Construction notes
This balancing machine was inspired by the design published on the website www.technologie-entwicklung.de, from which the mechanical drawings and all the electronics were taken, the latter built with skill and great passion by Santino Genovese. Thanks to his collaboration, a very precise and reliable machine has been developed.
Three substantial changes were made to the original German design.
The first concerns fitting the electronics to both "Y" supports, so that balancing can be carried out at the same time on both the compressor side and the turbine side. This system also allows the final balancing of the turbine once it has been fully assembled.
The second concerns the motor and the belt drive. After numerous tests we decided to "separate" the motor from the body of the machine, in order to greatly reduce the vibrations it transmits to the sensors. An idler pulley mounted on bearings was therefore added. This system brings vibrations below the threshold of 100 thousandths of a volt, against more than 250 thousandths measured with induction motors fixed to the machine body.
The third change concerns the reading of the imbalance, which the German design performs by means of an LED acting as a strobe. This system should also make it possible to locate the point of imbalance but, in practice, despite numerous tests, it proved not very practical, because to achieve the stroboscopic effect, so that the marks on the shaft become visible, you have to keep adjusting the rotation speed controller and the knob that sets the LED sensitivity. We therefore decided to give up looking for the position and to concentrate on finding the amount of imbalance by reading the voltage generated by the piezoelectric capsules. The system proved so effective that a multimeter (costing about 20 euros) was fitted directly to read the values, using the 20 volt AC range.
The balancing machine was then fitted with an infrared rev counter (Kit LX.1327 from issue no. 192 of Nuova Elettronica). Not an essential accessory, but useful for checking the speeds obtained by moving the belt onto the various pulleys. Note that the revs read on the instrument are exactly double the actual ones, because the infrared LED reading is taken through the hole in the nose cone. The best results for good balancing of the shaft are obtained between 2700 and 3100 rpm.
For the final balancing with the turbine assembled, a vacuum cleaner is used to suck air from the outlet cone of the balancing machine, bringing the turbine to around 4000 rpm. A small warning: worn bearings greatly alter the imbalance readings.
Photos
… and after balancing the turbine
The selector is moved to "L" to activate the compressor-side sensors
The reading shows an "imbalance", expressed in approx. volts, of 2.62 V.
Experience suggests preparing a small ball of "modelling clay" of this size
After a few attempts, the point where the "modelling clay" must be placed has been found
The "imbalance" volts have dropped to 340 thousandths
The operation is repeated with another, much smaller ball
Which is added to the previous one
The instrument shows that the "imbalance" has dropped further, to 180 millivolts
The machine's extreme sensitivity makes it possible to detect even a small piece of adhesive tape measuring about 1x2 mm.
Which is placed at the same spot as the modelling clay to check whether the balancing can be improved
The imbalance has indeed improved and is now only 0.1 volts, partly due to the belt drive