Wire ropes Flashcards
How are cables named?
By the number of strands followed by the number of wires in each strand.
Ex. 6 X 19 means 6 strands with 19 wires per strand.
What is a benefit of having more wires in a cable. At what cost?
More wires offers increased flexibility at the cost of reduced resistance to abrasion.
Give some differentiating factors of fiber vs steel cores
Fiber cores are soaked in lubricant and are more flexible than steel cores but they have a tendency to crush while traveling over the drum.
Steel cores are stiffer, stronger and resist crushing against drum but are less flexible
What does IWRC imply
Independent wire rope chord. Implies that the cable has a steel core.
IWRC vs strand core
INDEPENDENT WIRE ROPE CORE
- 6 x 7 strand steel wire rope with a 7 wire core
- best where ropes are subjected to severe pressure while running over sheaves or winding onto drums
STRAND CORE
-strand of steel wires, 7, 19 or 37 in numbers
-used in stranding ropes, guys, standing skylines
-provide extra strength, reduced stretch and best resistance to weathering
Regular lay vs Lang lay
Regular lay – wires in strand are wound in the opposite direction as the strands, causing the strands to run parallel to the direction of the cable. This is the typical logging lay since it is less subject to crushing than Lang lay.
LANG LAY
Wires and strands are wound in the same direction
Lang lay is more flexible and abrasion resistant but will crush more easily
In regular lay, the typical logging lay, what do right and left lay refer to?
Right lay: wires in cable run clockwise.
Left Lay: wires in cable run counter clockwise.
-Can be used to match the angle of pull.
What are the wire rope grades ? Which are used in logging ?
Improved Plow Steel – IPS and Extra Improved Plow Steel – EIPS for most logging ops.
Extra Extra Improved Plow Steel only if you wanted to put a smaller diameter cable on your tower for a longer Yarding distance.
- higher grade steel is just higher grade metal alloys. Improved strength but decreased flex.
What are two ways to make your line stronger?
Improved wire rope grade or swaged line
Compacted vs swaged
- Compacted means that the wire has been run through a die during manufacture to squeeze it in order to give more steel for a given x-section area
- Swaged is the same thing only they really squeeze it hard (it is stiff but very strong)
What does PFV refer to? Where would you expect to see it?
Plastic filled valley wire rope. The spaces between strands are filled. This is typically only used for Heli chokers.
Strength of wire ropes and weight per foot of wire ropes are proportional to…
Cross sectional area of wire rope
What is the elastic limit?
Refers to the load at which a cable will be stretched beyond its capacity to spring back to its original shape. It can be calculated by taking 50 % of the breaking limit.
Which systems use the biggest cables?
skylines tend to have the biggest cables.
What would be the standard size, grade and lay for cable ops?
- 7/8 inch
- 6X19 regular lay
- EIPS
What is the safe working tension and why do we use it?
- equivalent to 1/3 breaking strength to ensure that loads do not overstrain the cable past its elastic limit or breaking point.
- important that an engineer controls the line configuration and turn size to conform to safe working tension.
Cable logging deals with dynamic loads but uses static loads in the calculations. Why? How do loggers compensate?
Dynamic loads are extremely unpredictable due to shock loading and inherent imbalances. This is why loggers operate under a 3x safety factor so that a safe working tension can be implemented.
Is the safe working tension the load limit? Explain.
No.
wire condition, splices, and sheave (pulley) diameter all play a role in the reduction of the load limit.
- the larger diameter of sheave, the less tension on the line that bends around it.
What are the 3 components of wire ropes?
How are they measured?
Made of three components:
– Wires
– Strands (wires that are individually spun)
– Cores
- Diameter is measured at the widest point
