CORE FOR HEATING CORD WINDING COMPENSATING FOR EXPANSION

Abstract

Core for heating cord winding compensating for expansion The present invention relates to a device for electrical heating by means of a heating cord winding electrically wound on a core characterized in that the core is provided with one or more parts deformable under the effect of applied stresses, the deformation of which is capable of compensating for the variation in length of the cord under the effect of the variation in temperature and thus capable of maintaining said cord under mechanical tension Figure to be published for the abstract: [Figure 1]

Description

Title of the invention: CORE FOR HEATING CORD WINDING COMPENSATING FOR EXPANSION

[0001] FIELD OF THE INVENTION The present invention relates to a device for electrically heating premises by means of a heating cord electrically wound on a core provided with deformable parts allowing the ribbon to be kept under the mechanical tension necessary for proper operation throughout the operating temperature range.

[0002] BACKGROUND OF THE INVENTION Heating premises using electrical energy essentially uses the Joule effect in an electrical resistive element powered by electrical connectors from an electrical energy source. The transfer of heat to the premises, the air and the occupants occurs by thermal conduction and / or convection and / or infrared radiation emitted by the electrical resistive element due to its temperature.

[0003] The electrical resistive element may be in the form of a winding (coil) of a resistive cord on a core, for example made of ceramic. The core may be, for example, cylindrical in shape with a director in the form of a circle or a very flattened ellipse or a polygon with rounded corners. The core can be a solid solid body or a hollow body, generally the resistive element has proximity and / or extensive contact with the mass of the core The core may be structured, for example comprising at its periphery longitudinal beams distributed radially regularly at the vertices of a regular polygon, thus allowing support of the ribbon through contact of the ribbon with the beams and the absence of contact of the ribbon with the core in the inter-beam spaces. In an exemplary embodiment, the core is composed of a rectangular parallelepiped volume of large horizontal extension and much lower vertical height, two of whose opposite vertical faces are each joined by a semi-cylindrical volume of diameter equal to the height of said face. In another example of the core's realization, its shape is an ellipsoid with a major horizontal axis much larger than the minor vertical axis; for example, the major axis is ten times larger than the minor axis.

[0004] The resistive cord may, for example, be of cylindrical section, but not limited to, in the case of the winding of a conductive wire bearing an insulating varnish or by example of rectangular section in the case of winding a ribbon

[0005] Generally, the cord is wound during its installation on the core under a certain mechanical tension in order to maintain the cord in place on the core. However, thermal expansion during use causes the cord to lengthen without this lengthening being compensated by a dimensional increase in the core and therefore this potentially induces a relaxation of the mechanical tension and consequently potentially a disappearance of the maintenance in place of the heating cord. With the expansion coefficients of 14 E-6 / K for stainless steel, 8.6 E-6 / K for titanium, 23 E-6 for aluminum, the increase in length when going from 17°C to 37°C for a length of 600 mm long which typically corresponds to the dimension of a heating slab installed on the ceiling, is 0.168 mm for stainless steel, 0.103 mm for titanium and 0.276 mm for aluminum.For a double temperature difference, from 17°C to 57°C, T elongation would obviously be double these values. This problem is particularly important when the core is designed so that the wound ribbon has little physical and therefore thermal contact with the core. It is then difficult to secure the cord to the core to keep it in place. This situation is particularly encountered for heating devices for which low thermal inertia is necessary in order to obtain short temperature rise times. In such a case, between the contact areas with the core, the cord can only be held in place and without deformation due to mechanical tension which would be exerted and maintained along it.

[0006] DETAILED DESCRIPTION OF THE INVENTION The device which is the subject of the invention presented below makes it possible to produce a heating cord winding installed on a core and maintained under mechanical tension throughout the operating temperature range. This invention is particularly interesting for cores designed so as to have only small contact surfaces with the cord.

[0007] The device which is the subject of the invention consists of at least one three-dimensional winding of a single layer of a heating cord capable of being supplied by means of electrical connectors outside the scope of the invention, from an electrical energy source outside the scope of the invention, preferably in the form of a ribbon, made of electrically conductive material of N turns of pitch p on a core where a single layer means that the possible overlap between two consecutive turns is less than half the width of the cord.

