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After consultation by telephone with the Bureau of Steam Engineering, the following treatment was undertaken :

(e) Shafting wire-brushed and sand-blasted down to bare metal.

(f) Filled all deep pitholes with smooth-on.

(g) Wrapped with layer of Okonite waterproof tapeturns applied opposite to ahead rotation of shaft.

(h) Coated with shellac.

(i) Wrapped with layer of adhesive friction tape.
(j) Coated with shellac (see Fig. 2).

(k) Painted with one coat of anti-corrosive paint.

(1) Painted with one coat of anti-fouling paint.

The general dimensions of the tail-shafting, together with their areas of greatest deterioration, are shown in Fig. 3.

As a performance of war emergency, the whole operation of cleaning and preservation was accomplished in twenty-five hours of continuous work.

Upon re-examination of the propeller shafting in dry-dock on 28 June, 1918, it was found that the corrosion and pitting had not progressed over the condition existing in February. As a further protective measure, the following additional operations were carried out:

After the coat of anti-corrosive paint, mentioned under (k) above, the shafts were parcelled with canvas sheeting soaked in tallow. They were then served with housline, taking half hitches every four or five inches so as to prevent unravelling in case the housline was cut at any point; finally a coat of molten pitch and tallow, two parts pitch and one part tallow, was applied to complete the protective jacket.

[COPYRIGHTED]

U. S. NAVAL INSTITUTE, ANNAPOLIS, MD.

BALL BEARINGS

By LIEUT. COMMANDER H, D. MCGUIRE, U. S. Navy

PREFACE

"Where do we go from here?" is an expression characteristic of what we of the navy subconsciously are asking ourselves as life unrolls its phase of duties ashore and afloat. Very often we must unceremoniously change from an operating to a designing engineer. Naturally, in such changes we find "nuts to crack." If they are covered by good technical writings we are fortunate; if not, it's a case of dig. That's when we wish some one had blazed the trail with some notes, no matter how meager.

Duty, not long ago, brought me face-to-face with the necessity of determining upon the type of ball bearing to choose for certain high-speed instruments. This was the "nut to crack." From notes made in the investigation of the subject, certain general principles, upon which the theory of ball bearings depends, became apparent, and these are presented in the following paragraphs.

It is understood in a general way that the purpose of the ball bearing is to reduce friction. What else we may expect of it is rather hazy. If the question is asked, "Why are there different types of bearings?", can we answer intelligently? What would be the answer to these questions with reference to ball bearings for a certain machine?

1. Size of bearing required.

2. Type of bearing.

3. Accuracy of bearing.

4. Kind of lubricant.

5. Methods of lubrication.

A little investigation shows that the subject is one that is a profession in itself; consequently, this subject is taken up, not with the idea of writing a treatise on ball bearings, but with the idea of noting certain general principles upon which the theory and practice of ball bearings depend.

DEFINITION-PURPOSE

A ball bearing is a bearing device consisting of hardened balls and ball paths. (See Sketch 1 for names of parts.) This design reduces friction of motion as compared with ordinary surface bearings, because:

1. Reduction of surface of contact.

2. Bearings consist of accurate spheres rolling in accurate

paths.

Surface contact is reduced, as the ball has either two or three points of contact with the races instead of large surfaces in contact.

The reduction of friction, as claimed for accurate spheres rolling in accurate paths, may be illustrated by comparing the friction of running a motor-car on a smooth asphalt pavement (smooth path) with same on mud road (no defined path).

The friction coefficient of a well-made annular ball bearing is from 0.001 to 0.0002 of the load referred to the shaft diameter and is independent of speed and load.

The ball bearing, therefore, has the following advantages over plain bearings, viz.:

I. Reduction in friction.

2. More adaptable to high-speed work because of 1.

3. Less vibration because of accuracy.

4. Occupies less space along the shaft.

HISTORY

Ball bearings in modern use date from introduction of the bicycle. This brought in the adjustable cup and cone (threepoint contact) type. Under the demands of greater load resistance and reliability the two-point contact type, without adjustability, was evolved for use, carrying loads of from a few pounds to many tons.

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