Electrical Brushes Research Articles

Oral care practices in critical care unit

Sir: I appreciate the comments by Wise and Cole with regard to our article [1] evaluating oral care practices in intensive care units. The question of whether better cleaning of the oral cavity may help to reduce nosocomial infections is indeed intriguing; however, this is expert opinion. It remains unclear whether small brushes, normal brushes, or electrical brushes are equivalent. A randomized clinical trial is ongoing in our department to clarify this issue. Their observations also reinforce the variability of practices in different ICUs, explained in part by the different cultures of critical care in different European countries, which is well reflected in the participants at the European Society of Intensive Care Medicine (ESICM) congress. We believe this to be an opportunity to develop a consensus document to be implemented as an European guideline. The multidisciplinary approach used for the development of care bundles on hospital-acquired pneumonia developed by a panel of experts [2] is a good model to follow. Indeed, oral care is part of the recommended care bundles for prevention of ventilator-associated pneumonia (VAP), and is recommended by this panel. Once confirmed, however, additional efforts will be necessary to get these recommendations implemented, as recently demonstrated in a study which evaluated the knowledge of ICU nurses about guidelines for the prevention of VAP [3]. Previous reports also pointed out that simply publishing guidelines is insufficient to achieve a high rate of compliance [4, 5]. We believe that here. as well, the ESICM can play a pivotal role.

The effect of brush spring pressure on the wear behaviour of copper–graphite brushes with electrical current

Electrical brushes are used to conduct current between stationary part and moving part of a motor or a generator. To ensure proper current transfer and continuous contact, brushes must be loaded against the sliding contact surface with a sufficient force. High loads increase frictional losses and wear of the brushes and/or sliding surface. While relatively low contact pressure causes arcing and higher voltage drop. In this study, a novel pin-on-slip ring-type friction and wear test machine was designed and manufactured for the purpose of brush testing. Copper–graphite-based electrical brush containing 90 wt% copper and 10 wt% graphite was manufactured by powder metallurgy and the tribological behaviour and voltage drop were investigated at different brush spring pressures at 10–200 kPa with current. It was found that the specific wear curve showed three distinct wear rate regimes, such as low, mild, and severe. Severe wear was observed below 30 kPa and above 120 kPa brush spring pressures (BSP) (3 and 12 N loads, respectively). Arc erosion was the main wear mechanism below 30 kPa brush spring pressure while abrasion was dominant above 120 kPa BSP. Low and mild regimes were observed between 30–50 and 50–120 kPa BSP, respectively. SEM observations showed that a continuous surface layer was formed at the sliding surfaces of the wear samples in low and mild wear regimes. The wear debris was examined by SEM and X-ray diffractometer.

Tribological behaviour of graphite powders at nano- and macroscopic scales

With its high resistance, good hardness and electrical conductibility in the basal plans, graphite is used for many years in various tribological fields such as seals, bearings or electrical motor brushes, and also for applications needing excellent lubrication and wearreducing properties. But thanks to its low density, graphite is at the moment destined for technologies which need a reducing of the weight combined with an enhancement of the efficiency, as it is the case in aeronautical industry. In this contexte, the friction and wear of natural (named graphite A) and synthetic (called graphites B and C) powders were evaluated, first at the macroscopic scale when sliding against steel counterfaces, under various applied normal loads. Scanning Electron Microscopy and AFM in tapping mode were used to observe the morphological modifications of the graphites. It is noticed that an enlargement of the applied normal load leads to an increase of the friction coefficient for graphites A and C; but for the graphite B, it seems that a ‘‘limit’’ load can induce a complete change of the tribological behaviour. At the same time, the nano-friction properties of these powders were evaluated by AFM measurements in contact mode, at different contact loads. As it was the case at the macroscopic scale, an increase of the nano-contact load induces higher friction coefficients. The determining of the friction and wear mechanisms of the graphite powders, as a function of both their intrinsic characteristics and the applied normal load, is then possible.

Simulation Study of Aspiration using an Electrical Oral Brush Combined with an Automatic Liquid Supply/Suction System

Simulation Study of Aspiration using an Electrical Oral Brush Combined with an Automatic Liquid Supply/Suction System

Hybrid electromagnetic micro-relay with fast response and bistable operation mode

A hybrid electromagnetic micro-relay with a bistable wiggling microactuator and a micro-fabricated electrical brush is developed. The switching power consumption is only 28.8 mJ owing to the bistable operation but the switching time is as short as 0.3 mS because of the in-plane movement and sandwich driving mechanism. As a power relay its maximum load current is over 2 A.

