TECHNICAL WRITING SAMPLE:
Powder formulation is the
process used when the Formulations Operator makes the dry
Wessex. It involves, mixing together the active ingredient,
known as the technical., with the inerts Chimerical 57 and
Cab-O-Fair. The technical is taken from the tech hold bin
where it is stored after the Wessex Damp End makes it. Screw
conveyors take the technical to the primary blender for
formulation. The inerts are dumped from bags at the inerts
dump 'station on the first floor mezzanine. They are then
pumped to the inerts blender on the fourth floor. From the
inerts blender, a batch of inerts is released to the inerts
weigh feeder. The inerts are charged from the weigh feeder
to the primary blender., It is located below the feeder
on the third floor. There, the technical and the inerts
are blended together.
The formulation is then
released to the sifter on the second floor mezzanine. The
sifter divides up the materials according to their size.
The fine powder goes directly to the secondary blender on
the first floor mezzanine. Larger pieces of material are
sent to the mill on the second floor for grinding and, then,
on to the secondary blender. These two groups of product
-materials are blended together inside the secondary blender.
A third product size, those pieces too big to use in the
final product, are removed from the formulation and are
set aside as sifter rejects. The sifter rejects are used
in making the liquid formulation.
After the good product is
blended in the secondary blender, it is pumped up to a finished
product bin. There are two finished product bins. The tops
of the bins are visible on the outside balcony of the fourth
Each of the blenders, tanks
and bins has its own bin top dust collector. These dust
collectors remove formulation materials from the air. The
materials are then fed to the main dust collection system,
the primary and secondary dust collectors. The material
collected is used as rework. Such rework is added in small
amounts during the dry formulation process.
The mill, the sifter and
the dust collector blower are normally left on all the time.
However, the F.O. starting a shift must inspect each of
them and be sure they are operating normally. The Operator
starting up also checks the amounts of technical and inerts
available for formulation. Usually the last Operator on
duty will leave enough for the new Operator to start right
Whenever there is not enough
technical in the tech hold bin, the F.O. must wait until
the Damp End has started up. If there is a high level in
the tech hold bin, supervision may direct the Operators
to pack out pure technical in 50 kilo drums, or the Damp
End can be directed to shut down until the F.O. catches
The F.O. oversees the formulation
process at the F.O. control room on the second floor. (It
is also called the "F.O. Shack".) At the control room panel
board, the F.O. operates and monitors the two sequencers
for the primary and secondary blenders. These sequencers
regulate the operation of the two blenders and their related
equipment. They control the order in which the formulation
steps take place.
The mode of operation for
both the primary blender sequencer and the secondary blender
sequencer is controlled by one selector switch on the panel
board. There are three modes: MANUAL, SEMI-AUTOMATIC and
AUTOMATIC. In the MANUAL mode, each of the formulation steps
must be manually advanced by the F.O. In the AUTOMATIC mode,
the sequencers will start another batch when the previous
batch is complete.
The usual mode for the F.O.
is SEMI-AUTOMATIC: in SEMI-AUTOMATIC, the Operator starts
the sequencers and they complete their steps automatically.
When the sequences are completed, the Operator must push
the START push button again in order for another batch to
When additional inerts are
dumped at the inerts dump station, they are measured out
by the bag. The two types of inerts must be dumped in a
certain ratio. The ratio changes every other time the materials
are dumped. First, three bags of Chimerical 57 are dumped
with three bags of Cab-O-Fair; then, four bags of Chimerical
57 are dumped with three bags of Cab-O-Fair. The F.O. keeps
alternating between the two ratios as additional inerts
are dumped. (An air hood must be worn during all dumping.)
At the inerts dump station,
the Operator fills the inerts fluid flo pump. This is the
pump used to take the inerts up to the inerts blender. It
can be operated at either the inerts dump station on the
first floor mezzanine or at the pump itself on the first
The inerts fluid flo pump
has a four-stage cycle: FILL, ACTIVATE, DISCHARGE and PURGE.
