CA1169904A - Electric hotplate - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The disclosure teaches an electrical hotplate for use in a cooking appliance. The hotplate has a hotplate member with a downwardly projecting pin with an internal thread. A covering sheet covers the under-side of the hotplate member. Screw means secure both the covering sheet to the hotplate and the hotplate to the cooking appliance. The screw means include a hollow screw having an internal and an external thread and an outwardly projecting shoulder. The external thread is screwed into the pin and secures the covering sheet between the shoulder and the pin, A fastening screw is provided for mounting the cooking plate at the cook-ing appliance which fastening screw can be screwed into the internal thread.

Description

- 2 ~ 3~¢~

This application is a division of Application Ser. No. 358,108, filed August 12, 1980.
BACKGROUND OF THE INVENTION
.._ .
1) Field of the invention The invention relates to an e1ectric hotplate for thP use in cooking appliances, cookers, hobs or the like and more particularly to the fastening of a covering sheet for the underside of the hotplate and to the mounting of the hotplate tc a cooking applicance.

2 ~ of ~he Prior Art In applicants'U.S. Patents 4,122,330 and 4.153,833 it is shown to screw a threaded bolt into ~ central pin of the hotplate member and to fix the covering sheet in position by means of a n~t screwed thereon. Therefore~ two threading operations are required. Moreover, the threaded bolt protrudes some way out of the hotp1ate, with the result that th2 packed dimensions are twice as~large as the entire height of the hotplate and, furthermore, for transporting, adjacent hstplates have to be axially offset so as not to increase the packing dimensions still further. The protruding part of the threaded bolt is ;~ intended to attach the hotplate to a bracket by means of another nut screwed on, by which the hotp~ate is cla~ped downwardly.
U.S. Patent 2,6919719 shows additionally a tubular washer between ~he two nuts engaging the covering sheet and the : ~ bracketO
-.. ~ .

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved means for fastening the covering sheet to the hotplate and for mounting the hotplate to the coooking appliance. A further object is to proYide a fastening means which helps to minilnize the packed dimensions of the hotp7ate.

According to the invention, the screw is a hollow screw with an external and internal thread, a head or shoulder of which secures the covering sbeet, and into which it is possible to screw a fastening screw for the electric hotplate.
It is therefore only necessary to screw in the hollow screw to secure the covering sheet when assembl;ng the hotplate.
Later, when the hotplate is fitted, a conventional cap screw ~:
is used to secure the hotplate to the cooking applicance or the like. The hollow screw can be secured more satisfactorily :~ and the packing and transporting work is reduced. In addition. there i5 greater adaptability to different heights ::
of installation, as it is merely necessary to use different conventional cap sc rews as fastening screws.

`~ :

, ~

.

In accordance with a particular embodiment of the invention there is provided an electrical hotplate for use in a cooking appliance. The hotplate has a hotplate member with a downwardly projecting pin with an internal thread. A covering sheet covers the under-side of the hotplate member~ Screw means secure both the covering sheet to the hotplate and the hotplate to the cooking appliance, The screw means include a hollow screw having an internal and an external thread and an outwardly projecting shoulder. The external thread is screwed into the pin and secures the covering sheet between the shoulder and the pin. A fastening screw is provided for mounting the cooking plate at the cook-ing appliance which fastening screw can be screwed into the internal threadO

~ : ' :
,, : :
-: - : .
' ' BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter relative to preferred~ but non-limitative embodimentsof the invention and with reference to the attached drawings, wher~in show:
F~g. 1 a cross section through an electric hotplate installed in an electr;c cooker~ hob or the like, Fig. 2 a detailed Yiew, in section on the line II-II
in FIg. 1, Fig. 3 a section through an alternative embodiment of a detail from Fig. 1.
Fig. 4 shows the detail indicated by the dash-dot cirCle IV
in Fig. l, on a larger scale~ ~:
Figs. 5 to 7 show alternative embodiments of the detail shown in Fig. 4, Fig. 8 shows a detail, viewed in the direction of the arrow YIiI in Fig. 1, Fig. 9 shows an enlarged view of ~he detail showing the : central fixing of the hotplate according to Fig. 1~
Fig. lO shows three hotplates stacked one above the other, correspond;ng to the hotplate shown ~n Fig. 1, apart ~rom the earth connection, and the associated packing means, : Fig. 11 shows a detailed plan view in the direction of : : the arrow XI in Fig. 10, Fig. 12 shows a plan v~ew o~ a sheet metal part used to preven~ rotation and possibly act as an earth connection, .

