Considerations when cutting Cast Iron

[KMP04]

What concerns must I address when cutting 4" thick plate from a large Cast Iron object (to large to preheat)?
The methods used to cut these pieces would probably be Plasma Arc or Exothermic cutting rods. I am looking for specifics on max. allowable temperature before changing metallurgy, heat affect zones, rate of cooling etc...I would like to minimize the thermal stresses introduced which could cause cracks.

Thanks

 

[arunmrao]

It is a tough one. Any of the methods suggested would increase theheat locally,therby causing structural changes from grey to white. If you can machine the part out,you could avoid the heat related problem.

An unrelated question to you. What is the need for removing a 4inch thick plate, any repair work,envisaged?

 

[metengr]

Depending on cost, you could look at hiring an in-place or field machining contractor that has access to a portable milling machine. Cast iron is easily machinable. In the power industry, we have used field machining on many occasions in tight spots and on cast/wrought materials.

 

[KMP04]

The large blocks of cast iron were once guide vane blocks located in the draft tube of a turbine pit. With the recent re-runnering, we would like to eliminate any unused components which may cause hydraulic effects inside the draft tube. due to the curvature of the wall, we are limited to what we can use to safely access the area.

Our process used so far was to remove large pieces by making a cut, 1/2" away from the turbine casing. This way the heat affect zone remains in the cast block and not the turbine casing. We would then move in with the grinders to remove the last bit of material to try and achieve the profile of the wall.

I've been monitoring temperatures as we progress and have found the temperature range at the wall casing is anywhere from 160 deg. F. - 500 deg. F.

Lastly I plan to perform dye penetrant inspection to ensure no stress cracks were created.

Any thoughts on this process or temperatures I've recorded?