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GYPSUM REDUCTION AND CALCINING PLANT.

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~-= 00 Q 00 ==

During the last five years the Gypsum Industries
have advanced in remarkable strides, The increasing
demand for Fireproof building construction materials has
opened a large field to Gypsum Industries,

The demand for larger capacities and high grade
materials has placed the problem in the hands of modern
Engineeringe

To show the nature and processes involved in
the Engineering problems, the writer will describe and
explain the Reduction and Calcining Plant designed and
erected by him for one of the leading Manufacturers of
Gypsum Products in the United States,

The reason for taking only the Reduction and
Calcining Plant is that this portion of the whole Plant
produces Calcined Plaster, or Plaster of Paris, in its

finished state; and Plaster of Paris is the basis of

all Gypsum Products,
Ze

PROCESS OF MANUFACTURE,

Plaster of Paris is manufactured from Gypsum
Rock, which is Hydrous Sulphate of Lime (Ca SO, 2H390),
a soft Rock, generally found with few impurities and

in erystalline structure,

The average pure Rock Analysis is as follows:

Silica (SI 09) 0.50 %
Alumina (ALg 03) Trace
Iron Oxide (Fe 03) Trace
Lime Carbonate (Ca C03) 1.00 4%
Magnesium Carbonate (Mg C03) Trace
Lime Sulphate (Ca SO,) 78,50 %
Water (Hg 0) 20.90 %

Gypsum Rock is generally found in horizontal
layer formation or pitched veins, probably the result of
horizontal formation having been undermined by water
channels and the Rock pitched down. The Rock is generally
so near the surface that it can be quarried or mined in
shallow mines,

Gypsum Rock, being soft, is easily broken, and
even with low-pressure Explosives used in blasting nearly
@ll the Rock is reduced to man size and under; it is
then reduced, by Crushers, to 1" Ring and under,

As Gypsum Rock carries a great deal of free

water, which hinders the process of fine reduction, it is
Se

advisable to drive off some of the free water in some
sort of Dryer,

The Rock is then reduced to a fine uniform
powder ranging from 85% to 95% through a standard 100
mesh screen,

The finely pulverized Rock is now ready to be
Calcined,

Calcination of ground Gypsum Rock is the pro-
cess of driving off part of the water of crystallization,
which is about 20 per cent by weight, This is done in
a Calcining Kettle by applying heat to the material and
agitating it at the same time, thereby keeping the
material uniform and assisting in freeing the water vapor
from the material,

As the heat is constantly applied, the tempera-
ture rises to 250° Fahrenheit, causing the material to
roil and boil furiously; at the same time, large
volumes of water vapor escape from the surface, When
the severe rolling and boiling begins to decrease, the
temperature again rises until from 320° to 325° Fahren-
heit is reached; then the material seems to clear and
shows practically no signs of boiling, the surface level
of the material having dropped a noticeable amount, This
stage is called the "First Settle", and is used by some
manufacturers as a finished Plaster of Paris product,

If the process is carried beyond this stage,,
the material will again roll and boil almost as severly

as at first until 385° Fahrenheit is readéhed; then the
4.

material takes on the second settle, which is more pro-
nounced than the first. This material settles ina
lifeless mass and offers severe resistance to agitation.
This stage is known as the "Second Settle" product of
Calcined Plaster and is the highest point carried by
commercial manufacturers of Plaster of Paris.

Plaster of Paris made at the "First Settle"
shows a half hydrate (Ca S04 1/2 Ho 0), or contains
Lime Sulphate (Ca S04) 93.8% and Water (Ho 0) 6.2%.

Plaster of Paris made at the "Second Settle"
shows about 2% less Water (Ho 0) than the "First Settle"
product,

A clean setting-up Test made of "First Settle"
product and 80% of Water by weight shows an initial set
of 16 to 20 minutes; the same Test of "Second Settle"
product shows an initial set of 24 to 30 minutes,

The “First Settle”® product works creamier under
the trowel and the Second Settle" ‘product produces the
greater tensile strength.

Each material has its particular advantages for
the different classes of uses for Plaster of Paris.

Pulverized Rock, or Land Plaster, is often sold,

with no further preparation, as a finished product.
DESIGN OF GYPSUM REDUCTION AND CALCINING PLANT

The determining features of the Plant were as

follows;
Capacity of 1000 tons of Plaster of Paris in 24 hours,
cr double shift.
Individual and independent departments,
Plant to be twin grouping of units so that one-half
of the plant could be run as a complete Plant,
High grade product at minimum labor, attention, and
costs.

An attempt was made to re-design the old existe
ing Plant to suit the new requirements but was abandoned
on account of the large capacity desired, the old Plant
building being too small to accommodate the new equipment
in any acceptable system, and also because of the fact
that the old Plant would be thrown ouf of commission while
the new equipment was being installed,

The accepted location was a narrow strip of land
running parallel with the old Plant and between it and
another building. This available site was just wide
enough to permit a sufficiently wide Plant with a Railroad
Siding on each side, and conveniently located that the old
Plant could be used to the greatest advantage as a Warehouse

and Shipping Room,
A 12" x 12" Testing Ram was placed on the site

of the heaviest Mill loading at a depth of five (5) feet,
and loaded with four (4) tons cf Pig Iron, This Ram
settled 3/8" during the first day but showed no further
settlement during the next five weeks,
The Ram rested on a 5-fcot layer of hard stiff

Clay containirg some sand, Under this layer is a water
bearing strata of coarse Gravel and sand, As the bulk
of the foundations rested upon the stiff clay strata and
the remainder went through to the water bearing gravel,
the following soil bearing pressures were decided upon as
safe values;

Bearing on Clay strata - 24 tons per sq. ft.

