Article first appeared in Power Transmission Engineering blog on November 14, 2017.
Freudenberg Examines Sealing Requirements for Heavy-Duty Equipment
The seals and the hydraulic systems of any piece of mining, construction, agricultural or other heavy industry equipment operate under extreme conditions. Variable temperatures, aggressive hydraulic oils, dust and extended periods of operation place seals and their tribological systems under continuous duress. A new generation of material, 94 AU 30000, expands the boundaries for polyurethane use. This innovative compound can be used in standard cylinder applications where higher pressures, larger extrusion gaps, reduced internal friction, improved hydrolysis resistance and compatibility with bio fluids, among other factors, are important. DMRW2 hydraulic wipers made from 94 AU 30000 and sheet metal and the availability of this polyurethane as part of Freudenberg Sealing Technologies’ Xpress rapid replacement part service are applications discussed in the following article.
Today’s extreme environmental climates place extreme demands on the material and structure of the hydraulic seals used to maintain the performance and operation of heavy-duty equipment. The excavators, tractors, backhoes and tunnel boring machines that grind through the earth every day must work harder, longer, cleaner and more cost efficiently than ever to feed the plant, build its infrastructure and harvest its natural resources.
Sealing requirements for these machines must now include high values for tensile strength and elongation at break, resistance to oils and ozone, high elasticity and abrasion resistance. Polyurethane materials (PU) have traditionally met these industrial requirements. In comparison with elastomers, PU has a four times greater capacity for mechanical resistance, as well as outstanding resistance to ozone. At the same time, it stands up well to the stresses of mineral-based fluids.
But a standard PU seal is also subject to severe wear depending on the environment to which it is exposed. Seals operating in cold climates must have different performance attributes than those working in hot, tropical environments. In addition, the increased use of leased equipment in the heavy-duty sector necessitates seals that can perform over much longer periods of time because of continuous equipment operation and longer maintenance cycles.
Up until now, heavy equipment manufacturers have traditionally stocked a wide variety of hydraulic seals made of different PU formulas to meet a diverse range of applications. Seals made from Freudenberg Sealing Technologies’ 94 AU 30000, however, can handle the vast majority of these application requirements, thus eliminating inventory complexity, while providing superior performance compared to standard PU seals.
Freudenberg Sealing Technologies’ 94 AU 30000 offers excellent performance in heat and cold and can be used in mineral hydraulic fluids at temperatures ranging from -31°F (-35°C) up to 250°F (120°C). It can also be used in biodegradable media. The material is more resistant to water and synthetic hydraulic fluids and withstands major temperature fluctuations better than other existing polyurethane materials. 94 AU 30000 also offers protection against damage from hydrolysis. This new polyurethane material, in fact, meets the market’s requirements for potential universal use.
Significantly, 94 AU 30000 is highly effective when used to produce seals that come under extreme pressure. Test results indicate that 94 AU 30000 withstands 45 percent more pressure than the best material in the same class – 7250 psi versus 5000 psi. Tear strength under such punishing conditions is 61 percent higher than other PU materials. In a comparison test at 40 MPa and 100°C with large extrusion gaps, the seals made from this new generation of material show no appreciable signs of wear while conventional seals fail prematurely. This increases service life and resistance to wear. This means that cylinder makers can allow for nearly double extrusion gaps for the same operating conditions, reducing production costs. Or alternatively, significantly greater loads can be accommodated at the same gap width. Especially in construction equipment under severe stresses, this avoids potential damage when the pressure peaks.
94 AU 30000 functions three to five times longer in mineral oils than standard PU materials and shows no shrinkage or swelling. It functions up to 10 times longer in biodegradable fluids under humid conditions. Extensive compression set, tensile strength and tear strength testing demonstrates that 94 AU 30000 performs better than any current standard material being used in both Europe and North America.
One of the latest developments to incorporate 94 AU 30000 is a heavy-duty, double-lip dirt wiper, DMRW2, with a metal can that has a protruding wiper lip. This hydraulic wiper also includes an integrated pressure relief function for increased reliability. This extremely durable solution is easy to install, reduces dirt penetration to a minimum and is designed for any hydraulic cylinder based on ISO 6195 Type B. The DMRW2’s range of applications includes earth-moving and agricultural equipment, loading ramps and positioning cylinders and industrial vehicles and presses.
While impurities appear with a standard double wiper even after 1,400 double strokes, none can be detected after 17,000 double strokes in wipers made from 94 AU 30000 due to improved wiper function. An integrated pressure relief channel provides additional security. The DMRW2’s pressure relief function is achieved through strategically positioned holes around the internal lip which assist in achieving pressure relief and ensure that the internal wiper lip function is not interrupted. The wiper can subsequently reduce the hydrodynamic oil film thickness on the rod with optimum efficiency, creating a leak-free sealing system.
DMRW2 wipers made of 94 AU 30000 benefit from the material’s high wear and chemical resistance for an optimal seal lifespan. In addition, the wiper and internal lip geometry were designed with the aid of FEA software to insure a leak-and contamination-free system even under the harshest working conditions.
A Rapid Seal Option
In today’s aggressive economic environment, companies cannot afford extended downtime when a machine seal needs to be replaced. The availability of rapid replacement parts, prototypes and small-production-run seals have become crucial to heavy-industry customers. Freudenberg Sealing Technologies launched its own rapid replacement service in the Americas 10 years ago. Freudenberg Xpress has traditionally provided high quality, custom engineered, cost effective replacement seals from original materials and profiles in as little as a day. Xpress produces customized seals as a single piece or in economic small batches.
Recently the organization began stocking the largest billet range of 94 AU 30000 available in the region to take advantage of the material’s unique properties in the replacement part industry. With the addition of 94 AU 30000 to its portfolio, Xpress customers no longer need to buy different materials to meet unique sealing performance requirements. Virtually any seal can be made from this new material. Older equipment, in particular, can benefit from 94 AU 30000’s mechanical and chemical characteristics that accommodate almost double extrusion gaps and from its significantly extended lifespan at temperature that can fluctuate from extreme cold to extreme heat.
The high demands placed on today’s heavy-duty industrial equipment leave no margin for error. Companies must rely on continuous operation at optimal flexibility and performance to maximize work schedules, capabilities and profits. While seals made from standard polyurethane materials have functioned well in the past, new environmental challenges – extreme locations, greater temperature and pressure fluctuations, leased equipment and longer maintenance cycles, among others – have driven the need to develop a next generation of industrial materials. 94 AU 30000 is an alternative to standard PU options across an entire range of seals.
Steven Cowell, Martin Goerres and Bernd Luckhardt
Freudenberg Sealing Technologies
For more information:
Freudenberg-NOK Sealing Technologies
Phone: (734) 451-0020