Czesław Kundera

Investigating the stress relaxation of photopolymer O-ring seal models

Purpose – This paper aims to investigate the suitability of additive manufacturing to produce O-ring seals. Design/methodology/approach – The O-rings were made by the PolyJet-Matrix technology using four different digital materials and then tested for relaxation properties under static and dynamic (sliding) conditions. The approximation of the relaxation curves involved modelling with a Prony series. Findings – The PolyJet-Matrix technology offers new opportunities to model elastomeric elements, with examples being the O-rings produced and tested for their relaxation properties. Describing the behaviour of the particular materials fabricated with this technology by using relaxation functions will extend the knowledge base on digital materials. Research limitations/implications – The four types of photopolymers used in the experiment differed in viscoelastic properties. The analysis of the stress relaxation of the O-ring models was performed at four different step displacements of the loading element. Prac...

Research of the Elastic Properties of Bellows Made in SLS Technology

The article contains the result of studies on the effects of selected geometrical parameters of elastic bellows on their elastic properties. Bellows models were produced with using additive technology, selective laser sintering SLS, where the material used to build models was polyamide PA 2200. Based on the measurements of elastic deformation coefficients of each models bellows were determined. Comparing the results of the measurements there was found a significant effect of the thickness, number of corrugations and their length on the value of the coefficient of elasticity.

Proposal to Improve the Design of the Impulse Face Seal

The paper describes the construction and operating principle of the non-contacting impulse face seal. A mathematical model of the impulse seal was formulated. The method of control of the opening force by change of the cavity volume within sealing gap was described. The results obtained from the numerical calculations prove that the effect of the cavity volume on the axial vibrations of the flexibly mounted ring.

ASSESSMENT OF TRIBOLOGICAL PROPERTIES OF POLYMERS USED IN ADDITIVE TECHNOLOGIES SLS AND PJM

The paper presents preliminary results of tribological research on materials used in two additive technologies photo-curing polymer resin PJM and selective laser sintering of polyamide powders SLS. A Tribometer T-15 type ring-disk was used to determine the impact of technological parameters, e.g., printing direction and building layer thickness on the selected tribological properties and wear processes for elements generally used as machine parts. * Kielce University of Technology, Faculty of Mechatronics Mechanical Engineering, al. Tysiąclecia Państwa Polskiego 7, 25-314 Kielce, Poland. T R I B O L O G I A 5-2016 74 INTRODUCTION The dynamic development of mechanisms of precision machinery, e.g., technical active seals, sleeve bearings, or motor connections of machines puts extremely high requirements on the reduction of friction and wear processes. Tribological processes occurring in the friction area determine the reliability and durability of such devices and have a direct impact on the proper work of the object [L. 1, 2]. In conventional manufacturing methods, the tribological properties of the materials are much easier to determine because of the isotropy in mechanical properties and their structure. Problems of durability arise when we are using additive technologies to manufacturing end-used parts exposed to wear without additional finishing operations, i.e. grinding, and polishing. Additive manufacturing technologies are based on a layer manufacturing of physical models directly from a 3D three-dimensional solid model [L. 3]. The use of three-dimensional models makes the whole process of production much more flexible and competitive in relation to the conventional manufacturing technologies. Any design changes can be implemented quickly, without the need to setup technological machines, such as machining tools or forging dies. Because of the layer construction of the models, it is possible to produce endused components, where: it is difficult or impossible using traditional technologies. With the development of additive technologies and improved accuracy, designers increasingly started using the above-mentioned technologies for the production of fully functional co-operating machine elements, i.e. seals, bearings, and mechanical connection elements [L. 4]. Most additive technologies, especially those where: plastics are used as input materials, present anisotropy in mechanical properties and accuracy. This phenomenon mainly depends on the technological parameters and placement models on the building platform. This problem causes that the wear process of machine parts produced by using “Three Dimensional Printing” can be different for the same element. Selected tribological properties of materials used in SLS technology were described in [L. 5], where: the authors used a tribometer (type ring-pin) to determined basic tribological parameters of the friction elements. Samples were manufactured using bronze powder (EOSINT M Cu 3201). Countersamples were made by using polyamide with glass fibre. The research was carried out in a heating chamber with controlled temperature. This paper describes the preliminary study of the process of friction in a face contact surface of the ring-and-disk, using a T-15 tribometer. Rings (samples) for tests were made from different materials used in two commonly used additive technologies: PJM and SLS. The aim of the study was to determine the effect of process parameters, i.e. printing direction and building layer thickness on the wear processes of the rings (samples) and the coefficient of friction in a sliding connection. 5-2016 T R I B O L O G I A 75 TECHNOLOGY In the study, two types of modern additive technologies that use input polymeric materials were used: photo-curing polymer resin PJM, and selective laser sintering SLS. For PJM technology, a Connex 350 machine (Stratasys Company) and VeroWhite material were used. In SLS technology, to prepare samples, Formiga P100 (EOS company) and material PA 2200 were used. The mechanical properties of the materials used to build the samples are shown in Table 1 [L. 6, 7]. The printing process of samples and tribological research were carried out at the Kielce University of Technology in the Laboratory of Unconventional Manufacturing Technology. Table 1. Mechanical properties of materials: PA 2200 / Vero White [L. 6, 7] Tabela 1. Właściwości mechaniczne materiałów: PA 2200/VeroWhite [L. 6, 7] Mechanical Properties Value Unit Standard Youngs modulus 1700/2495 MPa EN ISO 527 / ASTM D-638 Notched Izod (23°C) 4.4/24 kJ/m ISO 180/1A / ASTM D-256 Shore’s hardness 75/83 ISO 868 / Scala D Density 0.930/1.18 g/cm EOS method / ASTM D792 Water absorption 1/1.5 % D-570-98 24hr Selective Laser Sintering SLS SLS technology is one of the most commonly used method of rapid prototyping. In this technology, polyamide powder with a grain of a diameter equal to 0.056 mm is distributed on the working platform by a machine arm. Then a focused beam of a CO2 laser by scanning a selected cross section of the model is sintered building a layer and combining it with the previously made surface. The process of building and cooling takes place in an atmosphere of inert gas (nitrogen) to prevent oxidation. After completion of the sintering process, a working platform is lowered by a value equal to the thickness of one layer, which is minimally 0.1 mm for PA 2200 material in SLS technology [L. 8]. Due to the used powder as a building material, SLS technology allows building models of very complex internal shapes. The powder, which has not been used during production, can be removed from the model in a cleaning stage by compressed air. Photo-curing Polymer Resin PJM PolyJet Matrix Technology (PJM) [L. 4] is based on photo-curing liquid polymer resins by used UV light. In the building process, printing heads sprayed thin drops of liquid polymer resin in the selected cross section of the model. Then a UV lamp initiates the polymerization process by scanning the T R I B O L O G I A 5-2016 76 newly formed layer. The main technological parameter presented in this technology is layer thickness, which has a significant impact on the accuracy and mechanical properties. The minimum layer thickness for a “single” material is equal 0.016 mm and 0.03 mm for the mixtures of materials, “digital materials” [L. 9, 10]. SAMPLES The samples for tests were designed using CAD software SolidWorks 2016 in accordance to tribometer T-15 instructions. This device was designed and manufactured at the Institute for Sustainable Technologies – National Research Institute in Radom. The samples were made in 3 variants. The samples angles between the building platform and sample-working surface (friction) were equal to 0°, 45°, and 90°. In the case of the first type of samples prepared using SLS technology, the layer thickness was equal 0.1 mm, and for the second type the layer thickness was 0.2 mm. In the PJM technology, the layer thickness was equal 0.03 mm. The geometrical dimensions of the samples and their placement on the machine platform are shown in Figures 1 and 2. Printing parameters are shown in Table 2. Fig. 1. Sample dimensions Rys. 1. Wymiary badanych próbek Fig. 2. Placement of samples on the machine platform Rys. 2. Rozmieszczenie próbek na platformie maszyny Table 2. Printing parameters Tabela 2. Parametry „wydruku” próbek Samples No. Angle [°] Layer thickness 1 0 0.1/0.2/0.03 2 45 0.1/0.2/0.03 3 90 0.1/0.2/0.03 5-2016 T R I B O L O G I A 77 METHODOLOGY OF THE RESEARCH Tribological research was performed using a tribometer. The T-15 device consists of a testing machine, measurement and control systems, and a computer with software to analyse and record research results. The principle of T-15 work is shown in Figure 3. The rotating disc made of C45 steel is in contact with the fixed sample in a form of ring (Fig. 1), which is pressed by clamping arm with lever ratio of 3:1. During the research, samples can be loaded with a maximum force of 150 N.

