Ball Bearings for High-Speed Dental Handpieces

Barden has introduced the X-Life range of super-precision ball bearings designed to enhance reliability, lengthen operating life and reduce noise levels in high-speed dental handpieces. In terms of bearing selection, it does not get much more challenging than choosing a bearing for a high-speed dental handpiece. As well as having to withstand the harsh operating environment in which the bearings are constantly bombarded with debris, the latest dental handpiece turbines typically have to operate at extremely high speeds of between 400,000 and 500,000rev/min.

The bearings also have to undergo repeated chemical or steam sterilization cycles, which can strip away the bearing lubricant. In addition, the bearings much also remain cool enough to avoid injury or discomfort to the patient and the dental surgeon, while also offering the lowest possible noise and vibration levels in order to reduce patient anxiety and allow for a more relaxed, comfortable operating environment. Wear on a dental handpiece is often limited to the bearing itself, which is typically located at the tip of the handpiece turbine.

High-speed operation, repeated sterilization and the effects of operating debris can cause the bearing to fail prematurely. However, due to a combination of features designed to retain lubricant and reduce contamination, Barden’s X-Life range of dental bearings offer a number of technical advantages over conventional bearings. Barden’s X-Life branded products are premium-quality bearings produced using manufacturing technologies that enable a more uniform surface over the whole contact surface between the rolling elements and raceway. As a result, under identical load, there is a reduction in the stress conditions present on the rolling elements and raceway.

This means reduced friction and lower bearing temperatures, less strain placed on the lubricant, higher basic dynamic load ratings, and an increased basic rating life. Robert Globe, sales and marketing manager at Barden, said that while Barden can provide suitable replacement bearings for any make or model of dental handpiece, very often there is a need for the company to customise the bearing in order to provide an optimised design for a particular application. The ability to custom engineer a bearing for an OEM is important, because OEMs are continually improving their handpiece designs, so the bearing has to be constantly improved too.

OEMs also need samples and prototypes of the bearing at short notice, which Barden is also able to provide. An important bearing feature is the use of ceramic balls rather than steel balls. Ceramic balls are harder, lighter and more wear-resistant than their steel counterparts. At speeds of around 450,000rev/min, this means the ceramic balls generate less centrifugal force, which reduces wear and internal loads on the bearing. Lubricant life is also extended, since ceramic balls produce fewer wear particles than steel balls. Barden, as a company, is in complete control of the quality, cost and delivery of the ceramic balls and has its own manufacturing facilities for producing them.

On the research and development side, Barden constantly develops and tests new cage designs and materials, as well as new coatings, surface treatments, seals and lubricants. Mark Pritchard, senior product engineer at Barden, said: ‘We have developed new improved sealing designs in which the shield is incorporated into the outer ring. ‘This reduces the critical gap between the integral shield and the bearing inner raceway by 60 per cent compared with conventional shield-and-circlip designs. ‘This provides significant advantages such as minimising the risk of shield ejection, preventing contamination and retaining the lubricant more effectively, which in turn results in a bearing with much improved operational life,’ he added.

A typical dental handpiece bearing and turbine assembly has not changed all that much over the last 50 years. Most dental turbine designs are based on a miniature Pelton wheel. The Borden rotor, which was introduced in 1957, was the prototype of the modern air turbine. Turbine bearings are extremely small, with most having a bore size of 3.175mm and an outside diameter of 6.35mm. Pritchard said: ‘The machinery we have here in the UK enables us to produce bearings with a typical roundness of less than 0.5um. ‘Special attention is also paid to ensure that the ring harmonic levels are kept low.

‘Both the rate of change, the magnitude and the number of lobes are carefully controlled. ‘All races are double-honed and super-finished, typically in the region of 0.01um Ra. ‘Our dental bearings are supplied with the bore calibrated in either 2.5um or 1.0um steps, which provides a more accurate assembly,’ he added. In dental turbines, cage breakage is responsible for 90 per cent of bearing-related failures. Turbine bearings do not fail due to fatigue, the cause of a cage breaking is normally due to cage wear and subsequent fracture.

Most cages for deep groove ball bearings are snap-type retainer cages. The opening for inserting the ball must be designed in such a way that the prongs do not break when pushing the balls in. To hold the balls in the pocket, a narrower width is desirable. This type of cage has been used for decades and is still being used today. Angular contact ball bearings have a ‘halo’ or window cage that is easier to manufacture and will not be ejected from the bearing when worn. This cage is stronger and less vulnerable to the effects of repeated sterilisation of the dental handpiece. Normally, for high-speed bearing applications, phenolic resin is the chosen cage material.

