757 Airplane Recovery Document 飞机恢复文件(63)

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4.  Chains
A.  Hoist chains are made from a good quality material (wrought iron) selected because of its properties (ductility and toughness). This material gives you a warning before it has a failure (it will bend or stretch). It is also easier to weld this material than it is to weld steel. The strength (tensile strength) is less than 46,000 lb/sq in. (3220 kg/sq cm).
B.  Chain is good equipment to select when you lift a load. Chain has the qualities that follow:
(1)  
Its components are smooth.

(2)  
It will not cause injury to the hands of a person.

(3)  
It is flexible and you can use it easily.

(4)  
It will not get kinks.

(5)  
It will not turn (twist or spin) the load.

(6)  
Its capacity does not change when you have the usual conditions that follow:

(a)
Heavy loads

(b)
Hard hits

(c)  
Heat

(d)
Corrosion

 

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MATERIALS AND ATTACHMENTS
Page 3-25 Jul 01/2005 D623N004
 

(e) Abrasion
C.  Be careful if you use chains near the surface of the airplane. It is flexible and it is heavy. It can easily cause airplane damage. We recommend some wire ropes if you are near the surface. Use wood pads to give protection to the surface if you must use chains.
5.  Wire Rope
A.  A wire rope is some wires around an element of a metal wire or a different material. A rope center element (hemp fiber) is frequently used for small loads. The center element holds the outer wires in their positions and it prevents damage (nicks) to them.
B.  A good wire rope (improved plow steel) has the properties that follow:
(1)
Strong

(2)
Very flexible

(3)  
Wear resistant

(4)  
Distortion resistant

C.  
There are two numbers that you use to identify a wire rope: the first number shows the quantity of units, and the second number shows the quantity of wires in each unit (a 6 x 7 wire rope has 6 units with 7 wires in each unit). The diameter of a wire rope is that diameter that goes tightly around the rope.

D.  
The factor of safety for a wire rope can be a low number (5) or a high number (12). Use a rope with a higher number when the conditions are dangerous to persons.

E.  
Be careful with a rope that has some deterioration. The deterioration usually occurs first in the low areas between the units. If one of the wires in a unit breaks, there is possibly other deterioration that you cannot see. If you can see that more than one wire is broken, you must replace the rope.

F.  
A wire will usually break where the rope goes around a sheave or a drum. It will also break where mechanical equipment frequently hits the rope.

G.  
See Figure 3-14 through Figure 3-18 for information and dimensions of hardware used with wire rope.
　
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