Chapter 9 - Bearings Flashcards

Question

Describe how preformed bearings are installed and held in place

Answer 1

- held in position by pins or dowels, screws, special bearing designs, compression, or a combination of these - when shells are first installed, they frequently extend past the face of the bearing by a small amount, which is knows as the "crush allowance" or "crush clearance" - if the shells are machined for the bearing, the crush allowance should not be changed - Shells can be installed and used in 2 cases: 1 - where there is no adjustment for wear - that is, when the shells are worn a certain amount, they are replaced (compressor/piston connecting rods) 2 - where adjustment for wear is obtained by shims between the cap and the base. To obtain effective crush or clamping action, the shims must be between the shell halves as well as between the cap and base * - one advantage of shell liners is that, in some designs, the worn liner may be replaced by taking weight of the shaft off the liner (by removing the cap) and rolling out the old liner and rolling in a new liner in the same manner

Answer 2

- fit an clearance is usually set by the dimensions machined into the housing and bushing - held in position by a press fit, a press fit and dowels, or by dowels and with clamping action between cap and the base - small bushings can be reamed to bring the bore to the correct diameter - large diameter bushings often require honing or scraping - if the bushing is supplied with an oil hole, you must align the oil hole with the supply line when pressing in the bushing. - some bushings the oil hole may be drilled after installation and should be scraped to remove high spots caused by the drill - when bushings are worn, they must be replaced

Answer 3

Low Speed Applications - thrust (axial force) is mainly controlled by the use of other components: - - controlled by a shaft collar fastened on the shaft - - thrust washer backed by a sprocket or any other hub High Speed Applications - thrust of the shaft is controlled by the shaft shoulder and a collar that adjusts the amount of end float - end float is the amount the shaft moves axially in a bearing. Also called end play, axial float, or axial displacement

Answer 4

- a revolving ring with a flat contact surface, usually hardened and ground - a stationary ring with a number of flat contact surfaces of a low-friction material - either brass, bronze, or a tinned-on, high-capacity babbitt on a brass backing - these surfaces are separated by lubricant grooves and have chamfers or slopes on the leading edges to set up oil wedges - due to centrifugal force of the bushing ring throwing oil outward, lubricant must be supplied to the centre of most bearing designs

Answer 5

- fixed pad - - a backing which has a convex shape and fits into a mating housing to correct for minor misalignment - floating or tilting pad - - individual load blocks are pivoted on the fixed ring to adjust for thrust and load

Answer 6

- guide bearings - - used for such things as machine tools and gas compressors - - often has a thin layer of bearing material on its surface to reduce friction, but normally operates with lubrication

Answer 7

- split journal bearing, used mostly for high peripheral speeds and shaft stabilization - - shoes are machined cylindrically to fit freely in grooves in a retaining ring - - operation is like a flat, tilting pad, Kingsbury bearing - - surfaces of the shoes and rings are corrosion resistant and low-friction - - bearing is dowelled for installation and to position the bearing axially and prevent rotation - - each shoe has a separate oil inlet, which keeps the operating temperature lower and uniform - - plates are bored so discharged oil is regulated without shaft contact * - carefully inspect the babbitted surfaces, pivoting surface and seat, and the diametral clearance between shoe and journal for signs of wear

Answer 8

- versatility - low-friction operation - ability to be packed to avoid frequent lubrication

Answer 9

- two hardened steel rings, cup and cone for tapered bearings - hardened balls, rollers or needles - separator - for specific applications, bearings may have other parts such as a snap ring used to set axial location

Answer 10

1 - ball bearings 2 - roller bearings - - cylindrical - - tapered - - spherical (surfaces of the rollers are curves across their width and run in concave channels) 3 - needle bearings

Answer 11

- can be used as a guide for axial shaft measurement using recirculating ball bushings - the balls circulate through radial grooves - each carries only a small amount of the toatl load at any one time

Answer 12

- open bearings - - foreign material is kept out of the housing by shaft lip seals or the equivalent - - the lubricant is expected to work through the bearing from one side to the other - shielded bearings (one or both sides) - - the bearing is exposed and the shield will keep out solids but not fluids - - the lubricant is metered out of the housing into the bearing - sealed bearings (one or both sides) - - the bearing is exposed and the seal will keep out solids and fluids - - the lubricant is to be kept in the bearing - sealed and shield bearings (pillow block cartridges) - - conditions are very dirty and abrasive * - when replacing a bearing with a single shield or seal, take care that the new bearing orientation during installation

