FR2466167A1 - Concrete heating plate for electric furnace - has resistance wires moulded in single stage in concrete base - Google Patents

Abstract

The heating element of the device is set directly in a refractory concrete block during moulding. The concrete used has high mechanical and resistance properties and may be set either as a cylinder or base. The material has low porosity, and is vibrated during setting to prevent void formation. The resistance properties etc. are maintained up to about 1900 degrees centigrade with negligible expansion. The resistance wire (2) forming the heating element may be set within the mould (3) initially by hooks (4) holding it in tension, and may be flush with the inner surface of the final shape. The block may be allowed to dry naturally in air or may be oven dried.

Description

 The invention relates to heating plates or shaped pieces for heating electric ovens intended for handicrafts and industry, as well as the manufacturing process.

 In electric ovens, or heating devices entering heat treatment installations, the transformation of electrical energy into heat is done by electrical resistances. These resistors are supported and insulated with materials having a good resistance to heat and dielectric, either in perforated plates, the wound resistance wire is then isolated from any external contact, or in plates with cells, the resistance wire is then visible from inside the oven which allows radiation and direct convection of the resistance in the oven.

 The resistors can also be placed on the outside of a thin, high-temperature ceramic envelope, the interior forming the oven's heating chamber, and they are maintained by a coating cement or by a second envelope.

 All these construction systems are linked to the support made of high temperature refractory insulating material, which requires complicated moldings and careful cooking to avoid deformation, which explains the high cost price of these parts.

Once the supports have been made, the heating resistors must still be placed.

 The object of the present invention is to produce heating plates or parts by directly incorporating the resistant wire into a refractory concrete, the latter being poured into a mold.

 The refractory concrete forming the heating element is a very good conductor of heat, it has sufficient mechanical and dielectric strength at high temperature (13,500 with conventional resistance wires and more with special wires), it is easily moldable, and does not require cooking because its coefficient of expansion is negligible, but only drying to evacuate the water necessary for its implementation. Its porosity is very low.

 The resistance (s) is achieved either by tape or wire. This resistor is attached to the mold in such a way that it remains in place during casting, with or without vibrations, and so that the mold can be removed quickly after setting. Reinforced outlets are provided for the electrical connection of the resistors outside the plates.

 The object of the invention is to provide a heating element presenting no risk to users, in the event of contact inside the oven with an electrically conductive tool, since the resistance is covered by refractory concrete.

On the other hand, the simplicity of the molds gives great flexibility in manufacturing, and cooking is eliminated.

 The elements made from dense vibrated concrete give a uniform distribution of heat, no shadow area being noticed even in the emerging colors.

The resistance being in contact on all its surface the heat is very well transmitted and avoids any overheating due to a bad convection. The resistors are protected from contact with products that can damage them, and they are not in contact with air, which increases their service life.

 The invention also includes the method of manufacturing this heating element. The best result is obtained by a resistance wound on a rod and stretched, then embedded in vibrated concrete.

 The invention may in any case be well understood with the aid of the additional description which follows, as well as of the appended drawings, which, supplement and drawings, relate to a preferred embodiment of the invention, and do not include well heard, no limiting character.

Figure 1 shows a flat element in perspective with partial section showing the arrangement and the components.

FIG. 2 represents a mold and a system for attaching the resistors.

Figure 3 shows in perspective a cylindrical heating element
Figure 4 shows in perspective a heating element of rectangular section.

FIG. 5 represents in longitudinal section a cylindrical heating element having the resistances flush with the interior wall o
In Figure 1 the heating element shown is composed of a molded plate 1 and a (or more) resistor 2 embedded in this plate The product used for the manufacture of the plate 1 is a refractory concrete resistant mechanically to high temperature, very good conductor of heat, cold and hot dielectric, easily moldable, and requiring no cooking.

 The concrete used in the preferred embodiment retains its properties up to 1900S C; its coefficient of expansion is negligible. Pouring on a vibrating table requires a very small amount of liquid for processing, and leaves a very low porosity. Drying takes place in air or in an oven.

 Resistor 2 is made with resistant wire wound like a coil spring.

 In Figure 2, the resistor 2 is shown in place before pouring. The mold 5 comprises hooks 4 of the same material as the resistance 2. The resistance portions are extended and held by the hooks 4, the elasticity securely keeps the resistance in place during the casting. Other attachment systems can be used, depending on the type of resistance. In the case of unwound wire, tension is effected by springs acting on the hooks 4. Reinforced outlets 5 allow the electrical connection.

 In FIG. 3, the heating element is composed of a molded tube 1, the resistor 2 is placed on a part of the tube.

One or more resistors can be placed over the entire surface of the tube.

 Elements of tubular shape with rectangular section as shown in FIG. 4, as well as any other shape, are only a variant of the cylindrical element in FIG. 3.

 The element shown in Figure 5 is composed of a molded cylindrical tube 6 and a wound resistor. This resistance z is wound around the mold core which facilitates its installation. In this case the resistance arrives flush with the inside, and the insulation is not sufficient. This system is only used for closed ovens when it is not possible to touch the heating element.

Claims (4)

EENDICAT I 0S  1) Heating element by resistance, constituted by a support good conductor of heat In refractory concrete mechanically resistant and dielectric at high temperature (1900 C), and one or more embedded resistors, characterized in that the element is obtained in only one casting operation, with or without vibrations, and ready to use after drying without cooking.  2) Heating element according to claim 1, characterized in that several resistors are arranged in the same plane.  3) Heating element according to claim 1, characterized in that one or more resistors are arranged on each side.  4) A method of manufacturing the heating element according to claims 1 to 3, characterized in that it consists in placing the resistors in the mold, and in pouring, (with or without vibrations), a wet refractory concrete, in a single time.