An Analysis of the Performance of Trolleybus Brushes Developed from Recycled Materials

applied sciences

Article An Analysis of the Performance of Trolleybus Brushes Developed from Recycled Materials

Adam Jakubas 1, Krzysztof Chwastek 1,* , Artur Cywi ´nski 2, Adam Gnatowski 3 and Łukasz Suchecki 3

1 Faculty of Electrical Engineering, Cz˛estochowaUniversity of Technology, Al. Armii Krajowej 17, 42-200 Cz˛estochowa,Poland; [email protected] 2 Company OMEGA Project, ul. Topolowa 1, 43-100 Tychy, Poland; [email protected] 3 Faculty of Mechanical Engineering and Computer Science, Cz˛estochowaUniversity of Technology, Al. Armii Krajowej 21, 42-200 Cz˛estochowa,Poland; [email protected] (A.G.); [email protected] (Ł.S.) * Correspondence: [email protected]

Received: 16 October 2020; Accepted: 6 November 2020; Published: 9 November 2020

Abstract: The paper presents an analysis of the performance of traction brushes produced from waste materials. Brushes are used to ensure good electrical contact between the rail and the pantograph. Slides are produced by the process of hot pressing, with the parameters of heating up to max 175 ◦C, at the minimal pressure value of 200 MPa. Some of the developed brushes with a high (55–60%) content of recycled materials are more durable and break-resistant than their commercial counterparts.

Keywords: trolleybus brushes; recycling; mechanical and electrical properties

1. Introduction Electro-mobility of public transport in cities has become an important issue in recent years, since passenger and freight transport consume more than a quarter of global primary energy and is responsible for significant greenhouse emissions [1,2]. Trolleybuses are commonly perceived as a valuable alternative to conventional buses in sustainable urban transportation systems [3–6]. However, the very presence of sliding current-carrying contact zone causes non-trivial problems. The traction brushes made of a mixture of graphite and copper filings have to be replaced on a weekly basis under standard operating conditions, because of their wear [7]. The issue of how to assure a proper electric contact has been the subject of numerous research works and monographs [8–11]. It should be stressed that the problem is extremely complex, taking into account the roughness of the contacting surfaces, random occurrence of contact spots, elastic and plastic deformations, the presence of dirt, grease, soot burnouts, as well as possible vibrations of the pantograph-catenary system. The interdisciplinary nature of the problem attracts researchers on materials science and tribology, physicists, and mechanical and electrical engineers. Senouci and colleagues [7] focused on anisotropic electrical and mechanical properties of graphite. The authors have noticed that the friction and wear behavior of copper-graphite are influenced by the magnitude of electrical current. The authors have also examined the effect of contact polarity on the surfaces of contact, on the transferred layers, on the contact electrical potential and on the contact wear. One of the most commonly used theories concerning the electrical contact resistance between two metal surfaces was developed more than fifty years ago by R. Holm (the year of publication of his monograph [8] is considered in this context (fourth edition, most often cited); however, Greenwood refers in his paper [9] to the results obtained by Holm presented in 1929 in a newsletter issued by a commercial company). Briefly speaking, Holm assumed the true points of contact (referred to as a-points) between two jagged surfaces might be approximated as ellipses. Next he computed the

Appl. Sci. 2020, 10, 7929; doi:10.3390/app10217929 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 10

