Dissertations / Theses on the topic 'Hydraulic constructions'

This report was written as a result of a Bachelor Degree Project, together with Swepart Transmission AB. The report contains the construction of a hydraulic press for the assembly operation.

The project started with a new construction of a hydraulic press for the bearings’ assembly. The goal within the thesis work was to fit the three bearings to the housing by only one press motion. This operation should be very safety because of the sensitive tolerance at the bearings and housing. Construction of the cylinders, rams and bolster were the most important parts at this project because this parts’ functions are very important for this assembly.

The next step of this thesis was to calculate the hydraulic press components’ parameters and then choose the suitable components. The focus was to choose more useful and reliable components.

The hydraulic press was modeled in the CAD program Solid Works and 2D technical drawing was drawn in the Autocad. The frame material was chosen and the frame was analysised in the Solid Works.

Utvecklingsavdelningen för hydraulcylindrar på Bosch Rexroth AB har identifierat ett marknadssegment för en lågpriscylinder som kan arbeta med högt tryck. Företaget har idag en lågpriscylinder på marknaden och vill vidareutveckla denna för att klara högre tryck. Detta examensarbete har utförts som en förstudie med syftet att presentera olika konstruktionslösningar av nuvarande cylinders ingående delar, för att erhålla de önskade egenskaperna. Arbetet började med att ingående bryta ner den nuvarande cylindern i mindre delar för analys. Det gjordes även en studie av konkurrenterna och vad deras sortiment har att erbjuda. I studien framkom att den sökta typen av cylinder redan idag finns på marknaden, vilket tyder på att efterfrågan finns samt att målet med utvecklingsprojektet inte är orealistiskt. När förståelsen av problembilden blivit klar kunde ett antal kritiska områden preciseras. För att få fler infallsvinklar om hur problemen kan behandlas, utfördes litteraturstudier. Litteraturstudierna resulterade i flera olika beräkningsteorier att använda. Teorierna utvärderades och applicerades sedan på de kritiska områdena. Ett flertal koncept att lösa problemen genererades fram och utvärderades mot de konstruktionskriterier som tidigt i utvecklingsarbetet hade identifierats. Trovärdigheten i de beräknade koncepten granskades sedan med hjälp av praktiska tester i företagets laboratorium. Slutligen kunde rekommenderade lösningar till företaget presenteras. Beräkningarna visar att förändringar behöver göras i cylindern. Godstjockleken i cylinderröret bör ökas för att klara det högre trycket. Även dimensionerna i framgavel och i bakgavel ökas för att erhålla en mer robust cylinder. Gängförband mellan kolv och kolvstång modifieras för att motstå den ökade spänningen som uppstår på grund av högre tryck. För att säkerställa att modifieringarna är tillräckliga måste fler prover utföras.

In the sector of mobile hydraulics, valve controlled systems are predominant. In these systems the load force and speed are adjusted by control valves. In machines where multiple drives are used in parallel at extremely varying loads the energy efficiency of such systems is often compromised over large working regions. Most valve controlled systems also lack the possibility to recuperate potential energy.

A different category of hydraulic systems, called displacement controlled hydraulics are based on the manipulation of the hydraulic flow using the relative displacement of the hydraulic machines as the final control element. This type of hydrostatic power transfer, yields a resistance free velocity control, ideally leading to lossless load actuation.

This thesis concerns the introduction of a new type of displacement controlled hydraulic system, adapted for construction machinery. The system decouples the hydraulic functions using one dedicated hydraulic machine for each drive. These machines are of open circuit type, capable of over center operation which enables energy recuperation. The system also comprises four separate valves that by means of switching allow the cylinder to be controlled over all four load quadrants. Depending on the selected valve hardware, the system may also include features available in a conventional valve controlled system, such as meter-out flow control. The system supports both symmetrical and asymmetrical cylinders. However, using the asymmetrical type the load may be controlled in two distinct states of operation. This yields an increased region of operation, which is otherwise generally stated as a drawback in displacement controlled systems. It also allows the selection between different control modes, where one of the modes is always more efficient than another.

In this research both theoretical studies and a practical implementation demonstrate the energy related benefits of the new concept. The target application of this study is a medium-size wheel loader. Measurement results using the wheel loader in a short truck loading cycle show a 10% percent reduction in fuel consumption. According to the theoretical investigation, this corresponds to a 20% reduction in energy consumption for the hydraulicsystem itself.

