Self-bunkering inductive proximity switches for welding applications

Paul Boughton
In abusive welding environments, 'bunkering' is the technique of mounting sensors within tough metal brackets to provide protection from impacts. However, many sensors have not been properly bunkered, resulting in repeated (and costly) failures from impact damage. Often it is too difficult and time-consuming to retrofit these applications with adequate bunkering protection.
Balluff's Bunkerprox, however, is a rugged, 'self-bunkering' M18 inductive proximity sensor that is specially designed to survive longer in abusive welding applications without external protection. The key to the Bunkerprox design is a strong, thick-walled housing that boosts the ability to withstand repeated mechanical impacts. The extra-thick housing also serves as an intermittent heat sink to shield the sensor electronics from the intense heat of red-hot weld spatter.
A frontal impact deflection ring helps to protect the high-temperature ceramic face from impact damage during part loading and unloading. The ceramic face also resists the melting and burn-through that can short out the sensing coil of standard proximity switches, causing them to fail. Additionally, the all-important sensing coil is reduced in diameter compared to standard M18 sensors, providing a perimeter 'crush zone' so that incidental corner impacts do not result in immediate coil damage and loss of sensor function.
An unusually thick connector/barrel junction helps to eliminate connector failures from excessive shock, vibration, heavy contact or undue cable stress. To repel hot weld slag and prevent it from sticking, the Bunkerprox is fully coated with slag-resistant material, while weld-field immune electronics eliminate false signals during the welding cycle. Offered in a PNP, normally-open output configuration with a micro connector, the nominal sensing range for the Bunkerprox is 4.0mm.
Bunkerprox sensors give plant maintenance personnel a new tool to combat excessive sensor failure. Installing Bunkerprox sensors into impact-prone weld fixtures can help to reduce unplanned downtime, sensor replacement costs and maintenance expenses. The increased profitability, higher throughput and lower operating costs can be dramatic, according to Balluff.
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