NEWS
1102
EDITION
New Tri-Clad Motor Introduced
Final inspection of new General Electric motors coming off production line CHANGING requirements of industry have resulted in introduction by the General Electric Co., Schenectady, X. Y., of an entire line of completely new polyphase induction motors in integral horsepower sizes Known as the Tri-Clad motor and representing one of the most extensive product changes in the company's history, this general purpose motor has called for new methods in manufacturing and introduces many protective features. In all ratings the new motor presents modern streamlined appearand*, more complete protection through use of a castiron frame, major advances in insulation of current-carrying parts, and improved bearing design and lubricating arrangements. It incorporates the cast-aluminum rotor and a pressure-relief system of greasing for bull-bearing motors. A cast-iron frame of the box type is used instead of the conventional open frame. End shields, designed to match the frame, are enclosed above the center line. This combination minimizes contact of vital motor parts with foreign material such as lubricants, coolants, other liquids, chips, and tacks, while also protecting it against accidental blows in handling. The new-type insulation, dusttight bearings, and use of Glyptal in the priming and finishing paints protect it against harmful materials. Large integrally cast rotor fans draw ample, low-velocity air through openings in the lower portion of each end shield. Efficiency of cooling is increased through use of smooth air passageways and baffles controlling air direction, velocity, and discharge, which is through openings in the frame just above the motor feet. The motor operates well within the standard 40° C temperature rise. For insulation the new magnet wire, Formex, developed by General Electric
after 10 years of research, is used on all ratings. Formex, a vinyl-acetyl-covered magnet wire, is tough and heat- and solvent-resisting, and is a considerable improvement on the older paper, cotton, and other fibrous coverings which absorb moisture and over a period of years deteriorate because of heat and chemicals. Abrasion tests have shown Formex to be superior to convent ional enameled magnet wire in the ratio of about 3 to 1. It will resist much greater elongation without cracking of the insulation film, and comparative aging tests with ordinary type enameled wire show a superiority for Formex in the ratio of 30 to 1. After motor coils of Formex wire have been wound, they are given a bonding and impregnating coat of an improved synthetic resin varnish unaffected by oil or most of the commonly used solvents such as kerosene and gasoline. This varnish,
Tri-Clad motor
Vol. 18, No. 23 when exposed to the concentrated action of oil for 19 months, showed no softening; ordinary insulating varnish showed softness at the end of a few days and was completely destroyed in 19 months. The bonded coils are coated with Glyptal red, an alkyd-resin material which gives a neat moisture-, acid-, oil-, and arcresisting surface. In evolving the new sleeve bearings, General Electric engineers studied principles long considered fundamental to sleeve-bearing design and found that basic changes could be made which would more than double bearing capacity for some applications Because of shaft deflections under load, the actual bearing pressures per square inch over the end portion of the lining were much greater than previously supposed. By use of bearings with the proper proportion of length to diameter, deflections of the shaft inside the bearing can be maintained at a value less than the thickness of the oil film. This, in general, leads to use of shorter bearings for a given diameter than employed in the past. Maintenance of an oil film over all parts of the bearing linings under heavy loads or, as a matter of fact, under any loading condition was recognized as the most important determinant of great bearing capacity and long lining life. The spiral type grooving developed for the new sleeve bearing gives assurance of thorough oil distribution under the worst operating conditions. The complete sleeve bearing utilizes hard-tin Babbitt centrifugally cast into a steel shell. The bearing is rigidly supported through 360° and is locked in a dust-light, oil-tight enclosure by a removable pin.
U. S. Zinc Supply Deemed Sufficient T H E 1941 supply ofxincto consumers in the United States will be sufficient to meet national defense and ordinary industrial requirements and may even exceed these needs, according to recent investigations of the situation conducted in connection with the national defense program. Next year the smelter supply of sine in all forms is expected to total about 860,000 tons. Since probable consumption for 1941 is estimated at about 780,000 tons, the total production may exceed domestic requirements by approximately 80,000 tons when calculated on this basis. Apparently attempts made by the sine industry to widen the smelter production bottleneck which has been checking the flow of this metal are meeting with success. Expansion plans, largely covering the rehabilitation of old smelting facilities, will probably be completed and production under way by May of the forthcoming year.