Examensarbetet har genomförts på Siemens Industrial Turbomachinery AB i Finspång. Arbetet innebär modernisering av ventiler till ångturbiner. Uppgiften består av två delar, där den första delen är att modernisera dagens tätningar i spindelgenomföringen. Syftet är att finna en mer vibrationstålig, driftsäker och mindre utrymmeskrävande lösning. Det andra delprojektet är att finna alternativ till dagens tallriksfjädrar i de servomotorer som reglerar ventilen. Anledningen till att nya fjädrar skall tas fram är att öka livslängden, minska slitaget och utrymmesbehovet på servomotorerna.

För att kunna genomföra uppgiften på ett effektivt och strukturerat sätt har en metodik för systematisk konceptutvecklings används. Denna metodik har varit hjälpfull för att finna nytänkande lösningar. För att kunna dimensionera komponenterna har beräkningsmodeller tagits fram för de ångkrafter som verkar i en ångventil samt för olika typer av packboxar och fjädrar.

Arbetet med moderniseringen av spindeltätningar har resulterat i att en ny typ av packbox har valts som minskar friktionen samt behovet av efterdragning. Två olika lösningar har tagits fram för att skapa den förspänningskraft som gör att packningen tätar. Båda lösningar minskar behovet av underhållsarbete samt underlättar monteringen. En indikation ges även när rätt kraft är uppnådd, vilket minimerar risken för läckage eller att ventilen inte går att manövrera.

Analysen av servomotorer resulterade i att inga möjliga alternativ till tallriksfjädrar hittades. Modifieringar har därför tagits fram för att förbättra dagens tallriksfjädrar. Dessa ändringar innebär att slitaget minskas och livslängden ökas betydligt.

This thesis was preformed at Siemens Industrial Turbomachinery AB in Finspång. The work is to make modernizations of steam turbine valves. The first part of the project is to modernize stem packing with the purpose to find a more reliable and space-saving solution that is less sensitive to vibrations. The second part is to find an alternative solution for cup springs in servomotors. A new spring type is desirable to increase the lifetime, lower the wear on stem shafts and to make it more space-saving.

To be able to perform the task efficiently and organized a method for systematic design has been used. This method has turned out to be quite useful tool in order to find new approaches to problems. Calculations of steam forces in a valve together with different types of box packing and springs have been done.

The modernization of stem packing has resulted in a new type of box packing. The winnings of changing packing are lowered friction and need of maintenance. Two solutions of live load systems have been created. Both solutions minimize the need of maintenance and make the mount and dismount easier. An indication makes sure that a sufficient force is applied on the box packing.

An analysis shows no alternative to replace the existing cup springs. The main goal was changed and modifications were made to improve the cup springs. The modifications results in a lowered wear and a significant increase of cup spring lifetime.

This study focuses on the wear of piston rings in a hydraulic radial piston motor. The piston ring has to satisfy increasing demands for reliability and longer service life. It has two contacting surfaces, the face and the flank, and operates under a boundary lubrication state.

This first part of the project aimed to detect and characterise piston ring wear. Measurement by weighing gives an overall value for wear defined as loss of mass. Two-dimensional form and surface roughness measurements show the distribution of wear on the piston ring face in contact with the cylinder bore and the piston ring flank in contact with the piston groove. Three-dimensional analyses, both quantitative and qualitative, allow the wear mechanisms to be identified.

The wear of piston rings from an actual hydraulic motor was characterised. As well, rig testing was performed in two different test rig set-ups, one simulating the sliding movement of the piston ring and the other the tilting movement at the end of the strokes. Wear during the running-in period was investigated, and the findings indicate that the period when this takes place is of short duration. In the long term, mild wear makes the surfaces smoother than they were when new, resulting in a very low wear coefficient. Significant levels of wear were measured on both contacting surfaces of the piston ring. In cases in which the flank exhibits more wear than the face, the wear on the flank can be reduced by proper design of the piston groove.

The second part of the project aimed to evaluate use of a textured surface for the cylinder bore counter surface and a coated surface for the piston ring. Three modelling experiments were performed to characterise the friction and wear properties under lean boundary lubrication conditions. Under such conditions, textured surfaces have the advantage of retaining more lubricant and supplying it over a longer time. Stable friction was also a distinctive feature of the textured surface. Use of a coating could also possibly reduce the amount of wear. Though a smooth surface, like a polished one, is hard to beat for a working texture, a coated surface is far ahead of a smooth uncoated one. Different manufactured and commonly used cylinder bore surfaces, including textured ones, were evaluated in the sliding movement test rig. That allowed favourable wear properties, such as lowest wear coefficient, to be determined with the use of a roller burnished surface.

A final part of the research involved simulating wear on the piston ring face throughout the entire service life of a hydraulic motor. This allowed us to determine the roles of surface roughness and coating in prolonging service life and achieving acceptable and secure piston ring operation. The model is simple and realistic, but still needs to be refined so as to correspond even better to reality.