Innovative fasteners avoid dangerous failures

Stage 8's patented GrooveLok technology locks the threaded fastener in place so there is no way it can come loose under the influence of externally applied loads.

From demolition machines to top-fuel dragsters, industry is adopting an innovative fastener locking system that uses a special wrenching technology to put a stop to failures and costly downtime, service and equipment replacement.

Joint failures due to loose and broken fasteners are often a very expensive problem, resulting in untimely repairs, replacement of equipment, production downtime, unhappy customers and loss of business.

Sometimes it is also a dangerous situation, and can even lead to lethal disasters.

What causes mechanical fasteners to loosen and shear is usually some external force, such as vibration, torsion, shock or temperature changes.

In the past, design engineers were forced to use bolts with insufficient stretch due to tight fit or other configuration problems.

Whatever the cause, once joint integrity is lost, even the most advanced equipment is likely to fail.

Product design engineers and service technicians know that attempts to save on costs by using commercial fasteners are often false economy.

Indeed, skimping on quality fasteners sometimes results in spending more rather than less, not only for scheduled maintenance that could be avoided, but particularly when equipment failures result.

"Even if the equipment itself is not severely damaged, it may be very time-consuming to repair, especially if the joint is difficult to get at," says Tim Brown at the Dayton, OH, USA, branch of Sunsource, a designer and distributor in the fluid power and motion control industry.

"Either way, in a production situation you are out of business for awhile and that's usually painful".

Generally, fasteners loosen and back out because that is the reverse of the mechanics applied for installation.

When that likelihood is obvious, mechanics and engineers may apply creative measures, such as wiring, welding, piercing and staking of bolts or using engineering adhesives on threads.

Whether or not those countermeasures actually work, the process usually begins with using a wrench (spanner) to install a bolt.

That basic installation procedure has caused one forward-thinking fastener manufacturer to look 'back' to the wrench as an alternative solution to the problem of fastener and joint failures.

The engineers at Stage 8 Locking Fasteners, an innovative San Rafael, California-based manufacturer, examined a novel idea: if the wrench is a good tool for tightening bolts, couldn't a retainer be used that acts like a wrench to lock a bolt tight? Theoretically, of course, the answer is yes.

But ,like most seemingly simple concepts, it took many years to develop and test the locking 'retainer' fastener designs that would serve the diverse applications of the firm's customer base.

Today, companies in a wide range of industries are using the resulting retainer-based locking fastener systems to solve critical joint requirements in a wide variety of applications.

This active mechanical locking system virtually eliminates critical joint failure due to bolt loosening, thereby virtually eliminating fastener replacement, emergency repair, costly production downtime, loss of customer trust, and potential liabilities.

Stage 8 manufactures what is believed to be the only active mechanical locking fastener designed to stop joint failure/production downtime by preventing thread loosening from starting.

Its patented GrooveLok fastener locking system acts like a small wrench locked onto a bolt head.

The locking retainer is braced against a nearby abutment (eg, frame, casting or protrusion), thereby locking a bolt or nut in place.

If there is no abutment to brace against to stop loosening, a bridge retainer can fit over two or three bolts, locking them together, or a retainer can be bent over an edge or frame.

For counter-bored applications, the locking fastener system incorporates a secondary counter-bore, a milled slot adjacent to the main counter-bore, into which a locking retainer (akin to a wrench handle) is fixed.

Once installed, fasteners never need to be re-tightened because loosening never has a chance to start.

The system can be retrofitted to existing components, is fully reusable, and has been used in items as small as eyeglass screws, to nuts as large as 8in holding generator propellers in a hydroelectric dam.

To date, the system has no reported failures in over 10,000,000 installations, ranging from industrial, mining, construction, manufacturing, automotive, railroad and miles-deep oilfield drilling assemblies.

Sunsource recently had a difficult fastener application on a rotary actuator used to raise and lower a large bowl used for collecting products at a food processing operation.

"The actuator was continually working loose from its assembly because of vibration," explains Tim Brown.

"This was a very costly situation, because when the actuator failed, production was brought to a halt until the fastener was replaced".

Brown says that servicing the actuator fastener was difficult and time-consuming because of its location and the design of the equipment it supported.

