Without them, much of the industrialized world comes to a halt--process
equipment stops, airplanes refuse to fly, and machinery crashes. Seals are the
unsung heroes of advanced technology. And Greene, Tweed knows how to make them.
"We understand materials, and how they perform under extreme temperatures and
pressures--that is one of the things we do very well." says Phil Paino,
president of Greene, Tweed & Co., a seal manufacturer headquartered in
Kulpsville, PA. This understanding shows. The 135-year-old sealing company grew
an average of 20% during each of the past 10 years. The division, dedicated to
the semiconductor industry, has increased more than 30% within each of the past
four years. Total annual sales--only $4 million 30 years ago--are well over $100
Such remarkable and sustained growth is unusual for a business that started
in 1863. What accounts for this? "Attention to our customers and our markets,"
says Paino. "In the late '80s we asked ourselves, "in what aspects of our
business do we really excel?" The answer: high performance, state-of-the-art
sealing-related products. At this point, the company made a conscious effort to
address the needs of industries where high performance is critical, such as
semiconductor equipment, aerospace, CPI, oil field equipment, and mobile
equipment. "We focused on developing products that meet the increasing
technological demands of these industries, providing sealing solutions where the
cost of failure far exceeds the cost of the right seal."
A prime example is CHEMRAZ®, a proprietary, Greene, Tweed
perfluoroelastomeric compound that "offers the broadest chemical, and now the
highest temperature resistance, of any elastomeric material," says the
compound's inventor, Harry Amin. According to Amin, seals can be comprised of
both plastic and elastomeric components to meet specific performance
requirements, including chemical resistance, corrosion, thermal effects, and
pressure, among others. Manager of elastomeric research and development for the
company, Amin says that raw elastomer is of no use to the sealing industry
because it has no useful basic properties. It has little strength, and cannot be
made to form an effective seal. Amin experimented with combinations of
elastomers, plus a variety of additives and processing parameters. After much
iteration, the first CHEMRAZ compound was developed.
This compound became the foundation for the fastest-growing segment of the
company: the semiconductor equipment manufacturing industry. There, seals are
critical to equipment that fabricates computer chips. "With companies like Intel
continually putting out smaller circuitry, contaminants become a serious
threat," says Robert Saylor, manufacturing manager. "A single wafer can cost
$250,000 or more. If contaminants--measured in parts-per-billion--are excessive,
volumes of chips can be rendered useless." Until comparatively recently, a lot
of companies didn't realize that seals could be a significant source of
contamination. Seals became increasingly important as photolithography produced
smaller and smaller circuits, he continues.
Greene, Tweed pioneered the use of a clean room for the express purpose of
producing seals clean enough for the semiconductor industry. In a class-1000
environment, with fully integrated class-100 workstations, numerous seals are
Besides semiconductors, the ISO 9001-certified company targets four other
industries: chemical processing, industrial hydraulics, aerospace and defense,
and oil field equipment. New CHEMRAZ products released in April, CHEMRAZ 615 and
653, perform at very high temperatures. "Both compounds retain excellent sealing
properties at temperatures up to 615F," says Amin. This makes them particularly
useful for "down hole" oil field applications, where aggressive gases exceed
25,000 psi pressure, and temperatures exceed 500F. They are also appropriate for
high-temperature applications in semiconductor manufacturing and CPI. Amin says,
"These are the highest-temperature sealing compounds currently on the market."
CHEMRAZ 615 O-rings resist attack by nearly all chemical reagents, including
inorganic and organic acids, alkalines, ketones, esters, aldehydes, alcohols and
fuels. They also demonstrate excellent resistance to steam and hot water, and
resist swelling and embrittlement while retaining their elastomeric qualities.
CHEMRAZ 615 O-rings are easily installed, conforming to irregular sealing
surfaces (resulting from assembly wear) better than metal seals. Unlike PTFE
seals, CHEMRAZ O-rings do not cold flow, or cause shaft fretting, the company
Small, but mighty. Seals are important to just about every
industry. Nearly 4,000 Greene, Tweed seals help keep the Space Shuttle Orbiter
flying. The Stealth fighter, the French Rafale, the Eurofighter, and the
commercial jet you fly on your next vacation or business trip all use Greene,
Tweed seals. The company provides landing gear and hydraulic system seals for
90% of the world's commercial and military aircraft. Manufacturers of
compressors, fluid-power equipment, and brakes and axles rely on Greene, Tweed
seals to produce zero leakage and long-term durability. Polyurethane rod seals,
buffer seals and wipers, GT rings, and energized MSE seals meet those
The company caters to the custom requirements of smaller businesses as well.
At Milwaukee Valve in Wisconsin, engineers needed a seal to withstand high
temperatures and pressures for a steam valve application. Greene, Tweed
developed a new material made from graphite and Teflon® to manufacture the
required part. "They worked out real fine," says Terry Malius, Milwaukee Valve
plant engineer. "We haven't had one reject in the four years I've been here."
A family trait. Attention to changes in technology is
inherent to the company. In 1863, brothers John and Ashton Greene, in
partnership with Henry Tweed, founded Greene, Tweed & Co. Originally a
merchandising company dealing in wholesale hardware and mill supplies, Greene,
Tweed quickly expanded into leather seals and belting, harnesses, buggy whips,
and related products. Forty years later, when the company incorporated, there
was a large demand for high-quality packings. The company met that demand,
producing Palmetto® brand braided packings. Palmetto Packings are still made
today by wholly owned subsidiary Palmetto Inc. (Denton, MD).
