EP0981929A1

EP0981929A1 - Heated floor system and method

Info

Publication number: EP0981929A1
Application number: EP98900153A
Authority: EP
Inventors: Eliezer Adar; Evgeni Sorkine
Original assignee: Advanced Metal Technologies Ltd
Current assignee: AFH ADVANCED FLOOR HEATING Ltd
Priority date: 1998-01-07
Filing date: 1998-01-07
Publication date: 2000-03-01
Also published as: CN1249893A; WO1999035887A1; BR9808182A; AU5339298A; JP2001519886A

Abstract

A heated floorboard includes a floorboard body (2) made of a thermal and electrical isolator material and shaped so that a plurality of the floorboards, when assembled one adjacent to the other, form a heated floor. An electrical heater (7) is located in the upper part of the floor body (2). Electrical contacts (73) are located on the floorboard body (2) and connect the ends of the heater (7) to an electrical bus (3). A latch pair (29) mounted near one end of the floorboard (2) is mechanically attached to an electrical bus (3), and snaps on the hole pair (39) to secure the floorboard (2) to the electrical bus (3). Additional hole pairs (392, 393, 394) in an electrical bus (3) serve to attach to other floorboards.

Description

Heated Floor System and Method

Technical Field

The present invention concerns floorboards heated with electrical elements. The invention relates in particular to such floorboards in which the heating elements are thin ribbons made of amorphous metallic alloys, embedded in the upper layer of the floorboards.

Background Art

At present, domestic electrical heating systems usually include an oven in each room, and operating at a relatively high temperature, typically in the range of 700-800 degrees C. This is the operating temperature range for wire heaters made of Kanthal or Nichrome.

A heater capable of operation at these high temperatures for prolonged periods is relatively high-cost. The high cost stems from the requirement that the heater be made of materials having good anticorrosion properties at high temperatures.

Commonly used heating elements for high-temperature heaters are made of, for example, NiCr alloy, Kanthal and Fechralloy. For operation at these high temperatures, the rest of the heating system is also expensive, since the supports and insulation have to also withstand the high temperature of the heater element.

Moreover, the body of the oven and the supports which carry the heater elements and the material the body is made thereof should be able to withstand the operating temperature of the heater, without changing the properties of the material as a result of the heating.

The high operating temperatures also create undesirable fumes and odors, for example odors arising from burning the organic dust particles in the air. Formation of benzopyrene, for example, starts at a temperature of about 180 degrees C. These odors have a particularly unhealthy effect while the heaters are used in closed spaces.

This is one of the reasons that it is not recommended to use spiral-shaped electrical heaters or combustion heaters in closed spaces without ventilation. These heaters consume oxygen from the air while in operation.

Ovens operating at high temperature also present a danger to users, and have to include means for preventing human contact with the heater element. An oven in the room occupies floor space, which may be inconvenient.

Moreover, the room heating is not uniform. Because hot air is lighter, the warm air flows up, creating a layer of hot air near the ceiling of the room, and a layer of cool air near the floor. The floor usually remains cold and uncomfortable to people walking barefoot.

It is required to supply fresh air to the heat generator, which air usually comes from the door, and is usually the coolest air in the room, since this air is found at the lowest place in the room, that is the floor.

The result is that there are currents of cool air and hot air in the room. Thus, the air in the room cannot have an uniform heat distribution.

Fig. 1 illustrates the air currents flowing in a typical room 5, using a prior art oven 55 which generates hot air streams and cold air streams.

The room 5 includes windows 51 , a door 52, floor 53 and ceiling 54. A heating device 55, like a stove or radiator, is located therein. The hot air 61 from stove 55 goes up, since hot air is lighter. A window 51 which is close to the stove 55 may not be hermetically sealed, and because of the large temperature difference between the hot air inside and the cold air outsiαe, hot air 62 escapes out of the room 5. This results in a loss of heat (energy), since hot air is lost. Stove 55 has a relatively small surface area, because of the limited dimensions of a stove in a room. To transfer a given rate of heat energy to room 5, stove 55 has to be very hot, to overcome the relatively large thermal resistance between stove 55 and the ambient air. This results in the high temperature of the air in air stream 61 .

Moreover, the hot air 62 is replaced by cold air 64 flowing into the room 5, usually through a lower opening or one located further away from stove 55, like a slit under door 52. The cold air 64 results in a further energy loss.