Greenwood refers in his paper [9] to the results obtained by Holm presented in 1929 in a newsletter Appl.issued Sci. 2020by ,a10 ,commercial 7929 company). Briefly speaking, Holm assumed the true points of contact2 of 10 (referred to as a-points) between two jagged surfaces might be approximated as ellipses. Next he ρ contactcomputed resistance the contact from theresistance relationship from Rthe= relationshipf (γ) where 𝑅 γ== √𝑓a/𝛾b iswhere a geometric 𝛾=𝑎𝑏 quantity⁄ is a geometric (the ratio S 4ac ofquantity two semi-axes (the ratio of of the two ellipse), semi-axesρ is material of the ellipse), speciﬁc 𝜌 resistivity is material whereas specifica resistivityc is the radius whereas of equivalent 𝑎 is the circularradius of spot equivalent with area circular equal to spot that with of the area elliptical equal toa-spot. that of Next, the theelliptical theory a-spot. was extended Next, the to theory cover thewas caseextended of similar to covera-spots, the cf.case Figure of similar1, leading a-spots, to thecf. Figure relationship 1, leading to the relationship 1 1 11 R𝑅=𝜌= ρ ++ 2na2𝑛𝑎 2α2𝛼 where 𝑎 is the mean a-spot radius (obtained from the averagingP ∑ 𝑎⁄𝑛 (𝑎 is the radius of i-th where a is the mean a-spot radius (obtained from the averaging i ai/n (ai is the radius of i-th a-spot, a-spot, n–the total number of a-spots), whereas 𝛼 is the radius of the cluster of a-spots, referred to as n–the total number of a-spots), whereas α is the radius of the cluster of a-spots, referred to as the the Holm radius. Holm radius.

Figure 1. A sketch representing contact points and current flow between two surface. Adapted from [12]. Figure 1. A sketch representing contact points and current flow between two surface. Adapted from The[12].Holm theory has been in use for several decades and a number of its refinements have been suggested to take into account different factors. It should be remarked that there is an annual The Holm theory has been in use for several decades and a number of its refinements have been international conference on electrical contacts, called the Holm conference [13]. Generally, the theory is suggested to take into account different factors. It should be remarked that there is an annual valid for contacts of much larger size than the mean free path of the electrons. Mikrajuddin et al. [14] international conference on electrical contacts, called the Holm conference [13]. Generally, the theory suggested an expression for the contact resistance that in the limiting cases reduces itself to the Holm is valid for contacts of much larger size than the mean free path of the electrons. Mikrajuddin et al. resistance and the Sharvin resistance (which is relevant for nano-electronic devices). Kogut and [14] suggested an expression for the contact resistance that in the limiting cases reduces itself to the Komvopoulos [15] derived, from the first principles, a general electrical contact resistance theory for Holm resistance and the Sharvin resistance (which is relevant for nano-electronic devices). Kogut conductive rough surfaces. The analysis was based on fractal geometry for the surface topography and Komvopoulos [15] derived, from the first principles, a general electrical contact resistance description, elastic-plastic deformation of contacting asperities, and size-dependent constriction theory for conductive rough surfaces. The analysis was based on fractal geometry for the surface resistance of microcontacts. Subsequently [16], the authors extended the validity of their theory by topography description, elastic-plastic deformation of contacting asperities, and size-dependent taking into account the presence of a thin insulating film between the rough surfaces, which was constriction resistance of microcontacts. Subsequently [16], the authors extended the validity of their treated as an energy barrier that impeded current flow due to the electric-tunnel effect. The authors theory by taking into account the presence of a thin insulating film between the rough surfaces, suggested that constriction resistance (computed from the Holm theory) played a less significant which was treated as an energy barrier that impeded current flow due to the electric-tunnel effect. role in the electrical contact resistance theory than the tunneling effects occurring in the thin film The authors suggested that constriction resistance (computed from the Holm theory) played a less layer. Next, Kogut developed a refinement of his theory to cover the case, where there is a significant significant role in the electrical contact resistance theory than the tunneling effects occurring in the contamination of electrical contacts [17]. thin film layer. Next, Kogut developed a refinement of his theory to cover the case, where there is a Regarding rather more experiment-oriented than theory-oriented papers, the following significant contamination of electrical contacts [17]. contributions should be accounted: Midya et al. [18,19] focused on electromagnetic compatibility Regarding rather more experiment-oriented than theory-oriented papers, the following issues, namely pantograph arcing and the related phenomena (distortion of supply voltage waveforms, contributions should be accounted: Midya et al. [18,19] focused on electromagnetic compatibility conducted and radiated emissions etc.). Samodurova et al. [20] described a novel simplified technology issues, namely pantograph arcing and the related phenomena (distortion of supply voltage of production graphite-plastic brushes in a single step. The main forming operation is carried out with waveforms, conducted and radiated emissions etc.). Samodurova et al. [20] described a novel the unit pressure of 30–40 MPa, at temperature from the range 150–170 ◦C. The semi-finished product simplified technology of production graphite-plastic brushes in a single step. The main forming is held under press for 3–5 min. Wu et al. [21,22] examined the evolution of the electrical contact Appl. Sci. 2020, 10, 7929 3 of 10 between pantograph and catenary with respect to electrical conductivity, temperature rise, as well as microstructure variation. The evolution mechanisms were discussed on the basis of Scanning Electron Microscopy (SEM) based microstructure analysis of five typical morphologies (craters, dull-red areas, bright areas, dark stream lines, and pits). The authors examined the effect of electric current on contact resistance and found that for smaller current values the decrease in contact resistance is more abrupt. Moreover, by means of infrared thermography, they found that temperature rise under current-carrying conditions is significantly higher than for a pure friction, current-free regime. This led them to the conclusion that the electric effect takes a dominant role in the temperature rise of carbon strips and heat accumulation regions are formed due to pantograph arcing. The authors noticed significant wear morphology differences under pure friction and current-carrying conditions. Khusnutdinov et al. [23] described a practical problem, similar to the one being addressed in this contribution: how to increase the service time of electrical brushes? The concept, introduced in Kazan public transport system, was to introduce a novel design of the brush holder, which allows one to reduce the cost of a new brush by 28.8% and to increase the service time of the brushes by 30%. Two recent open source papers [24,25] focused on yet another problem persistent for the pantograph-based supply units, namely the stability of the contact and possible vibrations of the pantograph head. From the presented literature review, it can be seen that the issue of energy transfer in the pantograph-catenary system is certainly an important subject of study for scientists and engineers representing different disciplines. The present paper is focused on the analysis of performance of trolleybus brushes with competitive mechanical and electrical properties compared to commercial solutions using recycled materials. In this context, the present paper is similar to the publications [20,23]. The authors of reference [20] suggest that simplified, one-step technologies of brush production may offer superior performance than the conventional processes, the same concept at the root of our paper. The paper [23] puts in the spotlight the economic benefits resulting from increasing service life of composite brushes.

