Position: This article's content is about the dispensing station helps the 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 mixing system 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 batch 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.
New Dispensing Stations Allow Batch Consistency, Reduce Cleanup
Installing the dispensing stations significantly improved minor ingredient automatic 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.
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 weigh hopper and transferred to the mixer.
Published in March, 1998 Powder & Bulk Engineering magazine