The hot air 62 leakage out and cold air leakage in 64 are not just a result of the non-hermetic condition of the room 5, but are mainly a result of the large temperature variations in the room because of the non-homogeneous temperature distribution caused by stove 55.

The heating system in the room 5 includes hot air 61 moving up toward the ceiling 54. The hot air 63 is cooled near the ceiling and flows down toward the floor 53. Usually, there is a layer of hot air near the ceiling 54, and cool air near the floor 53.

People close to the oven 55 feel uncomfortably hot, whereas others, at a distance from the oven, feel cold. Ovens cannot distribute homogeneously the heat throughout a room. A thin ribbon could be used as a heater and operated at lower temperature because of its larger surface area; however, the process of making thin ribbons or foils are expensive to produce. The process involves etching of a resistive material, or repeated rolling of a wire. The resulting foil assumes a metallic a crystalline structure. In recent years, new methods were found for the fabrication of thin amorphous metallic alloy ribbons, primarily for use in magnetic application. Amorphous ribbons are much cheaper to produce than crystalline ribbons.

A widely used process for manufacturing amorphous ribbons involves one-stage melt spinning technology, as detailed for example in Ohno US Patent No. 4,789,022.

Amorphous metallic alloy ribbons are widely used in magnetic applications; these ribbons are not used at present as electrical heaters, because of the low operating temperatures of these ribbons.

At higher temperatures, the ribbon deteriorates by losing its amorphous structure.

Moreover, there was no mention in prior art of amorphous ribbons used as heaters which are embedded in floorboards. Disclosure of invention

It is an object of the present invention to provide a user friendly and healthier heating system, capable of more uniform heating of a closed space.

This object is achieved by an electric heater element as disclosed in claim 1.

In accordance with the invention, the object is basically accomplished by a heated flooring, including floorboards with electrical heating elements therein. The heater in each floorboard is made of a thin ribbon of amorphous metallic alloy.

A thin ribbon has a large area, thus allowing to heat a large surface of the floor. The novel approach is based on the fact that a considerable heat power can be delivered to a room by a heater at a relatively low temperature, since a large area heater is used. Since the floor is not exceedingly hot, it can be touched by the user. People can walk barefoot. Thus, the heater is more user friendly. The relatively low operating temperature prevents the formation of unhealthy odors or gases, like carbon monoxide or benzopyrene. Thus, a more healthier heater is achieved. Moreover, since the floor is the lowest surface in the room, hot air will raise up, and achieve a more uniform heating of the room.

Another object of the present invention is to provide an easy to install flooring.

This object is achieved with a modular structure of floorboard and corresponding electrical bus means.

Thus, despite the advanced and effective structure of the floorboard, it is easy to mount the flooring together and to connect to the electrical power delivery means, to form the heated floor.

It is another object of the present invention to provide an effective heating system, with most of the heat being delivered to the room.

To achieve this goal, the heating elements have a new structure and operation: each heated floorboard includes a heating element made of an amorphous metallic ribbon of metallic alloy, embedded in the upper layer of the floorboards. The ribbons have a large area. This achieves good heat conductance to the heated room, that is lower thermal resistance to surroundings.

The lower thermal resistance allows to deliver more thermal power to the room, at a lower temperature differential, that is while the floor remains at a relatively low temperature. It is warm or hot, but not very hot. Moreover, the floorboard is made of a thermal isolator material, so that only a small fraction of the heat generated therein will flow down to the cement base and be wasted. Most of the heat will be delivered to the heated room.

Still another object of the invention is to provide a structure and method for the production of floorboards at a low cost. Innovative features at several levels of the floorboard production achieve the low cost as desired.

First, the floorboard has an easy to assemble structure, including an isolator body with a thin heated plastic sheet attached to the upper side of the isolator body.

Second, an efficient and low cost method for producing the heated plastic sheet is disclosed.

Third, the heater element in the plastic sheet is made of a thin amorphous ribbon, which is produced at low cost using existing production methods.

Fourth, the invention discloses a method for the integration of an electrical metallic heater element inside a laminate of wood or wood substitute or plastic, based on the fact that the surface temperature of the heater element is very low. Brief Description of Drawings

The invention will now be described by way of example and with reference to the accompanying drawings in which:

Fig. 1 illustrates the air currents flowing in a typical room of prior art heaters including an oven, indicating hot air streams and cold air streams.

