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Optimization of a plunger pump using simulation-based bearing design

Journal bearing optimization with high pressure

From cleaning surfaces to removing cover layers to waterjet cutting, Hammelmann’s plunger pumps find useful applications in virtually all industrial sectors. These high-pressure pumps reach pressures of up to 4,500 bar and flow rates of up to 3,000 liters per minute with a rated output of up to 1.1 megawatts.

In order to achieve high energy efficiency and extreme reliability, Hammelmann engineers rely on a combination of testing and simulation. This ensures that an innovative and robust design can be developed, while saving a great deal of time by reducing the number of prototypes.

About Hammelmann

Hammelmann GmbH (, with headquarters in Oelde, Westphalia, Germany, manufacturers high-pressure plunger pumps, process pumps, and high-pressure application systems and has subsidiaries in the U.S., China, Australia, Spain, France, and Switzerland, as well as 40 representatives worldwide. The German company is part of the Interpump Group from Italy.

As part of the EU Regulation 1907/2006 on the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH), a material changeover for journal bearing shells of a plunger pump was necessary. Test rig examinations are very time-consuming and costly, and the scope for changes is correspondingly narrow. Therefore, elastohydrodynamic (EHD) simulations were carried out for the small connecting rod eye of a plunger pump using the Tribo-X inside Ansys simulation tool. In contrast to experiments, changes to the simulation model can be implemented very quickly and computation results can be directly evaluated. Only when the desired result has been achieved does it then go to the test rig.

Starting from the previously used material, based on a copper-lead alloy applied to a steel backing, a material changeover to a bearing shell of the REACH-compliant bronze alloy without steel backing is carried out.

Initially, the simulations showed a deterioration of the load-bearing capacity over the course of the material changeover. This is due to the poorer support of the hydrodynamic pressures as a result of the missing steel backing. Additionally, there was mixed friction between the bolt and the bearing shell in the high-pressure load range of the pump, which is associated with wear and increased frictional losses.

In order to compensate for this deterioration in load-carrying behavior and improve the pump’s operating performance, a repositioning of the two lubricant pockets was also analyzed in the simulation model. To improve the load-carrying capacity of the system, a solution was found through the simulation of various bearing designs that would allow the REACH-compliant bearing shell to operate outside of mixed friction and thus without surface contact for the operating range analyzed. This means that, due to its optimized design, the new bearing shell can be used in the plunger pump with lower friction losses and longer service life.

Interview with Felix Hartmann

Felix Hartmann, team coordinator for pump design at Hammelmann GmbH, answered a few questions about the use of simulation in the optimization of journal bearings.

Why is simulation a useful addition to the existing design process?

Tests for plunger pumps are very time-consuming. Many hours or even days can quickly be spent carrying them out. Additionally, a considerable amount of empirical knowledge is required in order to achieve the desired goal on the basis of just a few tests. The use of simulation enables the simple comparison of different design variants, all with relatively short response times.

What is the significance of journal bearings in this context and how have they been designed up to now?

As force-transmitting parts, journal bearings are a core component of the high-pressure pump. A few micrometers are crucial here. In the past, we often designed journal bearings analytically. But this method can only be used to a limited extent, so we also carried out flow analyses when needed. However, we were faced with the problem of poor convergence behavior due to the low gap heights in the lubrication gap. This in turn led to long computation times.

When simulating the connecting rod journal bearing, what particularities should be considered?

Due to the pivoting motion of the small connecting rod eye, the direction of rotation reverses. This influences the hydrodynamic pressure buildup. With the reversal of the rotation, the critical point happens at the zero crossing, so to speak. Additionally, the loads are variable according to the operating cycles. Thus, the pressure buildup due to displacement (compression) leads to a load surge and an abrupt displacement of the bolt.

The high pressures in the lubrication gap also lead to elastic deformation of the bearing shell, thereby damaging the bearing gap. A sufficient oil supply therefore depends on many boundary conditions. A powerful simulation tool is needed to take all these important factors into account.

What benefits are there for Hammelmann by using Tribo-X inside Ansys to simulate the connecting rod journal bearing?

With Tribo-X, we can quickly and easily simulate extensive parameter variations for the connecting rod journal bearing. This allows us to better understand the behavior of our journal bearings and to analyze in advance which changes will accomplish which operating behavior. This is essential for an energy-efficient design of the journal bearings.

Simulation leads to less effort and cost, reducing the number of prototypes that would otherwise be required. Fewer prototypes in use also means less energy consumption. In figures, this means approximately €10,000 per saved test variant. However, only the pure material and energy costs were taken into account here. If personnel cost – as well as other additional costs – are considered, the total costs could exceed €50,000.

Another advantage is that, compared to the prototypes, the critical areas and the required tolerance limits can be analyzed more precisely during the simulation. Furthermore, the exact load limits can be determined, and the overall machine behavior can be better controlled. Additionally, in the future, variants, adaptations, customized configurations and new standards can be quickly and reliably implemented.

In terms of simulation, what are the next steps?

After successful verification, other pump types should also be simulated and optimized. Furthermore, it should be checked whether hydraulic rotary unions can be optimized by means of Tribo-X inside Ansys.

Thank you Mr. Hartmann for the interesting information about simulation with Tribo-X inside Ansys. All the best and future success with the plunger pumps.

Hammelmann GmbH
Felix Hartmann

Author: Gerhard Friederici, CADFEM
Images: © Hammelmann GmbH

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