Technical Note 3 - Turbine engine cover plate balancing

Some types of rotors, such as the General Electric series 3 and 5 assemblies, require a "cover plate" to accompany each blade to lock the blade in place. In some cases these plates come in two varieties - a "light" plate and a "heavy" plate. The light and heavy plates must be alternated during assembly. The BalancePoint.tech web app allows the optimal positioning of these plates to achieve best balance just as it does the blades.

If only one weight of cover plate is involved, and the plates are not required to be located in any predetermined location, the plates can be treated like a "Normal" blade set.

If the set requires the alternating Light-Heavy arrangement, the balancepoint.tech settings allow for this. Create a rotor set with alternating Light-Heavy types: Under "Blade Type" change the "Standard" type to "Heavy". Select "Add option" and type in "Light".

Press the "Open slot editor" button and select "Heavy" or "Light" for each slot.

Before the plates are weighed, mark them with numbers 1 to N. When entering the weight in the table select whether the plate is a Light plate or a Heavy plate using the drop-down menu in the Type column. Weigh all plates in order of plate number. Normally all heavy plates are weighed first, and then all light plates. In the example below however, the blades are ordered with alternating heavy/light so that we can see what the unbalance might be with a random arrangement. Then we will see the improved unbalance in the results.

When the Optimize button is pressed, the plates will be arranged for best balance in an alternating Light/Heavy pattern.

As you can see the random placement has an unbalance of 34.6g as shown by Initial Unbalance. The final unbalance is an incredible 0.0078g. This example shows how coverplates can add to unbalance and how it is an easy matter to correct with software balancing. Give it a try on one of your sets at balancepoint.tech.

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