Sometimes resolving a sticky situation requires a measured and delicate approach. For Miller Brewing Co.'s Fort Worth, TX, bottling facility, a conveying system designed in-house over a six-month period at its sister facility in Eden, NC, through ALL-CON World Systems, Inc., gently and efficiently alleviated its difficulties with hot-melt adhesive-chip handling.
Installed in Fort Worth in September, '01, after being put through its paces for five years in Miller's Eden plant, the ALL-CON hot-melt glue-conveying system was engineered to carry thermoplastic adhesives, in the form of pellets or 1/4-in. chips, to hot-melt glue melters. According to retired Miller employee Jim Good, an engineer who collaborated extensively with ALL-CON to develop the system in '96, the conveyor provides steady adhesive feeding for greater machine uptime and more consistent-quality melting and sealing than with hand loading. In addition, he says, the conveyor's filtration system greatly reduces the costs associated with clogged adhesive nozzles.
Manual feeding is problematic
In Fort Worth, the ALL-CON conveying system feeds three Nordson Vista melting units that provide adhesives to seal cartons and trays for 12-oz bottles of the brewer's beers, including Miller Lite and Miller Genuine Draft, among others.
|A flexible hose carries the chips from a gaylord to the melter.|
Before the conveying system was installed, Mike Chamberlain, technical services area manager, electrical, for the Fort Worth plant, says that operators at the facility were required to heft 40-lb cartons of the adhesive chips to the melter, where they would manually scoop them into the unit, as needed.
Explains Good, "One of the drawbacks of this method is that you get a stratifying effect." That is, while adhesive at the bottom of the tank might measure 350 deg F, the "layers" above would gradually be cooler, as the chips would change the temperature of the mixture as they were added.
"If you don't maintain a high enough or consistent enough temperature, then all of the glue will not penetrate through the wax coating on the cartons," he adds. Another problem was that operators, often required to simultaneously attend to other tasks, such as loading the carton magazines, would sometimes unintentionally let the level of the adhesive in the melter become too low. This resulted in adhesive charring, which led to clogged applicator nozzles and downtime.
Charring also occurred as the dust and powder that covered the glue chips in their original packaging would be inadvertently loaded into the melter. "Operators would pour a slug of that [powder] into the hot-melt tanks, and because the powder was so fine, it would char and would clog the nozzles," says Good.
Conveyor automates process
During operation, the ALL-CON glue conveyor uses a flexible vacuum hose to suck up the required volume of adhesive from a gaylord holding approximately one ton of the glue chips. The chips are then transported 125 ft through the hose and an aluminum conveying line to a vacuum chamber assembly, where they are filtered before being discharged into a receiving hopper.
|A three-part unit filters and transports adhesive chips to the hot-melt gluer.|
A radio frequency probe placed 11/2 in. from the bottom of the melting tank monitors the level of adhesive in the unit. When it senses that the melter needs to be replenished, it sends a signal to the conveying system's programmable logic controller, a Modicon Compact Series 145 from Schneider Automation, which then signals the system to transfer more adhesive from the gaylord.
To prevent foreign particles, such as fines (particulates measuring 10 microns or less) and powders, from entering the melter and clogging adhesive-applicator nozzles, the ALL-CON system filters material at various points in the conveying process. First, undersized chips and fines are separated by a 5-micron stainless-steel filter and are isolated from the material being processed. These particles are then directed to an in-line secondary filter on the vacuum power unit, which is located at floor level for easy servicing.
In the case of the Eden installation, Good says that the filtration system brought about "a radical change" in the number of glue nozzles needing replacement on a regular basis, if the filters were changed daily. Before the ALL-CON system, he notes, the plant could go through anywhere from 50 to 80 nozzles/month, while nearly 100 to 120/month might be used during periods of high humidity. But, with the new conveying system, that number dropped to a mere 12 per month. With nozzles priced at $30 apiece in '96, the reduction in their usage resulted in a sizable cost saving.
According to Chamberlain, the Fort Worth facility has not seen a dramatic change in nozzle use since the system was installed in '01, although charring and downtime have been considerably reduced.
Another unique feature of the conveying system, relates Good, is its ability to self-clean. At the end of each cycle, the system is automatically purged clean to assure that no buildup of material remains in the conveying line. "Almost all the other systems will leave the chips laying in the conveying tube," relates Good, "and that's not a good thing in high humidity."
|Cartons containing 12-oz bottles of beer are glued with the melted adhesive.|
In addition, the system also restricts moisture from entering the tubes due to heat transfer from the melter. This allows the chips to remain dry and prevents bonding before the glue begins to change to a molten state upon entering the melter.
All systems a go
Using the original Eden project as a roadmap for successful hot-melt glue conveying, Miller Brewing Co. now has ALL-CON units running on 10 of its packaging lines, including six in Eden, two at its Trenton, OH, plant, one in a facility in Albany, GA, and its Fort Worth line. Apparently, when Miller finds something that works this well, it sticks to it!
More information is available:
Conveyor: ALL-CON World Systems, Inc., 302/628-3380. Circle No. 259.
Melters: Nordson Corp., 800/683-2314. Circle No. 260.
PLC: Schneider Automation, Inc., 978/794-0800. Circle No. 261.