[0008] An example of a heating cord winding is a winding of circular cupro-nickel wire of 1 mm diameter with a pitch of 2 mm. Another example resistive cord winding is a winding of stainless steel or any other aluminum alloy ribbon where the width of the ribbon is between 25mm and 50mm typically having the value of 30mm and where its thickness is between 15micrometers and 100micrometers typically having the value of 20micrometers at 35mm pitch. Another example of resistive cord winding is a ribbon of polymeric material such as polypropylene or PET or Teflon 50micrometers thick and 25mm wide aluminized on at least one of its faces to a thickness of 5micrometers. The core of the device which is the subject of the invention is made up of three parts designated, as follows, by convention: a central part called the longitudinal part of oblong shape, that is to say of length greater than the thickness, and potentially concave over at least a fraction of its length two end parts, called uprights, composed of one or more cylindrical or cylindro-conical and convex sections, having a rounded and flat shape facing the rounded shape. The three parts can be part of a monolithic whole or assembled together.

[0009] The device which is the subject of the invention is characterized in that: -The section of the core is inscribed in a convex geometric figure whose perimeter p can be reduced in a range of elastic deformation, by exerting constraints on all or part of the core in such a way that the perimeter p goes from its value pO without constraints to its value pmin, where pO-pmin is at least equal to k times the variation in length of half a turn of heating cord between the temperature at zero power and the temperature at nominal power. We will take k >=1.5

[0010] The heating tape is installed on the core in a state of compression under the effect of stresses applied to the core. The exertion of said stresses may result from an external action, for example bearing forces exerted manually or by a machine and or from a stress exerted by the heating cord due to its installation on the core and the exertion of tensions on it during its installation, whether manually or by means of a machine. The reduction in perimeter due to applied constraints results from the choice of using one or more materials constituting the core whose intrinsic compressibility is sufficient and or from the choice of a design resulting in geometric deformability of all or part of the core.

[0011] -Preferably, the core comprises, at the level of the flank of the ends of the uprights, a raised and / or hollow structure, called a hooking device, intended to allow a device to be fixed, preferably in a removable manner, to the core, said constrictor device outside the scope of the invention, making it possible to exert between the two uprights a force tending to bring them together and thus longitudinally constrain the core. The constrictor device allows to keep the core in the state of reduced perimeter. This constrictor device is designed in such a way as not to disturb the winding of the heating cord.

[0012] -two so-called blocking and securing zones intended to secure the ends of the cord with the core as soon as the latter is in the state of perimeter reduction and the winding of the cord is completed. The securing must be able to withstand the tension exerted on the cord as soon as the core is released from the constrictor device.

[0013] The central part of the core can be designed so as to allow the perimeter p to be reduced within a range of elastic deformation. One of the embodiments is the variation of length of the central part. An example of the realization of this effect uses what will be designated by the term Spreader-Tensor It includes: -Perpendicular to the end uprights, along the X axis, a set of crosspieces called Spreader-tensors extending between the two end uprights These Spacer-Tensor Crosspieces have a length substantially equal to the dimension of the longitudinal part (for example approximately a little less than 600 mm) and preferably a height less than the nominal distance between the parts of the front face ribbons and parts of the rear face ribbons, such that these Spacer-Tensors remain at a distance from the inner faces of the ribbons, or by inner we mean the face of the ribbon which is oriented towards the inside of the winding. They have a compressible / extensible part in the direction of their length. The extension capacity of these parts and their response time are sufficient to, during a phase of temperature increase of the ribbon, compensate for the resulting expansion and the increase in length of the flat parts of the coil so that these always remain under tension.

[0014] Preferably, to facilitate the adaptation of the cord in its phase of elongation by expansion on the rounded parts of the upright, the surface region of the rounded parts of the uprights must allow a very slight displacement of the ribbon perpendicular to the axis, without the ribbon winding on this part. For this: either we make sure that the coefficient of friction between the ribbon and the said rounded part is very low, for example by Teflon coating the surface of the said part or by adding a Teflon shell either by inserting rollers into holding cavities, rollers (see [Fig.5]) perpendicular to the ribbon.

[0015] Another of the operating modes is the variable curvature of the central part, which could be called the arc method. In this embodiment, the applied stress has the effect of deforming the core, which in its unstressed state can be a parallelepiped, so as to curve it and thus obtain a crescent. The heating cord installed on this crescent is in the form of an arc in contact with the convex part of the crescent and in the form of a flat part stretched between the ends of the concave part of the crescent.

