January 19, 1998 Design News

FASTENING, JOINING, & ASSEMBLY

Latch holds key to clean air

Design helps McDonald's control pollution

Deana Colucci, Associate Editor

Concordville, PA--McDonald's covers the world. But what it doesn't want to do is cover the world with dirty air. For this reason, the giant fast-food chain called on United Air Specialists (UAS; Cincinnati, OH) to develop a custom air cleaner for its restaurants.

Called the Universal SMOG-HOGr, the all-stainless-steel, hood-mounted cleaning system fits into McDonald's standard kitchen equipment above a fryer or grill. It uses electrostatic precipitators to remove grease and other particles from the cooking process before they enter the store's ductwork and the outside air.

But the story doesn't end here. UAS called on its long-time partner Southco Inc. for help in designing a key element of the system: the latch.

Access doors on the front of the unit allow workers to clean internal components of grease and others debris, a process that can occur daily in McDonald's high-volume stores. The Southco latch had to withstand this frequent use, secure and seal the doors, and meet stringent UL fire and safety requirements. And it had to accomplish this at a competitive cost.

Taking the first step. Southco's line of E3 Vise-Actionr compression latches seemed perfect for the project. The latch's head design features special-tool access and requires a key for entry. The key prevents individuals not qualified to service the equipment from gaining access. And it can't be easily replaced by a screwdriver or common tool.

The latch also can apply up to 6.4 mm of consistent pressure to compress EMI or environmental gasketing. "The latch can pull down a gasket up to 1/4 inch, which gives us a good tight seal," says Neal Clevenger, product development engineer at UAS.

Moreover, the device allows quick and easy access, and provides perpendicular compression that helps eliminate rattle and won't scratch the cleaning system's frame. How? The latch first rotates 90 degrees, then pulls directly in, so there is no forcing the gasket closed, explains Clevenger. "The person closing the latch doesn't have to push the door and overcome the compression. Instead, the latch does all the work," he says.

Cleaning up the act. Even with all these features going for it, the E3 Vise-Action latch didn't quite fit the bill. In fact, Southco and UAS engineers determined the cleaning-system application would push the latch to its limits.

"The shaft, which serves as the main load-bearing member, was a little too light," notes Clevenger. "It would work fine as long as people didn't abuse the system. But we saw a potential problem down the road."

Another issue, Clevenger admits, was that the latch was a little more expensive than anticipated. Plus, manufacturing found that assembling the latch to the cleaning unit was difficult because the pawl didn't always locate properly.

Southco engineers immediately went to work to modify the existing latch. "By lengthening the shaft slightly and using a standard pawl, we achieved the optimum grip range and maintained the requested 'envelope' dimension," says Kevin LaValley, engineering technician, Product Specifications, at Southco. From concept drawings to prototypes, Southco turned the project around in about four weeks.

The new version features a larger, more robust shaft that easily withstands daily abuses. Southco also added a self-fixturing assembly, with double-D flats on the shaft that ensure the pawl fits correctly. That translated into less work in manufacturing.

Better yet, the new design delivered an unexpected cost savings. Minor modifications to the original E3 latch to obtain a UAS-specified dimension had required custom manufacturing, significantly elevating the cost. With the new version, made entirely of standard components, UAS realized a cost savings of 12%. "I expected the cost to go up slightly since I asked for heavier components," Clevenger recalls. "We thought it would end up being more of a specialized latch.

"In the end, we got a latch with heavier components for a reasonable cost savings," Clevenger adds. "And it's easier to assemble, saving time in the final assembly."

Latch criteria

Original latch complications

Design solutions

Access hardware evolution

Integrating materials technology with industry trends

John Fauerbach, Director of Engineering and Technology Southco, Inc. Concordville, PA

As telecommunications, electronics, computer, automotive, transportation, and other major industries face new challenges, a vast pool of creative opportunity opens for hinges, latches, and captive hardware. New products and applications are being developed from the innovative use of materials and the integration of new technologies, with a sharp eye for continuous improvement of products and processes.

Some of the current needs of Original Equipment Manufacturers (OEM) include latches that aid in the management of electromagnetic shielding, latches that withstand high levels of UV exposure, and some that resist a variety of chemicals or cleaning agents. In addition, everyone today expects shorter development-cycle times and a high value-to-cost ratio.

There are many factors influencing the access-hardware industry today--let's consider some of the key trends.

Design and production trends

Cycle times. From a product-development standpoint, reduction of development-cycle times continues to be a priority for OEM designers and for our engineers at Southco. Throughout industry, the constant pressure to shorten the cycle time of the development process is driven by the need to respond as quickly as possible to changing demands and expectations from the market. Along with the question, "Can you design a new latching system for our server?" come questions like: "How quickly can we see a prototype?" and "How soon can you deliver full-production quantities?" In response to these ever-increasing demands, Southco employs the latest CAD and rapid prototyping technologies that enable us to take a concept to a physical model in a matter of days.

Continuous improvement. Good quality is a given throughout industry. Everyone expects to have 100% on-time delivery of high-quality parts, all the time. The big news is continuous improvement. Companies must constantly work on ways to improve their own processes, not just in the engineering development arena, but in order entry, manufacturing operations, product delivery, and customer service.

Continuous improvement requires that we first understand, and then respond to, the evolving expectations of our customers. In some cases, our customers need a variety of options on the same basic product. For example, a customer might require the same latch or hinge in a variety of colors. This drives us to increase the flexibility of our production process in terms of turn-around time and lot size manufactured.

Environmental considerations. The end use of a latch--the environment that the fastener is operating in--must be understood at the very beginning of a project in order to yield an optimum design solution. Electromagnetic shielding is an important design consideration for electronic enclosures and the telecommunications industries. Resistance to salt spray is commonly needed for outdoor or marine applications. Resistance to UV light exposure is another frequently encountered specification in outdoor applications.

Plastics. In many cases, plastics, particularly injection-molded plastics, are being used in place of traditional metal components. The design freedoms offered with injection molding are far greater than with traditional metals, and in many cases, strength is not an issue. The environment of the plastic application is also important. In some applications, plastic is more durable than many metals (e.g. salt spray exposure). While the physical properties of plastics continue to improve, metals clearly have the upper hand when high strength is a primary requirement.

Simplicity. Another trend in access hardware supports the development of overall product simplicity. For example, using plastic-injection-molding techniques, a single latch component may perform the functions formerly carried out by three, four, or even five separate pieces. While this increases the complexity of the individual part, it simplifies the overall product design. This greatly improves the design for manufacturability and assembly and usually will yield a lower total manufacturing cost.

Modifications. More and more of the latch and access-hardware business involves custom development. Southco engineers are ofte