Tmoose
Mechanical
- Apr 12, 2003
- 5,626
We have a part cast from NiHard 1. The part is a trapezoid (actually more like a pizza slice with the tip chewed off) . It is 5/8" to 1" thick with 3 sides ~ 24 inch long and the nibbled side ~15" long.
Our standard note for this material calls for "Anneal:Stress relieve castings, heat slowly to 425°F ±25°F, (Do not exceed 450° F.), hold at this temperature for 1 hour for each inch of thickness plus an additional 3 hours, or 4 hours minimum. Leave castings in mold until casting temperature reaches 200° or less."
The dimensions of the decades old pattern suggest the old pattern makers were expecting shrinkage of 1 - 1.5%.
Presumably also the very same pattern produced acceptable parts back then, although by a different foundry.
Parts being delivered in recent times are undersized.
It appears the shrinkage “across” the part (pizza cut edge to PC edge) is on the order of 2.5 - 2.8%. I do not have measurements in the radial (pizza) dimension.
The Nickle Institute's handbook suggests shrinkage between 1.25 and 1.95 for NiHard 1, and 1.8 and 2.8% for NiHard 4.
The foundry just provided chemistry from a 3rd party confirming the material is NiHard 1. (Another wonderful theory goes down in flames)
I am about to look into the radial shrinkage, to see if the part is full sized in that direction, and possibly “restrained” thereby causing mega-shrinkage across the part.
The specified Stress Relief looks to be pretty standard for Abrasion Resistant Iron casting according to the Nickel Institute.
What I could not find in the Nickel Institute literature is the net shrinkage ( un-shrinkage) to be expected from the Stress Relief. Thus I am wondering IF the stress relief was skipped or done incorrectly, could the part end up 1% too small ?
Any comments or suggestions are appreciated.
We are not really considering modifying the pattern due to the small sales volume of this part in modern coal hating times,
But there are other similar parts that may suffer if the root cause of the excessive shrinkage is process related.
Thanks,
Dan T
Our standard note for this material calls for "Anneal:Stress relieve castings, heat slowly to 425°F ±25°F, (Do not exceed 450° F.), hold at this temperature for 1 hour for each inch of thickness plus an additional 3 hours, or 4 hours minimum. Leave castings in mold until casting temperature reaches 200° or less."
The dimensions of the decades old pattern suggest the old pattern makers were expecting shrinkage of 1 - 1.5%.
Presumably also the very same pattern produced acceptable parts back then, although by a different foundry.
Parts being delivered in recent times are undersized.
It appears the shrinkage “across” the part (pizza cut edge to PC edge) is on the order of 2.5 - 2.8%. I do not have measurements in the radial (pizza) dimension.
The Nickle Institute's handbook suggests shrinkage between 1.25 and 1.95 for NiHard 1, and 1.8 and 2.8% for NiHard 4.
The foundry just provided chemistry from a 3rd party confirming the material is NiHard 1. (Another wonderful theory goes down in flames)
I am about to look into the radial shrinkage, to see if the part is full sized in that direction, and possibly “restrained” thereby causing mega-shrinkage across the part.
The specified Stress Relief looks to be pretty standard for Abrasion Resistant Iron casting according to the Nickel Institute.
What I could not find in the Nickel Institute literature is the net shrinkage ( un-shrinkage) to be expected from the Stress Relief. Thus I am wondering IF the stress relief was skipped or done incorrectly, could the part end up 1% too small ?
Any comments or suggestions are appreciated.
We are not really considering modifying the pattern due to the small sales volume of this part in modern coal hating times,
But there are other similar parts that may suffer if the root cause of the excessive shrinkage is process related.
Thanks,
Dan T
