US 2515294 A
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Description (OCR text may contain errors)
Juy 18, 1950 w. w. cowcalm.v
FREEZING UNIT DEFROSTER Filed June 18, 1947 ATTORNEY Patented July 18, 1950 UNITED STATES PATENT OFFICE FREEZING UNIT DEFROSTER Application June 18, 1947, Serial No. 755,401
4 Claims. (Cl. 219-19) This invention relates to means for defrosting the freezing compartment of refrigerators and so-called deep freeze boxes, and is particularly well adapted for use to release the layer of iceforining frost from the inner walls of a deep freeze box, so that such sheet of ice may be lifted out of the box without the necessity of raising appreciably the temperature of the food stored in the box.
When a freezing compartment is kept below the temperature at which water freezes the moisture in such compartment will deposit on the top, bottom and sides of the compartment and form frost. As this frost accumulates it forms a layer of ice that, due to its insulating effect, reduces the efciency of the apparatus for reducing the temperature of the freezing compartment. It is therefore necessary to defrost such compartment from time to time.
The general practice heretofore in defrosting the freezing compartment of a deep freeze box has been to stop the supply of cooling fluid to such box and open up the lid of the box so as to expose the interior `of the box to room temperature and thereby cause the layer of ice upon the walls to melt, but this practice is open to the objection that the temperature of the food stored in the box rises unduly while the box is being defrosted. It has also been the practice heretofore to scr-ape the frost free from the walls of the freezing compartment and then remove the scraping from the box, but this is a comparatively difficult job, and allows the contents of the box to become warm while this is being done.
The present invention contemplates a simple and practical freezing unit defroster whereby the layer of ice-forming frost that has built up upon the walls of the freezing compartment may be quickly and easily released from such walls and then lifted out of the box. This is accomplished by heating the wall itself or other surface upon which the ice-'forming frost has become deposited so that this layer of ice will be released or decemented from the wall upon which it formed and can then be lifted out of the compartment. In this manner the layer of ice-forming frost may be removed from the interior of the freezing compartment in a short time and without causing any appreciable rise in the temperature of the food stored in the freezing compartment.
In order to carry out the present invention the walls, and also4 if desired the top and bottom, of the freezing compartment to be defrosted are each provided with a defrosting unit having the form of -a heating sheet of substantial area which is secured to each wall that is to be freed from ice. This sheet-like heating unit may be adhesively secured to the exposed porcelain lined face of the walls of the freezing compartment, or if desired it may be attached to the inner or concealed face of such walls against which the fibre glass or other insulating material normally rests.
The heating sheet, in accordance with the present invention, is so constructed that it will generate heat approximately uniformly throughout the entire area of the heating unit and is designed to produce only a moderate amount of heat say about F. to 200 F. throughout its area, since all that is required of such heating unit is to decement or release the bond between the sheet of ice and the wall of the freezing unit to which itis adhered. As soon as this is done the released sheets of ice may be lifted out of the freezing unit in large sections.
The heating sheet used in carrying out the present invention comprises a plastic sheet having electrical conductivity, the desired amount of conductivity is imparted thereto by employing .a plastic that contains conductive particles such as acetylene black. This permits an accurate control of the heating properties built into the plastic sheet, since the conductivity of such sheet may be increased as desired by applying thereto successive layers of a solvent plastic lm carrying the conductive particles. After a plastic sheet having the desired conductivity is produced, electrical conductors preferably in the form of metal ribbons are secured thereto in spaced parallel relation to each other, so that the conductor sheet will generate heat substantially uniformly throughout its area when a dierent electric potential is maintained between the spaced conductors. The heating sheet thus produced is preferably confined or sandwiched between two sheets of insulating material.
The above and other features of the present invention and novel arrangement of parts will be further understood from the following description when read in connection with the accompanying drawing illustrating good practical embodiments of the invention, and wherein:
Fig. 1 is a perspective view of a deep freeze box having the four side walls thereof equipped with defrosting units in accordance with the present invention;
Fig. 2 is a perspective view of a defrosting unit of the type used in Fig. l, and comprising an electrically heated plastic sheet;
Fig. 3 is a sectional view taken on the line 3 3 of Fig. 2;
Fig. 4 is a section view on an enlarged scale taken through one of the inner Walls of the deep Fig. l of the drawing shows in perspective vievr a low temperature box of the type commonly referred to as a deep freeze unit or deep freeze box and is designated generally:bymthesntunenal.1 it. This boxr has the usualflidll l`\sh'own\inizthe\ raised position so that the interior ofthe* box-- which constitutes the freezing compartmentmayl i These'tabs 23 provide a convenient means for conbe seen. The lid H is secured to the box lll by hinges not shown.