With the pump set for FILL, the F.O. dumps the inerts. The
Operator then pushes the ACTIVATE button. This causes the
pressure to rise. The rest of the cycle is completed automatically.
'When the pressure has risen to a certain level, a valve
opens, releasing the pressure and inerts and forcing them
up to the inerts blender. When the pressure drops, the main
discharge valve closes. A special purge valve opens to release
the remaining inerts up to the inerts blender. This also
clears any remaining inerts from the transfer line to the
inerts blender. When the fluid flo pump returns to its FILL
stage, it is ready to receive another batch of inerts.
As the inerts blender receives
each batch, its agitator comes on and blends the inerts
together until a timer cuts it off. (Note: Unlike the other
agitators, the inerts blender agitator always operates at
the same speed whenever it is running.)
During the primary blender
sequence, technical is charged from the tech hold bin, and
inerts are charged from the inerts weigh feeder. The amounts
of technical and inerts charged to the primary blender are
regulated by digital weight settings on the panel board.
There are two weight settings
which control technical charging: the technical fast weight
and the technical slow weight. These control the speed at
which the technical is charged, as well as the amounts.
Most of the technical is charged at a fast speed until the
fast weight is reached. Once the fast weight has been satisfied,
the last few pounds are charged slowly until the amount
of technical added equals the slow weight setting on the
panel board. Slow weight settings are used in order to assure
an accurate cut-off.
For example, for a typical
1265-pound technical charge the fast weight might read 1255
and the slow weight, 1265. The first 1255 pounds would enter
the primary blender at a fast speed. Then, the last ten
pounds would charge slowly until the 1265-pound slow weight
Notice that the technical
slow weight figure on the panel board is also the weight
of the entire batch: the 1265 pounds includes both the fast
and slow technical charges. Although only the last ten pounds
are actually charged slowly, the slow weight setting shows
the cumulative, final weight.
As the technical is charged
to the primary blender, the primary blender scale weighs
the amounts. The primary blender scale has a red digital
read-out on the panel board. When the technical charge is
complete, the inerts are charged to the primary blender
from the inerts weigh feeder. Earlier in the sequence, before
the technical has been charged, the inerts are prepared
when the inerts blender releases a batch to the inerts weigh
An inerts weigh feeder scale
registers the amount of material inside the feeder. The
scale has a red digital read-out on the panel board. The
inerts weigh feeder scale is used to show amounts subtracted
from the inerts weigh feeder. For this reason, the read-out
is a minus number. For example, after an 85-pound batch
has been charged, the scale would read -85 pounds. To refill,
the inerts blender would release another 85 pounds to the
inerts weigh feeder, and the feeder scale would rise from
-85 to 0.
The refilling and charging
of the inerts are controlled by three panel board settings:
the refill weight, the preset weight and the slow weight.
The refill weight is the
cut-off point when the inerts weigh feeder is refilled with
another batch. The inerts blender discharge valve releases
the inerts batch to the inerts weigh feeder to prepare the
feeder for the charge to the primary blender. As the refilling
nears completion, the valve will start to close whenever
the refill weight is reached on the inerts weigh feeder
As mentioned earlier, in
order to prepare an 85-pound batch of inerts, the inerts
weigh feeder scale must rise from -85 pounds to 0. However,
to assure an accurate cut-off, the inerts blender discharge
valve must start to close before the scale goes all the
way to 0.
Therefore, for an 85-pound
batch, the refill weight might be set for -10. When the
scale has risen from -85 to -10, the blender will start
to close. While the valve is still closing, the additional
10 pounds needed will fall through to the inerts weigh feeder.
This brings the weight of the batch up to the desired weight
of 0. (Note: In actual practice the inerts weigh feeder
scale may not read exactly 0 at the end of the refilling.
However, later in the primary blender sequence, the scale
is tared, that is, re-set for 0.)
The two other inerts settings,
the preset weight and the slow weight, control the charge
from the inerts weigh feeder to the primary blender. Like
the technical, the inerts are charged at a fast rate until
most of the batch is released; then, the last few pounds
are charged slowly. The principal works the same as with
the technical charge, but the panel board weight settings
are set up somewhat differently.
