High Temperature Pulleys ( 1 )
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Where does it apply?
COSMOS innovated high temperature pulleys, also known as harsh environment pulleys, for wire processing under:
Elevated temperature
Corrosive baths at elevated temperature
Molten metallic baths.
For example: Zinc galvanizing baths at 440o - 450 o C or the hydrochloric acid pickling bath preceding the galvanizing bath, where submerging metallic ball bearings to guide the wire is out of question. Furthermore, these high temperature pulleys also find applications in float glass manufacturing where a sheet of glass is made by floating the glass on a bed of molten tin. Figure 1 illustrates a NT 028 - 6000 TZP High Temperature Pulley by COSMOS capable of operating under environment temperature to 450o C.
What are they made of?
A COSMOS High Temperature Pulley consists 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 known. 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. A shaft with a thermal expansion coefficient matching that of the ceramic bearing further eliminates the damage done by the unequal expansion of a metallic shaft at high temperature.
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 cages made of Teflon are subject to premature failure as the temperature rises beyond 180o C. Cages made of TZP offer higher speeds and axial load capacity, but need not be cost-effective. All components in COSMOS high temperature pulleys are immune to corrosive baths commonly found in wire processing.