FR2661725A1 - DEVICE FOR SEPARATING TWO SPACES IN THE EVENT OF A TEMPERATURE RISING, METHOD FOR PRODUCING THIS DEVICE AND AMMUNITION COMPRISING SUCH A DEVICE. - Google Patents

Abstract

The device for separating two spaces (1a, 1b) in the event of a temperature rise above a threshold temperature (Ts) comprises at least two adjacent parallel plates (2a, 2b) provided with openings (3a, 3b ), placed between these two spaces (1a, 1b), at least one of these plates being made of a shape memory alloy whose shape changes in the vicinity of the threshold temperature (Ts). When the temperature of the device is below the threshold temperature (Ts), the openings (3a, 3b) made on two neighboring plates (2a, 2b) have an overlap zone (4). When the temperature of the device exceeds the threshold temperature (Ts), the openings (3a, 3b) narrow enough to cancel this overlap zone (4). Use in particular in pyrotechnic safety applications for ammunition.

Description

i The present invention relates to a device

  to separate two spaces if the temperature rises

  This device is intended in particular to provide a protective screen between these two spaces when the medium undergoes an abnormal heating, the two spaces being able to communicate in the absence of this heating. This device finds a particular application in the field of pyrotechnic safety, especially for ammunition. The invention also relates to a method for producing such a device, and a munition comprising

these measures.

  Explosive charges, in particular those included in ammunition, consist of a

  main charge intended to produce the desired effects

  chés (projection of splinters, blast effects, production of a jet) in which the detonation is initiated by a relay explosive, generally more sensitive, itself

fired by a detonator.

  Among the risks of accidental ignition is fire, with the consequence of successively switching from combustion of the relay explosive to deflagration and then detonation in the main charge. This last mode of reaction, the most catastrophic of the

  safety point of view, being all the more pro

  bable that the explosive mass is important The safety

  rity is generally ensured by the interposition of an inert barrier put in place and then removed by

  mechanical means including cost and size,

  everything if we take into account the controls

  annexes, constitute sensitive easements.

  The aim of the present invention is to remedy the above drawbacks by proposing a simple separation device, inexpensive, compact and

  particularly safe operation.

  Another object of the invention is to provide an intrinsic safety device which, by its

  constitution, is activated in temperate situations

  abnormally high ture without requiring the intervention of an operator or external mechanical means. The invention thus provides a device for separating two spaces in the event of a temperature rise

  above a threshold temperature.

  According to the invention, this device is charac-

  terized in that it comprises at least two adjacent parallel plates provided with openings, placed between these two spaces, at least one of these plates being made of a shape memory alloy, the shape of which changes in the vicinity of the threshold temperature, in that the openings made in two adjacent plates

  have an overlap area when the temperature

  ture of the device is below the threshold temperature and in that the opening made on the plate

  memory alloy is suitable for shrinking

  cir enough to cancel the overlap area

  between the openings made on two plates

  sines when the device temperature exceeds the

threshold temperature.

  The device thus constitutes a barrier which is interposed between the two spaces when it undergoes excessive heating. At low temperature, the overlap zone of the openings ensures communication between the two spaces and, at abnormally high temperature (i.e. - say higher than the threshold temperature), the intrinsic properties of the alloy used

  activate the barrier by removing this cover

  ment by contraction of the openings In the application to ammunition, one thus obtains a barrier activated at high temperature (for example in the event of fire) and a normal functioning of the ammunition if this abnormal heating does not occur, the deflagration propagating then through the overlap area of the openings

  in the case of a normal explosion of the ammunition.

  Since shape memory alloys often admit a large deformation in their phase at low temperature, the openings can be formed in the plates by exploiting this large deformation,

  which allows to obtain a large amplitude of

  cissement when the threshold temperature is exceeded which corresponds to the temperature of the phase transition in the alloy This large amplitude of shrinkage

  results in a significant sensitivity of the device.

  This sensitivity is further increased when several adjacent plates made of the alloy are used.

shape memory.

  Other features and advantages of the

  present invention will appear in the description below

  below, read in conjunction with the attached non-limiting drawing in which:

  Figures 1 and 2 are respective views-

  ment in side section and in plan of a device according to the invention at low temperature; Figures 3 and 4 are views similar to Figures 1 and 2 at high temperature; Figure 5 is a partial view in longitudinal section of a munition using a device

according to the invention.

  The device for separating two spaces comprises, in accordance with the invention, two juxtaposed plates 2 a, 2 b separating two spaces la, lb shown at low (respectively high) temperature on the

  Figures 1 and 2 (respectively 3 and 4).

  The plates 2 a, 2 b are made of shape memory alloy These known alloys -for example from "Shape Memory Alloy" (L McDonald SCHETKY,

  Scientific American, volume 5, November 1979, page 241) -

  have the property of undergoing a phase transition at a temperature Ts (below called threshold temperature) between an austenitic phase at high temperature and a martensitic phase at low temperature These alloys, such as Cu-Zn-Al alloys, Cu- Al-Ni or Ni-Ti, admit further significant deformation in their martensitic phase (low temperature), which is advantageous in the context of the present invention as

it will be explained later.

