K-10000 tower crane
TROLLEYS

 

-   -   -   - THE CONVERTIBLE HOISTING BLOCK  -   -   -   -
The hoisting block
of the main trolley
landed in its cradle
22-2Lnew.jpg (23221 bytes) The main hoisting block
is here carried in 2 parts
of hoisting line
The intermediate hoisting block,
which is always carried in 4 parts,
is lowered to the main block
When the intermediate block
is pinned to the main block,
we now have 6 parts of line
The winch has
a Line Pull of
22,000 lbs
=10.000 kg
    HOIST     - - CAPACITY - -
    LINES        LBS         KG

         2           22,000    10.000
         6         132,000    60.000
       12         264,000  120.000
Combining the outer 6 parts block
with the inner 6 parts block
results in 12 parts of line

 

Convertible Hoisting Blocks are a common feature among European built tower cranes.  The typical conversion, between 2 and 4 lines, appeared in the late fifties on a WEITZ tower crane.  It allowed 3 tons in 2 lines and 6 tons in 4 lines.  It was a revolution in the U.S. to be able to change reeving in a couple of minutes, and without anybody having to to touch the hoisting cable.

All Convertible Blocks work on variations of the same theme, the one Block is substantially heavier than the other Block.
On the K-10000 tower crane the Block hanging in the Outer Trolley consists of a Main Block and an Intermediate Block.  The Main Block, which is carried in 2 Parts, is heavier than the Intermediate Block, which is carried in 4Parts.  When the Main Block is suspended in its two Parts, the Intermediate Block (weighing less and carried in 4 Parts) is butt against the underside of the Trolley in an intended two-blocking.  The Main Block can be hoisted and lowered, empty or under load, and the Intermediate Block will always remain two-blocked under its Trolley.

When the Main Block is lowered into its Cradle, further lowering will cause the Intermediate Block to go down.  It is flared at the bottom to easily engage the Main Block.  When the Main and Intermediate Blocks are pinned together, we then have six lines, i.e. 132,000 lbs lifting capacity.  

In the K-10000 tower crane, this theme is taken one step further.
Before the Hoist Cable is reeved in the Convertible Block, it is reeved in 6 Parts in the Inner Trolley Tackle.
The inner Block, always carried in 6 Parts, and well lighter than the Convertible Block, will remain in intentional 2-Blocking, whenever the Convertible Block is hanging in its lines.
When the Convertible Block is lowered onto its Cradle, further lowering will cause the Inner Trolley Block to go down.
The Inner Block can be pinned and the Convertible Block hooked onto the Main Truss, which has its own double-J Hook.
The two 6-Part Blocks give the Truss a net capacity of 264,000 lbs. 
The counterweighting of the inner end of the Truss represents the difference between the weight of the Inner Block and that of the Convertible Block, resulting in the Truss staying near horizontal, even when raised or lowered w/o load.
Enlarged the photo of the Inner Trolley clearly shows the multi-tier boggie arrangement, giving equal wheel load distribution, regardless of the straightness of the roller path.
 
The long arms carrying small sheaves are automatic Trolley Locking devices.  The small sheaves rest on the Trolley Traction cable.  In case of a cable fracture, the arms will drop down and cause a locking of the Trolley Travel.  

 

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Copyrightę 1999 Tower Cranes of America, Inc.
Page Last Updated On 09/13/1999