Injection Molding Machine Reciprocating Cylinder (Mold Shifting Cylinder)

4 Metres of Stroke.
Hours of Changeover
Compressed to Minutes.

The shooting cylinder docks the nozzle. The ejection cylinder pushes the part out. The mold opening/closing cylinder opens and closes the mold. All three operate during every injection cycle. The mold shifting cylinder operates between production runs — sliding the old mold out of the machine and the new mold in. It runs a few times per day, but every minute it saves on changeover is a minute of production recovered. On a machine making $200/hour of product, a 30-minute faster changeover pays for the cylinder in weeks.

From Hours to Minutes — The Economics of Fast Changeover

Quick Mold Change (QMC) transforms injection moulding economics. Without it, long changeover times force manufacturers to produce large batches (to spread the changeover cost across more parts). With QMC, small batches become profitable — enabling just-in-time production, more product variants, and less warehoused inventory.

The other injection moulding cylinders have short strokes: the shooting cylinder needs 1,500 mm to retract the injection unit, the ejection cylinder needs 600 mm to push the part out, and the mold opening/closing cylinder needs 700 mm to separate the platens. The mold shifting cylinder needs 4,000 mm because it must move the entire mold — which sits between the platens — completely outside the machine frame to a staging position where technicians can safely access it from all sides.

The mold itself may be 400–1,200 mm wide (in the direction of travel). But the staging position must be far enough from the machine for the technician to walk around the mold, disconnect the water hoses, the hydraulic core-pull lines, the hot runner electrical cables, and the thermocouple connections — all without reaching into the machine frame. The 4,000 mm stroke provides clearance for the mold width plus the technician working space plus the connection access zone.

On large machines with wide molds, the full 4,000 mm is used. On smaller machines, a shorter stroke suffices — the same cylinder design with a shorter barrel accommodates the range. Korea Ever-Power manufactures the mold shifting cylinder at whatever stroke the machine builder specifies, up to the 4,000 mm maximum.

Injection moulds weigh from 50 kg (small consumer product moulds) to 30 tonnes (automotive bumper and dashboard moulds). The mold shifting cylinder must start, move, and stop these masses smoothly on the roller bed or guided carrier rails. The force to start the mold moving (overcoming static friction on the rollers) is higher than the force to keep it moving — the cylinder must deliver a burst of force at the start of the stroke without jerking the mold off its alignment.

At the end of the stroke, the mold must stop at an exact position — either centred between the platens (for the incoming mold) or centred at the staging station (for the outgoing mold). Overshoot or undershoot means the mold is misaligned with the platen bolt holes or the utility connection points, requiring manual correction that adds changeover time. Korea Ever-Power designs the mold shifting cylinder with adjustable end-of-stroke cushioning for precise positioning at both the machine-centre and staging positions.

The 4,000 mm stroke at 180 mm bore creates a long, slender cylinder that must resist lateral loading from roller bed misalignment. The rod guide bearing is oversized for the horizontal mounting — the same long-stroke engineering that Korea Ever-Power applies to the cement equipment roll over cylinder (#22), which shares the same long-stroke challenges.