Parts of Eccentric Presses

Parts of an Eccentric Press Machine

Frame

One of the most important characteristics of a press is the shape of its frame, the type of material the frame is made of, and its construction style. On low-tonnage presses, the frame is cast; on high-tonnage presses, the frame construction is made of welded steel plate. Low-tonnage presses are generally C-frame type presses.

The frame structures of high-tonnage presses are also generally manufactured as H-type steel constructions. Whether cast iron or steel, press frames are given a stress-relief anneal before machining to remove internal stresses.

Motor

This is the component that powers the press’s operation. The rotary motion from the motor is transmitted, at the desired speed, to the flywheel directly via a belt and pulley, or to the crankshaft (eccentric shaft) through gears.

Flywheel (Gear)

The flywheel is the press component that, because of its large diameter, reduces the rotary speed it gets from the motor while increasing it in terms of force.

Motion Transmission System

The rotary motion produced by the electric motor is transmitted to the flywheel via belts. On the shaft connected to the flywheel there’s a clutch-and-brake assembly. The clutch-and-brake assembly is operated by a hydraulic, pneumatic, or mechanical control system. The flywheel spins continuously with the rotary motion it gets from the motor, but the crankshaft (eccentric shaft) doesn’t rotate. When we want to press a part, we engage the clutch control (with a pedal or button), and the eccentric shaft begins to rotate. The eccentric shaft’s job is to convert circular motion into linear motion. The moving head (ram, slide), connected to the press’s crankshaft through what we call connecting rods, is made to travel a linear distance equal to twice the crankshaft’s eccentricity. (In one revolution) we call this the press’s stroke.

On low-tonnage presses, this stroke can be made adjustable. On high-tonnage presses, the stroke is fixed. A separate slide adjustment mechanism is provided for mounting dies of different heights. On a mechanical press, the position where the slide descends and then starts its return is called bottom dead center (B.D.C.), and the position where it sits at the top is called top dead center (T.D.C.).

Clutch and Brakes

The clutch and brakes are among the most important components of mechanical presses. The press’s safe and efficient operation depends on the clutch and brakes working flawlessly.

The system that transmits motion to the ram when needed is called the clutch. The system that engages the clutch, makes the ram complete its stroke, and stops it at top dead center is called the brake system. The moment the clutch disengages, the brake system engages and keeps the crankshaft stopped at top dead center.

Eccentric Shaft (Crankshaft)

The crankshaft is the most important part of an eccentric press, converting the circular motion it gets from the flywheel into linear motion.

Twice the offset between the crankshaft’s axes makes up the press’s stroke length. Mounted on the crankshaft are the flywheel, the clutch components, the brake assembly, the connecting rod, and the ram connected to the connecting rod.

Ram

On eccentric presses, this is the part the upper die assembly is attached to, and depending on the design, it’s guided by gibs at two or four points. The eccentric shaft’s circular motion is converted into linear motion through the connecting rod and ram, driving the die’s operation.

Role of the Eccentric Shaft

An eccentric press converts rotary motion into linear pressing motion by means of the eccentric shaft.

Strokes Per Minute

Eccentric presses can be designed to run anywhere from tens to hundreds of strokes per minute, depending on production speed.

Role of the Flywheel

The flywheel stores the motor’s energy, meeting the sudden power demand during the press’s stroke.

Bolster Plate

Used on hydraulic and mechanical presses between the die and the press bed. Bolster plates provide a suitable flat surface for mounting dies and can be reground if they wear. Bolster plates must be thick enough to properly support the dies without deflecting. On some large presses, movable bolster plates are used to speed up die changes.