Mechanical press
A mechanical press is a pressing machine and is used to reshape materials in their external shape, consistency or internal structure by applying pressure , to remove liquid or gaseous admixtures, or to connect different layers with one another.
Operating principles
The functional principles of the mechanical pressing machines are differentiated according to the generation of the upper punch - main movement by means of cams, spindle and friction wheel drive , eccentric , toggle lever or rotary table principle , regardless of whether the generation of the die or lower punch movement is also based on cam or eccentric systems or other mechanical- hydraulically combined systems are used. The type of execution of auxiliary movements is also not decisive for the conceptual assignment. They can also be based on pneumatic and hydraulic principles. Compared to hydraulic press machines, the maximum press forces of mechanical press machines are limited and are in the range ≤ 5000 kN.
Functional principles of mechanical presses in technical ceramics
For the requirements of wet and dry pressing technology in technical ceramics , curve, eccentric, toggle and rotary table presses have proven themselves, whereby curve presses are preferably used for the wet pressing of flowable masses. The pressing force range of mechanical pressing machines for products of technical ceramics is <2500 kN, which is derived from the low density of ceramic masses. As a rule, the upper punch, lower punch and die systems of mechanical press machines do not work with a multiple punch division.
Application advantages in technical mechanics
While the curve designs, which can be individually adapted to the respective products, meet the requirements of wet pressing technology for flowable masses, the areas of application for eccentric, toggle and rotary table presses primarily relate to dry pressing technology for slidable masses. While the sinusoidal motion sequence of eccentric presses offers advantages, especially for larger strokes of up to 100 strokes per minute, the distorted sinusoidal sequence of the toggle lever is particularly suitable for products that require a longer ventilation time in the compression and a longer relaxation phase. The stroke rates for this are limited and are less than 35 strokes per minute. Rotary table presses, on the other hand, are characterized by particularly high unit outputs and quantities of up to 30,000 units per minute can be achieved for small and simply shaped products.
Relationship between mechanical press technology and design principles of mechanical presses
The relationships between ceramic press technology and the design principles of mechanical press machines are based on the unity of product - process - press / tool! Differences in the die removal and ejection processes of the uniaxial dry and wet pressing technology in technical ceramics influence the achievable pressed part quality depending on the geometric shape of the products and depending on the selected press type. Since the achievement of speed-proportional compression ratios with purely mechanical press machines is very difficult and only with very high mechanical effort, combined mechanical-hydraulic operating principles based on punch subdivisions are becoming increasingly important in order to better meet the requirements of precision pressing. The design principles of predominantly mechanical powder presses shown in B. Froherz's dissertation, compared with their advantages and disadvantages, also offer a process and press-specific reference for the tool designer.
history
Mechanical presses were already known in ancient Greece and were used to squeeze olives.