Design News for Mechanical and Design Engineers

For example, White Cap LLC makes in-line vapor vacuum machines for sealing metal caps and lids onto jars. A stainless steel, duckbill-shaped part contributes to cap stabilization, holding caps in place as they are put onto jars. With increased speeds, however, the duckbill could not keep up. "We first noticed the problem with taller-profile caps at line speeds of 250 caps per minute," says Senior Project Engineer Rick Pollak. Engineers used high-speed films of the closure equipment in action to help put the lid on cap application problems. The films showed that the duckbill did not always maintain contact with the cap passing under it. At faster line speeds, the cap launched the duckbill upwards, causing it to bounce around on top of the cap, leading to misapplication and lid damage.

Cutouts reduce mass by 29% and a scalloped configuration allows the duckbill to life more gradually and stay in contact with jar caps during higher line-speed applications.

White Cap designers began working on new duckbill configurations that could better follow the movement of the lid. To test the new concepts, White Cap created welded metal prototypes and evaluated their performance at varying line speeds. The best performer was a duckbill part with a scalloped cutout configuration that allowed the duckbill to lift more gradually and stay in contact with the cap during application. As a result, it permitted better overall control and stabilization of the cap.

Compared to the previous duckbill design, which consisted of one solid piece of metal, the new design is 29% lighter, and the mass reducing cutout portions promote a quicker reaction time. Moreover, the previous design had a "real quick ramp-up," Pollack explains, "which we slowed down by cutting a scallop under the duck bill at the entrance ramp, which increases the distance required to ramp up to the full height by four times."

Once White Cap decided upon the scalloped cutout duckbill design, they took drawings to NPC. Since NPC had originally converted the part successfully from a weldment to an investment casting, White Cap sought NPC's recommendations for manufacturability of the new, more complicated design. Compared with the original solid-piece duckbill design, the new cutout design would be more difficult to cast because mold flow could potentially be impeded around the cutout areas. "We had to come up with creative investment casting tooling and techniques in order to keep the metal flowing through the entire mold, around the scalloped cutouts," says NPC's Jim Giovannetti, VP of sales and marketing. In addition, the design included both thin and heavy sections that would cool at different rates following the investment casting process. Without careful planning, the thin sections would run the risk of porosity, which would undermine part strength.

NPC used several techniques to help achieve White Cap's design goals. First, NPC engineers decided upon a non-traditional tooling and gating configuration. "Typically, the ideal cast shape is an inverted pyramid," explains Giovannetti, "with the molten metal fed from the top. We proposed rotating the part 180°, with the gating into the top of the investment casting cluster. This would help ensure proper filling of every section." To enhance the flow of molten metal into the thin opening, allowing more mass into the part, NPC used a unique "cone gate," also called a wedge gate.

To determine how the metal would cool, NPC used advanced solidification modeling software. This modeling technique allows the simulation of pouring, cooling, and expected shrinkage, saving the time and costs of evaluating such factors under actual production conditions. The modeling showed that the unique gating and tooling would promote optimum flow and cooling.

"The scalloped duckbill design lets us deliver closure machine speeds of up to 900 caps per minute," says White Cap Purchasing Manager Bill Callard. "And for our customers, the part reduces misapplications to just one in 100,000 jars."