Wax Molding Machine Accident


Thomas J. Cocchiola, PE, CSP ::::

Case Synopsis:  A worker was injured while operating a hydraulically powered machine that produces custom wax molds for casting precision metal parts.  When an operator initiates a cycle, a hydraulic cylinder forces the mold halves together while the machine injects molten wax into the mold cavity.  The hydraulic cylinder keeps the mold closed for a preset amount of time to allow the wax to cool before automatically raising the upper platen to open the mold at the end of the cycle.  The operator can then remove the finished wax mold and prepare for another cycle. The machine is equipped with a set of two hand controls to protect operators from the pinch point formed by the closing mold halves.  An operator has to keep both hands on the controls until the mold closes. The operator can then release the controls and wait until the end of the cycle.

On the day of the accident, the operator installed and adjusted a mold before initiating a cycle.  After the mold closed, he reached for a tool in the space above the movable platen.  The cycle time expired, and the machine automatically raised the platen to open the mold.  The operator’s arm was crushed between the moving platen and the molding machine frame.

Expert Analysis:  Normal operation of the wax molding machine creates a hazardous pinch point as the mold halves open at the end of each cycle.  Operators were unnecessarily exposed to the accessible, unguarded pinch point hazard during every machine cycle.  An engineering evaluation demonstrated the pinch point formed between the moving platen and machine frame required a guard in accordance with the requirements of applicable safety standards as well as recommended engineering practices.  The manufacturer could have, and should have, guarded the pinch point when the wax molding machine was originally designed and built. The manufacturer subsequently designed a guard for the virtually identical molding machines sold to American customers.  The manufacturer was aware that operators of existing American machines were exposed to unguarded pinch points but took no action to protect them.  The manufacturer failed to notify owners of existing machines or offer retrofit guarding kits for the accessible, unguarded pinch point hazards.  The operator of the incident machine would not have
been injured if the pinch point had been guarded.

Conclusion: Case Settled.

Categories: Case Studies


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