LGH Technical User Guide - Page 42



The Tirfor Principle
A Tirfor has neither wheels nor gears
• Two jaws alternately pull the wire rope and the load in the
required direction, just like pulling on a rope with both hands
• The jaws are self clamping, providing immediate and gradual safety
• The heavier the load, the tighter they clamp
PULLING
• A release mechanism allows the wire rope to be inserted between
the jaws
Mathematical method of calculating the effort required to move a given load
Where
E
Is the effort required to pull a load lying on the ground
W
Is the weight of the load
μ
Is the friction between load and ground which depends upon the area of contact of the load with the ground (presence of wheels, rollers,
sand, mud concrete, etc...) is the angle of the slope
The value of U the coefficient of friction, must be known or estimated. Here are some general values of this coefficent.
Steel on steel
0.4-0.6
Iron on stone
0.3-0.7
Leather on metal
0.6
Continuously lubricated surfaces
0.15
Wood on stone
0.4
Load on wheels
0.02-0.05
Multifunction:
Safe and Reliable
• Work can be performed in any position;
horizontal, vertical or at an angle
• Constant control of the load during lifting and lowering
with accuracy
• There is no limit to the length of
wire rope
• When stationary the load is automatically distributed between
the two jaw units
• The capacity can be increased
• Overload safety device
Operates in every direction
PULL
LIFT
TENSION
Increased Capacity:
• Using the sheave block technique, the capacity of the Tirfor can be increased by a factor of 2, 3, 4 or more by
sheaving (see diagrams)
• The figures given must be multiplied by the nominal capacity of the device
• When calculating the working load limit, include a loss of around 4% per sheave, due to the friction of the sheaves
42
Delivering excellence in lifting throughout the UK





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