Paper 22: Metal Surfaces in Contact under Normal Forces: Some Dynamic Stiffness and Damping Characteristics

1967 ◽  
Vol 182 (11) ◽  
pp. 92-100 ◽  
Author(s):  
C. Andrew ◽  
J. A. Cockburn ◽  
A. E. Waring
Keyword(s):  
Surface Finish ◽  
Dynamic Stiffness ◽  
Joint Interface ◽  
Force Frequency ◽  
Oil Viscosity ◽  
Engineering Structures ◽  
Oil Film ◽  
Good Surface ◽  
Joint Area ◽  
Surface Finishes

This paper describes an experimental investigation into the dynamic stiffness characteristics of flat joints subjected to an alternating force superimposed on a steady pre-load. The joints consist of the interfaces between mild-steel discs arranged in a column, in sets with surfaces either turned or lapped together. The influences of pre-load and of alternating force frequency were investigated for both dry and oiled joints, for different values of surface finish, apparent joint area and oil viscosity. The ranges of the conditions considered are compatible with those existing in typical machine tool structures. It was found that the dynamic stiffness of dry joints is independent of frequency and no energy dissipation is measurable. The stiffness is primarily a function of pre-load and surface finish, with apparent joint area becoming important only for very good surface finishes. If oil is introduced into the joint interface, a quadrature stiffness component arises and is accompanied by an increase in the ‘in-phase’ stiffness component. The magnitudes of the oil film stiffness components decrease sharply with an increase in the effective oil film thickness, which is governed primarily by the surface roughness. They increase with oil viscosity, the apparent joint area and the frequency of vibration, and represent a potentially valuable source of vibration damping in engineering structures.

Calculation and Measurement of the Stiffness and Damping Coefficients for a Low Impedance Hydrodynamic Bearing

1997 ◽  
Vol 119 (1) ◽  
pp. 57-63 ◽  
Author(s):  
M. J. Goodwin ◽  
P. J. Ogrodnik ◽  
M. P. Roach ◽  
Y. Fang
Keyword(s):  
Experimental Data ◽  
Dynamic Stiffness ◽  
Perturbation Technique ◽  
The Novel ◽  
Oil Film ◽  
Hydrodynamic Bearing ◽  
Damping Coefficients ◽  
Stiffness And Damping ◽  
Film Stiffness ◽  
Novel Design

This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.

Colour stability of surface finishes on thermally modified beech wood

2021 ◽  
Vol 114 ◽  
pp. 116-124
Author(s):  
Gabriela Slabejová ◽  
MÁRIA ŠMIDRIAKOVÁ
Keyword(s):  
Surface Finish ◽  
Beech Wood ◽  
Surface Finishing ◽  
Colour Stability ◽  
Colour Difference ◽  
Surface Finishes ◽  
Before And After ◽  
Thermally Modified Wood ◽  
Wood Surfaces ◽  
Modified Wood

Colour stability of surface finishes on thermally modified beech wood. The paper deals with the influence of the type of transparent surface finish on the change of colour of the surfaces of native beech wood and thermally modified wood. At the same time, the colour stability of three surface finishes on the surfaces of native and thermally modified beech wood was monitored. Beech wood was thermally modified at temperature of 125 °C for 6 hours. The thermal treatment was performed in a pressure autoclave APDZ 240, by the company Sundermann s.r.o in Banská Štiavnica. Three various types of surface finishes (synthetic, wax-oil, water-based) were applied onto the wood surfaces. The colour of the surfaces of native wood and thermally modified wood was measured in the system CIELab before and after surface finishing; the coordinates L*, a*, b*, C*ab and h*ab were measured. From the coordinates measured before and after surface finishing, the differences were calculated and then the colour difference ∆E* was calculated. Subsequently, the test specimens with the surface finishes were exposed to natural sunlight, behind glass in the interior for 60 days. The surface colour was measured at specified time of the exposure (10, 20, 30, 60 days). The results showed that the colour of the wood surfaces changed after application of the individual surface finishes; and the colour difference reached a change visible with a medium quality filter up to a high colour difference. The wax-oil surface finish caused a high colour difference on native wood and on thermally modified wood as well. On native beech wood, the lowest colour difference after exposure to sunlight was noticeable on the synthetic surface finish. On the surface of wood thermally modified, after exposure to sunlight, the lowest colour difference was noticeable on the surface with no surface finish.

