Jacob Snyder
Evans Enterprises, Inc.
When a modern temperature controlled (i.e., controlled pyrolysis) burnout oven is not available, the method described here can be used to process aluminum frame motors.
Before the burnout process, ensure all necessary iron dimensions are recorded and get a pre-burn core test on the motor. Once this information has been collected, the burnout process can be set up. If at all possible, it is recommended that the iron be removed from the frame so that it can be burned out by itself. If the core is dropped out of the frame, it may need to be secured against loosening when the stator winding is burned out. Consider methods such as cleats, through-bolts in several slots, or cautiously welding the length of the backiron. When iron removal isn’t possible and the aluminum frame must be burned out as well, an option is to burn the entire unit on a pan of sand.
The purpose of the pan of sand is to allow the stator to only be exposed to oven heat as the sand cradles the aluminum to keep the stator and frame from warping. Using the sand as a heat sink, this allows the stator to burn out without forming hotspots. There are a few important guidelines to follow in the setup that help ensure the best burnout situation possible.
Size of pan is critical
The size of the pan of sand is critical to the dimensions of the stator and frame to be burned out. A few choices of sand material would be standard playground sand or Dupont Starblast; it is recommended that you replace the sand after every 4-5 uses.
The depth of the sand should always be a minimum of 2-3 inches (50-75 mm) to ensure the heat is properly being pulled away and no residual heat is being held by the pan material.
If the stator and frame weighs more than 200 pounds (90 kg), it is recommended to add about 2 inches (50 mm) to the sand depth to ensure it is not sinking down too far into the sand. With the stator placed in the center of the pan (see Figure 1), the sand must extend at a minimum of one length of the stator and frame in all directions.
With this setup, you should be able to follow your standard burn time with EASA’s recommendation of not allowing the maximum core temperature to exceed 700°F (370°C). After the burnout process, ensure the stator and frame is cooled completely down before moving forward and removing the windings.
This method can be used on any size aluminum frame motor as long as the sand setup has adequate spacing for the stator and frame as described above.
Additionally, this method has been used while burning out other stators at the same time but, there needs to be a minimum of 12 inches (300 mm) separation between the pan of sand and the other stators.
An experimental method
In all, this is a possible method to burn out an aluminum frame motor when there are no other methods available to be used. This is an experimental method that is recommended to be tried on scrap motors to determine if it will fit your process.
There is no guarantee that the method described above will work in every situation. This method has been refined over time through experimentation. However, there is no guarantee that the method will work in every situation.
Hopefully this opens up another method that can become an option to use in service centers when they need it.
AVAILABLE IN SPANISH
ANSI/EASA AR100
More information on this topic can be found in ANSI/EASA AR100- Section 2: Mechanical repair
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