This offers modest but sufficient tensile strength, low friction and is less sensitive to poor lubrication. However, the material does degrade when exposed to heat, particularly at the temperatures required for sterilisation. Sterilising the dental handpiece after every patient requires a strong heat-resistant cage material and so more recent cage designs use graphite or PTFE fillers. Used predominantly in angular contact bearings, these materials are more sensitive to poor lubrication compared with phenolic. Dental bearings need to be protected against contamination from the outside and to keep lubricant inside.

Low noise and vibration are critical for good turbine operation. Not only does the air stream take the lubricant along with it, it also results in air noise. Also, when the turbine is stopped and no air is flowing, a vacuum is created within the turbine and so outside air that contains all kinds of contaminants will rush in if there is inadequate shielding. Normally, dental bearings use AISI440C stainless steel balls. These balls are between 1mm and 1.6mm diameter, depending on the type of bearing used. The ceramic ball first found use in dental bearings in the early 1990s due to drastic reductions in the cost of manufacturing ceramic balls and technological advancements.

The advantages of using ceramic balls are their lower density (3,200kg/m3) compared with steel balls (7,800kg/m3). This results in lower centrifugal forces and therefore improved kinematics (spin, roll and ball excursion), reduced build-up of heat, lower stress levels and reduced forces on the cage. In addition, ceramic balls are tribo-chemically inert, which reduces adhesive wear and improves the life of the lubricant. Also, unlike steel balls, there is no risk of ceramic balls cold welding to the rings. Assembly and cleanliness are also important in dental bearings. Pritchard said: ‘All Barden dental bearings are assembled in Class 10,000 clean rooms in the UK. ‘Actual assembly takes place in laminar flow clean air, Class 100 benches, with the number and size of airborne contaminants strictly controlled,’ he added.

Barden dental bearings can be supplied with a number of different lubrication options. Bearings can be oiled, where the customer uses their own lubrication, or greased with Barden’s own standard grease or with a type of grease agreed with the customer. Some dental bearings are supplied dry, when the bore is glued onto the rotor shaft. Lubricants must not contain toxic chemicals or carcinogens and must be safe for human contact. This means that there are only a small number of greases that are both safe and effective as a lubricant.

Article Resource: http://factory-automation.blogspot.com/2010/10/ball-bearings-for-high-speed-dental.html

More related post: http://news.thomasnet.com/fullstory/Precision-Ball-Bearings-suit-high-speed-dental-handpieces-586355

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Installation Method of Single Row Deep Groove Ball Bearing Assembly

Although single row deep groove ball bearing components can be a simple installation on the shaft staying the same, and can be up and running immediately, however, if errors occur during installation, early damage is possible generally as rolling single row deep groove ball bearings. Therefore, single row deep groove ball bearing components must be carefully installed in the early time. At the time of installation, you must be careful not to give too much impact, be sure to pay special attention to the installation point, and then start the installation.

In the cylindrical hole single row deep groove ball bearings occasion, the inner ring and shaft, for installation purposes, generally coordinate with a clearance fit. However, in the necessary operation of high-precision and high-speed operation, or a heavy load or withstanding shock loads occasions, the inner ring and shaft combines for an interference fit.

In taper hole single row deep groove ball bearings occasion, because they are installed using an adapter sleeve, even if error of axis dimensions is slightly larger,there will be no problem. Again, in a lot of axial loads occasions, use the stepped shaft as far as possible, contact the inner ring of single row deep groove ball bearings with cylindrical bore with the ledge of stepped single row deep groove ball bearings to used.

First remove the connecting bolts when removing single row deep groove ball bearings. As the thread surface deposits a layer of grease, corrosion products and other sediments, the bolt is not easy to remove, particularly for Severe corrosion bolts, and removal is difficult. You must choose the right tools to disassemble bolt, because the outer hexagonal or hexagon of bolt has been slipping to damage so that removal becomes more difficult. For bolts has rust or with large number of grease, spray at the joining of bolt and nut with solvents (such as rust remover), let solvent goes into thread, so that they are easily removed.

In the removal process of single row deep groove ball bearings, the most difficult job is to remove wheel from the shaft. For key wheels, generally use three-pin puller or four-legged puller for disassembly. Puller should go with the dimensions of wheels, combination right angles hook of every feet of puller with the wheel back side must be suitable, slippage will not occur when putting forth strength. This method is only for relatively wheel removal of small interference fit, for wheels with larger interference fit, often use heating method, or together with hydraulic jacks to demolish.

In the removal process of single row deep groove ball bearings, the most difficult job is to remove wheel from the shaft. For key wheels, generally use three-pin puller or four-legged puller for disassembly. Puller should go with the dimensions of wheels, horses tied to the feet at right angles with the wheel back side with suitable, slippage will not occur when the force imagined. This method only for relatively small wheel removal of interference, interference fit larger wheels, often using heating method, or together with hydraulic jacks to demolish.

