Hydraulic drives move high loads and ensure safety-relevant functions. Their failure can result in tremendous downtime costs. It is therefore important to maintain the interaction between material, surface quality and fluid as coordinated by the manufacturer. With spare parts and repairs according to original specifications, operators can secure original performance over a long period of time.
Every year, millions of euros are invested in the development of new hydraulic components. Each new generation of solutions is even more powerful, energy efficient and reliable than the one before. The underlying field of research is called tribology – the science of friction, lubrication and wear.
Ensuring smooth performance
Tribology investigates all frictional processes that occur between two surfaces moving in relation to each other and considers the type of material, surface quality and the lubricant (fluid) as the main influencing variables. If hydraulic components are developed according to tribological principles, important savings can be made both in energy and material consumption and in production and maintenance. How can operators secure the advantages of the latest product generation for as long as possible?
Figure 1: Material, surface and lubrication: The scientific field of tribology investigates the friction between two bodies and seeks optimal conditions for minimal wear.
Change a perfect system? Better not!
Hydraulic components in which materials, surfaces and fluid are matched to each other in such a way that they achieve optimum efficiency with minimum wear are called a “tribological system”. This perfect interaction stands and falls with maintenance. If only a single parameter is changed, the system loses its balance, i.e. the optimum efficiency is no longer achieved, energy consumption and electricity costs increase and the service life is negatively affected. This happens, for example, if spare parts made of a different material or with a lower surface quality are used, if components are improperly repaired or a fluid is used that does not match the material.
Figure 2: Fluid-related damage to various components of an axial piston pump.
Play it safe: Spare parts from the manufacturer
To prevent operators from suffering functional losses and damage, Bosch Rexroth subjects the evaluation of fluids to strict requirements that go far beyond the recommended standard. The manufacturer also sets the same high-quality standards for its own spare part production as for the original. Replicas, on the other hand, offer neither the same material composition nor the same surface quality. The consequences are unplanned outages, significantly higher life cycle costs and premature new investments. Choosing original spare part is already worthwhile with the smallest parts. For example, Bosch Rexroth provides completely ready-to-install seal kits in original equipment quality – including parts list and exploded drawing. Thanks to the precise instructions, the average time required for dismantling, cleaning and reassembling a pump is reduced from a good two hours to less than 60 minutes.
Figure 3: Surface comparison: In contrast to the original from Bosch Rexroth (left), the plagiarism (right) shows large scores. The unfavorable flow conditions decrease efficiency. Leakage and cavitation are increased, especially under high pressure.
Figure 4: Serious quality differences in material and processing: The plagiarism (right) cannot withstand high pressure and “breaks”. The result: premature wear and tear and damage due to liquid contamination.
Original repair receives manufacturer specification
Repairs that are not commissioned at the manufacturer or certified partners often also result in unforeseen expenses. This is because without access to current data and parts lists, without in-depth know-how and without the right test benches, other suppliers cannot restore the original specification including functional reliability. In the worst case, there is even a risk of liability.
What ultimately distinguishes an original repair from an uncertified one? Here’s an example: When a Bosch Rexroth axial piston pump is inspected and repaired by trained service personnel in a specially equipped, ISO 9001-certified service center, it undergoes qualified testing and repair according to standard guidelines and processes. All failure-critical components are replaced and the original manufacturer’s specification is tested and confirmed on the test bench.
Replacement is better than rework
Non-certified suppliers frequently rework components, thereby destroying the original surface quality of highly stressed components such as pistons with slide shoe, control plates or sliding disks. Control valves on pumps are usually only cleaned and reinstalled. This short-sighted repair practice leads to increased leakage and consequently to a strong vibration tendency. Both accelerate wear, reduce efficiency and shorten the service life. By repairing with original Rexroth spare parts from the manufacturer, however, operators can ensure the original performance and availability for the next few years, including a twelve-month warranty on new parts. In addition, fixed-price repairs and agreed throughput times ensure cost security. This way, operators are protected from surprises and can plan ahead.
Figure 5: Rework vs. replacement: Leakage oil measurements on a remanufactured pump controller (A4VSO) show significantly higher values than when the original component is replaced: Vibrations, increased wear and early failures can be the result.
Avoiding liability risks
In some countries, improper repairs can also result in liability risks for the operator. In Germany, for example, the manufacturer is not liable under § 1 Sections 2 and 3 ProdHaftG (German Product Liability Act ) for defects that occur after the product has been placed on the market. Instead, the operator is responsible for the consequences of improper repairs. If the operational safety according to the CE mark is no longer given, the insurance company might not pay for damages.
