Archive for August, 2011

The Baldor-Reliance Super-E

Friday, August 19th, 2011

In the mid-1970s, a southeastern tire manufacturing plant asked Baldor if it were possible to increase the operating efficiencies of motors in their plants. Baldor engineers determined that considerable energy savings could be gained from a better motor design. By adding more copper to the windings, upgrading the laminations to a higher premium-grade steel, designing precision air gaps between the rotor and stator, and reducing fan losses in the motor, Baldor was able to supply the plant with the premium efficient motors it needed.

This was the birth of the Baldor Super-E®. Today’s upgraded and expanded Super-E product line offers some of the highest levels of efficiency in more than 600 stock motors rated from 1/2 to 15,000 horsepower. Super-E, severe duty, close-coupled pump, IEEE 841, washdown, and explosion-proof models are also available with a three-year warranty or better. (Our IEEE 841 motors have a five-year warranty.) Called a “key breakthrough” by the Consortium of Energy Efficiency, the Baldor Super-E was recognized by the CEE in 1998 as the first premium efficiency motor line to meet their stringent efficiency criteria citing, “For the first time, one manufacturer will carry all qualifying products.” In 2001, the CEE efficiency levels were adopted as the NEMA Premium® efficient levels and expanded to 500 horsepower.

 Premium Efficiency Pays for Itself

To understand what a motor really costs, compare initial purchase price with the cost of theelectricity it uses over its working lifetime. Often, too much attention is paid to purchase price. For most motors, this initial cost represents less than two percent of its lifetime cost. Electricity accounts for about 97 percent. Baldor Electric Company’s motors and drives save customers money every minute they operate. Whether it’s lower energy costs or greater reliability, these savings go straight to the bottom line. Baldor is the industry leader in overall efficiency ratings. Better than 96 percent of the energy used by some of Baldor’s Super-E motors is converted to mechanical work. The Baldo•Reliance Super-E runs cooler and longer with greater reliability than any other industrial motor. When you consider that a typical 50 horsepower motor costs over $36,000 to operate continuously in a year, it’s easy to see how just a few percentage points of higher efficiency can quickly reduce electricity costs. Even seemingly modest percentage point differences in efficiency ratings can yield substantial electricity cost savings when the motor is operating continuously every day.

Baldor Electric Company — First in Energy since 1920

Tuesday, August 16th, 2011

The history of energy efficiency in industrial motors is really the story of Baldor Electric Company. For almost 100 years, Baldor has led the industry in developing products that deliver greater performance and reliability while using less electricity. From the company’s founding in the 1920s through today, Baldor has introduced one efficiency enhancing advancement after another. In fact, many of the advancements initiated by Baldor have later been adopted as industry standards.

The issue of energy efficiency for electric motors and drives is becoming increasingly relevant as electricity costs continue to rise. Companies are now competing in an environment of rising energy costs and the uncertainty of available electricity. These dynamics require the kind of forward-thinking industrial motor, drive, and generator supplier that anticipates customer needs and delivers products that save money and improve productivity. That company is Baldor.

 

Why is Energy Efficiency Important?

Electric motor-driven systems used in industrial processes consume some 679 billion kWh or 63 percent of all electricity used in U.S. industry, according to a Department of Energy report published in 1998. The report goes on to reveal that industrial motor electricity consumption could be reduced by up to 18 percent if companies were to apply “proven efficiency technologies and practices.” Specifically, the DOE recommends motor efficiency upgrades and application improvements. The purpose of this brochure is to show you the energy saving opportunities from using premium efficient motors and drives. The opportunities are real.

In 1992, the Energy Policy Act (EPAct) established minimum efficiency standards for industrial electric motors built after October 1997. Yet, only about 10 percent of all motors in use today comply with the minimum efficiency levels the Act mandates. When you factor in the savings potential of using adjustable speed drives in many applications, it’s easy to see that the environment, along with your profitability, stand to benefit significantly.

Timken Extra-Precision Bearings Part 4 of 4

Wednesday, August 10th, 2011

PRELOADING

Description

Preload is defined as the internal load existing in any device before an external working load is applied. The application of preload to ball bearings is utilized to increase the ball bearing unit’s rigidity; to guarantee intimate contact between the rolling elements and the races at all times, thus insuring complete utilization of the actual running accuracies of the bearings; to elimi­nate the possibility of looseness from all phases of bear­ing operation; and to obtain the added effects on the bearing’s basic geometry such as a change in contact angle, a change in strain pattern or a reduction of the minute inaccuracies caused by surface irregularities.

 

Selection

The selection of the type of bearing and the mount­ing arrangement to be used is a function of the operat­ing conditions and requirements of the assembly. A realistic evaluation of these conditions and require­ments must be made in order to establish the design parameters. Often these parameters are contradictory in practice; therefore, the designer must strive for the optimum design through compromise. Design consider­ations, such as speed range, operating loads, rigidity requirements, accuracy desired, and ambient and oper­ating temperatures, determine which type bearing must be used, which type mounting and lubrication is re­quired and whether or not preload is necessary. These factors also dictatethe magnitude of the preload required and the method of its application.