Cleaning, cleaning up and assessing quality all parts of single row deep groove ball bearings is a extremely important work after these ball bearings removal. Assessment means that each of the parts and components after operation, compared to the present state of its size, shape, and material properties and component design with the established quality standards, determine which parts can continue to be used, which parts should be repaired, and which should discard and replacenew ones.

The structure and uses of linear motion ball bearing

Structure of Linear motion ball bearing is that, it is equipped with retainer within the outer ring where there is more than one ball in. The balls are in infinite loop motion. Spring retaining ring fixed on both ends of the retainer are fixed with internal circlip,and a gap window is set in the straight track of balls force direction. This part is to enable loading steel balls rolling contact with axis, is relatively mobile with a very low coefficient of friction. Therefore linear motion ball bearings is the most suitable bearings for mechanical equipment, automation equipment, and energy-saving equipment. Linear motion bearings are being increasingly widely used in electronic, mechanical, instrumentation, robotics, tools, machinery, food machinery, packaging machinery, printing machinery, textile machinery, medical equipment, CNC machine tools, automobiles, and other general or specific machinery industry.

Advantages of linear motion ball bearing:

1. As mobile contacts can make the starting resistance of friction and dynamic friction resistance is minimal, so you can save energy, easy access to high velocity.

2. Load increases, but no sensitive changes of friction coefficient, so,under heavy load, minimal friction coefficient and long-term constant precision, which makes the service life longger.

3. Interchangeability is good, convenient installation and time saving and innovative mechanical structure, small, and light weight.

4. Oil-saving procedures, simplify lubrication and maintenance.

5. The bearing with additional oil seal on both sides is also applies in places easily penetrated more dust or foreign bodies.

Pressure ball bearings

Pressure ball bearing divides into one-way (Uni-directional pressure ball bearing)and two-way(Bi-directional pressure ball bearing) two types.

Uni-directional pressure ball bearing is a bearing with steel balls fitted in rolling ring, 90 ° contact angle, can withstand the unidirectional axial load only, and not suitable for high speed rotation. The bearings can be separated into three pieces, and there are arc-shaped deep groove for balls rolling on two gaskets.

Bi-directional pressure ball bearing is a bearing with the intermediate ring and two outer rings installed on the axis, between intermediate rings and the outer ring exsits the steel balls, can be subjected to bi-directional axial load. The outer ring of pressure ball bearings have plane seat type, aligning seat type and aligning washer seat type.

Uni-directional and bi-directional pressure ball bearings generally use steel stamping molding. Large-size bearings or special bearings use brass or mild steel turning retainer.

1,3-disc types: 511XX, $literal, 512XX, 514XX
2,5-disc types: 522XX, 523XX, 524XX

Single row deep groove ball bearings and tolerances

Single row deep groove ball bearings are particularly versatile. They are simple in design, non-separable, suitable for high and even very high speeds and are robust in operation, requiring little maintenance. Deep raceway grooves and the close conformity between the raceway grooves and the balls enable deep groove ball bearings to accommodate axial loads in both directions, in addition to radial loads, even at high speeds.

Single row deep groove ball bearings are the most widely used bearing type. Consequently, they are available from SKF in many executions and sizes:

–open basic design bearings
–sealed bearings
–ICOS® oil sealed bearing units
–bearings with snap ring groove, with or without snap ring
Other deep groove ball bearings for special applications, shown in the “Engineering products” and “Mechatronics” sections, include:

–hybrid bearings
–insulated bearings
–high temperature bearings
–bearings with Solid Oil
–sensorized bearings
–polymer ball bearings
The SKF product range also includes bearings with a tapered bore. This variant is not included in this catalogue. Information will be provided on request.

Tolerances

SKF single row deep groove ball bearings are manufactured as standard to Normal tolerances.

SKF Explorer single row deep groove ball bearings are produced to higher precision than the ISO Normal tolerances. The dimensional accuracy corresponds to P6 tolerances, expect the width tolerance, which is considerably tighter and reduced to

–0/–60 μm for bearings with outside diameter up to 110 mm
–0/–100 μm for larger bearings.
The running accuracy depend on the bearing size and corresponds to

–P5 tolerances for bearings up to a 52 mm outside diameter
–P6 tolerances for bearings above 52 mm up to 110 mm outside diameter
–Normal tolerances for larger bearings.
For bearing arrangements where accuracy is a key operational factor, some SKF single row deep groove ball bearings are also available with accuracy completely to P6 or P5 tolerance class specifications. The availability of these bearings should always be checked before ordering.

The tolerances for classes Normal, P6 and P5 are in accordance with ISO 492:2002.

Article Resource:http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_1_1

Guaranteed methods of quenching technology of deep groove ball bearings

Selecting an appropriate quenching medium is particularly important. It determines the bearing microstructure and properties after quenching. Quenching medium usually has solid, liquid and gas three forms.

