As tunnel workers know, boring machines are anything but. Ranging from merely large to staggeringly huge, these complicated devices chew through loam, clay, and solid rock to excavate large and small tunnels across the world. What’s also enormous is the degree to which the success of a tunneling project rests on the proper maintenance of the boring machine built (or reconditioned) for the job.
Whenever a boring machine is inoperable due to maintenance requirements, progress on the job grinds to a halt. Frequent or enduring maintenance delays can drive a project over budget, potentially causing potential contract that affect a company’s reputation as it bids for future contracts. Yet due to the heavy torque produced by these machines, the difficult conditions under which they operate, and the serious vibrations their operation produces, maintenance technicians can be pressed hard to keep their machines healthy. One important way to extend boring machine parts lifespan and reduce equipment downtime is to implement a torque control regimen, reducing fastener failures and the larger breakdowns they cause.
How Torque Control Can Extend Parts Lifespan in Boring Machines
Boring machines are complex combinations of many smaller systems, including hydraulic lines, conveyor belts, and electric motors. All of these systems must function effectively for the machine to be operational; operating the machine while some parts are not working properly can cause breakdowns in other systems. Threaded fasteners hold many of these smaller systems together and also attach them to the greater machine’s chassis and other systems. When fasteners fail, so do their systems; when these systems fail, so does the machine.
The farther a threaded fastener is from its ideal torque range, the more likely it is to fail. This is especially true under the heavy, dynamic vibrations produced by boring through soil and rock of varying compositions and densities. If a fastener is too loose, it can back out, releasing what it had held. If it’s in a confined space, it can rattle and cause further damage. If too tight, it can shear or deform under stress, as well as cause damage to the assembly. In either case, the failure of one fastener increases the load on all other fasteners holding the same part.
So, the best way to reduce the frequency of fastener failure is to tighten each screw and bolt to the appropriate degree. This must be done when the machine is assembled at the job site and again each time a part is removed for service or replaced. Maintenance inspections of the machine should look for any fasteners showing signs of overstress, looseness, or recent movement, both visually and with the aid of a torque verification tool, particularly for critical fasteners. The only way to accurately and repeatedly apply a designated amount of torque to a fastener is to use a tool capable of detecting and limiting the amount of torque applied—in other words, a torque wrench.
Selecting Torque Tools for Boring Machine Maintenance
Boring machines are complex devices comprised of many internal systems. As such, many different fasteners, from tiny screws to massive bolts, are used to hold these machines together. No one torque tool will fit every fastener on the machine; instead, you must use a range.
For screws, hand-driven, externally adjustable torque screwdrivers are best due to their reliability and versatility. These screwdrivers are built with internal clutch mechanisms. When the torque the screwdriver is applying reaches the set level, the clutch disengages. The tool’s operator, unable to apply more torque than the screw requires, can safely turn the tool until the clutch slips, ensuring the proper amount is applied.
For bolts, maintenance technicians have several options. If the boring machine is equipped with an accessible air compressor to feed internal pneumatic systems, then technicians can repurpose this air for pulse tools. These powerful, low-reaction air tools can quickly and accurately deliver high amounts of torque, enough to effectively tighten most bolts.
Without compressed air, or to supplement pulse tools for difficult-to-reach bolts, technicians can turn to hand torque tools, like the click wrench and cam-over wrench. While not as fast as pulse tools, hands tools are easier to clean and maintain, and they deliver torque just as effectively.
For large nuts and bolts that require higher torque output, torque multipliers are the ideal choice. These rugged tools provide precision tightening and loosening for all heavy-duty fastening connections. The torque multiplier shuts-off when the pre-set torque is achieved. These tools are non-impacting, and they operate at a smooth, continuous rotation. Torque multipliers also increase speed and productivity, as they are faster than hydraulic wrenches and less expensive.
Click wrenches can deliver an order of magnitude more torque than cam-over wrenches, and twice as much as even pulse tools, making them useful for the largest, sturdiest bolts. However, they lack a physical torque control mechanism, relying instead on an audible “click” that lets the operator know when to stop. Cam-over wrenches, while unable to match the torque output of click wrenches, share an internal clutch with torque screwdrivers. This makes them a far safer choice for bolts which cannot tolerate over-torque conditions.
Boring machines are truly phenomenal machines, weighing hundreds of tons, stretching hundreds of feet, capable of chewing through solid rock for 24 hours a day. But for these massive devices to work, each of the hundreds of fasteners that hold them together must be installed and serviced with the proper tools and a sharp eye to detail. Using the right torque tools to take care of a boring machine’s screws and bolts can help keep the machine operational and the tunnel on track.