WELDING EN32 build up with tig ?

[Russ7018]

Hi, I'll ask this in the tig section, as I'm going to be building it up with tig I think..

So, I have a build up job on some en32 hex bar,
It's about 3m long and 7" dia, it's machined at one end to accept a bearing, I've had somecracks machined out leaving a recess so it needs building up,

Can't allow it to distort, it's £14k to replace,
What I'm concerned about it change in structure with the rise in temp, bear in mind it's under huge stress,

So advise please.....
What filler rod,
Interpass ??
Is there a max temp ??

Much appreciated..

 

[TechnicAl]

Mild steel should do it..........7018 rods, A15 TIG or A18 MIG

Its relatively soft so unless you quench it you wont affect the structure

7 inch thick may need some preheat.........is it solid 7" thick?

Normally its case hardened but if youve machined it you will have removed the hardened surface

 

[Russ7018]

Yes it's solid....
I thought it was en24... But boss says en32

There is also some build up to do on the gears, there are a few chips to the teeth,
Not sure on material, maybe en24, not sure.
Same wire will do for both A15

I do have some er70-s filler rod

 

[TechnicAl]

ER 70S what.........there should be a number, probably 2 or 6

EN24 is a different beast all together............EN24 gear teeth will be a nightmare to weld

 

[Russ7018]

ER 70S what.........there should be a number, probably 2 or 6

EN24 is a different beast all together............EN24 gear teeth will be a nightmare to weld

It's 70-2 sorry.

I've never welded en24 but to replace these gears takes 2months, total of £20k...
So I'm looking to keep it running while they order the new parts,

 

[TechnicAl]

ER70S-2 is similar to A15

En24 needs at least 300 oC preheat and weld using E312 filler..........but gear teeth tend to crack whilst being preheated..........you will stand a better chance if you heat in an oven so the heat is spread evenly...........using a torch creates hot and cool spots

 

[Russ7018]

Er70s-2 is it same composition as 7018 low hyd ?

Company that makes these shafts have said it can't be welded as it will fracture,
I figured that they are seeing £££££ signs and a sale,

 

[TechnicAl]

Er70s-2 is it same composition as 7018 low hyd ?

Company that makes these shafts have said it can't be welded as it will fracture,
I figured that they are seeing £££££ signs and a sale,

Yes 7018 and S-2 are very similar composition

The EN32 is easily weldable...........7" thick makes anything prone to cracks.........preheat it 150 oC and it should be OK.............perhaps stagger the weld around the shaft

EN24 is a whole lot more difficult especaially when there are section changes

 

[Russ7018]

Yes 7018 and S-2 are very similar composition

The EN32 is easily weldable...........7" thick makes anything prone to cracks.........preheat it 150 oC and it should be OK.............perhaps stagger the weld around the shaft

EN24 is a whole lot more difficult especaially when there are section changes

Cheers....

 

[Spark plug]

Would a sleve on the worn shaft not be a better solution?

http://www.skf.com/uk/products/New-Market-Offers/SKF-SPEEDI-SLEEVE-new-generation.html

 

[Russ7018]

Would a sleve on the worn shaft not be a better solution?

http://www.skf.com/uk/products/New-Market-Offers/SKF-SPEEDI-SLEEVE-new-generation.html

Hi... It's on the hex part of the shaft,

 

[Spark plug]

Looke like welding it is I thort you ment the bearing spigot.

 

[Russ7018]

Looke like welding it is I thort you ment the bearing spigot.

No, where the hex meets the bearing area there are surface cracks, so we machined out the cracks and I'm going to build it up to hopefully keep it's strength,
Not sure it it will create a weak spot having machined off the case hardened surface....,

Wonder if sending it for stress relief would help ?

 

[TechnicAl]

No and No...........SR will weaken it, slightly

 

[Rudi McAnichal]

Does anybody know how easy it is to find out whether the material is actually EN24 or EN32? It is feasible to analyse scrapings, or would it be necessary to cut a slice off the end of the shaft?

Any idea what caused the material to crack where the hex meets the bearing area? Mis-use, overloading, etc, or could it be a design weakness? It would be a shame to spend £20k on new parts for a faulty design.

Torsion? If the bearing is on the end of the shaft, it won't be torsion cracking (unless there is a gear overhung outboard of the bearing).

Rotational bending fatigue? Quite possible, if the long shaft flexes and the designer didn’t specify self-aligning bearings.

Consequences of failure? If your welds failed, would the machine just come to a halt, or would the shaft thrash around and cause a whole lot of other damage? And who would get the blame?

Is it feasible to cold-fill the cracks and run the machine on reduced load while waiting for the new parts to arrive?

Sorry, I am not a TIG expert, so the above is just written from a general mech eng point of view.

 

[Russ7018]

This is a similar machine,
But the one that needs repairing is bigger and run from hydraulic motors, the cracks are formed at the point of the hex meets the bearings, cracks are created I think by not having the teeth regularly sharpened, and overloading so it forces the two shafts apart.

 

[Sidewinder]

So, it sounds like that the is a fundemental design flaw in the machine design, generating a stress point within the shaft which is a weakness when cyclic stresses are involved, slightly above design loads, so, built to a price, rather than a standard as it were.
You will need to look at the shaft geometry the sizing, corner radii etc. then work some numbers to see what the maximum defect sizeis based on the base material, weld procedures etc. the shaft design geometry, sharp corners, radii, etc and see what the acceptable are.
I suspect that the machine may not be fit for purpose, or built to a budget

 

[Russ7018]

Well......
Demo of the machine shredded cars, motorbikes, old vices, there pretty strong..
I wouldn't say built to a budget , a used/secondhand machine is around £250,000

I will try and get a few photos of the area I'm looking to build up ! !

 

[Sidewinder]

A £1,000M machine can be built to a budget, if the real deal would cost £100,000M
It is all relative.
I deal with machines of several £10's of k regularly, many are built to a price, if not most, rather than built to a standard.

I know of the machines you speak.
I also know that any machine can be built to a budget, no matter how much.
It's even easier with niche machines, I have seen it many times.
Does it even comply with the MD?
TBH I doubt it.

 

[Rudi McAnichal]

Massive torque. Enormous bending forces on the hex shaft, with stress reversal during each rotation. Stress concentration where shaft size has been reduced for the bearings. A classic situation to induce fatigue failure by rotational bending.

Have any shafts on this type of machine failed in the past? A cone-shaped fracture, with “beach marks” on the surface, would suggest rotational bending fatigue.

A replacement new shaft is quite likely to fail in a similar manner in due course. It would be important to relieve any extra stresses created during welding, otherwise the repaired shaft could fail quite quickly.

Sure, a new demo machine can probably crunch big lumps of metal. Just as the Comet airliners flew perfectly well when new - and then after a critical number of stress reversals they suffered fatigue failure and disintegrated in mid-air.

A better design might be to use a straight hex shaft, without any machining at all, and run the bearings on external sleeves (circular outside, hex inside – a nice job for somebody with a slotting machine).