Exotic they may not be,
but gaskets and seals are important in appliance assembly. Without
proper
gaskets and seals, one could have liquid leaks—think washers
and dishwashers—and gas leaks—think refrigerators and air-conditioners.
Gaskets and seals help in the opposite direction as well—by keeping
rain and snow from critical parts of outdoor appliances. They are also
important in noise reduction and in shielding EMI/RFI emissions.
Among gaskets and seals applications
mentioned by Joe J. Bruce, vice president and general manager at Automated
Gasket Corporation (Kirkwood, MO, U.S.) are air-conditioning compressors
and HVAC sealing, small engine sealing, and control valves and switch
sealing. Other appliance applications include fiber-based materials
for sealing of internal valves and mechanisms, plastic tape with die-cut
holes for sealing around control knobs, and a large variety of die-cut
washers for sealing of lids and spouts.
“An interesting application
we completed recently involved the development of tooling and feed
systems to cut-to-length and notch a half-circle into an extruded shape
for application in a dollar bill changer for vending machines,” he
says.” This is an example of one of the rare instances where
we are not die-cutting a flat material.”
| Good
seals are important on appliances such as dishwashers and clothes
washers that work with water. This is a top door seal from a
top-loading dishwasher made by German appliance producer Miele. |
 |
Gaska
Tape Inc. (Elkhart, IN, U.S.), provides PVC (polyvinyl chloride)
foam tapes and gaskets. “They are used in any application to
seal out air, moisture, light, and dust,” points out Sales
Manager Rica Holtzinger. “They also provide sound deadening
and insulation. In HVAC applications, our products can be used around
service/access doors for sound deadening and sealing. Under compressor
mounts they can supply damping and cushioning, while behind a motor
they supply vibration damping and sealing. Another HVAC use is between
two sheets of metal for damping and heat resistance.”
High
Heat Evolution
Gaskets are a critical application
for ovens and range doors. Many of these gaskets are silicone rubber.
However, in self-cleaning ovens, which can get up to 900°F, a silicone
gasket would be inadequate. “What is available today is a fiberglass
and stainless knit 304 stainless steel bulb that is overbraided with
fiberglass,” says Rick Schleef, director of Sales of Davlyn
Manufacturing Co., Inc. (Spring City, PA, U.S.). “Earlier,
door construction used two pieces of steel. The gasket was tadpole
shaped, with the ‘tail’ captured between the steel pieces
and affixed to the door. But in order to save money, most manufacturers
have gone to one-piece doors. That asked us and other suppliers to
develop an alternative gasket to affix to the single piece door. We
came up with wire-formed diamond shaped clips of 304 stainless that
are braided into the structure of the gasket. The method is proprietary
and patented. The clips are pushed into holes that are pre-drilled
in the oven door. Assembly takes just 15 to 20 seconds.”
He adds that each gasket
is custom made for the application. “The oven manufacturer relies
on the gasket manufacturer to develop the proper design. We work with
each new platform as it comes up, looking at such things as diameter,
compressive strength, and layout. The gasket makes a difference in
how much heat leaks out the door, and how hot the door gets.”
Material
Changes
Heat is a broader consideration
than just in oven doors. “Products today are getting smaller
and hotter, so we have started to use more materials that can stand
higher heat, are thinner and softer,” observes Rachel Magee,
marketing coordinator at LGS
Technologies (Dallas, TX, U.S.). “We’ve seen materials
evolve into compression set resistant, and have higher flame ratings.”
Reed Rubber Co. and Reed
Rubber Products (St. Louis, MO, U.S.) supply molded, die cut, and extruded
parts to the appliance market. “For years, the market has been
dominated by traditional thermoset rubbers,” observes Nelson
Reed, co-president. “We view the appliance market as primed for
a conversion to a co-processing of thermoplastics into composites for
improved functionality at a lesser cost. The functional applications
include improved tensile memory, sealing in fluid environments, compression
set, and part weight reduction.
 |
Here,
a high-temperature gasket is being installed in the corner of
an oven door. Photo courtesy of Davlyn
Manufacturing Co. |
“New TPEs continue
to come on the market and, combined with the use of high-speed automation,
make high-volume rubber parts used in the appliance market an ideal
conversion,” Mr. Reed adds. “The greatest opportunity as
we see it is in redesigning multiple components into a single component
using the broad range of TPE materials and available processes. This
can be achieved through insert molding or two shot molding. However,
due to mold cost, these methods are ideally suited for medium to high
volume parts.”
