Acid Etch & Penetration

[Kent]

I personally beg to differ cold steel with some thickness to it works as a big old heat sink, drawing heat energy out . As far as I am concerned energy in practical welding is actually based around heat, watch a weld get in deeper if not too deep and even blow holes in thin stuff as a weld proceeds along a joint and things get too hot, towards an edge were the heat cannot escape into the material ahead any further and everything gets full of HEAT, think also of upslope and downslope settings.

Now forgive my ignorance if there is some different way of expressing the way energy that actually melts metal works other than heat but that's what I see proceeding along a joint. Pre-heating has been used to boost inadequate welding penetration from a plant for a long time, yes cold cracking also . It isn't the only way but its a good one in my experience

If I am wrong here tell me what energy is used in OFW

 

[TechnicAl]

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/differ.html

http://www.twi-global.com/technical...when-arc-welding-steel-and-how-is-it-applied/

http://www.gowelding.com/weld/preheat/preheat.htm

 

[Kent]

Thanks,
Despite the mumbo jumbo stuff were someone is actively trying their best to sound clever (bumble bees cant fly stuff really) the last line sealed it for me and pretty much says it all "heat is energy" "temperature however isn't energy" well yes

A lump of metal taken to a good "temp" need less energy (heat is energy right) to take it to melting point though don't it just (that's just hands on experience ). Temperature could you see be sub zero but hit steel with an oxy fuel torch and it wont be cold for long as it absorbs and effectively stores that energy input . Slowly that heat/energy dissipates (hence watch the inter-pass temp don't fall to greatly)

 

[Kent]

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/differ.html

http://www.twi-global.com/technical...when-arc-welding-steel-and-how-is-it-applied/

http://www.gowelding.com/weld/preheat/preheat.htm

Ah, see you added two more now will have a read of them tomorrow and see if I can learn something new

Ta
Kent

 

[Kent]

with respect Al, non of these links actually discuss the subject purpose at hand. In a way this is to be expected as the std stock answer to Bede's penetration issue might be lash out on a bigger better plant (which will render the margin a minus on this one of type thing perhaps) or assume the guy cant do his job (which seems unlikely).

I am just fine with Hydrogen cracking prevention which is the subject adequately / well covered by the lower two links, the top one? well not so keen, author seems set out to sound clever rather than to inform the reader in any useful way to me (but again context is maybe out of kilter)

my suggestion to boost what is suspected as being a slightly underpowered set is covered in the following publication

Welding Fabrication and repair question and answers BY Frank Marlow on Industrial press isbn 0-8311-3155-1

Section 1 page 150 Common welding problems & their solutions

Extending the capacity of a welding machine

Can't quote his passage due to copyright but its a good book well peer reviewed and handy for all those one off issues slightly out of our own experiences that will always crop up no matter how good thinks one is at everything. Me? previously thousands of hours MIG welding heavy duty stuff with an old bloke wittering on how it should and shouldn't be done just sort of gives you a feeling

 

[hotrodder]

http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html the example in the link...

2 kg of carbon steel is heated from 20 oC to 100 oC. Specific heat of carbon steel is 0.49 kJ/kg0C and the heat required can be calculated as

dQ = 2 (kg) 0.49 (kJ/kg0C) (100 (oC) - 20 (oC))

= 78.4 (kJ)

Too lazy to do the calcs myself and unless i missed something about travel speeds used we don't have enough data anyway but http://www.mesteel.com/cgi-bin/w3-m...fo/metal_calculators/Welding_Energy_Input.htm suggests around 2kj/mm using their default travel speed

What i'm try to say (and maybe what Al was getting at?) is that the way heat energy is applied makes a huge difference to the weld (can't weld with a rosebud tip) as do the material properties... ally is a good example where preheat makes a noticable difference when the kit isn't really big enough. Melting temp is less than half that of carbon steel but because ally has near as damn it twice the specific heat capacity of carbon steel and over 4 times the thermal conductivity you typically need more amps to weld it unless/until the entire lump is heat soaked. My world is more about thin stuff and materials other than carbon steel so might be very wrong but while it'll help i can't see a bit of preheat transforming things personally

 

[Richard.]

We pre heat to dramatically reduce the rate the joint cools. If this was a thin peace of steel and we warmed it to the point it was glowing then there is no doubt you will penetrate deeper because the material is much closer to it's melting point. But we are talking about a 40mm thick section with 150-200 degree C. I don't believe this will make a difference personally to penetration. I suggest pre heat to reduce cooling rates because this is a high strain joint on thick section. To increase pen I would either step up on the machine or change prep design.

 

[Kent]

Of course Ali is a way different thing in the way it takes heating, its never been my thing in any big way though I have and do get it. I suggest Pre-heat is tried this is 40mm thick steel and it cant hurt, is recommended by more than just me.

