US2411180A - Varnishing armatures and the like - Google Patents

Description

* Patented Nov.19,1 946- VARNISHING ,ARMATURES AND THE LIKE Don F. Alexander, near Dayton, Ohio, assignor to The Sterling Varnish Company, Haysville, Pa., a corporation of Pennsylvania No Drawing. Application December 30, 1943, Serial No. 51.6,241

6 Claims.

This invention relates to the varnishing of articles that are capable of being rotated.

The invention is applicable particularly to the varnishing of armatures, for which reason it may be described with particular reference thereto. A customary practice has been to dip armatures in varnish for a comparatively long period of time to permit the varnish to penetrate as completely as possible into the interstices of the armature by gravity or capillary action, and sometimes by use of vacuum impregnating tanks, and then to suspend them vertically to cause excess varnish to drain ofl. Thereafter the armature is baked to evaporate the varnish solvent and to oxidize the varnish film, and in the case of heat convertible resin varnishes to cure the resin film also.

This practice has not been wholly satisfactory, partly because the distribution of varnish is imperfect, due, for example, to insufficient penetration in some areas, to imperfect distribution, as by excessive draining of varnish from some areas and accumulation of excess in others during the steps of drainage and the early stages of baking, or for other reasons. Particular difficulty has arisen from the tendency for the solvent to evaporate promptly at the surface of the armature so that a more or less hardened surface layer of varnish is formed that retards escape of solvent from the interior of the armature. As a result it has been necessary to bake the armature for long periods of time, even as much as 48 hours. Relatively long drainage, say one-half hour, has been necessary also. In addition to such time-consuming operations and the possibility of imperfect results, this practice has been objectionable also because parts such as shafts, screw threads and the like that do not require varnish are covered also, and the varnish film must be removed from them before the armature can be placed in use. This necessitates hand operation with attendant delay and increased cost.

Attempts have been made to varnish armatures by rotating them in a, bath of varnish in such manner that only the body of the armature is immersed, and then effecting draining while rotating the armature. In some instances the armature has been heated, but to a relatively low temperature, say about 200 F., because of the danger of curing the thermo-setting synthetic resins which are used in some of these varnishes, and also to avoid premature evaporation of the solvent. Penetration of varnish throughout the windings has generally been found to 'be very poor. Attempts to bake such dipped arma- 2 tures, whether with or without rotation, have been unsuccessful and impracticable for the reason that in this instance also, the varnish dries at the surface and traps the solvent interiorly.

It is among the objects of this invention to provide a method of varnishing armatures and other rotatable objects which require varnishing, which is simple, easily practiced, economical, and more eflicient than prior practice, which effects better and more uniform penetration and better retention of varnish, and which in comparison with prior practice greatly shortens the baking time and produces superior results with greater certainty and regularity.

Other objects will appear from the following description.

I have discovered, and it is upon that that the present invention is predicated. that armatures and other rotatable parts may be varnished more rapidly, more satisfactorily and more economically than according to the above-described prior practices by heating them .to a temperature such that upon rotative contact with the varnish the solvent will be caused to evaporate promptly from the film or coating of varnish that adheres to the surface as the armature emerges from the bath. Generally speaking, the armature is heated to a temperature at least approximately that of the boiling point of the solvent used in the varnish. The thus heated article is then rotated in a bath of varnish to apply varnish onto the part which requires it, after which it is rotated freely, i. e., without contact with the varnish bath, to distribute the varnish uniformly and allow it to penetrate, and then subjected to baking heat while rotating it.

More in detail, both the solvents and the resins used in making electrical varnishes vary widely. Hence, the temperature at which the armature is heated initially will depend upon the particular varnish that is used, and particularly upon the solvent which it contains. Accordingly, specific temperatures or ranges of temperature applicable to all purposes and to all varnishes can not be stated. Due regard will be given, of course, to the varnish-forming constituents to avoid premature reaction or hardening. This factor of the invention is illustrated, however, by the case of a varnish containing a heat-convertible phenol-formaldehyde type condensation product and petroleum naphtha as a solvent. With this varnish it suflices to heat the armature to about 275 to 300 F.

Preferably, the armature is rotated While it is being heated. Preferably also, heating is effected 3 by infra red radiation although it can be accomplished in various other ways known to the art, e. g., by currents induced in the armature and of a frequency adapted to produce the desired heating through the necessary depth.

The heated armature is then rotated in a bath of varnish, the. bath level being so adjusted that only the portion which is to be varnished moves through it, which avoids getting Varnish on the shaft and other parts that do not require varnish. Upon contact of the heated armature with the varnish bath the solvent begins to be evaporated, or to boil oil, and under the influence of the heat of the armature the solvent is driven promptly from the coating of varnish which adheres tothe armature as it emerges from the bath. The net is substantially solvent-free.

For most purposes the most satisfactory results are to be had by rotating the armature slowly in the varnish bath, and by slow enough rotation a single rotation of the armature through the varnish bath suifices in many cases to apply enough varnish for the intended purpose.

The armature is then removed from the bath (or the bath is lowered from the armature) and rotated to insure uniform distribution of the varnish coating, following which it is subjected to a baking temperature while continuing to rotate it, the heating being performed in any suitable way, for instance as referred to above. A very short pre-baking rotation sufllces.