Answer 13

- radial load - - maximum or total radial load means that all forces on the bearing are in a radial direction, with little or no sideways thrust load - - example - needle bearings / single-row ball bearings - thrust load - - a pure thrust (axial) load means there is no radial load. - - all forces run parallel to the shaft axis - - example - ball / needle thrust bearings - combination thrust and radial load (angular load) - - tapered and roller bearings - - ball bearings with angular contact - - spherical roller, self-aligning bearings

Answer 14

- ball bearings - - high-speed applications - - up to 40,000 RPM or as "rubbing speed" - roller bearings - - low-speed applications - - up to 20,000 RPM, normal range is 2000-20,000 RPM

Answer 15

- as the rated load capacity is increased, the bore stays the same but the diameter of the rolling unit and the width and thickness of the rings are increased - "service weight" or "service use" is a means of classifying bearings with the same types of rolling element and bore for their load capacity - service weight is shown in the code number of the bearings ``` - common service weight groups: 00 series -- ultra light 100 series -- extra light 200 series -- light 300 series -- medium 400 series -- heavy-duty *other grades also available ```

Answer 16

- outside diameter (OD) - bearing width (W) - bore (ID) -- last 2 digits of bearing number -- up to 20 mm, the bore is designated as 00 = 10 mm 01 = 12 mm 02 = 15 mm 03 = 17 mm -- from 20 mm to 480 mm, to find the bore, multiply the last two figures from the bearing number by five (example - 6204 ball bearing has a bore of 04 x 5 = 20mm) -- above 480 mm (number 6296), the bearing size is directly included in the bearing number * - indicated in millimetres (mm)

Answer 17

- are designed as a single piece - cannot be easily separated - example - single-groove, radial ball bearing, double spherical roller bearing

Answer 18

- can be easily taken apart. Consists of one of the following: - 3 separate parts: - - a housing washer - - rolling assembly - - shaft washer - - example - ball / needle thrust bearings (dual-direction thrust bearings use two housing washers, two rolling assemblies and a shaft washer) - 2 separate parts - - one separate ring with the rolling element, and a separator combined with the other ring - - example - taper roller bearing

Answer 19

- used in machines where the bearings are held in alignment by the bores in the housing

Answer 20

- self-aligning bearings can be identified by the curved surface of the outer ring, which gives a choice of positions for the balls or rollers - the degree of allowable misalignment is slight, as the balls or rollers must be in contact with the outer ring at all times - may be internal or external: - internal self-aligning bearing - - the inside of the outer ring is concave - - example - double ball / roller types for heavy-duty loading, single barrel roller types for light loading - external self-aligning bearing - - the outside of the outer ring may be convex - - example - pillow blocks for independent mounting

Answer 21

four-figure code: ?XXX - first figure -- indicates the types of rolling element X?XX - second figure - - indicates the service weight, outside diameter and width. - - this figure ranges from 0 - 4 (00 series ultralight - 400 series heavy duty) XX?? - third and fourth figure -- indicates bore size ``` SKF = indicates manufacturer 6 = Conrad = single-row, deep groove ball bearing 1 = service weight (extra light) 06 = 06 X 5 = 30 mm bore ```

Answer 22

five-figure code: ?XXXX - first figure -- indicates the types of rolling element X?XXX - second figure -- indicates outside diameter (OD) XX?XX - third figure -- indicates service weight, outside diameter and width. XXX?? - fourth and fifth figure -- indicates bore size ``` SKF = indicates manufacturer 22 = double spherical roller, self-aligning 3 = service weight (medium) 10 = 10 X 5 = 50 mm bore ```

Answer 23

Tapered-bore bearings are like the standard bearings, but are followed by a (K) to indicate a tapered bore ``` FAG = indicates manufacturer 6 = Conrad 1 = service weight (extra light) 08 = 08 X 5 = 40 mm bore K = tapered bore ``` * K = designates the common 1-in-12 taper * K30 = designates the 1-in-30 taper used for larger bearings

Answer 24

- it compensates for expansion of the inner ring or for contraction of the outer ring when interference fits are used - it compensates for differential expansion of the two rings when the inner ring of the bearing operates at a higher temperature than the outer ring - it affects the end play of ball journal bearings and their capacity for carrying axial loads. The greater the clearance, the greater the capacity for supporting axial load

Chapter 9 - Bearings Flashcards

(102 cards)