When a spindle designer begins a new product design, as a speed increaser for metal cutting applications, he may choose any of a few popular options in order to introduce power: electrical motor, mechanical gear, or turbines. The turbines are low cost and provide relative high rotation speeds.
There are two types of turbines: fluid (water, oil, emulsion) and gas (air, nitrogen, steam).
The turbines may also be categorized according the following: impulse and reaction turbines. Reaction turbines have the same operation principle as rockets. The media, fluid or gas, push the blade in the opposite direction, while in impulse turbines, the media flow through a set of jets which increase the media velocity due to dramatic reduction in the cross section (Bernoulli’s low).
Some physical principles:
The mass and velocity of the media create the kinetic energy.
E=mv²/2 (m – mass, v – linear velocity of the media via jets).
The kinetic energy of the the media (water, emulsion, air…) produce rotation energy.
E=Jω²/2 (J – Polar moment of inertia, ω – Angular velocity)
The high speed media flow (kinetic energy) comes in contact with the turbine blades and creates tangential forces.
The force is calculated according to stagnation force (relative velocity between the turbine blade and the media), area, and blade effective area.
The force multiplied with turbine blade radius provide the turbine torque.
The turbine output power is a function of torque and angular velocity.
In gas turbines the maximum tangential velocity will be 1 Mach (340 meters per seconds) as soon as the pressure reduction across the jet is higher than 1.8 [bar]. That’s why it is easier to deliver high rotation speeds with gas driven turbines as compared with emulsion driven turbines. In order to calculate the angular velocity of a turbine (radian per second), it is necessary to divide the tangencies velocity by the turbine blade radius; V=ω R → ω=V/R.
Obviously, only some of the energy is used for delivering the output power and torque, while the remaining energy is wasted due to mechanical and thermodynamic efficiency. Theoretically, the reaction turbines efficiency is higher than the efficiency of impulse turbines due to the constant operation mode. But in reaction turbines it is necessary to deliver high pressure to the rotor through a dynamic seal, which may further decrease the mechanical efficiency. As in impulse turbines the jet’s are in the stationary parts (housing) and no dynamic seal is needed, impulse turbines are easier to design and manufacture. Therefore, the impulse turbines are more popular and more cost effective.
Toodle Blue and Toodle Green models are equipped with impulse turbines (emulsion, oil or air). The jet’s are located in the Toodle housing, the number of jet’s, their size and location are part of the design intended to deliver high rotation speed, high power and high efficiency.
SFI technical team.