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normal speeds with grease or oil lubrication.

Ball bearings with ABEC 5 tolerances or better and ring-piloted composition cages lubricated with an efficient, non-churning, cooling oil-mist system have exceptional high-speed ability.

In the case of duplex mountings, as frequently used in a high- speed machine tool spindles, bearing preload and contact angle affect the permissible speeds.

The values in the accompanying table may be used as a general guide for determining the safe maximum speed of standard types of Timken ball bearings. To obtain the speed value for any bearing size with inner ring rotating, multiply the pitch diameter in millimeters (or, in the case of extra-small inch dimension bearings, the nearest millimeter equivalent) by the speed in revolutions per minute. Refer to page A164 for the most suitable bearing type, cage style, tolerance guide and type of lubrication.

For outer ring rotation of ball bearings, multiply the speed value (pitch or mean dia. in. mm x RPM of the outer ring) by the following factors before referring to the table of speed values.

Although the speed values shown in the tables on the following page are based on many years of research and accumulated data, numerous application of Timken bearings are successfully operating with speed values far in excess of those tabulated. Such applications require particular consideration of proper tolerance grade, lubrication, the effect of centrifugal force on rolling elements and other factors. For further information consult your Timken representative.

Conversely, under certain application conditions of load, temperature, contamination, etc., limiting speeds may be less than the figures shown. These values do not apply to certain special bearings, such as radial Tri-Ply series, square or hex bore bearings.

BALL BEARING SERIES FACTOR

Extra-small (30 and S) and extra-light (9100 and M9300) 1.3

Light (200, 5200 and 7200) 1.5 Medium (300, 5300 and 7300) 1.7

The speed capability of a bearing in any application is subject to a number of factors including:

•

Temperature.

•

Bearing setting or clearance.

•

Lubrication.

•

Bearing design.

The relative importance of each of these factors depends on the nature of the application. The effect of each factor is not isolated – each contributes in varying degrees, depending on the application and overall speed capability of the design.

An understanding of how each of these factors affects performance as speeds change is required to achieve the speed capabilities inherent in a bearing.

SPHERICAL AND CyLINDRICAL ROLLER

BEARINGS

For Timken cylindrical and spherical roller bearings, the thermal speed ratings are listed in the bearing tables. These values have been determined by balancing the heat generated within the bearing with the heat dissipated from the bearing. In calculating these numbers, the following assumptions have been made:

•

The radial load is five percent of the static load rating.

•

For oil, it is assumed to be in a bath with the fill to the middle of the lowest rolling element. For grease it is assumed a 30 percent bearing cavity fill.

•

The oil viscosity is assumed to be 12 cSt (ISO VG32) operated at 70˚ C, (158˚ F) and the grease base oil viscosity is assumed to be 22 cSt operated at 70˚ C (158˚ F). The bearing and its components are at 70˚ C and the bearing

environment is at 20˚ C (68˚ F).

•

The housing and shaft are steel or cast iron.

•

The bearing rotational axis is horizontal.

•

The outer ring is stationary and the inner ring is rotating.

•

The bearing radial internal clearance complies with class normal and standard fits are used.

•

The bearing does not contain seals.

•

The bearing does not experience misalignment or axial load.

The thermal speed ratings are for reference only and can be considerably lower or higher depending on your application. Consult your Timken representative for more accurate information regarding a bearing’s speed limitations in your application.

A

Note: Single or double normal contact (P or PP) sealed bearings should not exceed 300,000 PDN. Consult your Timken representative for limiting speed of RR or Tri-Ply sealed bearings.

* Bore + O.D. 2

(1) _{For oil bath lubrication, oil level should be maintained covering between} 1_{⁄3 to} 1_{⁄2 up} from the bottom of the lowest ball.

RADIAL BALL BEARINGS dm X N VALUES (dm* IN MILLIMETERS X RPM)

Bearing Type ⁄ Series Cage Type ABEC  ABEC  ABEC  and 

Circulating

Grease Oil() _{Grease Oil}() _{Grease Grease Oil}() _{Oil Mist}

BALL BEARINGS

SINGLE-ROW

Non-Filling Slot Ball Piloted Molded Nylon(PRB) 250,000 300,000 250,000 300,000 — 300,000 300,000 300,000 9300K, 9100K

200K, Pressed Steel, Brass 300,000 350,000 300,000 350,000 — 350,000 400,000 450,000 300K, Ring Piloted Molded Reinforced Nylon(PRC) 350,000 400,000 350,000 450,000 — 400,000 550,000 650,000 XLS, and variations Composition (CR)

Filling Slot Ball Piloted Molded Nylon(PRB) 250,000 250,000 — — — — — — 200W and variations Pressed Steel 250,000 300,000 — — — — — — 300W and variations

Angular Contact Ball Piloted Pressed Steel, Molded Nylon (PRB) 200,000 300,000 300,000 350,000 — — — — 7200WN Ring Piloted Brass (MBR), Ball Piloted Br (MBR) 300,000 400,000 — — — — — — 7300WN Ring Piloted Molded Reinforced Nylon (PRC) 350,000 400,000 350,000 400,000 — — — — Angular Contact-

Extra precision 2M9300WI, 2M200WI,

2M300WI, 2M9100WI, Ring Piloted Composition (CR) or (PRC) 350,000 400,000 750,000 1,000,000 1,200,000

2MM9300WI, 1,000,000 1,400,000 1,700,000 2MM9100,

2MM200WI, 2MM300WI

DOUBLE-ROW

5200 Ball Piloted Molded Nylon (PRB), Pressed Steel 250,000 300,000 — — — — — — 5300 Ball Piloted Brass (BR)

A

The usual measure of the speed of a tapered roller bearing is the circumferential velocity at the midpoint of the inner race large end rib (Fig. A-44). This may be calculated as:

Rib speed: Vr = Dmn 60000 (m/s) = Dmn 12 (ft/min) where:

Dm = Mean inner race large rib diameter mm, in.

n = Bearing speed rev/min

Fig. A-45 is a summary of guidelines relating to speed and temperature based on customer experience, customer tests and research conducted by The Timken Company. Consult your Timken representative with questions regarding high-speed capability.

The mean large rib diameter at the midpoint of the roller end contact can be scaled from a drawing of the bearing, if available, or this diameter can be determined by consulting your Timken representative. The inner cone mean large rib diameter can be approximated by taking 99 percent of larger rib O.D.

DN values (the product of the inner race bore in mm and the speed in rev/min) are often used as a measure of bearing speed by other bearing manufacturers. There is no direct relationship between the rib speed of a tapered roller bearing and DN value because of the wide variation in bearing cross sectional thickness. However, for rough approximation, one meter per second rib speed is about equal to 16,000 DN for average section bearings. One foot per minute is equal to approximately 80 DN.

In document Manual del usuario de SAP Crystal Reports para Enterprise (página 144-155)