All common drive technologies have their advantages and disadvantages and should be used according to individual requirements. With an isolated view, one quickly hits technological limits especially in complex projects. Using the example of a comprehensive customer project, we were able to demonstrate the value of thinking across technologies when optimizing the hydraulic machine process. Even more so when it comes to one of our most loyal and longest standing customers.
Increased power and accuracy, maximum energy efficiency – the optimization of a blow-molding machine as a prime example of a combined drive solution.
Optimization of a blow-molding machine for bellows.
Increasing locking forces, faster cycle times and ever larger and lighter products – the global polymer processing of auto components puts ever higher demands on the processing technology used.
As early as 1995, a market-leading manufacturer of blow-molding machines for bellows and shock absorber applications commissioned us with a drive concept for a unit type. Exactly 20 years later, the optimization of the hydraulic system in use took place. Due to the poorer energy balance compared to today’s standards, and the new specifications for wall thickness control, it was decided to operate the machine electrically, rather than hydraulically. The resulting disadvantages, such as excessive installation space or higher costs, quickly led to a comprehensive review in all directions. At this point, we were able to convince the customer to switch from a purely electromechanical drive solution to a hybrid strategy. After all, recent years have seen significant developments in hydraulics, thanks to more efficient pump drives and servo-hydraulic axles.
Traversing speed as a key.
As a first step, we analyzed the individual axles and motion profiles, as selecting a suitable drive technology must take the required speeds and precision into account. Next, the drive-technology design of the machine axles and associated drives was carried out.
We decided on an electro-hydraulic solution for the blowing unit due to the high force density, traversing speeds, temperatures and point loads. Especially when closing the blowing unit and locking via the non-return valves, hydraulics are clearly preferable to electromechanics, as they operate completely without energy. The hydraulic cylinder remains clamped in position via the non-return valve – accordingly, the pump could even be switched off completely. Apart from the blowing unit, the four axles for controlled ejection of the polymer material are also energy-efficiently designed and include an intelligent hydraulic drive unit. Especially challenging in this context was the high ambient temperature and the short stroke of two of these axles, which we were able to overcome using special seals.
An additional axle is moved via an electromechanical axle, the extruder is driven electrically. Thanks to the extremely smooth operation and rigid construction, it is possible to achieve exceptionally precise positioning even at high traversing speeds.
As an important component of the hydraulic system, not only the axles but also the entire pressure generation were optimized. In the process, we were able to replace the previous variable pump and constant electric motor with a Sytronix solution from Bosch Rexroth. The combination of an internal gear pump with a servomotor ensures a low noise level and reduced energy consumption over the entire life cycle.
Customer-specific development together with Bosch-Rexroth.
In a groundbreaking project, many of the machine components were optimized, cross-sections and flow velocities in the pipelines were analyzed and geometries were adapted to the working pressure of the pump. This is where the well-coordinated contact with our partner Bosch Rexroth paid off, as we worked closely together with their specialists throughout the entire project. Components were individually specified and adapted for usage. In order to offer our customer the best possible solution, the specialist department at Rexroth developed a complete control block with valve technology, which can not be found on the market in this form. Simultaneously, a new hydraulic tank was created that contained an energy-efficient cooler with a lower, but needs-based, cooling capacity.
And the result is one to be seen: The new blow-molding machine generates greater forces, positions even more precisely and significantly reduces the system's energy requirements. Each technology was applied exactly where its strengths lie: hydraulics in energy-efficient applications with high force density and load, and electromechanics when it comes to precision and high traversing speeds.