-.

. , ~ , FigO 13 shows a partially cut-away view on the line XIII-XIII in Fig. 12, Fig. 14 shows a detailed section through the lower central region of a hotplate in the installed state, and Fig, 15 shows a rear view of this hotplateO

:
: ~ :
~ ~ ' ::

:~ :
: ~ ~: : :

:: : :
. .

' ~ i : , , :~

3~ ~ ~

., , ~ . .
Fig. I shows an electric hotplate 11 comprislng a hotplate member 12 consisting of cast ~ron w~th a flat9 sealed, upper cooking surface 13. The unheated central zone 14 is recessed so as to form an annular cooking surface. At its outer periphery, the hotplate member enga3es over an overflo~ r~m 15 consisting of sheet materiat of substantially U-shaped cross sec~îon, which rests on the raised rim 16 of the opening ~n the work plate t7 of a cooking appliance, e.g. an electric cooker or hob.
In ~he heated annular zone, the hotplate is provlded ~ith ribs extending ~n a spiral configuration which form between them spiral grooves 18 ~n which there are provided heating coils 19 embedded in a reramics mass 20.
A downwardly directed, substantially cylindrical 15 border 21 projects ~n ~he circumferential region of the hot-plate member, while a flange-like border reg~on of a cy~indrical :covering sheet 24 wh~ch ~s deformed and relnforced by embossed ~ portions rests on the lower edge 22 of said border 21. The : c~Yering sheet has ~ border region 23 a30ined by a step 25 which ~s di~rected upwardly~ 1.e. towards the cooking surface, and which abuts on the ins~de of the border 21 and thus centers the covering sheet or cover.
At one point on ~ts c~rcumference, ~he border 21 has a rec:ess 2:6 ln the~for0 of a rectangular cutout (Fig.8) into which : : ~
.

-, ' , ' a corresponding embossed portion 27 of the coveringsheet fits and thus prevents rotation of the covering sheet 24 on the hotplate member in spite of the relatively tight seal provided, For its part, the embossed portion 27 o~ the covering sheet ensures that the finished hotplate can be aligned in the circumferential direction when being handled during production. As a result, no inner projection on the border 21 is required.
Adjoining the step 25 is a region 28 of the covering sheet which is recessed relative to the border region 23 and adjoining said region 28 is a central region 29 which projects to some extent relative to the border region 23 In the center of the unheated central zone 14, the hotplate member has a downwardly projecting pin 30 into which a threaded blind bore 31 projects from below. A hollow cap screw 32, shown in detail in Fig, 9, is screwed into this threaded bore. This 2~ screw 32 consists of a stamped or deep-drawn sheet metal part with a flange-like cap region 33 with a hexagonal spanner surface or key faces and a sleeve-shaped threaded portion 34 adjoining the latter, into which an internal and external thread is pressed or forced~ The screw 32 projects through a central hole 36 in the covering sheet 24 and is screwed into the thread 3S of the bore 32 so that the covering sheet 24 is pressed with its border region 23 against the lower edge 22 of the border 21 of the hotplate member 12. Interposed between the head 32 and the covering sheet there is a sheet metal part 37 (Fig.
2) in the form of a sheet metal strip having, on one side, a hole 38 through which the screw 32 passes, while the other end tapers somewhat and a bent end 39 (Figs 1 and 2) surrounds an earth lead 40. The earth ~ ~ lead may be pressed or welded on to the sheet metal :: ~ :
~: :

-c~

:"

' ' , ' ' .''' ;

