Ball bearing

In some applications, steel-ball bearings do not have the necessary hardness and corrosion resistance. Microwelds tend to occur between the balls and the race which roughen the surges and contaminate the lubricant. These problems can be alleviated by coating the steel balls with titaniiun carbide or by using monolithic silicon-nitride balls. 

TiC Coatings. TiC coatings by CVD on steel balls (usually SAE 52100 or AISI440C) provide much increased hardness, a smoother surface, and a lower coefficient of friction.0 100 

Monolithic Silicon Nitride. Solid Si3N4 balls are replacing steel balls because of their high hardness, chemical resistance, and low density (a feature important in high-speed applications). Further improvement results from coating the silicon nitride with CVD TiN.OO 

Applications. Typical applications of TiC-coated and solid silicon nitride balls are  

Ceramic composites, which consist of a ceramic fiber or whisker reinforcement embedded in a ceramic matrix, are less susceptible to the brittle failure which is characteristic of bulk ceramics because the reinforcement intercepts, deflects, and slows crack propagation (see Ch. 14, Secs. 6 and 7). At the same time, the load is transferred from the matrix to the fibers to be distributed uniformly. A common ceramic composite consists of a SiC-fiber array and SiC or Si3N4 matrices produced by chemical-vapor infiltration (CVI). Densities approaching 90% are achieved.0 10  

Elastohydrodynamic Lubrication (EHL) In journal bearings or other surface area interactions under lubricating conditions, deformation of the materials or the influence of pressure on viscosity of the lubricant can be ignored. However, in roller and ball bearings, the point of contact is deformed elastically tmder the high load pressure. This also increases the pressure on the film lubricant which increases in viscosity according to the equation 

The film thickness is about 10-50 pm and increases as the speed is increased. An increase in load has the effect of deforming the metal surfaces more, causing an increase in contact area rather than a decrease in film thickness. 

An important characteristic of EHL is the specific film thickness (.1) which is the ratio of the film thickness (h) to the composite roughness (cr) of the two surfaces, that is. 

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Recently ultrasonic spectroscopy has become a more common NDE technique and specialized instruments are commercially available now for inspection of aerospace structures, ball bearings, and even concrete [2],[3]. 

The performance of the classifier has been verified using a number of practical applications, such as civil engineering [3], inspection of aerospace composite structures, ball bearings and aircraft multi-layer structures. Here we present shortly some results, focusing on detection of disbonds in adhesively joint multi-layer aerospace structures using Fokker Bond Tester resonance instrument, details can be found in [1]. 

We have presented a neural network based spectrum classifier (NSC) aimed at ultrasonic resonance spectroscopy. The ultrasonic spectroscopy and the NSC has been evaluated in many industrial applications, such as concrete inspection, testing of aerospace composite structures, ball bearings, and aircraft multi-layer structures. The latter application has been presented in some detail. 

In the converse situation free of gravity, a drop assumes a perfectly spherical shape. At one point, the U.S. Space program tested this idea with the solidification of ball bearings from molten metal drops in microgravity conditions. 

Brinell. The first rehable indentation hardness test was developed by BrineU in 1900 and used ball bearings to make indentations in steel (1). The technique has remained rehable and essentially unchanged for nearly 100 years. The test, described by ASTM Standard ElO (2), is stiU in use. 

In the knee, the menisci form an interarticular fibrocartilage base for femural and tibial articulation. The menisci form a crescent shape in the knee. The lateral meniscus is located on the outer side of the knee, and the medial meniscus is located on the inside of the knee. If the knee bends and twists the menisci can overstretch and tear. Menisci tears occur frequentiy and the knee can sustain more than one tear at a time. If not treated appropriately, however, a menisci tear can roughen the cartilage and lead to arthritis. A meniscus tear acts like grit in the ball bearings of a machine. The longer the torn tissue remains affected, the more irritation it causes. 

Despite this past downward trend, which has persisted in the United States since 1979 with modernization of large suppHers in Japan and Europe, growth of 2 to 2.5% is now expected into the mid-1990s. This reflects increased demand for some military appHcations and commercial aircraft, plus growing needs for farm and constmction machinery (2). U.S. production of the relatively new ceramic ball bearings is expected to increase distinctively by about 50% yearly to reach 17 million in 1993 (3). 

The axial flow compressors in aero gas turbines are heavily loaded. The aspecl ratio of the blades, especially the first few stages, can be as high as 4.0, and the effecl of streamhne curvature is substantial. The streamline configuration is a function of the annular passage area, the camber and thickness distribution of the blade, and the flow angles at the inlet and outlet of the blades. The shafts on these units are supported on antifriction bearings (roller or ball bearings). 

The values of these factors are provided by the bearing manufacturers in their catalogues, based on the ratios F /Cg and F IFy, where C is the static load rating in kg or N (based on a contact stress of 4200 MPg for ball bearings and 4000 MPj, for roller bearings, also provided in these catalogues. MPg is the unit of stress in Mega-Pascals. 

C = basic dynamic load rating in kg or N (provided by the bearing manufacturer). It is the load which will give a life of 1 million revolutions P - equivalent dynamic bearing load in kg or N p = exponent of the life equation, which depends upon the type of contact between the races and the rolling elements. It is recommended as 3 for ball bearings and 10/3 for roller bearings = speed of the machine in r.p.m. 

The easy movement of the electrons gives the high electrical conductivity of metals. The metallic bond has no directionality, so that metal ions tend to pack to give simple, high-density structures, like ball-bearings shaken down in a box. 

Fig. 10.4. Ball bearings can be used to simulate how atoms are packed together in solids. Our photograph shows a ball-bearing model set up to show what the grain boundaries look like in a polycrystalline material. The model also shows up another type of defect - the vacancy - which is caused by a missing atom.

Demonstrations (a) Give four injection-moulded close-packed planes to each student to allow personal building of f.c.c. and c.p.h. (b) Atomix atomic model on overhead projector to show atom packing (Emotion Productions Inc., 4825 Sainte Catherine O, Montreal 215PQ, Canada) or ball bearings on overhead projector. 

Metal atoms tend to behave like miniature ball-bearings and tend to pack together as tightly as possible. F.c.c. and c.p.h. give the highest possible packing density, with 74% of the volume of the metal taken up by the atomic spheres. However, in some metals, like iron or chromium, the metallic bond has some directionality and this makes the atoms pack into the more open b.c.c. structure with a packing density of 68%. 

These quenched and tempered stainless steels are ideal for things like non-rusting ball-bearings, surgical scalpels and kitchen knives." ... 

These are single row ball bearings capable of handling extreme axial or thrust loads in one single direction only. They are generally mounted in pairs to handle any opposite axial/thrust loads. 

Improper procedure when mounting the bearing on the shaft is one of the most common causes of premature failure. Roller bearings and ball bearings are precision devices, and correct installation... 

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