Electrical Brushes Research Articles

Electro-Mechanical Behavior of Copper-Based Electrical Motor Brushes

This study was mainly performed in order to examine the properties of electric motor brushes (EMB). EMBs are electrically conductive and work under wear conditions due to direct contact with the moving part (rotor) of electric motors. In accordance with the scope of the study, EMB characteristics were investigated in two different groups and reproduced with a new technique at the end of this phase. New EMBs were produced via varying proportions of copper matrix, graphene, and silicon carbide reinforcements. The composite-alloy powder elements were carefully squeezed by a cold and single-axis hydraulic press under a pressure of 500 MPa (±5 MPa) following 8 hours of mechanical alloying (MA). The molded composite product (sample) was sintered at 900° C for 1 hour in a reducing gas atmosphere. 100 kPa spring pressure was tested on each sample thrice with 8, 16, 24, and 32 m/s rotational speeds and densities of 4, 8, 12, and 16 A/cm2. Following this process, the electrical conductivity, porosity, hardness, wear loss, surface roughness, and temperature changes were investigated for each sample. It was determined that the electrical conductivity decreased with increasing reinforcement ratio and, in terms of electrical conductivity, affected the brushes’ properties negatively.

Improvement of Ball Mill Performance in Recycled Ultrafine Graphite Waste Production for Carbon Block Applications.

A carbon block is a carbonaceous material used in various applications such as bearings, mechanical seals, and electrical brushes. This work aims to fabricate carbon blocks from industrial graphite waste, a residue from the cutting and tooling process of graphite block production. The ball milling process was used to fabricate ultrafine graphite waste to enhance the packing of carbon blocks. The milling performance was profoundly affected by dispersing agents in which sodium dodecyl sulfate (SDS), lignosulfonate (LS), and mixed dispersant (LS-SDS) were applied. The results showed that LS-SDS had the best milling performance, the greatest grinding index, and a flowable slurry, indicating the potentiality of this formulation for the environmentally friendly manufacture of ultrafine graphite waste. Carbon blocks were prepared from oven-dried ultrafine graphite waste, which was mixed with amorphous carbon and pitch. This carbon mixture was formed a block by compaction before carbonization and impregnation. The density of the fabricated carbon blocks increased from 1.76 to 1.83 g/cm3 after impregnation along with the increase in hardness, flexural strength, and reduction in electrical resistivity from 83, 62 MPa, and 40 μΩ m to 88, 81 MPa, and 39 μΩ m, respectively. The physical properties of carbon blocks prepared from ultrafine graphite waste were comparable to the properties of typical pristine carbon products.

Sliding electrical contact properties of highly oriented copper fiber brush

Metal fiber brush is a new electrical brush that has a promising application in high current density and non-lubricating conditions owing to its unique structure. The copper fiber brush comprised of highly oriented and uniformly distributed fibers was prepared by the knitting method with a packing fraction of 20%. The influence of current on the sliding electrical contact properties of the copper fiber brush as sliding against the steel disc was investigated. The worn surfaces of the copper fiber brushes and the steel discs were characterized to reveal the involved wear mechanisms. The results show that the static contact resistance decreases significantly from 55 to 18 mΩ with the gradual increase of contact force from 1 to 8 N, which is attributed to the elastic contact of multiple fibers and good compressive performance. The sliding contact resistance and electrical noise decrease with the increase of current, which is attributed to the micro-welding of contact spots induced by an electric arc. The wear rate of copper fiber brush increases significantly from 1.2 × 10−5 to 5.7 × 10−5 mm3/N·m with the increase of current from 0 to 8 A. The electrical wear caused by arc erosion becomes the dominant wear mechanism, which is more profound than mechanical wear under high currents.

Liquid metal motor.

