Outdoor industrial pulley systems are exposed to intense ultraviolet radiation throughout their service life. Without proper protective measures, the absorption of these rays will cause UV degradation (cracking and disintegration over time) to natural and synthetic polymers alike.
The materials most threatened by UV degradation are ones installed long-term or permanently in an outdoor environment, such as shade systems. However, any equipment that experiences regular sun exposure can be adversely affected.
On the surface, the relative immunity of galvanized or stainless steel to UV light can make steel components look like a sensible option, compared to plastics and fibers. But modern polymers like those in synthetic fiber ropes have too many advantages to ignore. Today’s synthetic hardware and soft goods have drastically lower weight, higher strength, and minimal injury risk in a failure compared to steel.
This has led manufacturers of industrial pulley systems (and the people who use them) to create a few solutions to the UV degradation of polymers. Here are a few ways cutting edge rigging materials can bring their impressive performance to high-UV environments:
Chemical Treatments and Coatings
One possible solution is to treat the preferred synthetic material with a chemical coating or spray that protects it from the sun. This isn’t much unlike using sunscreen on your body.
UV inhibitors like these might work well on some stationary equipment, but the abrasive forces on industrial pulley system sheaves and ropes would wear out any surface coating very quickly. You could eek extra mileage out of coated materials by re-treating equipment regularly, but this can be expensive and time consuming.
One solution is a deeply pre-treated rope—such as the upgraded SL coating on Ocean 3000 and Ocean 5000 Dyneema® ropes by Robline. These ropes have their fibers individually coated before the rope is woven together, allowing for longer and more complete protection. The ropes themselves would wear out well before re-coating becomes feasible.
When a rope is made with polymers that have poor UV degradation properties, an outer sleeve of UV resistant fiber can do the trick. The low natural UV resistance of Vectran, for example, often necessitates a protective braided cover for long-term performance in harsh sunlight. Sleeves can be added to most ropes to upgrade their outdoor service life while also protecting the rope from abrasions.
Many ropes are actually designed to protect high-strength core strands from the start with a sheath of UV resistant material woven around the core strands during manufacturing. In these cases, the outer layer of the rope acts like an added protective sleeve.
However, a protective rope sleeve still does nothing for the UV-sensitive plastics in your industrial pulley system’s blocks, sheaves, fairleads, and other rigging hardware.
Naturally UV-Resistant Materials
The easiest way to prevent UV degradation is to use equipment made from a material that needs no additional protection or maintenance to last a long time in the sun. Standard nylon and polyester, for example, both have higher UV tolerance than other common polymers like polypropylene.
Nylon (polyamide) is a versatile, durable polymer for synthetic pulley systems. It brings:
- Outstanding wear and abrasion resistance
- Excellent chemical resistance
- Low friction
- Lighter weight and cost than steel sheaves with comparable service life
Acetal is another possibility. The standard formulation is hard but somewhat brittle. It was originally selected as an industrial sheave material for two reasons:
- It can be easily molded
- It has impressive chemical resistance to fuels and solvents
However, acetal doesn’t have as much UV resistance as nylon in its original form. This leads us to the best way to fight UV degradation:
UV stabilizers for polymers can boost base material performance well beyond typical levels. Stabilization typically involves the addition of anti-UV chemicals to a polymer during formulation, such as the UV-stabilized acetal in Ronstan all-purpose pulleys.
This process significantly increases the natural UV resistance of a polymer throughout the material (unlike a coating that can scrape away due to abrasions). We prefer UV-stabilized acetal for both sheaves and ball bearings—or ball bearing sheaves—where the polymer’s natural librucity and strength bring high performance and low friction even to jobs with heavy UV exposure.
Products infused with glass fibers, such as glass-reinforced nylon pulleys, can also stand up well in constant sun. This is because glass is highly resistant to UV radiation. Glass is much more than a UV stabilizer, however. It dramatically increases the strength of the polymer so that the industrial pulley system can use fewer metal components and achieve great reductions in weight.
Which One is Best?
If your industrial pulley system is already assembled, a chemical treatment may be the simplest way to preserve existing equipment, but it will wear out quickly. Swapping out ropes for ones with sheathes or sleeves that protect vulnerable fibers can improve some of the system’s service life, too. The most reliable fix is to gradually upgrade all equipment—pulley blocks, fairleads, thimbles, anchor points, etc.—with new components that are built to last under harsh UV exposure from the start.