Industrial Applications - The Boundary Element Method with Programming - page 443

17.2 MECHANICAL ENGINEERING

17.2.1 A cracked extrusion press causes concern

A small company in Austria manufactures rolled thin tubes by extrusion. The extrusion
press in use was 35 years old and made of cast iron (see Figure 17.1). During a routine
inspection cracks were detected on the surface of the cast iron casing, as indicated. The
company was in the process of ordering a new press, however delivery was expected to
take more than six months. There was some concern that something dramatic might
happen during the extrusion process with the press suddenly breaking, meaning not only
a danger to lives but also the possibility of losing the press. With full order topics the
latter was a very serious economic threat.

Cracks
observed

Figure 17.1 35 year old drawing of extrusion press with location of cracks indicated

The aim of the analysis was therefore to determine:
x If the existing cracks would propagate
x If this propagation would lead to a sudden collapse of the structure

The geometry of the part to be analysed was fairly complicated and had to be
reconstructed from the original plans. For the purpose of the analysis it was assumed
that there were two planes of symmetry, as shown in Figure 17.2, although this was not
strictly true.
The cylindrical bar restraining the casing was not explicitly modelled but instead
appropriate Dirichlet boundary conditions were applied. Each time a tube is extruded the
casing is loaded with a force of 3700 tons (37 MN), as shown by the arrows. Although