Bearing on Sand and Gravel strata = 1 ton per sq. ft.

As the Plant was desired to ve absolutely

fireproof and it was essential to have a structure rigid
enough to damven out the vibration caused by the moving
machinery, the following materials were selected:

Concrete foundations.

Structural Steel for the frame

Terra Cotta Hollow Tile Curtain Walls,

Slag Concrete floors,

Plaster composition roof,

The inclined Elevator housing and the structure
above the cylindrical Rock Bin were covered with copper
pearing steel Corrugated Siding and Roof, This was done
to permis’. of light steel etructure,

The Windows are cf ribbed wire glass set in

steel frames, The glass are secured in the frames with
small metal glazing angles,

The Window Lintels and Sills are of reinforced
lees

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8.

(2) #11 Galvanized Steel twisted wires, spaced 2" apart
for 6-foot spans. At tre center of the span the wires
ave held neat the bottom of the slab by placing a 5/8"
round bar iron oger them and across the span; this also
gives it lateral strength and rigidity. The tension
wires are continuous over the beams and are secured to
the legs of the last roof beams by specially made hooks,

The floors in a Plant of this character often
receive severe oading, resulting from the moving of heavy
machinery and the discharge of large quantities of materials
on to the floors in case of breakdown or plug:-ed machinery,
In anticipation of such loading, all floors were designed
to support a load of 200# per aquare foot floor area and
are constructed of 3/8" square twisted reinforcing bars
imbedded in 5" thick cinder concrete = 1:32:34 mixture,

The reinforcing bars are placed upon the floor
beams, spaced 8" apart for spans up to 6 feet long, and
6" apart for spans fron 6 to & feet long. In each case
cross ties are placed 2 feet apart, consisting of a 3/8"
rod securely tied to each reinforcing rod,

Tne vottom of the floor slab is placed 3/4"

lower than the tops of tne floor beams, Coping angles

are used at all edges and openings,

Mostly all. the machines used in reducing and
dryinz the Rock produce severe vibrations and shocks, It
has been the object of the writer, as you will note by

the sections, to transfer tnese vibrations to the founda~
9.

tions and there absorb tnem by massive monolithic concrete
bases, Vibrations set up by lesser esurces are taken
care of by the structural steel bracing.

These vibrations not only weaken the structure,
but have a detrimental effect on the elevated Storage
Bins, packing the finer materials in between the larger
particles, and as a result the material will not flow
readily from the Bin; in tne case of Pulverized Rock,
or Land Plaster, it will become so hard as to necessitate
the use of a9 more severe tool than a shovel to dislocate
the material,

The Crushed Rock Bin was made of 1/4" steel
plate, cylindrical in shape, and placed on end overa
conical concrete base which takes the whole load. This
Bin stores Crushed Rock coming from the Crushing Plant
and has a capacity of 400 tons.

This type of Bin was selected for the purpose
because all the filling is done from one point and the
discharge is from two openinga in the cdncrete base, very
close together. A cylindrical Bin of this character is
@ low cost container for conditions at hand, It also
has the added advantage in thit practically all of its
contents are available without any manual assistance. This
Bin also serves as the superstructure for the Conveyor
Head framing and housing above the Bin.

The concrete base is reinforced and was cast a

monolithic structure, As the bearing soil showed a large

amount of soft wet clay, a concrete pad was placed under

the base of the Bin, 2 ft. thtck, and reinforced with old
10,

light railroad rails. The bearing loading was taken as
14 tone per square foot,

The Dry Rock Bins, of which there are two groups
divided into three compartments each, have a capacity of
100 tons per compartment or a total capacity of 600 tons;
they are also of 1/4" steel plate.

The suspension type of Bin was selected because
of the large amount of available material contained by then,
the clear, unobstructed head room underneath them, and the
economical design for an elevated bin.

These Bins are not a true catenary curve, the
side sheets running straight as they near tne side girder;
in tnis manner the side sheets act as a deep plate girder
and assist in carrying tne suspended load, It would be
rather hard to determine just how much tnis girder action
is; however, in these cases the writer assumed it to be
15% of the total load, A small plate girder carries the
remaining load,

The Bin ends and division walls were reinforced
by 7" Ie Beams runnins horizontally and riveted to the
1/4" Steel diffision plates, This construction carried
all the stresses to the 1/4" Steel side sheets of the
Bin. A small plate girder was placed between the columns
to take the compression due to the bin load at the bin
ends and division plates.

The Land Plaster Bins, of which there are two
groups, are each divided into two Bins, making four (4)

100 ton capacity separate bins. These Bins are similar

to the Dry Rock Bins in design and construction.
ll.