  Among the shape memory alloys likely to be used, we will propose for example Tinal (Nickel-Titanium) whose transition threshold is adjustable at will up to 1000 C by varying the composition: the specification in transpiration is to give to the manufacturer of the alloy Another alloy has the same threshold possibilities: Betalloy (Copper Zinc Aluminum) The deformation recoverable during the transition is 8% for Tinal and 4%

for Betalloy.

  The plates 2 a, 2 b of shape memory alloy are arranged, parallel and adjacent to each other, between the two spaces la, lb and crossed by circular openings 3 a, 3 b, 5 a, 5 b The size of these openings 3 a, 3 b, 5 a, 5 b changes when you pass

  from a temperature below the threshold T to a temperature

  ture above the threshold Ts, which explains the differences

  between figures 1 and 2 on the one hand and the

Figures 3 and 4 on the other hand.

  In FIGS. 1 and 2, the device is shown at low temperature (below T 5) and the circular openings 3 a, 3 b made respectively in the plates 2 a, 2 b made of shape memory alloy

  have an overlap area 4 which communicates

  the spaces la, lb. In Figures 3 and 4, the device is shown at high temperature (above Ts) and the circular openings 5 a, 5 b made respectively

  in plates 2 a, 2 b have shrunk, this results

  as long as the transition from the alloy of the plates 2 a, 2 b to the austenitic phase Consequently, the overlap zone 4 no longer exists and the device constitutes a barrier separating the spaces la, lb. FIG. 5 shows a separation device according to the invention used to separate a main explosive charge 6 from a relay charge 7 in a munition The main charge 6 is contained in a compartment 1b delimited on the one hand by a cylindrical wall 8 and on the other hand by one of the plates 2 b of the separation device, this plate 2 b being covered with a thermal insulating coating 10 on its face llb adjacent to the main load 6 On the opposite side, the load relay 7 is included in one room

  delimited on the one hand by the second plate 2 has distance

  positive and on the other hand by a metal wall 9 conducting heat which comes into contact with this plate 2a on its face lla adjacent to the chamber 1 A detonator 12 is further provided at the end of

  the chamber opposite to plate 2 a.

  To obtain the screen effect activated by excessive heating, the separation device is

  carried out as follows, in accordance with the invention

  We choose two plates 2 a, 2 b of memory alloy

  of shape having dimensions suitable for use

  desired device location Each of these two

  plates 2 a, 2 b is then heated above the temperature

  rature threshold Ts of the alloy, that is to say in its austenitic phase then pierced, at this temperature, with a circular opening 5 a, 5 b The two openings 5 a, 5 b have a shape and identical dimensions and they are offset so as to present no overlap zone when the two plates 2 a are superimposed,

  2 b, as illustrated in FIGS. 3 and 4.

  The plates 2 a, 2 b are then allowed to cool below the threshold temperature Ts, in the phase

  Martensitic of the alloy Then we enlarge the openings

  tures 5 a, 5 b to give them the dimensions 3 a, 3 b, shown in FIGS. 1 and 2 This enlargement is carried out by mechanical deformation at a temperature below the TS threshold, for example by means of a frustoconical spacer engaged in the opening 5 a, 5 b then

  pressed to enlarge to its desired shape 3 a, 3 b.

  In FIGS. 1 to 4, the amplitude of this enlargement between the openings 5 a, 5 b in FIGS. 3 and 4 and the openings 3 a, 3 b in FIGS. 1 and 2 has been exaggerated to make the invention clear. practical, the section of the openings is enlarged by a few percent This mechanical deformation is possible thanks to

  the deformability of the alloy in its martensi-

  tick which results from the different crystalline variants existing in this phase The enlarged openings 3 a, 3 b have, when the two plates 2 a, 2 b are superimposed, a covering zone 4, as illustrated in the

Figures 1 and 2.

  The two plates 2a, 2b are then brought together to form the device according to the invention by placing them parallel to one another so that the overlap zone 4 of the two enlarged openings 3a, 3b is present for establish communication between

  spaces la, lb and so that this overlap disappears

  raises in the event of heating of the device above the threshold temperature Ts which brings about a return of the alloy to the austenitic phase and consequently a return of the openings 3 a, 3 b practically to their initial form a, 5 b for which the overlap zone 4 enters

  openings 3a, 3b is canceled.

  The space separation device of the invention can be used when it is desired to make a partition which lets the two spaces communicate la, lb except in the event of abnormal heating resulting from an accidental cause such as a fire. The memory alloy of shape used is therefore selected for its deformability properties in martensitic phase as

  mentioned above but also depending on its temperature

  transition strip which defines the threshold temperature T beyond which the heating is considered

as excessive.

  If no overheating occurs, the device

  When the two spaces 1a, 1b always communicate, when the munition illustrated in FIG. 5 is detonated, the detonator 12 triggers the combustion of the

  relay load 7 This combustion produces a deflag-

  tion which results in a jet of high energy gas, which passes through the separation device for the covering zone 4 of the openings 3 a, 3 b to initiate the

  detonation of the main charge.

