The larger the sheave of the pulley, the greater the distance traveled by the rope on the latter is important, and thus the less movement at the pulley axis is large compared to the distance traveled rope.
A sheave 60 mm have a circumference of 3.14 x 60 = 188.4 mm .
A sheave 32 mm in circumference will 3,14x 32 = 100.48 mm.
So in a tower block with a sheave is 32mm has covered 53% (100.48 / 188.4) of distance traveled in a tower block with a sheave 60 mm
Warning: this means to map it takes to turn the pulley a little more to get the same level with the same force applied.
The size of the axis is also important.
An axis of 12 mm will have a circumference of 3.14 x 12 = 37.68 mm
an axis of 15 mm will have a circumference of 3.14 x 15 = 47.1 mm
A pulley 32 mm with a 15 mm axis will have a ratio of 100.48 / 47.1 = 2.13
While a pulley 32 mm with a 12 mm axis will have a ratio of 100.48 / 37.68 = 2.67
The pulley of 32 mm with pin 12 mm rope move 2.67 mm to 1 mm on the axis, while the pulley of 32 mm with an axis of 15 mm will move the rope 2.13 mm to 1 mm on the spindle.
So it's not just the size of the sheave that counts but the ratio of the size of the sheave on the size of the central axis of the pulley
And if the one compares with pulley of 60 mm with a 12 mm axis is obtained: 188.4 / 4.98 = 37.68 more than double that with a 32 mm sheave and an axis of 15 mm
The rotation of the central axis generating friction we must minimize it for better performance. Hence the interest of having a better ratio:
The pulley of 60 mm with an axis 12 mm rope move 4.98 mm to 1 mm from the axis, while the pulley of 32 mm with an axis of 15 mm move the rope 2.13 mm to 1 mm on the ' axis.
The rope: Of the friction on the rope sheave as it generates losses
|On a pulley , the best ratio is to have a rope with a diameter between 1 / 6th and 1 / 8th the size of the sheave, (beyond the rope does not have enough friction to rotate the sheave the pulley and slips it directly, it no longer serves in having a sheave that rotates). The ropes are strong and flexible and thus deformable under pressure. Over the line will end more friction and the crushing of the rope will be reduced and therefore the yield increase (in the limit of 1/8 of the size of the sheave, otherwise the yield is reduced).|
On a pulley , the best ratio is to have a rope with a diameter between 1 / 6th and 1 / 8th the size of the sheave (in addition, the cord has enough friction to rotate the sheave the pulley and slips it directly, it no longer serves in having a sheave that rotates). The ropes are strong and flexible and thus deformable under pressure. Over the line will end more friction and the crushing of the rope will be reduced and therefore the yield increase (in the limit of 1/8 of the size of the sheave, otherwise the yield is reduced).
If the rope is higher than 1/6 the yield will be reduced.
A sheave 60 so it would take a rope from 10 mm to 8 mm (60/8 = 7.5 does not exist in current rope).
On a sheave 32 mm would require a string of 5 mm to 4 mm (32/6 = 5.3 does not exist).
Small additional point: the ropes and the sheave will perform better over the throat of the pulley will be adapted to the diameter of the rope between a pulley grooves to 60 mm with a rope and a 10mm pulley 60 without grooves (flat) on performance decrease of approximately 5% (due to thecrushing of the rope thus increasing friction.)
The ball bearings:
There is something for all the prices and the quality. The "best bearings" are the SKF, the world leader in working.
The nomenclature of the bearings is always the same whatever the brand
- the figures show the dimensions
- If nothing is indicated after the figures indicates that the bearings are in the open air
- ZZ: turnover has anti-dust covers
- RS: the bearing is sealed
- C3: High speed bearing
The ball bearings are made to average speeds of 1,000 to 20,000 revolutions / minute depending on the Brooch explosio them .
The bearings will be more effective than the self-lubricating bushings to the usage limit charge. Above the CMU the ball will tend to deform. The working principle is to reduce the friction by reducing the contact point through the ball (instead of some cm² area is reduced to approximately mm²).
As against a small area of about mm² suffers any charge and will be a limit before deformation reached faster.
The self-lubricating bushings:
Made of bronze, copper, brass, they have the property not to join (seize) other metals (steel, aluminum).
They will yield reduced compared to ball bearings, but the limits of use of the ball bearing the rings will go much higher expense.
(Eg the cars are on ball bearings for the truck load is too great and the system goes on self-lubricated bushings because the load is too high for balls (except to have balls quadruple volume but this would be more interesting)).
Different performance simulation table rollers can be used in slackline.
The following calculations represent a theoretical value, in reality supplied forces vary and are not regular in time.
Please note the total sums of the sheave blocker and is only valid with a referral. Without reference that total is divided by the yield of the blocker.
Taking no competing brand in reference we will base on the returns provided by Petzl and Wichard. Please note all the brands do not have the same output quality.
Pulley Petzl ball bearings used as reference:
pulley sheave minder 51mm 97% yield
pulley sheave rescue of 38 mm 95% yield
pulley sheave Prussik 25 mm (axis of 10) 91% yield
Rope blockers as reference:
Protraxion Petzl sheave 38 mm (or pulley minder with Machard) yield 95%
Petzl Micro traxion 28 mm (or pulley rescue with Machard) 91% yield
Kong Robot 35mm 69% yield
Grigri 2 Petzl 52% yield
Gigi plate 48%
For four pulleys, we take the example of two double blocks put together a multiplier Mooring, additional performance loss is added because of the strings rubbing them on the Equalization of the system for the pulleys remain straight.