Fig. 2 illustrates the air currents flowing in a typical room using the new heated floor system.

Fig. 3 illustrates a top view of a heated floor, including heated floorboards and electrical bus means.

Fig. 4 illustrates a top view of another pattern of a heated floor, including heated floorboards and electrical bus means.

Fig. 5 details a perspective view of a heated floorboard corresponding to the floor in Fig. 3 .

Fig. 6 details a perspective view of a heated floorboard corresponding to the floor in Fig. 4 . Fig. 7 details a perspective view of the mechanical attachment of floorboards to electrical buses.

Fig. 8 illustrates a floorboard with a heater element embedded therein.

Fig. 9 illustrates a floorboard with a heater element of another shape, embedded therein.

Fig. 10 details the shape of a heater element to be used with the heated floorboard.

Modes for Carrying Out the Invention

The heat distribution in prior art systems using hot stoves was illustrated above with reference to Fig. 1. The deficiencies of such heaters were detailed.

The benefits of the new heating system using a heated floor is illustrated with reference to Fig. 2 .

A room 5 includes windows 51 , a door 52 and floor 533 with heater elements (not shown) distributed therein. Floor 533 is heated to a warm state, this resulting in hot air 66 from heated floor flowing up toward the ceiling 54. Because of the large surface of the heated floor 533, there is a relatively low thermal resistance between stove 55 and the ambient air. Thus floor 533 needs be heated only to a warm state to transfer heat energy at a desired rate to room 5. For example, for air in room 5 at about 20 degrees C, the floor needs to be kept at about 30 to 40 degrees C. This results in relatively low temperature of the air in air stream 65 moving up toward the ceiling 54.

The air heated to only a warm state moves up slowly, at a moderate speed, and hot air is generated uniformly throughout the floor surface.

Thus there are no large temperature differences in the room, but the air is more uniformly heated.

This achieves more pleasant conditions for room inhabitants, whenever they may be located in the room 5.

Moreover, the smaller temperature differences result in less hot air leakage out of the room and less cold air entering the room, this resulting in energy savings and a more efficient heating system.

Fig. 3 depicts a top view of a heated floor, including a plurality of floorboard means 2. The floorboard means 2 have the same shape and dimensions as those cf floorboards now in use in a parquetry floor or wood flooring. Thus, floorboards means 2 can be assembled together side by side to form a parquetry floor. Each floorboard means 2 includes electrical heater elements (not shown) therein, to heat the flooring.

Heat energy is thus delivered to heat the room, through the floor.

The heater in each floorboard is made of a thin ribbon of amorphous metallic alloy.

A thin ribbon has a large area, thus allowing to heat a large surface of the floor. The large area is achieved while the electrical resistance is not too low - thus the desired electrical power can be dissipated at a reasonably low current.

The thermal resistance from the heater to the air in the room is lower, because of the large area of contact between the floor and the air. The lower thermal resistance allows to deliver more thermal power to the room, at a lower temperature differential, that is while the floor remains at a relatively low temperature. Thus, it is possible to deliver a considerable heat power to the room, while the floor is usually warm, and in any case not too hot.

Since the floor is not exceedingly hot, it can be touched by the user. People can walk barefoot. Thus, the heater is more user friendly. Moreover, since the floor is the lowest surface in the room, hot air will raise up, and achieve a more uniform heating of the room. Thus, heating the floor provides an automatic air circulation, to mix the air in the room. This prevents the formation of cool layers of air near the floor, and hot layers of air near the ceiling.

The relatively low operating temperature prevents the formation of unhealthy odors or gases, like carbon monoxide or benzopyrene. Thus, a more healthier heater is achieved.

Since the floor is heated to a relatively low temperature, that is to about 20 to 40 degrees Celsius, all the materials in the floorboard are only required to withstand low temperatures. Thus, low cost materials can be used, including low cost plastics or wood or MDF. The low operating temperature also allows the use of heater ribbons made of an amorphous alloy, since there is no danger of exceeding the temperature limit where the alloy ceases to be amorphous. Amorphous ribbons can be produced at low cost.

It is easy to install the flooring with heater floorboards 2, because of the modular structure of floorboard 2 and corresponding electrical bus means 3, as detailed below.

