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

http://www.bardenbearings.co.uk/article28.html

Installation method and use of single row deep groove ball bearings

Bearings are precision components, and thus require considerable caution when used, even using the high performance of single row deep groove ball bearings, if used incorrectly, could not achieve the desired performance, and easy to make bearing damage. Therefore, you should be aware of the following considerations:

First, keep the bearings and the surrounding environment clean

Even if invisible dust into the bearing, bearing wear, vibration and noise will increase.

Second, be careful when you install

Do not punch powerfully, does not tap the bearings directly with a hammer and transmitting pressure on bearing through the rolling elements pressure is not allowed. Don’t open the single row deep groove ball bearings package until installing. General grease lubrication, do not clean bearings and fill the grease directly. Oil lubrication, generally do not have to clean, however, instruments or high speed bearings,clean bearing with clean oil, removing rust inhibitor coating on the bearing. Bearings after removing rust, are easy to rust, so they cannot be placed at random.

Third, use appropriate and accurate installation tools

Installing approach of single row deep groove ball bearings varies due to the bearing structure, conditions and fit. As generally are axis rotation, take the inner ring interference fit. Bearings with a cylindrical bore installation, press into with the press, or hot charging method. Bearing with tapered bore installation, directly fix on the tapered shaft or using an adapter sleeve. Using special tools as much as possible, avoiding using fabric and staple fiber or something.

Four, prevent corrosion of the bearings

Fully wash away the sweat on his hand when taking bearings directly by hand, and coated with high quality mineral oil before operation, paying particular attention to rust during the rainy season and summer.

However, in some special operating conditions, single row deep groove ball bearings get more longer life than the traditional calculation, especially under light load conditions. These special conditions are, when scrolling surface (track and rolling elements) is effectively separated by lubricant film and limiting surface damage caused by pollutants. In fact, in ideal conditions, the so-called permanent bearing life is possible.

Bearing life

Single row deep groove ball bearing life is detemined revolutions (or number of working hours in a certain speed), definition: bearings within this life, in any of its initial fatigue damage to the bearing rings or rolling on (off or defect). In tests in the laboratory or in actual use, however, can be clearly seen, looks the same bearings under the same working conditions, real life vary greatly. In addition there are several different definitions of bearing “life”, one of the so-called “working life”, represents a single row deep groove ball bearings in real life can be achieved before the damage is caused by wear and tear, damage is usually not the fatigue, but rather caused by wear and tear, corrosion, seals damage reasons.

Installation and removal of SKF 623 single row deep groove ball bearings

Files download: https://docs.google.com/document/d/1bOu_8uCmO1j5i3PiaaDzEOAvb7dvoUd6Ky_SXyCiY1g/edit?pli=1

Notes
Install bearings in a clean environment. Check the bearing housing, shaft and bearing components to ensure that it is clean.

The bearings should be left in the original packaging until the moment before installation to prevent pollution.

Size and shape tolerances of all components in contact with the bearing should be checked.

The diameter of cylindrical shaft neck, usually uses a micrometer to measure each of the four points of the three planes. Survey record forms can be obtained here. Filling out the measurement records and archives appropriately helps future tracking.

The bore diameter of the cylindrical bearing box, usually uses inner gauge to measure each of the four points of the three planes. Survey record forms can be obtained here. Filling out the measurement records and archives appropriately helps future tracking.

Install Program
Wipe off the rust inhibitor in bearing bore and the cylindrical surface.
If bearings greased and use in extremely high or low temperatures, or grease and rust inhibitors are not compatible, it need to be carefully cleaned and dried.

Axis is an interference fit
Slightly lubricate the hole of the bearing with mineral oil.
Ensure that the bearing is vertical with axis after installed.
When installing, use appropriate sleeve to force on the inner ring.

