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Needle Roller Bearing - information from LM Components

A needle roller bearing is a rather special type of roller bearing which uses long, thin cylindrical rollers that look like needles. Ordinary roller bearings rollers are only slightly longer than their diameter, but needle bearings typically have rollers that are at least four times longer than their diameter. Like all bearings, they are used to reduce the friction of a rotating surface.

Compared to ball bearings and ordinary roller bearings, needle bearings have a greater surface area in contact with the races, so they can support a greater load. They are also thinner, so they require less clearance between the axle and the surrounding structure.

Needle bearings are heavily used in automobile components such as rocker arm pivots, pumps, compressors, and transmissions. The drive shaft of a rear wheel drive vehicle typically has at least eight needle bearings, usually four in each U joint, and often more if it is particularly long, or operates on steep slopes.

Race bearing

The rolling elements of a rolling element bearing ride on races. The large race that goes into a bore is called the outer race, and the small race that the shaft rides in is called the inner race.

Design of the race bearing

In the case of ball bearings, the bearing has inner and outer races and a set of balls. Each race is a ring with a groove where the balls rest. The groove is usually shaped so the ball is a slightly loose fit in the groove. Thus the ball contacts each race at a single point. However, a load on an infinitely small point would cause infinitely high contact pressure. In practice, the ball flattens slightly where it contacts each race, much as a tire flattens where it touches the road. The race also dents slightly where each ball presses on it. Thus, the contact between ball and race is of finite size and has finite pressure. It should also be noted that the deformed ball and race do not roll entirely smoothly because different parts of the ball are moving at different speeds as it rolls. Thus, there are opposing forces and sliding motions at each ball and race contact. Overall, these cause bearing drag. The 'V' groove raceways distribute the load evenly over the balls as they travel on four points of contact, creating a straight line rolling effect and decreasing the amount of friction created by a full contact round groove design.

In some uses the two races may be arranged on plates parallel to the plane of the balls, rather than on inner and outer sleeves. In this case, the inner and outer sides of the grooves that form the race should have different angles with respect to this plane, with a steeper angle on the inside groove and a shallower angle on the outside groove, so that each ball can rotate properly without slipping.

Manufacturing process for race bearings

Centre-less grinding

The outer diameter of the races are often centre-less ground using the through-feed process. Centre-less grinding can achieve a very high degree of accuracy, especially when done in stages. These particular stages are: rough, semi finished and finished. Each grinding stage is designed to remove enough stock material from the casing so that the next stage does not encounter any problems such as burning or surface chatter, the finish stage achieves the final dimension. Each grinding wheel at all of the aforementioned stages has a varying degree of abrasive quality, finished clearly being the finest grade to achieve the appropriate stock removal for the next stage and final surface finish required.

Feeding

Bearing casings are introduced to the grinding action via means of a transfer from the delivery system to a pair of in-feed rollers, these in-feed rollers are tapered to a certain angle so that the casings are driven forward until the regulating wheel and grinding wheel catch them and slow them to their grinding speed which can be altered by speed control of the regulating wheel. The casings are constantly rotating and are fed into the grinding area to prevent separation which can cause finish or size problems or even a bump that can potentially crack or destroy casings and will damage the grinding and regulating wheels.

Work rest blade

Whilst grinding, the bearing cases run through the grinding stages in one long tube of casings that is showered with a cutting fluid. The tube rests on a hardened steel blade with an angled, highly ground surface held on a horizontal plane between the grinding wheel and regulating wheel, often named a work rest blade, the tube causes wear on the working surface of the blade so it must be reground at regular intervals. The height of the work rest blade perfectly aligns the bearing casing with the horizontal centreline of the grinding wheel creating a flawless ground finish, the work rest blade height can be altered using packing bars placed underneath the blade, height adjustments must be made depending on the diameter of the casings being ground.

Inspection

Each casing exits the grinding zone onto a high speed conveyor that delivers them to whatever storage and inspection arrangement a manufacturer may have, inspection is also carried out by the operator of the centreless line, by checking finish appearance, diameter, squareness and roundness by use of a dial test indicator in varying configurations, size allowances are permitted but are extremely tight depending on the customers requirements and can vary plus or minus within micrometres of finish diameter, Sizes can be adjusted on all grinding stages via a compensation button which can be pushed to remove extra material in varying micrometre units, the grinding wheel can move away at the same compensation to make the casings bigger if so required if the casing size moves from the operators target, and as the grinding wheel wears. Because a centre-less grinding line has typically three grinding machines the operator must be in complete control and must prevent blockages in transfers, grinding exits and packing areas, also size and quality must constantly be checked, so the operator is always alert while operating the line and checking for problems and quality issues.

