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Патент USA US2411180

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* Patented Nov.19,1,946- ’
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. (Cl. 171-206)
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 there
to. A customary practice has been to dip arma
tures in varnish for a comparatively long period
of time to permit the varnish to penetrate as com
pletely as possible into the interstices of the ar
tures, whether with or without rotation, have
been unsuccessful and impracticable for the rea
son 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 e?icient than prior practice, which effects
mature by gravity or capillary action, and some 10 better and more uniform penetration and better
times by use of vacuum impregnating tanks, and
retention of varnish, and which in comparison
then to suspend them vertically to cause excess
with prior practice greatly shortens the baking
varnish to drain ofl’. Thereafter the armature is
time and produces superior results with greater
baked to evaporate the varnish solvent and to
certainty and regularity.
oxidize the varnish ?lm, and in the case of heat 15
Other objects will appear from the following
convertible resin varnishes to cure the resin ?lm
I have discovered, and it is upon that that the
This practice has not been wholly satisfactory,
present invention is predicated. that armatures
partly because the distribution of varnish is im
and other rotatable parts may be varnished more
perfect, due, for example, to insufficient pene 20 rapidly, more satisfactorily and more econom
tration in some areas, to imperfect distribution,
ically than according to the above-described prior
as by excessive draining of varnish from some
practices by heating them .to a temperature such
areas and accumulation of excess in others during
that upon rotative contact with the varnish the
the steps of drainage and the early stages of
solvent will be caused to evaporate promptly
baking, or for other reasons. Particular difficulty
from the ?lm or coating of varnish that adheres
has arisen from the tendency for the solvent to
to the surface as the armature emerges from the
evaporate promptly at the surface of the arma
bath. Generally speaking, the armature is heat
ture so that a more or less hardened surface layer
ed to a temperature at least approximately that
of varnish is formed that retards escape of sol
of the boiling point of the solvent used in the
vent from the interior of the armature. As a 30 varnish. The thus heated article is then rotated
result it has been necessary to bake the arma
ture for long periods of time, even as much as 48
in a bath of varnish to apply varnish onto the
thetic resins which are used in some of these var
leum naphtha as a solvent. With this varnish it
part which requires it, after which it is rotated
hours. Relatively long drainage, say one-half
freely, i. e., without contact with the varnish
hour, has been necessary also. In addition to
bath, to distribute the varnish uniformly and
such time-consuming operations and the possi 35 allow it to penetrate, and then subjected to bak
bility of imperfect results, this practice has been
ing heat while rotating it.
objectionable also because parts such as shafts,
More in detail, both the solvents and the resins
screw threads and the like that do not require
used in making electrical varnishes vary widely.
varnish are covered also, and the varnish ?lm
Hence, the temperature at which the armature is
must be removed from them before the armature 40 heated initially will depend upon the particular
can be placed in use. This necessitates hand op
varnish that is used, and particularly upon the
eration with attendant delay and increased cost.
which it contains. Accordingly, speci?c
Attempts have been made to varnish arma
temperatures or ranges of temperature applicable
tures by rotating them in a, bath of varnish in
to all purposes and to all varnishes can not be
such manner that only the body of the arma 45 stated. Due regard will be given, of course, to the
ture is immersed, and then effecting draining
varnish-forming constituents to avoid premature
while rotating the armature. In some instances
reaction or hardening. This factor of the inven
the armature has been heated, but to a rela
tion is illustrated, however, by the case of a var
tively low temperature, say about 200° F., because
nish containing a heat-convertible phenol-form
of the danger of curing the thermo-setting syn 60 aldehyde type condensation product and petro
nishes, and also to avoid premature evaporation
suflices to heat the armature to about 275° to
of the solvent. Penetration of varnish through
300° F.
out the windings has generally been found to 'be
Preferably, the armature is rotated While it is
very poor. Attempts to bake such dipped arma 65 being
heated. Preferably also, heating is effected
and baked 6 minutes while rotating slowly. Upon
by infra red radiation’ although it can be accom
plished in various other ways known‘ to the art,
removal from the baking oven the ?rst-two steps
e. g., by currents induced in the armature and
of a frequency adapted to produce the desired
were repeated and the armature was then baked,
heating through the necessary depth.
time required was 45 minutes, which is to be
compared with cycles of from 6 to 12 hours that
while rotating it, during 12 minutes. The total
The heated armature is then rotated in a bath
have been required for this operation by the
of varnish, the. bath level being so adjusted that
dipping and draining practice used previously.
only the portion which is to be varnished moves
Moreover, no cleaning of the baked armature was
through it, which avoids getting Varnish on the
shaft and other parts that do not require varnish. 10 necessary whereas the necessity for cleaning shaft
extensions and other parts of these armatures
Upon contact of the heated armature with the
vamishe'd by prior dipping practice has consti
varnish bath the solvent begins to be evaporated,
tuted a serious production bottle-neck.
or to boil oil, and under the in?uence of the heat of
Varnish loss by drainage in the prior dipping
the armature the solvent is driven promptly from
the coating of varnish which adheres to‘the ar 15 practice has constituted a major expense item.
