TORQUE and POWER
The engineering term ‘torque’ or ‘twisting moment’, basing on etimology studies from ancient times, we found its origin at the latin word ‘torquere’, meaning ‘twisting’ and ‘turning, derived from a personal ornament, a necklace twisted with a spiral screw-shaped, this necklace, a sacred symbol of the soul, was used by Celts around their necks as a symbol of nobleness and good luck into the battles during their conquests in the europe. Today torque is the degree of screw and bolt tightening and the rotational force of motors, and regardless of torque is no longer a symbol of a good luck into the battles, torque still carries the charms of safety and power.
There are two main categories for torque, static and dynamic, and let′s starting understanding the difference between a static and a dynamic force, dynamic force involves acceleration, while a static force does not, the relationship between dynamic force and acceleration is described by Newton’s second law; F=ma (force equals mass x acceleration).
If the torque is just a force through a distance and has no angular acceleration, the torque is static, e.g., the torque exerted by a wrench. The torque transmitted through a gearbox at a constant speed would be an example of a rotating static torque, even there is rotation, at a constant speed there is no acceleration. But at start-up or when there is load fluctuations the torque produced will be both static and dynamic and the resulting dynamic torque is T = J x α (Torque = rotational inertia x rotational acceleration).
In physics, power is defined as the amount of work done divided by the time taked to do the work. The unit of power is the Watt (W), which is equal to a Joule per second (J/s); horsepower is the force needed to move 33,000 pounds, one foot in a minute;1 HP is approximately equivalent to 746W. A way to understand horsepower and torque is when you open a new pickle jar. When you are using all your strength to open the jar, you are applying a static torque necessary to break the load loose on its way to making the first revolution, regardless of whether or not the cap comes off.
Horsepower, however, only exists with movement. So you need torque to loosen the lid first, and then you can apply horsepower with your hand by spinning the lid of quickly.
When power is being transmitted through a shaft, a torque T will be present; This torque is given by: T = P / ω (Torque = power in watt divided by speed in rad/s); torque can be viewed as the “strength” of a motor or a gearbox.
ω = speed in rad/s = 2.π.n / 60 (where, n = speed in rpm)
T = P / ω
T= (60.P) / (2.π .n)
T = 9,55.P[W] / n[RPM]
T [Nm] = 9550.P[kW] / n[rpm]
Imperial system
1 HP = 33000 ft.lbf / min
P [HP] = Torque [lbf.ft] x rotational speed
P [HP] = (Torque [lbf.ft].revs[rpm] / 33000) x (2.xn--1xa.rads/rev)
Torque [lbf.ft] = 5252.P[HP] / n[rpm]
Torque [lbf.in] = 63025.P[HP] / n[rpm/
It is often necessary to increase or decrease the torque produced by a motor to suit different applications, and this be done through the use of gearing. The need for a gearbox between motor and the equipment is due to, the speeds required for the movement of the working elements of a machine differ from the speeds of standard motors, or a torque greater than the torque supplied on the motor shaft is required to drive the machine; noting that a decrease in rotational speed comes with an increase in torque.