Poth the Dry Rock and the Land Plaster Bins
have 1/8" steel tops placed on 6" I beams, to prevent
dusting and eliminate danger of falling into the Bins,

The following weights were used in computing
and designing the 3ins;:

Damp Crushed Rocke- 35 1lvs. per Cu. ft,
ory Crusned Rock-- 90 " " " "
Land Plaster-- 80 " " " «

Plaster of Paris-- 70 “ “ a“ “
BUILDING WALLS _

The walls of the building carry no loads:or
stresses excepting those due to the weight of the wall

tself,

Owing to the fact that the outside walls are
simply curtain walls, a light weight substantial material
was desired, Six cell, 8", unglazed, Hollow Terra
Cotta Building Tile was used,

The Tile was laid so that the cell partition
stood in a vertical position, This was advisable as the
walls ran from 30 feet to 55 feet high.

As the structural steel columns were of differe
ent sizes and many columns reduced in sections at their
upper end, it was necessary to place the walls at differ-
ent distances from the column faces, this distance varying
from 1 to 2$", The working face of the wall was kept at
equal distance from the column centers,

The method of securing the wall to the Steel was
very important, the pressures to ve taken care of being

Shat of wind from the outside and inside,
The vibration of tne building Was not taken into

consideration as the structural steel was designed to

absorb all vibration or transfer it to the building founda-~

tions,

The wind pressure from the outside was taken as

25 los, per square foot exposed area, This value was
156

considered sufficient ag the exposure was broken by
adjacent buildings.

The inside pressures on the walls, which may
develope through open doors and windows, was taken as
15 lbs, per square foot wall surface,

After makint some crude tests, the following
metnod was selected to fasten the walls to the structural
steel columns, which were 16 to 18 feet apart, no other
piaces of support being taken into consideration; however,
additional fastenings were put in where conditions were
favorable to do so,

The wall ties were made in two groups, viz: =
Tension Ties were designed to take pressures developed
from the inside and Compression Ties to take pressures
developed from the outside, All ties were made of 7/16"
round steel and were imbedded in the mortar joint
between the Tile.

The Tension Ties were made of two kinds, to suit
either side of an I section column, When the flat side
of the cadlumn was against the wall, two ties were used
at a joint in the tile and made in the following manner:

A piece of round steel was bent over itself at
the center and this double section bent into a hook with
a 2" leg, which was hooked over the leg of the column and
the two ends bent so that they lay in the center of the
Tile wall, forming a 4" long leg on each end pointing in

opposite directions,

When the legs of the columns faced the wall,

two ties were used and made in the following manner,
14,

A hock was forged in the end of a Steel rod so
that it hooked over the leg on opposite side of the
column; on the other end of the rod was welded a bar 8"
long, Which in turn was imbedded in the mortar joint,

The two kinds of ties described suited all the
requirements for tension ties,

The Compression Ties were made from one general
design and in the following manner:

The bar steel was bent in the form of the
letter "U" excepting that the ends were bent at right
angles and in opposite direction to forma 4" leg, In
position the bottom portion of the “U" bears against the
column and the two 4" legs are imbedded: in the wall
joint, When the flat side of the column is against the
wall, one tie is sufficient per joint, but if the legs

are facing the wall, two ties are required ~» one against

each leg,
A slab of tile was placed between the wall and

the cblumnns and resting on the Tension Ties, thereby

making them also an effective Compression Tie as well,

Every two (2) feet, for the first 30 feet in
height, there was a tie joint, alternating Tension and
Compression, attachirg the wall to the columns, From
30 feet up the spacing was reduced to one (1) foot,

Where floors existed, they wefe extended out to

meet the wall, which also made a good Compression Tie,
15.

ELECTRIC POWFR AND LIGHTING,

Electric energy is furnished to the Plant at
15,200 velts and is transformed to 440 volts, 3-phase,

66 cycles in a Transformer House irdependent of the
Plant buildings,

The Switchboard Room is a part of the Trans-
former House and the Switchboard has a panel for each
Power feeder, On these panels are placed the necessary
instruments and an automatic Oil Circuit Breaker, On the
face of each panel are placed current Transformer Testing
Clips and also potential terminals; these are for test=
ine the power of each circuit with very little trouble,

Fach Department in the Plant is supplied with
an independent feeder circuit. These circuits are run
overhead and at the outside of the buildings, on steel
brackets, to their centers of distribution; thence to
the individual motors,

Fach Motor is supplied with a sateel frame, upon
which asemounted the Starting Compensators, together
with an enclosed fused Knife-blade line Switch and running
Fuses enclosed in separate steel cases, This arrangement
permitted the Power to be thrown off at will from the
Starting devices, thereby allowing adjustments and repairs
to be made with safety.

In case of examining, ehtering or repairing

Power-driven Machines, where life would be in danger,
16,

should the Power be thrown on it is essential that the
Motor line Switch be opened and the steel case, enclosing
tne Switch, closed and locked, if necessary, thereby
eliminating the possibility of accident on that score,
The line Switches are high mounted that the steel case
may be clesed with Switch in full open position,

All Motor Startirg Compensators have no=voltage
release coils, which trip the Starting Compensators to
off position upon failure of the voltage, Push buttons
are placed in circuit with the no~voltage release coils,
in convenient locations, that the Motor can be released
from different parts of the Department, if desired. It
js alwavs necessary to use the Starting Compensator to
start the Motor, This is desirable in order that an

inspection of the starting and running condit#on of the

Motor can be easily made,
17.

