Sealing technology increases plant and process reliability

The service life of driven tools has a significant influence on the overall equipment effectiveness of machines. Sophisticated sealing technologies play a key role.

The influence on process reliability of sealing technologies used in driven mold systems is often underestimated. When tool holders were still predominantly externally cooled, the problem was manageable. With the advancement of cutting tool technology, more and more reliance is being placed on internal cooling technology. For the technology of driven tool systems, this means that the cooling emulsion must reach the internal cooling channels through a rotary union.

If you consider that machine tools run in concatenation or that there are machines that operate with three tool carriers, it becomes clear: The process reliability of tool systems plays an important role. The more driven tools are operated in a machining unit, the greater the risk that one of them will fail. As a result, the entire manufacturing cell comes to a standstill. Sealing units are often the Achilles' heel of the tool systems.

 

Sealing technology at EWS: On the way to a suitable solution

The topic of sealing technologies is nothing new, even decades old. However, today's requirements pose a whole new challenge to them. The influencing factor of sealing technology is reaching a significant importance. This is also clearly reflected in the development sprints of EWS Tool Technologies.

"With the introduction of EWS Matrix Seal technology, we got a solution that guaranteed 25 bar for the seals over the entire speed range of our machines," says Lorenzo La Rosa, Team Leader Application Engineering at DMG MORI Management GmbH. If more pressure was needed, additional rotary unions were available. With good emulsion quality, these could provide pressure resistance of up to 70 bar, which was necessary for the requirement profile of the high-tech machines.

The quality standard of the machines is very high, as they often work at the limits of what is technically possible - and usually around the clock. However, one problem was always present, explains Lorenzo La Rosa: "Whether EWS Matrix Seal or other sealing technologies, they all require the oil portion of the emulsion to lubricate the sealing lip or surfaces." Even a dry-running run-in process thus runs the risk of causing initial damage to the seal set. Using a dry-running technology instead is not a sensible alternative, as it is up to five times more expensive.

The challenge: On the one hand, the new rotary feedthrough technology was to reliably control pressures of up to 70 bar in a straight mold unit without an offset output spindle. On the other hand, it had to be capable of unrestricted dry running and be compact - and of course economical. "It was the interaction of the various influencing variables that first had to be analyzed. Frictional forces, hydrostatics, component geometries and manufacturing technologies had to be optimized and coordinated," says Michael Wiesenberg, project manager for sealing technology at EWS.

 

EWS HPC-Line: Novelty on the market for maximum process reliability

The result was the EWS HPC-Line (High Pressure Ceramics). At the heart of the ceramic-based cartridge sealing unit, which consists of several parts, are two coaxially mounted ring elements that float in the interior. When the tool system is used, the sealing elements contact the tangential flanks of the carrier system within milliseconds. During this process, the sealing elements stand still and seal against the rotating carrier system in frictional contact.

Polished running surfaces and a geometrically optimized pressure chamber reduce the frictional force* (Fr = µ x Fp) to a minimum, thus creating the prerequisite for transmitting up to 100 bar of pressure - at speeds of up to 12,000 rpm. The minimum leakage that occurs during the seal closing process is dissipated pressure-free on the machine side via an expansion chamber.

"Maximum process reliability in our technologies is one of the basic requirements for us, which we can use a bit more effectively with the EWS HPC-Line," says La Rosa. Nowadays, machine tools offer outstanding quality and great kinematic as well as dynamic possibilities. It is now important to recognize and optimize other influencing variables in order to increase the productivity level of the machine tools and ensure process reliability.

"It is precisely this knowledge that drives our development thinking and our product strategy," says Hüseyin Sivaz, sales manager at EWS. "Our sealing technology as well as our new gearboxes with polygonal power transmission in the area of angle heads are guarantors for an extended service life." Also not to be neglected, he adds, is the efficient remanufacturing drive provided by the EWS Varia quick-change system, true to the motto "Pit stops are where you win races."

 

* Fr = Frictional force | µ = Friction factor | Fp = Compressive force