Blocks are constructed for use with fiber line or wire
rope. Wire rope blocks are heavily constructed and have
large sheaves with deep grooves. Fiber line blocks are
generally not as heavily constructed as wire rope blocks
and have smaller sheaves with shallow, wide grooves.
A large sheave is needed with wire rope to prevent sharp
bending. Because fiber line is more flexible and pliable,
it does not require sheaves as large as that required for
wire rope of the same size.
Blocks, fitted with one, two, three, or four sheaves,
are often referred to as single, double, triple, and
quadruple blocks. Blocks are fitted with a number of
attachments, such as hooks, shackles, eyes, and rings.
Figure 13-45 shows two metal framed, heavy-duty
blocks. Block A is designed for manila line, and block
B is for wire rope.
Block to Line Ratio
The size of a fiber line block is designated by the
length in inches of the shell or cheek. The size of a
standard wire rope block is controlled by the diameter
of the rope. With nonstandard and special-purpose wire
rope blocks, the size is found by measuring the diameter
of one of its sheaves in inches.
Use care in selecting the proper size line or wire for
the block to be used. If a fiber line is reeved onto a tackle
whose sheaves are below a certain minimum diameter,
the line becomes distorted that causes unnecessary wear.
A wire rope too large for a sheave tends to be pinched
that damages the sheave. Also, the wire will be damaged
because of too short a radius of bend. A wire rope too
small for a sheave lacks the necessary bearing surface,
Figure 13-45.-Heavy-duty blocks.
puts the strain on only a few strands, and shortens the
life of the wire.
With fiber line, the length of the block used should
be about three times the circumference of the line.
However, an inch or so either way does not matter too
much; for example, a 3-inch line maybe reeved onto an
8-inch block with no ill effects. As a rule, you are more
likely to know the block size than the sheave diameter.
However, the sheave diameter should be about twice the
size of the circumference of the line used.
Wire rope manufacturers issue tables that give the
proper sheave diameters used with the various types and
sizes of wire rope they manufacture. In the absence of
these, a rough rule of thumb is that the sheave diameter
should be about 20 times the diameter of the wire.
Remember with wire rope, it is the diameter, rather than
circumference, and this rule refers to the diameter of the
sheave, rather than to the size of the block, as with line.
Safety items when using block and tackle are as
l Always stress safety when hoisting and moving
heavy objects around personnel with block and tackle.
. Always check the condition of blocks and
sheaves before using them on a job to make sure they
are in safe working order. See that the blocks are
properly greased. Also, make sure that the line and
sheave are the right size for the job.
. Remember that sheaves or drums which have
become worn, chipped, or corrugated must not be used,
because they will injure the line. Always find out
whether you have enough mechanical advantage in the
amount of blocks to make the load as easy to handle as
. You must NOT use wire rope in sheaves and
blocks designed for fiber line. They are not strong
enough for that type of service, and the wire rope will
not properly fit the sheaves grooves. Likewise, sheaves
and blocks built for wire rope should NEVER be used
for fiber line.
Chain hoists provide a convenient and efficient
method for hoisting by hand under particular
circumstances. The chief advantages of chain hoists are
that the load can remain stationary without requiring
attention and that the hoist can be operated by one man