How Ultrasonic Cleaning Speeds Aircraft Engine Maintenance

How Ultrasonic Cleaning Speeds Aircraft Engine Maintenance

Rigorous procedures are spelled out in maintenance manuals for aircraft engine parts, whether jet, turbine or piston. Ultrasonic energy plays an important role both for cleaning and nondestructive testing (NDT) operations by aviation maintenance technicians (AMT), aircraft maintenance, repair and overhaul (MRO) organizations and airlines’ own maintenance facilities.  Here are examples of how ultrasonic cleaning speeds aircraft engine maintenance.

Ultrasonic Cleaning Aircraft Generators

Customized ultrasonic cleaning systems may offer significant improvements in thoroughness and throughput for maintenance repair and overhaul (MRO) operations related to aircraft engine components such as generators. 

What Aircraft Generators Do

By way of explanation integrated drive generators (IDG) and constant speed drive (CSD) generators are units that provide uniform delivery of power to electrical and electronic circuits in aircraft.  They convert the varying input speed of jet engines to a constant output speed typically generating 115 volt alternating current for use throughout the aircraft.  

Generators are subject to contaminants including lubricating oils, chips and carbon.  These must be removed as part of established generator MRO procedures. The components have complex configurations that together with tenacious contaminants make cleaning a challenge.  Ultrasonic  cleaning, the implosion of millions of minute bubbles in ultrasonic cleaner baths, reaches all immersed surfaces to quickly remove these contaminants.

Cleaning Cycles for Large Aircraft Generator Components

The advantage of ultrasonic cleaning is that cleaning units can be configured to handle the many generator component parts in an efficient manner.

Generator housings, for example, because of their weight and bulk, can be manually suspended by overhead cranes into tanks filled with a cleaning solution formulation meeting applicable specifications. 

A candidate is an alkaline formulation suitable for removing oil, grease, combustion residues, soot and other organic contaminants. Agitating the housings by slightly raising and lowering them in the solution improves the sonication process thus shortening the cleaning cycle. 

The Elmasonic Flex 1 system in 5 tank sizes from 8.5 to 44.5 gallons provides this agitation.  These units can be paired with a wash, rinse and dry unit in the Flex 2 system.

Cleaning Smaller Generator Components

Cleaning the smaller internal generator components might be handled in a benchtop unit. A candidate ultrasonic cleaner for these steps is the 37 kHz, 7.5 gallon capacity Elmasonic S300H with basket dimensions 17.9 x 9.8 x 4.5 in. deep.

These units provide features including degassing fresh cleaning solutions, sweep to insure uniform distribution of cavitation action throughout the baths, timers, and heaters to match solution formulation recommendations. 

Nondestructive Testing of Aircraft Engine Parts

As an example we discuss overhauling  CFM56-7B, GE CF-6, and Pratt & Whitney JT8D-219 jet engines utilizing ultrasonic cleaning as a key part of its nondestructive testing (NDT) procedure to insure aircraft engine parts meet specification.

What is Nondestructive Testing?

As you might imagine NDT involves the testing aircraft engine components in a way that does not involve “destroying” the components.  Usually one or more methods involve ultrasound, eddy current, radiography, thermography, magnetic particle and liquid penetrant.  

The last two methods are where ultrasonic cleaning finds application.   Magnetic particle testing detects minute discontinuities such as cracks at or near the surface in ferromagnetic metals such as iron, steel, nickel, and cobalt.  Liquid penetrant works much the same way using colored dyes to penetrate the cracks.

It is essential that all traces of dyes and particles are removed after the testing procedure.   An ultrasonic cleaner has been most effective in assuring this is achieved.  It is faster, more effective and less costly  than vapor degreasing and other cleaning methods, and does not damage aircraft engine parts.

How Ultrasonic Cleaning is Employed in NDT

The ultrasonic cleaner is used to accomplish two tasks:

  1. cleaning disassembled parts by NDT inspectors following standard operating procedures relating to jet aircraft maintenance schedules
  2. Performing quality check standards

A quality check subjects a test panel with defects to the cleaning process to ensure that all traces of dye and other contaminants are removed from the defect.  This exercise is performed on a daily basis to check the performance of the liquid penetrant line. 

