Lifting Slings – Advanced Tutorial

(Continued from Product Spotlight – Lifting Slings, 2021Q3 Newsletter)

• MANUFACTURING STANDARDS: Sling manufacturing standards are maintained by the Web Sling & Tie-Down Association. Ancra is a member of the WSTDA and manufacturers our products to comply with their standards which includes the licensed use of their tri-lingual Warning Tags.

• SLING USE: Proper usage, inspection and out-of-service criteria standards are published by the WSTDA. It is the responsibility of the user to educate themselves and follow these standards which should help them comply with OSHA requirements. Customers can download these standards directly from the WSTDA website.

• WARNINGS: All Ancra slings have the WSTDA warning tags along with a permanent, WSTDA compliant warning placard sewn directly to the webbing on all four sides. The placard includes the manufacturer name, part number, working load limits for vertical, choker and basket hitches, and the UPC code which is presented on the outer side of the package for easy retail scanning.

• INSPECTION: To assist with inspection tracking, Ancra includes a durable inspection tag that is serialized and can be marked with the dates of inspection. While a formal in-depth inspection of a sling may only be required on a periodic basis, slings should be visually inspected prior to each use for cuts, tears, abrasion, chemical burns, dry-rot, and broken threads. If any of these are found, the sling should be removed from service and discarded. It’s also a good practice to remove slings that have lost all of their original color as this is a good indicator of excessive UV exposure. Additionally, slings should never be “knotted” to try and overcome a cut, tear, break or worn area.

• WEBBING: Lifting Sling webbing is different than traditional Tie-Down webbing. Essentially the number of threads used, and the weave pattern allows it to stretch and recoil and ultimately withstand the dynamic lifting forces better than tie-down webbing which is designed to be more static under constant tension to prevent cargo from shifting.

• POLYESTER vs NYLON: Both Polyester and Nylon webbing are used to make Lifting Slings. Nylon was invented in the 1930’s in the U.S. and therefore was the standard before Polyester was invented in the 1940’s. Polyester can be identified by a dark blue thread running down the middle of the webbing. Nylon will not have any marking. Polyester is softer, lighter, has less stretch, is more resistant to acids, oils and bleach, wicks moisture better to help prevent mildew and rot and is typically less expensive than Nylon. Nylon can absorb more moisture, stretch more, is more resistant to alkalis and sunlight and will typically cost more to produce. Either style will normally be sufficient for the job, but some users may have a preference depending upon the environment they are being used in and the specific application. If the lift tends to be very bouncy, they may opt for nylon with its ability to stretch and recoil with the bounce. If the lift requires tight headroom clearance, they might opt for polyester because it won’t stretch as much. For general lifting of less than 30 feet, the amount of stretch variation is fairly insignificant.

• CAPACITIES: Overhead lifting products require a 5:1 working load ratio to their original breaking strength. Cargo control tie-downs only require a 3:1. The capacity of the Sling is then affected by the style of hitch as well as the angles of the webbing during the lift. It is the responsibility of the user to know the calculations, but we do include a warning sheet with each sling that contains basic calculations. As a rule, a choker hitch will have ~20% less capacity than a vertical hitch and a basket hitch will have twice the capacity of a vertical hitch. This is due to the basic physics of the lift. In a choker style hitch, the webbing is pinched on itself. That stress concentration is what causes the derating. Conversely, the basket hitch benefits from the mechanical advantage of having 2 lifting points, hence the doubling of capacity.

  Web sling capacities can be increased by adding layers of webbing, called plys, by increasing the width of the webbing, or by a combination of both.  We offer 1 and 2 ply slings in 1”, 2”, 3” and 4” widths.  Our 1 ply slings have a yellow reinforcement around the loops.  Our 2 ply slings have a gray reinforcement.  The overall length of the sling has no bearing on the working load capacity. 

• WEAR INDICATORS: Some manufacturers imbed a red wear indicator thread below the surface of the web which is intended to alert the user that it’s time to replace the sling. While this appears to be a very beneficial attribute, the WSTDA determined that too many users were relying solely on the appearance of the red thread to remove a sling from service. They weren’t inspecting sufficiently for cuts and damage elsewhere on the sling. For this reason, the WSTDA does not recommend the use of the indicator thread and therefore, our slings do not include them.

• EYE TO EYE SLINGS: Designated by an EE, these slings have loops on each end and are probably the most popular style. We use a flat eye on our 1” slings and a tapered eye on our 2”, 3” & 4” Slings. Both are considered Type 3. The taper is designed to attach better to a crane hook but also helps keep the webbing from twisting when pulled as well as seat a choker hitch better. All Ancra Eye to Eye slings have reinforced loops which help prevent wear on the primary attachment bearing points.

• ENDLESS ROUND SLINGS: Designated by an ENR, these slings are made with a continuously spun polyester fiber that increases in strength as more fiber is wound into a loop. This is similar to the way a newspaper becomes more difficult to tear when multiple pages are rolled up to form a tube. A color-coded polyester webbed jacket is then sewn around the fiber to hold its shape and protect the inner core. Color coding the outer jacket helps identify the working load capacity of the sling and generally follows a standard industry practice by width of the sling. Endless round slings are typically used in a basket configuration. Their main advantage is that the sling can be rotated to prevent excessive wear on a single bearing point. They also exhibit good resistancy to common manufacturing fluids.

• CARE & MAINTENANCE: Slings should not be cleaned with harsh chemicals, abrasives or power washed. In fact, it’s typically best not to clean them at all. Chemicals and rubbing can compromise the integrity of the threads and power washing can break threads or imbed small particles in the webbing that will abrade the threads over time. If a sling must be cleaned, a very light solution of a non-abrasive, solvent-free cleaner, such a dish soap can be used with normal water pressure. The sling should then be left to dry completely before using. Slings should also be stored in a dry, non-sunlit area as UV rays will affect the webbing overtime.

• PRODUCT OFFERING: We offer only polyester slings made 100% of synthetic polyester webbing. We do not offer slings with metal hardware at this time. Our current offering covers the 20% of slings that make up 80% of the general end-user, commercial contractor, and light industrial needs. We do not carry the products that may typically be requested for the heavy construction, large building, and high-rise industries.

  Ancra does not offer any additional overhead lifting products such and chain or wire slings or replacement lifting cables and hardware intended for lifting.

  Ancra does not have the sewing equipment to effectively sew sling webbing. Therefore, we are unable to offer custom made slings for specific applications.

• PACKAGING: A key selling point for our slings, especially to retail customers is that each sling is shrink-wrapped and UPC coded. This keeps the product clean and factory fresh through the distribution process and also helps minimize the space required to store or display them. Additionally, we do not require them to be purchased in case quantities. A single sling can be ordered if that’s all they desire.

• CERTIFICATES OF CONFORMANCE: Ancra does not provide individual sling certifications. This is a service that dedicated sling manufacturers will offer for a fee and may be required for some applications. Effectively, the certification process pulls each strap to 2 times it’s working load to be certified. It is not a destructive test, because that would render the sling unusable. However, Ancra does follow WSTDA standards in our manufacturing process which tests a required number of slings per manufacturing lot. If one sling fails, the entire manufacturing lot is rejected. Ancra can provide a Certificate of Conformance to this extent but not on a per order, per sling basis.