A characteristic of the mechanized forging hammer is that, in contrast to the rather slow movement in a press , the deformation tool transfers the deformation energy to the workpiece at high speed . The tool used to transfer energy to the workpiece is known as a hammer bear . While drop hammers powered by water power ( water wheel ) were already in use in the late Middle Ages , the first steam hammers were realized during the industrial revolution in 1842 and 1843 in England by James Nasmyth and in France by François Bourdon . Towards the end of the 19th century, the spring hammer and a little later air hammers were developed, which today, in their further developed form and robust construction, are used alongside the presses for handicraft (e.g. art forging ) and industrial forging.
Types of mechanical forging hammers
A distinction is made between the following forms:
With this type of hammer, the bear is accelerated to an impact speed of around 5 to 8 m / s on the workpiece as a result of the weight acting on it .
The hammer bear can be lifted into its starting position in different ways.
Even before the industrial revolution, machine hammers were in use, in which the hammer bear is attached to a handle provided with a pivot and the handle and bear move up and down like a lever around the pivot axis of the pins. The drive takes place, often by water power, by means of a rotating drive shaft provided with a thumb (thumb shaft). Their thumbs hold the handle or bear temporarily, lift them up and then let them fall freely again so that the bear hits the workpiece accelerated by its weight. Depending on the attack position of the thumb, one speaks of a forehead hammer (attack on the bear itself), chest hammer (attack between the bear and the pivot) or tail hammer (attack on an extension of the handle on the side of the pivot opposite the bear).
With a more practical construction, the bear is guided vertically in such a way that, in contrast to the handle hammers, regardless of the workpiece height, the workpiece always hits parallel to the lower bear, the scabbot (so-called vertical hammer ). With these hammer types, the bear is lifted by an electric motor, a belt transmission or by a piston to which steam, compressed air or hydraulic fluid is applied. With the latter, the pressure medium must be able to escape from the piston as quickly and unhindered as possible during the fall process of the bear in order to avoid throttling losses. This model of a machine hammer is also known as a real drop hammer . The impact energy is calculated using the following formula:, where m = mass of the bear; H = height of fall. However, it should be noted here that:, where g represents the acceleration due to gravity . Drop hammers have a working capacity of 1.5 kNm to approx. 40 kNm. The bar mass moves between 100 and 2000 kg.
Upper steam hammer
With the Oberdampfhammer, in addition to the acting weight, the hammer is accelerated by steam or compressed air via a piston connected directly to the hammer via a piston rod. This results in a higher capacity of the forming machine, but also a higher energy consumption. Steam hammers of this type are also known as double-acting .
Upper pressure hammer
In contrast to the simple drop hammer and top steam hammer, when lifting the bear of a pressure hammer, a gas cushion is compressed over the bear. In this case, the bear moves back regularly using a hydraulic cylinder . The gas cushion located above the hammer stores energy and releases it to the piston when it moves downwards. Thus, in addition to the acceleration due to the force of weight, a further force caused by the gas pressure also acts here. This type of drop hammer is also known as the ideal drop hammer. The impact energy can be calculated using the following formula:, where A denotes the area of the piston which presses against the gas cushion and p the pressure prevailing in the gas cushion. Working capacities between 10 and 250 kNm are available for the upper pressure hammer. The body mass is between 15 and 10,000 kg.
In contrast to the other types of hammer, the scabbot, i.e. the lower bear, is not firmly supported in the counter-blow hammer. Rather, the scabbot moves upwards while the upper bear moves downwards. For this a coupling of the two bears is necessary. This coupling can take place via two principles. There can be a mechanical coupling by connecting the two bears with metal bands or a hydraulic coupling by hydraulic cylinders. With the counterblow hammer, the mass of the lower bear must be significantly greater than the mass of the upper bear. In order to achieve an equilibrium of forces, the lower bear moves much more slowly than the upper bear. With counter-blow hammers, work capacities between 63 and 1000 kNm can be achieved. The bar masses range between 10,000 and 205,000 kg. Compared to other designs, the counter-blow hammer has specific advantages and disadvantages. The largest counter-blow hammer in the world (Ladish) has a working capacity of 1250 KJ, the Müller Weingarten company is currently building a larger one with 1400 KJ (approx. 54000 t pressing force).
In contrast to other types of machine hammers, counter-blow hammers require around 35% less structural mass with the same work capacity. During operation, they generate fewer vibrations and thus place less stress on the hammer foundation or the entire structure of the site. Due to the significantly higher mass of the lower ram compared to the upper ram, the workpiece is released again "automatically" if the hammer fails. However, the more complex construction and the associated higher costs are disadvantageous.
Applications of machine hammers
Machine hammers are used both in series production, for example in the drop forging of crankshafts (see drop forging hammers ), as well as in the production of individual parts in the open die forging of workpieces of all sizes. Occasionally, it is also used for embossing .
Components of hammers
- Guide pillars
- Height of fall (no materially existing element)
- Saddle (upper and lower saddle)
Benefits of hammers
- high speed of impact
- low pressure contact time
- low investment costs
- overload safe
- high flexibility
Disadvantages of historical hammers
(largely negligible in modern hammers due to good insulation)
- high load on the foundation
- strong vibrations
- Hårvard Bergland: The art of forging. The great textbook of traditional technology. 4th, unchanged edition of the German edition. Wieland, Bruckmühl 2013, ISBN 978-3-9808709-4-8 , pp. 163-184: Chapter 8: Machine hammers and foundations ; Pp. 185–208: Chapter 9: Auxiliary tools for forging with a machine hammer .
- Dubbels paperback for mechanical engineering . 11th edition, Springer-Verlag Berlin / Göttingen / Heidelberg 1955, Volume II, p. 661 ff.
- Otto Lueger : Lexicon of all technology: steam hammers at Zeno.org .