Team-BHP - Use of Calcium Hydroxide/ Slack Lime/ Chuna in Electric Arc Welding

Hi Guys,

The loop of my pin type jack ( the place where you put hook of jack handle) broke, This happned because the jack handle is approx 4 feet and I was sitting at an angle rather then keeping the handle straight.

I took the jack to a welder , Welder took a steel strip and did a nice job of applying continuous weld from both sides ( inside and outside).

He used Chuna ( slack lime ) / Calcium Hydroxide to coat the welding electrode and used Kerosene to cool the welded joint in between.

He could not explain me the reason and just said that " weld majboot hota hai".

Can someone with technical knowledge please explain if coating electrode with slack lime helps in welding joint ? As I understand the job of electrode flux in electric arc welding is to create gases and residue which coveres the molten metal and prevents oxidation / contamination when it is hot.

Is use of chuna ( used in tobbaco) helpful in this process in anyway ?

PS: Carification about this topic being in technical section.
Actually you can be consider the topic as automative or not depending on what is being welded , Since cars may need welding at some point or other I thought it should be here.

Regards

I was bit verbose earlier so putting the question again ,

Does coating welding electrode with slack lime really improve the strength/quality of the welded joint or detoriate it ?

I am sure there are lot of people from automobile / mechanical fabrication industry who can explain this.

No idea on the technical reason.
But a welder once told me it helps keeping the area being heated in check.
So that the heat does not spread all over but it is focused on the area under this paste.

EDIT:
Found some info here:
http://simple.wikipedia.org/wiki/Welding

Quote:

Welding flux may be used in a solid, liquid, or paste form. During welding, the flux will melt and some of it will evaporate. This creates a small pocket of gas around the weld. This pocket of gas prevents oxidation of the metal under weld. Melted flux, through a corrosive reaction, cleans contaminants that prevent a proper weld. After welding, the flux solidifies. This layer of solid flux is called slag, and must be removed from the weld. The SMAW weld process most commonly uses flux, and is most commonly used on steel.

http://en.wikipedia.org/wiki/Flux_(metallurgy)

Quote:

Originally Posted by bblost (Post 2871460)

No idea on the technical reason.
But a welder once told me it helps keeping the area being heated in check.
So that the heat does not spread all over but it is focused on the area under this paste.

Well as per the text books ( and also the wiki link you provided ) the purpose of flux is not to prevent spread of heat but to cover the molten metal with gases produced and slug ( molten residue of flux) so that metal is not contaminated and original property is not changed.

For example if the carbon percentage goes up in the molten metal it will make the steel at the joint harder and brittel then the original part.

Quote:

Originally Posted by vikram_d (Post 2871481)

Are you sure he did electric arc welding?.

Yes welding was done in front of me , I just turned around to protect my eyes while he touched the electrode.

There are several kinds of coated electrodes available , My question is if there is any calcium coated one used for any specific purpose.

If this is the case then I appriciate the genius of welder to buy 1 rupee chuna and coat it himself rather then buying an expensive electrode.

Hi,
The most common electrode used to be Ferrospeed. Which is coated.

Can we put this up as SAW, frugal innovated/ juggadded?

Actually the only time I've seen what you are saying is when roadside welders braze. So like Vikram, I'm surprised.

Regards
Sutripta

Can possibly be used for shielding or removing the Ferric Oxides
On a conventional robotic Gas Metal Arc Welder usually CO2 is used as a shielding gas from atmospheric air to localize the arc as well as improve the quality of weld(no pores, weld splatter, mis aligned weld et cetera).
Carbon from carbonates being placed higher in series displaces any ferric oxide from the weld. No idea on the hydroxide though.

A good weld is attained if the surfaces to be welded are first thoroughly cleaned of dirt, oil, and other impurities. The flux generally acts to oxidize residual impurities thus driving them out of the welded joint. A clean joint is a strong joint; AFAIK. Welding rods are generally coated with flux, but then extra flux can be employed when needed; or non-coated rod with external flux can be employed as coated rods are expensive.

Heat from the electric arc melts the metal rod, and partially melts the two surfaces, which then sort of fuse together. A thin sheet would be "punctured" by the intense local heat of the arc hence in such cases gas welding is employed for better control on the heating.