The coating of solvent-free varnish soaks readily and uniformly into the armature. Because there is little or no solvent to be evaporated from it, the difllculties encountered in baking in prior practice are completely avoided inasmuch as in the practice of the present process there is no formation of hardened skin at the surface and in any event the varnish which soaks in is substantially solvent-free. The result is that baking is accomplished in a fraction of the time needed the prior practices briefly reviewed above.

By actual experience I have found also that in matures treated in accordance with the present method exhibit better varnish distribution than when'they are dipped according to prior practice, and a higher proportion of the varnish applied to the armature is retained by and penetrates into it. Generally speaking, there is no appreciable drainage in the practice of this insary heretofore is eliminated. These results mean, of course, greater economy through the reduction of the time cycle and the fact that all of the varnish is used effectively instead of a substantial proportion being lost by drainage.

If desired for any reason, the foregoing sequence'of steps can be repeated, as by passing the baked armature while still hot directly to the varnish bath, rotating it therein, rotating briefly after removal from the bath, and again baking while rotating it. v

As an example, reference may be made to the varnishing of armatures for an aircraft fuel pump motor. These armatures had an overall length of 5 /2 inches. They were treated with a thermosetting phenol-formaldehyde type varnish containing petroleum naphtha as the solvent. The armatures were heated to a temperature of about 300 F. during 15 minutes, rotated once at a speed of 1 R. P. M. in the varnish, rotated slowly for 2 minutes after removal from the varnish,

result is to coat the armature with varnish that when armatures are treated in accordance with addition to the foregoing major advantages arvention, and the prolonged drainage time necesand baked 6 minutes while rotating slowly. Upon removal from the baking oven the first-two steps were repeated and the armature was then baked, while rotating it, during 12 minutes. The total time required was 45 minutes, which is to be compared with cycles of from 6 to 12 hours that have been required for this operation by the dipping and draining practice used previously. Moreover, no cleaning of the baked armature was necessary whereas the necessity for cleaning shaft extensions and other parts of these armatures vamishe'd by prior dipping practice has constituted a serious production bottle-neck.

Varnish loss by drainage in the prior dipping practice has constituted a major expense item. From a total of 25 armatures treated in accordance with the presentinvention only 4 drops of varnish" drained away.

Armatures treated as just described successfully pass the speed and heat test to which these devices are put before acceptance. Armatures treated in accordance with the prior dipping practice do not consistently pass that tes after baking for 6 hours. I

In the practice of the invention it will usually be desirable to apply some means for preventing alteration of the varnish bath by heat absorbed from the heated armatures, either to prevent premature and undesired thermo-settlng or to avoid development of excessive viscosity through loss of solvent. Various ways of doing this will be evident to those skilled in the art. For instance, the armatures may be rotated in a varnish bath of the least practicable volume with maintenance of its level through periodic or continuous addition of fresh varnish, or a large volume of varnish may be used with circulation for cooling it to prevent undue temperature rise.

Although the invention has been described with.

especial reference to the varnishing of armatures, it will be understood from what has been said that it is equally applicable to thesvarnishing of other electrical windings that require impregnation with electrical varnish.

According to the provisions of the patent stat utes, I have explained the principle and mode of operation of my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim: I

1. That method of varnishing an armature which comprises heating the armature to a temperature at least approximately that of the boiling point of the varnish solvent, rotating the heated armature slowly, through the varnish and thereby applying thereto a coating of varnish substantially free from solvent, removing the thus coated armature from said bath and rotating it slowly to cause the varnish coating in its substantial entirety to penetrate it, and then heating it to bake the varnish while continuing to rotate it.

2. A method according to claim 4 in which the baked article while heated is again rotated in said varnish, then rotated outside of said bath,

' and then rotated while again baking the applied 4. That method of impregnating an electrical winding with electrical varnish which comprises heating the winding to a temperature sufiicient to cause evaporation of the varnish solvent from a coating of varnish applied thereto, rotating the heated winding in a bath of the varnish and thereby applying thereto a coating of varnish substantially free from solvent, and removing the thus coated winding and heating it to bake the varnish while rotating it slowly and retaining in substantial entirety the said varnish coat= ing.

5. That method of impregnating an electrical winding with electrical varnish which comprises rotating the winding and heating it to-a tern perature sufiicient to evaporate the varnish sol: vent from a coating of the varnish applied to it, rotating the heated winding in a bath of the varnish and thereby applying thereto a coat= ing of varnish substantially free from solvent, removing the winding from said bath and rotating it slowly to cause the varnish coating in substantial entirety to penetrate the winding, and heating the article to bake the varnish while continuing to rotate it slowly.

6. That method of impregnating an electrical winding with electrical varnish which comprises supporting the winding for rotation, rotating the winding and heating it at least to approximately the boiling point of the varnish solvent, rotating the heated winding in a bath of the varnish and thereby applying thereto a coating of varnish substantially free from solvent, and removing the thus coated winding and heating it to bake the varnish while rotating it slowly and retaining in substantial entirety all of the varnish coating.

DON F. ALEXANDWJ,