Positive Material Identification – again see google).

These checks are needed to ensure that the end user gets a product that complies with internationally recognised standards. Do we need such documentation for most of what we model engineers manufacture – probably not. Does the purchaser of the hospital bed need it? Very unlikely – especially as every certificate has a significant cost associated with it…….

Grum

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