The bearing box for the interference fit
Slightly lubricate the outer peripheral surface of the bearing with mineral oil.
Ensure that the bearing is vertical with bearing box after installed.
When installing, use the appropriate sleeve to force on outer ring.
Shaft and bearing box for interference fit
Slightly lubricate the inner-hole of the bearing with mineral oil.
Slightly lubricate the outer peripheral surface of the bearing with mineral oil.
Ensure that the shaft and bearing box are perpendicular to the axis after adapted and installed.
When installing, use the appropriate sleeve to force on the inner and outer rings at the same time.
Push the bearing to the correct location.
Fit with locking devices.
Determine shaft or outer ring can easily turn.
Bearings lubricate using oil, pay attention to use the correct lubricants and dosage.
Bearings lubricate using grease, be coupled with the grease.
If the bearing is to be put into the shaft and the bearing box both, grease may needs to earlier be added.
Under normal circumstances, this bearing should be completely filled grease, except applied to high speed. Fill grease in the remaining space in the bearing box (approximately 30-50%).
SKF grease LGMT 2 can be used for the general working conditions. Considering the actual working conditions to select grease, see SKF condensed grease selection guide.

Approach to deep groove ball bearings trouble

When checking the deep groove ball bearing equipment after periodic maintenance, operation and replacement of external parts of deep groove ball bearings are removed, you need to determine whether deep groove ball bearing parts in sequence can be used again and record the use of good or bad. Also carefully investigate and record down the appearance of deep groove ball bearing. In order to identify and investigate remaining quantity of lubricant, after sampling, properly wash deep groove ball bearings. In order to achieve higher device performance and minimum maintenance costs reliably, you must follow the correct approach. This includes the storage, removing, cleaning, testing and installation of deep groove ball bearings. Service life of any deep groove ball bearing depends largely on maintenance and care it receives. In industrial applications, in particular, often poor working conditions, loads, dust and pollution is a common scale.

Secondly, check damage and abnormalities of the raceway of deep groove ball bearings, rolling surface and the mating surfaces and wear of the cage, in particular to observe the running track of the raceway surface. Judge whether the bearing will use again after considering how bearing damages, machine performance, importance, operating condition, inspection cycles ,etc.

In inspection results, if found deep groove ball bearings are damaged and exceptional conditions, follow the identified cause of bearing damage to formulate policy responses. Also, check the results, if deep groove ball bearings have several flaws(inner and outer rings, rolling elements, cages, any exists cracks and debris), they cannot be used again, need to be replaced with a new one.

It applies to all anti-friction deep groove ball bearing design. Deep groove ball bearings are stored with special corrosion resistant coatings available for selection, but the majority of deep groove ball bearings are made of anti-corrosion material. When handling and storing deep groove ball bearings, you must take care to ensure that they will not rust or corrode. Even wet or unprotected chemical gloves left by hand causing etching in a small area, which could lead to fatigue of deep groove ball bearings.

Common problems and solutions When installing deep groove ball bearings

1, Any requirements on the mounting surface and the installation location of deep groove ball bearings?

Yes. If the scrap iron, burrs, dust and other impurities from entering in deep groove ball bearings, the bearing in operation will produce noise and vibration, or even damage deep groove roller and steel balls. Therefore, before the installation of deep groove ball bearings, you must make sure that the installation surface and environment clean.

2, Do deep groove ball bearings need cleaning before installation?

Deep groove ball bearings are coated with antirust oil, you need to carefully clean them with cleaner gasoline or kerosene, and then coated with a clean high quality or high temperature lubricant before installation. Influence of cleanliness on the service life of the bearing and vibration noise was considerable. But what we want to remind you is: sealed bearings do not need cleaning and refueling.

3, How to choose the right grease?

Lubrication on the operation and life of has a very important impact on the deep groove ball bearings. I briefly describe the general principles of selection of deep groove ball bearing grease. Grease is made of base oils, thickeners and additives. Grease functions of different types and same type with different brands vary, be sure to pay attention to duing to corresponding speed limit is different. Grease performance mainly determines by the base oil. Low viscosity base oil is suitable for low temperature, high speed situation, while high viscosity oil is suitable for high temperature, high-load situation. The thickener is also related to the lubrication function. Water resistance of the thickeners determines the water resistance of the grease. In principle, grease with different brands cannot be mixed, and, even if grease with the same kind of thickeners, also has a negative impact on each other due to different additives.

4, The more grease,the better when lubricating the deep groove ball bearings?

When lubricating bearings, the more grease,the better, this is a common misconception. Too much grease in bearings and bearing interior will cause excessive mixing of oils and fats, which results in extremely high temperatures. Number of bearing lubricant filling is covered with 1/2~1/3 bearing internal space,reduced to one-third when high speed.

5, How to install and disassemble the deep groove ball bearings?

Do not hammer directly on the surface and non-bearing surface of deep groove ball bearing when installation. Let bearing be an average force with block, sleeve or other installation tools (Tools) . Never install using the ball driving force. If the mounting surface is coated with lubricating oil, it will make the installation more smooth. If combined with interference is greater, put bearing in mineral oil, heated to 80~90℃ and install as soon as possible. Strictly control oil temperature not exceeding 100 ° c to prevent the effect of tempering hardness reducing the impact and recovery. Removing when you encounter problems, we recommend that you use the removal tool to pull on the inner ring at the same time carefully pouring hot oil, and heat makes the bearing inner ring expanding so that making it more prone to shedding.

Purpose and method of preload of deep groove ball bearings

What Is Bearing Preload?

Bearing preload is related to the issue of clearance and can be critical for the proper functioning of your bearing. There are multiple techniques and ways of looking at the preload process, and we will examine them in depth here. A bearing needs to be fitted with a shaft and housing and will have some level of clearance, meaning there will be some give between the different parts of the ball bearing. To remove this internal clearance and create an interference fit, a preload is necessary. The preload essentially describes the process wherein a permenant thrust load is applied to the bearing, essentially using force to push the bearing so that it is secure in the groove and has no axial clearance.

Do not allow powerful punch, tap TIMKEN bearings directly with a hammer and transmit pressure through the rolling element.

Using special tools as much as possible, avoid using fabric and staple fiber or something.

Even invisible micro dust caming into the TIMKEN bearings, also increase the bearing wear, vibration and noise.

When directly taking deep groove ball bearings with hands, fully wash away the sweat on his hand is necessary, and coated with high quality mineral oil before operation. Paying particular attention to rust during the rainy season and summer.

In some special operating conditions, deep groove ball bearings can be obtained relatively longer than the traditional calculation of life, especially under light load conditions. These special conditions are, rolling surface (track and rolling elements) were effectively separated by lubricant film and no surface damage by limiting pollutants enter. In fact, in an ideal condition, the so-called deep groove ball bearing with permanent life is not impossible.

(1) right decide about radial direction of the axis and axial direction, inhibit the shaft of the beating at the same time.
(2) increasing bearing rigidity. The spindle of the machine uses bearing, SKF deep groove bearing for differential mechanism pinion by bike.
(3) prevent vibration in axial direction and abnormal noise due to resonance. Small motor uses bearing.
(4) inhibit rotate and slide of rolling elements,including revolution slide and rotation slide. High speed rotating radial spherical plain thrust bearings, thrust ball bearings.
(5) for rings, keep in the correct position of rolling elements. use thrust ball bearings, spherical roller thrust bearings on the horizontal axis.

Preload method: locate the preload is to reset the SKF bearing the relative positions of axial direction, also does not change the preload method in use. Here are some examples:
(1) method that in order to implement preload adjusted width difference in advance or combinations of axial clearance of the bearing after fastening.
(2) method that using the adjusted size of liner and wedge, so that the bearing preloads.
(3) method that after tightening the screw and nut which can adjust the axial direction clearance. On this occasion, in order to get the appropriate amount of preload, determine the starting friction torque while adjusting.

Check more bearing preload information at http://www.nmbtc.com/bearings/engineering/preload.html and http://www.gobearings.com/preload_methods.htm.

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.