2.Appl. Materials Sci. 2020, and10, x FOR Methods PEER REVIEW 4 of 10 Traction brushes should fulfill their basic function, i.e., they should be used in current collectors fromelectrodes the traction alone do lines not at matter various as DCthe loadsmaterial and is besubject able toto withstandgrinding. Typi highercal values levels ofof vibrationselectrode andparameters thermal may shocks, be found not damage on the website the traction of one network of leading due manufacturers to the friction [26]. (brushes should wear out The electrode fragmentation process was carried out in several stages. In the first stage, the uniformly and contain an oiling substrate, lubricating the traction wires), and be used for as long as waste material from used electrodes was crushed into smaller pieces, which were then ground in a possible, which reduces the operating costs of public transport vehicles. This means an extension of high-speed mill. Under laboratory conditions we availed of an IKA A11 mill with A 11.3 beater the average time of their use (1 week) and getting rid of the problem of replacement caused by their (MERCK KGAA, Darmstadt, Germany) This device may be used for pulverizing substances cracks during operation. exhibiting hardness up to the ninth level on the Mohs scale. In the subsequent step, the obtained The concept was to avail of the recycled materials, wherever possible. For this purpose, materials powder was sieved with a Laboratory Sieve Shaker LPzE-2e with a sieve with a mesh size of 50 µm. obtained from local metal processing companies were obtained, selected, cleaned and crushed. Additionally, particle size was verified with a SEM microscope. The proposed solution is based on the hypothesis that very fine dust (<50 microns) from exhausted Proper lubricating properties are ensured by particles of the cooling lubricant remaining from carbon electrodes can be used for the production of traction slides (Figure2), with the addition of the material processing process, trapped in the structure of the composite and the natural lubricating pure graphite powder, reinforcement in the form of copper fibers derived from shredded braids of properties of graphite. Phenolic-acrylic resin was used as the jointing material—cf. Figure 2. Figure 3 power cables. presents a photograph of ready-made product.