GUARDING

All Stairways and Floor openings are railed
with Standard 14" Pipe Railings, 42" high, and with
2" x 6" toe boards,

All Belts, Pulleys, Shafting, etc, under
seven (7) feet from the floor are carefully guarded with
Steel guards made of #12 gauge sheet Steel and 14*
angles, The sheet Steel was perforated only in locas
tions where it was desirable and this method of perfora~
tion proved to be more economical and stronger than
using the all-perforated plates,

All necessary permanent steel Ladders and
grating runways were installed for safety in the oiling

and inspection of machinery.

As Grease is used throughout for the lubrica-
tion of Power transmission shafting, the dangerous or
inaccessible points of lubrication were piped away to

safe locations, thereby simplifying the Guarding

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18,

DESCRIPTICN OF UNITS IN PLANT,
#“-/= 00 0 00 =.=
ROCK CRUSHING DEPARTMENT,

The capacity of tne Reduction and Calcining
Plant is 1000 Tons of Calcined Plaster per day of tqo (2)
10-hour shifts, Gypsum Rock, in process of manufac-
ture to Calcined Plaster, suffers a reduction of about
20 per cent by weight; therefore, 1250 tons cf Gypsum
Rock will be required to produce the 1C00 tons of
Calcined Plaster,

The crude Gypsum Rock in the bulk storage at
the Plant is of 6" rine size and under, and it was
desired to reduce it to 1" ring size in one operation.

It was &lso desired to have the Crushing Plant
large enough to supply the necessary amount of crushed
rock in a single shift of 10 hours, This required a
capacity of 125 tons per Wour continuous service,

A large hammer pulverizing mill was selected
to make the reduction, with a capacity of 150 tons per
hour when the material is supplied to the Mill ata
uniform rate, As this mill required a feeder, the
following arrangement was made

The Rock comes from the bulk storage in 3-ton

side-dump Cars and is discharged in a hoppered bin placed

over a 30" high eide Pan Conveyor with 12" Pans and
19,

running at the rate of 50 feet per minute, This Pan
Conveyor acting as its own feeder draws the material from
the hopper and discnarges it into the hammer mill, The
hammer mill reduces the rock to 1® size and under, dis»
charging the material into a 20" inclined continuous
bucket belt Elevator running at 150 feet per minute, 674
feet centers, and inclined at an angle with the horizontal
of 63 degrees, The inclined belt Elevator discharges
directly into the 400 ton circular Rock Bin, which in

turn feeds the Dryers,

A 195 H.P. vback=-geared Motor runs the Pan Céne
veyor and also a car dump hoist,

A 125 H.P. External Resistance type Motor runs
the hammer mill at a speed of 700 R.P.M. The belt
transmitting the Power is a 20" double leather belt
running at a speed of 4375 feet per minute,

A 20 H.P. back-geared Motor drives the inclined
belt Elevator,

These Motors and those used in the Shed for
loading bulk rock are connected to one feeder circuit
coming from the Transformer House and terminating in
this Department, All the Motors have push button stops,
centralized at a convenient location for the operator,

The chutes to and from the hammer mill have
pressure operated hinged gates in them to avoid dusting
due to wind produced by the revolving hammers, These
pressure opened hinged gates are so designed that the
gate, which is hinged at the upper end in the chute, is

normally closed due to the angle and weight of the gate
206

iteelf, A low head of material coming between the chute
bottom and the gate will force the gate open and allow
the material to flow, but retains a sufficient head of:
material to counteract the closing properties of the
gate, The material thus retained makes an effective
seal, especially on the finer materials,

This Crushing Department is designed to
operate witn one attendant and it will also be his duty

to assist in discharging the rock cars,

wih YTV 3 OT
auld iP: + Pure eane:

In the process of drying, the Rock is taken
from tne Rock Storage Bin, “passed through the Drver,
wriich removes tne free water, and is discharzed into the
Ory Rock Bins for the Pulverizers,

The capacity of the Dryinz department was based
upon two (2) 1lOshour Shifts, as one attendant can operate

ne devartment to full sapacity and smaller units and
bin capacities could be used,

Two drvyinz units, each capable of drying 35
tons of Rock per hour, furnish ample capacity and are in
keeving with tne idea of a twin Mill. These Dryers were

designed complete by the writer &o meet the requirements

and are as followe:

heat rotary type, 490 feet

ce

Tie Dryers are direc

lone with en ineide diameter of 6 feet and supported on

two rolled steel tires 82" wide,

4

Le Dryer is driven by a three-set train of
Gears to a large girth zear , with 2" face, placed
around the Dryer shell, The pinion driving this girth
sear is offset two (2) feet fron the peependisular

center line of Orver and on the rising or liftins side,

The cupporting steel tires cum over sets of
two stationary Seunion rollers, Tnese rollers run in
water to keep their surfaces cleun, bind theust rollers

are placed agains one of the tires to nrevent end movee
ment of Dryes.

