plate miscasting (was "Fixing Plates")

[centipod at mac.com]

Thanks for that very clear description of the process, Frank.

So if I'm understanding this correctly, the top half of the pattern,  
or cope, would have had to have been refashioned (or at least the  
part in the triangle) once they had discovered the error?

Allen Wright

On 9 Feb 2007, at 00:32, Frank Emerson wrote:

>> Would the model and length designation would be a separate part of
>> the pattern in the moulding process?
>
> Some foundries stick on a series of numbers on the bottom side of  
> the plate
> pattern to produce a code representing a batch number or the date  
> the plate
> was cast.  The next day, they scrap of the numbers and stick on new  
> ones.
> This code will never see the light of day, until a rebuilder  
> removes the
> plate and exposes the bottom-side.   In the early days of a new  
> model the
> pattern may be made of wood with a "ton" of bondo or epoxy filler.
> Eventually, after all the "bugs" are worked out, a pattern will be  
> made of
> a more permanent material.
>
>> Or is a plate pattern simply two
>> large plate-sized pieces, top and bottom? (I don't know much about
>> the mechanics of plate casting).
>
> A plate pattern looks pretty much like the finished plate,  
> dimensionally,
> except that it is scaled up, about 1' 1/8" to 1', to allow for the
> shrinkage of the plate as it cools.  In areas where the finished  
> plate will
> have an internal void, the pattern will have a chunk of material  
> that will
> be filled in with a "core box" later.  The pattern is pressed into  
> a bed of
> sand to form the bottom half of the mold.  A wooden frame,  
> reinforced with
> a wire lattice is placed on top.  Sand is poured into this form.   
> The sand
> has a black coagulant to make it stick together well, when packed.   
> Once
> the sand is tightly packed around the pattern, the top section can be
> lifted off, and the pattern removed.  The top and bottom halves of  
> the mold
> are called the cope and drag, respectively.  The core box(es) are
> strategically positioned to prevent the iron from flowing into the  
> internal
> void areas.  The cope is replaced over the drag, and you have a  
> temporary
> mold in which to pour the molten iron.  There are more efficient  
> methods
> for mass production, but the method described is still widely used.
>
> Frank Emerson
> pianoguru at earthlink.net
>


Allen Wright
6 Clay Court, 219 Long Lane
London SE1 4PB
United Kingdom
020 7378 8265
0780-688-1325 (mobile)




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