Custom Made Spanner/Wrench Heat Treatment 3

[JCReynolds79]

Hello all,

I am tasked with creating the drawings for a set of special spanners, not something we can buy. We made one set before out of 304 stainless but after some use they started to deform. So I need to get more made and want to specify some more durable material probably with necessary heat treatment so the tools last. Also don't want any corrosion problems, hence why it was stainless before.

Could someone suggest any materials/treatments please as I am not very familiar in this area. I have been reading a bit and maybe it could be a medium carbon steel that is hardened and tempered, but I do not know how I would quantify that on the drawing. I do not know what hardness values would be acceptable, how to specify tempering. Maybe there are different treatments for stainless?

Hope someone can help

Thanks.

Regards,

Jon Reynolds

 

[redpicker]

First, you need to define your mechanical property requirements (hardenss, tensile strength, impact strength, etc...)

Next, consider environmental exposure (corrosion, H2S, Chlorides, etc...)

From these, you can see which materials are available in the product form you need to satisfy cost/delivery requirements.

rp

 

[CoryPad]

304 stainless steel is not well suited for use as a spanner material due to its low strength. Nitriding of stainless steel is an option to improve surface hardness and durability, especially the new low temperature colossal supersaturation (LTCSS) processes that do not destroy corrosion resistance.

Most spanners are alloy steel that is quench hardened and tempered or austempered. These would have low corrosion resistance without a surface treatment. A variety of surface treatment options are available, including zinc-rich coatings, zinc or zinc alloy electroplating, even physical vapor deposition (PVD) coatings.

 

[EdStainless]

Or make them out of a PH stainless grade, such as 17-4PH.
These will age harden to fairly high strength with a simple 1000F treatment after rough machining.
You would then want to finish grind the precision dimensions.

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Plymouth Tube

 

[tbuelna]

The first thing you might consider is determining exactly why the existing spanner wrench design failed. Was it really due to lack of material strength? Was it due to an improper fit between the tool and mating fastener? Or was it due to a lack of stiffness in the tool design itself?

I have not seen tools like a spanner made from 304 cres. In fact, I have not seen many wrench tools made from stainless steel at all. Wrench tools are usually made from alloy steels, and if they require corrosion protection they are plated with chrome or nickel. There are some wrenching tools that are made from high strength bronze alloys intended for applications where they must not produce sparks. And there even some wrenching tools made from titanium that are designed for use with titanium fittings, in order to prevent surface contamination of the titanium fittings from contact with the wrench tool.

 

[racookpe1978]

How many of these do you need to make?
What "clearance" or size limits do you have?
What tolerances can you live with to make them work? (Too tight, and the workers can't slide them on the nuts and bolts.) Too loose, and the wedging action of each nut will bend the wrench opening too wide.

Now, why can yo not make the head larger (thicker, wider, taller) so there is more meat in the head to resist failure with a slightly lower strength material or the same strength with more material at the corners or depth?

 

[StoneCold]

Can you post a picture of the wrench that is not working out well. You will get better responses to solve your problem then.

 

[JCReynolds79]

Hi All,

Thanks for the useful replies. I am uploading a photo (as photos are always nice) which shows the wear on the spanner.

Basically, it looks too soft as there are indentations on the working surfaces and also the C is starting to taper, as it must be getting splayed open.

Not sure if I need to re-design or can just remake in a stronger material/heat treatment. Its not used very often, but obviously often enough that it is not surviving in 304.

Thanks again.

Regards,

Jon Reynolds

 

[JCReynolds79]

Someone recommended something like 42CrMo4 (EN19T) T condition. On its own it has a UTS of about 950MPa and hardness of 24-32HRC. I am not sure the hardness is enough though. But I could always say on the drawing "make from 42CrMo4, harden and temper to 'T' condition, min. hardness 38HRC"

Regards,

Jon Reynolds

 

[JCReynolds79]

Just not sure whether to chemi-black or chrome plate.

Is chrome-plating more expensive? It might be deemed overkill if it costs too much. This tool is not used that often.

Regards,

Jon Reynolds

 

[TVP]

42CrMo4 hardened and tempered to 38-44 HRC would be a significant improvement over 304 for this application. If the tool is used inside in an area that is conditioned for temperature and humidity, then a black oxide coating (chemical blackening) should be sufficient. Definitely cheaper than Cr plating.

 

[tbuelna]

The photo definitely shows deformation of the wrenching flank surface. As TVP suggests, one improvement would be to use a much stronger thru hardened alloy steel instead of 304. From the picture, it looks like the outer profile of the wrench is not too bad. But I would recommend modifying the dimensions/tolerances of the wrench opening to ensure there is minimal clearance between the wrench flanks and the mating nut/bolt flats so that the wrench flanks do not edge load on the bolt/nut corners.

If you have the ability to machine the wrench flanks with a complex profile, you can machine them with a slight crown so that they contact the bolt/nut flats away from the corners.

 

[racookpe1978]

Does it have to be that thin? A thicker wrench will help as well.

 

[JCReynolds79]

Hi all,

Thanks for the answers. Tbuelna that's a great idea. I might be able to incorporate that crown.

racookpe1978, yes unfortunately it does need to be that thin. Working in a small place necessitating the thin tool.

Cheers all.

Regards,

Jon Reynolds

 

[mighoser]

Have you looked at

http://www.steritool.com/

They make a lot of custom spanners in 17-4PH, Custom 465 or 420