Motivation and content:

Demolition hammers are machines for crushing mineral structures. They are characterized by a hammer impact mechanism that combines the function of a chisel and a hammer in one machine. The chisel cutting edge shatters the mineral substrate using high-frequency impact pulses. The percussion mechanism is subjected to high loads. Tests with prototypes are essential for the development of lightweight yet robust machines, as computer-aided simulations are based on simplifications that give rise to uncertainties. However, long-term tests with mineral materials are difficult, as the material is destroyed during the test. The repeatability of such tests is also critical, as the substrate is a natural product or a dispersion consisting of natural products. Good reproducibility is particularly important in tests to evaluate vibration emissions. In order to avoid vibration-related illnesses, these tests are important for hand-held devices and are prescribed by legislation.
Demolition hammers come in different sizes: from small hand-held rotary hammers to pneumatic hammers and hydraulic hammers that are attached to excavators. For decades, efforts have been made to develop substitute substrates for rotary hammers that reproduce the impact behavior of a mineral substrate and solve the problem of material destruction. However, current substitute substrates do not meet all the requirements of machine developers and legislation. The aim of the research is to develop a substitute substrate based on hydraulic components that meets the requirements.

State of the art/research:

The Dynaload mechanical substitute base is currently used to determine the vibration emission of rotary hammers. This consists of a cylindrical tube filled with steel balls, which is sealed with a cylindrical disk mounted freely in the axial direction. If the system is hammered with a hammer drill, the steel balls are deformed. Friction creates a damping effect, which is intended to simulate hammering on mineral material. The weaknesses of the system are the lack of adjustability and the fact that the damping behavior changes with increasing wear. For larger demolition hammers such as pneumatic and hydraulic hammers, no substitute base with good damping properties is known.

Research gap:

It is not known how precisely the Dynaload replacement base can imitate the impact behavior of various mineral materials. It is not known to what extent a wear-free and adjustable replacement base can be realized with hydraulic elements.

Project objectives:

As part of the research project, a method for the evaluation of replacement substrates for demolition hammers is being developed. The method is used to analyze the Dynaload replacement base and evaluate its impact behavior for various minerals. A hydraulic substitute base for rotary hammers is being developed. This should be adjustable so that the impact behavior of different materials can be realistically simulated for rotary hammers of different sizes. For this purpose, a method is being developed with which hydraulic parameters can be determined for the combination of hammer drill and material to be tested. The extent to which the method can be used to design hydraulic substitute substrates for testing larger hammer impact mechanisms is being investigated.