The walls of the box are made thi-cli as shown forheatinsulating purposesand '.corrrprisean outer.v
meta-lgshellfhavin'aithenoutei wallsirlzfandia.. con. siderablysmaller-.innermetal shell havingsthe'bottom: l andgside.; walls; l 4r. The..I arrangement is.r
suchcthat-.a hollow; space is-.lefitibetween the.- inner. and outer yshells :,which; isiilfled'.; with bre .glass or otherI heat; insulating materiaL. not: shown. Theyinner; and outerL shells.. justy mentioned.y are connected atzthe upper.. end of'. the boxlby the.
nolinedmetal; wallsil 5: which' slope. torcorrespond Withithe beveloithe; thiclciinsulating. portion known .construction iand constitutesone form. ofV
freezingiunit which mayibe: readily,l equipped with the.; defrosting. uifiits contemplatediby .the present invention. One; such @frosting unit designated, by i8 is shown in perspectiveninsliigs,2;.of; the lIfvilfililehz Thisl vunit, may@l bei applied ...to'all `four vertical g wallsxv l 4': of the., innerqshell .off the. dee
freeze;unit, and ,if desired .-it may also, be. applied. to the bottom i3 and .to the. surface.vv lsof the lid i i, however: it;is;shown in Figs Al as. having been..
applied onlyitofthe-fon-r .Walls l 4l:
The heating; uniti. 84, preferably, comprises. a,
sheet` I9, seef` Fig,4;, hai/ing; electrical; conduce tivity,;, a-nd this sheet is sandwiched between ,two non-conducting-Vsheets 2D,and 2i.V Thesheetl.
.50. fabric, such asiondinaryrwoveni,cotton fabricoor..
preferably fisA formedaof. ag, sheeti of. thin Lwoven i \J- ofthefl-id Il... Thefbevelfledzportioni of thebox. iii-:has secured thereto .-th'e.I rubbersealing bead'l'i,A
The deep freeze..:,box:;so. far describedis ofwell...
a sheet'oftough durable-paper, ,and has applied to. one, face .thereofiaaplastic lm carrying,- electrical,conductiverptoperties.. This nlm Iis. preferably formed of rubber, and is appliedrto the fabric. or` paperv as .-a thin solvent coating having ofthe same .textile `fabric or paperas is employed; in the sheet i9 and are coated with a'solventv resin such for example as a phenolic resin or polystyrene. The insulating sheets 20 and,v 2 i are slightly larger in area than theconductive sheet i9 so that the insulating sheetsfwilhextend beyond the four edges of the conductive sheetto completely insulate itasfshown in Fig. 2.`
In order to supplythe conductivesheetl 9 vwith an operating electrical current `it has` placed lengthwise thereof .adjacent itsopposite edges, as
shown in Figs. 2 and 3, the tape conductors 22.
4 formed of thin strips of metal such as aluminum or copper. After the parts are assembled in the position in which they are shown in Figs. 2 and 3 the composite sheet thus produced with the conductive tapes 22 in place is preferably placed in a heated platen press, whereupon the press is closed for a suiiicient length of time to soften the lplastic coating on the sheets 2G and 2l and bond the several parts rmly together,- to thereby provide the finished heating unit having a thickness of only several hundredths of an inch. This completes the formation of the heating unit I8 exceptith'at contact tabs 23, shown as of the eyelet typeVare-preferably.secured to one end of each of theconduct-or =stripg-22 as shown in the drawing.
.Y enamel layer is designated.by'r MisimFigsA and 5 `of,- the. drawing, whereasthe: oppositeiaface of.: the`r Wall i4 which isf. normally g concealed; and L. against. which. the.-insulating material..commone 1y.restseisidesignatedzby. |45. intthese;itwoiguresr..