Electrical bus 3 elements are laid underneath the parquet floor, that is underneath floorboards 2. Each floorboard 2 includes an electrical contact 22 at each one of its two ends. When floorboards 2 are laid next to each other, on electrical bus 3 elements, then contacts 22 make electrical contact with the bus elements 3, to deliver electrical energy to floorboards 2. This electrical energy is then converted into heat, which is delivered to the room.

The structure of contacts 22 is detailed below. The contacts are underneath the isolating surface of the floorboards, to prevent electrical hazards and/or short circuits.

Electrical bus 3 elements are connected (not shown) to an electrical source of energy, for example the electrical mains, as known in the art. A voltage reducing transformer (not shown) may be used, because of the expected low electrical resistance of the flooring, and also to reduce the danger of accidental electrocution.

In one embodiment of the invention, a voltage source is connected between every two adjacent bus elements 3, so that an electrical voltage is applied to each floorboard 2 . For example, it is possible to use one electrical source with one output wire connected to the odd bus elements (the first, third, fifth etc.) and the other output wire connected to the even bus elements (the second, fourth, sixth etc.) . This is an economical solution, using one source for providing the voltage to all the floorboards 2.

Another advantage is that the same voltage is applied to each floorboard 2, the voltage being equal to the voltage of the source. A third advantage is that all the voltages in the circuit are low, for any floorboard. Moreover, if part of the floorboards 2 are disconnected or removed, this will not influence the performance of the others. The reason is that all the floorboard elements 2 are connected in an electrical parallel circuit.

This type of connection may be a disadvantage if the electrical resistance R of each floorboard is low, since the total resistance of N floorboard elements is still lower, and equal to R/N . This may require a high current, to achieve the desired thermal power. A high current places demands of still lower resistance for the bus elements 3 and electrical contacts 22.

Another method for applying electrical energy to the heater elements in the floorboards 2 is to connect only the busses 3 at extreme locations to the electrical power source, that is the leftmost bus 3 and the rightmost bus 3 as depicted in Fig. 1 . This achieves a parallel/serial electrical connection, with floorboards 2 between any two adjacent bus elements 3 being in parallel to form a heater block, and all the heater blocks being in series. In this configuration, the bus elements 3 which are not at the edges only serve to connect the floorboards 2 to each other, that is end to end. The electrical contacts 22 are preferably mounted only on the lower part of the floorboard 2, to make contact with bus 3 but to be isolated from the upper surface. The electrical circuits is thus concealed from people in the room, and located inside and under the flooring. The contacts 22 may include clips (not shown) means to mechanically attach to bus elements 3 so as to provide good electrical contact. Additionally, this structure achieves an easy to assemble floor. Each flooring 2 is placed on bus elements 3 and adjacent to the flooring elements 2 already mounted, and the electrical contact is immediately achieved. Moreover, this is a low cost structure.

Alternately, a male/female structure contact (not shown) may be used, with corresponding parts on the floorboard element 2 and the bus 3.

Therefore, the modular structure of floorboard and corresponding electrical bus means provide an easy to assemble floorboard. Thus, despite the advanced and effective structure of the floorboard, it is easy to mount the flooring together and to connect to electrical power delivery means, to form the heated floor.

In another embodiment (not shown) of the invention, the electrical contacts 22 are located on the side of the floorboard 2 at each of its two ends, to allow direct electrical contact between adjacent floorboards 2. Thus, bus elements 3 are only necessary at the two ends of the flooring; in the middle of the flooring, electrical current passes directly from one flooring element 2 to the other, from one end of the floor to the other.

Thus, despite the advanced and effective structure of the floorboard, it is easy to mount the floorboards 2 together and to connect to electrical power delivery means through bus means 3, to form the heated floor.

Referring to Fig. 4, a top view of another pattern of a heated floor is detailed, including heated floorboards 2 and electrical bus means 3. Again, each floorboard 2 has two electrical contacts 22, one at each of its ends.

The various methods for applying electrical energy which were detailed with reference to Fig. 1 above, also apply for the flooring structure depicted here.

In a preferred embodiment, terminal bus means 33 are located at the two ends of the floorboard line, and only these means 33 are supplied with the electrical energy. Intermediary bus means 3 are only used to connect adjacent ends of floorboards 2 to each other, to achieve a continuous path for the electrical current (not shown) flowing in the heater elements. Fig. 5 details a perspective view of a heated floorboard 2 corresponding to the floor structure illustrated in Fig. 3 . The floorboard 2 is shown upside down.