The interior of the Dryer has a series of
piteniny and lifting flights so arranged thit the Dryer,
wren set perfectly horizontal, will. feed the material

tons of rock at

on

throuch rapidly and will not nold over
one time, when operating at a capacity of 35 tons per
nour per unit, Tnese Lliftine Pliehts are so shared
that they will carry the material to the top of the
Dryer and discharge it throueh the hot gases about ten
times in zoing tne length of the Dryer,

The furnace for susplying not gases to the
Dryer is leeat ocd at tie discharwe end of the Dryer, This

urnace has a large chamber,back of the briisze wail, for

ry

he purpose of settling the ash and foreigh matter coming

14 ale

from the fuel, as it is desired to nave wne rock as

ble and the Dryer is to aid in freeing the

p-t-

clean as poss
rock of forei
Tne sloping furnace arch tos, rising from the

furnace front towards the dryer turvat connection, Was

lesioned to insure verfect combustion before tne gaee3
wa Py
rN

pagsed into the Dryer proper, Stationary Grates are
used with 30 square feet Grate area, A clean grade of
farnace coke is used asa uel, An auxiliary stack

connects with the furnace through the floor and just
vack of tne bridze wall, which is used in starting fires
and t9 cactry away the cases arisins from a heavy fire
should it be necessary to stop the Dryer,

The rock to be dried enters the rotary Oryer
ay the end oppraite the furnace and travels against the
flow of hot gases, discharging at the furnace end.

A 30” diameter Dryer neck connecticn csannects
the feed end of the Dryer to a 70" Exhaust Fan, which in
hfurn discharges into a dustesettlinge chamber, This
Dryer neck also contains tne feed chute to the Dryer,
The Exnaust Fan preduces the necessary drauvent for the

furnace and carries away the water vapor driven off from

tne Lock, As the finer particles of the reck are
osrried by the air, it is advisable to keep the aix

velocity not to exseed 499 Lineal feet par minute; hence

a isreze exhaustec was selected and mins at slow sreecd,
The Dryer neck makes a very snarp anele after

leavinz the Dryer and rises nearly vertical *t9 the

exnauster, which is located abcve it. This was lone 7a

as atr ab thant low velocity will

: . + +
depesit material on the flatter runs; consequently, the

The Exhaust Fan discharges, through a short
connection with a sloping bottom, to the dryer dust-settling

chamber,
Se

the dustesettliing chamber was located idrectly

y

over the vrves to save as much floor space as passidle
and also to keep the walls cf the chamber warm, This

Q.- 4- +e +4
r x om 7 ” a
AO SLOT ak 14

v2

cnamver should be kept warm enough to keep
the water vapor fron condensing, as it is hishly desirable

t 42, Tae Gust whamber

(3

reclaim the @ust ina dry s
has a cross-section of 159 square feet ani is 54 feet lone,

with the gas entrance at one end and the discharse at the

Other end, in the roof, There are no obstructions or
baffles of any kind in the chamber, The settling

capacity of the chamber is based on the gentile flow of
expanded air pressure, The hoppered bottom with steep
sides anda 9" screw conveyor in the bottom,running its

length, carries the dry dust away as fast as it settles,

cr

Bach Dryer unit has its ow furnace, exhauster

and dust-settling chartber,

The rock is delivered to the Dryers frou the
circular rock bin by a reciprocating feeder, placed uncer
the bin bage, operating at 830 strokes per minute with a

stroke fron 3" to 6" long, to suit the feed required,

de

This feeder delivers to an 13" Belt Conveyor runnin

feet per minute ani discharges ts a 19% x 6" bucket

rey

+
cj
©)

elevators thence to the Dryer, Zach Dryer has an

niependent feed system as above,
After the rock is dried it is discharged from
each Dryer into a separate 14" x 7" bucket Hievator «

ore for each Dryer = elevated 35 feet, and both dis-

— -

charged on an 18" Belt Conveyor running at 399 feet per
‘alnute, 36 feet centers and with a 24" magnetic heal
Pulley, rils Bett Conveyor discharges over the dry
rock vins,

A 24" Belt Shuttle Convevor is used to dis-«
ibuate fne rock over the dry rock bins, There are
six (5) dry rock bins, made in tWo groups of three bins,

$+ »

in nas a capacity cf 1090 tors or a total capacit,

td
()
Cy
oy
Oo
~

of 609 tons.
Toe rotary magnetic head Pulley is for remov~
ing tne stray iron that may become mixed with the roek,
The settlings fron the dryer dust chambers are
conveyed by 9" screw convevors ts a 14" x 7 pucket
elevitor and elevated 43 feet to a 12" screw conveyor,
w:iicn discnarges into the conveying systen over tne

@nd Plaster, cr can be spouted directiy into one of the

t-4

dry rock bins. Tne dust settlings from eacn Dryer are

about three (3) per cent of the material delivered to

The odject iff keeping the dryer dust room

settlings and the dry rock from tre dryer discharge
eparate is as Tollows;

The trade demands two grades of Plaster of
Paris, which can be called First and Second Grades,

First grade Flaster of Faris must be absolutely
pure clean and » uniformiy white in color.

Second grade Plaster uf Faris may contain a
small percentage of foreign matter, which may discolor

the oroduct slightly but not effect the strength and

setting properties,
To meet the demand of the Wirst prade preiuct,

e in the process

wo
pte

advantage was taken of the sevaration m:

RS

of drying,
The rock, in the process of drving, is tumbled
aocoub in the rotary Dryer until the ertire surfaces of

he Gypsum have been cleanse1 cof fsrelern matter by the

avrasive action of the mass cf rock, The fToreien mate
ter, tometner with other Llisthter particles, veccmes very

dry from beine in contact witn the hot gases anid is
carried oy the air currents throurh the Sxhaust Yan and
deposited into the duatesettling chamber, The material
discharved by the Dryer is therefore clean rock of
sufficient size and weizht not to te effected ov the air
velocity within tne oOryer,

trust »vroduces a maximum amount of

a

é

This m

br

material for First erade products and all that is necess-
ary is to keep the two materials separate in the vrera~
tions to follow.

