material for drive axle 8

[mechanodan]

I would like to have some feedback on some material we are considering for half shafts in a custom car application.The app.is a shaft 24" long with a 1.2"spline journal diam.with 29 splines 45 degree pressure angle 24-48 pitch angle.The axle is exposed (visually)and I didn't want corrosion.I would also like to avoid any paint.Ford uses a necked down or waisted area of 1.437 down to the 1.2 spline diam.My concern is that if I make these shafts from 17-4 or 15-5 and use H-900 cond.Would it compromise the spline area in a torsional shock load? The parallel would be 4340 material which is used in the aftermarket and is presumably stronger than stock.

 

[metman]

One of the reasons that I was called back to work for National Mine Service Mining Machinery Div four years after leaving them is because of a recommendation to use Maraging Steel where a previously unknown [COLOR=red yellow]REVERSE[/color] load was being applied causing fatigue failure of:

C300 doubled fatigue life in one case for splined shaft of (4340 with most sophisticated surface hardening and core treatments available including shot peening and electro-polishing). Also these maraging steels have excellent corrosion and SCC resistance.

Design for RELIABILITY, manufacturability, and maintainability

 

[metman]

The reverse loads were discovered during a dynamic load test. A 120,000 pound continuous ripper miner had the cutter head plunge down onto a limestone rock measuring about 4ft x 6ft x 10ft so that the machine was bouncing off the ground. Strain guages had been attached to a 3.5" dia splined shafts (RH&LH drives) driving through CV joints. The strain guages were monitered via lead wires through slip rings at the outboard ends of the drum drives.

The measured stresses on the oscilloscope and print out verified calculated stresses. However, because MSHA (Mine Safety Health Administration)requires a max limit on inrush current of underground Coal machines during startup (an electric motor can develop 300% Full load current during start up), the LH motor had to have a 3 second time delay after the RH motor was energized.

The drum drive motors on this machine were located on the chassis with a long drive train of two drive shafts and several CV joints besides the CV joints connected to the notorious FAILING 4340 SPLINED SHAFTS. Inside of and upstream of the SHAFT was more drive train including a planetary, bevels etc.

This long drive train would wind up like a spring during start up on the RH side and by the time that the LH drive was energized, the RH side was UNWINDING and Powww! Reverse loading fatigue from START UP LOADS. Of course cutting loads added significantly to the fatigue history but the REVERSE loads were discovered during this dynamic testing which solved the mystery.

Maraging was a temporary solution -- the M shafts increased the fatigue life but still eventually failed because it was a geometry problem where the shaft had to pass thru the sun gear of the planetary to drive the center drum and later a second generation drum drive was designed to allow for a larger diameter splined shaft.

To reiterate and because cost is a factor for mechanodan's project, Maraging Steels are prohibitively expensive -- the shafts used to temp solve the above problem cost about $700 each -- no problem for Formula One folks.

Look at TVP's 17-4 suggestion!



Design for RELIABILITY, manufacturability, and maintainability

 

[CoryPad]

Maraging steel reversed fatigue data from the ASM Handbook. Better than martensitic steel with 700 MPa (100 ksi) yield strength, not quite as good as H11 tool steel.

Carroll Smith had some definite technical deficiencies, and this mistruth illustrates one of the worst ones.

 

[edstimator]

I know nest to nothing but if it is the paint that you find objectionable why not polish the steel on the exposed shaft to the max amount of luster that you can achieve and then clear coat it with a catalyst based finsh coat and the luster will remain unchaiged unless the clearcoat is compromised.

 

[tbuelna]

Maraging steel reversed fatigue data from the ASM Handbook. Better than martensitic steel with 700 MPa (100 ksi) yield strength, not quite as good as H11 tool steel. Carroll Smith had some definite technical deficiencies, and this mistruth illustrates one of the worst ones.

CoryPad,

Appreciate the correction and reference.

Terry