Ceramic Bearing: SMB Bearings

Ceramic Bearing: SMB Bearings

Season's Greetings

From us all at SMB Bearings Ltd,

A very Merry Christmas

&

a Happy New Year!

We look forward to meeting up with you again in 2009;
we will be back into the office on 02.01.2009, see you then!

We do all kinds of wheel bearings!

Check out our catalogue here!

SKATE Bearings

Have you ever tried to shop for skate bearings before? How many times have you been faced with a confusingly large range of skate bearings?We haven't given them fancy names to entice you and we won't offer you a dazzling range of different grades, lubricants etc.
We have used our extensive experience and knowledge of miniature bearings to produce three types of skate bearing to satisfy the most demanding skate and skateboard specifications. Our two most important design criteria were high performance and value for your money.

Please visit http://www.smbbearings.com/Skate_bearing.htm for more details & technical advice on what makes a great skate bearing. Abec rating? Lubrication? Seals? Cage/retainer? The answer is all of these. The problem is that some retailers will throw a lot of jargon at you to convince you that their bearings are superior. You have to decide what is relevant but, not being a bearing expert, how are you supposed to know? As experts, we will try to explain in plain simple language in the hope that you will go away with a better understanding of what to look for.

Technological innovation brings us the "Warmseat"

For slightly more practical help with your bike, why not visit www.smbbearings.com/BB_BRGS.htm

for a great article about replacing your bike's bottom bracket bearings, the photos are a real help too.
To help you get a better understanding of bearings & their performance on/in bikes,

check out www.smbbearings.com/SMBtechdata.htm

for loads of technical information & help on bearings.

Bearing materials

What materials are used for our bearings?


SAE52100 Chrome Steel (no prefix)

This is the standard steel for most ball bearings. It is harder than stainless steel and gives greater life ratings. It also has superior low noise qualities to standard 440 grade stainless steel. Chrome steel actually has a low chromium content and is not corrosion resistant so not suitable for corrosive environments or for dry (no lubricant) bearings as chrome bearings require a protective oil coating on the exterior surfaces which can contaminate the inside of the dry bearing. Chrome steel can tolerate continuous temperatures of up to 120C. Above this temperature, chrome steel undergoes greater dimensional change and the hardness is affected, reducing load capacity. It can withstand up to 150C intermittently but above this temperature, bearing life is significantly reduced.

AISI440 and KS440/ACD34/X65Cr13 Martensitic Stainless Steel (prefix "S")
More resistant to corrosion due to the greater chromium content and the addition of nickel, 440 grade stainless steel is the most commonly used for corrosion resistant ball bearings. The chromium reacts with oxygen in the air to form a chromium oxide layer, known as the passive film, on the surface of the steel. It is hardenable and gives a good combination of strength and corrosion resistance. It is magnetic unlike some 300 grades. The load capacity of 440 grade is approximately 20 percent less than chrome steel so life ratings will be slightly reduced. This grade exhibits good corrosion resistant when exposed to fresh water and some weaker chemicals but may corrode in seawater environments or in contact with many aggressive chemicals. The corrosion resistance also depends on the surface finish. Iron particles and other impurities left on the surface during maching can lead to premature localised corrosion while surface irregularities or poorly finished surfaces also increase the likelihood of corrosion. KS440/ACD34/X65Cr13 grade stainless steel with a lower carbon content is used by EZO Japan and has greater corrosion resistance and superior low noise qualities to the standard AISI440C grade. Corrosion resistance can be increased by passivation (see section below). The 400 grade stainless steel will also withstand higher temperatures than chrome steel, coping with up to 250C constant and up to 300C intermittent with reduced load capacity. Above 300C, bearing life can be considerably shortened.

A note on passivation....
Passivation is a process by which free iron particles and other impurities are removed from the surface of stainless steel by immersion in nitric or citric acid, thus regenerating the passive film. This reduces the likelihood of surface discolouration so making it a useful process in some corrosive environments. Passivation does not increase the resistance of stainless steel to pitting corrosion. This means that where a bearing has incidental contact with, say, salt spray, passivation may be beneficial but it will not offer long term protection in harsher applications.

AISI316 Austenitic Stainless Steel (prefix "S316")
Used for greater corrosion resistance or where bearings must be non-magnetic, bearings made from this material are semi-precision and fine for applications such as marine pulleys but not suitable for precision instrument use. The main problem here is that 316 grade stainless steel is non hardenable, therefore as a softer steel, it will only support low loads and low speeds. The dynamic load rating of a 316 grade bearing may only be 10% of the 440 grade equivalent whereas the maximum speed may be 5% or less of the 440 stainless steel version. 316 grade stainless steel exhibits good corrosion resistance in sea atmosphere and may perform well submerged in seawater. However, as the passive film on the surface of stainless steel relies on the presence of oxygen to regenerate itself, in a low oxygen underwater marine environment (e.g under washers or o-rings) the steel may be prone to pitting or crevice corrosion although 316 grade is still much more resistant to corrosion than 440 grade. Bearings made from 316 grade stainless steel can be used at high temperatures provided a suitable cage material is used. Due to the difficulty of using 316 grade for the cage, 304 grade stainless steel is normally used for metallic cages and nylon for non-metallic cages. Please remember that, as 316 grade bearings are far less popular, minimum quantities may apply and some smaller instrument bearings may not be available.