(a) (b) (c)

FigureFigure 2. 2.Components Components forfor makingmaking upup trolleybustrolleybus brushes from recycled materials, materials, ( (aa)) carbon carbon powder powder mademade from from used used electrodes, electrodes, (b(b)) shreddedshredded coppercopper braid,braid, ((cc)) phenolic-acrylicphenolic-acrylic resin.

Figure 3. An exemplary ready-made brush.

3. Measurements and Results The research was carried out for various component mixtures and for commercially available brushes. Electrical, mechanical, and load properties were tested. It should be remarked that the some electrical properties (e.g., current ampacity) were examined using a laboratory stand at direct current value equal to 150 A, which might be considered as a value comparable to those obtained in real-life conditions. Figure 4 presents a photograph of the laboratory stand for testing current ampacity, whereas in Figure 5 the connection scheme of the setup is presented. The system brush-traction electrode is supplied from a 230 V alternating current source via a coil with adjustable inductivity (D) and an assembly box. The main current Ip in the examined system as well as auxiliary control current Ip1 are measured with ammeters. Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 10 Appl. Sci. 2020, 10, 7929 4 of 10 electrodes alone do not matter as the material is subject to grinding. Typical values of electrode parameters may be found on the website of one of leading manufacturers [26]. RecycledThe electrode graphite fragmentation was obtained process from was electrodes carried used out inin electricalseveral stages. discharge In the machining first stage, (EDM) the usedwaste inmaterial manufacturing from used and electrodes other application was crushed areas into suchsmaller as pieces, mold making,which were general then engineering,ground in a andhigh-speed micro-machining. mill. Under The laboratory properties conditions of manufactured we availed graphite of dependan IKA significantly A11 mill with on its A applications.11.3 beater Less(MERCK critical KGAA, applications Darmstadt, might Germany) use graphite This with dev coarseice may grains; be used however, for pulverizing for more critical substances EDM, moreexhibiting stringent hardness criteria up have to the to beninth fulfilled. level on On the the Mohs other hand,scale. In there the are subsequent only a few step, grades the ofobtained copper commerciallypowder was sieved available. with a In Laboratory the considered Sieve application,Shaker LPzE-2e what with is verya sieve important with a mesh is the size high of 50 purity µm. (fromAdditionally, 99.9% upwards) particle size of the was electrode verified material, with a SEM because microscope. it results into low resistance (up to 9.0 µOhm) and highProper thermal lubricating stability properties and high are resistance ensured to by thermal particles shocks. of the The cooling shape lubricant and size ofremaining the electrodes from alonethe material do not processing matter as the process, material trapped is subject in the to st grinding.ructure of Typical the composite values of and electrode the natural parameters lubricating may beproperties found on of the graphite. website Phenolic-acrylic of one of leading resin manufacturers was used as [the26]. jointing material—cf. Figure 2. Figure 3 presentsThe a electrode photograph fragmentation of ready-made process product. was carried out in several stages. In the first stage, the waste material from used electrodes was crushed into smaller pieces, which were then ground in a high-speed mill. Under laboratory conditions we availed of an IKA A11 mill with A 11.3 beater (MERCK KGAA, Darmstadt, Germany) This device may be used for pulverizing substances exhibiting hardness up to the ninth level on the Mohs scale. In the subsequent step, the obtained powder was sieved with a Laboratory Sieve Shaker LPzE-2e with a sieve with a mesh size of 50 µm. Additionally, particle size was verified with a SEM microscope. Proper lubricating properties are ensured by particles of the cooling lubricant remaining from the material processing(a) process, trapped in the structure(b) of the composite and the natural(c) lubricating properties of graphite. Phenolic-acrylic resin was used as the jointing material—cf. Figure2. Figure3 Figure 2. Components for making up trolleybus brushes from recycled materials, (a) carbon powder presents a photograph of ready-made product. made from used electrodes, (b) shredded copper braid, (c) phenolic-acrylic resin.