The bulx of the foreizn matter to be contended
with is.in the form of a clayei substince on the surface
of the rock and is verg satisfactorily removed by the
above method,

The dryer dust settlings, ordinarily, are cf
about 85 per cent through 190 mesh product and can be
used as a Second grade material with no% further reduction,
and as sucn can be conveyed directly to the Land Plaster
bins.

Fach Dryer is a unit in itself and can be run

independently or together, as desired. The Dryer feed

oD. Yotor and feeds two (2)

Ww

ends 2re run by one (1) £5 2

_
Dryers. Each Dryer i3 driven uy a f5 U.P, Mctor, The
Dryer discharge ends are run ty one (1) 25 HeP. Motor and
take the material from two Dryers, celiverins it to the
different cins,

The Dryer department is in charz2 of one

T)

<
o
3
ao
ce
CC
r$
eo

The cirenlar rock bin feeling the Dryers is
provided witn a safety ladder and man weil cn one side,
and also has safety belt strap rines made of 1" pipe
placed on inside perimeter of bin at intervals of 5 feet
apart, starting from bottom up. Tnese safety precautions
were made so that should it be necessary for aman to
enter the bin to dislocate the material or do other work,

a safety belt should be worn and attached to the rings,

thereby preventing sliding into a crater and the sossi-

bility of vbetne huried unter o slide,

 

The fineness and uniformity of the product
obtained by pulverizing the dry rock is an essential
fenture of a superior grade product

Gypsum rock is more or less of the selenoid
crystal formation, and as such reduces very easily to a
coarse product, but to reduce it further that 92 percent
will pass 100 mesch standard screen represents a great
deal of work and is the protlem to be met,

In the writer's exneriences the smooth pressure

rolling vrocess nas proven very successful as a Gypsum
27,

palverizins medium, when the contact areas are so placed
that the material cannot lay or collect cn them, with
this process itt is essential trnrt the rock shalj. be dry,

To produce the desired fineness air separation
seems the most capable, as there is very little to cet
out of order and it is practically impogsible tc geta
coarser product than the air veldcity is designed to
CATTY. The power cost of air spyaration is very hizh
in comparison with a vibrating cr mechanical screen,

The pulverizing machines selected embodied
voth the roll process and the aftr separation system in
one complete unit. The capacity of eacti unit is from
seven to eight tons per hour when reducing 14" ring
material to 92 per cent through 190 mesh standard screen,

The pulverizing rolis have a 75 H.P. Wotor
direct connectea throum a flexivle coupling, and the
saration system has a 49 HF. Motor direct connected
to a 42" fan, through a flexible coupling.

To secure the desired capacity, this department
was tzken on the dceuble shift basis, with six (6) pulver-

izing units to furnish the capacity required,

xf

1 pulvericine unit has a separate rock bin

Lac

+

with a capacity of 170 tons dry rock, Tre rock is fed
t@ the mill through a telescoping chute; the feed is
controlled by a roll feeder on the mill itself, The
air separation system takes ‘he pulverized produc* from
the mill and delivers it to the Zand Plaster bin.

Tie air separstion system is a closed air cir

wT ne . hv
culating system produced hy a large Exhaust Wan, and with
the roll mili in the air eirenit, The sgenvarating chame

‘ )

ot
-)
“ty

ber of the system is madre 2 p fF the mill itsel?, The
air passes up thrauen the yulverizivce reston of tre mill

and carries with it such particles 2s ave reduced enough

to flot. in the giv velcrtty rrotured in the separation
chamber. The separation chamber is above the mill
proper and forms the top heusing of the same, From the

separator, the air, with the reduced material, passes

"7 h the exhansgter to the top of the tuilding and

‘3

Os

Gischarazes into 2 Pefaot Cyclone tyne Collector located

~>

over the Land «slaster hine, The bulk of the material

q

arried wy the air is dischargei in passing trrougn this

Collector and is delivered, throveh a material seal
pressure cperatei hinged gate to two (2) 12" distributing
screw conveyors over the tand Plaster bin, The air,

after nassing throusmh the Collector, returns *othe

mivecizine mill to be used over ac2in

h~
e

As it is practically impuasthle to keen a1]

yarts of the system air-tight, the excess air cettine

into tre system jis allowed to escape through an 8" vent
pipe riaeed at the hizhest point in the return atr cire-

cult and piped to a tubular dust collector, where the
material carried by the air is retrined andthe air

allowed to escape, A separate elevating and conveying

Special

on

system is installed tc deliver ttiis material to a
bin in the warehouses, as the product is extremely fine

and as such is marketable 43 a spesial product, The

c.