. , ' ' part 37. Thus, this sheet metal part is simply placed under the screw head 33 like a washer and provides a safe earth connection. It is particularly advantageous if the sheet metal part lies flat against the underside of the covering sheet 24 during production and shipping and is not bent away from the covering sheet until required, As a result, the earth connection does not substantially increase the height of the hotplate.
The left-hand side of Fig. 9 shows that the abutment surface or shoulder of the head 33 can be pro-vided with a preferably star-shaped groove ~1. The sheet metal part 37 is correspondingly structured on its top and bottom, and so is the covering sheet 24 (cf.
Figs 2 and 15), thus preventing the screw 32 from accidentally working loose. However, other securing methods may also be used.
The hotplate is held in the opening in the work plate which receives it by means of a bracket 42 which rests on the underside of the work plate 17 and has a flat U-shape. Its long back is reinforced by means of lateral bends 43. A cap screw 45 which is screwed into the internal thread in the hollow screw 32 projects through a hole ~4 in the centre of the bracket. In this way, the hotplate is clamped down by the screw and bracket and is securely fixed in position. This method of attach-ment uses only cap screws, which can easily be tightened using automatic screw driversO The screw 32 is a simple ~stamped sheet metal part and the screw ~5 is a simple machine screw. Until now, hot plates have been fitted with screw bolts which were screwed into the pins 30 and projected far beyond the underside of the hotplate. Two or more nuts screwed on to these bolts secured the cover ing sheet and hotplate to the bracket. Consequently, it was not possible to pack the hotplates in a space-saving manner. ~ow, however, the hotplate when packed takes up only the room which it requires for itself and there is the additional advantage that the length of the - ~ .

: . . . ' - :, . . .
; ~ . ' . ' ~ ', . ~ ' ' ' . :
- ~ , .. .

''3~

screw 45 can be se1ected according tn the height of the bracket.
This is particularly important if the hotplate is to be fixed in very flat built-in hobs. Thus, one type of thotplate can be used for brackets of al 1 heightsO Previously, the var~ous types of ho~plates had to be f~tted with screw bolts of differen$
lengths for this purpose.
Riveted to the bracket 42 ~s an upwardly projeot;ng rod 47 which enga~es in a sleeYe-like recess 46 formed inwa7dly in one piece with the covering sheet, and thus pre~vents the hotplate fro~r rotating relative to ~he bracket. In order 'to prov1de a number of`
possib~e methods of installation for the hotplate, which is particularly ~mportant because of the position of the ronnecting . leads, a plurality of recesses 46 may be provided on the circum- ' ference, optionally also offset by 90 relative to one another.
The fact that the anti-rotation rod 45 is mounted on the bracket instead of on the hotplate as before means that the overa~l dimensions of depth of the hotplate are kept small. The recess 46 is closed off so that the hot ~nner space 48 of the hotplate formed between the covering sheet 24 and the hotplate member 12 ~s sealed of~.
Fig. 3 shows an ~lternative embodiment for the recess 46 :which may be used ~f the sheet metal from which the covering plate 24 is made should not be subjected to any great deformation .
A separately produced s~eeve 46' ~s tightly secured in an opening ~5 in the covering sheet 24 by means of a two-s1ded flange 46''. It ; ~s also poss~ble to pro~ide the sleeve~ ~n the region of the flange 46 ' ', for examp1e, with a pressed-in thread for the subsequent screwing-in of a rod. - !
Fig.4 shows a detai7ed viekl wherein a sealing ring 2~c~

. .
: . :

.

~L~L~

which may be flat or circular in cross section and which is made of a heat-resistant sealing material, is inserted between the border region Z3 of the covering sheet 24 and the lower edge 22 of the hotplate border 21, Suitable materials for the sealing ring 25c include silicon rubber, asbestos-containing sealing materials, etc, Other em-bodiments of seals are shown in Fi~s, 5 and 6, the seal 25a in Fig, 5 consisting of a paste which is introduced into the angle between the border region 23 and the step 25 and spreads over the lower edge 22 and the inside of the border 21 when pressure is applied, This embodiment provides a particularly advantageous method of sealing in the region of the recess 26, Fig, 6 shows, at the corresponding point, a prefabricated sealing ring 25b of Z-shaped cross section which covers the lower edge 22, the inside of the border 21 and part of the inner surface of the recessed portion 28 of the covering sheet 24. This sealing ring may con-sist of a moulding compound produced from an alumina-silicate fibre and impregnated with a lacquer based on silicon resin.
When a seal is used on the outer periphery it is also advisable to provide a seal in the region of the screw 32, The seal is intended to prevent moisture from penetrating into the inner space 48 of the hotplate and thus possibly into the embedding mass 20 if the hotplate is exposed to extreme conditions, such as being trans-ported by sea. Certainly, the hotplate will immediately repel any moisture which get in, without producing any inadmissible leakage currents, but the seal provides an ; additional protection. The seal is established parti-cularly by the abutment o~ the covering sheet on the lower ~lange, since this means that the seal is pro-vided in a region of lower temperature and can be arranged better. Earlier covering sheets were placed .
, .

