Contact Face Research Articles

Thermal design and development of actively cooled brushes for compact homopolar generators

The thermal and hydraulic design of actively cooled current transfer brushes for compact homopolar generators (HPG's) is described. The development of high-energy-density HPG'S at the Center for Electromechanics at the University of Texas at Austin (CEM/UT) requires brushgear capable of handling high current densities and large thermal loads. Platelet technology has been applied in the design of actively cooled brushes with coolant injection directly from the brush contact face into the brush-rotor interface. Coolant channels a few thousandths of an inch in diameter have been designed in brushes constructed of photoetched platelets of copper (0.020 to 0.005 in. thick) and then bonded to form the cooled brush. Platelet construction of brushes also permits the incorporation of internal instrumentation for temperature measurement. The brushes have been designed to provide data on the effects of rotor speed, current level, coolant flow rate, and coolant injection pattern. These brushes will establish the data baseline required for future cooled-brush designs.

The Giessen model of a cement-free implantable total endoprosthesis for the hip joint

Complete endoprostheses of the bitrochanteric type were implanted in Giessen in 111 patients the average age of whom was 74 years. Computer-assisted evaluation showed that more than 70% of these patients developed autonomous mobility. The rest had not been able to walk before surgery, but could be nursed or became able to sit after the operation or were still followed up. At the end of follow-up treatment, a rate of 90% of mobile patients with or without stick is to be expected. Initially, the implantation technique is certainly more difficult to learn with this model than with other allo-endoprostheses of the hip joint. This is due to the fact that the implants are an exact replica of the pertrochanteric region, thus permitting a broad contact face to the cortical substance instead of the punctiform contact of some other models. Once learned, the technique can be applied without considerable problems. At our Department it has proved to be successful.

Hydrostatic Effects in a Mechanical Face Seal

In a mechanical face seal, the total applied load is supported by hydrostatic and hydrodynamic fluid pressures and often by partial contact of the seal faces. Hydrostatic load support is affected by the initial seal interface geometry and the modification of this geometry due to component distortions. A model developed for static (non-rotating) conditions demonstrates effects of face convergence, spring pressure, and secondary seal friction on the hydrostatic fluid film thickness. The previously reported film thickness probe system has been used to measure the fluid film geometry in a standard wedge-type seal up to 4.5 MPa pressure, for comparison with theory. It is shown that the experimental results verify the hydrostatic model, in particular, confirming the prediction of the hysteresis effect due to the secondary seal friction. Application of the model for a hydrostatic seal design is also discussed. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Tribology Conference i...

焼付き防止型軸継手リーマボルトの開発

The product name of the bolts newly developed is PILLAR NS REAMER BOLTS. They represent resins coated reamer bolts and nuts used as the torque-transmission coupling bolts for ships' propulsion shafting systems.The bolts are featured by the ease of their pressure fitting and extraction, also their freedom from seizure though they are provided with 0.01 to 0.05 mm of interference against reamer holes.The PILLAR NS REAMER BOLTS can ensure electrical discontinuity between the matching shafts by inserting an insulating sheet in a space between the flange surface and contact face of bolt head. The intermediate shafts of a ship electrically insulated by this method can effectively prevent spark erosion which is otherwise generated between the crankshaft journal and main bearing of the main engine due to potential induced between ship's propulsion shafting and hull.

Nickel and chromium plated terminals in current transformer circuits

When nickel or chromium plated terminals are used in the circuits of precision current transformers, instabilities are often observed in their calibration. The nature of these instabilities suggests the cause to be small DC components flowing in the transformer windings. In the paper, the DC components are explained in terms of semiconducting oxides on the terminal contact faces. Experimental results indicate that chromium in contact with oxidised copper produces the worst effects. It is concluded that the problem would be solved if manufacturers simply used unplated copper or brass terminations.

The Vacuum Interrupter Contact

A survey of developments in electric contact design for vacuum interrupters is presented. The major emphasis is placed upon those characteristics of contact design that have led to practical vacuum interrupters. A brief description is given of the different modes of vacuum arc that have been observed and how these modes occur during one-half cycle of high current arcing. In the main body of the paper the design philosophy behind vacuum interrupter contact design is presented. It is shown that only two classes of contact have achieved practical utilization. The first of these design classes causes a magnetic field to be impressed at right angles to the arc current and hence, causes the arc to move rapidly over the contact face. The second design class impresses a magnetic field parallel to the arc current. This forces the arc into a diffuse mode with many widely separated cathode spots and a diffuse current collection at the anode even at very high currents. Each of these contact designs is discussed and their advantages and disadvantages are deline- ated.

Multiposition amplitude device

First Page

Errors in the measurement of bubble size distribution in foam

The determination of foam bubble size by planimetric measurement of the area of the contact face a the glass wall of a column containing essentially homogeneous new foam yielded excellent agreement with the bubble size as known a priori. Furthermore, the said determination proved to be more reliable than measurement based on either the longest chord or the commonly employed longest median of the contact face. However, for highly heterogeneous new foam, all three measures of foam bubble size underestimated the true mean. Apparently, small bubbles wedge large bubbles away from the wall. The effects are presented quantitatively, along with correlations for their approximate prediction.