Floorboard 2 includes at each end a depression 21 for the electrical bus (not shown) located underneath. The depression 21 here has a triangular shape because of the electrical bus which is mounted at an acute angle, for example 45 degrees.

A thin plastic sheet with an electrical heater included therein 23 forms the upper surface of floorboard 2. The external plastic layer is an electrical isolator, to isolate the electrical current carrying heater element 7.

The plastic sheet may be made of one of various high-pressure laminated plastic sheets of melamine and phenolic materials which are used in prior art to achieve chemical and heat-resistant surfaces. These laminates are known as "Formica" .

The floorboard body 24 may be made of a material which is an electrical and thermal insulator like wood, MDF (medium density fiber) or a suitable plastic material. The floorboard 24 also provides a mechanical support.

A sealing layer (not shown) may be attached around floorboard 2, to be applied on the side surfaces thereof. The heating element 7 is shown for clarity as reaching the sides of the floorboard 2, however this is not necessary, as illustrated below.

The electrical contact comprises electrical contact surface 72 which is part of the surface of the heating element 7, and mechanical latch means 27 to mechanically attach to electrical bus. If heating element 7 is embedded in Formica 23, then its ends are to be scrapped or plastic otherwise removed to reveal the metallic surface 72 of heater 7 underneath. If heating element 7 is attached to one side of the upper plastic surface of the floorboard 2, then there is no need to prepare the surface 72, since it is already there and uncovered.

The latch 27 is shaped so as to attach to a (not shown) corresponding hole in the electrical bus. Thus, when floorboard 2 is pressed down towards the electrical bus, latch 27 snaps on in the hole therein, to secure the floorboard to the bus.

Thus, the flooring is easy to install, with each floorboard 2 including electrical means 72 to receive electrical power, and mechanical means 27 to mount easily over the electrical bus bars.

The floorboard body 24 is made of a material which is an electrical and thermal insulator like wood, MDF (medium density fiber) or plastic. The low operating temperature allows to use these low cost materials, to achieve low cost floorboards 2.

The body 24 provides both mechanical support and thermal isolation.

At the upper part of the floorboard 2 there is attached a thin sheet 23 of Formica or plastic laminate with a heater therein. The heat generated in heater element 7 flows through the thin upper layer of sheet 23 and into the room, to deliver heat energy thereto.

The heater 7 is embedded in an electrical isolating material, so that there is no danger that people may come into contact with electricity-carrying wires or heater elements. The thin upper layer of sheet 23 is made of an isolating material.

A thin layer 23 is used, to achieve low thermal resistance thereof. Thus, good heat transfer from heater 7 to the ambient air is achieved.

Since the floorboard body 24 is made of a thermal isolator material, only a small fraction of the heat generated therein will flow down to the cement base and be wasted. Most of the heat will flow up, to be delivered to the heated room. This achieves a more effective heating system.

An optional sealing layer (not shown) is attached to the floorboard 2 on the lateral sides thereof, and close to the upper layer 23. The sealing layer may be made of rubber, silicone, RTV or other elastic and water resistant material. When adjacent floorboards 2 are placed close to each other, the sealing layers form a hermetic seal, to prevent water or humidity from penetrating the floorboard body 24 or coming into contact with the electrical bus underneath.

Fig. 6 details a perspective view of a heated floorboard 2 corresponding to the floor in Fig. 4 . The floorboard 2 has a depression 21 for electrical bus, here has a rectangular shape since the electrical bus is mounted at a normal angle to the floorboard 2.

The electrical contacts located at the ends of the floorboard 2 couple electrical energy to the heater 7 inside Formica or plastic sheet 23.

The heating element 7 is shown for clarity as reaching the sides of the floorboard 2, however this is not necessary, as illustrated below. An electrical contact 72 is part of the surface of the heating element 7, with latch pair 28 to mechanically attach to electrical bus (not shown).

The latch 28 is shaped so as to attach to a (not shown) corresponding hole in the electrical bus. Thus, when floorboard 2 is pressed down towards the electrical bus, latch 28 snaps on in the hole therein, to secure the floorboard to the bus. Similarly, on the other end of floorboard 2, there is the other contact surface 73 and two additional latch pair 29 to attach to an electrical bus.

