The BobTail HuckBolt has a gripping thread instead of a needle tail. Since the fastener is 40% lighter than a standard locking bolt, installation requires much less effort.Photo courtesy of Alcoa Fastening Systems
Standard and BobTail stop bolts install using direct pull technology in approximately 2 seconds. Insert the pin of a standard stop bolt into the prepared hole, place the ring on the pin and place the installation tool over the groove on the pin (far right). When the tool is activated, the puller at the front of the tool pulls the pin into the tool, causing the anvil to press against the bead and pull out any gaps between the sheets (right).
With a given force, the anvil begins to press the shoulder into the locking groove of the pin. Continuous swaging lengthens the sleeve and pin to create a precise clamping load (left). After the crimp ring into the pin lock slot is completed, the tool pulls out the pin shank and snaps it off. This completes the installation. For BobTail, after the crimp is complete, the tool is released from the fastener (far left). Image courtesy of Alcoa Fastening Systems
Standard straight-pull lock bolts consist of two parts. They consist of a short unthreaded cylindrical sleeve and a long non-threaded pin with a styloid tail that breaks off during installation. Photo courtesy of Alcoa Fastening Systems
For decades, welding has been considered the only way to ensure the integrity of joints in complex load-bearing structures or structures with high vibration. Therefore, companies producing heavy equipment or manufacturing large metal structures are limited to welded joints.
Today, there is a fastener that can replace welding: the straight-pull compression bolt. These two-piece fasteners consist of a bolt and a rivet. They consist of a short unthreaded cylindrical sleeve and a long non-threaded pin with a styloid tail that breaks off during installation.
These fasteners are installed using the direct pull method, in which the pin is pulled out and the collar is pressed into the locking groove of the pin, deforming the collar into the groove.
Stop bolts create permanent connections with high clamping loads, stability and excellent vibration resistance. Because stop bolts are a faster and safer installation process than welding and do not require trained personnel, manufacturers are increasingly using them to assemble truck suspensions and chassis, railroad crossings and heavy military equipment.
For many years and millions of joints, welding has proven to be one of the most reliable ways to protect joints. However, it has several drawbacks. The welding process is time consuming and requires several costly and time consuming quality control procedures. Welding also requires skilled and often well-paid technicians who are difficult to find and retain in industries such as oil and gas.
Another problem associated with soldering is heat. The heat generated during welding can significantly reduce the strength of the metals being joined and damage important surface coatings. In addition, welding dissimilar metals or parts of different sizes can be challenging. Experienced welders also know that removing and reworking welds can be problematic.
Finally, soldering is dangerous and messy. Safety is paramount and constant practice is a must as an accidental spark can start a deadly fire. It is also important to properly dispose of used electrodes and other residues from the welding process to keep work areas and factories safe and clean.
Stop bolts were introduced in the mid-20th century and are available in a variety of pin diameters. Alcoa Fastening Systems offers HuckBolts with pin diameters from 0.1875″ to 1.375″. The company also offers similar metric sizes.
Stop bolts are usually made from steel, stainless steel or titanium. However, they can also be made from aluminium, as their non-screw threads do not wear out during installation. As the material wears, part of it is drawn out by the contact surfaces. Spiral threads on conventional fasteners often wear out during wear.
The pins can be round, brazier, truss, mushroom or countersunk. Collars are available with or without a flange. Both components can be plated or plated to prevent corrosion.
The main advantage of a locking bolt is its long-term vibration resistance. In traditional bolted connections, there is always a gap between the threads of the nut and the bolt. These gaps can cause backlash in high vibration applications. In contrast, the installed locking bolt has no play because the shoulder is fully inserted into the shallow locking groove of the pin. These shallow grooves provide high bond strength – up to five times higher than conventional nuts and bolts.
Other benefits include high shear and tensile strength. Data from the Junkers test, a standard procedure for subjecting bolted joints to lateral vibration, shows that lock bolts maintain a constant clamp load over time without the need for additional devices such as lock washers, wire, or thread sealant.
Most stop bolts, including Alcoa Fastening Systems’ HuckBolts, can be used with almost any metal. Dissimilar metals with different coefficients of thermal expansion are not a problem. Parts of different joint sizes can be easily placed without compromising surface finish.
BobTail HuckBolt is Alcoa’s latest development. It has gripping threads instead of needle tails. This design provides two important benefits to the end user.
First, the BobTail weighs 40% less than a standard lock bolt and requires much less effort to install. For example, a 0.625″ diameter BobTail requires a 10 lb tool, while a similarly sized standard stop bolt requires almost 20 lb tool.
This lower force provides a smooth crimping action, reducing operator fatigue and repetitive stress syndrome. It also provides a quieter installation.
Second, the clamp threads remain open during installation. This eliminates a possible point of corrosion and the need to clean the material.
The clasp also has a specially designed ring with lugs along the flange. When the ring is fully crimped, the tongue compresses giving the operator a visual signal that the clasp is set correctly.
The operating parameters of the locking bolt depend on the diameter and material of the fastener. For example, a Grade 5 carbon steel BobTail with a diameter of 0.1875 inches provides a clamp load of 1200 pounds, a tensile strength of 2200 pounds, and a shear strength of 2430 pounds. In comparison, aluminum versions of the same deadbolt offer 550, 1000 and 1050 pounds respectively.
Similarly, the 0.375″ BobTail provides a clamp load of 5980 pounds, a tensile strength of 9300 pounds and a shear strength of 9600 pounds. Aluminum versions are available in 2200lbs, 4200lbs and 4200lbs respectively.
Standard and BobTail stop bolts are installed using the direct pull method. Insert the pin of a standard stop bolt into the prepared hole, slide the ring over the pin, and place the mounting tool over the groove in the pin. When the tool is activated, the puller at the front of the tool pulls the pin into the tool, causing the anvil to press against the collar and pull out any gaps between the sheets.
With a given force, the anvil begins to press the shoulder into the locking groove of the pin. Continuous forging lengthens the bushing and pin for precise clamping loading. After the crimp ring into the pin lock slot is completed, the tool pulls out the pin shank and snaps it off. This completes the installation. For BobTail, after the crimping is complete, the tool is released from the fastener.
A conventional stop bolt (0.625″ diameter Class 8 fastener) can be installed in as little as 2 seconds, not counting the time required to drill holes. The cycle time is short because the tool picks up the pins very quickly.
Once the operator pulls the trigger, the crimp and ejection sequence is programmed to complete the cycle without any further intervention from the installer. A quick visual inspection is all it takes to make sure the fasteners are installed correctly.
In addition, operators can skillfully install stop bolts with minimal training, making the use of stop bolts a cost-effective assembly process.
Tools for installing lock bolts are either hydropneumatic or hydraulic. Hydropneumatic (also called pneumatic) tools are best for stop bolts less than 0.5″ in diameter; larger diameter fasteners require hydraulic tools. Each tool is versatile enough to install fasteners of various diameters. However, the nose pad of the instrument needs to be modified to match the diameter of each clasp.
The tools are usually operated by hand, but semi-automatic work cells also work. These applications install stop bolts with a diameter of 0.1875 to 0.25 inches. Operators manually load parts and insert pins and bushings. Then, at the push of a button, several tools mounted on linear actuators simultaneously grip the pin and rings and crimp all rings onto the pins.
However, locking bolts have one significant drawback. After installation, part of the pin remains and protrudes above the collar. For applications where projections cannot be placed, manufacturers may be forced to use conventional welding.
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