Candidate Ultrasonic Cleaners for NDT Aircraft Engine Components 

An Elmasonic 37 kHz S series ultrasonic cleaner in 13 tank sizes from .2 to 23 gallons has features proven in the field for NDT aircraft engine components. 

These cleaners are equipped with a heater and timer that use LED lights to indicate both set and actual cleaning time and cleaning temperature.

Other useful features on the Elma unit include:

  • a sweep mode that assures even distribution of ultrasonic cleaning energy throughout the bath
  • a degas mode that speeds the removal of air in fresh cleaning solutions
  • An on-off switch for the unit
  • A switch to initiate or turn off ultrasonic cleaning cycles
  • A lid to reduce noise and cleaning solution evaporation.  Reversed as a tray it collects drained solutions from baskets.

Ultrasonic Cleaning Jet Engine Fuel Nozzle Assemblies

Regular maintenance procedures are prescribed for aircraft jet engines and include thorough cleaning and inspection of fuel nozzle manifold adapter assemblies.

Cleaning Challenges for Aircraft Fuel Nozzle Assemblies

Baked-on carbon deposits are particularly difficult to remove. 

Mechanical methods such as soaking, brushing or using steel wool in solvents are not only time consuming; they risk damage to precisely fabricated, highly machined fuel nozzle surfaces.  Moreover, no mechanical cleaning procedures have the ability to reach into tiny internal fuel nozzle orifices where contaminants may deposit. 

A representative process depends on ultrasonic cleaning to restore jet engine fuel nozzle assemblies to a like-new condition.  The procedure incorporates a tabletop Elmasonic E+ Series ultrasonic cleaner with 8 tank capacities and operating at 37 kHz and equipped with a heater, timer and drain. 

Why is Ultrasonic Cleaning so Effective?

Ultrasonic cleaning involves the implosion of billions of microscopic bubbles against surfaces being cleaned.  Bubbles are created by generator powered ultrasonic transducers bonded to the bottom of the tank containing the cleaning solution.  As bubbles violently implode they blast and carry away the most tenacious of deposits but without damaging the highly machined surfaces.

Because the bubbles are so small they are able to penetrate areas unreachable by mechanical cleaning methods.  The Elmaultrasonic units described here are equipped with what is called a continuous ‘sweep’ mode that evenly distributes cleaning action throughout the cleaning solution to avoid areas of overly intense and lack of cavitation action.  Units equipped with a pulse mode provide bursts of higher cleaning energy to blast away the more tenacious contaminants.  

Another advantage using ultrasonic cleaning is that personnel avoid contact with cleaning solution chemistries that may be employed with manual cleaning processes. 

Ultrasonic Cleaning Formulations for Aircraft Engine Components

A variety of biodegradable ultrasonic cleaning solution formulations are available from Elma Ultrasonic Cleaners, each designed for specific cleaning tasks.  These concentrates are diluted with water and are supplied in various pH ranges to satisfy the bulk of cleaning challenges. 

Trapped air in fresh cleaning solution interferes with the ultrasonic cleaning action and should be removed before cleaning cycles commence.  This can be accomplished by running the ultrasonic cleaner without a load for a period of time. 

As suggested earlier a more efficient alternative is to select a cleaner with a degas function that accomplishes the task faster.  Degas is especially desirable when using large volume cleaning tanks.

As contaminants removed during the cleaning of aircraft engine assemblies build up in the cleaning solution, cleaning efficiency diminishes.  This calls for periodic replacement.  Old solution is disposed of following local regulations.  The cleaning tank is rinsed and cleaned following the manufacturer’s operations manual and new cleaning solution is prepared.

Questions on Cleaning Aircraft Engine Parts?

For more information on cleaning aircraft engine parts with ultrasonic energy, contact the scientists at Elma Ultrasonic.  They will provide unbiased recommendations on cleaning equipment and cleaning solution formulations.