Friction less Electro magnetic braking

Topics: Magnetic field, Electromagnetism, Magnetism Pages: 13 (3649 words) Published: December 19, 2014
    7. TORQUE
    9. WEAR



Electromagnetic brake
Electromagnetic brakes operate electrically, but transmit torque mechanically. This is why they used to be referred to as electro-mechanical brakes. Over the years, EM brakes became known as electromagnetic, referring to their actuation method. Since the brakes started becoming popular over sixty years ago, the variety of applications and brake designs has increased dramatically, but the basic operation remains the same. Single face electromagnetic brakes make up approximately 80% of all of the power applied brake applications. This article mainly concentrates on these brakes. Alternative designs are shown at the end of this article. Electromagnetic brakes have been used as supplementary retardation equipment in addition to the regular friction brakes on heavy vehicles. We outline the general principles of regular brakes and several alternative retardation techniques in this section. The working principle and characteristics of electromagnetic brakes are then highlighted.    



Horseshoe magnet red silver iron
A horseshoe magnet  has a north and south pole. If a piece of carbon steel contacts both poles, a magnetic circuit is created. In an electromagnetic brake, the north and south pole is created by a coil shell and a wound coil. In a brake, the armature is being pulled against the brake field.The frictional contact, which is being controlled by the strength of the magnetic field, is what causes the rotational motion to stop. All of the torque comes from the magnetic attraction and coefficient of friction between the steel of the armature and the steel of the brake field. For many industrial brakes, friction material is used between the poles. The material is mainly used to help decrease the wear rate. But different types of material can also be used to change the coefficient of friction (torque) for special applications. For example, if the brake was required to have an extended time to stop or slip time, a low coefficient material can be used. Conversely, if the brake was required to have a slightly higher torque (mostly for low RPM applications), a high coefficient friction material could be used. In a brake, the electromagnetic lines of flux have to attract and pull the armature in contact with it to complete brake engagement. Most industrial applications use what is called a single-flux two-pole brake. The coil shell is made with carbon steel that has a combination of good strength and good magnetic properties. Copper (sometimes aluminum)

magnet wire, is used to create the coil, which is held in shell either by a bobbin or by some type of epoxy/adhesive. To help increase life in applications, friction material is used between the poles. This friction material is flush with the steel on the coil shell, since if the friction material was not flush, good magnetic traction could not occur between the faces. Some people look at electromagnetic brakes and mistakenly assume that, since the friction material is flush with the steel, that the brake has already worn down, but this is not the case.           3. WORKING PRINCIPLE

There are three parts to an electromagnetic brake: field, armature, and hub (which is the input on a brake) (B-2). Usually the magnetic field is bolted to the machine frame (or uses a torque arm that can handle the torque of the brake). So when the armature is attracted to the field the stopping torque is transferred into the field housing and into the machine frame decelerating the load. This can happen very fast (.1-3sec).Disengagement is very simple. Once the field starts to degrade flux...

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