SummaryLiquid metal has demonstrated an enormous potential for developing soft functional devices and machines. However, current liquid metal enabled machines suffer from several issues, such as the requirement of a liquid environment, generation of weak actuating forces, and insufficient maneuverability. To overcome these restrictions, here, a motor is developed based on the electrical actuation of liquid metal droplets without the need for conventional electromagnets. The approach is distinguished by (1) the encapsulation of electrolyte and multiple liquid metal droplets within an enclosed system, and (2) the creation of stable and continuous torque outside a liquid environment. In addition, a liquid metal electrical brush is introduced to operate the motor with low friction and low wear. The unique driving mechanism endows the motor with several advantages, including low friction, no sparking, low noise, versatile working environment, and being built from soft materials that could offer new opportunities for developing soft robotics.

Liquid Metal Motor

As an emerging soft material, liquid metal has demonstrated enormous potential for developing high performance functional devices and machines. However, current liquid metal enabled machines suffer from several issues, such as the requirement of a liquid environment, generation of weak actuating forces, and insufficient maneuverability. These restrictions limit the application of liquid metal in constructing more complex, flexible and powerful actuating systems. Here, a motor is developed based on the electrical actuation of liquid metal droplets without the need for conventional electromagnets. The approach is distinguished by (1) the encapsulation of electrolyte and multiple liquid metal droplets within an enclosed system, and (2) the creation of stable and continuous torque outside a liquid environment. In addition, an electrical brush is introduced to contact liquid metal with solid electrodes and operate the motor with low friction. The parameters affecting the actuation behavior are further investigated. Moreover, the versatility and maneuverability of the motor is demonstrated by applying it to drive untethered vehicles and boats. The unique driving mechanism endows the liquid metal motor with several advantages, including low friction, no sparking, low noise, versatile working environment, and being built from soft materials that could offer new opportunities for developing soft robotics.

Prediction and Optimization of Parameters for the Al5083/ B4C Composite Wear Rate

Background:Al5083 has been basically used in marine and aerospace applications where it is intended for higher corrosion resistance and better weldability. Again this, Al5083 matrix has not been suitable for various other applications such as electrical contact brushes, cylinder liners, artificial joints and helicopter blades due to its poor wear resistance properties.Objective:The aim of this research is the optimization of wear rate of the composite with Al5083 matrix, reinforced with B4C (Boron carbide) particles, and it is achieved through the investigation of the subsequent effect: wt.% of the reinforcement, applied load and sliding speed.Methods:The material used for specimen is Al5083 and Al5083/B4C composite which is melted at 750°C in an induction furnace; the composite is prepared by stir casting technique. It was developed by an ex-situ technique. The liquid melt poured into preheated cast iron mould for carrying out the specimen preparation of wear testing.Results:The wear rate of Al5083/B4C composite is less than Al5083, the most influencing factor on wear rate is applied load and mechanism of deformation induced in the sliding surface of the pin was analysed by SEM (scanning electron microscope).Conclusion:Wear rate of Al5083 and Al5083/B4C composite increases with the increase of applied load, sliding speed and decreases as the wt. % B4C increases. The contribution of applied load is more in wear rate as compared to the other two factors and the value predicted by Taguchi, obtained by RSM (Response surface methodology) and evaluated by experiment are almost similar.

Low electrical resistance metal graphite brush reinforced with epoxy resin for electrical motor

Electrical conductive coals were invented about a hundred years. Coals often were composed of carbon materials, solid lubricants, metals, resins and etc. The main use of coal is in electric motors. In this paper Graphite, Copper and Ferromolybdenum were used as conductive carbon material, conductive metal and auxiliary material respectively. Further, epoxy resin was used as reinforcing material. Carbon brushes with resin due to suitable properties such as low resistance, conductivity and high speed are used. In this experiment first, the mixture of all materials was molded. The electrical conductivity test, FE-SEM images, Raman spectrum, and I–V diagram were carried out. FE-SEM images indicated the rate of scattering of the main materials in the samples. In this work, the electrical resistance of the optimum sample was 0.87 Ω.

Processes and Equipment for the Preparation of Coke Pitch and Graphitoplast Compositions for Pressing of Intermediate Products for Electrical Engineering

This article discusses advanced developments in the field of manufacture of electrical machine brushes. A new method for manufacturing by mixing coke pitch and graphitoplast compositions for making brushes, a new mixer design, and a new graphitoplast composition are presented.

