Repairing sheared tube
 

Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. The fracture hasn't caused any
distortion to the tube, and the two halves still mate nicely.

Main problem is that the fracture is just at the end of a curved
section, so making a suitable plug to tap into each end won't work.

The tube is aluminium (or an alloy), so 'simple' welding doesn't seem
to be an option for repairing it. The tube is also one of several
welded into a reasonably complex array, and so isn't easily detachable
for popping some type of replacement in.

I have thought of two ways of repairing it:

1) Cut the tube off at a lower straigh point, make up a replacement
section and join to the original: a) with suitable plug/dowel; b) by
welding old to new. From these two I'd prefer 1a as I can just about
do all of that myself.

2) Align and secure the two parts, then fill with some suitable epoxy
or meltable resin. Once set the resin would need to have the strength
and durability under flexing to keep the joint stable.

Can anyone comment on the merits or otherwise of these suggestions, or
contribute more?

In case it helps, the tube OD is about 22mm, with a wall thickness of
about 3mm.

TIA
IanC

wrote in message
ups.com...
Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. snip

So why has it fractured ?....

wrote in message
ups.com...
Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. The fracture hasn't caused any
distortion to the tube, and the two halves still mate nicely.

Main problem is that the fracture is just at the end of a curved
section, so making a suitable plug to tap into each end won't work.

snipped
In case it helps, the tube OD is about 22mm, with a wall thickness of
about 3mm.

TIA
IanC


A piece of tubing of a similar size with a slot cut along its length to form
a wrap round would probably do the job. Fitting jubilee clips (hose clips,
elephant clips) or drilling through each end and fixing with self tapper
screws or rivets might be a good way of holding it in place tighter.

You could also just place strips of metal along two sides of the tube,
drilling through both metal and tube, and then fixing in place with self
tapper screws or rivets.

:::Jerry:::: wrote:
wrote in message
ups.com...
Hi

I have a strut on a pram that has sheared. It's at a 'springy'
point
but isn't particularly load bearing. snip

So why has it fractured ?....

Because its flexed a lot? I can understand that it takes an amount of
force to flex it, but that isn't (to my mind) the same as it being
under a compressive or tensile load. I'm happy to be corrected on this
if I'm misunderstanding the cause of failure.

Cheers
IanC

BigWallop wrote:
wrote in message
ups.com...

Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. The fracture hasn't caused any
distortion to the tube, and the two halves still mate nicely.

Main problem is that the fracture is just at the end of a curved
section, so making a suitable plug to tap into each end won't work.


snipped

In case it helps, the tube OD is about 22mm, with a wall thickness of
about 3mm.

TIA
IanC



A piece of tubing of a similar size with a slot cut along its length to form
a wrap round would probably do the job. Fitting jubilee clips (hose clips,
elephant clips) or drilling through each end and fixing with self tapper
screws or rivets might be a good way of holding it in place tighter.

Was going to suggest that - did it with a McClaren Buggy 20+years ago
using jubilee clips and it worked very well - in the end there were more
splints, jubilee clips and new wheels than I could count. The only
problems in your example seem to be the curve and the ability to flex,
although I cannot imagine how a plain 22mm tube could flex.

You could also just place strips of metal along two sides of the tube,
drilling through both metal and tube, and then fixing in place with self
tapper screws or rivets.


Malcolm

In article . com,
" says...
Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. The fracture hasn't caused any
distortion to the tube, and the two halves still mate nicely.

Main problem is that the fracture is just at the end of a curved
section, so making a suitable plug to tap into each end won't work.

The tube is aluminium (or an alloy), so 'simple' welding doesn't seem
to be an option for repairing it. The tube is also one of several
welded into a reasonably complex array, and so isn't easily detachable
for popping some type of replacement in.

I have thought of two ways of repairing it:

1) Cut the tube off at a lower straigh point, make up a replacement
section and join to the original: a) with suitable plug/dowel; b) by
welding old to new. From these two I'd prefer 1a as I can just about
do all of that myself.

2) Align and secure the two parts, then fill with some suitable epoxy
or meltable resin. Once set the resin would need to have the strength
and durability under flexing to keep the joint stable.

How about this:
Take a piece of aluminium mesh (the sort you use with car body filler
for bridging holes) and roll it up so it's a snug fit inside the tube
and several layers thick. Jam one end of the rolled mesh into the
curved tube section so it takes the right shape (ish), then remove
it. Now lag the inside of the curved tube and the curved half of the
mesh with epoxy and jam it back together. Try to get plenty of epoxy
through the mesh so it bonds all the layers. Then glue the straight
piece of tube and the other end of the mesh. Although the ultimate
strength of the repair won't be great it should be adequate, and will
hopefully reduce flexing and the chance of a further fatigue failure.

wrote in message
ups.com...
Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. The fracture hasn't caused any
distortion to the tube, and the two halves still mate nicely.