The preset weight decides
the total amount of inerts charged the primary blender.
It is the combined weight of both the fast and slow inerts
charges. If 85-pound batches are being charged, the preset
weight is set for 85 pounds.
The slow weight is set on
the panel board for the actual number of pounds which are
charged at the slow speed. In the case of an 85-pound batch,
the slow weight might be set for 5 pounds. This would cause
the first 80 pounds to be charged at the fast speed and
the last 5 pounds to be charged at the slow speed.
Notice that, unlike the
technical, there is no "fast weight" setting, as such, for
the inerts. The inerts panel board settings also differ
from the technical in that the slow weight setting is only
the amount of the actual slow charge. It is not the cumulative,
final weight. (Recall that the slow weight number for the
technical is the total of both the fast and slow charges.)
THE POWDER FORMULATION
To begin the primary blender
sequence, the F.O. selects the mode of operation and sets
the sequencers' START-STOP switch to START position. These
controls affect the operation of both the primary and secondary
sequencers. In the MANUAL mode, the Operator will have to
turn on each of the sequencers' steps individually in order
to control the formulation process.
In the following summary
of the formulation process, it is assumed that the F.O.
has chosen either the AUTOMATIC or SEMI-AUTOMATIC mode.
It is also assumed that each of the succeeding sequencers'
steps are satisfied and that they proceed normally from
step to step. However, the Operator must always be aware
of the potential for problems and the fact that the sequencers
can not advance automatically unless the preceding steps
As soon as the primary blender
sequence begins, the sequencer refills the inerts weigh
feeder. The inerts blender discharge valve releases a batch
of inerts to the weigh feeder. When the refill weight is
reached, the valve starts to close and the weigh feeder
scale stops at, or near, 0. Since the technical is charged
before the inerts, the inerts batch remains in its feeder
until it is time for the inerts charge to the primary blender.
The primary blender agitator
starts running at slow speed. Two technical screws charge
technical to the primary blender at fast speed until the
fast weight is reached on the primary blender scale.
Next, the primary blender
agitator stops and the screws feed additional technical
at slow speed until the slow weight (the final, cumulative
weight of the technical) is reached on the primary blender
During the slow technical
charge, it may be necessary for the F.O. to operate the
tech hold bin unloader. The tech hold bin is normally kept
at a relatively low level, and the unloader is used whenever
the bin is nearly empty. The tech hold bin unloader is a
rotary arm inside the tech hold bin which assists the removal
of technical and keeps the material in the bin at an even
level. The F.O. must be sure the unloader is turned off
once the slow weight is satisfied.
When the technical charge
is completed, the primary blender sequencer prepares for
the inerts charge. The inert weigh feeder scale is tared
to 0. The primary blender agitator starts running at a slow
The fast inerts charge begins.
The inerts weigh feeder charges the inerts at fast speed
until the amount of inerts charged is the difference between
the preset weight (the total weight of the inerts charge)
and the slow weight (the amount to be charged at slow speed).
For an 85-pound inerts charge (with a preset weight of 85
pounds and a slow weight of 5 pounds) the fast charge ends
when 80 pounds of inerts have been charged to the primary
With the fast charge completed,
the inerts weigh feeder switches to slow speed and adds
the slow weight to the primary blender.
At this point, the primary
blender scale should show the total of the combined technical
and inerts charges. The inerts weigh feeder scale will show
the amount of inerts subtracted from the inerts weigh feeder
(In out example, -85 pounds).
As the primary blender sequencer
advances, the primary blender agitator switches from slow
to fast speed. This is to assure that the technical and
premix materials are thoroughly blended together. When a
timer times out, the fast blend ends, and the agitator changes
to slow speed.
The primary blender sequencer
checks the secondary blender sequencer and makes sure the
secondary blender is ready to receive another batch. When
the secondary blender is ready (in its HOME position), the
primary blender bottom valve opens, and its rotary valve
starts turning. The primary blender agitator continues at
This releases the materials
to the sifter. The bottom valve allows the formulation to
drop from the-primary blender. Then the materials pass through
the rotary valve.
