The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1885-11-07
The Manufacture Of Plate Glass.
From tie Scientific american.


glass. One is located at New Albany, Ind,
one at Jefferson, Ind, one at Crystal City,
Mo, and the one described in this paper at
Creighton, Pa Plate glass is made by
casting and afterward polishing. The pots
in which the materials are melted and the
glass made are of great capacity, and re-
quire heavy and convenient machinery for
pouring. The casting is done on heavy
metal slab, larger than the largest sheet of
glass produced, and this slab rests on a car
which runs on tracks leading from the
melting furnaces to the annealing rooms
4 large iron roller, running on strips Of
iron at each side of this table, presses the
molten glass into a sheet as the workmen
pour it in front of the moving roller. The
thickness Of these strips of iron, on which
the roller rolls, determines the thickness Of
the plate of glass. While the glass is yet
hot it is thrust into an annealing oven,
where the temperature is gradually lowered
for several days until it is cold. The sur
face of the glass is now very rough and
uneven, and, though it is translucent, it is
not transparent. In this form it is used
for skylights, and for places where strength
and light are required without Transparent
cy. After the plate comes from the oven,
it is firmly fxedupon large rotating table
or platform, which revolves quite rapidly.
Over its surface two disks rotate and re-
yolve in such manner that they cover the
entire surface Of the glass at each rotation
Of the platform The attending workmen
throw common river sand upon the surface
of the glass, which is kept constantly wet
by small streams of water. This process
grinds off the rough exterior, after which
it is ground with emery, on machines of
similar construction. Beginning with coarse
emery, they gradually change the grade
until the finest powder is used to finish the
grinding. After the grinding is complete,
the surface is polished by rouge on ma
chimes constructed on the very best prin-
ciplcs for making perfect surfaces.
From the time the glass leaves the an
healing ovens until it is perfectly polished,
Tire wCrkmen examine it, from time to time,
for any flaws, bubbles, or defects, as grains
Of annulled sand. Only those large plates
which are free from defects of any kind
arc polished entire When flaw is dis
covered in large plate of glass, the plate
is cut into smaller ones of marketable di-
mansions. This branch of the trade re-
quires trained and skillful workmen who
have good judgment After the glass has
been properly polished and cut into re-
quired sizes, it is boxed ready for ship
ment. The manufacturers insure large
plates of glass, for which the buyer has to
pay This makes the purchase without
risk 10 the purchaser.
The works of the aPittsburg Plate
Glass Company" are located at Creighton,
about twenty miles above Pittsburg on the
west bank of the Allegheny River. There
are about eight or nine acres covered with
baildings, along side track of the West
Pennsylvania r. R., which are used for
the various purposes of manufacture, store
houses, furnaces, casting houses, stables,
offices, etc. One of the buildings, $50 /
feet long by 100 feet wide, is the casting
house 1t contains sixty ovens for anneal-
ing glass and two furnaces for melting
Each annealing furnace is over forty feet
long by nearly twenty in width. Each
melting furnace contains fourteen pots
The apparatus for casting consists of two
iron tables, seven inches thick and 8 feet |
long by IA feet wide; two iron rollers
thirty inches in diameter and Is feet long.
These tables arc on carriages which move
on track which reaches every furnace,
and is nearly one mile in aggregate length. !
There are also cranes, tongs, ladies, and
pulleys, which are most conveniently ar
ranged for rapid work. The first build
ing in which the plates of glass meet ma
chinery driven by steam is the grinding
house. This building is over 200 feet
long by so feet wide. There are eight ro-
tary grinding machines in this building.
Each machine requires forty horse power,
and all are driven by two double vertical
engines There is second grinding de-
partment, which contains two machines of
the latest French pattern. These machines
require one hundred and twenty horse
power, and do most excellent work rapidly. I
The glass is smoothed in a building
about loo feet by 200 feet. In this house
there are twenty smoothing machines, which
require the power of two engines of forty
horse power each to drive them. Next in
order is the polishing house. This is the
same in size as the smoothing house. There
are sixteen polishing machines, each eleven
by twenty feet, driven by two engines Of
over eight hundred horse power.
The company make their own melting
pots, and in this building steam engine
of thirty horse power grinds and mixes
clay There is a department where plate
glass mirrors are made, and this requires
the help of large engine to drive machine
ry for beveling the edges of plates Of glass.
This department has proved perfect sue
cess, and many beautiful mirrors are made
here, ranging in price from 81 to $500
There is also large foundry and ma
chine shop, where all the machines used in
the "plant'' are made or repaired; and a
shop for making boxes, where an engine
runs saws and planners. The company en-
ploys three hundred and forty-fye men,
forty-fve boys, and fifteen women and girls.
They have lately built steam dredge for
collecting sand from the bottom of the river
for grinding glass; Three million bushels
of sand are required each year for grinding
purposes alone. The white sand from
which the glass is made is shipped from
McVeytown, Pa. The amount of glass
cast each month is $4,000 square feet.
About per cent of this is used for sky
lights; the rest is polished, making an out
put Of 10000 feet of polished glass per
month, after allowance is made for cutting
and breakage.
The novel feature about these vast works
where engines aggregating nearly 1900
horse power are fed by steam, and sixty
annealing ovens and two melting furnaces
require fuels the entire absence Of coal
and the use Of natural gas in its stead.
The company owns two gas wells, which
are about 1850 feet deep, and they are
now running their entire works with lit
tie over one-half the production of one
we'll The pressure at the well is 260
pounds per square inch. This pressure is
reduced at the well to 120 pounds and as
the line works wide open, the pressure in
the regulator, at the works, is lowered to
40 pounds. The pressure is still further
reduced before it enters the furnaces. The
pipe which conveys the gas to the works is