# Gear failure whilst engaging the Scharnhorst.



## TurboTyne (Aug 30, 2012)

In 1943 the 9,000 ton British cruiser HMS Sheffield engaged the German battleship Scharnhorst. At this crucial moment whilst under full power, the pinion on her inner port hp turbine failed. The attached photo shows the pinion after failure. 

Would anyone care to speculate, especially if based on actual experience of a failed gear, about what the men in the engine room are likely to have experienced during this failure and how would they have reacted to the situation. Apart from the fact that they were engaging the enemy, I guess this would have been a frightening moment for those nearby (but I don't place too much faith in my guesswork). Was that likely to be the case or would such a failure not have caused as much noise and vibration as I imagine ? 

The pinion was probably about 12” diam, tooth pitch very approximately 0.6 ins, and it would probably have been transmitting in the region of 9,000 shp at the time, assuming the ships 72,500 shp total output was equally divided between hp and lp turbines in each of the 4 sets.

Mike


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## Coastie (Aug 24, 2005)

I don't know much about the engineering side, but I'm sure there'd have been a funny smell in the engine room!!


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## steamer659 (Mar 18, 2009)

Hi... Would need to know the conditions of the forward and after pinion bearings, interestingly enough the wing/helix contact area especially to the left (coupling side?) looks clean, without much to go on, I would say foreign body damage, possibly from a oil spray nozzle coming adrift....


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## TurboTyne (Aug 30, 2012)

steamer659 said:


> Hi... Would need to know the conditions of the forward and after pinion bearings, interestingly enough the wing/helix contact area especially to the left (coupling side?) looks clean, without much to go on, I would say foreign body damage, possibly from a oil spray nozzle coming adrift....


The description I have says "Fourteen teeth cracked at forward end of forward helix", no mention of the bearings. The article this came from is about effects of slight inaccuracies in gear tooth machining on gear failure. It says that failures in larger ships such as the Sheffield tended to arise on the infrequent occassions when they used maximum power. This indicates the failure was not thought to be from foreign bodies etc but ????

Mike


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## jmbrent (Feb 3, 2010)

Hi Turbo Tyne, Prior to running turbines up under load, the gear meshing would be checked by taking blue marking checks. In the photo it would appear that something has passed through the gearing as there are teeth badly damaged. If this was the HP primary pinion it would be hurtling round at a great speed and I am sure the noise would have been greater than any background noise in the engine room, and very frightening. Micky


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## berbex (Feb 17, 2013)

I suppose it would be like something from hell, a lot of "gnashing of teeth".

The shading of the working face seems to indicated there was no misalignment. The two bands of badly broken teeth, all around and in the same manner seems to indicate something particular. I would guess a foreign object stuck in the teeth of the bull wheel. The damage is bad but not catastrophic, so likely they were broken one at a time. The other damage nearby would be collateral.


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## makko (Jul 20, 2006)

I go with the slight inaccuracy in the teeth machining as the cause.

The inaccuracy would lead to reduction in the meshing surface area with a subsequent rise in localized stress. This would lead to a cyclic loading of the individual teeth and at full power would quickly lead to a stress crack developing at the tooth root. The crack would quickly propagate and the tooth become liberated causing subsequent domestic object damage, liberation of even more material and extensive cracking. At the time, there would have been one heck of a racket but nothing quite as impressively dangerous as when turbine blades become liberated and exit the casing!
Great pic by the way.
Rgds.
Dave


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## makko (Jul 20, 2006)

Just to add, I have investigated several similar losses in gearboxes. The off machining lead to galling on the teeth faces - This is basically the "scouring" out of material due to extreme pressure overload of the lube oil film. A number of these failure were due to a well known manufacturer making parts at different factories - The machine tools in the former "eastern" factory were worn, resulting in a very small deviance in the tooth face angle.

A majority of the other failures (clinker mills) was due to overloading which destroyed the main roller bearing. The design was subsequently change to incorporate an additional stage and to use solid machined bearings.

Rgds.
Dave


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## John Rogers (May 11, 2004)

makko said:


> I go with the slight inaccuracy in the teeth machining as the cause.
> 
> The inaccuracy would lead to reduction in the meshing surface area with a subsequent rise in localized stress. This would lead to a cyclic loading of the individual teeth and at full power would quickly lead to a stress crack developing at the tooth root. The crack would quickly propagate and the tooth become liberated causing subsequent domestic object damage, liberation of even more material and extensive cracking. At the time, there would have been one heck of a racket but nothing quite as impressively dangerous as when turbine blades become liberated and exit the casing!
> Great pic by the way.
> ...


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## steamer659 (Mar 18, 2009)

A very interesting run up on topic... Separation and overload of the oil film between the gear tooth loading surfaces? Wouldn't localized hot spots be shown at the heavily loaded contact areas? If this is in fact a latent defect during the manufacturing process, why is only the right helix section the one with the most damage? 

Today of course, we could do all kinds of scientific testing, checking the metal's alloy mix, the microscopic examination and etc...

Here's a thought- when in a Naval Battle involving large caliber guns, is there not large variations of atmospheric pressure due to the firing and receiving fire? Although it is interesting enough that the turbine was being operated at probably overload, wasn't there a safety factor during design? Surely the designers were probably using empirical rules....

An interesting twist.... Would have loved to surveyed the damage first hand... By the way when I was a Class Surveyor during the late 80's, we had a containership powered by a 28,500 SHP, articulated, tri-plane double reduction gear which suffered cracks and discontinuities in way of the HP HS Pinion, we simply ground those teeth areas back and continued to operate... The vessel was the Lancer Class SS Carolina.....


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## berbex (Feb 17, 2013)

Makko above describes a very common mode of failure for this type of mechanical equipment, and as he says failure occurs at the root.

I have looked for this but I do not think it is evident. Look at a little right of midway, the teeth are curiously damaged, all in similar manner, and at the tip. Those tips were likely damaged by being forced into a groove with foreign matter lodged in. Further to right the damage is nearer to pitch circle.

To the right the bearing journal does not seem to have suffered unduly. If that is so then the damage occurred slowly, a tooth at a time. 

cr


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## makko (Jul 20, 2006)

Here are some pics of an overloaded pinion from a clinker mill gearbox. 

The origin of the overload was substantially harder than usual clinker. In order to maintain production, the pinion was changed out a further two times but not the crown wheel (they should both be replaced as a matched pair). The new gear box then arrived and was swapped in (four stages instead of three stages and solid phosphour bronze bearings).
Rgds,
Dave


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## berbex (Feb 17, 2013)

That's a nice headache you show there.

As I make it that is a pinion and wheel gearbox with axes at 90 deg, ie non parallel. Correct? If so you have sliding faces along with the forces involved = compound trouble. With roller bearings I guess then relatively slow speed.

On double helical wheel and pinion, I always saw white metal bearings, and they usually suffer badly along with the teeth. They were speed increasing for feed pumps. The bigger ones, 47000hp 5000rpm pinion for gas turbines, those mercifully I survived (no mishaps).


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## makko (Jul 20, 2006)

Hi Berbex,
Yes, you are right, 90° pinion and crown. If I remember correctly, about 90 rpm. I was subsequently at another cement plant in Guatemala which had suffered the same sorts of failures. On that visit, I witnessed the strip down under the supervision of a technician from the OEM. It was he who told me that they had redesigned the boxes with 4 stages and solid bearings. The only trouble is reversing the direction of the motor to ensure correct rotation!
Rgds.
Dave


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