US2627838A - Apparatus for impregnating solid bodies - Google Patents

Description

Feb. 10, 1953 P. HUGGlNs APPARATUsFoR IMPREGNATING SOLID Sunnis Filed June 8, 1949 Patented Feb. 10, 1953 APPARATUS FOR IMPREGNATING SOLID v BODIES Percy Huggins, Sale, England, assigner of onehalf to Lancashire Dynamo & Crypto Limited, Manchester, England Application June 8, 1949, Serial No. 97,793 In Great Britain June 8, 1948 4 claims. (01.118-64) This invention relates to the impregnation of solid bodies, and has particular, though not exclusive, application to the impregnation of electrical windings for dynamo-electric machines and transformers, in connection with which it will be described.

Impregnation of windings is normally carried out by placing the work in an impregnating chamber, having at the bottom an inlet for the varnish or other impregnant, and near the :top a connection with a pump whereby Vacuum cr pressure conditions may be induced in the chamber. The vacuum is used for drawing the impregnant into the chamber, and may also be used for additional purposes, such as assisting pre-drying of the work and evacuation of solvent from the impregnant after impregnation. After the work has stood in the varnish for a predetermined period the varnish is allowed to drain back into `a stock tank, or is forced back by pressure. The work is then stoved.

It is an object of the present invention to reduce the time, fuel, and labour required for impregnation and to increase the degree of control thereof; a further object is to retard unwanted drainage of the impregnant from the Work and ,thereby improve the eiiiciency of the impregnation.

f According to the invention, a method of 4impregnating a solid body comprises immersing it in an impregnant for the requisite period, re- ,'moving the bulk of the impregnant, and then subjecting the body to an upward blast of heated air.

After removal of the bulk of the impregnant,

and prior to the application of the hot blast, the f `body may be subjected to a vacuum.

l Aproportion of the heated air, after passing overthe body, may be re-heated and re-circu- 4 lated.

means serving to seal the impregnating chamber `atwlll.

Each of .the ducts may include a telescopic connection mounted on one part of the duct and arranged to be coupled with the other part, and a sealing plate arranged to be secured to said other part when it is uncoupled from the telescopic connection.

Alternatively, the impregnating chamber may be provided with a pressure lid, for use during conditions of pressure, and with a coupling lid, arranged to replace the pressure lid and formed with ducting to couple the impregnating chamber with the circulating means.

The means serving to feed the blast of air into the impregnating chamber may include a vertical duct leading from the top to the neigh bourhood of the bottom of said chamber and apertured at intervals throughout its length to permit part of the blast of air to be delivered to the upper and middle parts of said chamber. Two or more such vertical ducts may be provided at spaced intervals around the interior of the impregnating chamber and arranged for delivery of the blast of air.

A sump may be provided between the impregnating chamber and the source of impregnant, for the collection of used impregnant which has become undesirably viscous.

Two embodiments of the invention will be described with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic sectional elevation of one form of impregnating plant,

Figure 2 is a fragmentary diagrammatic view showing the blanking means in operation, and

Figure 3 is a fragmentary diagrammatic view of another form of impregnating plant having a coupling lid.

Referring to Figures l and 2, in one embodiment of the invention, for the impregnation of electrical windings, a cylindrical impregnating chamber I0 is employed, having a connection II at the bottom communicating with a sump I2, the function of which will be described hereinafter. A pipe I3 in which is located a valve I4 communicates with a stock tank I5 of varnish, and the chamber I0 has a connection I6 near the top coupled, through a valve I1, with an air pump (not shown), and a ilanged upper edge I8 arranged to receive a pressure-tight lid I9 seating on a sealing ring 20. In addition, vertical ducts 2| extend down the inside of the chamber I0. Each duct has a flange 22 at its upper end, which is approximately level with the upper edge I8 of the chamber, and with its open lower end 23 terminating a. short distance above the bottom of the chamber l0. Just above said lower end, a platform 24 extends across the chamber to support the Work, and is formed with perforations such as 25 so as to act as an air diffuser, as will be seen hereinafter. To assist varnish drainage and airdiffusion, the perforations 25 may be formed by a very open grid on the top of which are welded closely spaced angle irons with vertices upwards. at intervals along its length with louvres 26.

Adjacent to the impregnating chamber I6 is a circulating system comprising an air inlet 2'| to draw air from the atmosphere, a heater 28 to heat the air, and a circulating fan`29 toA drive the heated air through a delivery duct 30 to the chamber I0. The duct 30 is; provided. witha pressure-tight telescopic section 3| which may either be extended, as shown in Figure 1, or retracted, as shown in Figure 2. In its extended' position the telescopic section 3| is arranged to be secured to distributor 32' from which branch Short ducts 32 leading through the lid I6 ofthe chamber |0- to the top of the verticalduct 2|. WhenL the telescopic section 3| is in its retracted position theouter end of the duct 32 maybe blanked off by a sealing plate 33 secured thereto by a captiveclamp (not shown).