scholarly journals An Investigation To Achieve a Good Surface Integrity in WEDM of Ti-6242 Super Alloy

2021 ◽  
Author(s):  
Sonia Ezeddini ◽  
Wajdi Rajhi ◽  
Mohamed Boujelbene ◽  
Emin Bayraktar ◽  
Sahbi Ben Salem
Keyword(s):  
Surface Roughness ◽  
Pulse Duration ◽  
Surface Integrity ◽  
Surface Finish ◽  
Feed Rate ◽  
Cutting Parameters ◽  
Machined Surface ◽  
Good Surface ◽  
Pulse On Time ◽  
Super Alloy

Abstract Ti-6242 is a super alloy which exhibits the best creep resistance among available titanium alloys and is widely used in the manufacture by WEDM of aircraft engine turbomachinery components. However, the final quality of wire EDMed surface is a great challenge as it is affected by various factors that need optimization for surface integrity and machine efficiency improvement. The aim of this study is to investigate the effect of a set of cutting process parameters such as pulse on time (Ton), servo voltage (U), feed rate (S) and flushing pressure (p) on surface roughness (SR) when machining Ti-6242 super alloy by WEDM process using a brass tool electrode and deionized water as a dielectric fluid. WEDM experiments were conducted, and SR (Ra) measurement was carried out using a 3D optical surface roughness-meter (3D–SurfaScan). As a tool to optimize cutting parameters for SR improvement, Taguchi's signal‐to‐noise ratio (S/N) approach was applied using L9 (3^4) orthogonal array and Lower-The-Better (LTB) criteria. Substantially, the findings from current investigation suggest the application of the values 0.9 µs, 100V, 29 mm/min, and 60 bar for Ton, U, S and p cutting parameters, respectively, for producing a good surface finish quality. Percent contributions of the machining parameters on SR (Ra) assessed based on ANOVA analysis are 62.94%, 20.84%, 11.46% and 4.74% for U, S, Ton and p, respectively. Subsequently, accurate predictive model for SR (Ra) is established based on response surface analysis (RSA). The contour plots for SR (Ra) indicate that when flushing pressure p converges to a critical value (80 bar), a poor-quality surface finish is highly expected with the excessive increase in U and S. Electron microscope scanning (SEM) observations have been performed on machined surface for a wide range of cutting parameters to characterize wire EDMed surface of Ti-6242. SEM micrographs indicate that the machined surface acquires a foamy structure and shows white layer and machining-induced damage that the characteristics are highly dependent on cutting parameters. At high servo-voltage, the decrease in pulse on time Ton and feed rate S results in a large decrease in overall machining-induced surface damage. Moreover, for high servo-voltage and feed rate levels, it has been observed that pulse on time could play a role of controlling the surface microcracks density. In fact, the use of a low pulse duration of cut combined with high servo-voltage and feed rate has been shown to inhibit surface microcracks formation giving the material surface a better resistance to cracking than at high pulse duration.

A Theory of Oil Whip

1959 ◽  
Vol 26 (2) ◽  
pp. 189-198
Author(s):  
Yukio Hori
Keyword(s):  
Negative Pressure ◽  
Higher Order ◽  
Inertia Effect ◽  
Oil Viscosity ◽  
Oil Film ◽  
Oil Whip

Abstract Oil whip was investigated theoretically and experimentally. In the paper it is shown that the inherent instability of the rotor in previous theories can be avoided by assuming zero pressure in place of negative pressure in the oil film and that the “inertia effect” in occurrences of oil whip can be understood by distinguishing small vibrations and large vibrations of the rotor. It is also shown that oil whip of higher order and the effect of oil viscosity on amplitude of oil whip give possible causes of some peculiar phenomena.

Direct Palladium-Gold on copper as a Surface Finish for next generation Packages.

