Mixer keeps hot melt adhesives cool
Gears and Bearings Insights
- Due to no cure time, HMT’s hot melt adhesives save time and maximizes on productivity because it doesn’t have a cure time.
- Hot melt adhesives can join any material to any substrate, which allows hot melt adhesives manufacturers serve customers with many different backgrounds and needs.
The company blends heat-sensitive hot melt adhesive ingredients using a rotary batch mixer that imparts no shear or heat into the material and produces uniform blends quickly, while requiring minimal maintenance.
The making of hot melt adhesives
HMT first blends the ingredients, primarily pellets of hydrocarbon resins and polyethylene waxes, as well as a mineral-based powder filler, a job handled since 1994 by a model 700-TS-40-MS rotary batch mixer from Munson Machinery. Its horizontal vessel rotates on external trunnion rings located at each end, eliminating the need for an internal shaft and precluding material contact with bearings and seals.
“It doesn’t hurt our material or overheat it, which is important to us. I’ve checked the temperature of the material going in and coming out, and it’s always the same,” said Glen Bennett, HMT plant manager.
“Some batches are actually done in about five or 10 minutes, but we find that 20 minutes is ideal for all our formulas,” Bennett said. “It’s also a comfortable speed for the operator.” When necessary, minor ingredients can be added manually through a side door.
At the end of the cycle, the operator flips a switch, actuating an air cylinder that opens the mixer’s stationary outlet. With the vessel continuing to rotate, the 1,000 lb. batch discharges through a collapsible chute into a mobile bin. Dust collection pickups are located at the mixer’s outlet, at the screw conveyor’s discharge and at the bag breaking station. The mixer itself operates dust-tight with a single radial seal preventing dust leakage.
Once filled, the bin is wheeled to low-pressure extruders, which feed the mixture into the hot melt film-casting process. HMT has eight standard formulas, each with six or seven ingredients. The plant averages six batches a day.
Although some ingredients are slightly sticky, the mixer empties itself completely, and no cleaning is required between batches, Bennett says. “It stays remarkably clean inside. After some 40,000 batches over 27 years, you’d think we would see buildup, but there’s virtually nothing. That’s a big plus when switching from formula to formula to formula all day long. I don’t have to worry about contamination.”
Bennett has not detected any wear inside the mixer from the abrasive mineral-based filler, although dust has prompted the company to make two repairs. The first was replacing the packing seal at the mixer’s inlet where the screw conveyor discharges. “It wasn’t affecting the performance, but it allowed dust to drift,” Bennett says. The second was replacing the air cylinder that opens the discharge gate after the seals wore out from contact with the abrasive dust.
A ‘green’ alternative
HMT’s hot-melt adhesives are also environmentally friendly compared to the alternatives, such as white glue and contact sprays. “White glue is inexpensive, but it’s messy and involves a lot of wastewater,” says Bennett. Contact sprays, he added, involve unpleasant fumes and wasteful overspray. In contrast, hot-melt films are 100% solid adhesive, so there is little waste and no cleanup.
“There is not a batch in the last 27 years that hasn’t gone through that Munson mixer,” Bennett said. “It’s built for heavy-duty work. The longevity has more than surpassed our expectations.”