Manufacturing Engineer and Factory Safety Engineer Discusses Bungee Cords

Manufacturing engineer discusses bungee cord safety from a safety engineering view point. Stretching a bungee cord imparts a significant amount of potential energy into the system that can be released and make the end hook a dangerous projectile. There are safety warnings on most cords; however, these are often ignored or torn off. It has been suggested to limit the extension (to 50%) to limit the danger. Streth tests were performed (upper left photo). to examine the difference between a limited bungee cord and one without limits. The bungees were stretched and the force-distance data ploted (upper right figure) The area under each curve is the stored potential energy. This is converted to kinetic energy (KE). From the KE the hook velocity can be calculated. The unlimited bungee generated a maximum hook velocity of 100mph. The maximum hook velocity for the limited bungee is 70mph. Both bungees can still be dangerous.

It appears that the limited bungee was made more robust to increase the holding force for 50% elongation. This has a negative effect on this cord's safe use.

Manufacturing Engineer and Safety Engineer Discusses Crane Safety

Manufacturing Engineer and Safety Engineer advises, for factory safety, that if a crane is being used to lift objects over and into baths that contain harmful liquids such as acids, caustics and high temperature liquids. the event should be treated as a "lock out tag out" type of event. All personnel should be cleared from the area, and the crane operator should be behind an appropriate protective screen. If there is a crane malfunction and a splash occurs, no one will get hurt.

Glass Expert Analyzes Wine Bottle Defect

A glass expert was asked to examine poor quality bottles received by a winery. The issue was whether this product defect would significantly lower the strength of the bottle and would present a product liability problem. The photo on the upper left is a photograph of the manufacturing defect. It is a 4 inch horizontal "gash". The center picture is a photo-micrograph of the defect cross-section. The cross-section shows that the edges of the defect are rounded. This is a molding defect that occured when the glass was at or above the its softening point. The edges of the defect are rounded; therefore, in the opinion of a manufacturing engineer, they are unlikely to cause a low stress bottle failure. The picture on the upper right is a photo-micrograph of the top of the defect. There is a thin sheet of glass over the center mound of the defect. It is believed that this defect was formed in the blow molding step of the bottle manufacturing process.

Glass Expert Performs Failure Analysis of Glass to Metal Seals

California failure analysis expert and manufacturing engineer was engaged to perform a root cause failure analysis of shallow cracking in the seal glass. These glass to metal seals were made by one manufacturer and then sent out to another processor to be plated. The photograph on the left shows two sight glasses. The body of the seal has male pipe thread and there is a screw driver slot on the top. The intent is for these seals to be screwed into a container wall. The glass window allows one to view the container interior (i.e. see the fluid level). The photomicrograph on the right shows a typical crack. These cracks occured during plating; they are always shallow and always associated with the one of the screw driver slots. The "rainbow" that is seen is due to the air wedge created by the shallow crack. The stress pattern of these seals is symetrical; therefore, sealing stresses are not implicated. Because glass only fails in tension and because these cracks are associated with a screw driver slot, the glass expert believes that they occur when the seals come out of the hot plating bath (195°F) and cool rapidly either in the air or when spray rinsed.