Figure 3. An exemplary ready-made brush.

3. Measurements and Results The research was carried out for various component mixtures and for commerciallycommercially available brushes. Electrical, Electrical, mechanical, mechanical, and and load load properties properties were were tested. tested. It should It should be remarked be remarked that the that some the someelectrical electrical properties properties (e.g., (e.g.,current current ampacity) ampacity) were were examined examined using using a alaboratory laboratory stand stand at at direct current value equal to 150 A, which might be considered as a value comparable to those obtained in real-life conditions. Figure 44 presentspresents a photograph of of the the laboratory laboratory stand stand for for testing testing current current ampacity, ampacity, whereas whereas in inFigure Figure 5 5the the connection connection scheme scheme of of the the setup setup is presented.presented. The system brush-tractionbrush-traction electrodeelectrode isis supplied from a 230 V alternating current source via a coil withwith adjustableadjustable inductivity (D) and an assembly box. The main current Ip inin the the examined examined system as well as auxiliary controlcontrol currentcurrent IIp1p1 are measured with ammeters. Appl. Sci. 2020, 10, 7929 5 of 10 Appl. Sci. 2020, 10, x FOR PEER REVIEW 5 of 10 Appl.Appl. Sci. Sci. 2020 2020, ,10 10, ,x x FOR FOR PEER PEER REVIEW REVIEW 55 of of 10 10

Figure 4. A photograph of the laboratory stand for testing current ampacity. FigureFigure 4. 4. A AA photograph photographphotograph of of the the laboratory laboratory st standstandand for for testing testing current current ampacity. ampacity.

FigureFigure 5. 5.TheThe connection connection scheme scheme of ofthe the setup. setup. FigureFigure 5. 5. The The connection connection scheme scheme of of the the setup. setup. TheThe measurements measurements of ofelectrical electrical resistance resistance were were carried carried out out using using the the bridge bridge method method with with the the TheThe measurementsmeasurements ofof electricalelectrical resistanceresistance werewere carriedcarried outout usingusing thethe bridgebridge methodmethod withwith thethe SonelSonel MMR-650 MMR-650 device device (Wokulskiego, (Wokulskiego, Swidnica,´Świdnica, Poland).Poland） The. The four-wire four-wire (Kelvin) (Kelvin) method method [27] suited[27] SonelSonel MMR-650MMR-650 devicedevice (Wokulskiego,(Wokulskiego, ŚŚwidnica,widnica, PolandPoland））. . TheThe four-wirefour-wire (Kelvin)(Kelvin) methodmethod [27][27] suitedfor measurements for measurements of small of resistancessmall resistances is implemented is implemented inside theinside device. the Adevice. sketch A of sketch the connection of the suitedsuited forfor measurementsmeasurements ofof smallsmall resistancesresistances isis implementedimplemented insideinside thethe device.device. AA sketchsketch ofof thethe connectionscheme to scheme the device to isthe presented device is in presented Figure6. Red in Figure wires and 6. Red clamps wires pertain and toclamps the current pertain part to ofthe the connectionconnection schemescheme toto thethe devicedevice isis presentedpresented inin FigureFigure 6.6. RedRed wireswires andand clampsclamps pertainpertain toto thethe currentmeasurement part of the circuit. measurement Blue wires circuit. and clamps Blue wire pertains and to theclamps voltage pertain part to of the the voltage measurement part of circuit. the currentcurrent partpart ofof thethe measurementmeasurement circuit.circuit. BlueBlue wirewiress andand clampsclamps pertainpertain toto thethe voltagevoltage partpart ofof thethe measurementThe blackened circuit. ovals The denote blackened the contact ovals points denote between the contact theexamined points between brush andthe examined the wire. “TEMP”brush measurementmeasurement circuit.circuit. TheThe blackenedblackened ovalsovals denotedenote thethe contactcontact pointspoints betweenbetween thethe examinedexamined brushbrush anddenotes the wire. a thermopile “TEMP” (a denotes temperature a thermopile sensor) for (a monitoring temperature ambient sensor) temperature. for monitoring The measurement ambient andand thethe wire.wire. “TEMP”“TEMP” denotesdenotes aa thermopilethermopile (a(a temperaturetemperature sensor)sensor) forfor monitoringmonitoring ambientambient temperature.range for the The device measurement was 1.0000–1.9999 range for m Ωthe, resolution device was 0.0001 1.0000–1.9999 mΩ, and the mΩ fundamental, resolution measurement0.0001 mΩ, temperature.temperature. TheThe measurementmeasurement rangerange forfor thethe devicedevice waswas 1.0000–1.99991.0000–1.9999 mmΩΩ, , resolutionresolution 0.00010.0001 mmΩΩ, , anderror the fundamental(0.25% result measurement of the measurement error ± (0.25%+ 2 digits). result of the measurement + 2 digits). andand the the± fundamental fundamental measurement measurement error error ± ± (0.25% (0.25% result result of of the the measurement measurement + + 2 2 digits). digits).