“New materials become
available from our suppliers on a regular basis,” observes Mr.
Bruce of Automated
Gasket. “In the area of fiber-based materials, new technology
has led to the development of materials with superior sealing performance
at lower flange pressures. These materials are available for a wide
range of applications and temperature ranges. One supplier has developed
a combination of fiber material with polymer edges applied to selective
openings for improved sealing in unevenly loaded joints, with the ability
to apply different polymers in the same gasket where multiple working
fluids are used.”
Formed-In
Place
An alternative to a die-cut
gasket is one that is formed-in place. “Our formed-in-place gaskets
provide appliance producers the fastest and easiest way to automate
and assemble gasketed parts,” asserts Clai Bachmann, vice president
of Marketing for Dymax
Corp. (Torrington, CT, U.S.). “Our UV-curable resins are
unique products in that they can be applied and cured in seconds. Unlike
other FIP products, these gaskets completely cure with UV light and
require no additional heat or moisture to cure, so no delays nor special
ovens nor humidity control are required.
“Automated equipment
can dispense the gasket in any configuration in seconds,” she
continues “This process eliminates quality problems, labor, and
inventory costs associated with precuts. In addition, form-in-place
gaskets allow the engineer to quickly change the design of the gasket
or opening without waiting for months for a prototype precut.”
Ms. Bachmann notes that the
gaskets are particularly useful for applications requiring sound dampening
as well as closure. For example, their use in speaker design resulted
in higher tonal quality due to their reduction of sound diffusion from
the speaker cones into the surrounding materials of construction.
Master
Bond Inc. (Hackensack, NJ, U.S.) has developed two liquid one-component,
100-percent reactive elastomer compounds with properties especially
for form-in place sealing and gasketing applications. The company’s
Polymer System UV21 is a liquid one-component UV curable urethane
elastomer compound. It cures essentially upon demand when exposed
to a source of UV light emitted at 320-365 manometers. The Sil 711
compound is a one component, non-corrosive type, flowable silicone
elastomer compound that solidifies within as little as 2-3 min at
ambient temperatures and then achieves full cure quickly.
They do not contain any solvents
or other volatiles. The cured elastomer compositions exhibit flexibility,
physical strength properties, electrical insulation properties along
with long-term resistance to water and other hostile environments.
Additionally, these products can be stored at ambient temperatures
for as much as 6 months and reportedly show very low shrinkage upon
cure.
Liquid
Control Corporation in North Canton, OH, U.S., reports its gasket
and seals are used in glass ceramic cooktops, refrigeration systems,
seals for air filtration, washer transmissions, and furnaces, among
other applications. It is now working with UV material gaskets. Brad
Smith, business manager for Composites/General Assembly, says “They
are easy to process, and UV materials are more economical to use
for gaskets and seals.” Among the applications for its Posimeter
FR meter, mix, and dispense machine is a wine storage unit from Sub-Zero
Freezer Company, Inc. (Madison, WI, U.S.). The machine dispenses
seals for the doors, which have UV-resistant glass.
Bringing
Music Control Outdoors
Audioaccess, a division of
Madrigal Audio Labs (Middletown, CT, U.S.), wanted to extend the capability
of its popular multi-room audio system to allow keypad control from
an outdoor location (e.g. patio). The keypad contains sophisticated
circuitry and eight pushbuttons to select and control audio sources
(e.g. tuner, CD, tape), and for volume control and on/off. In addition,
each keypad contains status LEDs and an infrared receiver to control
the system from a handheld remote.
| Figure
1: The single piece silicone rubber keypad seal is located in
the middle. |
 |
To make the keypad weatherproof,
Audioaccess needed a transparent seal that would permit reading the
legends on the buttons, facilitate through-seal operation, be easily
integrated into the keypad design, and be mounted to a standard outdoor
electrical box. APM
Hexseal (Englewood, NJ, U.S.) designed a single-piece, crystal-clear,
precision-molded silicone rubber seal that nests neatly into a perimeter
groove of the keypad’s front plate assembly (Figure 1). This
pliable, UV-tolerant seal permits easy viewing of the keypad legends
and operation of each button through the seal. It has tolerance to
weather/dust, and has molded-in recesses for the mounting screws (Figure
2).
 |
Figure
2: Detail of the seal shows molded-in recesses for mounting screws,
and a shape that fits into the control’s perimeter groove. |
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