Electric Hot Plate Heating Unit With A Ceramic Cover

Abstract

A hot plate cover of ceramic is used to cover an in-situ vacuum molded heating element. The cover has a dependent flange therearound which is positionable over the open top of the heating element when the cover is in position thereon. The inner faces of the flange contain indentations which receive resilient latches of the heating element assembly to retain the cover in position.

Description

The present invention relates to a surface heating unit and, more particularly, to the mounting of an electrically heated hot plate on the top of an enclosure.

One form of a surface heating unit comprises a hot plate such as used in a laboratory, home or office. Such a hot plate has a housing or enclosure with a surface heating unit. One form of a surface heating unit comprises a ceramic member having a heating element embedded therein and constructed to have a low thermal mass to enable the unit to heat up in a very short period of time. Since the heating top plate is of ceramic construction, certain obstacles are encountered in securing the top plate to an enclosure which is generally of a metal or plastic construction. Previous proposals for mounting such top plates on an enclosure have been unsatisfactory since they were either unduly complicated in structure or were not reliable since they brought about destruction or damage to the top plate after a period of use.

One of the objects of the present invention is to provide an improved structure for retaining a ceramic top plate upon an enclosure of an in-situ molded surface heating unit.

According to one aspect of the present invention, a surface heating unit may be provided having means to define an enclosure having an open top with resilient latch means at the top edges of the enclosure. The heating element may be an in-situ molded insulating or refractory body with the heating coils embedded therein. A ceramic top plate is positionable upon the enclosure open top and has a dependent flange therearound. There are indentations in the flange to receive the latch means when the top is in position on the enclosure with the heating unit whereby the top plate is retained thereon.

Other objects, advantages and features of the present invention will become apparent from the accompanying description and drawings, which are merely exemplary.

In the drawings:

FIG. 1 is a front elevational view of a surface heating hot plate with a portion shown in section;

FIG. 2 is an overall perspective view of the top plate partially in section;

FIG. 3 is a top plan view of the heating assembly and top plate with a portion of the top plate broken away;

FIGS. 4A, B and C are sectional fragmentary enclarged views of a portion of the top plate and heating unit assembly showing the manner in which the top plate is positioned upon the enclosure and then retained in position; and

FIG. 5 is a schematic perspective of the heating unit enclosure.

Proceeding next to the drawings wherein like reference symbols indicate the same parts throughout the various views, a specific embodiment of the present invention will be described in detail.

In FIG. 1 there is indicated generally at 10 what is commonly known as a laboratory hot plate incorporating the present invention. Housing or base 11 has mounted thereon a heating assembly 12. The base 11 is of a type known in the art and can be provided with switches, controls and dials to provide accurate and precise control over the temperature to which the top plate unit may be heated and also to automatically control the duration of time the plate remains at a selected temperature.

Heating unit assembly 12 has a rectangular box 13 (FIGS. 1, 5) with inwardly tapering faces or sides 14 which define an open top 15. The upper edges 16 of each of the enclosure faces 14 are provided with a latch means 17. The latch 17 is a resilient member extending along a face 14. Latch 17 can be moved inwardly as shown in step B of FIG. 4.

The top plate 18 can be made of suitable ceramic, such as shatterproof glass which will resist thermal shock, chemical corrosion and discoloration.

The top plate 18 has downwardly extending flanges or sides 19 which in the form shown are tapered outwardly. On the inner face of each of at least two of the flanges, there is an elongated slot or indentation 20 for receiving a mating latch tab or extension 17 of box 13.

The heating unit 22 can be composed of coiled heating wire element 23 which is in-situ molded into the inorganic fiber body 24. The heating unit 22 can be made by a vacuum molding process as described in copending Application Ser. No. 371,752, filed June 20, 1973. One example of suitable material is described in U.S. Pat. No. 3,500,444 and No. 3,500,464.

The problem of assembly and of securing the top plate 18 to the enclosure 13 is eliminated according to the present invention since, as illustrated in FIGS. 4A, B and C, the top plate is mounted by merely positioning the flanges over the open end of the enclosure as shown in FIG. 4A. The top plate 18 is then moved downwardly in the direction of the arrow 21 to cam the latch tab 17 inwardly as shown in FIG. 4B until the top plate 18 is in its intended position as shown in FIG. 4C. At this point the sloping surfaces of the hot plate flange and the faces of the enclosure conform, and the tab 17 is urged into the indentation 20 because of the inherent spring force of the latch.

As can be seen in FIG. 3, the latches are in the form of a sheet or plate and the tabs are elongated so as to provide a substantial length of securing surface between the latches on all of the faces of the enclosure and the respective indentations.

While the embodiment has been described with an enclosure and top plate which has a rectangular transverse section, it should be born in mind that the enclosure may have other cross sections such as circular or polygonal, and the hot plate may have corresponding sections. The latches would then be positioned and shaped to conform to the cross section of the respective enclosures.

Thus, it can be seen that the present invention has provided a simple and effective arrangement for attaching a ceramic top plate to the top of an enclosure which may be of metal, plastic, or other suitable material. No special tools or skills are required for the assembly, and the danger of cracking, chopping, or breaking the ceramic top plate are virtually eliminated.

It will be understood that changes in various details of construction and arrangement of parts may be made without departing from the spirit of the invention except as defined in the appended claims.

Claims

What is claimed is:

1. In an electric hot plate heating unit, the combination of means defining an enclosure having a bottom and sides, electrical heating and insulating means arranged in said enclosure, latch means at the top edges of said enclosure, a thermally conductive top plate heating surface unit positionable in heat conductive position over said heating and insulating means, said top plate unit having depending flange means there-around positionable over the top of said enclosure and said heating and insulating means, there being indentations in the inner faces of said flange means to receive said latch means when said top plate is in position on said enclosure and heating and insulating means whereby said top plate is retained thereon.

2. In an electric hot plate heating unit as claimed in claim 1 wherein said latch means is resilient and has a portion projecting outwardly of said enclosure whereby positioning the top plate downwardly on the enclosure will cam the projecting portion inwardly until said latch is urged into said indentations upon said top plate reaching its intended position.

3. In an electric hot plate heating unit as claimed in claim 1 wherein said electrical heating means is in-situ molded in said insulating means and said heating and insulating means is carried therein.

4. In an electric hot plate heating unit as claimed in claim 1 wherein said latch means comprises a plurality of resilient latches on the faces of said enclosure with each latch means having a portion projecting laterally of said enclosure and adapted to engage indentations in said top plate flange.