The primary blender rotary
valve controls the overall rate of the formulation process.
This is because it regulates how fast the materials can
be discharged from the primary blender. It is contained
inside the chute between the primary blender bottom valve
and the sifter. The rotary valve turns around much like
a steamboat paddle. The formulation can only pass through
the valve when it is turning. It scoops up the materials
arriving from the blender and drops them on the other side
toward the sifter. The speed at which the valve turns can
be adjusted by the Operator when directed by supervision.
Inside the sifter are two
sifter screens which divide up the materials. The sifting
is helped by a two-horsepower motor which shakes the screens,
and by a number of bouncing balls kept between the first
and second screens.
The first screen stops the
sifter rejects. These pieces of material are too big to
use in the powder formulation. They drop down a chute into
a sifter rejects drum kept by the mill on the second floor.
The second sifter screen
holds back the good product which made it through the first
screen but can not pass the second screen. These materials
are dropped down a chute to the mill. Inside the mill they
are ground down to product specifications. The mill contains
a rotor with a large number of blades. A mill screen holds
the product inside the mill until it is ground down to the
right size. After grinding, the materials drop into the
Meanwhile, the fine pieces
of product--those that manage to pass through both sifter
screens--go directly into the secondary blender.
It takes about thirty minutes
for the formulation to pass from the primary blender to
the secondary blender. Inside the secondary blender, the
two types of good product--those materials which passed
straight through the sifter and those materials which had
to be run through the mill--are blended together to become
final product. As this happens, the secondary blender sequencer
stays in its HOME step 0 while its agitator runs at slow
When the primary blender
has released all its materials, its bottom valve closes,
and its rotary valve stops turning. The primary blender
scale is tared to 0, and the secondary blender sequencer
starts to advance. A batch counter on the panel board advances
by one digit.
As the secondary blender
sequence gets underway, the secondary blender agitator runs
at fast speed for about two minutes. When a timer times
out, the agitator switches back to slow speed.
The secondary blender releases
the materials to the finished product fluid flo pump. Like
the inerts fluid flo pump, the product fluid flo pump has
a four stage cycle of FILL, ACTIVATE, DISCHARGE and PURGE.
The product fluid flo pump has a fill valve that must be
open in order to receive materials from the secondary blender.
Assuming this is the case, the secondary blender agitator
returns to its fast speed.
Located between the secondary
blender and the fluid flo pump fill valve is the secondary
blender bottom valve. This valve opens and releases the
product from the secondary blender to the fluid flo pump.
When the secondary blender scale drops to 0, the fluid flo
pump fill valve closes, but the bottom valve remains open.
The pump completes the cycle
bringing the batch to a finished product bin.
There are two finished product
bins. They are located on and below the outside of the fourth
floor. Each of the bins holds about 15 batches. A selector
switch in the F.O. shack decides the bin used.
When the product fluid flo
pump is empty (after the PURGE stage), the pump fill valve
opens and the secondary blender bottom valve closes.
The preceding discussion
is intended to give the trainee an overview of what is happening
during the formulation process. The F.O. must also learn
the specific step numbers for the primary and secondary
sequences and what happens during each step number. These
steps are listed and described in the two sections that
called the HOME step. At this point the primary blender
sequencer is not contributing to the formulation process.
The mill, sifter, and dust collection system are already
on, operating continuously. The secondary blender sequencer
is also in its HOME position unless it is still finishing
an earlier batch.
In the AUTOMATIC mode,
the primary blender sequencer will automatically advance
to step 1. In SEMI-AUTOMATIC, the Operator must push
the sequencer start switch in order to advance. In
MANUAL, the Operator must set the sequencers to start
and manually advance each succeeding step
sequencer sets up the inerts weigh feeder to weigh in.
inerts weigh feeder refills.
The inerts blender
agitator starts running. The inerts blender discharge
valve opens to the inerts weigh feeder. The valve
releases inerts from the blender until the refill
weight setting is reached on the inerts weigh feeder
scale. When the scale has risen to the refill weight,
the inerts blender discharge valve starts to close.