Plastic - acetal resin (prefix "AC") Bearings made from acetal resin with balls made from 316 stainless steel or glass are more corrosion resistant. They will however, corrode in the prescence of certain chemicals for which made-to-order polyethylene or polypropylene bearings with glass balls may be a better choice. These are generally termed as "plastic" bearings and like 316 stainless steel bearings, are not suitable for anything other than low loads and low speeds and should not be used in temperatures of greater than 90C. These types are also low precision so not suitable for instrument use. The smaller bearings are not usually available in these synthetic materials.

Ceramics - Silicon Nitride (prefix "CB" or "CC")
Some types may be available with steel rings and ceramic balls (hybrid) or "all ceramic" bearings with ceramic rings and balls. These types may not be stock items and could be subject to minimum order quantities. There are many advantages to silicon nitride such as a lower friction coefficient, much greater hardness and temperature resistance. Silicon nitride has 40 percent of the density of bearing steel but is about twice as hard. The lower density means that the balls exert less force on the outer raceways reducing wear while the extra hardness means greater wear resistance. Some ceramic materials such as Zirconia or Alumina are heavier and not as suitable for hybrid bearings although they can be used in full ceramic bearings. Hybrid bearings are also capable of higher speeds (usually up to 30 percent) and can also operate better with limited lubrication as the lower friction material generates less heat. However, ceramic bearings can be significantly more expensive, particularly "all ceramic" bearings partly due to the material and partly due to very low production quantities. The cost may be prohibitive for some sizes or quantities.
WARNING: Ceramics are often overrated particularly hybrid bearings.It is often thought that they will provide incredibly high speeds which is not correct unless you use special retainers or no retainer and the bearing still needs to be high quality. Customers often expect very low frictional torque with low noise and vibration levels. This may be possible but the bearing rings must have very good roundness and a high quality raceway finish while the balls must also have very good roundness and surface finish. There are many cheap hybrid bearings on the market that do a worse job than a good quality bearing with steel balls. Good hybrid bearings often prove too expensive for an application. Most sizes are made to order.

For further information, see cerbec's comments at
http://www.cerbec.saint-gobain.com/HybridBearing/Hybrid.asp
Click on the following for a compatibility check for several different materials and chemicals:
http://www.coleparmer.com/techinfo/ChemComp.asp

ABOUT SMB

Originally formed in 1985 to cater for a growing demand for miniature ball bearings and small ball bearings in the UK, SMB Bearings has grown over the years to become a major specialist supplier worldwide.

We have expanded the range slightly from the original micro ball bearing, miniature ball bearing and small ball bearing range but are still very much specialists in our field. We still concentrate on a fairly narrow range of ball bearing types. We continue to supply miniature ball bearings,instrument ball bearings (mini bearings and micro bearings) but we have added stainless steel bearings, plastic bearings and electric motor bearings. Being specialists allows us to know our products better and serve you more effectively.

Most of the micro/miniature bearing, stainless steel bearing and thin section bearing range is supplied either in high precison EZO brand or, for low cost applications, SMB China brand. EZO are a well respected and highly reputable Japanese manufacturer of precision miniature bearings, thin section bearings and stainless steel bearings and our association with them goes back many years to the first days of SMB Bearings.

Miniature Bearings / Micro BearingsThis is a range of miniature ball bearings or mini bearings starting with micro ball bearings of only 0.6mm bore up to 9mm bore (plus inch equivalents). These include micro and miniature radial ball bearings (including the smaller instrument bearngs) and miniature thrust ball bearings.

The range encompasses both metric and inch micro bearings and miniature bearings, miniature flanged bearings and miniature extended inner ring bearings while for specialist applications, ceramic bearings and hybrid bearings are available in many sizes.

We supply miniature bearings for a wide variety of uses including instrumentation, small motors, gearboxes, fishing reels, cycles, skates, skateboards and inline skates. We stock radio control model ball bearings for radio control cars, helicopters and engines, in fact most model engineering applications.Stainless Steel BearingsStainless steel ball bearings are available from 0.6mm bore up to 50mm bore or inch equivalent. Most of the range of miniature bearings and thin section bearings are also available in 440 grade stainless steel. The larger "popular metric" stainless steel bearings are from 10mm bore up to 40mm bore and often used in the food industry or for high temperature applications. We can also supply 316 grade stainless steel bearings in many sizes but these may need to be made to order.

