FR2589167A1 - Process for obtaining metal objects whose shape changes on heating, and objects obtained by this process - Google Patents

Abstract

Process for obtaining metal objects whose shape changes on heating. This process comprises: - the manufacture of an object made of an alloy which has shape memory properties, preferably with a transition point between 50 and 100 DEG C, such as the Ti-Ni alloy in equal atomic proportions, a Cu alloy containing approximately 20 atom % of Zn and 12 atom % of Al, a Cu-Ni-Al alloy; - forming the object at a first temperature above the transition point, preferably by forming cold and heating in a mould up to this temperature; - cooling to a second temperature, which may be room temperature. Applications to candles, to detoxification cigarette-holders, to the fastening of objects, decoration, entertainment and the like.

Description

 Method for obtaining metallic objects whose shape changes by heating, and objects obtained by this method.

 The present invention relates to a process for obtaining metallic objects whose shape changes by heating, and to the application of this process to various objects, in particular candles, cigarette holders, fixing devices, decorative objects or fun.

 The present invention is based on the existence, known since a relatively recent date, of alloys having shape memory properties.

 Alloys of this type, currently known, sense at high temperature a crystallographic structure comprising a so-called "mother" phase, and at lower temperatures a structure with a martensitic phase. By heating or cooling, one passes from one structure to another, and the transition to the high temperature structure is accompanied by a return to the external shape of the object as it had previously been given to it by forming. in the same area of high temperatures. The shape change takes place towards a temperature that will be called for simplicity, the "transition point". The specialist knows that it is not actually a fixed and precisely defined temperature, with passage abrupt from one structure to another, but from a transition zone, spread over a temperature range specific to and each alloy, which varies according, in particular, to the heating or cooling rates and which, as a result of hysteresis phenomena, is not the same when heating or cooling. However, the expression "transition point" has been retained in the present specification, the meaning of which is clear to the specialist.

 The invention therefore provides a method of obtaining metallic objects whose shape changes by heating, and which has the particularity that it comprises the following steps: - making an object from an alloy having properties shape memory, - shaping of the object at a first temperature, higher than the transition point of said alloy, - cooling of said object to a second temperature, lower than said transition point.

 For several applications, it is preferable to provide that the method also comprises a step consisting in giving the object, after it has cooled to the second temperature, a second shape, different from that which has been imparted to it at the first temperature.

 The field of alloys with shape memory properties is currently in rapid evolution, as it is the subject of much research.

 Among the known alloys, which are preferred for the envisaged applications, there may be mentioned: - the Ti-Ni alloy in approximately equal atomic proportions, - Cu-Zn-Al alloys with atomic proportions varying around approximately 20% Zn and I2% Al, - various Cu-Ni-Al alloys.

 These alloys have different properties from each other; however, they have in common that they have transition points at temperatures between 50 and 100 ° C., that is to say fairly low temperatures, which facilitates their use and their shaping at the first temperature specified above, while the second temperature can be room temperature.

 When the second temperature can be room temperature, a preferred embodiment of the invention consists in that, for the shaping of the object at the first temperature, the object is given, at room temperature, the desired shape ; it is kept in this form for example by enclosing it in a mold, then it is heated, while maintaining it in this form, until the first temperature, above the transition point.

 A first application of the process of the invention relates to candles comprising in the usual way a wick and a mass of combustible material, wax or stearin, and which further comprises, embedded in this mass, an object obtained according to the process of invention, this object having a shape, imparted to the second temperature, such that it does not protrude outside the candle, and being capable of resuming, by heating in the vicinity of the flame of the candle, a chosen shape, by decorative or humorous example, which was given to it at the so-called first temperature.

For example, the object can be formed of thin rods arranged along the wick, and which, when the heat reaches them, take the shape of a heart, or to celebrate an anniversary, that of suitable figures.

 A second application of the process of the invention relates to a cigarette holder intended for the detoxification of a smoker, and which comprises a metal rod obtained in the manner indicated above, this rod having a rectilinear shape, imparted to said second temperature , and being arranged to sink into a cigarette parallel to its axis when this cigarette is placed on the cigarette holder to be smoked, and being able to resume, by heating under the effect of the combustion of the cigarette, an angled shape which was given to it at the first temperature, the transition to this angled shape causing the cigarette to break. Preferably, said rod has, at room temperature, mechanical properties such that it can be straightened by hand, thus allowing its use for a new cigarette.

The manual for such a cigarette holder is obvious. One can provide several rods whose angulation point under the effect of heating is more or less far from the end, so as to allow a progressive detoxification.

The rod can be connected to a mount allowing attachment to a pre-existing cigarette holder.

 A third application of the method relates to a device for fixing objects.

Welding techniques require relatively high temperatures, which limits their field of application.

The techniques of riveting by shock or forced deformation are ill-suited to fragile or deformable objects. Screwing and gluing require long time and / or delicate operations. The invention makes it possible to solve certain delicate problems which are poorly solved by conventional techniques, for example certain assemblies of electronic parts for the space industry. The invention indeed provides a fixing device comprising a part such as a rivet or a clamp, which is able to undergo a deformation after its establishment to secure the objects, this part being obtained according to the method described above, and having a shape, imparted to said second temperature, which allows its establishment, and being capable, under the action of suitable heating, of resuming a shape which has been imparted to it at said first temperature, and which allows it to secure said objects. Heating, given the low level of the transition point, is done at a low temperature, which is not likely to cause deformations. This heating can be combined with an oven normally provided for either sterilization or hardening of certain adhesives or resins. It can also be done locally by passing in front of a suitable radiation emitter.

 The invention is also susceptible of a large number of applications. Among these, mention may be made of obtaining an object, according to the method described above. For example, as a game, a rod can be deformed cold to represent the profile of a person, and, by heating, it deforms to come to represent the profile of another person.

Claims (7)

I) Method for obtaining metallic objects whose shape changes by heating, characterized in that it comprises the following steps: - making an object from an alloy having shape memory properties, - shaping of the object at a first temperature, higher than the transition point of said alloy, - cooling of said object to a second temperature, lower than said transition point. 2) A method according to claim I), characterized in that it further comprises a step consisting in giving the object, after it has cooled to the second temperature, a second shape, different from that which has been given to it at first temperature. 3) Method according to one of claims I) or 2), characterized in that said alloy is formed essentially of titanium and nickel, in atomic proportions approximately equal. 4) Method according to one of claims I) or 2), characterized in that said alloy is a copper-based alloy containing about 20 atoms per cent zinc and I2 atoms per cent aluminum. 5) Method according to one of claims I) or 2), characterized in that said alloy is formed essentially of copper, nickel and aluminum. 6) Method according to one of claims I) to 5), characterized in that said alloy has its transition point above room temperature, and in that, for the shaping of the object to the first temperature, the object is given, at room temperature, the desired shape, it is maintained at this shape for example by enclosing it in a mold, then it is heated, while maintaining it at this shape, until at the first temperature, above the transition point. 7) Application of the method according to one of claims 2) to 6), to obtain a candle characterized in that, in the first shaping, the object is given a decorative shape, and in this that in the second shaping, the said object is given a shape adapted to allow it to be drowned in the mass of the candle in such a way that, when it burns, the said object reaches the vicinity of the flame, and that the transition point temperature is reached when the object is in the vicinity of the flame.