Evening star., 1927-04-24
NEW PISTON HELD
FREE OF DEFECTS
Research in Manufacturing
of Aluminium Product
Aids Engineers.

Research and tests in the art or
manufacturing aluminium pistons dur
ing the past several years has re-
suited in the production of a piston
free from all the defects that former
ly troubled automotive engineers, ac.
cording to G. d. Welty, research en-
gineer If the Aluminium Co. of Amer
lea, who recently addressed the Buf-
falo section of the Society of Auto.
motive Engineers.
The piston, as developed, is com.
posed of an alloy of approximately 80
per cent aluminium and 10 per cent
copper. These pistons are close.
grained, free from porosity and blow
holes, they have twice the hardness
of former aluminium pistons and will
run with less clearance in the cylin-
ders than any other type of piston
vet produced, according to Mr. Welty.
25,O0O,0OO Produced.
Improvement in the art of casting
the alloy by forming the pistons in
permanent molds instead of in sand
molds has resulted in the production
Of between 25,000,000 and 30,000O0c
such pistons since 1920, he said, and
improvements in the heat.treating
process have played an important
part in their success.
The alloy weighs only about one
third as much as an equal volume of
cast iron, and the advantages of this
light weight in pistons are so great,
especially in four-cylinder engines,
that some of the largest builders of
four-cylinder cars almost owe their
success to the performance they have
been able to obtain with these pistons,
Mr. Welty stated. In the siX-cylinder
engine they also greatly smooth out
the vibration, and in the Vtype eight
cylinder engine they almost totally
eliminate two of the three vibration
periods.
Their high ability to conduct heat
results in a cooler engine head and
the engine can be operated with a
higher compression than is normal.
The lower head temperature also re-
suits in better fabrication, less car
bon formation and consequently less
pre ignition, cleaner and cooler oil and
cooler bearings.
One serious disadvantage of alum
inum, however, is that 1t expands
with heat more than twice as much
as does cast iron, so that formerly it
was necessary to give the pistoTis ex-
cessive clearance in the cylinders.
Develop Insert Type.
To meet the demand for closer
clearances. the insert type of piston
has been developed. This has split
skirt with steel inserts that act as
spacers between the bearing faces and
prevent excessive expansion. If the
inserts are of cold rolled steel the pis.
ton can be fitted to about the same
clearance as the cast iron piston Of
the same diameter, but if made of
invar steel, which contains about S5
per cent OF nickel and does not ex-
pand at all at engine temperatures,
the piston can be fitted with clear.
ance of only slightly more than half
a thousandth of an inch per inch Of
diameter. Such invar-insert pistons
have a very long life, according to Mr..
Welty, because they never come into
contact with the cylinder wall due to
their own expansion.
More perfect fabrication is required
with aluminium pistons than with cast
iron pistons, he admitted, but lubri-
cation difficulties usually are due to
too small oil pipes and to condensa-
ton of water in the engine, with re-
sultant oil dilution.