INDIA Cerobear vFINAL DR 24/6/08 11:05 Page 35
Semiconductor India
Fig. 2: Friction force of steel-angular contact ball bearings 7306 Fig. 3: Friction force of hybrid-angular contact ball bearings
in dry run mode (2,6 kN preload) 7306 in dry run mode (2,6 kN preload)
temperatures and surrounding parts are such as X30 (Cronidur 30) and X40 are The question regarding a lifetime
necessary to determine the optimal fit. used for the production of the rings. These calculation of hybrid or full ceramic
HNS materials demonstrate extreme over bearings is often asked. Unfortunately
The usage of tolerance compensating rolling and high corrosion resistance. lifetime calculation according to DIN ISO
elements, such as tolerance rings, is often Hybrid bearings have profited through the 281 cannot be applied for usage with
necessary in order to allow functioning usage of these high value steels and have special demands. This calculation assumes
under higher temperature ranges. almost caught up to full ceramic bearings. that the lubrication of rolling bearings is
This is characterised by their capabilities optimal and does not consider the
Zirconium oxide (ZrO
2
) is used as under media lubrication, dry running characteristic of ceramic.
alternative ring material in full ceramic conditions as well as by the use with high
bearings. This newer development of oxide- rotational speeds under greased lubrication. Instead, the lifetime is estimated with the
ceramics distinguishes itself through its help of the Hertzian pressure and the
steel like material properties. For instance, The standard material used for Cerobear experience gained with the usage of
the connection to metallic surrounding parts bearing cages is PEEK. Through its very ceramics in equal applications. Special
is simplified through an almost identical good properties this high performance attention needs to be paid towards
heat expansion co-efficient as it is found thermoplastic is already used in multiple insufficient lubrication or dry running
with standard bearing steel. areas of the semiconductor industry. operations which put additional strain on
the material through tangential and shear
The various material characteristics of PEEK is light, has very good mechanical stresses in the rolling contact.
Si3N4 and ZrO
2
in comparison to standard properties, a high operating temperature and
bearing steel 100 Cr6 are demonstrated in a good media resistance. All these The analysis of test stand experiments and
Tab 1. properties, together with excellent the experience showed that there are
machinability make PEEK an optimal cage different limit loads and speeds depending
Many advantages of full ceramic bearings material for high performance bearings. on the lubrication condition.
can already be used in hybrid bearings. Under extreme conditions, where PEEK The influence of additional operating
Hybrid bearings, besides full ceramic does not work any longer, a variety of other conditions needs to be estimated as well.
bearings, can also be used in semi- cage materials are available.
conductor and vacuum technology. A statement regarding the lifetime of a
PCTFE for example is used for bearing can therefore often only be obtained
The rings of this bearing type are temperatures down to -253
0
C and for even through tests. Although this is true,
manufactured of high value bearing steel; better media resistance. In coating units, experience has shown that a hybrid or full
the rolling elements consist of silicon with temperatures above 500
0
C heat ceramic bearing may have a factor 2 to 100
nitride. Mainly high nitrogen steels (HNS) resistant steels are used as cage material. higher lifetime than a standard bearing.
Summer 2008 | www.semiconductor-india.com 35
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