How was the new Premium Sine Seal developed and how does it work?
An oil seal that has what it takes
Seals are often the weakest link in a gearmotor. These days more and more drives are run continuously for 24 hours a day and six days a week. SEW‑EURODRIVE, therefore, has developed a completely new sealing system in collaboration with the company Freudenberg. Dr. Markus Wöppermann and Eiko Filler respond to the most important questions.
A long-term and innovative partnership
Freudenberg Sealing Technologies GmbH & Co
Freudenberg Sealing Technologies GmbH & Co. KG is focused on innovation and accessibility to its customers – which makes it the perfect supplier and partner for SEW‑EURODRIVE.
Interviewee from Development
Dr.-Ing. Markus Wöppermann
Head of the tribology & sealing systems technology group, with SEW‑EURODRIVE for 7 years
Interviewee from Product Market Management
Dipl.-Ing. (BA) Eiko Filler
Product Market Manager Gearmotors, with SEW‑EURODRIVE for 24 years
"Our drive technology is the only one on the market with this sealing technology"
Was the Premium Sine Seal oil seal the first joint development from SEW‑EURODRIVE and Freudenberg, or is this a long-running collaboration?
SEW‑EURODRIVE has been successfully collaborating with Freudenberg for many years now. As early as 1994, our two companies developed a combined sealing ring for the output side of a gear unit. This sealing ring can now be ordered normally from Freudenberg's catalog under the name MSS1 (Modular Sealing Solution 1).
The new Premium Sine Seal oil seal, on the other hand, is produced by Freudenberg exclusively for SEW‑EURODRIVE. That is to say, our drive technology is the only one on the market that offers this innovative technology as an option.
Why was the Premium Sine Seal developed? What customer requirements made this new development necessary?
The reliability of a system depends strongly on the reliability of its drive technology. The requirements placed on the drive technology are becoming increasingly demanding. In the past, production areas primarily operated on a single-shift schedule. Nowadays, however, drives often operate on a three-shift basis, depending on the application. In general, this corresponds to 24 hour per day, six days a week, or up to 7000 operating hours per year. Under such demanding conditions, the seal is often the weakest link in the gearmotor.
Assuming a conventional sealing ring has a maximum service life of about 10 000 operating hours, it is quickly apparent that, under such conditions, this limit will be exceeded in just about a year and a half.
In addition to the number of operating hours, however, a seal's service life also depends on the application-specific strain to which it is subjected. Factors that determine this strain include the number of starts and stops, the rotational speed, the dynamics, changes in direction of rotation, the lubricant, the operating temperature in the gear unit and thermal overpressure within the gear unit.
The most critical location is the motor side, which is subject to high speeds and dynamics. We designed our new oil seal specially for this side of the gear unit for the seal on the input shaft. Regardless of the strain to which it is subjected during operation, in relative terms every customer can more than double the service life of their seal under ideal operating conditions.
How does a seal change over the course of these operating hours? What causes it to age?
As I mentioned earlier, that totally depends on the strains to which the gearmotor is exposed during operation. In addition to wear, the temperature also has a not insignificant effect. If it increases, the material, i.e. the elastomer from which the sealing ring is made, ages more quickly, becomes hard and loses elasticity. The result is that the sealing ring starts to leak and oil comes out. This process also varies depending on the lubricant.
Anyone who owns a car is familiar with this: When the wiper blades start to age and the rubber lips become harder and less pliant, the wipers no longer lie tight against the windshield. And these places where the material is not in close contact cause irritating streaks on the windshield.
Can't you just replace the faulty sealing rings?
In principle yes, but here again the example of a car is instructive. When the engine starts to leak oil after a few years, the workshop is happy: The seal itself costs only a few euros, but it is difficult to replace and costs can quickly rise into the thousands.
It's not much different for industrial gearmotors. By using the Premium Sine Seal, the time until the next required maintenance is nearly doubled. Therefore, it's to the user's benefit to employ this seal from the time the drive is purchased, just to be on the safe side.
