Screw press

A screw press is a simple transmission, which converts a rotary movement into a vertical -acting displacement (translation ) in the axial direction of the threaded spindle. By translating on the long lever arm of the rotary motion to the inclined plane of the thread of gear ratios can be achieved, for example, 1:100. The achievable high pressure forces were technically used in many ways in the Middle Ages, especially in book printing.

History

The invention of the screw is the Greek polymath Archimedes attributed to ( 287-212 BC) (see Archimedean screw). Screw presses are based on the same principle, but are historically known only from the late Middle Ages.

The first screw presses were pushing or Balancierwerk (French balancier ) called and probably first built in Italy. The first attested use of a simple screw press is (very limited) on Donato Bramante and Benvenuto Cellini go back. Screw presses were first used mainly for the production of medals.

Around 1550, the first time should have been used to mint coins, a spindle stamping of the Augsburg goldsmith Max Schwab. Then strove Elois Mestrelle to introduce the spindle embossing also in Paris and London, but failed because of the resistance of the coin. It was not until over a hundred years later, the spindle stamping was generally introduced in all major mints. The mature spindle stamping allowed an increase in the amount of discharge and a clarification of the embossing, creating up to 30 coins were minted in the minute.

Operation

Hand screw presses

The upper punch is lowered by means of a spindle screw on flan and lower punches. To generate the stamping pressure, the force is transmitted to the spindle by a double-arm swing axle at the ends of heavy balance weights are attached. The swing arms were several workers fired up or triggered (depending on the strain energy 2 to 12 man) by pulling strap. By the momentum and leverage the heavy weights of the embossing pressure was so strong that a reduction of the upper punch to achieve a very good embossing effect sufficient ( by the hand or hammer embossing often had to be run on the flan several hammer blows to achieve a satisfactory effect ) Due to the severity of the impact, the screw press works of the mint had to be firmly anchored in the foundations on the ground floor or basement. Before the work spindle usually a depression or pit set into the foundation in which sat a coin, the appeal before the flan in the lower punches and the minted coins were retrieved after the spindle shock. The spindle stamping was applied until the 19th century and was gradually supplanted only by the 1817 invented by Uhlhorn toggle stamping.

Our illustration shows a screw press, can be pronounced with a diameter up to 30 mm with the medals. A large Spindelpesse from the mid-18th century had the mint Gotha (see picture here ) with the coins and medals of all sizes were minted. It was set up in 1981 under the arcades of the palace peace in Gotha.

Reibradspindelpressen

Reibbradspindelpressen at the machine head, two drive wheels are arranged, which can be displaced axially. Drives the discs via flat belt by electric motors. At the upper end of the spindle is the flywheel, which is equipped with a peripheral leather bandage.

The triggering of the hubs via lever or modern machines by foot or hand switch. The drive wheels are axially displaced and pressed one of the two discs to the flywheel. The transmitted by friction on the flywheel and spindle movement results as with the hand screw press for downward movement. For raising the driving wheels are moved in the opposite direction, the second pane is pressed against the flywheel, and thus the direction of rotation of the flywheel and the spindle vice versa.

For larger machines, the two drive wheels can be driven and moved independently. This serves to minimize utilization of the rebound stroke and a slower-running belt pulley for the upward stroke, the wear of the leather bandage.

Clutch Spindle Presses

The drive a clutch screw press consists of a in the axis of the spindle lying, constantly rotating flywheel. The down-stroke the flywheel is connected via a friction coupling with the spindle and separated just before the bottom dead center. Since the direction of rotation of the flywheel is not reversed, a separate drive is not required for the upward stroke.

Screw presses with direct drive

The drive of the machine based on the fact that the rotor is part of the flywheel, and the stator part of the machine body. For the upward stroke, as in the Reibspindelpresse, a reversal of the direction of rotation of the spindle and the flywheel necessary.

So far, direct-driven screw presses were performed using the principle of the induction motor. This design is characterized by robustness and virtually maintenance-free. By means of a frequency converter high starting currents reduced and a very precise controllability can be achieved. In addition, can be regenerative brakes and the brake is thus claimed only as a holding brake in the return stroke. More recent developments aim to use a synchronous motor with permanent-magnet excited rotor. Here again, the stator is part of the machine base and the rotor part of the flywheel. The main difference is that the rotor is very simple. Instead of a squirrel-cage rotor, the rotor consists of a steel ring at the outside diameter of the permanent magnets are attached.

The advantages of this type of machine are an exact dosage of the deformation energy and the elimination of wear parts such as the leather bandage at Reibradspindelpressen or the clutch pads for coupling screw presses.

Screw presses with servo drive

Through modern torque drives the complete surrender of a flywheel or a transmission is possible. A torque drive acts via a coupling directly onto the spindle and through reciprocal right or left rotation for the up and down motion of the ram. Since the synchronization of individual drives are very accurate, correspondingly large forces can thus be generated by the use of multiple spindles. Advantage of this press concept is the availability of the complete nominal press force over the entire stroke. By using several spindles of the plunger may also be constantly kept parallel and therefore not tilted. Since the spindle very transmit large forces and Genauigeitsanforderungen are high, planetary roller screws are used.