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Plain Bearings Made of Silicon Carbide Section 3

This test provides much more information as the objective of the development of plain bearings suitable for dry running cannot be a centrifugal pump which runs dry once over several hours but rather the proof that plain bearings provided with SAFEGLIDE PLUS also survive frequent dry runs without suffering any damage. 10 minutes are normally enough for the operator to detect a functional error and to take appropriate action.

As a final test, a dry run over 75 minutes was conducted again. A sub-sequent evaluation of the plain bearings showed that no damage to the components had occurred.

It is understandably very important for industrial practice that the dry-running properties are also retained after a long period of operation and that this dry-running safety feature is still present when the pump is repeatedly switched off and started up again. To this extent other coating systems which have an additional soft carbon layer on a hard support material to achieve as long a dry running time as possible are not viewed as being favorable. The reason for this is that the soft layer wears down during pump operation and then after de-activation and renewed start-up of the pump it might possibly no longer satisfy the requirement. This aspect would be even more important for solids-containing media.

Finally, another test was conducted to determine whether, after a dry run followed by a sudden supply of cold medium, the silicon carbide bearings with ?SAFEGLIDE PLUS? are damaged by the temperature shock. In this test an MNK 50-200 was allowed to run dry until the temperature had risen to about 110?C (230?F) on the impeller plain bearings and to 150?C (302?F) on the rotor plain bearings. Then the suction valve was opened while the pump was running so that 20?C (68?F) cold water could flow directly into the pump. The temperature at the bearing points fell within 3 seconds to about 20?C (68?F). A subsequent examination of the plain bearing components showed that all the parts had survived the test without suffering any damage.

Summary

The problem of dry running has virtually been eliminated by the plain bearings made of silicon carbide with a SAFEGLIDE PLUS coating which are now available to magnetic drive pumps of the MNK and MNK-B series. Dry-running times of half an hour up to several hours, depending on the pump size, are now possible. Bone dry running of half an hour is possible even with the pump size with a transmitted magnetic drive rating off 65 kW at 2900 rpm without reaching the tem-perature limit of the pump and in particular that of the PFA lining. A dry run of several minutes up to one hour is also possible with pumps with less temperature-stable plastic linings made of PVDF (tempera-ture limit 90°C/194°F).

The SAFEGLIDE PLUS coating has been proving its universal applicability for many years in a very large number of pumps of the MNK and MNK-B series with their very different and sometimes extreme operating conditions. The coating is still fully functional even after years in operation in highly corrosive media. The plain bearing SAFEGLIDE PLUS offer the user even greater safety reserves, which means that damage to these magnetic drive pumps through dry running can virtually be excluded.
sec j3 fig3 temp curve