By the time the valve is completely closed, the inerts
weigh feeder scale gives a read-out at, or near, 0.
sequencer tares the primary blender scale. This causes
the scale to read 0. This is to insure an accurate weight
for the new batch. A timer cuts off the taring process.
primary blender sequencer checks the primary blender
scale and makes sure it is tared to 0.
The sequencer checks
that the primary blender bottom valve is closed. Assuming
this is the case, the technical is charged to the
primary blender at fast speed while the primary blender
agitator runs at slow speed.
The technical is brought
from the tech hold bin to the primary blender by screw
conveyors. There are five technical screws altogether,
but only the first two are used for charging to the
primary blender. They are the number one and the number
two screws. The technical is first brought from the
tech hold bin by the number one screw. The number
one screw takes the technical to the number two screw.
The number 2 screw can then take the technical in
either of the two directions. In one direction, the
technical goes directly to the primary blender for
powder formulation; in the opposite direction the
technical goes to the three other screws for either
liquid formulation or technical pack-out.
At the panel board
are selector switches for the numbers one and two
screws. These switches decide whether the screws are
used for powder formulation, liquid formulation or
direct technical pack-out. The selector must be set
for PRIMARY BLENDER in order for the technical charges
to occur during the primary blender sequence.
When the selector
switches are set for PRIMARY BLENDER and the primary
blender sequencer is in step 5, the number one screw
will run at its fast speed and the number two screw
will run toward the primary blender. (Note: Toward
the primary blender is the so-called REVERSE direction)
Once the fast weight
is satisfied, the number one technical screw changes
to slow speed. This is to insure an accurate weight
cut-off point. The primary blender agitator stops.
The number two screw continues to charge toward the
primary blender. Normally it is the goal of the F.O.
to bring the tech hold bin down to a low level during
the technical charge. If necessary, the Operator runs
the tech hold bin unloader during the slow charge.
Be sure to turn unloader off at end of charge.
The slow tech charge
continues until the technical slow weight (cumulative,
final weight) is reached on the primary blender scale.
technical screws nos. one and two stop. The sequencer
checks the weight of the charge. If the weight is within
normal tolerance limits, the sequencer can advance to
the next stop.
sequencer tares the inerts weigh feeder scale. The scale
is reset for 0 in case it did not read exactly 0 at
the end of the refilling.
The primary blender
agitator re-starts at its slow speed. The number two
technical screw momentarily runs away from the primary
blender. (This is the so-called "FORWARD" direction.)
This is to keep extra tech from going into the blender.
sequencer resets the internal timers of the formulation
checks the inerts weigh feeder scale. If the scale is
properly tared to 0, the sequencer advances.
checks the balance of the inerts weigh feeder scale.
charge to primary blender. Both the fast and slow charges
are included in this step.
With the primary blender
agitator still running on its slow speed, the inerts
weigh feeder charges at fast speed until the "fast
weight" amount has been subtracted from the inerts
weigh feeder scale and added to the primary blender
scale. The fast weight amount is the difference between
the preset weight and the slow weight.
When the fast charge
is complete, the inerts feeder switches to its slow
speed. At this point, the feeder charges additional
inerts in the amount shown on the panel board slow
weight setting. The charge continues until the panel
board preset weight is reached. (The "preset" weight
is the total amount of the inerts charge, including
both the fast and slow weights.)
inerts weigh feeder stops.
The sequencer checks
the inerts weigh feeder scale and makes sure the amount
released is within normal tolerance limits.
inerts weigh feeder reverses momentarily (runs away
from the primary blender back into the weigh feeder)
to make sure no more inerts enter the primary blender.
The feeder stops when a timer times out.
The primary blender
agitator is still running at its slow speed.
At this point, the
primary blender sequencer will stop advancing if it
is set for the AUTOMATIC mode. In order to advance,
the Operator should change the mode to SEMI-AUTOMATIC
The primary blender
agitator switches from slow to fast speed. Eventually,
a timer ends the fast blend.
primary blender agitator continues to run at slow speed.