on the underside of the embedding compound 20 The step 25 provides an additional seal and perfect centering.
Fig 7 shows an embodiment wherein the border 21' of the hotplate member comprises a step-shaped recess 49 on its inner underside so as to form an external con-tinuous border portion 50 of the border 21l which extends somewhat further downwards than the abutment surface for the border region 23 of the covering sheet 2~. This means that, if there is a risk of water running down under the hotplate, which can only happen in exceptional circumstances, the water will drip away without being sucked into the inner space 48 by a capillary action.
Fig 1 shows that a metal foil 51, more parti-cularly a piece of bright crinkled aluminium foil, is located in the inner space parallel to the covering sheet. It is clamped between the border 21 and the , covering sheet 24 or the seals provided (see Figs. 4 to 7) and encloses, between itself and the covering sheet 24, a coating 52 which preferably consists of silica gel or kieselguhr or contains the latter. This material not only provides good insulation but also ensures that any moisture which has got in, e.g. as moisture from the air, is absorbed in the silica gel which acts as a drying agent. As a result of the auto-matic heating during operation of the hotplate, thedrying agent is constantly regenerated automatically as the water is expelled and thus remains permanently effective. If a drying agent is used, it may be a good idea to perforate the metal foil or to place the drying 30~ agent in other containers in the inner space 48 to ensure that it is effective.
If there is no danger of any extreme condi-tions occurring as regards moisture levels, the coating 52~ may be made from highly heat-resistant insulating materials such as inorganic fibres like -: . . .

, ~ .. . ~ ., . . - .

- 13 _ asbestos or other known insulating materials. In conjunction - with the metal foil 10cate~ above~ very effective insulation i5 obtained which further reduces any downward heat losses and caused by radiat~on and convec~ion, which are in any case very slight 1n contact-type hotplates. Howe~er, ~n particular this ensures that the temperature of the cover-~ng sheet 24 ls kept low, so that the hotplate can be ~nstalled even ~n the flattest hobs near wooden parts of kitchen furniture.
10Fig. lO shows three ho~plates stacked one aboYe the other; apart from the fact that the sheet metal part 38' (cf. Fig. 1l) is provided with a flat insertion tongue 53 for the connection of a corresponding flat p1ug 54 for the earth lead 40, these hotplates are identical to the one shown in Fig~ 1. rhroughout the description, the same .
reference numera~s have been used to denote identical partsO
The direction of the section in tig. 10 is offset by 45 relative to Fig. 1 Sc as to show that~ projecting through the covQring sheet 24, there is an insulatinq member 55 which rests inside the ~atter and contains a temperature limiting means in ~ts portion located in the ~nner space 48 and comprises continuous openings 57 ~Fig. 15~ arranged side-by side, thrQugh ~hich connect~ng leads 58 haY~ng ~ highly heat-resistant ~nsulation pro~ect out of the inner space 48 : 25 where they are welded to connecting pins projecting out of ~he embedding mass 20. The basic form of the insulating , . .

