Technical Note 1 - Steps to balance turbine engine blade sets

Typically turbine stages are balanced on a balance machine through an iterative process of measuring imbalance, swapping blades, and finally adding balance weights. Blade arrangement software provides several benefits to aid in this process.

The blade arrangement steps for new engines and overhauled engines are very similar. For overhauled turbine engines, follow the standard methods of cleaning, repair, replacement, and prepping. When a full blade set is ready to assemble into the disc, use the following steps:

  1. Mark each blade with a blade number. Also clearly define slot numbers on the disc. Some discs already have a mark at slot 1. Make sure you know the direction for increasing slot numbers. This generally should be the same direction the balance machine uses for positive angle.

  2. Weigh the blades. Use the weighing method and precision recommended by the manufacturer. Longer blades benefit from moment-weight measurements because the center of gravity may be slightly different from blade to blade. However, pan weights are commonly used and avoid the complications of moment-weight machines. We suggest starting with a good precision pan scale, and if it helps your balancing process, consider moving to a moment-weight scale to get further improvements. Contact us if you have questions about weighing.

  3. Enter blade weights in the balancing software. This is where our services at come in. Be sure to create an account, and then click on "Blade Sets". Click "+Add blade set". For the Set Id, enter a name for the set such as the disc serial number. Enter the number of blades, and click Save. In the table editor, enter the blade weights.

  4. Measure disc unbalance without blades. Setup the disc on a dynamic balance machine without any blades. Configure the balance machine to give an unbalance reading at a radius equivalent to the blade center of gravity (CG). To get a blade's CG radius, measure the distance from the root end of the blade to the blade's balancing point when rested on a pencil. Measure the disc radius to the root of a slot. Add these two measurements to get the blade CG radius, which will be entered in the balance machine. Run a balance test to get the recommended adjustment weight. In, click Settings when in the set editor, and click Advanced. Enter the disc unbalance and angle reported by the balancing machine. If the machine reports the light side of the disc, enter the weight as negative. will now arrange blades to compensate for both the disc unbalance and the weights of the blades.

  5. Get an optimized blade arrangement. After entering blade weights, click "Optimize", which goes to a report page with an optimized listing of slots with a blade for each slot. A circular map shows the distribution of blade weights. Print this report.

  6. Assemble blades in the disc according to the optimized blade arrangement report. For example blade 1 may no longer go into slot 1, it may go into slot 35 instead.

  7. Perform a dynamic balance on the bladed disc. It should show a very low unbalance. If not, check the blade weights for any typos from data entry. Also, double check the disc unbalance sign and angle. Once everything is correct, it will give excellent results.

Other things to consider might be to use to optimize bolt and nut weight arrangements. Bolts tend to have tighter weight tolerances than blades, but in worst case scenarios, small differences in bolt weights could add up to be significant. In some turbine engines, nuts are designed to have different weights to facilitate balancing. It may be useful to use to produce an evenly distributed pattern for nut placement.

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