Free-wheeling parts: Inertia

The heavier a part is and the faster it moves, the longer it will continue to move after the power that moves it is shut off. This characteristics is often called “free wheeling” – just like a toy top that continues to spin long after the child has pulled the string to start it.

Many farm machines, especially those that cut or harvest crop materials, have components or parts that continue to move for quite a while after the power that drives them has been shut off. The parts continue to move because of their own inertia, or the inertia of other moving parts connected to them.

Free-wheeling parts

Some free-wheeling components on farm machines continue to rotate up to 2 or 2½ minutes after power is disengaged. Though moving slowly, they’re still dangerous. Examples of free-wheeling farm machinery include:

·         Cutter heads of forage harvesters.

·         Hammer mills of feed grinders.

·         Rotary mower blades.

·         Fans and blades on ensilage blowers.

·         Flywheels on balers.

How injury occurs

Why do people get injured by free-wheeling mechanisms? There are probably several reasons. For instance, they may disengage the power, open an access door and reach it to clean or unclog the machine before the part stops moving. Perhaps they concentrate so much on servicing the machine they forget parts are still  moving – they are preoccupied. Perhaps they get impatient – just can’t wait for the last movement to stop. Even though the part may have almost come to a stop, its inertia still may be enough that it can cause serious injury.

It is almost impossible and usually impractical to completely protect a person against such injuries with guards or other machine design. So it is necessary to recognize the potential hazards of free-wheeling parts and make sure you and others stay away from them until they are completely stopped and all power is shut off.

Avoiding free-wheeling parts

Listen! Almost any free-wheeling, rotating  part makes some sound – often whirring or humming sounds – especially at its higher speeds. Also, clutch devices on many machines may make a fairly loud and distinctive clicking or clanking noise until free-wheeling parts stop.

Watch for motion! Watch flywheels, pulleys, PTO shafts or the ends of shafts to see if parts are still moving. Make sure you understand that free-wheeling parts, even though moving very slowly as they are finally coasting to a stop, can still cause serious injury because of their weight. Objects in motion want to stay in motion until they are stopped by some other force or object. Don’t let your hand or foot be that object.  

June 26, 1995. A 56-year-old farm worker died after being struck by a flywheel of a hay baler. He was lying on his side under the baler, oiling a chain, while the baler was operating. A flywheel for the bale tosser cycled and struck the victim on the top of the head, instantly killing the farm worker. Source: Wisconsin FACE Report.

Thrown-object hazards

An object thrown near people represents a potential personal injury hazard whether it is a stone from a slingshot, a baseball, or a pea from a peashooter. If it strikes with enough speed and momentum, it will cause serious injury.

Some farm machines can hurl objects great distances with tremendous force. Recognize machines with this type of potential hazard so you can avoid injury, and so you can operate machinery in such a way that others will not be injured.

Machines that throw objects

Perhaps the greatest potential for injury by thrown objects exists around machines that have rapidly rotating parts designed to cut or chop crops in the open field. In order to cut or shred, the machine must strike the crop with considerable energy. Examples of such machinery are rotary mowers, cutters and shredders. Crop material such as corn stubble is relatively light in weight (low density) so it is not thrown a great distance, but if a much heavier object (high density), like a stone, is struck by the machine, it can be flung much farther and with greater force than the crop material. Such thrown objects can cause serious injury.

Another type of thrown-object hazard may exist around machines that chop or grind crop or feed material. Particles of that crop may be thrown from the machine. For instance, a straw chopper on a combine or a feed mill may fling pieces of corn cob or a kernel of corn. It may not be thrown as far as a rock thrown by a rotary mower, but persons may be near enough that such objects may injure eyes.

Avoiding thrown-object hazards

1.       Recognize what type of machines may throw objects.

2.       Keep the machines properly shielded to reduce the possibility of them throwing objects that may injure you or others. Some operations may require removing or adjusting shields or deflectors to handle certain crops or feeds (e.g. rotary shredders or brush cutters), but make sure you replace the shielding before you begin the next job. Follow the manufacturer’s instructions for use of shielding to reduce the hazard of thrown objects.

3.       Know how far and in what direction the objects may be thrown, even though shielding is in place.

4.       Stay a safe distance away from the likely path of thrown objects when you approach a machine.

5.       When operating a machine that may throw crop materials or heavier “foreign objects,” such as rocks or sticks, always make sure the machine will not discharge crop materials near people or animals.

June 4, 1996. A 45-year-old farmer died from injuries he sustained when he was struck by a chain that was being used to pull a cultivator stuck in the mud. Attempting to free the cultivator, he hooked one end of the chain to the cultivator and hooked one end of the chain to a stretchable “snap strap” and the other end of the strap to the tractor. On one attempt to pull the cultivator free, the chain slipped from where it was hooked to the cultivator. The chain was propelled toward the tractor and the victim seated in the enclosed cab. It shattered the rear and front windows of the tractor cab and struck the victim. He lost control of the tractor, hit a ditch, fell from the tractor and was run over by the left dual wheels. Source: Minnesota FACE Report.