.. . .
;
- .
~' `: ' ' : ~ ~

member is elongated in ~he tircum~erential direc~ion and it projects through the covering sheet in the region of a bulge 60.
The connecting leads 58 are connected to a common S connecting member 75 of ceramics ~nsulating material (Figs. 10 and 15~ which contains plug-in or screw connection clips 76 for the connec~ion of current feed lines 78. Ow~ng.to/the~arrangement of the insulating member ~n ~he radial direction substantially in ~he center 1~ of the annular heated zone and the~dimensions of the connect-ing leads, the outer edge 77 of the connecting member 75 is preferably ~t most at ~ spacing from the outer edge there-of which is less than a radius of the hotplate and can flexibly be adapted to the particular conditions of installation, the connecting leads ac~ing as a flexible strip which permits slight pivoting and greater mobility o~ the connecting member ~n the vertical direction but more :~strongly restricts rotation and lateral moYement.
~: : Diametrically oppos~te the insulating member 55 and at 20 ~ corresponding rad~al distance from the center of the hotplate t:here is prov~ded, ~n:the overing sheet 24, a dep~ress:ion 61 the dimensions of which are such that it can ;: s~fely receive the project~ng port~on of the ~nsulating.
`
member ~n th:e mutual arrangement of the ho~plate shown in 25 : Fig. 10, ~ithout~the connecting leads 58 having to be bent too sharply. The width of the depression ls substantial ly : ~ g~reater than that; of the insulating member so ~ha~, as can ~ ~ : : ::

:

.
~:
'' .

be seen in Fig. 10 in the top ~two hotplates, the connecting leads 58 can be folded inwards and the connecting member 77 together with the insulating member can be placed in the depress~on 610 It ~s also poss~ble to fo~d the conn~cting member 77 (bottom of Fig. 10) outwards and place it sub stantially in a plane with the hotplate, while the connect-~ng leads 58 pass through a sorresponding cutout in the pac ki ng pl ate- G3 .~
Thanks ~o the de_pression ~n the covering sheet~ 1t la ~s possible to pack the hotplates in a particularly safe and space-saving manner for storage ~nd dispatch. For this .
purpose, the hotplates are stacked one above the other . with their central axes in alignment and with their flat cooking surfaces 13 and their undersides covered by the covering sheets 24 directed towards each other" while, between the cooking surfaces 13, only a sheet or film 62 is inserted, to preYent scratches, and between the under-sides of the hotplates a packing pla~e 63 is placed, which may consist of plywood or press-board and which has recesses designed so that the hotpla~e ~s centered when ~t is placed thereon. Parts of the hotplate pro~ecting downwards relative to the outer edge 23 of ~he covering plate pro~ect into the recess 64 in the packing plate 63.
The hotplates 11 are offset by 180 relative to one another in the circumferent1al direction, so that the insulating member 55 with the connect;ng leads projetts in-to the depression 61 and the hotplate even takes up less ,~
, packing spaee than ~ts own overall height. The borders 21rest on one another, via the interposed packing plate 63, to form a firm stack wl~h no tendency to t~lt over. Th~
aligned ~rrangement of the hotplates one abov@ the other also part~cularly contributes to this. Depending on the desired packaging or pallet slz~, the packing plates 63 have a plurali~y of ~ecesses 64 arranqed side by side and beh~nd one another so that a large number of hotp7ates can be stored and transported ~n a solid block; this not only saves storage and transporting eosts but also giYes greater protection against damage. Packing can also be carried out ' fully au~omatically by means of gripping devices.
The hotplates according to Fig. 10 do not have the siliea ge1 filling. For insulation purposes only, crinkled aluminium foil 51 ~s placed parallel to ~he covering ~ sheet 24.
: Figures 12 to 15 show another apparatus for prevent-~ng the:hotpla~e from ro~ating rel~tive to the securing ~eans, e.g. the bracket 42. For this purpose, a sheet metal ~; 20 part 65 is used in the form of ~ flat right-angled strip which ex~ends through in the region of the bend 66..Lateral : :~ lndentations 67 form separa~e border areas at the ends of :~the portions 68, which are bent over or rolled round at the ends (cf. Fig. 13 in particular), ss that the ends are :~ Zs ~in the form of pins. U-shaped cutouts 70 are provided ~n : :

