is a general term for a press machine that generates pressure by rotating more than one set of outer and inner bolts in a frame.
Screw presses can be divided into two methods, one in which static pressure is generated by applying torque to the bolts, and the other in which the rotational energy of the flywheel fixed on the bolts is concentrated and used in a single pass for forming.
As long as the press is used to generate the forming torque up and down the ram by means of a screw structure, it is considered a type of screw press.
History of screw presses
The screw press originated in Germany in the 15th century when a man called Johann Tonderberg invented a movable type printing machine in which an inked plate was pressed onto paper by means of a screw mechanism. This machine was used as a wooden bolt press for pressing grapes and olive oil and can be said to be the origin of all pressure machines. It used a method of applying hydrostatic pressure that took time to compress gradually.
In European museums there are also displays of screw presses for hot forging by means of hydrostatic pressure. It is thought to have been used in the Middle Ages to manufacture steel doors, windows and hardware for cities and churches.
Later screw presses for forging were developed with the possibility of mounting a rotating wheel on the upper end of the shaft of an external bolt and using a flywheel to accumulate energy for driving.
Initially the flywheel was rotated by hand, but later, because of the inefficiency and intensity of the manual work, two friction discs were fitted to the upper part of the machine, which could run continuously, and succeeded in winding the hides around the flywheel by means of a connecting rod, so that they ran in contact with each other to generate power. This is the friction screw press, which uses the friction drive method.
In the early days the friction screw press was controlled by the operator using a manual steering wheel to operate the linkage, and the degree of up and down movement of the ram and the degree of pressure applied was entirely dependent on the skill of the operator.
Later the linkage method disappeared and was replaced by a hydraulic or pneumatic cylinder and relay controlled key switch and foot pedal to operate the method.
Later on, a direct sensing of the sliding speed through a coding device was adopted to control the pressurised energy.
In addition, the drive method is not limited to the friction clutch method, people also developed a hydraulic motor drive, electric motor direct drive, switched reluctance motor drive, permanent magnet synchronous servo motor drive and other ways. Among them, the use of servo-motor-driven CNC presses in the replacement of friction presses and friction press retrofitting have achieved very good results.
Screw presses are mainly used to carry out the processing of various high, medium and low grade refractory forming products, or the processing and forming of various metal material products (cold and hot forging processing, cold forging of thin forgings, casting forging).
Generally the lower part of the screw press is equipped with a forging ejector. Screw presses are also die forging hammers, mechanical presses and other forging machinery, versatile, can be used for die forging, punching, deep drawing and other processes. In addition, screw presses, especially friction presses, are simple in structure and easy to manufacture, so they are widely used. The disadvantage of screw presses is their low productivity and mechanical efficiency.
The forging machinery that uses screw and nut as transmission mechanism and relies on screw drive to transform the forward and reverse rotary motion of flywheel into up and down reciprocating motion of slider. When working, the electric motor makes the flywheel rotate faster to save energy, while pushing the slider downward through the screw and nut. When the ram touches the workpiece, multi-disk screw press the flywheel is forced to decelerate to a complete stop and the stored rotational kinetic energy is transformed into impact energy, which strikes the workpiece through the ram to deform it. At the end of the blow, the motor reverses the flywheel, driving the ram up and back to its original position. The specifications of screw presses are expressed in terms of nominal working force.
Screw presses are usually driven by an electric motor that rotates the flywheel by driving the rim of the flywheel through the friction disc, so this type of press is also known as a friction press, and the largest friction press in China is 25 MNT. Larger screw presses with a hydraulic system drive the flywheel, called hydraulic screw presses, the largest specification has 125 megawatt. Later on, there appeared electric screw presses with electric motors directly driving the flywheel, which have a compact structure and few transmission links, but due to frequent reversing, the control electrical requirements are higher and require special motors.
The screw press has no fixed lower dead point, and for larger die forgings, it can be struck and shaped several times, allowing for single strikes, continuous strikes and inching movements. The striking force is related to the amount of deformation of the workpiece, with small striking forces when the deformation is large and large striking forces when the deformation is small (e.g. cold striking). In these respects, it is similar to a forging hammer. However, its ram speed is low (about 0.5 m/s, only 1/10 of a forging hammer) and the striking force is enclosed by the frame, so it works smoothly and vibrates much less than a forging hammer, and does not require a large foundation. The screw press is equipped with a slipping safety mechanism, which limits the maximum striking force to 2 times the nominal pressure to protect the equipment.
The basic working principle of an electric screw press
The motor drives the flywheel of the screw press, the sleeve shaft and the nut together with frequent forward and reverse movements, the nut and the screw form a motion payment, the nut drives the screw and the slider up and down to generate the striking force. The control system with PLC as the core is designed with several working program segments, the striking speed of each program segment can be adjusted by the corresponding electrical; the number of strikes of each program segment can be set by the corresponding counter. It is possible to collect the working state of the press at each instant for logical determination, to complete the control and braking of the motor, the control of the inlet and outlet devices and the control of the pneumatic discharge of the die. The press can be fully automated by means of inlet and outlet devices for each type of workpiece.