Deep groove ball bearings in heat treatment furnace heated to fully austenitic, for obtaining the required organization and performance, it need for a quenching treatment. Workpiece after cooling to obtain martensite organizations, its cooling rate must be greater than the critical cooling rate, but too cool and too fast will make volume shrinkage and microstructure transformation violent, caused a great deal of stress. Thus conditions for martensitic “f” should enable the cooling rate as low as possible.

NTN bearings after correct repairing are the same performance with new bearings. The precision parameter such as its clearance can meet the requirements of new bearings. It is important to understand and identify damage degree to choose the correct rehabilitation program. For example, surface finishing treatment can clear some minor damage, but could not clear the real fatigue and the debris or wear caused by depression. Therefore, if only for the NTN bearing surface finishing treatment, generally it is not suitable for serious injury deep groove ball bearings. And if fully repair remanufacturing technology, the fatigue of bearing layer is completely clear, replace the rolling elements, also cage being undertaken a comprehensive consolidation so that bearings can meet the performance requirements of a new bearing.

Once the deep groove ball bearings injure, they must go through a very rigorous testing procedures to determine whether the injury NTN bearings can be repaired. Bearings must be fully cleaned, and then a very rigorous and comprehensive testing. The first is to detect whether the bearing damage, such as cracks, spalling and thermal discoloration, bearing with these injuries are likely beyond repair and must be scrapped.

Raceway surface of deep groove ball bearings, due to contacting with the roller elements, its running track is the dark side, track attached to the roller surface is within the exception, which may be able to tell the load conditions, so in removing the NTN bearing cases, pay strict attention and observe of raceway surface running track, you will learn the it bears only radial load, subjected to an axial load, tolerance for moment loads, or extreme inequality of rigid on the bearing box.

1, appropriate clearance of NTN bearing, too large will impact, too small will be poor lubrication, may be burnt.

2, improve lubrication quality and control oil pressure, temperature and flow, strengthening the oil filter.

3, geometry and surface quality of NTN bearings and axle should be strictly guaranteed.

4, adopted the fuel and lubricating oil in accordance with the demarcation.

5, take control of engine temperature, overheating or in cold case work is negative. In cold weather, diesel engine should warm up before starting, scroll with the hand crankshaft oil into the friction surface.

Common failure analysis of FAG deep groove ball bearing failure

Bearing is as main parts of locomotives, especially traction motor and axis box bearing, plays an important role on security transport .When locomotive is online, once FAG bearing goes wrong, it will led to whole column train not running, and block transport line, especially passenger train is in a malfunction, it causes bigger negative effect. Once locomotive bearing goes wrong, it is difficult to repair. Therefore, preventing and reducing locomotive bearing fault, is important for security transport of locomotive. So, detect the deep groove ball bearings front bearing with security risks, and ensure qualified bearing parts on the train are.

1. Contact fatigue failure

Contact fatigue failure means, bearing surface is subjected to alternating stress and failure. Contact fatigue spalling happens on the FAG bearing working surface, often accompanied by fatigue crack. Firstly occurs from the contact surfaces of the following maximum alternating shear stress, and then extends to surface forming different peeling shapes. Flaking surface is expanding gradually, and tends to spread to deep, forming a deep peeling. Deep spalling is the source of contact fatigue failure.

2. Wear failure

Wear failure means that the bearing surface’ sliding relative friction causes constant wear and tear of its surface and then failure. Constant wear will cause damage of FAG bearing parts gradually, and eventually led to the loss of dimensional precision of deep groove ball bearings and other related issues. Wear can affect the shape change, clearance increased and surface morphology changes, might affect the lubrication function of lubricants, thus the loss of rotational accuracy of bearings and even fail to operate properly. Wear failure is one of the common failure modes of all kinds of bearings, it is generally divided into abrasive wear and adhesive wear by its wear form.

Serious damage of deep groove ball bearing is often not caused by single reason, but under the several combined effects, and in bad running conditions, leads to serious burning loss of FAG bearing, therefore, after accident occurs, it is often difficult to judge what reasons it is due to, So for discussion convenient, i analyze the causes for you from several aspects.

When bearings are used after a period of time, bearing inner ring, rolling elements and cage, outer ring, raceway etc all have certain defects, and injuries, which causes poor lubrication and fever of FAG bearings. Fever for a long time will cause results below:

1, dilution of bearings lubricant

2, accelerate material fatigue and decline in hardness.

Further vicious circle of these reasons accelerates the bearing overheated then burning loss. Significant displacement of the inner ring of deep groove ball bearings, rolling element out-of-round, overheated, eventually are melt together. When the locomotive is running, if found severe heat and smoke, don’t stop it, and maintain to run to the front station. Because overheated bearings are in the melt state at the moment, once stopped to cooling, you can no longer walk then plug the line.