Determination wear intensity of electrical brushes in DC machines considering impact of collector’s surface

One of the most loaded units affecting the reliability of DC machines is the collector-brush unit. There is a continuous process of mechanical, electrical and chemical interaction of the electric brushes with the collector during operation of the DC motor, which increases the wear of the electric brushes. In a result of the analysis of the works, devoted to the study of the operation of the collector-brush unit’s elements, the authors proposed a mathematical model for determining the intensity of wear of electric brushes, which allows taking into account the effect of the collector profile on the electric brushes wear intensity. The basic data and dependencies for modelling the movement of the electric brush on the collector surface, which based on the design scheme, are presented. A distinctive feature of the developed scheme is that the elastic force at the contact of the brush with the surface of the collector is determined from the side of each collector plate. For the above scheme, a system of differential equations is compiled, allowing simulating the movement of the brush in the radial and tangential direction during its interaction with the surface of the collector. The resulting mathematical model allows us to determine the trajectory of the brush and the oscillations of the elastic force that occurs at the point of contact of the brush with the collector, with different parameters of the collector-brush unit’s elements and modes of operation of the machine, causing a certain frequency of rotation of the armature. Taking into account the above mathematical model, a software product has been developed for calculating the wear rate of DC motor electric brushes during its operation. The practical value of the work is that the use of the developed software allows you to find more optimal operating parameters for the collector-brush unit of DC motor with a minimum of time.

Vibration model as a system of coupled oscillators in a direct current electric motor

This article describes a vibration model connected by individual nodes of a DC motor. The purpose of the article is a mathematical model allowing to predict the work of machines with a depreciation resource and search for ways to increase the information content of assessing the functioning of the rolling stock condition without dismantling them. Currently, the operational reliability of the DC motor is reduced after the development of the service life. Study and evaluation of the vibration effect on the brush-collector node. The main components of the DC motor (bearings, electrical brushes) are unrecoverable. Therefore, any interference with their normal operation leads to premature wear of the entire DC motor. Existing methods for life-extending maintain the operational reliability of a DC motor equal or close to the passport data for several years. This model allows vibration diagnostics without dismantling the DC motor and stopping the rolling stock. The mathematical model describes the oscillations of each node of the DC motor in the direction of movement of the rolling stock, showing the excess of the permissible value. After mathematical processing of the results, a machine reliability model under study is obtained (usually in the form of polynomials) as a function of the needed parameters – the influencing factors. Due to this model, pre-detected defects can save on repairs and maintenance in the future. This model is the basis of software for online diagnostics. The proposed model allows providing an objective use of repair and restoration compositions depending on the current technical condition, which will lead to an increase in the service life of the mechanism and savings in operating costs. On the one hand, extending the operating life of a DC motor should produce an economic effect, and on the other hand, technical measures to maintain operational reliability cause an increase in material costs.

Influence оf gravity and thermodynamics on the sliding electrical соntасt

The motivation behind this work is to develop a dynamical systems understanding of the wear processes. We present a model for wear particle detachment from a surface of electric brushes and slip ring (collector) in the commutator-and-brush assembly. The geometry of the contact area is analysed and debris shape modification is estimated. The investigation accounts for the dependence of the properties of the sliding contact layer on the deviation of this layer from land contour under Earth’s gravity and on the Joule–Thomson effect. With stochastic simulations we demonstrate that analytical model of the third body may explain the different lifetime of the electrical brush depending on it position relative to the slip ring axis, and we predict their durabilities.

Physical model of the sliding contact of conductors of the alloy Cu-Zr and Cu-Re under high current density

The model of formation and dynamics of the sliding contact layer using hydrodynamic approach is suggested. This model is considered through the example of electrical slip brushes of high-temperature (∼500 ° C) conductors Cu-Zr and Cu-Re sliding on the turbogenerator ring. In this study (a) the analysis of the geometry of the sliding layer forms by the particles breaking away from the brush surface and (b) the dependence of the contact layer deviation from the land contour, taking into account the Earth’s gravity effect is carried out. The model shows the non-linear behavior of the friction coefficient and the current-voltage characteristics of the contact layer between electrical brushes of high-temperature conductors Cu-Zr and Cu-Re and slip ring (collector) under the electric current of high density.