Our conclusion: Sometimes saving money doesn’t pay off – preserve values instead
Those who want to save costs in the short term – by using counterfeit products and non-original repairs – pay extra in the long term. To benefit permanently from the original performance and a long service life, it pays off to include the manufacturer’s expertise in terms of technology, industry and application in maintenance, too. Only with proven manufacturer specifications can the original performance data and resulting function, productivity and efficiency be guaranteed.
Close cooperation with Bosch Rexroth is also worthwhile for other reasons: for example for engineering support, for professional instruction and training of operating and maintenance personnel, or to update the cost-effectiveness, energy efficiency and safety of existing systems. This way, a supplier relationship becomes a profitable partnership for a perfectly smooth operation.
Autor: Volker Tenhaeff Head of Global Service Support E-Mail: Volker.Tenhaeff@boschrexroth.de Autor: Andreas Tintschl Global Service Sales Support E-Mail: Andreas.Tintschl@boschrexroth.de
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Professor Dr.-Ing. Eberhard Abele was Head of the Institute for Production Management, Technology and Machine Tools (PTW) at the Technical University of Darmstadt for 20 years, until March 2020. Under his leadership, the ETA-Factory was set up and expanded. With his PHI-Factory and other projects, he turned his institute into a scientific hub for energy efficiency and energy flexibility in industry.
Where did your interest in energy efficiency come from?
As a young student, I had an internship at a foundry and was amazed by the amount of energy wasted there. Since then, I’ve become increasingly interested in energy efficiency – initially as a student, then in manufacturing development and planning in industry, later as a technical plant manager, and finally as a researcher.
What’s special about the ETA-Factory in Darmstadt?
At the beginning of the 2000s, we set up a process learning factory called CiP. The concept was really well-received by industry. This experience was the springboard for the ETA-Factory. Together with two employees, we considered setting up an energy efficiency factory on campus where students could learn about industrial processes. We also wanted to provide doctoral candidates with an opportunity to conduct practice-based research.
How did you win over the skeptics?
We attracted industrial partners, including, first of all, Bosch Rexroth. The ETA-Factory would never have existed without industrial partners. We finance ourselves through projects that we work on together with our partners. The ETA-Factory has more than 30 employees today.
Are people still interested in the ETA-Factory?
It still attracts strong interest. The ETA-Factory is a learning factory. We’ve welcomed more than 5,000 visitors, taught 1,500 students about energy efficiency and trained 400 to 500 skilled employees and managers from industry.
How has the topic of energy efficiency evolved over the years?
Over time, we’ve expanded our focus. In the beginning, we focused on energy efficiency within machine tools – primarily electric drives – pumps as well as friction. The results were quickly incorporated into state-of-the-art technology. In the next phase, we used the ETA-Factory to examine all machinery and building technology. With the PHI-Factory and the SynErgie project, we’re now taking elements surrounding the factory into account. In future projects, we want to think even further about the energy system in so-called pilot regions, which cover an entire city with private households, public transportation and industry.
Can such ideas be incorporated into daily operations yet?
Yes, they can. We conducted a project with an energy-intensive company in the aluminum industry. Today, the plant can increase or decrease its energy consumption by 25 megawatts without impacting the production process – for 48 hours. We’re currently working on about 20 other projects with similar potential.
What will factories look like in 10 years?
In the future, every production company will work on lowering its CO 2 emissions and possibly even a roadmap for becoming CO 2 neutral. Only a few companies currently have the relevant competence. But going forward, every company will be under pressure to do more in this area. Our graduates and applicants for companies are increasingly asking what future employers' contribution to sustainability actually is.
What role will Industry 4.0 play?
We now have a number of options for using sensors to monitor energy consumption and identify potential savings. A superordinate system can manage energy consumption in a way that takes the edge off energy peaks. The system ensures that heavy consumers don’t all consume the maximum amount of power simultaneously. Instead, they run in staggered operation. This has a direct impact on operating costs because, in Germany, the electricity rates of industrial companies are based on the maximum energy peak over a period of 15 minutes.
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Maintenance and repair of hydraulic power units and components all too often confront technicians with major challenges. Ordered spare parts, often seals, arrive in unlabeled bags, and the technician has to struggle through manuals until he gets the appropriate support. It is different at Rexroth: The hydraulics specialist has switched to over 15,000 ready-made spare parts kits with all the necessary installation documents. In addition, Rexroth's eShop on the Internet makes it much easier to find and order the right spare parts. The result: time savings of 50 percent in in-house repairs, lower overall costs and longer service life.
