EN24 Rockwell Hardness

[tomcannon]

Hi, I am soon going to be rolling some threads from EN24 bar before having them heat treated. Looking at page 10 of this pdf

http://www.landisthreadingsystems.com/ThreadRolling/Library/TechnicalSupport.pdf

how should I know what column I should be referring to? They refer to material hardness, which I am unsure of. EN24 is equivalent of SAE 4340. The threads will be 7/16 unf and unc.

I am also getting myself confused between the difference in class 2 and class 3 shown on the same page.

 

[Wrenchbender]

Looks to me like one of the columns labeled "30-50C or Alloy [whatever Rockwell C hardness range you have]" would be applicable. 30-50C must be referring to the carbon content in 1/100th of a percent (customary in US).

Thread Class refers to the tolerances and allowances (i.e. slop). Class 1 thru 3 get progressively tighter. Its all defined in American National Standard Institute (ANSI) B1.1, titled 'Unified Screw Threads'. There are probably online calculators, but here's an example.

.4375-14UNC-[what the class is]A ('A' means external.)
EXTERNAL Class 2 Class 3
Major Dia 0.4360 +.0000 - 0.0103 0.4375 +.0000 - 0.0103
Pitch Dia 0.3896 +.0000 - 0.0050 0.3911 +.0000 - 0.0050
Minor Dia 0.3587 Max, Ref 0.3602 Max, Ref


.4375-20UNF-[class]A
EXTERNAL Class 2 Class 3
Major Dia 0.4361 +.0000 - 0.0081 0.4375 +.0000 - 0.0081
Pitch Dia 0.4036 +.0000 - 0.0047 0.4050 +.0000 - 0.0047
Minor Dia 0.3820 Max, Ref 0.3834 Max, Ref

 

[TVP]

Bestwrench is correct, the 30-50 C means 0.30-0.50 mass % carbon, which is the category for EN24. Depending on the exact processing history, it will either be "soft" or "15-25 RC".

 

[PeterCharles]

EN24 is a well known UK steel. It is commonly available in "condition T", meaning it has been heat treated to give a tensile strength of 55/65 T/in2
Depending on ruling section and heat treatment it can achieve 100 T/in2, "condition Z".
We use condition T for shafts.

 

[tomcannon]

Excellent thanks very much, I have been referring to

http://www.westyorkssteel.com/EN24.html

for information, and wondered about the carbon content but it was not on the same scale (0.4% where the thread rolling chart suggests only 30-50) but now I know. I will be heat treating the studs to V condition to finalise, as suggested by an incredibly well respected person in the industry.

Can I assume that some of the information I will been and have been using is slightly complicated by the fact that the EN24 info is UK based whereas most of the thread rolling etc info is US based?

 

[TVP]

Hi Tom,

I don't understand your last question, but if you want information on thread rolling that is from a European company, LMT Fette will have standard sizes, etc. for metric threads:

http://www.lmtfettetools.com/catalo...ads/2023 Rollkopfkatalog deutsch englisch.pdf

 

[tomcannon]

Hi, sorry the first part was a statement, the 2nd part was just wondering if some of my confusion was because of the cross over between UK and US units and terminology, I am to be rolling imperial threads anyway so US is fine for measurements, just the hardness scales etc I wasn't sure about. Thanks for all your help.

 

[CoryPad]

Yes, units can be confusing, particularly in this field.

 

[tomcannon]

It's not just me then! I'm trying to remember all that I learned at college 8 years ago as since then I've been doing dirty engineering and automotive stuff!

 

[KENAT]

Unified threads aren't American, they are unified between US, Canada & GB as I recall.

There is a BS for unified threads, I was going to say 1936 but I think that's undercuts for unified threads.

http://www.boltplanet.com

has a calculator for unified threads which can be useful to check your own calcs.

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[PeterCharles]

My memory is that UNC and UNF were post-WW2 standards when the UK was still looking West to the US and Canada.

However in the late 1960's the UK started looking East to Europe and metricated.

 

[KENAT]

Yes Britain is officially metric however, unless things have changed in the last 7 years, there are still British Standards for Unified threads and associated things such as standard undercuts etc.

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