Fatigue crack repair
christop...@gmail.com
I have a question of curiousity here. I have a backhoe with a fatigue
crack in the chassis. The chassis is made from rectangular mild steel
box section. The crack is where a piece of 6" x 2" x 1/4" box section
is welded to a piece of 4" x 2" x 1/4" box section at 90 degrees. The
crack is in the butt welded section and is about 1" long.
Someone else has tried to fix the crack once before. They appear to
have welded up the crack, then created a broad "patch" of weld metal
about 1" wide and 1/8" thick across the affected area. Their weld isn't
messy, but there's a lot of weld metal present. I don't know if this
was a sensible way to fix the crack, but it is just starting to
reappear again. I wonder if they didn't get complete penetration and
left a tiny depth of crack which has helped the crack to grow again.
I can think of three ways to fix this crack. The first is to grind off
all the visible weld metal, vee out the crack and then make a narrow
weld closely resembling the original. The second is to do the same, but
then add a broad patch of weld metal over the top as the previous
repairer did. I wonder if the previous repairer didn't vee out the
crack beforehand? If I was doing this, I would be a little concerned
about the amount of heat I was adding to the metal, but then I'm not an
expert welder. The third method is the same as the first, but
afterwards grind the weld flush, cut a large piece of 1/4" plate to go
over the joint and weld it on as a patch. My gut reaction would be to
use the third method, but I'm a little concerned that the fresh welds
and the unwelded space behind the plate might act as new sites for
crack initiation.
Anyway, I don't plan to do this. The crack doesn't appear to be growing
and, given its location, failure of the joint would be most unlikely to
cause an accident. I'm just interested in welding technology and am
curious to know the technologically best way to fix this joint, if you
absolutely had to fix it and didn't care how long it took or how much
it cost you.
Best wishes,
Chris
Grant Erwin
I suspect there's more to it than the weld. I am guessing that the joint is
built a little too lightly so it's flexing too much in service. I would scarf
out the built up weld, grind all smooth, vee out the crack and weld it up, then
fit a solid gusset to reinforce the corner and weld that up solid, and paint to
match.
GWE
Ecnerwal
One thing you're not mentioning that I consider a critical part of any
crack repair is to drill out the ends of the crack. You can plug weld
those holes as part of the repair process, but it is essential to get
rid of the stress concentration points at the end of the crack so it
does not continue/come back.
Some "glob on a big patch" repair methods are actually more likely to
cause future cracking than simply repairing the crack site with a smooth
surface. The rigidity and edges of the patch provide stress
concentrations which a less impressive-looking repair does not. Partly
this depends on whether the original failure is due to substandard
design, so you need to find some way to effectively beef the joint up
without making it worse, or abuse, in which case you should be able to
repair it to original condition and then stop abusing things.
--
Cats, coffee, chocolate...vices to live by
Martin H. Eastburn
What I have seen - just saw it on the 20 ton press in my shop - C channel
is welded to box tube. There is 4 areas that can be welded on each joint
but only across the top and across the bottom is welded. The verticle
sections are left bare. QUESTION: is that left for expansion between
the welds ? or just not done ?
I consider it 'got enough done' weld, but then I'm not qualified so I'm not sure.
Any ideas ?
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
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Potblak
Using it as a starting point, drill a 1/4" hole right through it.
NOW weld it up.
the reason it reappeared was the previous repair didn't go right to the end.
"Ecnerwal" <Lawren...@SOuthernVERmont.NyET> wrote in message
news:LawrenceSMITH-E3E...@news.verizon.net...
Gunner
<lion...@consolidated.net> wrote:
>I'm not a pro, not even a novice level :-) but I try to weld myself.
Damn...I did that by accident once and it really really hurt!
Gunner
Political Correctness
A doctrine fostered by a delusional, illogical liberal minority and
rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible
to pick up a turd by the clean end.
c.henry
to clean metal , that is all traces of the old weld would be removed
then the joint would be rewelded , the option of adding reinforcements
would be considered carefully and the factory may even be consulted .
there is a reason it cracked , maybe was welded incorrectly in the plant
, machine used improperly , so on , the reason why it cracked would be
the determining factor on reinforcing . everything needs a weak point ,
if you make that corner invincible and the flexing / cracking moves to
the hydrostatic transmission mounts ??
\
christop...@gmail.com
> built a little too lightly so it's flexing too much in service. I would scarf
> out the built up weld, grind all smooth, vee out the crack and weld it up, then
> fit a solid gusset to reinforce the corner and weld that up solid, and paint to
> match.
