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Surgical Steel

gwelo62

Cast Iron
Joined
Sep 17, 2011
Location
ga,usa
Can anyone recommend a stainless steel/s that could be used in an operating theatre? Exposed to blood etc. and then washed and steamed-sterilized for reuse.
 
All I was told, 18-20%Cr, no more than 30 ( think it was interstitial corrosion but feel free to check, autoclaving was the sterilisation method)
Get in touch with an instrument maker, they should happily put you right
Mark
 
Hi gwelo62:
For blades the most common is 440C
For instruments that don't have to be very strong it's 316L
For things that need to be moderately hard and moderately strong it's 17-4 PH H900 (It's the same grade as 630 that Laverda references in post #2)
For miscellaneous bits and bobs that need to be hard-ish but not that strong it's 416.
For bits that must be a bit tougher and harder than 17-4 PH it's 420.
For instrument handles that must be welded it's 316L or 304.
For weird applications it can be any other grade that will fit the bill.


No one size fits all.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Hi again gwelo62:
You can further subdivide your choices based on what you must to do to make your parts.
For example:
303 and 416 cannot be welded with any hope of a decently strong weld.
440C has too much carbon in it to weld easily.
420. 17-4 PH 304 and 316 are all readily welded.

If hardness is a necessary feature you may heat treat it:
440C goes to about 58-60 RC
420 goes to about 52-54 RC
17-4 goes to about 44 RC
416 goes to about 43 RC

304 and 316 can only be work hardened...they are austenitic and do not respond to heat treatment.
Full hard 304 is about 38 RC

If corrosion resistance is a priority:
Duplex 2205 is very good
316L is slightly less good
then 304
303
17-4
420
416
440C

If machinability is a priority:
416 and 303 are the easiest to machine in volume and are often used in screw machine parts.
17-4 PH is also very popular but quite a bit more challenging, especially to drill and to tap.
So is 420
After that it's a bit of a crap shoot.
440C is like other high carbon steels...it doesn't turn or mill for shit when it's annealed, but it grinds very nicely once it's hardened, and it hard turns and hard mills quite nicely too.

So you pick based on the balance of properties you need.

In addition some alloys are widely used, and comparatively easy to get past FDA scrutiny in applications where there is a predicate device already certified for your use case:
The poster child for implants is Titanium or cobalt chrome...in the stainless steel category 316L is also comparatively easy to certify as fit for use, depending on what you want to do with it.
For single use blades it's 440C.
Others less so.

All this says it's a complex engineering challenge to pick the ideal alloy for the project...in my experience engineers will sometimes spend considerable time and money to sort out the best choice.
Often it's done empirically (with prototypes and test rigs).

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
All this says it's a complex engineering challenge to pick the ideal alloy for the project...in my experience engineers will sometimes spend considerable time and money to sort out the best choice.
And in my experience, your analysis just exceeded the life work of any materials engineer I ever worked with. This has been an exceptional breakdown of those alloys--to the point that I'm bookmarking it and may even send that on to a few youngins.
 
Don't forget Carpenter Custom 465 stainless. It always seems to show up in surgical robotics parts. Or you know...after you make the first prototype on 17-4 (it bends or breaks) and they try to save the :poop: design by making it in something stronger.
 
I’d listen to Marcus, he makes stuff that gets poked in you, what a thought, though I have to go get some stainless trimmed soon as the twisted wire gets to poke out my chest ( it’s holding my ribs together or was at least)
Mark
 
Fwiw and it was about 40 years ago when I did some surgical instrument work, .......and then I used 316 L - used to order it in specially from Macs (for our Brit members) with material certificates.
 
I’d listen to Marcus, he makes stuff that gets poked in you, what a thought, though I have to go get some stainless trimmed soon as the twisted wire gets to poke out my chest ( it’s holding my ribs together or was at least)
Mark
It's going to be real fun when they pull the wires out, find a spare bullet to bite on.
 
Hi again gwelo62:
You can further subdivide your choices based on what you must to do to make your parts.
For example:
303 and 416 cannot be welded with any hope of a decently strong weld.
440C has too much carbon in it to weld easily.
420. 17-4 PH 304 and 316 are all readily welded.

If hardness is a necessary feature you may heat treat it:
440C goes to about 58-60 RC
420 goes to about 52-54 RC
17-4 goes to about 44 RC
416 goes to about 43 RC

304 and 316 can only be work hardened...they are austenitic and do not respond to heat treatment.
Full hard 304 is about 38 RC

If corrosion resistance is a priority:
Duplex 2205 is very good
316L is slightly less good
then 304
303
17-4
420
416
440C

If machinability is a priority:
416 and 303 are the easiest to machine in volume and are often used in screw machine parts.
17-4 PH is also very popular but quite a bit more challenging, especially to drill and to tap.
So is 420
After that it's a bit of a crap shoot.
440C is like other high carbon steels...it doesn't turn or mill for shit when it's annealed, but it grinds very nicely once it's hardened, and it hard turns and hard mills quite nicely too.

So you pick based on the balance of properties you need.

In addition some alloys are widely used, and comparatively easy to get past FDA scrutiny in applications where there is a predicate device already certified for your use case:
The poster child for implants is Titanium or cobalt chrome...in the stainless steel category 316L is also comparatively easy to certify as fit for use, depending on what you want to do with it.
For single use blades it's 440C.
Others less so.

All this says it's a complex engineering challenge to pick the ideal alloy for the project...in my experience engineers will sometimes spend considerable time and money to sort out the best choice.
Often it's done empirically (with prototypes and test rigs).