The pressure lid I9 is formed with an exhaust duct 34y arrangedto collect exhaust'air from the top of the4 impregnating chamber |0 and deliver it 'to' one end of a duct 35from which there stem two branch ducts 36, 3"|.` The duct 35 is provided with a pressure-tight telescopic section 38 similar to the section'3 I, and the duct 34 may be blanked ofl by a sealing plate 39 in the same manner as theduct 32 hereinbefore described. 'I'he branch duct 35 constitutes an exhaust flue to atmosphere, and is provided with an exhaustfan at the base of stack 36a. The other branch duct 31 leads to the heater 28, and is formed with an aperture 2'I which constitutes the previously mentioned fresh air inlet to the system. At the junction of the ducts 35, 36, 37 is a damper 4| which serves to open or close simultaneously the fresh air inlet 2l and exhaust`ue'36, and at the same time to close or open the passagebetween the main exhaust duct'35`from the impregnating chamber I0 and the'heater 28so`causing, theA air from' the impregnating chamber I!!` toV Ibe guided intol the exhaust flue 36 to atmosphere, or into the heater 28, or in varying proportions into each, asmay be desired.

The heater 28may be of'any suitable type, but preferably is of the direct firedV gas type, with thermostatic control.

The sequence of operations is as follows: the work is placed in the impregnating chamber. IIJ on. the .perforated platform 24 andthe pressure lid I9 is bolted on. The work mayv or` maynot have been pre-heated in the chamber IB. The need for this step depends on the nature of the impregnant, and with some types of'varnish preheating is not only unnecessary,V but indeed undesirable. If it is considered necessary,.it.can 'bev carried out with the work in the chamber Ill-by coupling the chamber with the circulating system, which is then run for the prescribed period with the heater 28 in operation. The ducts 32, 34 are then blanked olf by the sealing plates 33, 39 as shown in Figure 2, so isolating the chamber I0 by means of the air pump acting through the pipe i6 and valve from the circulating` system. Vacuumis then formed in the chamber I04 andrmaintained for a. suf'cient I period to extractair andmoisture fromthe wind- The vertical duct 2| is formed ings of the work. The valve I1 lis then closed and the valve I4 to the stock tank I5 is then opened and the varnish is sucked up through the pipe |3 into the chamber I0 until the work is immersed. The valve I4 is then closed and the. vacuum isl broken as by admitting air through the pipev |6.

The work remains in the varnish for the ,prescribed period, and if desired pressure can be applied atthis stage. The valve I4 to the stock tank I5 is then opened and the varnish is blown back or allowed to drain back into the stock tank..

It'has'been foundV that some of this is too thick to mix with the next upward flow of impregnant from theY stockY tank I5. Were provision not madetocounteract its effect, it might accumulate in the pipe I3 and in time congest it. This is overcome, however, by the sump |2, which collects that portion of the impregnant which hasincreased in specific gravity during the impregnating and is decanted into the sump, while not impeding the flow of impregnant to and fro between the chamber I0 and the stock tank I5; The sump l2 may be cleared periodically.

The sealing plates 3339 are then removed and the telescopicv sectionsA 3| 38 are coupled up to the ducts 32, 34. The air inlet damper 4| is fully opened, and is therefore simultaneously'set for full exhaustion to atmosphere. fan 29 is started up and the system is-runl in this condition for a short time toclear it of solvent vapour4 or any other inflammable gaseous content.

The heater 23 is then put 4into operation and the damper 'II is moved so as partially to close the air inlet 21 and admit exhaust to the heater 26'for recirculation. The setting of the damper 4| permitsY any desired degree of recirculation to 'be obtained. The hot airv blastY is delivered down the vertical ducts 2| inside the chamber I9, andpasses up through the perforations 2,5 ofthe'platform 24 and so is diffused over the Work. In addition, a proportion of the hot' air blast' passesxcut through' the louvres 26 into the upper'and middle'iparts of theA chamber I0. This proportion is selected to` suit the nature and size of .the work being impregnatedand the number, size, location, and'direction'of' the'louvres 26 are chosenzaccordingly. In m-ost instances very much under50% of the hot air rblast is'required to 'be dispersed through the louvres.` The turbulence caused 'thereby is benecial in sweeping irregular surfaces with the hot air, and in minimizing the slight temperature gradientwhich inevitably exists between the bottom and the. top ofthe cham.- ber III. By its upward movement the hot' airarrestsrthe downward'drainingA of the varnish and permits ofmore eiiicient impregnation, which is further improved'by the absence of solventladen air, theipresence of which is undesirable during. curing. Any inflammable solvents: re'- leased'from the work are carriedV in the exhaust 34, 35 partly to the. atmosphere and partly to the heater 28 (dependingY onv the degree of recirculation forwhich the damper. 4I is set) and such solvents as are carried. to the heater 28 are there burnt, if' the heater is of. then direct fired type. The hot air blast is'l maintained for the time necessary to cure the varnish. The circulating fan 29and the heater 28 are thenshut down and the lid' |9 and the work-are removed.