It is not always profitable to call the service of the machine manufacturer or the hydraulic supplier for every problem. Many users carry out minor repairs and regular maintenance on their own, even if the manufacturers often do not make it easy for them. This begins with the time-consuming search for the right and necessary spare parts for the repair, through to ordering via paper and then rolling through manuals.
Spare parts logically combined
Rexroth has significantly simplified this process and thus helps to reduce the life cycle costs of hydraulic systems even further. More than 15,000 spare parts kits cover almost all Rexroth components and systems still in use. These range from switching valves, continuous valves, hydraulic pumps, hydraulic accumulators, power units and systems, blocks and interlinked systems, compact hydraulics, cylinders and special cylinders. Low-value spare parts or those that should be replaced in one-step are logically combined in one package. For example, a spare parts kit for pumps consists of all wear parts that should be replaced when the pump is removed: seal kit, rotor and control disc. The spare parts are adapted to the respective pump design. All spare parts kits contain a parts list and a clear exploded drawing for installation.
Figure 1: Seal kits contain the original seals of Rexroth hydraulic components
Seals optimally protected
Around 98 percent of the spare parts kits consist of seal kits. The seals used at Rexroth are subject to strict criteria in terms of material, manufacturer and quality, as these are decisive in hydraulics for the tightness, performance and service life of the systems. This begins with the correct dimensions of a seal for a given installation space. Without appropriate design tools, it becomes very difficult for the user to find a working solution. Rexroth-specific R-ring seals in particular - in comparison to the somewhat simpler O-rings - cannot be designed with externally available online tools.
Errors can also easily occur in the material. For example, the common designation NBR says little about the exact composition and thus about the mechanical, thermal and chemical resistance. Of the numerous seal manufacturers on the market, hundreds of so-called compounds are available, the differences between which can only be determined by extensive testing and whose service life in the hydraulic system varies enormously.
The seal kits therefore contain the original seals of Rexroth hydraulic components, i.e. also the correct materials in original equipment quality, optimally matched to the installation situation.
The complete seal kits from Bosch Rexroth always contain all necessary sealing rings for maintenance. A uniform packaging system with standardized cartons protects the spare parts from negative environmental influences and simplifies storage by the user. The seals are individually welded onto seal kit supports and protected against oxygen, light and UV radiation. This prevents deformation, hardening, ageing, corrosion and weathering, especially in the case of sensitive high-performance seals, even during long periods of storage. This allows the user to exploit the full service life of the seals in the system.
Figure 2: Spare parts kit with exploded drawing and seals
Twice as fast with instructions
Almost any spare parts kit includes a parts list and an exploded drawing. This is an important simplification of work, especially with older machines and systems, where the paper documentation is often no longer available or incomplete. The description reduces the average time required for disassembly, cleaning of old seals to establish an allocation and assembly when repairing a pump, for example, from a good two hours to less than 60 minutes. These times are taken from field observations where the workload of skilled technicians was measured. In addition to the significantly reduced working time, the clear repair instructions prevent errors during assembly and thus also increase the functional reliability considerably. This effect significantly increases with the complexity of the repairs.
And another advantage: the costs of the sealing kits are negligible compared to the total cost of replacement including removal and reinstallation of the component.
Those who want to save costs in the short term - by using non-original spare parts - pay extra in the long term. To reduce the total cost of ownership, components should be professionally repaired to achieve the longest possible service life. Because only with proven manufacturer specifications can the original performance data and thus function, productivity and efficiency be guaranteed.
Link to the eShop: www.boschrexroth.com/SpareParts
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Sustainability isn’t a new topic for us. Here, Anne Redelberger from the GoGreen initiative talks about our approach to energy efficiency in the past, the present and the future. She studied renewable energies and energy efficiency, and at GoGreen, she uses her knowledge and experience to create an action plan, not just for us, but for other companies as well.
Why was the GoGreen initiative introduced and what are its goals?
We launched the GoGreen initiative internally almost ten years ago and developed the Rexroth 4EE system (Rexroth for Energy Efficiency). Using four levers energy system design, efficient components, energy recovery, energy on demand), we exploit all energy efficiency potential – from all automation technologies, applications and the entire life cycle, to the plant as a whole.
Under the umbrella of this initiative, we saved over 620,000MWh between 2011 and 2019. In effect, we’ve taken one medium-sized German city off the grid for a year.
This is certainly a good result, but surely there’s more?
We’re already buying green electricity and are generating regenerative power with photovoltaic systems on our factory roofs. We’re reducing our consumption with a number of energy efficiency measures. At our Beijing plant, for example, we managed to reduce energy consumption for infrastructure (heating and cooling) by a good 40 percent between 2010 and 2017.
How do you approach new measures?