Thanks for the suggestions. I think there is a weakness in the design,
though not a huge weakness as the machine in question has done 9000
hours of work. Personally I would have used a thicker gauge of steel.
It's good to know I was on the right track with the idea of adding a
reinforcing plate.
I still get a little puzzled by some of the terms you use, Grant. Some
of them like "scarf" and "swage" I never hear in Britain. I figure
"swage" is some kind of crimping, but what about "scarf"? Does it refer
to a bevelled edge or something?
Thanks to everyone for the thoughts.
Best wishes,
Chris
Grant Erwin
Yup, we're divided by a common language! :-)
Scarfing = arc/air gouging (it's a US shipyards term)
Swaging = uniform compressing of a round item to effect reduction in diameter
for example to connect some fittings to welding cable you 'swage' them on
By "gusset" I mean something spanning the corner which when welded in would tend
to greatly stiffen the corner from flexing. If you stood on your front stairs
and cut out a 45-45-90 triangle, equal legs about 4", and set that so the
cardboard was dead vertical, one edge vertical up the stairs, one edge
horizontal but perpendicular to the front edge of the stair, that would be one
kind of gusset shape.
Grant
Andrew Mawson
"Grant Erwin" <gr...@NOSPAMkirkland.net> wrote in message
news:12nbq7v...@corp.supernews.com...
Chris, rather puzleled by your comments - swage & scarf or quite
common. We were talking of scarfing the joints in bandsaw blades
before silver soldering only last night on the
uk.rec.models.engineering group and I've been swaging copper joints
all week and have a set of swages in my blacksmiths kit for necking
down shafts!
AWEM
christop...@gmail.com
> christop...@gmail.com wrote:
> >>I suspect there's more to it than the weld. I am guessing that the joint is
> >>built a little too lightly so it's flexing too much in service. I would scarf
> >>out the built up weld, grind all smooth, vee out the crack and weld it up, then
> >>fit a solid gusset to reinforce the corner and weld that up solid, and paint to
> >>match.
> >
> >
> > Thanks for the suggestions. I think there is a weakness in the design,
> > though not a huge weakness as the machine in question has done 9000
> > hours of work. Personally I would have used a thicker gauge of steel.
> > It's good to know I was on the right track with the idea of adding a
> > reinforcing plate.
> >
> > I still get a little puzzled by some of the terms you use, Grant. Some
> > of them like "scarf" and "swage" I never hear in Britain. I figure
> > "swage" is some kind of crimping, but what about "scarf"? Does it refer
> > to a bevelled edge or something?
>
> Yup, we're divided by a common language! :-)
>
> Scarfing = arc/air gouging (it's a US shipyards term)
Alright. I've never worked in a shipyard, but air/arc gouging I
understand. I thought it was rather crude though. Or is it like
oxy-acetylene cutting? Crude in the hands of a novice but precise in
the hands of an expert?
> Swaging = uniform compressing of a round item to effect reduction in diameter
> for example to connect some fittings to welding cable you 'swage' them on
Sounds like I was pretty well right when comparing it to "crimping".
> By "gusset" I mean something spanning the corner which when welded in would tend
> to greatly stiffen the corner from flexing. If you stood on your front stairs
> and cut out a 45-45-90 triangle, equal legs about 4", and set that so the
> cardboard was dead vertical, one edge vertical up the stairs, one edge
> horizontal but perpendicular to the front edge of the stair, that would be one
> kind of gusset shape.
Gusset I understand. I've heard and used that term plenty.
Thanks for explaining.
Best wishes,
Chris
christop...@gmail.com
> common. We were talking of scarfing the joints in bandsaw blades
> before silver soldering only last night on the
> uk.rec.models.engineering group and I've been swaging copper joints
> all week and have a set of swages in my blacksmiths kit for necking
> down shafts!
Then I guess they're just terms I haven't come across in the UK before.
There's always something new to learn about metalworking. So you
air/arc gouge the joints in bandsaw blades?
By the way, Andrew, is it you who's the casting expert? Someone at
r.c.m or uk.r.m.e mentioned cast steel recently and it got me thinking.
Can you successfully cast mild steel (say, steel with 0.2% carbon or
less) and come out with a decent result which has all the usual
properties of mild steel? You just don't seem to hear people talk about
it. Either things are fabricated mild steel or cast iron. Just
curious...