-yvever, is Less one-fourth (1/4) of cne per

capacity,

cent of the output of the pulverizing units
The fibular Collectors discharee ints a 95"

ies the

r

screw ccnvevor running undernerith them and car
material to a 19% x €" bucket elevater, elevatine 20

feet and discharging into a 9" screw conveyor running to

Tie air system not only sdparates the product

Dut elevates the material as well and discharges it into

bifurcated snout, or directiy into the bin below, as
desired,

Owing to tne fact that two classes of materials
are to be made and that pulverized rock, or Land Plaster,
is often disposed of with no further preparation, a system
of 12" screw convéyors was placed over the Land -laster
pins whereby two screw convevors placed side by side and
travelling in opposite directions, with connections to
receive material from each pulverizer discharge and to
discharge into any of the Land Plaster bins; also into
a 12" screw conveyor running to the Land Plaster bin in
the Warehouse, This arrangement makes it possible to
handle and separate the material, as desired,

The Land Plaster bins are placed in two groups
of two bins each, Three pulverizer: collectors are
arranged over eacn group of bins. The capacity of each

bin is 199 tons, or a total Land Plaster capacity of 450

CONS.

cr
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The pulverizing departiman

by two men = one to each three unites,
30 6

CALCINING DEPARTMENT _

In the process of calcination, or dehydration
of pulverized rock, or Land Plaster, the larger part of
combiied water is driven off,

To produce a superior grade of Plaster of
Faris it is essential that the dehydrating process be
carried to the same dezree at the completion of the
operation and that the product ve absolutely unifcrm
throughout,

The writer has studied the action of materials
and fuel gases on other designs, and by havine carefully
watcned for the first signs of weaknesses and their
developments, gathered a great deal of ir ‘*ormation. In
the design of this new Calcinging Kettle, the writer
attempted to eliminate all former troubles and
weaknesses, ani also aimed to get greater capacities and
output, higher fuel economies, and small maintenance costs.

Tne principle of the Calcining Kettle is the
batch process. The general dimensions are as follows;

T},e Kettle proper is 10 feet in diameter and
15 feet high, with four (4) 15" diameter flues running
horizontally throush tne shell, and a four-arm agitator

shaft running in its center from above. The bottom of

the Kettle is spherical in shape, with a rise cf 12"
in its center, and is .ocated 10 feet above the Grates,
The furnace is of the exteniei front ynattern and has

26 square feet cf grate area. Bituminous Coal is used

as fuel,
 

 

 

 

 

 

 

 
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The Kettle preyer is located over a rortet cone
seructicn fire brick hase,
rettcm and pass sround the Kettle, threvech the flues, and
thence to the Stack. The entire unit is encased in a
3/16" Steel jacket 14 ft. 3 in, in diameter erd 24 ft,
€ in, hich, with the necessary insnecticn and cleancut
acore secured to it,

Fach Calciriny; Kettle has a 100 Ton Land Flaster
bin from wrick to draw its materiel, This material is
deliverea to the Nettle from the tin ty a special cesisnedc

onsistinge of

Q

Power aperated serew conveyor Teeder
two 9" screw conveyors in alo" ¥.I, pipe, delivering te
one 14" screw conveysr runnirs on an incline anc deliver-

ine the material to the Kettle threucsh an opening in the

p-4e

TOLe Tre Kettle vertical saft carries a hottom sweep

arm and three eritator arms placed three feet apart from

(a

bottom up. The bottom eweep arm is curved te suit the
curveture of the kettle bottom, with a space of 4" between

them, and hare attached to it 3/4" anchor chains, erranred

fn

week

o tint the draccing chains sweep the camplete

[~.

Nn LOOZS
osttem at all times, This sweep prevents any material
far chovuld this

4

becoming atirrred to the Kettle bottom,

condition exist the bottom would readily he destroyed by

over heating and mirnire.
The vertical shatt is criven at 25 “U.P.). oy a

25 HP. back-geared Motor and a heavy set cf bevel

Then the Caletning Kettle is startel in oper-

ation, the material is delivered into the Fewtle with
rr
wy e

s ~ oo 2 2,4,
+ a ea fale 3 “ Viele t the

ver stall not te less than 212° Fahy,

r, a - - yo -.-
re? Ltic vi Ge

The weter vapcr formed by the calcining of the
3

2 4 ~ = ~=
material is enrred te the kettle dustecetilirs chamber
2A

12,
7 A oy ye ' . " ~ a 2 4 4 . +£
a JO" stew «tack rising from tre kattle top ts

po - nt ee? yetopuwedtaetted pate Mra
T4" cperntans binges counterwelented cite losnted at the

bettem of the Kattite, and passes inte the Hot Fit, ox

, - ve . + > on m7 ~ -~ £ -, aA 4 - 9% 2 = ~~ ms ~ _
ravirag a canacity sf @0 Tons af freshly calcined Plaster,
Te nk TA 34 + “1 3 ° 34 7 A L”
rack Net Pit kas a 10" vent cire leacin-= te the rocf far

v.. . no « . TOT gare 4. Lae , . + TP WT at
the pursose of aliowing the air to escape ans the Nettle

wa

p>

a

f.

j- te
n

~

erercved Into it, The Not Pit dls encicsed with a
cerncrete top, and tras a Manehole with raised scides in ite
cerfer, sa that ne foreien matter can enter the Pit,

The cepacity of each Calcining Kettle was
pilacec at 15 Tons per batch cf Calcined Plaster, and with

a“

mn average cf 250 tonsa per unit in 79 hours, o7 two skhtfts.

