[Jewelry making - Article 00753] - [Orchid] Ignot mold explosions

[Alden & Glenda Blood]

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    The occurrence of molten metal being violently ejected from an ignot
    mold with a loud bang while pouring could be caused by oil as well
    as water. 

    The auto ignition temperature of most lube oils is in the range of
    465 degrees F to 815 degrees F.  If a significant amount of oil (2 -
    3 ml?) is left in the bottom of the mold thru insufficient wiping,
    inattention, or not being aware of of the potential hazard, it is
    possible an explosion as described by Renate Sommer could occur. 
    Heating the mold to the smoking point to coat it with carbon would
    probably not reach a temperature sufficient to ignite the oil.  When
    oil is heated to the flash point or fire point it needs a source of
    ignition to burn.  However, when the molten silver at about 1570
    degrees F reaches the oil, auto ignition temperature is reached
    instantly with the generation of large volumes of hot gasses trying
    to escape past the in-rushing hot liquid silver, and thus resulting
    in an explosion .  The result will be the volcano described.  When I
    have time, I may set up an experimental situation and test to see
    what the minimum amount of oil left in the bottom, corners, etc.
    would be required to produce a catastrophic result. 

    The described situation could happen to an inexperienced person
    simply because they are not aware of the potential hazard and do not
    follow instructions exactly, ie; "wipe the oil off the surface
    thoroughly leaving just a thin coating".  It could also happen to a
    person of considerable experience thru inattention or carelessness. 
    A case of "familiarity breeds contempt" where contempt would
    translate as careless. That situation is , of course, the reason
    aircraft pilots go thru the check list item by item every flight
    regardless of how many hours flying time they have logged. 

Captain Blood
"Marlinespike Seamanship in Precious Metals"
mariner AT tgtel.com



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