Development of Metal Fiber Electrical Brushes for 500 kW SSMG Sets

The effort that this paper reports began in 1996 as a Team Submarine sponsored Navy SBIR N96-103, and expanded into a multi-year NAVSEA (SUB-RT) sponsored, Phase III, applied research and development project. Therein a combined government, university and industry partnership are designing, building, integrating and testing metal fiber electrical brushes for the AC (slip ring end) and DC (commutating end) of a 500 kW Ship's Service Motor Generator set and other submarine DC motors. These revolutionary brushes are being designed and laboratory-tested, then transitioned toward Navy use via the submarine MG set land based test facility, and later at sea on US Navy submarines. The metal fiber brush project was previously reported on at the ASNE sponsored Navy Electric Machines Conference in 1999.

Four-year experience with pleural abrasion using a rotating brush during video-assisted thoracoscopy.

Due to the high recurrence rate in primary spontaneous pneumothorax (PSP), surgical therapy is currently a well-accepted method of treating this condition. There is no general agreement about the best time for surgical intervention (i.e., after the first or second episode) or the optimal surgical approach,--i.e., tube thoracocenteses, thoracotomy, or video-assisted thoracoscopy (VATS) with or without pleurectomy or pleurodesis. The aim of this study was to verify the efficacy of VATS and mechanical brush pleurodesis using a rotating electrical brush system. We treated 47 patients with PSP between June 1993 and June 1997. Follow-up ranged from 20 to 56 months. There were 38 male and nine female patients with a mean age of 26 years. Emergency thoracocenteses due to tension pneumothorax became necessary in three patients. All patients were treated by VATS and mechanical brush pleurodesis. Wedge resection was done if bullae or blebs were present (68.1%). Operating time was 20-60 min (mean, 35). There were no intraoperative complications and no conversions to conventional surgery. In the first few postoperative days, postoperative pain was controlled with nonsteroidal antirheumatic drugs and additional morphines. Drainage time was 3-7 days (mean, 4). Hospitalization time was 4-8 days (mean, 5). The recurrence rate was 2.1% (one patient). No postoperative bleeding or wound infection occurred in any of our patients. VATS combined with mechanical brush pleurodesis using the electrical brush system is a highly effective and safe treatment for patients with recurrent primary spontaneous pneumothorax.

New Electrical Oral Brush with Auto-Liquid Supply and Suction-System

New Electrical Oral Brush with Auto-Liquid Supply and Suction-System

Electrical fiber brushes-theory and observations

The performance limits of electrical fiber brushes are assessed by means of an expanded, refined theory. Measurements back to 1979 are in accord with the theory, including 1993 measurements on a set of 64 fiber brushes in a homopolar motor at the U.S. Navy Annapolis Laboratory, At /spl nu/=7.6 m/s velocity and j=1 MA/m/sup 2/ the electric loss was 0.026 W/A, and after a 20 h test the brushes showed no detectable wear. On the other end of the scale, electrical brushes are being developed for a maglev train system (American Maglev Tech of Florida, Inc.) to operate up to 150 m/s. According to the theory, this will be possible in the open atmosphere with dimensionless wear rates smaller than 10/sup -8/ at current densities up to a few MA/m/sup 2/. At speeds to 300 m/s, projected losses may range up to 4.3 W/A at flash temperatures at and below 100/spl deg/C. The newest fiber brushes preserve the high contact spot density at the ends of individually flexible fibers, independent of amount of wear. Correspondingly, with 10 cm long brushes, for example, the projected maglev brushes should last at least for a New York-Los Angeles return trip. Also, on account of the changed method of construction, manufacturing costs have decreased by more than a factor of ten in the past two years. Prospects are that with industrial manufacturing techniques the cost of fiber brushes, based on ampere hours conducted, will become easily competitive with monolithic graphite brushes. Pending further practical experience, it is therefore expected that: (1) metal fiber brushes will expand the range of sliding brush applicability and (2) ultimately displace graphite brushes for most of their present applications.