The floorboard body 24 may be made of electrical and thermal insulator like wood, MDF (medium density fiber), or plastic of suitable mechanical strength to provide a mechanical support. It also provides mechanical support. A sealing layer (not shown) is preferably applied around the floorboard, on the lateral surfaces.

Fig. 7 details a perspective view of the mechanical attachment of floorboard 2 to electrical bus 3, illustrated topside down.

A floorboard 2 is mounted at a normal angle to the electrical bus 3 . An electrical contact 73 is part of the surface of the heating element 7.

The latch pair 29 mounted near one end of floorboard 2 serves to mechanically attach to electrical bus 3. Latch 29 is shaped so as to attach to a corresponding hole pair 39 in electrical bus 3. Thus, when floorboard 2 is pressed down towards the electrical bus, latch pair 29 snaps on in the hole pair 39 therein, to secure the floorboard to the bus. Additional hole pairs like 392, 393, 394 in bus 3 serve to attach to other floorboards (not shown).

Fig. 8 illustrates a floorboard 2 with a heater element 7 embedded therein. For clarity, the upper isolating layer was removed, to reveal the heating element arms 74 in parallel, connected at one end to a first electrical contact 72, and to a second electrical contact 73 at the other end.

The electrical contacts 72, 73 are part of the surface of the heating element 7, and are connected to the electrical bus (not shown). A floorboard body 24, made of a material which is an electrical and thermal insulator like wood, MDF (medium density fiber), or plastic, provides a mechanical support and isolates between arms 74.

Fig. 9 illustrates a floorboard with a heater element of another shape embedded therein.

For clarity, the upper isolating layer was removed, to reveal the heating element 7 having a meandering shape. Heating element 7 is connected at one end to electrical contact 72, and to contact 73 at the other end. The electrical contacts 72, 73 are part of the surface of the heating element 7. A floorboard body 24 is made of a material which is an electrical and thermal insulator like wood, MDF (medium density fiber) or plastic, also providing a mechanical support.

Each contact 72, 73 is preferably located at one end of floorboard 2. This allows to supply electrical energy to a heater which spans the whole length of floorboard 2. Thus, all the floorboard is being heated. The upper layer of floorboard 2 comprises a thin sheet of Formica or plastic laminate, with an electrical heater layer 7 embedded therein. Thus, heater 7 is embedded between a (not shown) external isolating layer and an internal isolating layer.

In a preferred method, the upper layer and the floorboard body 24 are manufactured separately and then attached to each other.

The electrical heater 7 is made of a ribbon of amorphous metallic alloy. The heater ribbon 7 is very thin, having a thickness of preferably between 20 to 35 microns, and a width of between about 1 and 100 mm. The thin ribbon has a relatively high resistance, despite the wide surface area. In any case, the preferred thickness is less than 100 micron.

Amorphous ribbons have a noncrystalline structure, which is achievable in specific alloys by rapid cooling. To achieve low cost ribbons, the heating elements may be produced using for example the one-stage melt spinning technology. The amorphous ribbons may be produced with a method known in the art, see for example Ohno, US Patent 4,789,022.

These ribbons were not hitherto been used as heaters because of the embrittlement of the ribbon at relatively low temperatures. At temperatures of about 250 to 300 degrees Celsius the amorphous materials become brittle, whereas existing heaters operate at 600 degrees Celsius or more.

The present invention solves this problem with a novel approach - a large surface heater embedded in the floor is used, thus allowing operation at low temperatures only. This allows the use of the amorphous ribbons, since there is no danger of exceeding the embrittlement temperature.

To further lower cost, the heating elements may use lower cost alloys, that is alloys capable of withstanding oxidation only at low temperatures.

The following alloys are examples of materials usable to manufacture amorphous ribbons and suitable for the production of the heater elements described in the present invention: Fe40 Ni40 B15 Cl Si4

Ni70 Sil5 B15

Fe85 B15

TJ48.5 CU45 Ni5 Sil.5

AI65 C010 Ge25

Fe78 B18 Si4

Additionally, low cost insulation materials are used, that is materials intended for use at low temperatures only.

The heating element ribbons are preferably manufactured using the process developed by scientists at AMT Ltd., that is overheating the melted (liquid) alloy before rapid quenching. This process achieves ribbons with fewer local micro-defects.

These micro-defects are the main cause of the cracks propagation as the electrical current passes through the ribbon, which cracks in the end result in the heating element failure. Therefore, the ribbons are more reliable so that heating elements made therefrom are capable of operation for prolonged periods.