I am not about to suggest anyone cant weld who does so for a living, no doubt at all it happens and I have seen it with my own eyes but I aint about to teach grandma to suck eggs right until I am sure she is loosing her marbles

 

[Bede]

Sod it, I'll use araldite instead. What could possibly go wrong?

 

[Kent]

We pre heat to dramatically reduce the rate the joint cools. If this was a thin peace of steel and we warmed it to the point it was glowing then there is no doubt you will penetrate deeper because the material is much closer to it's melting point. But we are talking about a 40mm thick section with 150-200 degree C. I don't believe this will make a difference personally to penetration. I suggest pre heat to reduce cooling rates because this is a high strain joint on thick section. To increase pen I would either step up on the machine or change prep design.

I certainly agree on the prep and reducing the rate of cooling but I just do not get why NOT to try a pre-heat and see if it has any great effect on things as regards increasing the penetration before buying / hiring in costly gear. Heating cost? about £25 a hours worth say?

 

[Kent]

Sod it, I'll use araldite instead. What could possibly go wrong?

Oh you don't wanna do that there are way better glues to use I will find you something on wikipedia

 

[Bede]

I've hired a 400 amp set for £65 a week. Negligible against the cost of two of these beams. It's only a 12 tonne single point load when all's said and done, MPI'd and Load Tested.

 

[Richard.]

I would warm up that joint before I welded it and I'd keep it warm through out the job and cool it slowly it's thick steel and it will suck the heat from the weld quickly I'd just not be worrying about doing it to aid penetration. I'd take a different approach to overcome that.

 

[TechnicAl]

with respect Al, non of these links actually discuss the subject purpose at hand.

Exactly but the topic is preheating.....and they dont mention penetration......wouldnt you expect them to mention penetration if it was influenced by the headline topic ???

I dont think I said dont preheat..........just dont expect preheat alone to solve the problem

 

[TechnicAl]

with respect Al, non of these links actually discuss the subject purpose at hand. In a way this is to be expected as the std stock answer to Bede's penetration issue might be lash out on a bigger better plant (which will render the margin a minus on this one of type thing perhaps) or assume the guy cant do his job (which seems unlikely).

I am just fine with Hydrogen cracking prevention which is the subject adequately / well covered by the lower two links, the top one? well not so keen, author seems set out to sound clever rather than to inform the reader in any useful way to me (but again context is maybe out of kilter)

my suggestion to boost what is suspected as being a slightly underpowered set is covered in the following publication

Welding Fabrication and repair question and answers BY Frank Marlow on Industrial press isbn 0-8311-3155-1

Section 1 page 150 Common welding problems & their solutions

Extending the capacity of a welding machine

Can't quote his passage due to copyright but its a good book well peer reviewed and handy for all those one off issues slightly out of our own experiences that will always crop up no matter how good thinks one is at everything. Me? previously thousands of hours MIG welding heavy duty stuff with an old bloke wittering on how it should and shouldn't be done just sort of gives you a feeling

http://books.google.co.uk/books?id=UT5HM71MHe8C&printsec=frontcover#v=onepage&q&f=false

 

[TechnicAl]

Thanks,
Despite the mumbo jumbo stuff were someone is actively trying their best to sound clever (bumble bees cant fly stuff really) the last line sealed it for me and pretty much says it all "heat is energy" "temperature however isn't energy" well yes

A lump of metal taken to a good "temp" need less energy (heat is energy right) to take it to melting point though don't it just (that's just hands on experience ). Temperature could you see be sub zero but hit steel with an oxy fuel torch and it wont be cold for long as it absorbs and effectively stores that energy input . Slowly that heat/energy dissipates (hence watch the inter-pass temp don't fall to greatly)

Look at this...........here we have the BBC being "clever"...........will it ever end

 

[Kent]

http://books.google.co.uk/books?id=UT5HM71MHe8C&printsec=frontcover#v=onepage&q&f=false

aye that the one

 

[norlander]

Sod it, I'll use araldite instead. What could possibly go wrong?

 

[Mid Wales welder]

This must be pre heated to help prevent hydrogen cracking!

 

[Dimitri De Spiegeleer]

What are the requirements? No need to achieve extreme penetration depth if the calcs show that a fillet of 1/4" is enough.
I do understand that more is better, but how much exactly is the local stress at the welds, what is required (throat) by the customer? I can only hope someone ran some calcs over this one... That guy's the one that should be able to answer your questions.

For S275 and 40mm thickness, I would apply preheat as standard, but you should check the material certificates for the carbon equivalent. depending on the quality of your steel, you would need 70-80 °C upto 220°C.
btw, S275 doens't quite cut it: you'll also need to know the charpie values and temper/finishing (eg. S275J2+AR) in order to calculate the needed preheat temp.