There are some options available for heavy lifting, but the most commonly used is the sling, which is typically found where heavy load requirements and rugged lifting conditions are a factor.
Wire rope is used for heaving lifting, and the most commonly used one is called a sling. Wire rope is made from individual wire strands that are then twisted together to form the rope. The rope can be solid steel core or fiber core, and each has its pros and cons.
Heavy-duty hoisting is a highly specialized endeavor. There are several factors to consider when using wire rope, like the weights involved and the structure of the rope itself, so let’s take a more detailed look at heavy-duty hoisting using wire rope.
The Basic Components Of A Wire Rope
Wire ropes essentially consist of three basic components, the strands, the wire, and the core. The wire makes up the strands and can be wound in various geometric configurations to form the strands.
The strands can consist of wires depending on the lifting application. These are arranged around the core in varying helical shapes and configurations, again based on the type of lifting application required. Most ropes have six strands as standard configuration, and these can be made of different kinds of steel, which we will look at later on, and these offer various levels of tensile strength for additional lifting requirements.
The core is either steel or fiber, and fiber cores are more flexible but will be used in lighter lifting applications than a rope with a steel core. The core can be made from polypropylene, hemp, or sisal, known as the Fiber Core.
Other core constructions are classified as Independent Wire Rope Core or Wire Strand Core, and both of these are usually referred to as steel wire cores or steel center cores.
In some cases, a fourth component is added, which is a lubricant; and this serves to maintain rope performance during lifting and is usually recommended for all lifting applications.
Types Of Lubricants Used
Lubricants can include petrolatum which is a hydrocarbon mixture derived from petroleum distillation and is very effective in colder temperatures.
Asphaltic lubricants are use bitumen combined with a base mineral oil that is applied as a spray and create an oil film between the contact surfaces.
Greases have oil , additives and a thickening agent and are applied as a semifluid and will partially penerate the rope to provide protection against corrosion, friction, wear and pressure.
The fourth lubricant is vegetable oil and this is the easiest and cheapest one to use. Because it is a liquid, it penetrates the wire rope to provide excellent against corrosion and wear.
Let’s look at the different rope materials that make up the wire and the strands.
What Are The Different Wire Rope Materials
Wire rope can be made from various metals depending on their specific applications and weight, with some offering more flexibility and others greater tensile strength.
The most common material for wire rope is carbon steel, but wire strands can be made from stainless steel, iron, bronze, and Monel metal.
Where affordability is a factor, zinc-coated galvanized steel may be used instead of stainless steel as it also affords good protection against the elements and corrosion.
Stainless steel is used where the external conditions are harsh and corrosive, as in environments with high acidity, where salt corrosion may be a factor, or where protection against chemical corrosion is needed.
Steel rope is used for general conditions where there is not a high risk of exposure to corrosion as with indoor lifting and available industry applications.
One of the more uncommon materials used in wire rope is iron drawn from low-carbon steel and is galvanized for use with older elevator installations.
The Strand Wire Patterns In Wire Rope
While the strands are usually arranged in spiral patterns around the core, different types of patterns can be used, and five patterns are most common with wire rope cores:
- Centerless pattern – where the wires are all of the same thickness and size and are wound together to form the helical shape.
- Single Layer Pattern – A center core with several different wires wound around the core to form the helical pattern. The wires and the core are usually the same thickness.
- Multiple Layer Pattern – The wires are placed over each in successive layers, and each layer fits securely into the preceding layer, and all of these wrap around the core wire.
- The Seale Pattern – In this configuration, smaller diameter wires are wrapped around the core, with a larger diameter outer layer then wrapped around the core layer. Each layer has the same number of wires.
- The Warrington Pattern – similar to the Seale pattern with the smaller diameter wires around the core, the outer layer has wires of different diameters and uses alternating thinner and thicker wires.
Other patterns include the filler pattern, where smaller diameter wires are used to fill the spaces between the inner and outer layers. The flattened pattern is the triangular strand, where three round wires form the core.
The outer surface is flattened, giving the triangular strand greater surface area and more strength.
Wire rope is also often coated for additional protection against corrosion and abrasion, so let’s look at the different coatings used for wire ropes.
Wire Rope Coatings
There are four basic coatings used for wire ropes: PVC, polypropylene, nylon, and braided wire.
- PVC is the most common coating and is a low-cost general-purpose coating with good flexibility. It can operate safely in temperatures ranging from -30F to 180F.
- Polypropylene – Use where more protection is needed against abrasion and corrosion. It is a durable and inexpensive coating material that is resistant to chemical leaching and impact damage.
- Nylon- This coating is the preferred coating choice in cold environments and is particularly resistant to abrasion and impact. It is well suited for harsher environments where fluctuations in temperature could cause less resistant coatings to fail. While not as flexible as PVC, it has a greater operating temperature range between -65F and 230F.
Wire rope is designed to handle the stresses and immense pressures and weights involved in heavy-duty hoisting. The coating and lubricants used will be based on the environmental factors concerned to ensure safety and efficiency when lifting.
Knowing which type of strand configuration to use, the coating, and whether a lubricant is required will all come down to the kind of lifting and environment and ensure safe and consistent heavy-duty lifting operations in whatever application.