Figure 6. A sketch presenting the connection of brushes to the Sonel MMR-650 device. Figure 6. A sketch presenting the connection of brushes to the Sonel MMR-650 device. FigureFigure 6. 6. A A sketch sketch presenting presenting the the connection connection of of brushes brushes to to the the Sonel Sonel MMR-650 MMR-650 device. device. Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 10

The measurement results concerning the resistance of the samples are given in Table 1. The values provided are averaged from ten individual measurements. Description of the samples: Appl.1—graphite Sci. 2020, 10+, 792920% resin + 20% copper, 2—original, commercially available mixture, tradename6 of 10 RH84, 3—graphite +15% resin + 20% copper, 4—another original, commercially available mixture, tradenameThe measurement MY7D, 5—graphite results concerning + 20% resin the +resistance 20% copper of the+ 30% samples graphite are givenrecyclate, in Table 6–graphite1. The values + 20% providedresin, 7—graphite are averaged without from resin. ten individual measurements. Description of the samples: 1—graphite + 20% resin + 20% copper, 2—original, commercially available mixture, tradename RH84, 3—graphite Table 1. Resistance of the samples. +15% resin + 20% copper, 4—another original, commercially available mixture, tradename MY7D, 5—graphite + 20% resinSample+ 20% copper1 + 30%2 graphite3 recyclate,4 6–graphite5 6 + 20%7 resin, 7—graphite without resin. resistance (mΩ) 8.63 7.23 6.45 8.67 9.84 14.85 6.37 deviation (mΩ) 0.022Table 1. 0.018Resistance 0.016 of the0.022 samples. 0.025 0.037 0.016 Sample 1 2 3 4 5 6 7 Hardness tests were carried out with the HB ball indentation method with the hardness tester resistance (mΩ) 8.63 7.23 6.45 8.67 9.84 14.85 6.37 HPK 8411 in accordance with PN-EN ISO 2039-1: 2004. During the tests, the ball with diameter 5 ± 0.025 mmdeviation was used. (mΩ The) succesive 0.022 0.018load values 0.016 were 0.02249 N, 132 0.025 N, 358 0.037 N, and 0.016 961 N. The measurements were made at a distance at least 5 mm away from the sample edge, and the distance betweenHardness successive tests weremeasurement carried out point with was the 10 HB mm. ball indentationThe tests were method carried with out the on hardness samples tester with HPKsmooth, 8411 even, in accordance mutually parallel with PN-EN and perpendicular ISO 2039-1: 2004. surfaces During to the the direction tests, the of ball the withforce, diameter without 5bubbles,0.025 mmscratches, was used. pits, The or succesiveother visible load defects. values were The 49tests N, 132were N, carried 358 N, andout 961at variable N. The measurements temperatures ± wereof 80 made°C, 23 at °C, a distance and −32 at°C. least The 5 results mm away are fromshown the as sample graphs edge, in Figures and the 7–9. distance between successive measurementDesignation point of wasthe 10samples: mm. The 1—graphite tests were + carried 20% resin out on+20% samples copper, with 2—original, smooth, even, commercially mutually parallelavailable and mixture, perpendicular tradename surfaces RH84, to 3—graphite the direction + 15% of the resin force, +20% without copper, bubbles, 4—another scratches, original, pits, orcommercially other visible available defects. The mixture, tests were tradename carried outMY7D, at variable 5—graphite temperatures + 20% ofresin 80 +C, 20% 23 C,copper and +32 30%C. ◦ ◦ − ◦ Thegraphite results recyclate, are shown 7—pure as graphs graphite in Figures without7–9 resin..

