The necessary force to form the heated polystyrene strip is provided by a crank and slip mechanism, which itself has components such as electric motor and gearbox, etc. After producing this reciprocating motion, transferring this motion to the mold part is the most important working factor of the press machine part. Using guide rods, this reciprocating driving force is transmitted to the mold holding plates. Due to the continuous movement of these moving arms and the heavy weight of the mold and the molding plates, the material, heat treatment and machining required in this section are very important.

The operation of the mechanism of seedling tray production machine is such that the rotational driving force of the drive motor of the machine is transferred to a cam piece by the gearbox after the changes in its torque, and this cam piece (so-called crank) moves in a circular path. Incomplete turns this rotational force into a simple reciprocating force. Among the advantages of the crank mechanism is its simplicity as well as the need for periodic maintenance and repairs, while in similar systems such as reciprocating hydraulic systems, to achieve this type of movement, high costs such as hydraulic pumps, jacks, valves are required. Path control, speed control valves, oil tank, oil cooler, etc., and the urgent need to service these devices requires a lot of time and money.