Plastic Ball BearingsPlastic bearings can be supplied from 6mm bore up to 25mm bore from stock and even larger sizes of plastic bearing can be supplied to order. Generally made from acetal resin with 316 stainless steel balls or glass balls, plastic bearings are used where greater corrosion resistance is required.
Thin Section Ball BearingsThin section bearings can be supplied from 10mm bore up to 50mm bore. Many of the miniature bearings are also thin section bearings but the term generally applies to 10mm bore and upwards.

Electric Motor BearingsElectric motor ball bearings are designed to run with low noise and vibration for any noise critical application. The term "Electric Motor Bearing" is often loosely used which is why our electric motor ball bearings have been tested in comparison with leading brands.

Supply from StockOver the years we have developed extensive product knowledge and offer technical help with all apsects of our range. We keep comprehensive stocks across the whole range so offer a same day despatch worldwide on most sizes if required. We receive incoming shipments every week so stocks are always changing. For the most up to date stock situation on any item, please contact us.

RelubricationOur relubrication facility has been in operation for over 15 years allowing us to provide miniature bearings, stainless steel bearings, thin section bearings and electric motor bearings with any one of a wide range of lubricants from oils and greases to dry lubricants or no lubricant at all. In addition to cleaning and re-lubricating bearings with a range of customer specified oils and greases, we also have the facility to treat bearing raceways with molybdenum disulphide for vacuum applications. We re-lubricate our own bearings and customer supplied bearings every day. The benenfit of having an in-house operation means we can supply you with small quantities, quickly. Our customers find this particularly useful for urgent, small or one-off requirements or sample approval although we regularly deal with larger quantities too.

Miniature, corrosion resistant & motor bearings and re-lubrication of bearings

Bearing Technical Talk... Radial Play

Radial play, or internal clearance, is an important consideration when choosing a bearing. Quite simply, there must be at least enough play in a bearing to allow rotatation without too much resistance after fitting or it will fail quickly. It is normally preferable to only have a small clearance left once the bearing has been fitted to minimize ball skidding and reduce axial play (end play). Selecting the correct radial play can avoid faster wear and reduce unwanted play. Radial play before fitting is called "initial" radial play. "Residual" or "operational" radial play is what exists after fitting.

So what might change the radial play in the bearing? A shaft that is slightly larger than the bearing inner ring (an interference fit or press fit) will stretch the inner ring reducing radial play. The same thing happens if the outer ring is a tight fit in the housing. This can compress the outer ring so a bearing with a greater radial play may be needed. High temperature can also be a problem where the shaft and housing temperatures differ. If a bearing inner ring gets hotter than the outer ring, it will expand more and reduce radial play. If the outer ring gets hotter, radial play can increase. These problems can also occur where inner and outer ring are the same temperature but made of materials with different expansion coefficients.

In most cases, a standard radial play is suitable and, of course, easier to obtain but there are certain conditions where a non-standard clearance is preferred. A tight radial play gives greater rigidity and running accuracy which is important in low noise, low vibration applications. This is why many of our small electric motor bearings are MC3 radial play. In fact, to further eliminate vibration and noise, a small axial preload is often applied to reduce the radial play to zero. Elsewhere, a loose radial play is desirable. For example, a loose radial play should be considered for high axial loads as it increases the bearing's axial load capacity. Also, a loose radial play will better accommodate misalignment between the shaft and housing and cope better with heavy loads or shock loads.

Finally, it is sometimes thought that when there is too much play, a higher precision grade will solve the problem. Actually, the answer is often to use a bearing with a tighter radial play or introduce an axial preload to the bearing to eliminate the play. When a bearing is manufactured, the balls and rings are carefully matched to produce the desired radial play so a higher precision grade will make no difference to the "looseness" of the bearing. Its just as possible for a high precision bearing to have a large radial play as it is for a standard grade bearing to have a tight radial play. Remember, loose does not necessarily mean poor quality!!
For more information, see the "Technical" page on our website and scroll down to the Radial Play section.











We recently added material specification tables in the Technical section of our website. These give details of the different grades of chrome and stainless steels used in the rings, balls, cages and shields in our bearings. For more details, go to the web page at: www.smbbearings/materialtables.htm
We now have stocks of plastic (acetal resin) bearings with glass balls to complement our existing stock of plastic bearings with 316 stainless steel balls.





Miniature & instrument bearings Stainless steel and plastic corrosion resistant bearingsLow noise electric motor bearings Cleaning and re-lubrication of bearings.


See the range and lots more online at www.smbbearings.comor telephone sales on 01993 842555 or fax us on 01993 842666