FigureFigure 7.7. HardnessHardness HBHB atat elevatedelevated temperaturetemperature (80(80 ◦°C).C). Appl.Appl. Sci.Sci.2020 2020, ,10 10,, 7929 x FOR PEER REVIEW 77 of of 10 10 Appl. Sci. 2020, 10, x FOR PEER REVIEW 7 of 10

Figure 8. Hardness HB at room temperature (25 °C). Figure 8. Hardness HB at room temperature (25 ◦°C).C).

FigureFigure 9. 9.Hardness Hardness HB HB at at temperature temperature below below zero zero Centigrade Centigrade ( (−3232◦ °C).C). Figure 9. Hardness HB at temperature below zero Centigrade (−−32 °C). DesignationCommercial ofbrushes the samples: made of 1—graphite commercial+ mixtures20% resin reveal+20% considerable copper, 2—original, hardness commercially (in particular Commercial brushes made of commercial mixtures reveal considerable hardness (in particular availablethe mixture mixture, RH84), tradename but it varies RH84, to some 3—graphite extent with+ 15%temperature resin +20% variations. copper, For 4—another the RH84 original, mixture the mixture RH84), but it varies to some extent with temperature variations. For the RH84 mixture commerciallyan increase in available hardness mixture, was recorded tradename at lowe MY7D,r temperatures, 5—graphite +whereas20% resin for+ the20% MY7D copper mixture,+ 30% an increase in hardness was recorded at lower temperatures, whereas for the MY7D mixture, graphitecomparable recyclate, hardness 7—pure values graphite were noticed without both resin. for the room and for the negative temperatures. The comparable hardness values were noticed both for the room and for the negative temperatures. The lowestCommercial hardnessbrushes values madewere ofrecorded commercial for mixturesthe commercially reveal considerable available hardnessmixture (inMY7D” particular and thefor lowest hardness values were recorded for the commercially available mixture MY7D” and for mixturegraphite RH84), samples. but Graphite it varies tosamples some extentwith the with addition temperature of graphite variations. recyclate, For theresin, RH84 and mixture copper, an as graphite samples. Graphite samples with the addition of graphite recyclate, resin, and copper, as increasewell as graphite in hardness samples was recorded with the ataddition lower temperatures, of resin and copper, whereas possess for the higher MY7D mixture,hardness comparablevalues than well as graphite samples with the addition of resin and copper, possess higher hardness values than hardnessthe original values commercial were noticed mixtures. both for the room and for the negative temperatures. The lowest the original commercial mixtures. hardnessTable values 2 presents were recordedthe results for related the commercially to abrasion available tests for mixturesome of MY7D” the considered and for graphitebrushes. Table 2 presents the results related to abrasion tests for some of the considered brushes. samples.Notation: GraphiteRH84 and samples WY7D withdenote the commercially addition of graphiteavailable recyclate, compositions; resin, S1—a and copper,mixture as of well carbon as Notation: RH84 and WY7D denote commercially available compositions; S1—a mixture of carbon recyclate, “new” carbon and 15% copper and resin; S2—a mixture of carbon recyclate, “new” carbon recyclate, “new” carbon and 15% copper and resin; S2—a mixture of carbon recyclate, “new” carbon Appl. Sci. 2020, 10, 7929 8 of 10 graphite samples with the addition of resin and copper, possess higher hardness values than the original commercial mixtures. Table2 presents the results related to abrasion tests for some of the considered brushes. Notation: RH84 and WY7D denote commercially available compositions; S1—a mixture of carbon recyclate, “new” carbon and 15% copper and resin; S2—a mixture of carbon recyclate, “new” carbon and 15% resin; S3—a mixture of “new” carbon and 15% copper and resin. ∆10 denotes the loss in brush weight, in grams, after sliding it for 10 m distance along the traction wire, ∆100 after sliding it for Appl. Sci. 2020, 10, x FOR PEER REVIEW − 8 of 10 100 m distance, respectively. These values are also referred to the original brush weights and given in percentageand 15% resin; units S3—a (denoted mixture as ∆of10% “new” and carbon∆100%, and respectively). 15% copper and From resin. a comparisonΔ10 denotes the of loss the weightin loss results,brush weight, a conclusion in grams, may after be sliding drawn it for that 10 them distance wear performance along the traction of sample wire, Δ100− S1 is after superior sliding to it other presentedfor 100 ones. m distance, respectively. These values are also referred to the original brush weights and given in percentage units (denoted as Δ10% and Δ100%, respectively). From a comparison of the weight loss results, a conclusionTable may 2. Loss be drawn in brush that weight the wear after performance sliding. of sample S1 is superior to other presented ones. ∆10, g ∆10% ∆100, g ∆100% RH84Table 0.05 2. Loss in brush 0.09 weight after sliding. 0.15 0.26 WY7D 0.044 Δ10, g Δ10% 0.05 Δ100, g Δ 0.114100% 0.14 S1RH84 0.03 0.05 0.09 0.03 0.15 0.160.26 0.14 WY7D 0.044 0.05 0.114 0.14 S2 0.07 0.07 0.28 0.29 S1 0.03 0.03 0.16 0.14 S3S2 0.09 0.07 0.07 0.08 0.28 0.520.29 0.49 S3 0.09 0.08 0.52 0.49 Figure 10 depicts a SEM photograph concerning an exemplary brush developed partially from Figure 10 depicts a SEM photograph concerning an exemplary brush developed partially from the waste materials with shredded copper braid. In the Figure we have noticed an increased graphite the waste materials with shredded copper braid. In the Figure we have noticed an increased graphite interlamellarinterlamellar spacing, spacing, due due to to the the increase increase in in copper copper level. level. This This in turn in turn may mayexplain explain the decrease the decrease in in resistance.resistance.