Best wishes,
Chris
Andrew Mawson
<christop...@gmail.com> wrote in message
news:1165366602.9...@n67g2000cwd.googlegroups.com...
Chris, scarfing originally wass necking down two pieces so when put
together overlapping they are the same thickness, and the term in the
ship yard is presumably refering to preparing the edges of plate for
welding in a similar beveled fashion which could well be done with air
/ arc gouging kit. Scarfing joints are very commonly used in woodwork
to increase the gluing contact area and it is the same with bandsaw
blades when silversolder becomes the glue.
I would no way claim to be a casting expert, but I do play. As for
casting mild steel, I should be able to tell you in a few weeks as I
now have my induction furnace running so am able to get up to the
(significantly) higher temperature required for steels over iron. It
certainly is possible but I've not yet done it.
AWEM
RoyJ
air/arc tool/
Scarfing on a metalworking NG would refer to joining old style flat
belts (usually leather by tapering the ends very gradually and glueing
together.
On a woodworking NG, a scarfed joint is two pieces of wood joined end to
end using a long taper (5:1 or 10:1 angle)
go figure!!!
christop...@gmail.com
> I would no way claim to be a casting expert, but I do play. As for
> casting mild steel, I should be able to tell you in a few weeks as I
> now have my induction furnace running so am able to get up to the
> (significantly) higher temperature required for steels over iron. It
> certainly is possible but I've not yet done it.
Let me know how it works out. I just wonder why people make castings
from cast iron instead of mild steel? I guess it has a few advantages
like being more corrosion resistant, nicer to machine and perhaps
having slightly better bearing properties, but it's also brittle and
hard to weld. I can't help but wonder if mild steel is harder to cast.
You just rarely hear about it being done.
Best wishes,
Chris
christop...@gmail.com
> Scarfing on a welding NG would mean gouging out a bad weld using an
> air/arc tool/
> Scarfing on a metalworking NG would refer to joining old style flat
> belts (usually leather by tapering the ends very gradually and glueing
> together.
> On a woodworking NG, a scarfed joint is two pieces of wood joined end to
> end using a long taper (5:1 or 10:1 angle)
>
> go figure!!!
Thanks, Roy. That's a bit clearer now!
Best wishes,
Chris
David Billington
christop...@gmail.com wrote:
Chris my understanding is that steel is far less fluid than CI and so
cannot be cast into as intricate a shape but it certainly can be cast.
Some years ago I read of a UK company that cast hotrod axle ends in
steel and exported them to the US for a change, these ends were welded
to tubular steel axles. Recently I read in IIRC "The Engineer" of
Sheffield Forge Masters that cast Europes or the worlds largest steel
casting at 360 tons from a 600 ton melt. This was for a hydraulic press
for an Austrian company and was to be used for things like forging
turbine rotor hubs.
Carl McIver
news:1165073963.9...@l12g2000cwl.googlegroups.com...
> Hi folks,
>
> I have a question of curiousity here. I have a backhoe with a fatigue
> crack in the chassis. The chassis is made from rectangular mild steel
> box section. The crack is where a piece of 6" x 2" x 1/4" box section
> is welded to a piece of 4" x 2" x 1/4" box section at 90 degrees. The
> crack is in the butt welded section and is about 1" long.
>
> Someone else has tried to fix the crack once before. They appear to
> have welded up the crack, then created a broad "patch" of weld metal
> about 1" wide and 1/8" thick across the affected area. Their weld isn't
> messy, but there's a lot of weld metal present. I don't know if this
> was a sensible way to fix the crack, but it is just starting to
> reappear again. I wonder if they didn't get complete penetration and
> left a tiny depth of crack which has helped the crack to grow again.
I'll throw in my thoughts here. You're getting what you pay for here...
What stresses are causing the crack to start with? Is the joint too
stiff to start with? Should it be allowed to flex a bit, or are the
stresses too concentrated and it's cracking? Perhaps the weld appeared from
normal use and then a bad weld job was applied, or even welded up wrong to
start with, and the crack was created when the weld cooled. I'd be looking
for the very ends of the crack and drilling that out first, or at least
punching a hole in it with a torch. Gotta stop the crack's formation or it
will continue to run.
Can the patch/gusset be made larger to spread out the stresses of
movement? How possible is it that the cracked weld could be ground out,
left alone and weld in the gusset to pass the stresses around the joint? My
thinking is that if you can't alleviate the stress at that point, you at
least could spread out the loads across a larger area.
Gunner
In the oil fields..scarfing is the beveling of pipe ends prior to
welding them together.
