Press clutch-brake system

01

Choose dry friction or oil shear for the duty

US patent 5,806,641 (Independent clutch and brake for a press) explains that dry friction clutch/brakes start and stop a press by rubbing dry friction material against reaction members, which wears both and generates heat; the faster the press runs and the flywheel turns, the more wear and heat, requiring periodic gap adjustment, and the unit's mass limits heat dissipation and so the trip rate, while adding mass adds inertia to start and stop. Oil shear units were developed to remove these problems: properly designed, they give little or no plate wear and no brake fade, more precise operation and longer uptime, and the oil film carries heat away from the disk stacks so there is practically no limit on trip rate or flywheel speed, with unlimited inching. [2]

US patent 6,095,298 (Wet clutch/brake for a mechanical press, 2000) adds that the flywheel, belt-driven from the motor and mounted on one end of the crankshaft, stores the press's energy; when the clutch engages, the flywheel slows as the driven parts come up to speed and the motor restores the lost energy. It notes that multiple-disk stacks reduce clutch/brake inertia, allowing mechanical interlocking of clutch and brake without an inertia penalty, and identifies undamped clearances at drive disks, driven disks and drive pins as wear points in wet units. [3]

Editorial note: give the supplier the press tonnage, flywheel energy and speed, strokes per minute, inching needs and existing mounting, and ask for the stopping time it guarantees at 90° of crank rotation.

Give the supplier the press make, model and tonnage, crankshaft and flywheel arrangement, flywheel speed, required torque, strokes per minute and continuous or single-stroke duty, inching needs, dry or oil shear preference, air or hydraulic supply, control valve and brake monitor requirements, guarding type used, target stopping time, mounting dimensions, and maintenance access.

02

Meet the clutch, brake and control rules

OSHA's mechanical power press rule (29 CFR 1910.217) requires friction brakes for stopping or holding the slide to be inherently self-engaging, needing external power or force to disengage, with capacity to stop the slide quickly and hold it at any point. For part-revolution clutches, the clutch must release and the brake apply when the clutch engaging means is removed or de-energised; a red stop control must immediately deactivate the clutch and apply the brake; Off, Inch, Single Stroke and Continuous modes must be selectable; air-clutch controls must not significantly lengthen stopping time on a valve failure and must then inhibit further operation; and the control must deactivate if clutch air or counterbalance air fails. [1]

Where required, a brake monitor must prevent the next stroke if stopping time or braking distance deteriorates beyond what the safety distance allows, and monitor brake performance on every stroke. For two-hand controls and presence-sensing devices the safety distance is Ds = 63 in/s × Ts, where Ts is the press stopping time measured at about 90° of crankshaft rotation. Employers must inspect and test each press at least weekly for the condition of the clutch/brake mechanism, antirepeat feature and single-stroke mechanism under the directed inspection programme, and keep certification records. The rule excludes press brakes and hydraulic and pneumatic power presses. [1]

Editorial calculation: a stopping time Ts of 0.2 s gives Ds = 63 × 0.2 = 12.6 in (about 320 mm); a slower brake directly pushes the guard or control further from the die. [1]

03

Size the unit by clutch torque, brake torque, speed and inertia

Nidec Drive Technology's DESCH Lutex LKB, a dry-running clutch-brake unit for mechanical presses and shearing machines, shows the ratings a combined unit is sized by: 15 sizes from 05 to 75, clutch torque from 250 to 115,000 N·m, brake torque from 140 to 65,000 N·m, allowable maximum input speed from 500 to 2,800 rpm and moment of inertia from 0.018 to 255 kg·m². The clutch torque is a static value at an actuating pressure of 6 bar, and the maker offers customised designs. [4]

Editorial calculation: at the top of this series the brake torque is about 57% of the clutch torque (65,000 ÷ 115,000), so quote clutch and brake torque separately, and ask what torque the unit delivers at the air pressure available at your press rather than at 6 bar. [4]

Editorial note: ask for the moment of inertia of the unit, because US 5,806,641 notes that added mass adds inertia to start and stop [2], and OSHA ties the guard's safety distance to the press stopping time [1].

04

Trace the clutch-brake system

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your press

A clutch-brake quotation needs values for your press. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the press, duty and safety data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Press: [make; model; tonnage]
Drive: [flywheel speed; mounting]
Duty: [SPM; single/continuous; inching]
Type: [dry; oil shear]
Torque: [clutch; brake]
Stopping: [Ts at 90°; overrun limit]
Controls: [valve; monitor; mode selector]
Guarding: [two-hand; presence sensing; gate]

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