Analysis of the Radial-Axial Oscillations of the Rotor of a High-Speed Pump

The joint radial-axial oscilations of onemass model of rotor of high-speed pump are considered taking into account hydrodynamic forces, arising up in the radial clearance of annular seals. Connection of axial oscilations with radial is conditioned by dependence of conductivity of annular throttle, consequently, and axial force of balancing device, from the excentricity of shaft in the annular collar. amplitude and phase frequency characteristics of the forced oscilations, excited by harmonically changing pressure and static unbalance.

Elastic Bellows Prepared by Selective Laser Sintering

The article contains the results of studies concerning the effects of selected parameters of the manufacturing process of elastic bellows on their elastic properties and strength. Bellows models were made using additive technology SLS selective laser sintering, in which the material used to construct models was a polyamide PA 2200. Bellows printing process proceeded in a surface parallel to the axis of the bellows and in a surface perpendicular to it. Based on measurements of deformation coefficients of elasticity of bellows were determined, also the measure of the maximum axial force exerted by the bellows while loading the internal pressure was carried out. Comparing the measurement results a significant effect of process parameters on the flexible properties of elastic bellows and their resistance to internal pressure were determined.

The Calculation of Static Characteristics of Impulse Gas Seal

Mathematical background for static analysis of impulse gas seal is created in current paper. It includes evaluation of gap and flow rates of gas in turbocompressors. This paper consists of two parts. In the first one all logical steps of creation of the theoretical model for impulse gas seals are given. It should be mentioned, that they are valid for isothermal steady process which is observed here. The verification of derived theory is shown in the second part on a calculation example.

The Centrifugal Pump with the Impeller Supported in Sealing Clearances

The paper presents the construction of single-staged centrifugal pump with the impeller supported in longitudinal and transversal sealing clearances. In the state of equilibrium the impeller is supported by axial and radial forces and moments of pressure, which occur on both sides of the impeller in annular clearances. In the result the impeller adopts optimal non-contact position in which all the external forces that works on this are in balance. A description of the statics and the dynamics of the impeller has been presented.