If the design dictates that preload is required, a proper level must then be chosen. It should be stressed that while preload on bearings increases their rigidity it also reduces their life expectancy and increases their frictional drag. Therefore, the choice of the preload level to be incorporated must be made with care. Too often, however, the basic design parameters are contradictory and a compromise preload must be selected.

The Fafnir Bearing Company offers three standard preload levels for the various bearing types and sizes. These preload levels were established to satisfy most application requirements.

In the determination of limiting operational speeds corresponding to the permissible ball bearing preloads for machine tool spindles, many influencing factors are involved. Among those considered are spindle mass and construction; type of mounting; spindle rigidity; accu­racy requirements; spindle loads; service life; type of service, intermittent or continuous; and method of lubrication.

Because of the complexity of this subject, encom­passing all of the factors is difficult. Over a period of several years, data from actual field applications has been accumulated and compiled.   Extra precision ball bearings of the three basic series are included. In certain applications, such as the high-speed motorized spindles, specially preloaded extra-precision ball bearings are required. These bearings are zero preloaded (desig­nated FS-223). This means that the faces of the inner and outer rings are flush ground under negligible load.

Width Tolerances

The width tolerance for individual inner and outer rings is +.000 to —.005, but to allow for face grinding for various preload levels the total width tolerances for duplex pairs of bearings are as follows:

NOMINAL BORE MILLIMETERS                      WIDTH TOLERANCE

       over                   inclusive                      maximum            minimum

o

80

+.000

-.020

80

180

+000

-.030

 

If additional bearings are involved, the total width tolerance is in proportion to the number of bearings.

 

Timken Extra-Precision Bearings Part 3 of 4

Thursday, August 4th, 2011

SHAFT AND HOUSING DESIGN

Shafts

Shafts  are generally made from steel, hardened and ground all over. During the  design of a spindle or shaft it is highly desirable to plan the design  so that the shafts can be ground all over from one setting as a final opera­tion to assure true balance and running accuracy.  This is a basic requirement  for extreme accuracy or high­speed operation.

Housings

Housings  are generally made of cast iron and usually are seasoned to lessen possible distortions. The bore of the housing should be ground or precision bored and checked  at a number of points throughout its length and diameter to assure that it  is uniformly round and not tapered. It is preferable to mount the bearings in one casting. In this way the two or more housing bores required can be machined during one setting, thereby, helping to assure accurate alignment.

In many applications, a quill-type design is required in order to obtain spindle adjustment. This type of assembly can be advantageous,
in certain applications, in that it allows assembly of the bearings on the shaft and insertion of the bearings and shaft into a housing as a
bench assembly. Quill-type designs are also used when the main frame is made of materials having low hardness such as aluminum.

Where screws are used to fasten parts into the main housing, adequate section should be left under the screw holes to prevent
distortion of the housing bore when the screws are secured and the covers or other parts are pulled tightly into place.

Bearing Spacers

Spacers mounted between units of a pair of bear­ings are preferably made of steel, hardened and ground and should be sturdy in cross-section. The length should be produced by grinding the inner ring spacer and outer ring spacer simultaneously. It is important that faces of the spacers are square and that their parallelism is the best possible. All corners should be rounded to remove sharp edges and burrs.

The inside diameter of the inner ring spacer should clear the shaft, but not be so loose as to make it possible to mount and run them
eccentrically. For short spacers and high operating speed a clearance of less than .001″ over the maximum shaft diameter is generally satisfactory. For long spacers and low speeds this clear­ance may be increased to prevent the shaft from dis­turbing the face parallelism of the spacer.

The outside diameter of the outer ring spacer should be about .001″ less than the minimum bore of the housing. The overall design of the inner ring and outer ring spacers should be made so that a minimum of dead air space is left in the cavity between the bearings.

Housing Seals

A labyrinth combination of slinger and end cover provides a highly effective seal against intrusion of foreign material. This seal
design is recommended for use over a wide range of speeds. For exceptional slow speed applications a combination of slinger and com­mercial contact type seal is usually employed.

Slingers should be completely machined to assure true running. Their diameters should be concentric with the bore. The outside diameter of the slinger is often tapered, to throw off cutting compounds, coolants, etc., from the point at which such liquids may enter the spindle. A drip or runout groove adjacent to the open lip of the end cover is highly desirable and practical.

The axial clearances of the internal faces between slinger and end cover should be about 1/16 of an inch. The first radial clearance opening on any design through which liquid may pass should be made very close, approximately .003/.005″ on a side. The inner radial clearance should be between .0075″ and .015″. These figures are based on successful practice.

In sophisticated oil-air-mist lubrication systems it has been found that exhaust porting must be supplied between the bearings and
labyrinth type seals in order to insure adequate lubrication of the bearings and suffi­cient air flow for cooling.

