Pigment Producer Cleans Up
Minor Ingredient Batching

Stimsonite Corp. makes numerous types of thermoplastic roadway marking
material using multiple major and minor ingredients. Major ingredients are handled
two ways.  The primary ingredient, calcium carbonate, is pneumatically conveyed
from storage silos to a mixer.  Other major ingredients in 50 pound bags are
manually added to the conveyor hopper and transferred to the mixer.

Each product recipe calls for five minor ingredients on average.  In the past,
preparing minor ingredients (or "odds") for batching involved carrying a 50 pound
ingredient bag to a stationary scale and slitting it open.  If the recipe called for 13
pounds of the ingredient, that amount was poured into a bag sitting on the scale. 
Then the partially used 50 pound bag was set aside, and the next ingredient
was weighed out into the bag on the scale.

The batching worker followed a recipe sheet that listed each ingredient amount
needed for the batch.  When all minor ingredients were weighed out in bags,
they were dumped to the same pneumatic conveyor transferring the major
ingredients for mixer loading.

Manually Adding Minor Ingredients Creates Clutter and Spills

Because recipe preparation involved manually scooping several minor ingredients
from a 50 pound bag, various problems occurred.  "There was a lot of dusting and
spillage and the problems associated with that," says Process Engineer Bill Floor. 
"The batching workers would change uniforms probably two or three times a day. 
They had to wear special masks, caps and gowns. And we had material loss from
spillage.  At cleanup, we could fill a couple garbage cans with various spilled materials."

The many opened 50 pound minor ingredient bags were also a problem for the
producer.  And, unlabelled bags with small quantities of weighed out ingredient
lay all around the batching area.  "It was a mess; we had lots of open bags and
many were identifiable only to the worker who assembled the minor ingredients. 
" Floor says, "Somebody new coming into the area wouldn't know what was what."

Manually adding minor ingredients also created a potential for operator error. 
Floor says, "When adding so many scoops of several different ingredients,
it's possible to forget where you are."

When this happened, it wasn't known until the batch had gone through all
production steps.  "Sampling shows if something isn't right.  To fix a batch,
we have to reprocess the whole thing," says Floor.  "If the batch was short of
a material, the easy remedy was to simply add more of the ingredient.  But if
the batch had too much of a material, the remedy was more difficult."

The ingredient-adding operations were very labor intensive as well.  Bag handling
was excessive because each 50 pound bag had to be picked up and moved several
times.  Also, Floor says a typical batch has "about 75 pounds of minor ingredients,
and a scoop size is one pound.  So for every batch, a worker had to scoop once
for each ingredient pound needed.  It was a very slow process."

The producer had considered ways to make their minor ingredient operations
more efficient and to minimize dusting so worker exposure would stay at
acceptable levels.  "We did some industrial hygiene tests on worker exposure
to dust." Floor says, "The OSHA 8-hour exposure limit is .050 mg/m3. 
We found we were above that at times, so we researched ways to improve
operations and stay in compliance."  They decided to upgrade the
batching operations.

Producer Looks at Ways to Streamline Ingredient Handling.

Unlabeled bags with small quantities of weighed out ingredients lay
all around the batching area.  "Somebody new coming into the area
wouldn't know what was what."

To find a solution, Floor and a coworker visited the Powder & Bulk Solids
Exhibition in Chicago.  "We were searching for anything that could help
streamline weighing and loading minor ingredients, " Floor says.  "We considered
dispensing odds from a standard steel container [IBC] with a slide gate at the
bottom.  We considered an [IBC] with a loss-in-weight feeder, and we looked
at a fully automated loss-in-weight [bulk bag dispenser]."

"The OSHA 8-hour exposure limit (for airborne dust) is .050 mg/m3. 
We researched ways to improve operations and stay in compliance."

They found a manufacturer that built a semi-bulk dispensing station with a
polyethylene bin and a slide-gate valve.  "It was exactly what we were looking
for," Floor says.  After discussions with the dispenser manufacturer about the
application, the manufacturer proposed a design.  "They supplied excellent
drawings that allowed us to make several revisions to fit our needs," said Floor.

"One of the nice things in considering the equipment was that the
manufacturer offered an upgrade program.  They said they would
buy back the equipment and upgrade us to an automated system
if we wanted," Floor said.

Dispensing Bins Provide Accurate Ingredient Discharge

In April 1997, the producer installed two Ingredient Masters dispensing stations
that hold eight bins each, for a total of 16 dispensers.  The bins' rectangular
upper section slopes down to a cone-shaped bottom where material discharges
through a slide-gate valve are made of Type 304 stainless steel.

The bins are available in various capacities, and the producer selected 28 Cu. Ft.
units.  The inner surface is liquid smooth and has no right angles that can trap
material; each inside corner has a 2-inch radius.  These features allow a first-in,
first-out material rotation and eliminate the need for bin cleanout.

The dispensing stations have a loading platform and a pallet cart that can
move a pallet of bags to the bin being loaded.  The bins are filled through a
top screw-on lid. Although workers lift 50 pound bags to fill each bin,
each bag is lifted only once and quickly emptied into the bin.

A battery-operated portable scale on a rolling cart is used to weigh dispensed
ingredients from each bin.  "The batching worker puts a bucket on the scale,
wheels it over to an ingredient dispenser, and opens that slide-gate valve,"
Floor says.  As the target weight nears, the worker can adjust the flow
to a trickle.

"We probably get 10 times the productivity from that worker now,
because he or she can accomplish a lot more with the new method."

Exact weighments are possible because the valve is accurate, Floor says. 
"When we shut it off, it's an immediate [flow] shut off; there's no spilling." 
After each minor ingredient is added to the bucket, the worker tares the
weight and adds the next ingredient.  When the bucket contains all the
required minor ingredients, it's manually dumped in the conveyor hopper
and transferred to the mixer.

New Dispensing Stations Allow Batch Consistency,
Reduce Cleanup

Installing the dispensing stations significantly improved minor ingredient
batching operations.  Opened and unlabelled bags no longer clutter the batching
are floor. "We did a major cleanup of the area," Floor says.  "Dusting is significantly
reduced, and we've cut our cleanup time to almost nothing, because there's
essentially no spillage.  We have less material loss as a result."

With the dispensing stations, the producer keeps its operations in compliance
with OSHA regulations.  Workers dispensing material to buckets don't need to
wear masks.  "We have a safe and clean work environment," Floor says.

Minor ingredient production costs have been reduced.  Only one batching
worker is now needed.  And the worker's productivity has gone up.  "We probably
get 10 times the productivity from that worker now because he or she can
accomplish a lot more with the new method," Floor says.  "Now a worker simply
opens the valve at the bin's bottom and weighs out the material in probably
one-tenth the time it used to take."

Another productivity benefit is that the worker has more time to perform
other functions.  "We de-bottlenecked the area.  Our throughput is up about
150 percent in the odds [minor ingredients] batching area," says Floor.

Besides saving labor expenditures, the producer saves space in the batching
area, according to Floor.  "We've reduced the floor space needed for the entire
odds area.  I'd say we're using roughly 40 percent less space than before."

Floor is satisfied with the dispensing station manufacturer and the production
results.  "Batch accuracy and consistency have improved greatly.  Reworking
batches due to improper minor additions no longer occurs.  I've been totally
satisfied with the service I received, from initial contact to system installation."

The producer is now considering installing similar equipment in other plants,
according to Floor.  "It took only six months to get a return on our
investment," he says.

Published in March, 1998 Powder & Bulk Engineering magazine.

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