Main problem is that the fracture is just at the end of a curved
section, so making a suitable plug to tap into each end won't work.

The tube is aluminium (or an alloy), so 'simple' welding doesn't seem
to be an option for repairing it. The tube is also one of several
welded into a reasonably complex array, and so isn't easily detachable
for popping some type of replacement in.

I have thought of two ways of repairing it:

1) Cut the tube off at a lower straigh point, make up a replacement
section and join to the original: a) with suitable plug/dowel; b) by
welding old to new. From these two I'd prefer 1a as I can just about
do all of that myself.

2) Align and secure the two parts, then fill with some suitable epoxy
or meltable resin. Once set the resin would need to have the strength
and durability under flexing to keep the joint stable.

Can anyone comment on the merits or otherwise of these suggestions, or
contribute more?

In case it helps, the tube OD is about 22mm, with a wall thickness of
about 3mm.

TIA
IanC


==============
An aluminium tube of 22mm od and a wall thickness of 3mm is quite a strong
tube. If such a strong tube breaks it suggests a possibly dangerous design
fault. I would ask the manufacturers for a repair and if they are difficult
ask Trading Standards to intervene. Children have died in prams which
unsafe.

Cic.

On 22 Dec 2004 13:44:34 -0800, wrote:

Hi

I have a strut on a pram that has sheared. It's at a 'springy' point
but isn't particularly load bearing. The fracture hasn't caused any
distortion to the tube, and the two halves still mate nicely.

Main problem is that the fracture is just at the end of a curved
section, so making a suitable plug to tap into each end won't work.

The tube is aluminium (or an alloy), so 'simple' welding doesn't seem
to be an option for repairing it. The tube is also one of several
welded into a reasonably complex array, and so isn't easily detachable
for popping some type of replacement in.

I have thought of two ways of repairing it:

1) Cut the tube off at a lower straigh point, make up a replacement
section and join to the original: a) with suitable plug/dowel; b) by
welding old to new. From these two I'd prefer 1a as I can just about
do all of that myself.

2) Align and secure the two parts, then fill with some suitable epoxy
or meltable resin. Once set the resin would need to have the strength
and durability under flexing to keep the joint stable.

Can anyone comment on the merits or otherwise of these suggestions, or
contribute more?

In case it helps, the tube OD is about 22mm, with a wall thickness of
about 3mm.

Hi,

How about a plug of smaller dia tube held in with JB Weld? Or use a
polyurethane sealant/adhesive which would absorb some flexing.

cheers,
Pete.

Pete C wrote:
On 22 Dec 2004 13:44:34 -0800, wrote:

Hi

I have a strut on a pram that has sheared.

Hi,

How about a plug of smaller dia tube held in with JB Weld? Or use a
polyurethane sealant/adhesive which would absorb some flexing.


Hi

This is the way I'm going at present, using a length of 12mm mild steel
stud bent to follow the curve.

This leaves a gap of about 2mm all around that I'd like to pour a
suitable glue or resin into, drive out the air pockets and hope it'll
all hold.

In the end, the adhesive/resin will (I think) need to flex to transfer
the load from the pram chassis into the steel, and not fracture too
much itself and hence fall away from filling the void effectively.

Is JB Weld pourable, or at least 'pokeable' into position with a bit of
wire to fill the voids? I'm not at all familiar with polyurethane
adhesives: would they (or something else) be better?

And finally, I'd like to pop out and get the product tomorrow or
Monday. Suggestions for suppliers for more specialist products would
be useful.

TIA
IanC

This leaves a gap of about 2mm all around that I'd like to pour a suitable
glue or resin into, drive out the air pockets and hope it'll all hold.

Araldite or similar epoxy won't flow down a gap like this. But if you
arrange the joint so that it is vertical, put a fillet of freshly mixed
araldite over the gap, then heat the tube below with a hot air gun the
araldite will liquify and flow down the gap (rather like end-feed soldering)
before setting. You will need to keep feeding fresh mix to get enough volume
(i.e. penetration). Better to use 24 hour than 5 minute araldite for this.
You will need to do the two "directions" separately. That said, I have never
had much success in repairing buggies: the stresses are high at the joints
and the alloy tubes very prone to fatigue.

Newshound wrote:

... if you put a fillet of freshly mixed
araldite over the gap, then heat the tube below with a hot air gun
the
araldite will liquify and flow down the gap. Better to use 24 hour
than 5
minute araldite for this.

Hi

Did exactly that and it worked like a charm, better than I would have
hoped. I warmed the work pieces before hand, but the araldite flowed
like oil after a gentle warming so am not even sure this was necessary.

It feels like a very sturdy repair, but time will tell.
Thanks for the help.

IanC