Talkis When the entire face of a lug must be machined to remove damage, the new lug transition radii should be shaped and positioned in accordance with CMM requirements. Similar grinding burns also have led to the fracture of flap carriage spindle journals figs. This article discusses some factors that cause damage in service or during overhaul. This damage often is caused steeel improper maintenance practices such as jacking adjacent to a jack pad or an inadvertent impact with tools or ground-support equipment e. Abrupt changes in sections, holes, and sharp-cornered keyways should be avoided.
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Mazura Boeing also is developing supplemental, specialized techniques, such as the Barkhausen inspection, to detect base metal heat damage under chrome plating or other protective finishes. Steel visible evidence of chrome plate distress can indicate the likelihood of base metal heat damage. By reducing the space required for these components, the wheel well size can be minimized and aerodynamic surfaces can be optimized, which allow an increase in fuel tank size optimal wing spar location or additional space for other uses.
Processes that must be followed with relief baking include chrome, sulfamate-nickel, and LHE cadmium plating; stripping operations; and many nital etch inspections.
Common techniques include detailed visual inspections and other nondestructive inspection methods, such as magnetic particle inspection MPI and fluorescent penetrant inspection FPI.
When properly maintained and overhauled, high-strength alloy steel components demonstrate high levels of service reliability. This may result in a shorter than planned time between component overhauls. Testing to these requirements will determine whether a cleaner or chemical is detrimental to protective finishes or base metal.
All portions of a component that are to be shot-peened should first be completely stripped; no cadmium residue should remain on the surface. Overhaul should reflect the same careful, detailed review that occurred during the original design. UTM indications show white during temper etch inspections and often are found within patches of OTM, which show dark gray to black during temper etch inspection.
Rework that requires low-hydrogen embrittlement LHE cadmium stylus plating should be performed when the component is not loaded. As the pit forms, it damages the shot-peened layer locally at the surface. Finer surface finishes also may be needed to eliminate unnecessary stress concentrations, especially in areas of machined radii or undercuts. The new plating deposits frequently are thicker than the original design configuration and deterioration of the plating adhesion. Salvage was not possible.
M Alloy Steel M TW Metals Airline personnel who participate in component rework, maintenance, and overhaul tasks should be familiar with the properties of high-strength steels and understand the negative effects that can result from. Touching up damage to accessible enamel and primer in a timely manner can prevent the formation of corrosion pits and reduce the need for excessive rework during overhaul. Maintenance efforts focus on corrosion prevention and removal in addition to normal checks for wear and free play.
Proper design will reflect generous fillets, gradual changes of shape, and the use of relief grooves in areas of high stress. Similar grinding burns also have led to the m of flap carriage spindle journals figs.
There are few options to restore these machined depressions to meet interface requirements. Spot face depressions typically are not filled with plating to restore the dimension but instead are finished in the same manner as the original design.
Corrosion pitting also can lead to fatigue crack initiation depending on the component, the location of pitting, and cyclic loading conditions. Bushings should not remain installed during overhaul unless retained by specific CMM requirements. Landing gear truck fractures have occurred in service because of corrosion on the inner diameter of the main gear truck beam figs.
Improper rework and overhaul practices may result in loss of finish, corrosion, and damage to or alteration of the base metal, which may require unscheduled maintenance between overhauls. Overheating damage can be caused by. Stress concentrations can lead to initiation of cracking by fatigue, stress corrosion, or hydrogen-assisted stress corrosion.
Discoloration of the enamel, primer, or chrome or evidence of cadmium damage ateel the inner diameter of the axle steel require the heat-damaged component be removed from service. The planning flowcharts in CMMs, and are value-added guidelines for planning the rework of any high-strength alloy steel component on a Boeing airplane. Operators also will benefit from the enhanced reliability and durability m high-strength alloy steel components on their airplanes.
In general, the best practice is to initiate baking as soon as possible following a plating operation. This can reduce the possibility of chrome chicken-wire cracking and poor runout details. Operators should ensure that cleaners and chemicals are tested before use in accordance with Boeing document D6Evaluation of Airplane Maintenance Materials.
Overheating damage can be caused by Frictional heating while in service. This widespread reduction in metal hardness Rockwell-C hardness readings may indicate that the component cannot be salvaged. Steeel cadmium sheel is left on a part during overhaul processing to protect it k corrosion. Visual evidence of chicken-wire cracking after chrome grinding indicates poor chrome quality and also may indicate the possibility of base metal heat damage.
Transitions or radii that are sharper than original design. Determining whether cadmium has migrated into the grain boundaries of cadmium-plated, high-strength alloy steel components requires destructive testing of the components. Airline personnel should follow proper maintenance procedures and Boeing-provided rework practices, checklists, and planning guidelines during maintenance and overhaul of these components. Truck fractures most often occur at maximum ground loads such as after fueling or during preflight taxi.
Ultrasonic or eddy current inspections also may be useful for in situ inspections. SOPM provides details about the inspection process and interpretation of the results.
This technique can be used successfully to screen components with suspect damage. High-strength alloy steel components should be stripped completely during overhaul including removal of bushings and bearings in all structural components. Stress concentrations can be created by mechanical damage that compromises the protective finishes and alters the compressive shot-peen layer.
Using high-strength alloy steel for component design provides an opportunity to do the same job with less material. Shop procedures such as magnetic particle inspection and LHE cadmium stylus plating can cause arc burns if appropriate precautions are not maintained during processing.
These cracks may result in a fracture or scrap of a component when stesl while in service or during overhaul. Personnel must ensure that materials used for activities such as cleaning and deicing conform to Boeing document D requirements and will accomplish the intended task wteel by the material provider or operator. Organic coatings or sealants may crack or become brittle or discolored wide range of temperatures.
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