Hot forging: power hammers

The ability to “beat” metal has evolved over the course of human history, passing from the manual beating of the blacksmith to the automated one, through power hammers, initially operated by water mills, then by steam e finally through an electric motor, a hydraulic pump or an air compressor.

The most important feature of power hammers is related to the temperature of the material being forged. By their action they maintain, or even raise, the temperature of the material, first heated in the furnaces. This favors the sliding of the material in the die and eliminating the risk of cracks.

The power hammers currently used can fall into three distinct categories: “Berta” or drop hammer, hydraulic or piston hammer, air hammer.

“Berta” or drop power hammer

The Berta works via an electric motor which raises the hammer fixed to a belt inserted between a major or load-bearing roller and a “tambourine” or minor roller, which meeting generates the lifting. Consequently, the moving away of the two rollers generates the gravity fall of the mallet, guided by guide columns converging in a V shape.

Moderner versions of this type of power hammer are equipped with PLC and brake.

This type of power hammer is characterized by:

  • low construction investment
  • low frequency of the “hits”, but very powerful
  • precise adjustment of the fall, of the “hit”

Hydraulic or piston hammer

A hydraulic pump, equipped with mechanical or electromechanical valves, drives a piston at the lower end of which the mallet is placed. In this case the mallet is pushed and no longer, simply, dropped.

The hydraulic power hammer has a piston stroke shorter than a drop power hammer belt. Furthermore, this class of machines is characterized by:

  • high power
  • high frequency of the “hits”
  • high maintenance or rise in temperature

Due to the speed and short stroke of the piston, also a lower precision than the drop power hammer.

Air hammer (formerly steam hammer)

In machines of the category of air hammers, the mallet is pushed by the air pressure. This, in ancient times, was generated by the steam of a boiler, while nowadays by a compressor.

This type of mallet is very powerful, but definitely the least precise of the three. For this reason the air hammer is mainly suitable for free or open die forging.