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
Thanks for the info. The item is a fitting to go on the end of some 1/4 pvc tubing and then be removed for reuse. Turned and drilled.
 
Bookmark, hell! I am going to save and print it.

Yes, you should write a book.



Hi again gwelo62:
You can further subdivide your choices based on what you must to do to make your parts.
For example:
303 and 416 cannot be welded with any hope of a decently strong weld.
440C has too much carbon in it to weld easily.
420. 17-4 PH 304 and 316 are all readily welded.

If hardness is a necessary feature you may heat treat it:
440C goes to about 58-60 RC
420 goes to about 52-54 RC
17-4 goes to about 44 RC
416 goes to about 43 RC

304 and 316 can only be work hardened...they are austenitic and do not respond to heat treatment.
Full hard 304 is about 38 RC

If corrosion resistance is a priority:
Duplex 2205 is very good
316L is slightly less good
then 304
303
17-4
420
416
440C

If machinability is a priority:
416 and 303 are the easiest to machine in volume and are often used in screw machine parts.
17-4 PH is also very popular but quite a bit more challenging, especially to drill and to tap.
So is 420
After that it's a bit of a crap shoot.
440C is like other high carbon steels...it doesn't turn or mill for shit when it's annealed, but it grinds very nicely once it's hardened, and it hard turns and hard mills quite nicely too.

So you pick based on the balance of properties you need.

In addition some alloys are widely used, and comparatively easy to get past FDA scrutiny in applications where there is a predicate device already certified for your use case:
The poster child for implants is Titanium or cobalt chrome...in the stainless steel category 316L is also comparatively easy to certify as fit for use, depending on what you want to do with it.
For single use blades it's 440C.
Others less so.

All this says it's a complex engineering challenge to pick the ideal alloy for the project...in my experience engineers will sometimes spend considerable time and money to sort out the best choice.
Often it's done empirically (with prototypes and test rigs).

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Hi gwelo62:
What goes through the tubing?
I ask because some fluids are very sensitive to contamination.
Some materials preferentially attract biofilms if the fluid is water or worse, stuff like D5W (glorified sugar water).

Some fluids, like sterile saline are mildly corrosive, especially galvanic corrosion.
There's a famous "Oopsie" by a dental implant company (one of the big ones too) where they made a surgical irrigator and a contractor furnace brazed the parts together not realizing that oral surgeons routinely irrigate surgical wounds with sterile saline.
There was a big "Oh Shit" moment when all the tips started falling off the irrigators because of galvanic corrosion and implants were failing at an accelerated rate because of all the contaminants.

One thing also to worry about that isn't obvious until you've spent time in the medical device field, is that coolants and other contaminants introduced during machining can be very bad news.
It's worse when surfaces are rough or when there are joints or crevices.
A common one that gets overlooked this way is "brassing" during wire EDM cutting...a micro layer of brass from the EDM wire can be transferred to the part surface, rendering it bio toxic.
But Rapidtap trapped in a rough surface (like tears and fissures in the rough walls of a drilled hole) is not a good thing either.

So lots to be aware of when you plan to make medical bits.
How you cut them, how you fixture them, how you pack them, how you clean them, all may (or may not) matter.

I assume you're prototyping these parts and the customer did not give you clear instructions on what to make them from.
If that is so, I encourage you to press the customer to pick the material or at the very least approve the material IN WRITING before you build stuff.
If you are the machinist you shouldn't have to take that responsibility...you don't have nearly enough information to do so, and you're not getting paid for taking that responsibility either.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Last edited:
Don't forget Carpenter Custom 465 stainless. It always seems to show up in surgical robotics parts. Or you know...after you make the first prototype on 17-4 (it bends or breaks) and they try to save the :poop: design by making it in something stronger.
Thanks for bringing back old nightmares lol. That stuff can be a horror show to machine lol.
 
Hi gwelo62:
What goes through the tubing?
I ask because some fluids are very sensitive to contamination.
Some materials preferentially attract biofilms if the fluid is water or worse, stuff like D5W (glorified sugar water).

Some fluids, like sterile saline are mildly corrosive, especially galvanic corrosion.
There's a famous "Oopsie" by a dental implant company (one of the big ones too) where they made a surgical irrigator and a contractor furnace brazed the parts together not realizing that oral surgeons routinely irrigate surgical wounds with sterile saline.
There was a big "Oh Shit" moment when all the tips started falling off the irrigators because of galvanic corrosion and implants were failing at an accelerated rate because of all the contaminants.

One thing also to worry about that isn't obvious until you've spent time in the medical device field, is that coolants and other contaminants introduced during machining can be very bad news.
It's worse when surfaces are rough or when there are joints or crevices.
A common one that gets overlooked this way is "brassing" during wire EDM cutting...a micro layer of brass from the EDM wire can be transferred to the part surface, rendering it bio toxic.
But Rapidtap trapped in a rough surface (like tears and fissures in the rough walls of a drilled hole) is not a good thing either.

So lots to be aware of when you plan to make medical bits.
How you cut them, how you fixture them, how you pack them, how you clean them, all may (or may not) matter.

I assume you're prototyping these parts and the customer did not give you clear instructions on what to make them from.
If that is so, I encourage you to press the customer to pick the material or at the very least approve the material IN WRITING before you build stuff.
If you are the machinist you shouldn't have to take that responsibility...you don't have nearly enough information to do so, and you're not getting paid for taking that responsibility either.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
Blood and saline.They have a shortage of plastic disposable 'suckers' and wanted a reusable alternative.
 








 
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