V-Band Clamps encounter many extremes. When it comes to turbochargers, which are increasingly used in light trucks and cars to deliver the power of a V8 engine in a V6, the clamps seal off hot exhaust, forcing compressed air into the intake. The result is lighter vehicles and better fuel economy. But component temperatures around the seal can reach 1,300°F, and V-Band clamps fail when traditional fastening nuts loosen in the extreme heat and vibration.
Making matters worse, turbocharges typically hang off the side of the engine, meaning less structural support and more vibration. Because V-Clamp nuts must run down the length of the long T-bolt stud, which can be 6 to 8 times the body diameter of the nut, prevailing torque type locking features can gall and wear out before the nut is seated. If this happens on an assembly line, each incident can cost up to $2,000 to stop the line, remove the engine and redo the V-Band clamp assembly. For that reason, plain metal V-clamp nuts are typically used. But as soon as they lose tension, they start to back off and cause performance and warranty issues.
That happened at one heavy truck turbo manufacturer. It regularly broke T-bolts after they galled with clincher nuts during assembly. In response, the factory switched to a new design for the V-band clamp: the free-spinning Spiralock. The Spiralock uses a 30-degree wedge ramp at the root of the thread that mates with standard 60-degree male thread fasteners. The factory says it saved the loss of 15 V-band clamp assemblies every day.
The wedge ramp allows the bolt to spin freely relative to female threads until clamp load is applied. The crests of the standard male thread form are then drawn tightly against the wedge ramp, eliminating radial clearances and creating a continuous spiral line contact along the entire length of the thread engagement. This continuous line contact spreads the clamp force more evenly over all engaged threads, improving resistance to vibrational loosening, axial-torsional loading, joint fatigue, and temperature extremes.
With higher heat in gasoline engines than in diesel engines, the U.S. auto fleet may benefit the most from Spiralock V-Band Clamp Nut. It’s already being used on one of the first applications of dual turbo engines in light trucks. As vehicles from light trucks to SUVs and crossovers look to produce V8 power in a V6 engine with turbo, the innovative V-Band Clamp Nut may be just what engineers need to keep turbochargers sealed and prevent exhaust leaks.
Filed Under: Design World articles, Clamps, Fastening + joining • locks • latches • pins, Screws • nuts • bolts