"The sinusoidal shape of the sealing lip substantially reduces wear and thermal strain."
What is special about the new oil seal? What makes it so durable?
With a normal sealing ring, the actual seal is formed by a very fine straight line along the circumference of the shaft. The contact width on the shaft is therefore comparatively small.
With the Premium Sine Seal, this contact is not straight but rather follows a sinusoidal path on the shaft. This triples the effective contact surface on the shaft, which results in significantly better distribution of the heat generated in the sealing gap and reduces thermal strain by several times, which in turn slows the aging of the elastomer.
In laboratory tests, the sinusoidal shape of the sealing edge has not been found to cause run-in on the shaft. This means that when the seal is replaced, you do not need to replace the shaft and can install the new Premium Sine Seal on the old shaft in the same location.
Another feature of the Premium Sine Seal is that it does not require a tension spring. The stiffness of the membrane alone is sufficient to provide the radial pressure. Power losses from the Premium Sine Seal are thereby reduced by up to 45% compared to standard oil seals. This has a positive effect on the energy efficiency of the drive.
A significantly longer service life is achieved by reducing the wear per unit time by about half and improving temperature conditions at the sealing lip to slow the aging of the material.
But the sinusoidal shape of the sealing lip also has another positive effect: lubricant is exchanged all along the seal contact surface. If dirt particles or small metal particles are present, they are "pumped" out of the seal contact area, so to speak, and therefore do not disrupt the contact of the seal.
For which motors and applications is the Premium Sine Seal intended?
The benefits of the new oil seal over conventional sealing systems are especially evident in applications with high dynamics. That is why our first step is to make the new technology available for the CMP.. series of synchronous servomotors and the MOVIGEAR® family of mechatronic drives.
But we won't stop there. The second step will be to make the outstanding Premium Sine Seal technology available for asynchronous motors as well.
Have you received feedback from the field yet?
Drives with the new oil seals have only been on the market since the start of 2018. Several pilot customers have been using MOVIGEAR® units equipped with the new seal for about the last three quarters. As expected, there have been absolutely no complaints.
Nevertheless, we continue to run our long-term experiments in our test laboratory according to SEW 070040313. In these experiments, drives with standard sealing rings compete against the new Premium Sine Seals under extreme conditions far exceeding those that are likely to occur in real industrial use. They have been running for more than two years with excessive speed and maximum temperature.
One of the drives with a conventional seal is already exhibiting oil losses. The drives with the new sealing technology, on the other hand, continue to run without any problems. In total, we have observed over 400 000 hours of positive test results with the new system in the laboratory.
We are especially pleased that, on March 20, 2018, we won the "Industriepreis 2018" award for our Premium Sine Seal and were crowned the champions of the "Drive and Fluid Technology" category. This renowned industry prize is being awarded for the thirteenth time by the Huber Verlag für Neue Medien publishing house. This year we came out on top of the hundreds of other companies that also competed.
Freudenberg and SEW-EURODRIVE – A long-standing and innovative partnership
Freudenberg Sealing Technologies GmbH & Co. KG, based in the town of Weinheim in northern Baden-Württemberg, is by many accounts the worldwide leader for sealing system technologies and innovations. They are also responsible for the famed Simmerring® seal, developed in 1929. Today the company employs over 15 000 employees and has a large portfolio of sealing and damping technology, which they continually refine according to their customers' requirements.
Its talent for innovation and strong customer focus make it the perfect supplier and partner for SEW‑EURODRIVE. That's because we, too, pride ourselves on our accessibility to our customers. No matter how their processes and requirements may change, we always stay at the cutting edge of technology and offer our customers optimal and innovative solutions.
Freudenberg and SEW‑EURODRIVE have been collaborating on development projects for more than 60 years and continue to set new milestones in drive sealing technology.