Worn Cast Iron Pump Parts
A slide and the two guideways of a pump had to be disassembled already during run-in time after approximately 20 h because they had galled completely, before the rated speed of 800 rpm was reached. Chemical analysis of the slide showed the following composition: 3.60C, 3.22Graphite, 2.49Si, 0.51Mn, 0.485P, and 0.112S. The iron was thus distinctly hypereutectic. The galling of the pump parts therefore was favored by an unsuitable structure caused by improper composition and fast cooling. Distortion by casting stresses may have been contributory or may have played the principal part. In order to prevent a repetition, the use of hypoeutectic or eutectic iron, slower cooling of the casting, inoculation of the melt with finely powdered ferrosilicon, and possibly rounding-off the edges or machining of the surfaces are recommended.