They make seals big deals

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 million today.

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 produced daily.

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 says.

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 specifications.

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."

Seal lingo

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 definitions:

Seal: Any device that prevents the passage of a gas or liquid.

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 assembly.

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."