Gunner
Rule #35
"That which does not kill you,
has made a huge tactical error"
John Husvar
RoyJ <spam...@microsoft.net> wrote:
> Scarfing on a welding NG would mean gouging out a bad weld using an
> air/arc tool/
> Scarfing on a metalworking NG would refer to joining old style flat
> belts (usually leather by tapering the ends very gradually and glueing
> together.
Hmph, and I always thought that was called skiving.
Go figure indeed. <EG>
--
Bring back, Oh bring back
Oh, bring back that old continuity.
Bring back, oh, bring back
Oh, bring back Clerk Maxwell to me.
Richard Smith
I worked in a research foundry for a while.
Cast iron is very easy to cast, compared to most other metals, for at
least one specific and clear reason. It doesn't shrink as it cools.
The rejection of graphite from the melt is expansile, counteracting
shrinkage on solidification. To put it in perspective - with
Aluminium you loose 7% of volume between casting temperature and fully
solidified. If you don't want void defects (you don't!) you have to
feed that, which means that the casting must solidify progressively
from its extremities towards a reservoir of liquid metal - a
"feeder"or "riser". So same as for steel - it isn't going to be easy
to get a good casting.
There's probably a host of other reasons which a foundry person could
tell you about.
Richard Smith
Martin H. Eastburn
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
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Don Young
"John Husvar" <jhu...@sbcglobal.net> wrote in message
news:jhusvar-7BF2D5...@newsclstr02.news.prodigy.com...
> In article <v_Adh.7507$ql2....@newsread3.news.pas.earthlink.net>,
> RoyJ <spam...@microsoft.net> wrote:
>
>> Scarfing on a welding NG would mean gouging out a bad weld using an
>> air/arc tool/
>> Scarfing on a metalworking NG would refer to joining old style flat
>> belts (usually leather by tapering the ends very gradually and glueing
>> together.
>
> Hmph, and I always thought that was called skiving.
>
> Go figure indeed. <EG>
>
clear information sometimes. One word can have many meanings and one concept
can have many words to describe it. What is really interesting is to see how
many heated arguments this causes, where everyone is correct.
Don Young
Andrew Mawson
"Don Young" <no...@nonesuch.com> wrote in message
news:12nhpnd...@corp.supernews.com...
>>>SNIP<<<
<EG>
> >
> It is. It amazes me how imprecise language is in conveying complete
and
> clear information sometimes. One word can have many meanings and one
concept
> can have many words to describe it. What is really interesting is to
see how
> many heated arguments this causes, where everyone is correct.
>
> Don Young
>
>
The word that amuses me is 'cleave' as it has two entirely opposite
meanings. It can mean to split apart as in cleaving pieces of slate
from the native sedimentary rock, or it can also mean to adhere or
cling or stick fast. How a word can get such opposite meanings is
distinctly odd!
AWEM
Gunner
wrote:
English..and its many "dialects" is said to be one of the hardest
languages in the world to learn to speak like a native.
How many meanings and attributes does a simple word like "bow"
have..as a single example?
And a Native of WHICH english speaking country? <G>
christop...@gmail.com
> I worked in a research foundry for a while.
>
> Cast iron is very easy to cast, compared to most other metals, for at
> least one specific and clear reason. It doesn't shrink as it cools.
> The rejection of graphite from the melt is expansile, counteracting
> shrinkage on solidification. To put it in perspective - with
> Aluminium you loose 7% of volume between casting temperature and fully
> solidified.
That sounds like a good reason. The funny thing is, though, that I see
plenty of aluminium sand castings but few in mild steel (I can think of
only one right now). Maybe David's suggestion about the viscosity at
casting temperatures is important here. Is aluminium much less viscous
than mild steel at casting temperatures? If mild steel is both viscous
and it shrinks significantly on cooling, I can imagine it would be a
real pain to cast.
Best wishes,
Chris
Richard Smith
Chris
Liquid steel isn't viscous, as much as I can say from having worked in
the steelworks - it runs very thinly. That is at white hot, by the
way - you need a dark visor!
"White hot" might bring a problem regarding sand. Sand "burns" onto
big cast iron castings. With steel it would be something else
(~1300degC pour for cast iron, ~1700degC for steel).
Can't rightly comment much - have only worked so so much with casting
- and this is a welding forum :-)
There is
rec.crafts.metalworking
where folk do a range of stuff with metals.
And you could search the Web for the sites of hobbyists.
Richard Smith