The Joy Mining Machinery TX-3 radio remote control unit was originally distributed in the US with open switch pockets that allowed debris to accumulate during operation. While Joy recommended the unit be periodically flushed out with water switches were sometimes reported to be sluggish or sticking, resulting in erratic machine performance.
MSHA said Joy initially addressed the problem by applying a gasket under the faceplate, which partially covered the open switch pockets but this was unsuccessful. A toggle switch "boot" was designed to cover switch pockets of the radio remote control unit but the wear life of these boots was limited. The boots also increased the amount of force required to activate the switches.
In February last year, MSHA issued a bulletin recommending several design changes, one of which was the use of "rubber boots" to prevent the entry of coal or dust into the open switch pockets.
Joy has since redesigned the switch boot and introduced the change in Revision D of the TX-3 radio remote control unit. Although made of the same material, the new boot is larger than those it replaced and over the past year, mine operators' experience with these changes have proven the change a success.
“Field testing has shown that the boots introduced in Revision D are the most effective method in reducing the accumulation of dust and debris in the switch pockets of the remote station,” MSHA said in the bulletin.
MSHA said any lightweight radio remote control unit with no revision, or with Revisions A, B, or C, should be returned to the manufacturer for upgrade to Revision D. Otherwise operators could purchase a kit from Joy to upgrade the unit to include the improved switch boots.
MSHA also recommended mine operators provide training for personnel addressing the safe operation and maintenance of the remote controllers.
“Machine operators should be trained to inspect the remotes for cracked or damaged boots and to inspect the switch wells for an accumulation of debris when switch movement becomes irregular,” MSHA said.
The revision does not affect the radio remotes used on Australian Joy continuous miners.