General engineering analysis

Case Study

Enabling Rammer to Hit Harder

Rammer, part of Sandvik Mining and Construction in Finland, manufactures hydraulic attachments for rock excavation, demolition and recycling. The company have been users of LUSAS for many years, analysing hammer parts, hammer housings and cutter-crusher and pulverizer parts for their Rammer range of products. Rammer is recognised as a world leader in the design and manufacture of hydraulic hammers for primary and secondary breaking work.

The 1m long cylindrical piston of a large hammer is made from case hardened steel and weighs over 200 kg. The piston strikes a work tool with a velocity approaching 10 m/s. Transient 3D dynamic analysis using LUSAS Analyst was necessary to understand what happens to the piston and tool as a result of the impact. Of particular interest during the initial analyses was the degree of bending caused by the tool being driven at an inclined angle to the ground. As a result of using LUSAS a better understanding of the effects of an inclined impact was obtained.

Due to symmetry only half of the piston needed to be modelled in LUSAS. Approximately 840, three-dimensional solid elements having linear material properties modelled the piston and joint elements with nonlinear material properties representing the ground that the tool strikes. Slidelines automatically modelled the contact between the piston and the tool. The initial load case was the velocity of the piston towards the tool. Typically, 120 time steps modelled the impact event using a time step of 10 microseconds.

From the results obtained, the displacements caused by the bending load cases were of particular interest. The analyses showed that when the tool is asymmetrically thrust against the ground, the tool bends highly with the bending stress wave propagating into the piston causing it to bend as well. The degree of bending experienced by the piston was unexpected indicating that it may be necessary to try to reduce inclined impacts when operating with a hydraulic hammer. It also indicates the importance of supporting the piston with good bearings to avoid seizure effects.

rammer_model.gif (4874 bytes)

results plots

Eero Ojala, the engineer responsible for the analysis found LUSAS straightforward to use. He said: "Contact between the piston and the tool was easy to model in LUSAS with the slideline technique being especially useful. As an extension to this work, it would be interesting to model the whole hammer body to see what happens when the piston and tool are perfectly supported in relation to it".

"Contact between the piston and the tool was easy to model in LUSAS with the slideline technique being especially useful."

Eero Ojala, Rammer


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