A Modular Superconducting Generator for Offshore Wind Turbines

In this study, a new claw-pole type transverse flux superconducting generator topology is presented. The machine has a stationary superconducting field winding, which eliminates electrical brushes and cryocouplers. The machine is specifically designed for low-speed high torque applications such as large offshore wind turbines. The proposed machine is robust and has a modular structure. A 30 kW, 100 rpm prototype is planned to be manufactured to prove the concept. MgB2, YBCO, and BSSCO wires are compared in terms of wire length, operating temperature, and critical temperature. The magnetic flux penetrating into superconducting wire has been simulated using 3D FEA software. Moreover, mechanical loads are estimated and the deflections in the structure are analysed.

Correlation analysis of brush temperature in brush-type DC motor for predicting motor life

Some critical components of motors and generators have sliding electrical contacts. Electrical brushes are usually used in these contact points to conduct current between the stationary part and the moving part of the motor. In this paper, studies on brush wear against copper commutators are briefly reviewed. The main influential factors in brush wear are associated with both mechanical wear and electrical wear. Brush wear is affected by various factors, including temperature, material properties, sliding speed, contact force, and interfacial as well as environmental conditions. The mechanical wear of brushes is proportional to brush spring pressure and sliding speed, and the electrical wear of brushes is associated with current and contact voltage drop. For characterization, a brush wear test machine is designed, and influential factors, such as electrical contact resistance, temperature, wear mass loss, and so on, are measured. The wear tests are processed using a small brush-type automotive DC motor. The study primarily aims to investigate the effects of the wear behavior of copper-graphite brushes on small brush-typed DC motors. The variable conditions of electrical current are obtained by changing the brush spring pressure and the sliding speed. The results are electrical contact resistance, voltage drop, brush surface temperature rise, and so on. Brush wear is greatly changed by electrical current, which indicates that high current itself not only produces more Joule heating but also causes an increase in voltage drop that will result in additional Joule heating.

Wear and Life Characteristics of Microwave-Sintered Copper-Graphite Composite

Copper-graphite composite is an important tribological material used in electrical sliding contact applications like electrical brushes in motors and generators. The electrical sliding contact experiences multiple stresses such as mechanical pressure and temperature. Traditional life tests under normal operating condition would be a time-consuming process due to the longer expected life of the composite. Accelerated wear testing was carried out to evaluate the life characteristics of the composite. This work focuses on evaluation of tribological performance of microwave-sintered copper-graphite composite using accelerated wear testing methodology using high temperature pin-on-disc tribometer. Microstructural studies of worn out surfaces were carried out using SEM with EDAX. Reliability and analysis on life characteristics were performed on the time-to-failure data using temperature-nonthermal-accelerated life-stress model. The obtained times-to-failure data from the accelerated wear testing was extrapolated to normal usage condition. Temperature and pressure are significantly affecting the wear performance. Self-lubricating action of graphite and improvement in wear resistance is helpful in extending the life of copper graphite composite. The life of the composite obtained through testing at mean and 99% reliability are 18,725 and 16,950 h, respectively.

Electroless Coating of Silver on Multiwall Carbon Nanotubes

Silver reinforced with carbon nanotubes, instead of graphite, would increase both the electrical conductivity, hardness and wear resistance of the electrical brush materials. The effective utilization of carbon nanotubes in the Ag/CNT composite depends strongly on its uniform distribution and strong interfacial adhesion to the silver matrix and thus demands for its surface modification. In order to carry out the surface modification of carbon nanotubes, electroless coating was given to them after liquid phase oxidation, sensitization and activation process. The room-temperature chemical treatment results in a nominally complete coating over the entire outer surface of multiwall carbon nanotube. The surface morphology of the carbon nanotubes after each step has been studied using TGA, DSC, XRD, FTIR and SEM.

