High Temperature Pulleys ( 1 )
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Where does it apply?
We innovated in 2008 high temperature pulleys, also known as harsh environment pulleys, for wire processing under:
Elevated temperature
Corrosive baths at elevated temperature
Fig. 1 A high temperature pulley Molten metallic baths.
For example: In zinc galvanizing baths at 440o - 450 o C or the hydrochloric acid pickling bath preceding the galvanizing bath, where using ceramic pulleys mounted on metallic ball bearings to guide the wire is out of the question. Figure 1 illustrates a solid ceramic pulley
NT 028 mounted onto a TZP bearing 6000.
What are they made of?
A COSMOS High Temperature Pulley is consisted of:
A solid ceramic pulley made of alumina
A full ceramic ball bearing
A ceramic-to-ceramic bonding between the pulley and the bearing
An optional factory-fit, thermally matched shaft
A non-sticking groove surface.
The superior high temperature resistance of the solid alumina pulleys is well documented. However, the need for a heat-resistant ceramic ball bearing, particularly a full-ball ceramic bearing without a cage, is not obvious.The ceramic-to-ceramic bonding addresses the issue of bond failure as a result of mismatched thermal expansion. For example, sink rolls in galvanizing baths. An optional shaft with a thermal expansion coefficient matching that of the ceramic bearing further eliminates the catastrophic damage inflicted by the unequal thermal expansion between the metallic shaft and the ceramic bearing.
The service temperature
The service temperature of the solid alumina pulleys, the alumina shaft and the ceramic-to-ceramic bonding all exceeds 1,000o C. The governing factor is the ceramic bearing material, of which TZP and Silicon Nitride are the most prominent:
TZP (Tetragonal Zirconia Polycrystal) 450o C
Silicon Nitride (Si3 N4 ) 1,000o C
The above figures apply to full ceramic ball bearings. Ceramic ball bearings with ball cages made of Teflon are subject to premature failure as the temperature rises beyond 180o C. Ball cages made of TZP which offer higher speeds and axial load capacity are available upon request. All components in COSMOS high temperature pulleys are immune to corrosive baths found in wire processing. Additional why's in the next page.