New copper powders for electrical brushes and microbearings: G.M. Rankinen, D.F. Berry (SCM Metal Products Inc., North Carolina, USA), Int. J. Powder Metallurgy, Vol 30, No 2, 1994, 173–178

New copper powders for electrical brushes and microbearings: G.M. Rankinen, D.F. Berry (SCM Metal Products Inc., North Carolina, USA), Int. J. Powder Metallurgy, Vol 30, No 2, 1994, 173–178

Evaluation of subsurface stresses in a thermal mound with application to wear

Presented are calculations of elastic and thermoelastic stress within an evolving thermal mound present on the interface between a carbon graphite brush sliding against a fast moving rotor. Thermal mound temperatures, due to frictional and electrical power dissipation about the individual brush to rotor contact spots, evolve from cold to hot and are based upon the thermally nonlinear temperature fields calculated by Lu and Bryant (C.T. Lu and M.D. Bryant, Thermoelastic evolution of contact area and mound temperatures in carbon graphite electrical brushes, Wear, 174 (1994) 137–146. M.D. Bryant and J.W. Lin, Photoelastic visualization of contact phenomena between real tribological surfaces, with and without sliding, Wear, 170 (1993) 267–279). Presented are contours of thermoelastic stresses that correspond to the aforementioned temperature fields. Under normal operating conditions for carbon graphite sliders and brushes, these stress fields do not exceed material strengths. In light of this, additional simulations are presented of hypothetical perturbations to the overall stress field that could cause stresses to exceed material strengths, resulting in material rupture that could lead to particle detachment and wear.

Thermoelastic evolution of contact area and mound temperatures in carbon graphite electrical brushes

Using the finite element method to estimate coupled electrical, thermal and thermoelastic fields, and an exact solution to analyze elastic contact stresses, electrical and frictional heating of a thermal mound present in the interface between a carbon graphite block sliding against a fast moving conductor is simulated. Heating due to frictional power dissipation is modeled by internal heat sources uniformly distributed within a very thin layer beneath the sliding contact interface. Internal Joule heat sources are estimated from the electric field and resistivity. The thermal mound possesses the highly temperature-dependent electrical resistivity, thermal conductivity and specific heat common to carbon graphite materials. Evolution of the mound temperatures from cold to hot and the contact radii from large to small is studied. Results show that the type of thermal boundary condition prescribed on the contact surface has a marked effect on the entire evolution. To simulate the extreme reduction of contact area observed in the evolution to thermal mounding from normal contact, an insulated thermal boundary condition was needed.

Effect of temperature on wear rate of homopolar pulse consolidated electrical brushes

Binderless copper-graphite composite electrical brushes are being developed using a high-energy, high-rate pulse sintering technique by the Center for Electromechanics at The University of Texas at Austin (CEM-UT). Experiments were done to investigate temperature's effect on the homopolar pulse consolidated (HPC) brush wear rate for an apparent brush current density of 180 A cm −2, a brush downforce of 44.5 N, and rotor surface sliding speeds of 10 m s −1 and 40 m s −1. At a sliding speed of 10 m s −1, it was found that brush wear rate dropped steeply as the brush bulk temperature increased from 80 °C to 103 °C. Other than this unusual wear finding in this particular sliding speed and temperature range, test results indicated that brush wear rate generally increased with increasing brush bulk temperature. At a sliding speed of 40 m s −1, it was found that brush wear rate suddenly increased by several times as the brush bulk temperature approached 149 °C. In the case of 10 m s −1 sliding speed, no stepwise rise in brush wear rate was observed even as the brush bulk temperature reached 156 °C.

Automated apparatus for long-term testing of electrical brushes : Daniel M. Alleyet al. IEEE Trans. Compon. Hybrids mfg Technol.14(1), 31 (1991)

Automated apparatus for long-term testing of electrical brushes : Daniel M. Alleyet al. IEEE Trans. Compon. Hybrids mfg Technol.14(1), 31 (1991)

A particle ejection mechanism for brushwear

A hypothetical mechanism to explain wear associated with thermal mounding in carbon graphite electrical brushes is introduced. Contact between a brush thermal mound and a sliding/conducting rotor initiates a thermal cycle in which extreme temperatures inside the mound alter material property values and intensify stresses. Temperatures and stresses evolve until mound failure occurs, probably near the edge of the contact zone between the thermal mound and the rotor. The mound detaches from the brushface, and with the mechanical support provided by the mound removed, the entire brush body tilts until contact is reestablished with some other elevated portion of the brushface. A thermal mound is born, and the thermal cycle begins. Using the particle ejection mechanism as a basis, wear rates, hot spot speeds, and thermal mound lifetimes are calculated, related, and compared to experimentally obtained values. Agreement between theory and experiment is shown to be excellent. Finally, an attempt is made to demonstrate how this mechanism may account for moving hot spots, widely varying wear rates, environmental effects, and vastly different performance characteristics in electrical brushes. >

