COMEUP DHC Hoist (Ver:03) - Manual (Page 9)

IV. Hoisting Principles
7
Load Rated
Load and speed varies according to
how much wire rope is on the drum. The first
layer of rope on the drum delivers the slowest
speed and the maximum load. The top layer
of rope on the drum delivers the maximum
speed and the minimum load. For this reason,
all hoists are rated at their top layer capacities.
The flanged drum end plates shall
protrude beyond the rope wound on the drum at the top layer by at least 1.5 x the nominal
rope diameter.
Calculating Head Loads
P: Rope tension
η: Sheave efficient
θ: Angle
W: Load
μ: Friction factor
First layer (Min.speed Max.load)
Half layer (Med.speed Med.load)
Top layer (Max.speed Min.load)
Flange of drum
P
W
P= W η
P
W
P= W
2
η
P
P= W
4
η
W
P
W
P= W
μ .
μ
P
μ
W
θ
P= W
μ . .
sinθ + W
.
cosθ
Calculating Fleet Angle
● The hoist should be mounted as close to centre
and as perpendicular as possible to the direction
of the line pull. This will keep the wire rope fleet
angle centred on the drum as small as possible.
● If the proper fleet angle is not maintained, the
wire rope could wind onto one side of the drum.
This could cause failure of the hoist or wire rope, resulting in damage, injury or death.
● Experience has shown that the best wire rope service is obtained when the maximum fleet
angle is not more than 1.5° for smooth drums.
● Therefore the correct distance between centre of drum and of should be derived as a fleet angle
of 1.5° is the equivalents of approximately 19 cm of lead for each centimetre of overall drum
length.
θ
θ
Correct Distance
Drum Length
Fleet Angle
No. of sheaves 1 2
Roller bearing 0.98 0.96
Sleeve bearing 0.96 0.92