Hoist Side Pull Detection
Side pulling a hoisted load is an unsafe practice that may cause tragic consequences when bystanders are struck or pinned by the swinging load. Side pulling is written into most operations manuals as a forbidden operational practice because of the inherent danger.
In addition to personal injury, intentional and unintentional side loading causes millions of dollars of equipment and product damage every year. Sideloading is also damaging to the hoist as rope guides and hoist drums, as well as hoisting cable, can be easily damaged by the act. There are products available to crane modernization providers that can be installed on new and existing hoists to operationally restrict the ability to sideload a hoist.
Side pulling and Sideloading Defined
Side pulling is the act of lifting a load out of proper vertical alignment with the hoist’s natural lifting point. When a load is lifted out of vertical alignment it places a sideload on the hoist. The side pulling can occur several different ways: 1) The operator pulls the hook and block out of the vertical plane with the hoist in order to attach to a load to be lifted.
Often the operator is trying to lift a load that is located outside the normal x-y hook coverage area. This can also occur when the hoist hook was not properly centered over the load to be picked. Another way this side pulling occurs is when the hoist or trolley motions are engaged prior to lifting a load. This caused the load to be dragged and the cable is pulled from the vertical plain.
In any of these cases, if the load is subsequently lifted out of vertical plain then the load will swing in a pendulum arc. This load swinging in an arc is where the danger to people and potential damage to product and equipment is most likely.
The effect is not only on the ground! Up in the air, the hoist, trolley and crane have all been subjected to potentially damaging side loads. The side loading of the hoisting cable may apart sensitive rope guides, cause the rope to cross drum grooves or even allow the rope to lift out of the sheaves. These situations could cause damage to the wire rope resulting in a dropped load. In addition, the side loading may cause premature or immediate failure of other critical hoist and trolley parts.
Operator Training and Oversite
The best method of prevention is to adequately train all operators and riggers in the proper operation of the equipment. Properly trained and supervised operators will be far less likely to engage in this practice as the have been trained in the proper operations and understand the risks and hazards of side pulling.
Safety Devises to Decrease the Likelihood of Side pulling
Where operators must handle loads in tight spaces near people, the value of the picked load is very high, or when all practical measure available will be employed to assist in proper crane and hoist operation, the technology exists to easily limit the ability to perform excessive side pulls or sideloading.
Limit Bars can be installed that shut down or momentarily reverse lifting and travel motions when the mechanical bars sense a side load in one direction or another. Another method uses a mechanical limit box, with a limit rod attached to the hoist wire rope.
Operartion outside of the allowed vertical axis triggers limits within the box that subsequently stop the hoist and or travel motions. Both of these mechanical means take up some space and ultimately decrease hoist hook height and also add additional electrical componentry that needs to be inspected routinely and repaired when malfunctioning. These methods are also fairly fragile and can be damaged under heave use and operator abuse.
A two axis MEMS based tilt sensor is mounted on a bracket clamped to the dead end of the wire rope on the hoist near the frame to detect side pulling. The inclinometers, also called tilt sensors, measure the slope or angle of wire rope it is mounted to based on gravity.
The sensor then transmits a signal to the control box that stops the hoist trolley and bridge motions that it is connected to. The sensor-based limit systems are more expensive; requires wiring and or battery power source to the sensor that is often located near the hoist block. These systems are less likely to be damaged during normal operation.
If your operation has applications where crane users continually engage in a practice of side pulling or if you want to limit the risk of an unintentional side load, CRANE 1 can perform an equipment and application assessment and recomment the most reliable or cost efficient system for your canes and hoists.
Give us a call at 888-658-1212 and one of our CRANE 1 Experts will help assist you.