[SEL] Re: Alamo piston pattern update

[Curt]

jbcast at charter.net wrote:

>
>> ---- Curt <curt at imc-group.com> wrote:
>> . The riser's purpose is to provide molten metal to  
>>
>>> the casting as it cools and the metal shrinks. On your piston for 
>>> example, you want to bring metal in at the crown. Once filled the 
>>> casting should begin to solidify from the skirt moving toward the 
>>> crown. The riser is attached to the largest section thickness thru a 
>>> short gate. The gate and riser need to be sized such that they will 
>>> freeze off last. This ensures molten metal can continue to flow into 
>>> the crown as the rest of the piston cools and shrinks.
>>>   
>>
>>
>> Curt, have you had any problems with shrinkage in the pin boss area? 
>> I made a pattern and had some pistons cast, we had to add risers to 
>> supply the pin boss, the first one sunk in on both sides of the 
>> piston at the boss. J.B. Castagnos
>>
>>  
>>
> JB,
> So far no troubles with this. But there may be a reason now that I 
> think about it. In the core box photos you will see that there is a 
> rib that runs under the crown of the piston and then down each side of 
> the piston connecting to the boss area. I always thought this was a 
> strengthening rib and admittedly I also thought it was overkill. But 
> since you mention the shrinkage problem perhaps it has more to do with 
> assuring a path for molten metal to continue feeding the boss areas 
> while cooling.
> So far all of the piston patterns I've made have this rib going under 
> the crown and connecting to the bosses. However, over the weekend I 
> started on a pattern to make pistons for the 3HP Herc/Jaeger/Economy 
> engines and that piston has the rib under the crown, but it does not 
> have the rib extending down toward the bosses. I am planning on 
> duplicating this exactly as Hercules did and will certainly let you 
> know if this results in a shrinkage problem at the bosses. Very 
> interesting thought you have brought up!
> Curt
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