From a total of 25 armatures treated in accord
mature as it emerges from the bath. The net
result is to coat the armature with varnish that ‘
ance with the presentinvention only 4 drops of
is substantially solvent-free.
varnish" drained ‘away.
Armatures treated asv just described success
For most purposes the most satisfactory results
are to be had by rotating the armature slowly 20 fully pass the speed and heat test to which these
devices are put before acceptance. Armatures
in the varnish bath, ‘and by slow enough rota
treated in accordance with the prior dipping
tion a single rotation of the armature through
practice do not consistently pass that test after
the varnish bath sui?ces in many cases to apply
baking for 6 hours.
enough varnish for the intended purpose.
In the practice of the invention it will usually
The armature is then removed from the bath 25
be desirable to apply some means for preventing
(or the bath is lowered from the armature) and
rotated to insure uniform distribution of the var
nish coating, following which it is subjected to a
alteration of the varnish bath by heat absorbed
from the heated armatures, either to prevent pre
mature and undesired thermo-settlng or to avoid
baking temperature while continuing to rotate
it, the heating being performed in any suitable 30 development of excessive viscosity through loss of
solvent. Various ways of doing this will be evi
way, for instance as referred to above. A very
dent to those skilled in the art. For instance,
short pre-baking rotation su?lces.
the armatures may be rotated in a varnish bath
The coating of solvent-free varnish soaks read
of the least practicable volume/with maintenance
ily and uniformly into the armature. Because
there is little or no solvent to be evaporated from 35 of its level through periodic or continuous addi
tion of fresh varnish, or a large volume of varnish
it, the di?lculties encountered in baking in prior
may be used with circulation for cooling it to
practice are completely avoided inasmuch as in
prevent undue temperature rise.
the practice of the present process there is no
Although the invention has been described with.
formation of hardened skin at the surface and in
any event the varnish which soaks in is substan 40 especial reference to the varnishing of armatures,
it will be understood from what has been said
tially solvent-free.‘ The result is that baking
that it is equally applicable to thesvarnishing of
is accomplished in a fraction of the time needed
when armatures are treated in accordance with "
other electrical windings that require impregna
the‘ prior practices brie?y reviewed above.
tion with electrical varnish.
According to the provisions of the patent stat»
utes, I have explained the principle and mode
By actual experience I have found also that in
addition to the foregoing major advantages ar- ,
of operation of my invention and have described
what I now consider to represent its best em
bodiment. However, I desire to have it under
matures treated in accordance with the present
method exhibit better varnish distribution than
when'they are dipped according to prior prac
tice, and a higher proportion of the varnish
applied to the armature is retained by and pene
trates into it. Generally speaking, there is no
appreciable drainage in the practice of this in-v
stood that, within the scope of the appended
claims, the invention may be practiced otherwise
than as specifically described.
I claim:
1. That method of varnishing an armature
vention, ‘and the prolonged drainage time neces- _
sary heretofore is eliminated. These results mean, 55 which comprises heating the armature to a tem
perature at least approximately that of the boil
ing point of the varnish solvent, rotating the
heated armature slowly, through the varnish and
thereby applying thereto a coating of varnish sub
stantially free from solvent, removing the thus
coated armature from said bath and rotating it
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 substan
tial proportion being lost by drainage.
If desired for any reason, the foregoing se
quence'of steps can be repeated, as by passing
the baked armature while ‘still hot directly to
the varnish bath, rotating it therein, rotating
brie?y after removal from the bath, and again
baking while rotating it.
As an example, reference may be made to the
varnishing of armatures for an aircraft fuel pump
slowly to cause the varnish coating in its sub
stantial entirety to penetrate it, and then heat
ing 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,
51/2 inches. They were treated with a thermo
' and then rotated while again baking the applied
setting phenol-formaldehyde type varnish con 70 varnish.
3. A method according» to claim 1 in which the
taining petroleum naphtha as the solvent. The
baked article .while heated thereby is again ro
armatures were heated to a temperature of about
tated in said varnish, then rotated outside of
300° F. during 15 minutes, rotated once at a
the varnish bath, ‘and then rotated while again
speed of 1 R. P. M. in. the varnish, rotated slowly
for 2 minutes after removal from the varnish,‘ 75 baking the applied varnish.
motor. These armaturesvhad an overall length of
4. That method of impregnating an electrical
winding with electrical varnish which comprises
heating the winding to a temperature su?icient
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 retain
ing in substantial entirety the said varnish coat=
5. That method of impregnating an electrical
winding with electrical varnish which comprises
rotating the winding and heating it to-a tern“
perature su?icient 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 rotat
ing it slowly to cause the varnish coating in sub
stantial 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, rotat
ing 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.
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