Automated apparatus for long-term testing of electrical brushes

The meaningful evaluation of electrical brushes and the development of novel electrical sliding contacts can require exhaustive testing. An automated testing system has been developed in which a personal computer both controls test parameters for a matched brush pair running on the same rotor according to a preselected program, and stores test data. Specifically controlled are the brush forces, brush polarity, and the current. The voltage drops across each of the two brushes, their wear, and the rotor temperature are monitored. Additionally, traverses, meaning brief periods of ramping the current up and down between preselected limits while measuring the associated voltage drops, can be programmed into the tests. The duration of the various phases in complex testing programs and the intervals between data taking can be varied between seconds and months, but the system is switched off automatically when the voltage across either of the two brushes or the rotor temperature exceeds a preselected value. The accumulated data can be recalled in various graphical representations and program changes can be made at any time without interrupting the test.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Invited general interest paper

With the development of a manned space station permanently circling the earth, an efficient system is needed to provide both electrical power and propulsion. The electrodynamic tether system being developed by NASA will do this by using a long (e.g. 10 km) conducting tether to interact with the earth's magnetic field. In a low earth orbit, the induced voltage would be on the order of a few tenths of a kilovolt per kilometer of tether. Assuming sufficient electrical contact can be maintained with the ionosphere, a 10 km tether would supply several kilowatts of electrical power. The extraction of power via an associated current results in an I × B force that reduces the orbital speed of the spacecraft. Conversely, if a sufficiently large reverse voltage is applied to reverse the current, then the I × B force will increase the orbital speed and electrical energy will be converted into energy. Consequently, the electrodynamic tether system is expected to perform as a motor/generator system providing a simple, reliable and economical means of efficiently converting orbital energy into electrical energy in a fully reversible process. In addition to a general discussion of the electrodynamic tether system, this article will concentrate on the dynamics of the tether, the proposed electrical contacts or current brushes and the Alfven waves that will carry the charge through space.

Electrically and frictionally derived mound temperatures in carbon graphite brushes

Numerical and analytical simulations of mound temperatures are presented as the mound evolves from cold to hot. The temperature field about a thermal mound in an electrical brush is estimated using a heat conduction equation with frictional and electrical internal heat sources. Computed temperatures seem to agree with measured temperatures, but thermal nonlinearities can result in temperatures that are higher and hot zones that are larger than the mathematical sum of the frictional and joule thermal fields. It is found that combined heating coupled with nonlinear effects can significantly shorten the formation time of very hot temperature zones. Computed thermal fields mature within about 4 ms, the approximate lifetime of a stationary mound on the brush face. This suggests validity for the assumption that the mound is stationary on the brush during thermal evolution. >

Temperatures at Interfacial Contact Spots: Dependence on Velocity and on Role Reversal of Two Materials in Sliding Contact

Based on the theory by Blok and Jaeger, simple equations have been obtained for the theoretical evaluation of flash temperatures, i.e., the temperatures of circular or elliptical contact spots between two homogeneous materials, when friction heat and/or Joule heat is evolved at the interface. The parameters appearing in the equations have been expressed in terms of experimental data, the coefficient of friction, known materials properties, and the ellipticity and number of contact spots. The equations are especially simple in the limiting cases of very high and of very low speeds, and were indeed known in these limits for circular, albeit not for elliptical contact spots. As an example, the flash temperatures of plastic contact spots on account of friction heat have been computed for (i) an electrical brush material sliding on copper, and (ii) a carbon steel sliding on itself. In these examples the dependence of the flash temperature on the velocity of the contact spots relative to either or both of the two sides has been investigated, wherein the effect of sliding rate on the flash temperature via the strain rate dependence of local hardness has been taken into consideration,- it is believed for the first time in any theoretical investigation of flash temperatures. In the high-speed case, in agreement with intuitive expectation, the numerical examples show that under otherwise same conditions and same macroscopic velocity, minimum flash temperature is attained when the spot moves relative to both sides. Typically, that minimum does not occur when the contact spot speed is one half of the relative speed on each of the two sides, however. Moreover, and somewhat unexpectedly, the results show that the previously neglected strain rate dependence of the hardness has a considerable effect.

Mechanical seals: some developments in face materials

Carbon has been used as a face material in mechanical seals for well over fifty years. The first grades of carbon used were developed from carbon electrical brush materials, but the continuous increase in the severity of mechanical seal operating conditions has necessitated ever improving grades of carbon. This paper details some of the means available to the carbon technologist to achieve these improvements and gives examples of some special applications.