We take a holistic view of our plants using the universal Rexroth 4EE system, taking both production processes and infrastructure into account. Examining these two areas together often reveals huge potential savings. In addition, we use insight from scientific projects funded by the Federal Ministry for Economic Affairs and Energy (BMWi), such as the ETA-Fabrik or the PHI-Factory, to increase energy efficiency and energy flexibility.
Do you use your own technologies for your energy efficiency measures?
Of course! Our control systems offer special energy-monitoring and energy-controlling functionalities to identify and optimize power consumption. Machine energy characteristics can be read easily, and machines can be set to energy-saving mode. But we also look at the components, especially those with high power consumption, and take measures, such as replacing displacement pumps with CytroBox hydraulic power units. By exchanging these components, we reduce energy consumption by up to 80 percent.
And what’s energy flexibility all about?
The increased use of renewable energy leads to fluctuating energy production depending on the variable supply of wind and sunshine. This creates new challenges for an affordable and stable energy supply. One solution here would be to adjust the energy demand to the fluctuating supply, in other words becoming energy flexible with regard to our own consumption.
How could this work for factories specifically?
We investigated this in cooperation with other companies and institutions, for example in the publicly funded PHI-Factory project. We’ve tested the interaction of fluctuating power supply with machines and storage facilities in a research factory under real conditions and implemented flexible electric factory grid control. In the midst of all this, we have our Rexroth converters for high power output. They make it possible to use machines flexibly, connect electric and kinetic energy storage systems and to switch the plant’s operating mode to a microgrid. With PHI-Factory, we even went one step further and successfully tested supplying network services, such as power factor correction or harmonics compensation, with our devices.
Do you think that other companies will follow?
Undoubtedly. The GoGreen team is receiving more and more requests from around the world. Many companies are actively seeking an exchange of knowledge.
To find out more click here.
Contact: Anne Redelberger Job title: Deputy project management of the GoGreen initiative E-mail: firstname.lastname@example.org
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Laser localization software awarded in the category “Intralogistics Software”
“The IFOY AWARD in the category “Intralogistics Software” goes to – the Locator from Bosch Rexroth.” These words caused great excitement among the Locator team. The whole team had gotten together to watch the virtual awards ceremony on July 13. We are very proud of this success, as the IFOY AWARD is a highly regarded award under the patronage of the Federal Ministry of Economics and Technology. It is sponsored by the VDMA Materials Handling and Intralogistics Sector Association.
The International Intralogistics and Forklift Truck of the Year Award, in short IFOY AWARD, recognizes the best intralogistics products and solutions of the year. The winners are selected in a multi-step process by an international expert jury of acclaimed specialist journalists. In advance, they assess test protocols from independent experts and the results of the IFOY innovation check for market relevance, customer use, manner of execution and level of innovativeness conducted by renowned scientists. Among the finalists, the 27-member jury selects the winners for the 13 categories. Our Locator, a software component for the reliable positioning and orientation of mobile robots, was able to convince in the „Intralogistics Software“ category. Using a laser sensor, it automatically creates a dynamic map, thus creating a basis for autonomous driving in intralogistics and production environments.
Anita Würmser, Executive Chairperson of the Jury of the IFOY Award, describes the initial situation: “The systems available on the market to date do require considerable adaptation and calibration effort in practice and require expert knowledge. Bosch Rexroth has anticipated this engineering work for many applications and environmental factors and integrated the adaptation functions into the software. The innovation thus lies in the tailoring and design of the product, which is specifically geared to current market requirements.”
We gladly accept this praise, as it goes right to the heart of our solution. The Locator significantly reduces the effort for introducing mobile robots. Previously, this was always a complex project. The relevant areas had to be equipped with markers, reflectors or mirrors. Then, specialists had to program the paths for commissioning. The Locator significantly reduces these efforts, and no expert knowledge is required for the setup – which was also confirmed by the independent testers. Operators can commission the vehicle in just a few steps and teach it with its surrounding in a one-off orientation drive. The Locator maps out its environment using a laser scanner. The software creates a map, saves it internally or on a server to share it with the rest of the fleet. Afterwards the immediate localization without prior knowledge is given.
The development team surrounding Christopher Parlitz has also made sure that the Locator fits perfectly into the controls of vehicles of all sizes and types: from dollies to forklifts, from milk runs to mobile robots. Thanks to this one-for-all approach, manufacturers can uniformly equip all their models and thereby significantly reduce production costs. By the way, the Locator can be used in a wide range of industries and application areas.
We thank the IFOY organization and our entire Rexroth team.
Jörg Heckel, Project Director Intralogistics Robotics, Bosch Rexroth AG
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