A sheave or pulley is a grooved wheel on an axle, used to support movement and redirect the force applied to or by a rope, cable, or belt. They're often made of metal or plastic and can be used individually or in combination with other sheaves to create a mechanical. They are commonly found in various applications, like elevators, cranes, forklifts, stacker and reclaimers for the mining resource industry, as well as conveyors.
Service Life of Wire Ropes – Wire ropes tend to last 2-6 times longer when operating on plastic. This is due to the lower friction levels, as well as better elasticity that creates an increase in surface contact, therefore reducing contact pressures.
Service Life of Wire Rope Sheaves – Plastic Wire rope Sheaves tend to last 2-3 times longer than steel sheaves as plastic-on-metal wear rates are lower that metal-on-metal.
Light Weight – Plastics such as Sustamid (which are the most commonly used) are 1/7 the weight of steel. Apart contributing to increased lifting capacity, the lower weight reduces in lower inertia forces, and therefore reduced slippage in operation, contributing to lower wear rates.
Non-Corrosive – The lack of corrosion compared to steel means that the surface finish does not deteriorate, therefore contributing to improved wire rope life.
Dotmar has qualified engineers that can provide direct support with plastic sheave and pulley designs, including conducting calculations.
Crane Wire Rope Sheave
Typical for mobile and tower cranes
Dragline Sheave
Mining equipment for loading on trucks
Sorter Bin Sheaves
These are used in the timber industry in the saw mills
Curtain Pulleys
Used in theatres and cinemas to operate the curtains
V-Belt Pulley
Used in drive systems
Container Handling Pulley
Used for shipping container handling and lifting
Material selection is a critical consideration when choosing plastic for wire rope sheaves and pulleys, as it directly impacts the load capability, durability, and life service life. Here are some key material selection considerations for plastic sheaves and pulleys:
Load
The loading of a sheave or pulley is directly related to the line pull and the angle of wrap (contact) of the rope or belt on the sheave or pulley.
Time
Taking into consideration creep (deformation under load over time), it is imperative to have a good understanding of the duration of the sheave and pulley loading.
Temperature
It is typical for sheaves and pulleys to operate in ambient conditions, but if there are extreme, either high or low, then this is a consideration for material selection.
Environmental Conditions
Generally, the main environmental conditions to consider are resistance to UV light and weatherability. Sustamid is suitable for outdoor use in direct UV light.
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