After some research on the internet, Brown noticed the Stage 8 locking fastener technology and decided to explore the possibility of using it.

A counter-bore application, Sunsource wanted the supplier to evaluate both the size and configuration of the fastener.

"They recommended what was actually a standard component, so there was no prototyping required, although I understand that Stage 8 provides that service," says Brown.

"It ended up working beautifully.

"The service crew now does only scheduled inspections, and there have been no production disruptions since the new fastener system was installed".

Sometimes engineers and mechanics accept frequent service intervals, including repeated tightening of fasteners as a 'fact of life'.

When it comes to extreme joint applications, they might be even more resigned.

On the racetrack, engineers are forever searching for improved fastenings to battle the extreme abuse racing puts on machinery.

Take, for example, the fasteners used to hold the hub bushing on the rear end assembly of a 7000HP top fuel dragster or funny car.

"We had problems with the way our old fasteners were retaining," says engineer Jeff Capek of Strange Engineering, a Morton Grove, IL, USA, manufacturer of racing equipment.

"Due to extreme pressure and vibration, the hub was moving around and flexing on the axle.

"The fasteners would back out, so we tried staking them, which was just a temporary solution.

"Some racing teams actually weld these fasteners to the steel bushing, to keep them from rotating out.

"But then the fasteners can shear off if the bolts are not big enough.

"The bushing walks out, and then the hub moves around on the axle - a dangerous situation because it causes erratic handling at speeds of over 300mph".

Capek adds that loose fasteners in the rear end of a top fuel dragster or funny car can get chewed up in a bearing or in a gear.

"You could wreck a $20,000 rear end assembly, simply because four screws came loose.

"And, you could loose prize money and ranking or somebody could get hurt".

Capek contacted Stage 8 to see what type of fastener arrangement they might recommend.

"We sent them some parts and they mocked up what they thought would work.

"They're willing to customise fasteners if necessary, but in our case we were able to use something off the shelf.

"So we tested the prototype and we have had no problems at all in field trials.

"The payoff is that the hub runs true and everything stays together," he says.

"There is no maintenance, and you do not have to check to see if the fasteners are tight, because they are mechanically locked.

"This is still a prototype situation for us but, so far, these new fasteners are looking good".

Because vibration, shock and heat energy are the natural enemies of joint integrity, Stanley LaBounty, the Two Harbors, MN division of The Stanley Works from New Britain, CT, USA (the maker of Stanley tools), has now incorporated this new fastener technology into some of its tool designs.

One such tool is their Universal Processor, best described as a large, hydraulic pair of scissors that is attached and powered by a hydraulic excavator.

This tool is used to take down large structures such as bridges, buildings, above-ground storage tanks and other structures around the world.

"This tool is subjected to extreme vibration and loading," explains Mike Swanson, a Stanley LaBounty project engineer.

"Because it is used to crush concrete and cut beams, this is about the most demanding application you can think of.

"You have everything from beams and walls to buildings falling down on the product - one of the harshest environments imaginable".

Swanson says they wanted to avoid fastener problems on the machine's newly designed jaw pivot assembly (where the upper, moveable jaw connects to the lower jaw) that might create expensive downtime and require thousands of dollars in warranty service.

"We wanted to enhance the service life of the pivot.

"While conventional fasteners were desirable from a cost standpoint, they would not have provided the reliability we are looking for in a primary tool that must endure the extreme stresses and environmental harshness," he explains.

"After reviewing the Stage 8 fastener designs, we decided it might be an excellent way to avoid premature pivot failures.

"We field tested the setup, and it worked very well.

"In fact, we are now using these in our production," Swanson says.

When it comes to fasteners and many other commodity items that may be engineered into a product, cost is always a consideration - or should be.

Yet, savvy engineers also evaluate cost-performance benefits of components that can make their products better, safer and less expensive to operate.

Even though slightly more expensive, the use of specialised fasteners could result in major savings through prevention of premature failures and related service cost.

In addition, considering an active mechanical design, like GrooveLok, could eliminate the cost associated with fastener inspection.

Finally, when fastener clamp load is critical, you might want to consider this new locking retainer technology - and put a 'wrench' into your application.

For more info on Stage 8's patented GrooveLok technology and products, visit the company's website.

Back to top