In another*embodiment ofl the invention, part of" which' is illustrated diagrammati'cally' inf Figure 3, and which embodies only one vertical 'duct' The' circulating 2l the impregnating chamber l!) is the same as before, but instead of having a lid i9 it has the usual type of pressure-tight lid (not shown) which has no ducts communicating with it, and which seats on the ilanges I8. In addition it has a second lid 42, termed the coupling lid, whichvis arranged to be secured to the top of the chamber lil instead of the pressure lid. For this pur pose the chamber and both the lids are formed with co-operating means of known type such as locating studs and apertures mating therewith, to ensure the rapid and easy substitution of one lid for another.

The coupling lid 42 is formed with a duct 43 arranged to register on the one hand with the vertical duet 2l extending within the impregnating chamber l0, and on the other hand with the delivery duct 3l)8L in the circulating system. The coupling lid is formed with another duct 44 arranged to register with the duct 35a. Suitable pressure-tight flanged connections are provided to permit of rapid attachment of the cou pling lid @E to these ducts. The remainder of the circulating system is the same as that shown in Figure l.

If desired, the coupling lid 42 may incorporate a pressure release door or other device to safeguard against explosion when the impregnant contains volatile inammable constituents.

The incorporation in the removable coupling lid or" the ducts to put the impregnating chamber 19 in communication with the circulating system obviates the necessityT of cutting openings in the chamber, and enables an existing chamber to be rapidly converted without being taken out of commission. Moreover, it renders unnecessary the provision of valves in the circulating ducts to seal oi the air blast equipment from the chamber when vacuum or pressure is applied to the latter. Further, it is impossible to apply air blast heating to the chamber until the coupling lid is in position. This is an important advantage when volatile inflammable impregnants are employed, and pressure release means are provided in the coupling lid. By the use of this separate lid the provision of a safety interlock is obviated.

By the above methods there is accomplished an economy in fuel, owing to the recirculation of the hot air, whereby the heater has only to make up the heat lost by the air during its passage round the system. The work is more quickly heated by the hot blast, and therefore the stoving time is reduced. There is also achieved an economy in labour, due to the whole process being accomplished in one chamber without removal of the work therefrom, and under conditions of greater control than have heretoiore been possible.

I claim:

1. Apparatus for impregnating a solid body comprising an impregnating chamber, tank means for holding a supply of liquid impregnant, means connecting said chamber and said tank means for conveying sufficient impregnant into said chamber to immerse the solid body and for withdrawing and returning excess impregnant to said tank means, circulating means, ducts connecting said circulating means with the top and bottom of said chamber, a telescopic connection in each duct, whereby when the connections are uncoupled sealing plates may be secured to the parts of the ducts connected to the chamber to close ofi the circulating means from said chamber, a heater connected to said circulating means, and said circulating means feeding a blast of air through said heater into said chamber near the bottom thereof, and exhausting said air from the top of said chamber.

2. Apparatus :for impregnating a solid body as in claim 1, said circulating means further comprising a vertical duct in said chamber extending from the top thereof to adjacent the bottom of said chamber, and apertures spaced along the length of said vertical duct for delivering part of the blast of air to the upper and middle portions of said chamber.

3. Apparatus for impregnating a solid body as in claim 1, said circulating means further comprising at least two vertical ducts spaced apart in said chamber for the delivery of the air blast into said chamber.

4. Apparatus for impregnating a solid body as in claim 3, further comprising said vertical ducts extending from the top to adjacent the Abottom of said chamber, and apertures spaced along the length oi each vertical duct for delivering part of the blast of air to the upper and middle portions of said chamber.

PERCY HUGGINS.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,221,776 Turner Apr. 3, 1917 1,285,615 Canepa et al. Nov. 26, 1918 1,445,872 Davis Feb. 2), 1923 1,729,056 rTexier Sept. 24, 1929 1,733,794 Parker Dec. 10, 1929 1,789,999 Clark Jan. 27, 1931 1,849,844 Goff Mar. 8, 1932 1,888,573 Sadwith Nov. 22, 1932 1,968,764 Harris July 31, 1934 1,984,414 Lee Dec. 18, 1934 2,156,382 Ferla May 2, 1939 2,296,361 Mayer Sept. 22, 1942 2,303,257 Campbell et al. Nov. 24, 1942 2,400,726 Wright May 21, 1946

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