Cracks


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compressor blade damage

compressor blade damageclick for a larger image
Various types of damages that compressor blades can sustain. Only one or two may take place simultaneously though these have been combined in this illustration.
The various types of damages to compressor blades and their appearances are as follows:
i. Bend. The blade gives the appearance of ragged edges. Smooth repair of the edges or surface in question can be carried out, but the extent of the damage that can be repaired is limited.
ii. Bow. The main source of this type of damage is a foreign object. The blade is bent at the tips and the edges.
iii. Burning. The damage is caused by overheating. The surface of the blade is discolored. If the overheating is severe, there may be some flow of material as well.
iv. Burr. A ragged or turn-out edge is indicative of this type of damage. This takes place during the grinding or cutting operation of the blade at the manufacturing stage.
v. Corrosion. Oxidants and corrosive agents, especially moisture present in the atmosphere, are the main reasons for the corrosion or pitting of the blades. Normally, regular washing is sufficient to prevent it. The blade gives a pitted appearance, and there is some breakdown of the surface of the blade. Also called pitting.
vi. Cracks. Excessive stress from shocks, overloading, or faulty processing of blades during manufacturing can cause cracks and result in their fracture.
vii. Dent. These can be caused by FOD (foreign-object damage) or strikes by dull objects like those in bird strikes. Minor dents can be repaired.
viii. Gall. This type of damage is from the severe rubbing of blades, in which a transfer of metal from one surface to another takes place.
ix. Gouging. The blade gives the appearance of displacing material from its surface, and a tearing effect is prominently visible. This type of damage is from the presence of a comparatively large cutting material or foreign body between moving parts.
x. Growth. The damage manifests itself in the form of elongation of the blades. Growth type of damage takes place because of continued and/or excessive heat and centrifugal force.
xi. Score. Deep scratches are indicative of scoring, which is caused by the presence of chips between surfaces.
xii. Scratch. Narrow and shallow scratches are caused by sand or fine foreign particles as well as by mishandling the blades.
xiii. Pitting. Pitting takes place because of atmospheric corrosion, especially seawater. The surface of the blade shows signs of pitting.
References in classic literature ?
They heard a frame crack stickily, saw it heaved high and twirled round between enormous hands--a blotched, bulged, and perished horror of grey wax, corrupt brood, and small drone-cells, all covered with crawling Oddities, strange to the sun.
One day Tom was in the act of dosing the crack when his aunt's yellow cat came along, purring, ey- ing the teaspoon avariciously, and begging for a taste.
The man opened it a crack, and then he let us in and shut it quick.
Only a moment stood they thus, for Eric, intent on teaching this rash beggar a lesson and sweeping him speedily off the stage, launched forth boldly and gave the other a sounding crack on the shoulder.
I did not hate her so much, however, when I was running about the room and peeping through the crack in the screen.
Natasha glanced at her and at the crack in the pantry door, and it seemed to her that she remembered the light failing through that crack once before and Sonya passing with a glass in her hand.
Next minute there was a roar and a sharp crash, and at her side Dorothy saw the ground open in a wide crack and then come together again.
I wonder if hot sunshine is liable to crack pumpkins," said Jack, with an anxious ring in his voice.
Sheldon promptly swerved to the left to seek similar shelter, when the faint crack of a rifle came to his ears, and almost immediately the bullet, striking the hard sand a hundred feet beyond him, ricochetted and whined onward on a second flight, convincing him that, preposterous and unreal as it was, it was nevertheless sober fact.
Cocky, staring at the open door, was in just the stage of determining whether or not he should more closely inspect that crack of exit to the wider world, which inspection, in turn, would determine whether or not he should venture out through the crack, when his eyes beheld the eyes of the second discoverer staring in.
The rocks will soon crack the shell," was the Crow's answer; and the Eagle, taking the hint, let fall the Tortoise on a sharp rock, and the two birds made a hearty meal of the Tortoise.
Some three feet lower, however, his eye lit upon a long jagged crack which slanted downwards, and this he must reach if he would save not only his own poor life, but that of the eight-score men above him.