The Jasper weekly courier. [volume] (Jasper, Ind.) 1858-1922, 1874-04-17
The Sand. Blast.

ms curious mechanical process was.
we believe, first exhibited at the fair Of the
American Institute, in New York City, a
number OF years ago. The main object OF
the process Is to engrave devices clearly,
sharply, and cxpeditiously on glass, stone,
plies chiefly to intaglio and fiat-relief en-
craving. Ii is based on the fact that when
glass, stone or metal is subjected to the
impact of blast of sand, the exposed sur
face is rapidly worn away.
The Popular Science Rerieso, i'm mention
ing some recent experiments on this pro-
cess, says that, although the sand-blast
acts with energy upon hard or brittle sur
faces, it has little or no effect upon elastic
and soft substances, such as india-rubber,
wax, paper and lace. and II is upon such
substances, therefore, that reliance is
placed for protecting those parts Of the
surface which il is not desired TO act upon.
Thus piece of lace spread over and ce-
mented To sheet OF glass will so efiectu-
ally protect the glass when exposed TO the
sand-blast, that the threads of the network
will, after few seconds exposure, be imi-
tated on The glass by bright interlacing
lines, while the rest of the glass surface
will be reduced to a ground or frosted
state. The efficacy of the blast depends
PEELED either by steam. water, or air; but
steam is generally preferred where high
velocities are required. When large
quantity is TO be removed. as in the orna-
menting of stone, steam-jet of from sixty
TO eighty pounds pressure Is used. In
this case the stencil Is made of iron or
rubber; but when small quantity OF ma
terial Is to be worn away, or the surface
merely depolished, as In ornamenting
glass. a Jet of air of from one-tenth to one
pound pressure is preferred. With low
pressure. soft and delicate substances,
such as paper designs, lace and leaves.
may be used.
With steam-jet using two horsepower
of steam at seventy pounds pressure. and
one pint of sand, two cubic inches of gran
lite. four cubic inches of marble, or ten GU
bic inches of sandstone NAV be cut away
per minute. Flat or curved substances
may be alike acted on by this process, the
blast being always perpendicular to the
exposed surface. This process may also
be used for cutting grooves in quarries
and tunnels, for dressing stone, for cut
ting stone in lathe. for cleaning scale from
metals. for granting photographic zinc. and
for producing pictures, any variety OF de-
sign. and even the most delicate line en-
cravings.
The Popular Science Monthly says that
at a recent meeting of the British Micro
scopical Society. Mr.. Wenham exhibited a
piece of glass ground by this process,
which. under the microscope, presented a
very different appearance from common
ground glass. IL Is found that the glass or
other material acted upon Is not ground
away at all, but broken up by a battering
action similar to that Of leadcn bullets
against a block of granite. Hence 1t Is
that, although by the usual grinding pro-
cess, ordinary sea-sand can make no inn
preston on corundum. blast with pres
sure of three hundred pounds to the
square inch will perforate II In a short
time. Even the diamond may thus be
speedily worn away.
A polished glass surface, exposed for an
instant to the sand-blast, shows an az
gregation of points of impact. from which
scales of fractured glass have broken away
in an irregular radial direction. Ii APP
pears as II pellet of glass had been driv-
en- in by the collision of the sind. and the
wedge-likc action thus set up had driven
away the surrounding glass. All these
spots. when tested BY the polariscope,
show colored halos. proving that the sur
face is under strain. aud ready 10 yield "a
further fracture. The action. therefore, il
due not so much To the hardness Of the
striking particles rs to the velocity Of inn
pact. This Is sufficient to destroy the co
hesion of the material operated upon
The external layer Is carried against the
under stratum, and the material - crushed
and disintegrated by portion of It's owl
body.