The; enamelacoveredzfaeesi 2.4!:y ofrtheiverticall walls l4,;.when ,the-.z freezing; unit isin..operation. to. c keep.;y the..` food. thereinir. frozen',- arei: ther.wal-ls, upon whichiiceeformingfifrost accumulates:4v As*` this frost increases in thicknessrit.forms;:a.;heatt insulating layerr. that aseriously' interferes with the. zefficiency; of.; the 'boimtosmaintain i ther-freezes.v
ing compartment i. at\T thee .desired r low. tempera-.f ture,whi.ch .in-.most cases should ybe ;around. zero i Fahrenheit., Itris;1 therefore. important'.v to..v de-s frost; ther deepj freeze vunit-l from'. time; toi times., say.. at.l least .onceisinzthnee monthsp. butiA if a the.;E
freezing uidto theeboxsis -.cutpoff and itheelid is zleft openisoL-thati the `vfreezing; compartmenti. becomes. warnrxenoughetormelt.: the ,i ice deposited n uponsuchs walls;J ,theI frozen'.: food: stored;` in: then, box :.is, likely. to..spoitidueztogitsfrisesin;.texnperaer ture..
Having in mind the dilcu-ltyiemaerencediflfiereej tofore in defrostingrthei-freezingtcompartmentnot;
freezing unitS.- thee presenti inventiorrzbonteme plates the userl of s a; defrosting., unit .comprisingf.
the; heating-sheet I 8,.;best-:sh1ownginiFig-...2 lof the.: drawing, and whichisheetfisiused nponaeaclnwalli of ,theibox or othenfreezing'eunit ,tdzbe -defrosteda `It will.lgiioted; that" each; ofi the .foum vertical.
Walls lll f, of: thesbox lihas secured; thereto: as heatingmnitl 8i that is;` large enough itoicoyer sube ,Y stantially theeentiregarea ofiithe wallrlll. to which;
it'is secured.V Theeheatngaaunit; ISeniayrbe.fape:`
p1ied;. to ithenenam'el ifacec 2.4.-
each:` Walle] 4 as i. shown,y in.. Fig-:i.4-i'of1'theidrawing.. or it 1:. may. bei. applied;;to;the innen concealedzfacex l 4if'ofi. said i walls-asl shown inggFigs, 5mt-the drawngr.. In.;
either; case iti wille serve to generates.sumcient;n
heat throughout.; its .entirei areae. toerelease ion decement .theebond'i which* securesV theialayer of iceto` such ;w,all.v Asesoon assthislfis.:.donau-thetintegralilayerV office, .,or; `aalarge:portion-.of sucha:V layer which'isi-now..:releaseils fronma walnut-main berlifted-bodilyyout ;ofthe .-boxe., Asgaaresult thea mates.
defrosting of the box may be carried out quickly withoutjthe temperature of the )frozen food stored' inthe box rising appreciably, since the ice in the lbox-does not have to'be melted vbeyond the-point where its bond to the Wall I4 is releasafed.-l Due to the high vh eat insulatingpropernesy of the'lfrost ice the heat'appiied to the box walls will be conned to thefvicinity of such walls bythe Alayer of ice deposited thereupon -and will not raise the temperature of the storage space appreciably.
The heating unit I8 may be secured to the enamel face 24 or to the innerface I4 of a Wall I4 by simply Aadhesively bonding it to such wall to cover a large area thereof.
In the construction shown in Figs. 1 and 4 the ice-forming frost will be deposited on the exposed iace of the heating unit I8 rather than upon the wall it covers, so that when the heating unit is supplied with a heating current the ice will quickly release its grip upon the outer face 2D of the heating unit. On the other hand if the heating unit is secured to the inner face I4 of the wall I4 as shown in Fig. 5 of the drawing and current is supplied to this heating unit, its heat will be quickly transmitted through the wall I4 to cause the ice deposited on the enamel face 24 to release its hold.
In some cases it may be desirable to avoid the expense of applying the enamel 24 to the walls I4, and in place thereof apply the heating units I8 directly to the metal face of the walls I4, and then cover the entire interior of the box with a protecting iilm of polystyrene so that it will cover the pads I8 and exposed portions of the walls I4.
If the heating unit is applied to the face I4' of the wall I4 as shown in Fig. 5, the problem of supplying operating current to the conduc tive strips 22 is a simple one, since all that is necessary is to connect one conductor wire 25 of an insulated conductor 26 as shown in Fig. 5 to the upper tab 23 of each heating unit I8, and a similar conductor 25 to the corresponding lower tab 23 of such heating unit.