The primary blender
sequencer checks the secondary blender sequencer.
The primary blender
sequencer will remain in this step until the secondary
blender is ready to receive another batch. When the
secondary blender sequencer is in its step 0 (the
HOME step), the primary blender sequencer advances.
primary blender rotary valve starts turning.
The primary blender
sequencer checks that the primary blender rotary valve,
the sifter, the mill and the secondary blender agitator
are all running.
primary blender releases the material.
The bottom valve opens,
and the rotary valve controls the speed at which he
formulation drops to the sifter. The sequencer stays
in this step until the weight on the primary blender
scale drops to 0. When it does, the sequencer advances.
and grinding continues.
The primary blender
is finished with this batch. The primary blender bottom
valve closes, but the rotary valve continues to turn.
The material still between the primary and secondary
blenders continues to sift and grind. The secondary
blender sequencer remains in its HOME step until time
has been allowed for the additional material to enter
the blender. When a timer times out, the primary blender
primary blender scale is tared to 0. The primary blender
rotary valve stops turning. The primary blender agitator
stops. The entire batch should now be inside the secondary
When the primary blender
sequencer reaches this step, the secondary blender
sequencer starts. (See the "Secondary Blender Sequence"
description which follows in this section)
primary blender sequencer checks the secondary blender
sequencer and makes sure that the secondary blender
sequencer has started. If the secondary blender sequencer
is in any step besides its HOME step 0, the primary
blender sequencer advances.
22, 23, AND 24
are spare steps. The sequencer goes through them without
causing any additional action.
batch is counted. On the F.O. panel board is a digital
counter which advances by one digit. The primary blender
sequencer returns to its HOME step 0.
is the HOME step for the secondary blender sequencer.
The sequencer remains in this step until the secondary
blender receives an entire batch from the primary blender.
The secondary blender agitator runs at slow speed. When
the primary blender sequencer enters its step 20, the
secondary blender sequencer advances to Step 1.
The secondary blender
agitator goes into its fast blend cycle. The various-sized
materials are thoroughly blended together until a
timer ends the fast blend cycle.
product fluid flo pump is checked. The agitator returns
to its slow speed, and the sequencer prepares for discharge.
The secondary blender scale is activated. The sequencer
checks that the product fluid flo pump is in its FILL
stage, and the fill valve is fully open.
sequencer checks the internal relays.
to fluid flo pump begins.
The agitator returns
to fast speed, and the secondary blender bottom valve
opens. This step ends when the secondary blender scale
drops to 10 pounds.
to fluid flo pump is completed. This step is controlled
by a timer, not the secondary blender scale. The timer
is set to allow enough time for the additional product
to leave the blender and drop into the fluid flo pump.
While this happens, the secondary blender agitator continues
to run at fast speed, and the bottom valve remains open.
When the timer times out the sequencer advances to step
fluid flo pump is signaled to cycle. Another timer briefly
delays the operation while the fluid flo pump fill valve
The fluid flo pump
completes its ACTIVATE, DISCHARGE and PURGE steps.
While the pump operates, the secondary blender bottom
valve remains open. When the pump cycle ends, the
pump fill valve re-opens, and the secondary blender
bottom valve closes. However, should the fluid flo
pump fail to enter the ACTIVATE stage, the secondary
blender bottom valve will still close when the sequencer
returns to the HOME step 0.
7, 8 9 AND 10
last four steps are spares. The secondary blender sequencer
quickly advances back to its HOME step 0.
Lights on the panel
board tell the Operator whether the sequencers are
advancing normally. The panel board also has warning
lights, which can alert the Operator to specific problems
such as high or low levels in bins and blenders, slow
cycles for the sequencers and low nitrogen purge levels.
The F.O. must also
be aware of the interlock system. These interlocks
will prevent certain pieces of equipment from operating
unless certain other equipment are turned on. Information
on the interlock system and on other trouble-shooting
situations is contained in the Operating Procedures
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