[modeleng] Re: Model Engineers Laser Company

Harry

I can understand the Oxy/Acet problem because you can easily get the same
effect on a weld by using a carburising flame (one too rich in Acet which is
a Carbon Compound gas).  What you've effectively done is turned the material
local to the weld into hi-carbon steel and allowed it to rapidly cool from
white-hot.

When cutting, it's usual to pre-heat the material using a near "neutral
flame" and then turn to near pure oxygen (bur still with some Acet) which -
effectively - allows the steel to "burn". I don't know exactly how this can
add carbon, but suspect that it may have an adverse effect on the MS at the
cut due to the inclusion of "products of combustion" in the white hot metal
since most "carbon gasses" (eg Methane, Ethane, Propane, Butane, etc), when
burnt, produce compounds of Carbon (CO, CO2) and water.

It's a long time since I studied Organic Chemistry so I may be well off
track !

Andy 

-----Original Message-----
From: modeleng-bounce@xxxxxxxxxxxxx [mailto:modeleng-bounce@xxxxxxxxxxxxx]
On Behalf Of Harry Wade
Sent: 21 July 2007 17:09
To: modeleng@xxxxxxxxxxxxx
Subject: [modeleng] Re: Model Engineers Laser Company

At 11:17 PM 7/20/07 +0100, you wrote:
>Ordinary Mild Steel (MS) can't be hardened by heating/cooling(except by
>using case-hardening methods) - Andy

Andy,
    In my experience it can, at least when the steel has been oxy/acetly
flame cut.  I had some 1" hot rolled mild plate flame cut a few years ago
and found that almost 1/8" of material at the cut edges was glass hard and
ruined HSS cutters.  I assumed the oxygen and/or acetylene somehow altered
the skin near the cut and I ended up having to have the pieces annealed.  I
can't speak to any other combination of materials.

Regards,
Harry

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