tailieunhanh - Mechanical Devices Sourcebook 3rd ed [McGraw-Hil 2001] Episode 10

Tham khảo tài liệu 'mechanical devices sourcebook 3rd ed [mcgraw-hil 2001] episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | __CHAPTER 10 TORQUE-LIMITING tEnsiOniNG And governing devices CALIPER BRAKES HELP MAINTAIN PROPER TENSION IN PRESS FEED A simple cam-and-linkage arrangement drawing works in a team with two caliper disk brakes to provide automatic tension control for paper feeds on a web press. In the feed system controlled tension must be maintained on the paper that s being drawn off at 1200 fpm from a roll up to 42 in. wide and 36 in. in diameter. Such rolls when full weigh 2000 lb. The press must also be able to make nearly instantaneous stops. Friction-disk brakes are subject to lining wear but they can make millions of stops before they need relining. In the system two pneumatic disk brakes made by Tol-O-Matic Inc. Minneapolis were mounted on each roll gripping two separate 12-in. disks that provide maximum heat dissipation. To provide the desired constant-drag tension on the rolls the brakes are always under air pressure. A dancer roll riding on the paper web can however override the brakes at any time. It operates a cam that adjusts a pressure regulator for controlling brake effort. If the web should break or the paper run out on the roll the dancer roll will allow maximum braking. The press can be stopped in less than one revolution. SENSORS AID CLUTCH BRAKES Two clutch brake systems teamed with magnetic pickup sensors cut paper sheets into exact lengths. One magnetic pickup senses the teeth on a rotating sprocket. The resulting pulses which are related to the paper length are counted and a cutter wheel is actuated by the second clutch brake system. The flywheel on the second system enhances the cutting force. This linkage system works in combination with a regulator and caliper disk brakes to stop a press rapidly from a high speed if the web should break. This control system makes cutting sheets to desired lengths and counting how many cuts are made simpler. 340 WARNING DEVICE PREVENTS OVERLOADING OF BOOM Cranes can now be protected against unsafe loading by a .