低砥石速度による研削法に関する研究(第1報)

In creep feed grinding the grinding force and its distribution on the contact face between wheel and workpiece is discussed theoretically. The conditions for the occurrence of grinding burn in up cut grinding is analyzed according to the relation of an out-flow and an inflow of the grinding heat energy at the end of contact face. From the results, the effects of operating parameters on the occurrence of grinding burn are investigated theoretically and verified experimentally. The following phenomena in creep feed grinding are clarified. (1) The difference between up cut grinding and down cut grinding has larger influence on horizontal grinding force thanvertical grinding force, and the horizontal grinding force in down cut grinding is remarkably smaller than it in up cut grinding. (2) The maximum grinding energy flux at the end of contact face when grinding burn begins to occur varies with chip volume and the time that grinding wheel require to pass contact face. (3) The critical wheel speed without grinding burn is determined by wheel depth, work speed and percent wear flat area of grinding wheel, but it is not under the influence of grinding width. (4) To avoid grinding burn in no case of changing wheel depth and work speed, wheel speed less than a few hundred meters a minute is effective. In the case of the precision dressing remarkable reduction of wheel speed is recommended.

Densification of Powders by Particle Deformation

Based on a previous experimental study of particle deformation during powder compaction, a model is developed for describing the densification behaviour of an irregular packing of spherical particles. Using the radial density function of a ‘random dense packing’, the increase in both the average size and the number of contact faces are calculated. A simple criterion for local yielding allows the compaction pressure to be determined for relative densities up to 90%. In the final stage of compaction, particle deformation, now constrained by neighbouring contacts, is modelled by extrusion into the remaining pore space. A compaction equation encompassing both stages is presented; its application to non-spherical powders elucidates the role of particle shape during powder densification. PM/0150

Experimental Evaluation of a Mixed Friction Hydrostatic Mechanical Face Seal Model Considering Radial Taper, Thermal Taper, and Wear

In this paper the results of experimental investigations of the effects of radial taper on mechanical face seals are presented and compared to theory. The previously published theory considers the effects of thermal taper caused by a temperature gradient in the seal rings; mixed friction in the case where load support is shared between hydrostatic support and partial contact of the seal faces; surface roughness, which affects both load sharing and leakage; and wear, which alters the radial profile. Fifteen tests were run using a 100 mm diameter carbon versus tungsten carbide seal at 1800 rpm and 3.45 MPa in water. Test duration was up to 100 hr. Varying amounts of radial taper were used. Tests were run at balance ratios of 1.00 and 0.75. Initial and final surface profiles were recorded. Seal torque, leakage, and face temperatures were recorded as functions of time. Results show that theory predicts initial torque and leakage as functions of initial taper quite well, given knowledge of seal surface characteristics. Predicted equilibrium thermal taper as a function of torque for a balance ratio of 1.0 is good. For a seal having a balance ratio of 0.75, predicted equilibrium thermal rotation shows some agreement but more experimental data are needed. The results of 1.00 balance ratio tests suggest that after a long period of operation, any initial taper will be worn away and the seal would continue to operate as a parallel face seal. Results from long-term tests indicate that the wear coefficient is not a constant. While the experimental results support the basic concepts of the model, the results show where further work must be done to better understand the role of surface roughness and wear processes in mechanical face seals.

Uniqueness for Elastic Crack and Punch Problems

Uniqueness of solution is shown for equilibrium states for elastic bodies in smooth contact. The cases considered include a body with a crack that may open only partially under load with parts of the faces in frictionless contact. Indentation of a body by a smooth rigid punch and contact with an elastic foundation are also treated.

Shape Changes in the Upsetting of Slender Cylinders

Mild steel and aluminum alloy cylinders were incrementally upset with good lubrication and with sticking friction, and the development of shape was followed by measuring the diameters of the barrel and the contact face. These dimensions changed according to a power law as a function of reduction and initial diameter-to-height ratio of the specimen. Formulas are given for predictive calculations of barrelled dimensions, and these were found to be reasonably applicable also to hot forging. The expansion of the original end face was highly sensitive to friction and the material’s strain hardening characteristics, and could not be generalized.

