Machine Design

Serious vibration and missing guard factors in hay-grinder accident

From the safety files of Lanny Berke: A man was injured when part of the hay grinder he was operating broke free and struck him in the chest. The grinder was running without a drivetrain guard at the time of the accident.

The hay grinder developed a worrisome vibration in its drivetrain 14 months after getting a new engine and flywheel cover. The grinder’s operator removed the guard over the drivetrain between the engine and the grinding mechanism and took the machine to the mechanic who had installed the engine to have the vibration diagnosed and repaired.

The mechanic wasn’t able to complete the repair that day, so the operator took the machine back to grind large, round bales of hay at a farmer’s field as scheduled, leaving the guard off. The farmer was working about 50 ft from the grinder when it stuttered and stopped. He subsequently found the operator face down on the ground and called 911.

Investigators determined a bent driveshaft caused the severe vibration. During grinding operations, the hammer mechanism of the grinder hit something hard that sent a shock through the driveline. The shock, combined with the stress from the bent shaft, fractured a universal joint. Without a guard to stop it, a knuckle of the joint flew out of the machine and struck the operator in the chest. At the same time, the engine overloaded and stalled.

The investigation determined that the previous installation of the engine and flywheel cover had nothing to do with the accident. It also found the guard, had it been installed, would have been substantial enough to stop the U-joint knuckle from flying out of the machine. The machine also contained warnings alerting users that parts could fly out of the drivetrain and that a guard was needed for safe operation.

However, the guard was not large enough or extensive enough to fully protect operators who could reasonably be expected to be working around the drivetrain while the machine was running. Because it was not hinged to the machine, it was reasonably foreseeable that the machine could be operated without the guard; there were no interlocks to prevent this.

The hay grinder manual could have discussed the operation of the machine’s components — including the engine, flywheel and housings, clutches, drivetrain, and guards — in greater detail along with their potential hazards. A list of symptoms indicating serious mechanical problems and a toll-free number where users could contact the manufacturer could also have helped the operator avoid the accident. MD

This month’s safety violation comes from the files of Lanny Berke, a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a safety violation to share? Send your images and explanations to [email protected].

Edited by Jessica Shapiro

© 2011 Penton Media, Inc.

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