January 19, 1998 Design News
FASTENING, JOINING, & ASSEMBLY
Latch holds key to clean air
Design helps McDonald's control
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
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
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
Incorporate a 1/4-inch grip range to ensure a tight
Withstand abuse of high-volume fast-food store.
Include a head design that accomodates special-tool
Meet both UL fire and safety regulations.
Be cost competitive.
Original latch complications
Too light a shaft that might succumb to abuse.
High cost due to use of custom component.
Difficult assembly caused by problems with pawl
Larger, more robust shaft.
Self-fixturing assembly that automatically locates
pawl correctly, easing assembly.
Use of all standard components, reducing cost by
Access hardware evolution
Integrating materials technology
with industry trends
John Fauerbach, Director of Engineering
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
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
Modifications. More and more of the
latch and access-hardware business involves custom development.
Southco engineers are ofte