THE POLLEN-STIGMA INTERACTION IN THE GRASSES. 2. POLLEN-TUBE PENETRATION AND THE STIGMA RESPONSE IN SECALE

SUMMARY After an initial period of hydration on the stigma, viable pollen grains release an exudate which becomes continuous with the stigma surface secretions. This is accompanied by an enhancement of surface esterase activity, and eventually the stigma cuticle is eroded at the contact face. Simultaneously the pectin-rich outer layer of the wall of the stigma papilla gelatinises. Germination of the grain begins with the gelatinisation of the pectins of the Zwischenkorper, which displaces the operculum. The emerging tip passes through the eroded stigma cuticle and enters the outer pectin-rich layer of the wall. Enzymic removal of the proteinaceous part of the stigma surface secretion before pollination interferes with the capacity of the tube tip to penetrate, but does not prevent germination. During further growth in the stigma, the tube passes through the intercellular material of the branch axis, which occupies some 10% of the volume of the branch before pollination. The advent of the tube brings about a rapid increase in the permeability of the affected cells, preceded in some species by the blockage of the plasmodesmata by callose. The membranes of the cells immediately adjacent to the pollen-tube pathway undergo dissolution, and the nuclei become pycnotic. Calculations based upon the changes of volume of the grain during the first 500 µm of pollen tube growth show that the water requirement of the tube may be met entirely by transfer from the hydrated grain, and not by uptake from the stigma tissues. This implies that all of the initial events of germination, tube emergence and growth through the secondary stigma branches are driven by the hydrostatic pressure built up in the grain during the period of hydration following upon capture.

Electromagnetic transducer head

An electromagnetic transducer head for a tape recording and reproducing system comprises a pair of generally U-shaped single crystalline ferrite cores having their first legs secured together and their second legs spaced from each other to form a magnetic gap in which a wafer of glossy material is provided. Each of the ferrite cores has crystal planes (211), (110) and (111). The magnetic gap is aligned to the crystal plane (111) and the second legs of the cores are shaped to provide a tape contact surface which is parallel with the crystal plane (211). The crystal plane (110) is at right angles to the planes (211) and (111) and forms a passage for magnetic flux. The crystallographic axis of each core extends at an angle to the magnetic gap so as to meet the axis of the other core at a point aligned with the tape contact face.

Experimental Studies on Thermoelastic Effects in Hydrodynamically Lubricated Face Seals

Experiments are reported where face-seat specimens were operated hydrodynamically at conditions close to thermal equilibrium. Changes in surface waviness and mean film thickness were monitored, and compared with theoretical predictions of thermal growth of waviness. Discrepancies were attributed to imperfect response of the gimbals to axial run-out. This run-out was increased by thermal effects at high sliding speeds and led to interactions which influenced the growth of two-lobed waves on the contact face. Operation proved stable, as predicted, under the carefully controlled operating conditions of fixed axial load and self aligning contact.

AN INTERPRETATION OF THE HYDRODYNAMICS OF POLLEN

The pollen grains of angiosperms are usually desiccated to some extent at the time of dispersal. Rehydration is an essential prelude to germination, and this takes place by uptake of water from the stigma after capture, water entering from the cells of the stigma surface following a water potential gradient. The passage of water into the pollen grain is regulated by the cuticle of the stigma papilla in the vicinity of the contact face, and also by the apertural mechanisms of the pollen grain exine, which act by varying the degree of exposure of the underlying pectocellulosic intine according to the degree of hydration of the grain. The sequence of events during rehydration suggests that at first the vegetative cell of the male gametophyte is without a normal plasmalemma, so that the initial dilation of the grain is followed by an interval of exudation. Thereafter, with the re‐establishment of the cell membranes, the vegetative cell behaves in the manner of a normal plant cell through the period of germination.

Rupture of glass upon local contact loading

In de te rmin ing the s t ruc tu ra l s t rength of hollow sect ional shel ls made of g lass l ike m a t e r i a l s , it is i m por tan t to know the conditions of f r a c t u r e of glass under contact loading. In this case high level s t r e s s e s occur at the jo ints , caused by the m i c r o r e l i e f of the contact ing su r faces and by the mode of the i r fastening. Local contact loading was effected in the p r e s e n t work by the in te rac t ion of a r igid s tee l sphere with a g lass plate. The theory of e las t i c i ty (Her t z ' s solution) [1] makes it poss ib le in this case to de te rmine the magnitude and dis t r ibut ion of the s t r e s s e s in dependence on the s ize of the sphe re , the e las t ic p r o p e r t i e s of the contacting m a t e r i a l s , and the applied force . Maximum p r e s s u r e P0 occu r s at the center of the sur face of contact , and it is equal to 3/2 of the mean p r e s s u r e Pm:

Acoustical pick-up for reception of signals from a drill pipe

An acoustical pick-up apparatus for use with a borehole acoustical telemetry system and which may be positioned on a drilling rig at a number of locations above the drill pipe, includes an electro-acoustical transducer coupled to a pick-up block having an arcuate contact face to conform to a cylindrical member on the drilling rig and a strap connected to the contact face at points spaced from the edge thereof.

On the frictional contact in crack analysis

Following the idea of Bowie and Freese we consider a crack in a field of pure bending. The crack is closed over part of its extent, and the two crack faces in contact are allowed to slip under frictional constraints. The solution is constructed under the assumption that the applied loading is monotonically increased. It is discovered, however, that it is possible to analyze unloading by suitably superposing the present solution and that of Bowie and Freese.