Despite its phenomenal growth, the old-fashioned family atmosphere initially
instilled by the founding fathers still permeates Greene, Tweed's corridors and
offices. Even with a recent influx of new employees, added to accommodate rapid
expansion, the plant manager still greets each one by name; they respond in
kind. Even more impressive, Chairman Michael Delfiner knows many employees on a
first-name basis as well.
"Most of our employees know each other well," says Manufacturing Manager
Saylor. "The average person working at Greene, Tweed today has a seniority of
more than 20 years. It's hard to find anyone in Kulpsville who doesn't have a
friend or relative here. We don't always advertise for employees--they just come
to us. And they stay."
They stay because the company considers each and every employee to be a
valuable resource. For example, when Greene, Tweed decided to build its first
clean room, it brought in people from the elastomer production area and taught
them to operate in a class-100 environment. "We hired from within," says Saylor,
"instead of bringing in people who were already trained. There is a lot of pride
here because of that."
Today, Greene, Tweed offers more plastic and elastomer compounds than any
other company in the world, says Paino, together with the broadest selection of
seals. "A wide variety of problems requires a wide variety of solutions." In the
past, when a customer had 20 different problems, there might be only two
possible solutions--because the number of available products was severely
limited. He adds, "One of our major challenges was letting customers know that
we could offer them a wide range of sealing solutions." The company now designs
parts to meet highly specific needs, also offering complete sealing systems.
Greene, Tweed now finds itself in the enviable position of having less direct
competition than it did 10 years ago. "Many of our competitors, have gone the
route of offering standardized products in order to gain the benefits of
higher-volume production runs," says Paino. "This strategy does provide lower
manufacturing costs and lower product prices. Frequently, however, standard
products fail to perform satisfactorily in applications having non-standard
requirements. In these instances, the lower-cost seal does not provide the
lowest-cost solution. Providing products that perform in non-standard,
high-performance applications is where Greene, Tweed excels," Paino adds with
un-masked pride. "Our goal is simply to solve the customers' problems. And as
engineering requirements evolve, we will continue to satisfy them."
The making of a clean room
Employees make the lucrative white CHEMRAZ for the semiconductor industry in
the company's Class 100 clean room area. "Most surgical rooms are only a
class-100," points out Robert Saylor, manufacturing manager of Green, Tweed's
Fluid Handling group.
While designing a pristine environment in the middle of an active black
elastomer manufacturing area was not easy, the major engineering challenge was
room. "We needed to capitalize on space," says Saylor. "We built a miniature
factory in a 5,800-sq ft clean room, surrounded by 100,000 sq ft of
manufacturing." To keep contaminants out of the product, everything from batch
weighout to class-100 packaging is done within the confines of the room.
Engineers miniaturized all the processes and related equipment associated in
the making of seals, says Saylor, such as the air hose used to unload the parts
from the molds and the cutters used to trim excess from finished parts.
Greene, Tweed even designed and built several of its own machines. A stretch
trimmer, for example, holds long, thin ropes of white CHEMRAZ taut, while an
inspector smoothes rough edges with a pencil-like sanding tool.
Multiple HEPA filters extract particles as small as 0.5 microns from the air.
"We had no model to follow," says Saylor. "It took a long time to design and
build the facility; once we had equipment in, there was a lot of trial and
error." For example, clean room employees found out that they couldn't use latex
gloves because they got caught in the machines.
Saylor looks around and even he is awed. "You know, carbon black has always
been a staple of the seal industry--and those who use it know that it gets all
over everything around it. Twenty years ago, this place was virtually covered
with it. Today, it's absolutely spotless."
"Talk about the circle of life," he adds, "the computer we use inside the
clean room was made by one of the companies we sell seals to so they can
manufacture semiconductors for computers."
As with any field, specific terms can mystify the uninitiated. To help take
the mystique out of picking a seal, here are a few of the more common sealing
Seal: Any device that prevents the passage of a gas or
Breakaway friction: Frictional force required to start a
body in motion over a surface.
Breakout friction: See breakaway friction.
Diametral interference: Difference between the I.D. (inside
diameter) of the seal and the shaft diameter, or between the O.D. (outside
diameter) of the seal and the housing diameter.
Extrusion: Displacement of part of a seal into the extrusion
gap under the action of fluid pressure or thermal expansion.
Extrusion gap: The clearance on the low-pressure side
between components which confine the seal.
Interference load: Pressure loading which arises at the
surface to be sealed, caused by deformation of the seal material during
Inter-seal pressure: Fluid pressure that may, in some
circumstances, arise between two seals fitted to a double-acting piston.
Kinetic friction: Minimum frictional force required to
maintain a body in motion sliding over a surface.
Radial interference: Difference in dimension between the
radial section of a seal and the radial space into which it is installed.
Running friction: See kinetic friction.
Squeeze: The deformation of a seal caused by the difference
in dimension between the seal and the space into which it is installed.
Static friction: See breakaway friction.
Stick-slip: The jerky motion of one surface when it is
dragged across another surface.
Stiction: The increase in static friction, which occurs with
time, of stationary contact of a seal.
For more terminology, see Greene, Tweed's "The Right Seal, Your Guide to
Sealing in Semiconductor Processing."