: ~ tw
we

ive the decrired

ce
'@
q

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‘)
0

¢

Four Calciring unites were necessary

capacity of 1000 tons of Catcived Plaster,

Se

One Lorge dustesettiing charter of 260 square

feet din average cressesection and 235 feet lera arzcocmce
dates two Calcinirg Kettles. It is lecatet ancve the
Mattles and has tvo heppered vaottens with 9" screw
conveyers in them, to carry the settlings back to tre

ce
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Lund Plas
t

eare ir ercntect wy

disc wall of Gyoeunm Rlocks was used, es t
akle to keen the tetrerature of the dist

ber ish ensich te prevent any ocn@ensat

ttlirngs cannot be returned

+}
ie
2
the
+>
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- TWh LL: be. Al a- ~
re Fettle emuke steck prsces

9

a fine water syray and any dust vrecent.

and onurried avey with the wabte water, v

‘ % < a o one VN
th the ouildine wills,

throush

raotected by a steel enetl

an

th

fo

e Land

26

rlaster

the dust

rrirns £4 Aw

pass o@t cf tre ventiltatcrs in the roof c 4s
cramner,
Plaster of Paris is the product dischars
the Caicining Kettles into tre Het Fit. Trig yx
are ®x] handling and

due to its nature, reguires ces

precautions muct be taken t’ait it dees not

tact with danpnes or any wunecalcines

materi is discharred intc the Hot Fit s
cf from 3040 to 320 fecrecs Fanr, and EYSk

e
eeme 1:

fluidity cf water, but if allcwed to remain

skort time until scme of the entrained

materia] mey refuge ta flcw at all, wit:
The Hot Pit was cestaned with
conical bottom terminating in a snecialt

Screw convevor feeder,

hig feeder al

4
miterial,.

+ anwms
Ley 7

“Mees +

7a Chiu

a
id A "s ny oO
yo cecsigned 9
eckaretes the

ure
‘oe |

4
dy e

7

material inte cne cf twa Lk" serew canveysors rlaced under

yw

the’ feecer, The 9" sere conveyor feeter has a 4" to SG

@?
G
a
$s»
>
t

varying pitch screw pisced ina 10" 7,1, ctreé

9

driver. by power.

a.

The Caitcineda Flaster js dcischarsed from the

Kett te bry gravity intc the Mot Fit, as it jie desiratle
tO get the material cut in a short time, me average
diachering tire is less than cne minute, To get the

eravity ectecharre it is nececsary to hianve the Hot Fit
as Jow as the aischaree gate, wrich, in vwakinz a Not
Fit large enough to nolad two batches from the Kettles,

. & 7. - a dt ome 1. . ~ ‘ae “ a . 9
bkerdrpog tie bottom of tee cantatner well [cw tre

ad

TF, 4 4”

ground floor lire of the KRettie, end in a resion savjected
to water ant pround ccoicture, Ta overcome the ehiection

wee

to water ani dempness in connection with the Fot Pits,

Eievators and Conveyors carrying this msterial, the follow
ing provisions were mace;

Tue Hot Pit, bins are supvorted clear from the
foundations and are not in contact with them, The
Stevator boots are mide vatereticzht up te 12" abcve the
floce line and the screw conveyors are set clear cf the
floor oy over 12", sa that not until the water is 128
nign over the Hot Fit basement floor will any water enter

the aystem the dampness, however, jis objecticnable

e
aa 04 me 3

and under ordirary conditions sisuld not exist te any

In case of an accident or failure cof powe

in cueration and it becomes
C8
cn
e

ies completed, “iis material would have to be returned te
tre Land Plaster bin and reecalcined, As the rew ar

uncalcinedc wanterisl] is very detriments1 to the finished

act, en entirely separete syvetem of conveying and

s

so
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‘

ej.evating is suprited to ta’

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- Teal 2 2, ye URS.
Lana Plaster vin,

The material is denen from the Mot Pit ty the
power feeder ana disclarged into the firgt LE" screw
corveyer, which carries the matcrial to a 14" x 7"
bucket Blevater ard ie eleveted to a yocirt abcve tre
two (2) 12" dietritutine serew conveyora cver the Tarn?

2
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4 ° ” “ns +. %.. £ @ 9 + . re 4 7 2 a ~
fo the Land Fiaster Yin in the Warehncuse, by the aia cf
“a e “ , se or YT ° w 2 -“. om - 2 - 4+ + .
a sreécial threeeway exncut, Ry Gisckarsing tre material
- - i | tL 7 4 + aa a
From the elevetcor ts one of the (2\ Lard Plaster

$3 £3.,- ws . bh ~ 08 3
Sistrivutineg conveyors, the material can be placei in

my ore cf the bins desired,

The Catcine? Plaster is taken frou the Hot Pit
by the evecial feeder and Cischorgel into the secund ih"

screw conveyor runrins to tre TE" x EE" bucket Tlevatcr,

. : A 345. os yt ate Ae
elev ratec OF Poet ama tfscka zed tnto A ke we Srrcw etn=

we!

veyor, which in turn @ischarges into two 12" screw con=

p+.
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vevors running at rickt anzles throurk ah
the Calcitred Plaster storage bins in the Varesuse. These

4 yx ae | 4 Pa . 4.
6 22 2PM, andoat that speed the

CONVEYORS arte Man a
oaveyor flicnts agitate and tend to 1ift the material

Ny

somewnat as it is veins conveyed, As these conveyors

1 tops this agitation and exposure +9 «(the air

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