When the heating unit I8 is applied to the enamel face 24 of the wall I4 as shown in Figs. l and 4 it is then preferable to form a hole through the wall I4 at each point where a tab 23 is positioned so that each tab may be connected with a conductor wire 25 of an insulated conductor 26 disposed adjacent the inner wall I4. One construction for connecting such tab with a conductor wire is shown in Fig. 4 and comprises a stud 21 which is tightly secured in an insulating sleeve 28, which sleeve extends through a hole formed in the wall I4. This stud 2l is internally threaded at one end to receive the screw 29 which is employed to clamp a tab 23 to the outer end of the stud 21. The inner end portion of the stud 21 has mounted thereupon the insulating disk 30 and the clamping nuts 3| to clamp between such nuts the conductor wire 25. In the construction of Figs. 1 and 4 the head of the screw 29 may be painted over with shellac or other insulating material, and the clamping nuts 3l and other exposed portion at the inner end of a bolt 2l may be covered with suitable insulating material. Likewise in Fig. 5 an insu lating sheet 32 is preferably provided between the tab 23 and the wall I4, and the parts 23, 25 may be further protected by insulating material not shown. The insulated conductors 26 are the positive and negative Wires secured to the tabs 23 to operate each heating unit I8 and are led inwardly 'from the cable 33 that i enters a yhole i in a lWall of the Ibox. Thiscable- 33 mayb'e con-v 'l nected `tothe ordinary volt outlet box.
It will be understood thatthe heating units I8 may beapplied also to the bottom I3 and top'IB of the box I0; but the application of the heating` unit I8 to the four upright'v walls I4 will` enable' the box tobe quickly freed from the most objectionable vdeposits of ice within the freezing'comy partment. It is desired to point out that while;
the freezingi unit defros'terf of the present invention has been shown and described in connection with a deep freeze unit, it is also Well adapted for use in defrosting the low temperature `compartment of the ordinary household refrigs,
erator, and for use to defrost various other types of low temperature boxes having a freezing compartment provided with walls upon which a layer of ice-forming frost tends to accumulate.
Having thus described my invention, what I claim and desire to protect by Letters Patent is:
l. In a low temperature box having a freezing compartment, top, bottom and side Walls enclosing said compartment and upon which a layer of ice-forming frost tends to accumulate, a defrosting unit comprising a flexible heating sheet adhesively secured to one face of at least one of said walls so as to cover a large area of such face and heat this area approximately uniformly to free it from the layer of ice, including a plastic sheet having electrical conductivity and spaced current supply conductors attached thereto so that this sheet will generate heat substantially uniformly over its surface when a difference in electric potential is maintained between said conductors and heat the wall to which it is secured.
2. In a low temperature box having a freezing compartment, four upright walls enclosing said compartment and upon which a layer of iceforming frost tends to accumulate, a defrosting unit for each wall comprising a flexible heating sheet adhesively secured to one face of each of said walls so as to cover a large area of such face and heat the area approximately uniformly to free it from the layer of ice, including a plastic sheet having electrical conductivity and spaced current supply conductors attached 'thereto so that this sheet will generate heat substantially uniformly over its surface when a difference in electric potential is maintained between such conductors and heat the wall to which it is secured.
3. In a low temperature box having a freezing compartment, walls enclosing said compartment and upon which a layer of ice-forming frost tends to accumulate, a defrosting unit comprising a laminated heating sheet adhesively bonded to at least one of said walls so as to cover a large area of this wall and heat this area approximately uniformly to release the layer of ice formed upon such sheet, including a plastic sheet having electrical conductivity and spaced current supply conductors attached thereto so that this sheet will generate heat substantially uniformly over its surface and heat the wall to which it is secured when a difference in electric potential is maintained between said conductors, and an insulating layer covering the heating sheet.
4. In a low temperature box having a freezing compartment, walls enclosing said compartment and upon which a layer of ice-forming frost tends to accumulate, a defrosting unit comprising a heating sheet adhesively secured to one face of a wall of such compartment so as to cover a large area of such wall and heat this area. approxielectricakconductivityj and spaced conductors ail-1 5 1,815,324; 1,974,146 235mm.Y 2,321,5s7t 2500168 Number