US2171977A - Heating plate - Google Patents

Description

sept. 5, 1939. A Fm 2,171,977'

HEATING PLATE Filed Aug. 17, 1937 xymxymxmxxxvmxmmxm l IAQ@ Passed. sept.. s, 1939 UNITED STATES PATENT OFFICE Q Application August 17, 1937, Serial No. 159,48?

In Germany March 2, 1935 3 Claims.

My invention relates to heating devices and more especially to electric heaters suitable for use in the manufacture of veneered boards used i in the construction of furniture or for other pur- P poses. It is an object of my invention to provide a heater of this kind which is bf particularly simple design and more eiiicient than similar devices hitherto suggested.

The heaters hitherto used in connection with most veneer presses are either made of strong steel plates, formed, or of combinations of tubes inserted between two aluminum plates, the tubes forming the supports for the sheet metal plates and serving to take up the pressure and to transmit heat or cold from the medium iiowing through the tubes to the aluminum plates and to the woodto'be pressed. Electrically heated plates, in which the heating resistances are accommo- 0 dated between strong metal plates or in boxshaped metal castings, .or envelopes of the cushion type involve the drawback of being-comparatively bulky and containing large masses, more especially insulating substance, which must g5 rst be heated up before the electrical current is utilized for the heating purpose proper. In proportion to the useful heat a disproportionate mass of material required to impart to the heaters the necessary strength must be heated and cooled.

l In connection with curved veneer sheets it has already been suggested to heat very thin metal sheets by an electrical current of low tension, however these very thin metal plates are not suitable for the pressing of plane articles. Since they do not possess any rigidity, they must be inserted` between the veneer sheets and therefore, whenever a new charge is placed in the press, the electrical connections must be removed from and replaced on the metal sheets. This is the reason why presses with rigid heating plates were hitherto preferred lnotwithstanding their lack oi economy, because here the veneer sheets could be placed on the rigid plates without these L5 latter sagging. .On the other hand, in presses designed for the dehydration of moist cardboard piles comparatively thick electrodes have been 'arranged below and above and within the pile and the cardboard has then heen heated by the vcurrent passing through it. In these cases a comparatively high voltage must be applied which renders the attendance of the press somewhat4 dangerous, and there further exists the danger of short circuit when piling up the sheets. AThe heater according to the present invention in which heating conduits are' avoids all these drawbacks., Each press plate is formed of a strong middle plate capable of taking up the mechanical stresses and this plate is insulated, on at least one si'de, against heat and electrical current and coated above this ins sulation with thin resistance plates.

Thus the new heater forms a rigid self-sup-v porting plate capable of supporting the veneered boards. When heating the thin resistance plates mounted on the insulation, only that amount of m heat energy is supplied to the press, which is required to heat up the veneered boards. The heat taken up by the thin plates themselves does not play any appreciable rle.

'I'he middle plate may consist of a suitable u metal or even of insulating material and inthe lattercase separate insulating layers below the resistance plates can be dispensed with.

The middle plate might however also be replaced by a combination of rods, tubes or the 90 like. lWhen a particularly high output is desired, the plate may also be traversed by cooling conduits serving the purpose of quickly abducting the heat after the heating operation has come to an end.

' In the drawing affixed to this specification and forming part thereof some forms of an electric heater embodying my invention are illustrated diagrammatically by way of example.

In the drawing Y Fig. 1 is an elevation of a heating plate press,

Fig. 2 being a horizontal section.

Fig. 3 is a cross section, drawn to a larger scale, of a heating plate, the middle part of which is formed of insulating material, and

Fig. 4 is a similar view of a heating plate, the

imiddle part of which possesses electrical conf ductivity.

As shown in Fig. 1 a are the standards of the press and b are the heating plates guided on $0 lthese standards, these plates, if constructed in accordance with Fig. 3, consisting of a plywood body c, both faces of which are covered altogether with thin coherent material sheets d fixed 'thereon by means of a cement. By means of 45 spring contacts e the resistance plates d are connected to the bus bars f, which are arranged laterally of the press in parallel to the standards a and insulated therefrom. The current leads are indicated at g in Fig. 1. 50

In the plate shown in Fig. 4 the middle part consists of meta-l, for instance steel, insulating layers i covering both faces of the steel plate and supporting the thincoherent material sheets d iixed thereon by means of a cement. .66

I wish itv to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modications will occur to a person skilled in the art.

I claim:

1. A heater plate, particularly for use in a veneer press, comprising in combination a rigid base capable of withstanding deformation under the pressure of the press, thin continuous at sheet metal plates `adapted to act as heating resistances covering the tcp and bottom of said 2. A heater plate according to claim 1, wherein the base consists of conductive material, a

layer of insulating material being interposed between the base and each sheet metal plate.

3. A heater plate according to claim 1, wherein 'the base consists of insulating. material.

ADOLF FRIZ.

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