Remanufacturing of High Temperature Ball Valve by Surface Engineering Technology

Four kinds of coating materials and two kinds of brush plating materials were screened and sprayed on the surface of valve ball by plasma spraying technology and brush plated on the surface of valve seat by electrical brush technology, respectively. The wear resistance of the sealing pairs and the properties of the plasma sprayed coatings were tested. The results indicate that the sealing pair composed of the valve ball with the plasma sprayed coating of Al2O3-TiO2 and the valve seat with the brush plating layer of nickel tungsten has best combination property. The gap of the sealing pair at room temperature and the leakage rate at elevated temperature of the high temperature ball valve were obtained by FEM method and analysis method, respectively. Therefore, the open and close torque of the high temperature ball valve was determined. According to the results of the research, the failed ball valve was remanufactured, and the performance inspection was also conducted. The remanufactured ball valve has much longer service life than the original one and its sealing behavior was also improved significantly.

An analysis of the main factors on the wear of brushes for automotive small brush-type DC motor

Some critical components in motors and generators have sliding electrical contacts. Electrical brushes are commonly used in those contact points to conduct current between the stationary and moving parts of a motor. Brushes are exposed both to mechanical and electrical loading. In this paper, studies on the wear of brushes against copper commutator were briefly reviewed. The main influential factors of brush wear are associated with both mechanical and electrical wear. Brush wear is affected by various factors including temperature, material properties, sliding speed, contact force, and interfacial and environmental conditions. The mechanical wear of brushes is proportional to the brush spring pressure and sliding speed, while the electrical wear of brushes is associated with current and contact voltage drop. To characterize the wear, a brush wear test machine was designed, and influential factors were measured such as electrical contact resistance, temperature, wear mass loss, and so on. The wear tests were processed using a small brush type automotive DC motor. The main objective of this study is to investigate the effects of the wear behavior of copper-graphite brushes in a small brush-type DC motor. The variable conditions are with and without electrical current by changing the brush spring pressure and sliding speed, and the results are electrical contact resistance, voltage drop, brush surface temperature rise, and so on. Brush wear greatly changes with electrical current. This shows that the high current not only produces more Joule heating but also causes an increase in voltage drop, which will result in additional Joule heating.

Effect of Plasma Sprayed Ceramic and Cermet Coatings on Wear-Out Failure of High Temperature Ball Valve

Three kinds of coating materials, namely Cr2O3 ceramic, Al2O3-TiO2 ceramic and WC-Co cermet, were screened and sprayed on the surface of valve ball by plasma spraying technology, and two kinds of brush plating materials, namely high speed nickel and nickel tungsten, were also screened and brush plated on the surface of valve seat by electrical brush technology. The microstructure and morphology of the plasma sprayed coatings were analyzed by means of scanning electron microscopy. The tribological properties of the plasma sprayed coatings sliding against the high speed nickel and nickel tungsten layers were investigated on a pin-on-disc friction and wear tester. The microhardness, thermal shock property and bonding strength of the coatings were also tested. The results indicate that the sealing pair composed of the valve ball with the plasma sprayed coating of Al2O3-TiO2 and the valve seat with the brush plating layer of nickel tungsten has the best combination property.

Hexagonal Phase of CdS Thin Films Obtained by Oscillating Chemical Bath

Cadmium sulfide thin films were deposited in an oscillating chemical bath using a Teflon vane connected to an electrical dental brush oscillating at . The range of the bath temperature was from 65 to in intervals of and different deposition times. By this agitation technique we obtained films with a highly oriented hexagonal structure (α-greenockite) in the (002) direction as measured by X-ray diffraction patterns. Images of atomic force microscopy and stoichiometry values obtained by energy-dispersive analysis by X-ray confirm the good quality of deposited films. High stoichiometry on the films was measured by elemental analysis with variations less than 3.5% in all samples. The mean value of the gap energy was about , a close value for these films.