FigureFigure 10. An10. An exemplary exemplary SEM SEM photograph photograph depicting the the microstructure microstructure of developed of developed brush brush..

Appl. Sci. 2020, 10, 7929 9 of 10

4. Conclusions The research was necessary in order to select the optimal composition of the mixture, which will ensure the best possible electrical and mechanical values and the possibility of processing in the process of hot forming at temperatures up to 175 ◦C, minimal compaction pressure was 200 MPa. This task is to eliminate compounds that contain ingredients that can cause corrosion of the traction line or reduce the life of the brushes. As a result, mixtures were prepared from which prototypes of traction contact brushes can be made. The developed brushes contain 55–60% recycled materials. They are fraction-resistant and deﬁnitely more durable than their commercial counterparts. Moreover, they are customized to varying ambient conditions (summer–winter temperature variations).

Author Contributions: Conceptualization, A.J., A.C. and K.C.; methodology, A.J; validation, A.J., A.C. formal analysis, A.J.; investigation, A.J., A.G., Ł.S.; resources, A.J.; writing—original draft preparation, K.C.; writing—review and editing, A.J.; visualization, A.J.; supervision, A.J., A.C.; project administration, A.J.; funding acquisition, K.C. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. It was supported by the Dean of Faculty of Electrical Engineering, Cz˛estochowaUniversity of Technology from the statutory funds for research purposes. Acknowledgments: The research was financed within the PARP project No. POIR.02.03.02-24-0006/18, 2018–2019, titled “Development and implementation of innovative trolleybus slides” carried out at Cz˛estochowaUniversity of Technology for the company OMEGA–PROJEKT, Tychy, Poland. The authors are grateful to the organizers of the virtual PTZE Symposium, held online from 13th to 16th September 2020 for the possibility to present their work. Conflicts of Interest: The authors declare no conflict of interest.

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