The upper surface of a floorboard with a heater element embedded therein is manufactured as follows.

A plastic sheet (not shown) is manufactured in a process similar to that for manufacturing decorative laminates known under the trade names like Formica. That is, the sheet is a high-pressure laminate, produced from melamine- or phenolic-impregnated papers or fabrics, and compressed under high heat. Several layers of these materials are stacked on top of each other, then pressure and high temperature are applied to produce the laminate. The overall width of the finished product is about 0.7 to 2 mm.

Whereas the process of producing high-pressure laminates is known in the art, the present invention discloses a modified process, wherein a plurality of conductive, thin metallic ribbons 7 are placed side by side, without touching each other, between the impregnated paper or fabrics layers, prior to the application of pressure and heat.

The result is a thin plastic sheet, with metallic ribbons 7 embedded therein, between layers of isolating material. The ribbons 7 are preferably placed in parallel, so as not to make undesired electrical contacts therebetween. The distance between adjacent ribbons should be equal to the width of one floorboard so that, after the laminate is produced and is cut into separate pieces, each piece contains therein one metallic ribbon.

Alternately, the distance between ribbons may be a precise fraction of the floorboard width, for example one fourth that width, so that after cutting pieces apart there will be that number of ribbons in parallel in each piece, in this example there will be four ribbons.

A plastic sheet contains layer units for a plurality of floorboards. These are separated by cutting the plastic sheet along cutting lines, that is top to bottom and side to side. This results in a plurality of top layers (not shown), each including a heater element therein, surrounded by plastic, isolating layers.

Prior to attaching a top layer to the isolating body of a floorboard, part of one side of the isolation may be scraped off at each end of the top layer, to prepare locations 72, 73 for electrical contacts there. The area scrapped off may be the size of the electrical contacts to attach there, an area preferably in the range between 1 and 10 cm-square. These areas may be scrapped prior to cutting the sheet to separate pieces, each to be attached to a floorboard body, or after the cutting.

Thus, a method for preparing the upper layer of a heated floorboard comprises the steps of:

A. Prepare a first isolating layer by placing layers or thin sheets of melamine- or phenolic-impregnated papers or fabrics, to a width about half that required for a high-pressure laminate;

B. place a plurality of conductive, thin metallic ribbons 7, side by side and without touching each other, on top the first isolating layer laid in step (A);

C. prepare a second isolating layer by placing layers or thin sheets of melamine- or phenolic-impregnated papers or fabrics, to a width about half that required for a high-pressure laminate, on top the metallic ribbons layer; and

D. apply high pressure and heat to the whole structure, including the layers laid in steps (A), (B) and (C) above. An optional stage, after step (D) above, would be:

E. after removing the high pressure and lowering the temperature to normal at the end of step (D), scrap off part of either the first or the second isolating layer, the size suitable for an electrical connector, at distances corresponding to each end of the upper layer, to prepare a location 72, 73 for an electrical contact there.

An optional stage, prior to or after step (E) above, would be:

F. cut the resulting laminate into pieces, each piece having the length and width of a floorboard, and each piece including at least one piece of metallic ribbon therein.

In another embodiment of the invention, the heater elements may be attached to only one isolating layer in lieu of the two isolating layers, each on one side of the heaters, as detailed above. The isolating layer is used only to isolate from the ambient; the side with the metallic ribbons is attached to the floorboard body, itself an isolator, to isolate the metallic ribbon on the other side.

This is implemented by the cancellation of step (A) above. This is preferred to removing step (C), since the metallic ribbons being heavier than the isolating layer, the ribbon being on bottom achieve a more stable structure during the application of heat and pressure. Fig. 10 details one preferred embodiment of a heater element to be used with the heated floorboard.

Electrical heater ribbon 7 has a wide area at its two ends, that is the location for electrical contacts 72, 73.

The ribbon 7 as shown is part of a longer ribbon (not shown) , which was cut along cutting lines 77 at its ends. Cutting lines 77 serve to separate a continuous ribbon into heater elements.

To create the zig-zag section of the heater element, areas 78 of the ribbon are stamped out.

The stamped out areas 78 are used to leave a thin meandering conductive path 79 between contacts 72, 73. The strip 79 thus formed has an increased electrical resistance, to keep total current lower, while distributing generated heat more homogeneously over the surface of a floorboard.

