Brush (electricity)
In electricity, it is often necessary to establish an electrical connection between the fixed part and the rotating part of a device. This is the case of electric motors or generators, where a connection must be established between the fixed part of the machine and the rotor coils.
To make this connection, two rings are attached to the rotating shaft, usually made of copper, insulated from the electricity of the shaft and connected to the terminals of the rotating coil. In front of the rings, there are some graphite blocks that, by means of some springs, put pressure on them to establish the necessary electrical contact. These blocks of graphite are called brushes (carbons, colloquially) and the rotating rings are called collectors.
In some types of electromagnetic machines, such as DC motors or generators, the slip rings are divided into two or more parts, isolated from each other and connected to one or more coils. In this case, each of the parts into which the collector is divided is called thin.
Since the friction caused by turning the device causes wear due to abrasion, the brushes must be replaced periodically. For this reason brushless electric motors have been invented.
History
The fact that an element with a polyhedral structure is called a brush is curious, when for us the term brush is always associated with something filamentous. Actually, the brush itself arose as a result of a problem that arose when the first electrical machines were developed. The problem they had to solve was to carry an electric current from a rotating mass to a stationary mass (what is known today as rotor and stator).
The first element that was used to carry electrical current from a rotating mass to a stationary mass was, precisely, a broom, a brush. The inventor took a cable with a series of metal filaments, like foundry shavings, grouped them with a metal ring, like a shaving brush, and arranged them in contact with an energized surface, the slip ring of an alternating current generator. rudimentary. Hence, the original name of it in the English language was brush , a name that responded exactly to the element that was being invented. This solution turned out to be relatively practical for small machines and slow machines. But as the power of the generators became larger, the metal bristle brush was already discarded, because they overheated, melted quickly and broke. For this reason, the need to move to a more resistant material was seen.
Then we arrive at what a brush for electrical machines is, which is defined in the first instance as a current conductor-wiper. A mechanical and electrical element whose mission is to transfer current of highly variable intensity, between the rotating mass and its external supply or use circuit.
The first mistake that was made was to think about the use of a conductive material. Brushes made of copper, iron and bronze were thought of, which did their job very well as conductors, but they did not turn out to be good materials in terms of friction, since due to the high coefficient of friction between two metallic surfaces, both deteriorated. quickly. Because they quickly wore out the rings, so-called "wire brushes" they were removed.
As a result, the analysis was reversed. It was necessary to first look for a good frotador who had acceptable conditions as a driver. After many evaluations, a solid material, such as coal, was reached. At that time it was an amorphous carbon, with very different characteristics from those known today. However, the idea has persisted until today (2018), because the molecular structure of carbon is excellent for friction. The truth is that it deteriorates over time and also wears out the collector itself, although a very long period of time must pass for this to happen.
The molecular composition of carbon in the form of graphite is reminiscent of the shape of a book. They are hexagonal molecules arranged in the form of sheets as if it were a book and it is very easy to remove their outer layers. This can be verified if we hold a brush and pass our finger through it; we will notice that the layer is very easy to detach. This characteristic makes this material an excellent candidate for friction.
Carbon is a self-lubricating material, which does not attack the surface on which it is rubbing and does not wear out quickly. Graphite or carbon is not an excellent conductor of electricity; however, you can intervene electrically and chemically on it to turn it into a "regular" or "good" conductor of electricity, a condition that is of incalculable value when the direct current machine is reached later.
The development of electrical machines quickly promoted the development of various materials for the manufacture of brushes. That is, if the first machine was the alternating current generator, later the alternating current motor itself would appear, the appearance of direct current with its generator, its motor and a series of developments such as the Universal Fractional Machine and AC motors with variable speed, or the same wound rotor induction motor that presents a series of challenges for brushes and forced manufacturers to develop special grades and continuous innovations in this field.
Railroads in most countries have adopted DC motors with converter units, either in substations or on a train. Rolling machines and electric traction used in coal mines frequently require direct current power, which also offers advantages in marine propulsion and auxiliary plants. In summary, the development in the design and control of direct current machines makes them extremely useful for jobs of all kinds.
The satisfactory operation of direct current machines has been due, in large part, to the use of special carbon brushes with a correct graduation, and commutation poles. The study of carbon brushes and their correct application in modern machines is of great importance for all users of electrical machinery.
The correct application and selection of brushes, together with proper maintenance, translates into improved machine performance and lower downtime costs.