2013 ◽  
Vol 2013 (DPC) ◽  
pp. 001145-001184
Author(s):  
Mustafa Ozkok ◽  
Sven Lamprecht ◽  
Gustavo Ramos ◽  
Arnd Kilian
Keyword(s):  
Surface Finish ◽  
Copper Wire ◽  
Environmental Issues ◽  
Wire Bonding ◽  
Gold Layer ◽  
Test Results ◽  
Fine Line ◽  
Surface Finishes ◽  
Copper Wire Bonding ◽  
Bond Tests

A new surface finish is entering the market. The need for this finish comes from needs for new assembly technologies like copper wire bonding or chip assembly by thermo compression bond. Furthermore Nickel an element, which is the base of many surface finishes like ENIG or ENEPIG, is more and more regarded as an unpleasant element as of several disadvantages, such as for high frequency applications, for environmental issues or for fine line applications were a 5 μm Ni Layer is just simply too thick. All these concerns supporting the introduction of a new surface finish, a direct EP and direct EPAG finish. In particular, its suitability for copper wire bonding and its fine line capability makes it very attractive from a cost standpoint of view. In addition, the mentioned technological handicaps of nickel based finishes could be solved by applying a revolutionary surface finish – A Direct Palladium with an optional gold layer. The direct deposition of palladium on copper with an optional gold layer does have further technological, environmental and economical advantages. The suggested paper will describe and discuss the advantages and chances using this new surface finish, as well as demonstrate soldering on various wire bond tests on the Direct EP and EPAG finishes as well as soldering test results.

A Comparison of Immersion Gold and Tin Surface Finishes on Sensing Electrodes for PCB Environmental Saltwater Concentration Sensors

2016 ◽  
Vol 2016 (1) ◽  
pp. 000557-000562
Author(s):  
Robert N. Dean ◽  
Frank T. Werner ◽  
Michael J. Bozack
Keyword(s):  
Surface Finish ◽  
Printed Circuit Board ◽  
Chemical Constituents ◽  
Low Cost ◽  
Circuit Board ◽  
Testing Environment ◽  
Printed Circuit ◽  
Sensor Performance ◽  
Sensing Applications ◽  
Surface Finishes

Abstract Printed circuit board (PCB) sensors using low-cost commercial printed circuit board fabrication processes have been demonstrated for environmental sensing applications. One configuration of these sensors uses exposed electrodes to measure saltwater concentration in freshwater/seawater mixtures, through monitoring the resistance between the electrodes when they are immersed in the saltwater/freshwater solution. The lowest cost commercial PCB processes use an immersion Sn HASL surface finish on exposed copper cladding, including the sensing electrodes. This commercial PCB process has been demonstrated to make an effective, low-cost, short-lifetime sensor for saltwater concentration testing. The Sn finish, however, may not be optimal for this application. Sn oxidizes, which can interfere with sensor performance. Additionally, Sn and Sn oxides are potentially reactive with chemical constituents in seawater and seawater/freshwater solutions. An immersion Au (ENIG) surface finish is certainly less reactive with the atmosphere and chemicals likely present in the testing environment. However, an immersion Au finish increases the cost of the sensors by 30% to 40%. To investigate if the possible benefits of the more expensive Au surface finish are worth the extra expense, a study was performed where identical PCB sensors were procured from a commercial vendor with their standard low-cost Sn HASL finish and with their standard ENIG surface finish. Both sets of sensors were then evaluated in concentrations of seawater and freshwater, from 0% to 100% seawater concentration, using freshwater samples from a natural freshwater source near the coast where the seawater was obtained. Testing demonstrated an insignificant difference in sensor performance between the Sn HASL and the ENIG coated sensing electrodes. The results of this investigation indicated that for applications where the sensors will not be used for long periods of time, the added expense of an immersion Au surface finish is not worth the added cost.

A STUDY OF SURFACE FINISHES FOR IC SUBSTRATES AND WIRE BOND APPLICATIONS

2011 ◽  
Vol 2011 (1) ◽  
pp. 000516-000520 ◽  
Author(s):  
John Ganjei ◽  
Ernest Long ◽  
Lenora Toscano
Keyword(s):  
Surface Finish ◽  
Printed Circuit Boards ◽  
Performance Enhancement ◽  
High Reliability ◽  
Cost Effective ◽  
Electroless Nickel ◽  
Gold Wire ◽  
Electronics Industry ◽  
Surface Finishes ◽  
And Performance