SHAFT AND HOUSING FITS

Shaft Fits

The main purpose of the shaft fit is to assure proper security of the inner ring to the shaft. Under normal conditions of shaft rotation, a loosely fitted inner ring will creep on the shaft leading to wear and peening. This condition will be further aggravated by increase of load or speed. To prevent creeping or slipping, the inner ring should be mounted firmly in place and held securely against the shaft shoulder. However, it is important that the shaft diameter should not be so great an inter­ference fit as to cause undue radial preloading of the bearing. Such a condition could lead to excessive heat generation and increased power consumption.

As a general rule it is recommended that the shaft size and tolerance for seating extra-precision bearings be the same as the bearing bore.
In the case of pre‑ loaded bearings, the ideal shaft fit is a line-to-line fit since an excessively tight fit expands the bearing inner ring and
increases the bearing preload which can lead to overheating. In the case of extremely high-speed applications, however, a minimum press fit of the inner ring is required to insure that the proper fit will be maintained at operating speed. This press fit must be sufficient to compensate for expansion of inner ring due to centrifugal force. Any creeping or shifting of the inner ring on a high-speed device would tend to destroy the balance of the shaft assembly.

The extent of preload change due to an interference fit on the shaft can best be illustrated by the following example: A duplex pair of 2MM9111WI CR DUL bear­ings, with 35 pounds built-in preload, mounted on a shaft that provides an interference fit of .0004 inches will
have a mounted preload level of approximately 180 pounds. This significant increase in preload will result in elevated operating
temperatures.

Housing Fits

Under normal conditions of rotating shaft, the outer ring is stationary and should be mounted in the housing with a hand push or a light tap fit. Should the housing be the rotating member, the same fundamental considera­tions apply in mounting the outer ring that were used for the inner ring mounted on a rotating shaft.

As a general rule for rotating shaft applications, the minimum housing bore dimension for extra-precision bearings should be established
as the maximum bear­ing outside diameter. The tolerance of the housing bore should be the same as the tolerance for the outer ring.

Numerous designs utilize the fixed and floating principle. The previously mentioned fitting practice should be utilized on the fixed
end only. In order to insure that the opposite end will float, and to corn pen-sate for thermal changes within the device, it is neces­sary to supply a looser housing fit. Generally this fit will be sufficient if the average fit is made .0002″ looser than the average fit of the fixed end. If a heat source is present, such as an integral motor, added looseness in the housing will be required.

 

Timken Extra-Precision Bearings Part 2 of 4

Tuesday, August 2nd, 2011

BALL BEARING TYPES

Non-Filling Slot Type

M-K and MM-K type ball bearings are designed to carry radial, axial or combined loading. Because of the fully shouldered inner and outer races, these bearings can carry axial load in both directions and have relatively high-speed capability.

Annular Contact Type

2M-WI and 2MM-WI types, with 12° contact angles, maximum complement of balls, and one-piece inner ring-piloted retainers are designed to meet the needs of machine builders for extra-precision bearings which will operate with minimum temperature rise for a wide range of speeds and operating loads. In order for machines to produce more accurate work at a higher production rate, the bearings must provide a high degree of rigidity in both axial and radial directions. For example, on precision turning machines, cutting tools impose heavier loads on bearings than those en­countered in precision grinding. In the former, speeds are slower and loads heavier than in the latter, where speeds are high and loads light. 2M-WI and 2MM-WI types give machine builders the flexibility required to meet such variations in application requirements.

3M-WI and 3MM-WI types, manufactured with 25° contact angles, maximum complement of balls, and one-piece inner ring pilot retainers are designed primarily for use on applications where the loading on the bear­ings is predominately thrust and a high degree of axial rigidity is a definite requirement, or when a closer balance between the axial and radial bearing spring constants is required. Typical applications for these bearings are large, vertical, rotary-surface-grinders, horizontal and vertical disc-grinders, heavy-duty lathes, boring machines and milling machines.

2MM-WO types, with 18° contact angles, are de­signed for extremely high-speed applications where the centrifugal force of the balls must be considered. Unlike the MM-WI type which has counterbored outer rings and inner ring land piloted retainers, the 2MM-WO type has full shoulders on both sides of the outer race and a low land on one side of the inner ring. This design permits assembly of a maximum complement of balls and a one-piece channeled retainer piloting on the pre­cision ground lands of the outer ring.

Ball Screw Support Bearings

To meet the requirements of the highly sophisti­cated numerically controlled machinery field, The Fafnir Bearing Company has developed a new family of ball bearings especially designed for ball screw applications. The design criteria for these bearings are maximum axial rigidity, low drag torque and extreme control of lateral eccentricities. These bearings have been used successfully on all types of tape controlled machinery, precision instruments, missiles, and slide actuators or in-feed mechanisms used on standard machine tools.