Product category:
Bearings and guideways - rotary and linear
News Release from: Micromech | Subject: Ceramic linear bearings
Edited by the Manufacturingtalk Editorial
Team on 15 August 2007
Ceramic linear bearings are more
reliable
Ceramic linear bearings maintain longer and more reliable performance and are claimed to have an exceptional life span while requiring little or no lubrication, reports Micromech.
PM Bearings have applied more than 20 years of research and testing to show that ceramic linear bearings maintain longer and more reliable performance These bearings are non-magnetic, have reduced friction, retain their stiffness and operate at higher temperatures
This article was originally published on Manufacturingtalk on 28 Apr 2004 at 8.00am (UK)
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They also have an exceptional life span and require little or no lubrication.
Exclusive UK agents for PM Bearings are Micromech.
Ceramic bearings have been well accepted for many years in demanding ball bearing applications as they superior to steel for density and hardness.
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Because of the non-magnetic properties this is an ideal material for use in non-magnetic or ultra-high vacuum environment.
As the first linear bearing company in the world to realise practical use of ceramic linear bearings, PM Bearings can supply their high precision positioning stages to operate under very harsh conditions.
The bearings are very lightweight as the ceramics density is about 40%-60% of traditional bearing steel DIN 1.3505.
Because force is directly proportional to mass, the low-density silicon nitride used significantly reduces the starting force, which is required to move the slide/stage.
High Rigidity is achieved because ceramic ways and balls (silicon nitride and alumina) have a Youngs Modulus which is about 50% higher than steel, making them an ideal linear bearing material.
These are the qualities of rigidity and precision at high speed needed for use in high-speed X-Y stages as used for wirebonding machines in the semi-conductor industry.
The lifespan of linear bearings is directly related to hardness, the most critical mechanical property of a bearing material.
With an impressive 78 HRC, this is twice as hard as many bearing steels.
They also have a high compressive strength, about five to seven times that of steel therefore silicon nitride improves wear resistance, minimising the damaging effects of repeated surface contacts.
* Higher heat resistance - the mechanical properties of ceramic bearings do not change in extremely low (cryogenic) or extremely high temperatures, which makes it very suitable for use as a heat resistant material.
A major problem caused by such high temperatures is lubrication as oil and grease can normally be used in temperatures of up to 300 deg C.
When temperatures are higher, only solid lubricants can be used, but even then, they can only be used for temperatures up to 500 deg C.
However ceramic bearings can exceed the best high temperature bearing steels by a factor of three, as they can operate at temperatures up to 800 deg C.
Ceramic linear bearings have other characteristics such as vacuum compatibility show they exhibit less particle generation about 1/3 in both air and vacuum compared with stainless steel.
In special applications, the chemically inert, corrosion resistant and electrical non-conductivity characteristics can also enhance linear bearing performance.
* Longer life - ceramics outperform most other materials in bearing life, and without lubrication, as they are extremely hard and have outstanding wear resistance.
In the rigorous comparison tests it was shown that the rollers in the steel linear bearings exhibited flaking and a loss pre-load was observed after only 40% of the calculated life while the ceramic linear bearings were still operating after 2x the life-span of steel.
Inspection of the rails and rolling elements revealed no wear was found and the accuracy of travel was still the same.
The test confirmed that the life without lubrication is dramatically longer for ceramic linear bearings than for steel ones.
* Standards - currently there are no standards published by ISO or JIS regarding the static and dynamic load ratings of ceramic linear bearings.
PM engineers are being studying the static load ratings of ceramic bearings in which Si3n4 rolling elements are used.
Based on material testing, they are working on the assumption that the load ratings of ceramic beings will have the same values as for the conventional steel ones based on the fracture load of silicon nitride rolling elements.
Test results have proved that depending on operating conditions ceramic linear bearings often achieve a longer life - up to three to five times greater.
* Benefits - the benefits of being non-magnetic, having reduced weight, reduced wear giving longer life, being corrosion resistant and lower thermal expansion has opened up many applications for these bearings.
They are presenting many exciting opportunities for designers of spectroscopy, lithography, wirebonding and X-ray machines to take their equipment to higher levels of performance.
Ceramic bearings' relative magnetic permeability at <1.001 allow them to operate in magnetic fields such as electron beams.
Ceramic linear bearings and slides are manufactured on a made-to-order basis.
In this way the ceramic bearing specifications can be matched with the customers system to meet their exacting requirements of speed, operating temperature and accuracy.
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