What applications dictate the use of pneumatic chucks? One example is turning large diameter pipe, swallowed by the through-hole of the chuck, mounted on the spindle of a large bore turning machine.
Usually, the through-hole ID of a hydraulic chuck is limited by the chuck’s draw tube. The draw tube is threaded into the chuck which is mounted to the front end of the machine’s spindle. The chuck’s hydraulic actuator is mounted to the back end of the machine spindle. The draw tube moves in and out to open and close the chuck jaws and to maintain chuck jaw force/pressure when the jaws are closed on the part.
Hydraulic chucks are usually preferred because hydraulic chuck pressure is always higher when comparing air versus hydraulic chucks by size. But when large pipe is being machined, the cost of the machine can be much higher, just to get the larger through hole of the spindle. It’s often difficult to justify the higher expense on that feature only. So, many shops consider pneumatic chucks because the actuation of the jaws and the maintenance of chucking pressure is achieved through the chuck body’s self-contained pneumatic system, which frees up all of the machine’s spindle bore for larger diameter pipe. But as stated, there’s a tradeoff. Maximum chuck pressure generated by a pneumatic chuck is usually lower than it is for the same size hydraulic chuck. So the clamping force may be insufficient for the job.
But the SCHUNK ROTA TB2 pneumatic self-contained power chuck sets a new chucking pressure standard that expands the capabilities of machines to handle rod and pipe for the oil industry.
Despite the compact outer dimensions, the ROTA TB2 has a large through-hole of up to 560 mm. With an air pressure of 6 bar it is possible to achieve high clamping forces of up to 280 kN, which surpasses typical pneumatic chuck pressure specifications on the market today.
Additionally, the ROTA TB2 has an anti-corrosive coating applied to the most important functional components which, significantly increases the service life, according to Schunk. The base jaw guidance is equipped with a special seal to prevent penetration of contamination, dust, and chips, which reduces maintenance costs. The design and the guidance of the base jaws have been optimized for minimal loss of centrifugal force even at high rotational speeds. According to a Schunk spokesperson, the lubrication system maintains constant clamping forces and high process stability and an optional integrated pressure sensor provides for maximum process reliability and operational safety in daily use.
To increase the cycle rate in the machining of pipes and rods, the ROTA TB2 features a double acting check valve with extra-large channel bores, which speeds up the clamping process. After completion of machining, the quick action ventilation system releases the clamping set-up. If needed, the jaw stroke can be mechanically monitored by a radial stroke indicator on the outer diameter.
The TB2 is available in sizes from 470 mm to 1,000 mm with bore diameters from 185 mm to 560 mm.