Stop Pouring, Start Casting

Páginas: 30 (7381 palabras) Publicado: 24 de febrero de 2013
HOYT MEMORIAL LECTURE
“STOp pOURIng, START CASTIng”
J. Campbell
University of Birmingham, UK
Copyright © 2012 American Foundry Society

Editor’s Note: The Charles Edgar Hoyt Memorial Lecture is presented each year during the American Foundry Society’s
Metalcasting Congress to provide an opportunity for leading metalcasting experts to express their thoughts on a topic of their
choosing.The lecture is intended to represent the many diverse voices in the metalcasting industry. The words and opinions
expressed are those of the author and are reprinted with minimal editing.

Abstract
The necessity to stop the pouring of liquid metals is becoming urgent. Pouring is the main source of entrained bifilms.
Bifilms are the fundamental mechanisms which initiate all
our familiar castingproblems including porosity, hot tears,
low mechanical properties, corrosion initiation etc. As lattice dislocations explain plasticity, bifilms explain pore initiation and fracture initiation. Only when pouring is eliminated (or, at second best, sufficiently controlled) will casting
processes start to achieve their potential to deliver routinely
sound and reliable castings (with theadditional potential to
make healthy profits!).

Furthermore, with simplified foundry designs, including the
elimination of pouring, the casting industry has the potential to
produce products which in some cases might expect up to 1000
% improvement. Engineering throughout the world would be
revolutionized. Although not widely realized, evidence for massive benefits from bifilm-free metals alreadyexists in the Al alloy and Ni alloy casting industries. The groundwork is in place
for a historical revolution in the casting industry.

Introduction

finally migrated from the industry into the University, where
I was able to set up a video x-ray unit through which we put
thousands of castings to see what happened during pouring. I
finally started to find some answers. The answers wereawesome. I had to throw away the textbooks. The existing books
gave the wrong answers.

Today, I want to share my vision for the casting industry with
you. At this time I see us making mediocre products, with significant difficulty, and significant hard work. My view is that
this need not be so. Today, I want to explain why.
We all know that there are easier ways to make money than
makingcastings! The fact that we stick with it indicates that
there is more to it than the money. Some might even suggest
we are in it for the love of it. Whatever the reason, we know
we must need our heads examined.
The opportunity to make this presentation today makes me
feel particularly humble; there will be many of you here today
who in a lifetime in the casting industry may have made even
morescrap than me. Many know the feeling of standing over
our scrapped casting, already having run out of delivery time,
and with the customer threatening to take away the pattern
work at the end of the week. There has to be a better way. As
I mentioned earlier, that is what I want to talk about today.
There is a better way. Furthermore, it promises to be exciting.
Earlier in my life, when I setup and managed a foundry,
I was constantly frustrated by not knowing the answers to
casting problems. Eventually, after what seemed a lifetime, I

International Journal of Metalcasting/Summer 2012

Keywords: Bifilms; counter gravity; Al alloy; superalloy;
casting revolution.

The correct answers were so simple, deceptively simple in
fact, but life-changing. They concerned the surfaceoxide on
the melt. The entrainment of the surface oxide caused the
surface oxide to fold over, entraining either (1) a lump of air
that we call a bubble, or (2) entraining nothing, but folding
dry side to dry side, creating a doubled-over film with a central unbonded interface like as a crack (Fig. 1), eventually to
be known as a bifilm. The turbulent pouring of metals fills
the liquid with...
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