Contributed by Bob Kozickie, Technical Sales Support Manager
Edited by Christy Kutchma, Product & Marketing Associate
There are three styles of grab hooks manufactured for overhead lifting: Non-Cradle, Cradle, and Chain Shortening Grab Hooks. Each are designed to shorten, choke, or basket alloy chain slings in a variety of lifting applications. When used correctly though, all three styles perform their functions with safety and reliability.
The non-cradle grab hooks’ existence has endured the test of time. It’s been a reliable hook that riggers have utilized since alloy chain slings first came into existence. The non-cradle grab hooks’ use in lifting applications has seen gradual reduction over the years due to safety concerns. The non-cradle grab hook requires that the rigger take a 20% reduction in sling capacity when used in any overhead lifting application. The chain sling itself is tested and certified at twice the working load limit under controlled ASTM conditions; however, the rigger is responsible to reduce the capacity when he utilizes the non-cradle grab hook. This requires that the rigger not only has to be aware of the hardware on his chain sling, he also has to take the extra step to calculate the maximum load he can lift with that chain sling when the non-cradle grab hooks are used. The 20% reduction may require that a larger diameter or higher chain grade chain has to be used to safely lift the load. It’s easier and much safer to equip the sling with one of the two other grab hooks so the margin for error is greatly reduced.
There is a reasonable explanation as to why the 20% reduction is required to be taken. Throughout the years, it was discovered that the alloy chain being used in conjunction with the non-cradle grab hook experienced a number of failures. The failures occurred in such a fashion that the chain appeared to have been cut rather than experience an elongation shear break due to overloading. The main reason for this reduction is that the surface area at the bowl where the chain is in contact with the hook is narrow. Depending on the amount of grinding that is done at the forger to “clean up” the hook, the edges on which the chain rests can be relatively sharp. This is what leads to the chain failures when used close to the maximum capacity. Advancements in testing and failure analysis have led to the determination that the slings capacity is required to be de-rated by 20% when non-cradle grab hooks are used in all overhead lifting applications.
The good news is the non-cradle grab hook is not going away by any means. It has seen a resurgence in use by the Cargo Control Industry. The alloy non-cradle grab hooks are used on the ends of higher grade binder chain assemblies to secure heavy loads. The advantage of using these hooks for cargo control is two-fold. First, they easily slide down between the side rails and the truck body. The other styles of alloy grab hooks are too wide to fit through the slot. Second, they have the strength to maintain full capacity when used in a friction load securement application. There is no reduction in capacity required. The non-cradle grab hooks have been repurposed for use in this growing market application.
The problems that were being seen by the non-cradle hook then forced manufacturers to look for a safer alternative. The challenge was put out to their engineers to develop a hook that would perform better than what the market currently offered. The result was a hook that would cradle the length of a single link along the bottom of the throat opening, leaving enough room for a single link diameter to extend downward from the link on both sides. Thus, the cradle grab hook was born. There would no longer be the requirement to have any reduction in capacity with shortening, choking, or basketing scenarios. The only stipulation is that the flat barrel portion of the chain link has to rest on the hook while the weld nugget faces upward in the throat. The rigger now has the ability to connect the load or shorten the chain without the need to perform the calculation for capacity reduction when this style hook is used.
The latest evolution in grab hook development has led us to the chain shortening grab hook. This design is slightly larger than existing grab hooks but it is also the safest style available. The hook is forged with a deep curved throat that is designed to prevent most alloy chain from bottoming out out in the bowl. The alloy chain weld nugget can be placed either up or down in the bowl. The throat groove has a significant curve that is designed to retain the chain in slack conditions. There is also an optional locking pin style chain shortening grab hook available that will ensure that the chain will be retained within the hooks’ throat in all slack conditions.
The way this hook style functions is uniquely different than any other. The center link will “float” while the two adjacent links compress against the sides of the two angled protrusions that extend from both sides on the bottom. This is the portion of the hook that will see the load weight. An added safety feature is that the throats’ tip is made wide enough that the hook cannot be “tip loaded” between two links of chain. The chain shortening grab hook maintains 100% of the chains rated capacity when under load. No reduction is required by the rigger for any application. Even though the hook is heavier, the safety and security is far beyond any other design.
Grab hooks are a valuable component in the rigging industry no matter which style is selected. They are used to make single link adjustments to balance a load level. They also secure the pipes being lifted for use in infrastructure projects like water and gas lines when they are placed into the ground and can basket large drain pipes on sewer projects. Knowing the capabilities and limitations that each design offers will help assure that the best component is being used to perform the safest lift possible.