The continuing drive for ever increasing performance enhancement in the electronics industry, in combination with the recent, very significant increase in precious metal costs have left fabricators and OEMs questioning what the best, most cost effective, surface finish is for high reliability applications. Currently, the IC substrate market relies heavily on electrolytic nickel and gold as a solderable and superior wire bondable surface. The use of this finish has allowed manufacturers to avoid the reliability concerns However, this choice also results in significant design restraints being imposed. Many in the industry are now investigating the use of electroless nickel/electroless palladium/immersion gold (ENEPIG) to achieve both high reliability and performance, without the negative design restraints imparted by the use of electrolytic processes. However, over the last year alone, the industry has watched the price of gold increase by 50% and that of palladium double [1]. With this in mind, and considering the historic precedent set in the mid 1990’s when ENEPIG was also evaluated as a surface finish for printed circuit boards, when coincidentally, the cost of palladium also reached an all time high, it should be remembered that the electronics industry quickly moved to evaluate alternate, more cost sustainable, surface finishes. This paper details the use of lower cost, alternate surface finishes for IC substrate applications, with particular experimental focus on gold wire bonding capabilities and BGA solderability of the finishes described. The paper also discusses related process cycle advantages and the significantly reduced operating costs associated with these new finishes.

Modelling and simulation of surface topography machined by peripheral milling considering tool radial runout and axial drift

2019 ◽  
Vol 233 (12) ◽  
pp. 2227-2240 ◽  
Author(s):  
Hui-Qun Chen ◽  
Qing-Hui Wang
Keyword(s):  
Surface Roughness ◽  
Surface Topography ◽  
Surface Finish ◽  
Dominant Frequency ◽  
Peripheral Milling ◽  
Stability Lobe Diagram ◽  
Vector Operation ◽  
Good Surface ◽  
Stability Lobe ◽  
Feed Mark

Based on the Z-map model of a workpiece and the dynamic cutting forces model of peripheral milling in which the regenerative effect of tool radial runout and axial drift are considered, a model for the prediction of surface topography in peripheral milling operations is presented. According to the stability lobe diagram obtained by the zero-order analytical method, the relationship between spindle speed and surface topography, the tool radial runout, and the axial drift following the chatter are studied. The results show that a stable cutting status but a poor surface finish is obtained at the spindle speeds at which the dominant frequency of the milling system is integral multiples of the selected machining frequency, and a stable cutting status with a good surface finish can be obtained near and on the left side of the resonant spindle speeds determined by the predicted stability lobe diagram. The motion equations of any tooth end mill for peripheral milling are established, and these equations are based on the transformation matrix and the vector operation principle of motion-homogeneous coordinates. In addition, the simulation algorithm and the system of surface topography generated in peripheral milling are given based on the Z-map model. Cutting tests are carried out, and good agreement between the measured surface topographies and the topographies predicted by the model in this study is found in terms of their shape, magnitude, feed mark, profile height of cross-section, and surface roughness. The simulation results show that the milling surface roughness increases with the increase in feed per tooth, which further shows that this simulation system has high credibility. Thus, the simulation and experimental results can provide some practical instructions for the actual peripheral milling in determining the optimal machining conditions.

scholarly journals Numerical Model of Oil Film Diffusion in Water Based on SPH Method

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Daming Li ◽  
Zhu Zhen ◽  
Hongqiang Zhang ◽  
Yanqing Li ◽  
Xingchen Tang
Keyword(s):  
Particle Density ◽  
Numerical Models ◽  
Viscosity Coefficient ◽  
Oil Viscosity ◽  
Local Pressure ◽  
Sph Method ◽  
Film Diffusion ◽  
Oil Film ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

The smoothed particle hydrodynamics (SPH) method is applied to study the oil film diffusion in the water. By modifying the SPH equations of fluid dynamics, the multiphase flow SPH equations are obtained to establish the computational oil film diffusion model. By discussing three kinds of particle pairing schemes in the calculation of oil particle density, the redistribution mode of particle density is determined. The diffusion process of oil film is simulated, the effects of oil viscosity coefficient and particle density on oil film diffusion are analyzed, and the distribution of local pressure near oil particles in the process of oil film spreading is calculated. Finally, the calculated value of the oil film expansion diameter is compared with two other numerical models, and the calculated result shows a high coherence with the others.

Sign in / Sign up

Export Citation Format

Share Document