[0016] Another embodiment uses flexible fins (3022) with which the uprights of the core (302) are provided, fins which by design tend to apply outward pressure to the heating cord and thus spread it apart, having the effect of increasing the length of each turn of the cord. The shape of the core and therefore of the turns is preferably oblong so that the winding has in its lower part a radiating surface of large extension while keeping a limited vertical dimension.

[0017] DESCRIPTION OF THE DRAWINGS Other objects, characteristics and advantages of the invention will be better understood in light of the detailed description which follows, with reference to the appended drawings in which:

[0018] [Fig. 1] represents an embodiment of the invention where the heating cord (101) is wound on a core (102) whose longitudinal part is made up of extenders (1022) between two uprights (1023). On the side of the ends of the uprights we see the attachment device which is made up of a cylindrical cavity intended to accommodate the tenons (1024) of the constrictor device (1025) shown. [Fig.2] shows an embodiment of the invention where the heating cord (201) is wound on a core (202) whose longitudinal portion is capable of being curved. One view shows the core (202) without the heating cord and not curved. Another view is oriented to show the concave side (2021) where the heating cord wound on the core is not in contact with the longitudinal portion. Another view is oriented to show the convex side (2022) where the heating cord is in contact with the longitudinal portion.

[0019] [Fig. 3] shows an embodiment of the invention where the core uprights (302) are provided with flexible fins (3022) tending to apply pressure to the cord outwards and thus spread the heating cord thus increasing the length of each turn of the cord. A first view shows the core alone. A second view shows the heating cord (301) as it appears once it is wound, but in this view the core is not shown. A third view shows the heating cord assembly wound on the core. [Fig.4] represents an embodiment of the invention where the heating cord is wound on a core (402) whose core section in the longitudinal part is of doubly concave shape (4021). The end of the uprights has a cylindrical housing (4022) capable of receiving the reel (4023) intended to receive one end of the cord (401) which can be secured to the reel thanks to the support plate (4011), or without the support plate by making a number greater than 3 turns of the cord around the reel and thus benefit from the capstan effect type locking effect. A figure shows the cord alone (401) as it appears once installed on the device. Another figure shows the core (402) with its two end housings (4022) which, due to the odd number of half-turns, are each located on one of the uprights and the winders (4023) removed from their housings.Another figure shows the entire device with the support plates (4011) where the screwing is not shown. [Fig. 5] shows a particular embodiment of an upright (5021). The rollers (5022) are seen inserted into cylindrical cavities (5023) in the upright (5021) and intended to support the cord (not shown here) during its path around the upright, not shown here, around the upright in such a way that any movement of the cord around the upright is carried out almost without friction. The attached view shows in an enlarged form a section of the upright where the rollers (5022) are seen inside the cavities (5023).

Claims

Claims

1. Device for electrically heating premises by means of a heating cord electrically wound on a core, characterized in that: the core is provided with one or more parts deformable under the effect of applied stresses, The section of the core is inscribed in a convex geometric figure whose perimeter p can be reduced in a range of elastic deformation, by exerting stresses on all or part of the core in such a way that the perimeter p changes from its value pO without stresses to its value pmin, where pO-pmin is at least equal to k times the variation in length of half a turn of heating cord between the temperature at zero power and the temperature at nominal power. k is at least equal to = 1.5

2. Claim according to 1 wherein one of said deformable parts is the longitudinal part.

3.

4.

5. Claim according to 2 where the deformation is of the shortening type Claim according to 2 where the deformation is of the curvature type Claim according to 1 where one of said deformable parts is of the flexible fin type secured to an upright

6. Claim according to 1 to 5 where the core is provided at the sides of the uprights with hooking devices intended to allow the securing of constrictors to the core.

7. Claim according to 1 to 6 where at least one of the uprights of the core comprises at its end a part free to rotate around the axis of the upright intended to serve as a support for winding and fixing one end of the cord.

8. Claim according to 7 where said free rotating part comprises a pre-glued surface and / or provided with threaded holes for screwing a support plate onto the cord

9. Claim according to 7 to 8 where said free rotating part is made of electrically conductive material and serves as an electrical contact between the heating cord and the external electrical circuit.

10. Claim according to 1 to 9 wherein the heating cord has the form of a ribbon.

Images