:

the portions 68 so as ~o ~orm sheet metal tabs which are bent out from the pl~ne of the portions 68. Fig. 14 shows th~s sheet met~l part S5 ~n the ~ns~alled po;ition. L~ke the sheet metal part 37 in F~g. 1 i~ is securet to ~he . .
hotplate by ~he screw 32 and ~s prevented from rotat~ng thereon by the tab 71 which pro~ec~s ~hrough an opening 72 ~n the hotplate. Instead of the open~ng 72 ~ corresponding embossed portion could.~lso/be prov~ded so as not to .
perforate the cover~ng sheet. Pre~erably, ~he ends 69 are not bent out through about 90 until the hotplate is 1nstalled ~n a cooker or the like; this bending is easily effected thanks to the indentations 67. Only the end 69 ~hich is to be inserted ~n a hole 73 ~n the fixing bracket 42' has to be bent out. This, too, provides lS a protection against rotation without increasing the transporting space.
Flg. 12 shows, by means ofdash-dot lines, that the a~i~otation sheet metAl part 65 may be provided ~th ~
third portlon 37'' on whose end there ls provided a f~at 20 ~nsertion tongue 53 for the connect~on of an ear~h lead.
:: In this ~ay, one oomponent can be used for 3 double :
function 9 namely preventing rota~ion and proY~ding the .
; earth connectlon. HoweYer, ~s shown ~n F~g. 159 ~t 1s also posslble for the sheet metal part 37' ~n ~dd~t~on to the anti-rotation part 65 to be screwed on by means - of the screw 32. Since the part 6S ~s ~n any c~se " ' ~'. '' ~ ' , ' ';, ' ' - 18 ~ 3~

preventeJ from rotating~ a grooved portion 41 on the latter ~s sufficien~ and none ~s needed on the coYering sheet. - . F
S7noe the hotplates are preferably packed in a ~ .
po5it~0n offset by 180, the depress~on 61 ~s diametricall-ly opposite the ~nsulating member 55. Of course,, ~t would ~lso be possible to offset the hotpla~s by ~ different ~ngle. The depress70n 61 ~ould then also have to be offset by a different angle relat~ve to the ~nsula~ing member 55.
In ~ny case, the ad~antage of the cov2ring sheet fs tha~
~t is easy to produce owing to ~ts not very great deform-~tion, in spite olF be~ng suf~ioiently rigid, and it provides a sealed inner space which gives good insulation.
In an embodiment having a central perforation for a central sensor cel1,, the cover could abu~ bnth on the outer border 21 and al50 on the inner edge surrounding the sensor recess, with 1~ step, tc follow the covering sheet.
Here, again, hollow screws could be used for seur~rlg.
In this case, therefore" the p~n w~th ~he ~nternal thread 20 : 71ouid, for example, not be located centrally but b~ould be ln the reg~on of the outer border.

: , ; :

-- - ~, . ...

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. An electrical hotplate for use in a cooking appliance having:
- a hotplate member with a downwardly projecting pin with an internal thread, - a covering sheet covering the under-side of the hotplate member, - screw means to secure both the cover-ing sheet to the hotplate and the hotplate to the cooking appliance, the screw means comprising:
- a hollow screw having an internal and an external thread and an outwardly project-ing shoulder, - the external thread being screwed into said pin and securing the covering sheet between the shoulder and the pin, and a fastening screw for mounting the cook-ing plate at the cooking appliance, which fastening screw can be screwed into the internal thread.

2. An electric hotplate according to claim 1, wherein the screw consists of a sheet metal sleeve, the shoulder being flanged thereto and the sleeve being provided with a pressed thread.

3. An electric hotplate according to claim 1, wherein the shoulder has a grooved portion to engage a correspondingly shaped portion on the covering sheet.

4. An electric hotplate according to claim 1, wherein the shoulder has a grooved portion to engage a correspondingly shaped portion on a member interposed between the covering sheet and the shoulder.

5. An electric hotplate according to claim 1, wherein an interposed member consistinq of sheet metal is clamped between the shoulder of the screw and the covering sheet and has at least one projection projecting outwards from the central region of the hotplate.

6. An electric hotplate according to claim 4, wherein the projection has a terminal for an electrical earth connection.

7. An electric hotplate according to claim 4, wherein the interposed member comprises a projection shaped to be bent away from the covering sheet in order to engage fixing means on the cooking appliance to prevent the electric hotplate from rotating.

8. An electric hotplate according to claim 6, wherein the interposed member is clamped nonrotatably to the electric hotplate by means of tabs bent out of the plane of the interposed member and penetrating in recesses of the covering sheet.

9. An electric hotplate according to claim 1, wherein the hollow screw and the fastening screw comprise screw heads provided with key faces.