This is an optional feature, to increase the electrical resistance so as to keep the total current lower. This achieves a more effective distribution of electrical power. At the same time, this structure achieves a large total heater area, to achieve lower thermal resistance, so as to deliver thermal energy while the floor is not too hot. In a preferred embodiment, metal ribbons 7 are made of an amorphous alloy, to manufacture thin ribbons at low cost.

Various other embodiments would occur to persons skilled in the art upon reading the above disclosure.

For example, the heater elements may be directly placed on the floorboard body, and covered with a thin isolating material, to achieve floorboards with electrical heaters in the upper layer thereof. This replaces the abovedetailed method of separately preparing the upper layer comprising an electrical heater between isolating layers.

Temperature-regulating means may be added, for example including (not shown) temperature sensing means connected to a controller, with electrical switch means between the mains and the heaters in the floor. Thus, electrical power is applied until the temperature reaches a desired value, then the switch is automatically turned off. The system operates in a closed loop to keep the temperature close to the desired value. The switch means are implemented with electronic power components like triacs or SCR.

In a preferred embodiment, a voltage reducing transformer is used, to supply a low voltage and higher current to the heaters in the floorboards. In this implementation, the switch means are connected between the mains and the transformer, that is in the primary circuit. This allows to implement a more cost-efficient switch, with components operating at lower current.

The temperature sensor may be located in the floorboards or attached to the wall of the room. The temperature control is more efficient in the present invention, because of the more homogeneous heating of the room. Thus, there will be no large temperature differences between the various locations in the room.

Although the illustrated embodiments relate to floorboards for assembling a parquetry floor, other shapes of floorboards may be used, to assemble other types of floor, without departing from the scope and spirit of the present invention.

Claims

1. A heated floorboard usable for assembling a heated floor, comprising:

A. a floorboard body made of a thermal and electrical isolator material and shapes so that a plurality of the floorboards, when assembled one adjacent to the other, form the heated floor;

B. electrical heater means located in the upper part of the floorboard body, wherein the heater means are covered with a thin isolating layer;

C. electrical contacts located on the floorboard body and connected to the ends of the heater, to couple electrical energy to the heater; and wherein the electrical heater comprises a thin ribbon made of an amorphous metallic alloy.

2. The heated floorboard as claimed in Claim 1 , wherein the shape of each floorboard is such that, when the floorboards are assembled together side by side, they form a parquetry floor.

3. The heated floorboard as claimed in Claim 1 , wherein the floorboard body is made of an isolating material only capable of withstanding low temperatures of about 20 to 40 degrees Celsius, for example low cost plastics or wood or MDF.

4. A heated floorboard usable for assembling a heated floor, comprising:

B. a thin sheet of plastic laminate attached to the upper part of the floorboard body, wherein electrical heater means are embedded in the plastic laminate, so that at least one side of the heater is covered with a layer of isolator material;

C. electrical contacts located on the floorboard body and connected to the ends of the electrical heater, to couple electrical energy to the heater; and wherein the electrical heater comprises a thin ribbon made of an amorphous metallic alloy.

5. The heated floorboard as claimed in Claim 4, wherein the shape of each floorboard is such that, when the floorboards are assembled together side by side, they form a parquetry floor.

6. The heated floorboard as claimed in Claim 4, wherein the floorboard body is made of an isolating material only capable of withstanding low temperatures of about 20 to 40 degrees Celsius, for example low cost plastics or wood or MDF.

7. A method for manufacturing a thin sheet of plastic laminate with electrical heater means embedded therein, to be attached to the upper part of a floorboard body, comprising the steps of:

B. place a plurality of conductive, thin metallic ribbons side by side and without touching each other, on top the first isolating layer laid in step (A);

D. apply high pressure and heat to the whole structure which includes the layers laid in steps (A), (B) and (C) above.

8. The method for manufacturing a thin sheet of plastic laminate as claimed in Claim 7, further including, after step (D), the step of:

E. after removing the high pressure and lowering the temperature to normal at the end of step (D), scrap off part of either the first or the second isolating layer, the size suitable for an electrical connector, at distances corresponding to each end of the upper layer, to prepare a location for an electrical contact there.

9. The method for manufacturing a thin sheet of plastic laminate as claimed in Claim 7, further including, after step (D), the step of: