Before and after shots show how a Microstar microfinishing attachment for lathes imparts a flawless finish on a plunger for glass molding at Libbey Glass.
LIBBEY GLASS IN TOLEDO, OHIO, PRODUCES UP TO 400 dozen glasses/hr and has to change glass-mold components every 8 hr of production to maintain product quality. One such component is the plunger, a cast iron cylindrical part that pushes molten glass into the mold. Its surface finish must be precise and clean, or it produces cloudy glasses.
To achieve proper surface finishes, operators chucked the plunger in a lathe and manually applied abrasive film to the part for up to an hour. The process was time-consuming, and results varied among different operators. Libbey wanted a more reliable, faster, and controlled system for polishing plungers. What the company found was a microfinishing attachment for lathes.
The attachment, from Impco Machine Tools, produces specified, measurable finishes repeatably and consistently for a fraction of the cost of a lathe or standalone machine, reports Jeff Kreft, supervisor at Libbey. "The Impco Microstar attachment is at least 50% more productive than other finishing processes," he says.
Microstars generate any finish — Ra, Rz, Rt, and bearing areas at less than 1 Ra optical-mirror finishes. They use abrasive film backed by oscillating roller platens to make contact with workpiece diameters. Film automatically indexes to present fresh abrasive to each workpiece, and the process works on materials ranging from soft rubbers and urethanes to tungsten carbide and hard coatings.
According to Kreft, Impco honed the process for Libbey until it reached surface specifications of 2 Ra µin. or better in less than 15 min.
The polishing process starts with operators chucking the plunger in the lathe head and mounting the Microstar to a platen fastened to the bed of a Monarch manual lathe. Automatically pivoting across the platen, the attachment addresses any portion of the plunger surface. Operators oversee process parameters through the attachment's control panel.
"A Wall Colmonoy hard coating covers the plunger's surface. This is the material that is polished," explains Tom Miller, Libbey operator of the Microstar. "The Ra specifications are the same as with the manual operation, but that operation always left circular rings on the surface. The Microstar eliminates such imperfections.
Impco Machine Tools