Safety

Safety features include an emergency stop button which immediately moves the grinding wheel away from the ground rings on its revolutionary axis. Because of the wheels momentum, it cannot be stopped but the power is cut and the wheel slows naturally, it cannot be reactivated until the emergency stop is reset. After the emergency stop is activated, the size of the workpiece must be re established before the line can be reactivated into production mode.

Finishing

The outer and inner bearing casings are then sent on for raceway grinding, fine finishing and final assembly.

Tapered roller bearing

Tapered roller bearings are rolling element bearings that can support axial forces. In other words, they are good thrust bearings as well as radial forces.

Description

The inner and outer ring raceways are segments of cones and the rollers are tapered so that the conical surfaces of the raceways, and the roller axes, if projected, would all meet at a common point on the main axis of the bearing. This geometry makes the motion of the cones remain coaxial, with no sliding motion between the raceways and the outer diameter of the rollers.

This conical geometry creates a linear contact patch which permits greater loads to be carried than with spherical ball bearings, which have point contact. The geometry means that the tangential speeds of the surfaces of each of the rollers are the same as their raceways along the whole length of the contact patch and no differential scrubbing occurs.

The rollers are stabilized and restrained by a flange on the inner ring, against which their large end slides, which stops the rollers from popping out due to what has become known as the pumpkin seed effect, this is because of their conical shape.

The larger the half angles of these cones the larger the axial force that the bearing can sustain.

Tapered roller bearings are separable into a cone assembly and a cup. The non separable cone assembly consists of the inner ring, the rollers, and a cage that retains and evenly spaces the rollers. The cup is simply the outer ring. Internal clearance is established during mounting by the axial position of the cone relative to the cup, although preloaded installations without clearance are common.

Metric tapered roller bearings follow the designation system defined by ISO 355.

History

In 1895, a farmer and carpenter from Wilmot, Indiana was awarded a patent from the United States Patent Office for his invention of the tapered roller bearing. The purpose of his invention was to improve the performance of wagon wheels used in farming. In 1898, another inventor was awarded a patent for the tapered roller bearing. At the time, this inventor was a carriage maker in St. Louis and already held three patents for carriage springs. However, it was his patent for tapered roller bearings that allowed his company to become as successful as it was.

Tapered roller bearings were a breakthrough at the end of the 19th century because bearings used in wheel axles had not changed much since ancient times. They consisted of a cylindrical seat on the frame and part of the axle enclosed in a case or box that held a lubricant. These were called journal bearings and relied on the lubricant to form a fluid bearing. Without adequate lubrication, journal bearings would fail due to the excessive heat caused by friction. The inventor was able to significantly reduce the friction on his axle bearings by adding tapered elements which actually rolled while transferring the load evenly from axle to frame through the hardened steel inner and outer rings and the rollers. This was his tapered roller bearing.

The tapered roller bearing in combination with modern lubricants is extremely durable and is used almost universally in applications involving rotating axle and transmission shafts. Bearing durability is such that these shafts often require no maintenance for hundreds of thousands of kilometers of operation.

Applications

In many applications tapered roller bearings are used in back to back pairs so that axial forces can be supported equally in either direction.

Pairs of tapered roller bearings are used in car and vehicle wheel bearings where they must cope simultaneously with large vertical, being radial and horizontal, being axial forces. Tapered roller bearings are commonly used for moderate speed, heavy duty applications where durability is required. Common real world applications are in agriculture, construction and mining equipment, sports robot combat, axle systems, gear box, engine motors and reducers, propeller shaft, railroad axle box, differential, wind turbines and so on.

So if you want to learn more about the benefits of needle roller bearings and their applications, why not contact LM Components today?

Further Information

If you would like to know more or are interested in a quote we would be happy to help. Phone us on 01438 791 076, email us at sales@lmcomponents.co.uk or fill in our enquiry form and we will be in touch as soon as possible.

LM Components
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Contact LM Components on 01438 791 076

01438 791 076

sales@lmcomponents.co.uk

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