  In the event of a fire, the temperature of the device

  tif increases, the thermal conductive member 9 in contact with one of the plates 2a promoting the transfer of heat to the separation device When the temperature reaches the threshold temperature Ts it is exceeded, the alloy constituting the plates 2a , 2 b undergoes

  a phase transition which puts it back in the marten phase

  sitics The openings 3 a, 3 b then resume sensi-

  clearly their initial form 5 a, 5 b, thus making dispa-

  the communication 4 between the two spaces 1a, 1b. If this abnormal heating leads to the combustion of

  explosive relay 7, the deflagration produced does not work

  will not be detonated by the main charge because the jet of initiating gas cannot pass into the space 1b containing the main charge 6 because of the barrier formed by the two plates 2 a, 2 b The thermal insulating coating 10 furthermore prevents heating by conduction of the load 6 which

  could also cause it to explode.

  The invention therefore makes it possible to reduce the damage caused by fires in the depots of

  ammunition without the use of amo screens

  as in the prior art, these screens and the associated mechanical means being expensive, bulky and often requiring the intervention of a

  operator to be mounted or dismounted on the muni-

  The invention overcomes these disadvantages by using in an original way the properties of the alloys.

with shape memory.

  The invention is not limited to the examples

  described above In particular, it is not limited to

  as to the number or shape of the openings 3 a, 3 b, 5 a, 5 b made in the plates 2 a, 2 b provided that at least one communication zone 4 between the spaces la, lb is present at temperature normal and disappears in

overheating.

  Likewise, the invention can be implemented

  with a number of parallel plates greater than two.

  Some of these plates can also be made from a material different from shape memory alloys II

  it is enough that a plate is of such an alloy to per-

put to realize the invention.

  Finally, it should be noted that the step of piercing the openings 5 a, 5 b in the plates 2 a, 2 b can be carried out below the threshold temperature Ts, before

  their enlargement by mechanical deformation.

  The advantage that one observes when one carries out this drilling in the austenitic phase as described above is that one controls more precisely the morphology of the

  openings 3 a, 3 b, 5 a, 5 b in the two phases.

Claims (9)

  1 Device to separate two spaces (la, lb) in the event of a temperature rise above a   threshold temperature (Ts), characterized in that it comprises   takes at least two adjoining parallel plates (2 a, 2 b) provided with openings (3 a, 3 b, 5 a, 5 b), placed between these two spaces (la, lb), at least one of these plates (2 a, 2 b) being made of a memory alloy   of form whose form changes in the vicinity of the temperature   threshold erasure (TS), in that the openings (3 a, 3 b)   practiced in two adjacent plates (2 a, 2 b) presented   tent an overlap zone (4) when the device temperature is lower than the threshold temperature (TS) and in that the opening (3 a, 3 b, 5 a, 5 b) made on the plate (2 a , 2 b) in shape memory alloy is adapted to shrink enough to cancel the overlap zone (4) between the openings (5 a, 5 b) made on two adjacent plates (2 a, 2 b) when the temperature of the device exceeds the temperature of threshold (Ts).   2 Device according to claim 1, characterized in that it comprises two plates (2 a, 2 b) in shape memory alloy provided with openings (3 a, 3 b, 5 a, 5 b), these openings (3 a, 3 b) having undergone   enlargement by mechanical deformation at a temperature   ture below the threshold temperature (Ts).   3 Device in accordance with one of the claims   tions 1 or 2, characterized in that the openings located on two adjacent plates (2 a, 2 b) have the same shape and the same dimensions and are offset with respect to each other so as to present a zone of cover (4) when the temperature of the device   is below the threshold temperature (Ts), this overlap   really disappears in case of temperature rise   above the threshold temperature (TS). he   4 Device in accordance with one of the claims   1 to 3, characterized in that it comprises a thermal conductive member (9) in contact with one of its faces (lia).   5 Device according to one of claims 1 to 4, characterized in that one of its faces (llb)   is covered with a thermal insulating coating (10).   6 Method for producing a separation device between two spaces in accordance with one of the   Claims 1 to 5, characterized by the successive steps   following sives: openings (5 a, 5 b) are drilled in the plates (2 a, 2 b); the section of each opening (5 a, 5 b) made in each plate (2 a, 2 b) made of shape memory alloy is enlarged by mechanical deformation, at a temperature below the threshold temperature (Ts); the plates (2 a, 2 b) are placed in parallel so that the openings (3 a, 3 b) made in two adjacent plates (2 a, 2 b) have a zone of   overlap (4) and so that this overlap area   ment (4) is canceled if the openings (3 a, 3 b) retrou-   substantially wind their initial shape (5 a, 5 b) when the temperature rises above the threshold temperature (TS).   7 Method according to claim 6,   characterized in that the openings (5 a, 5 b) are permissible   created in the shape memory alloy plates (2 a, 2 b) at a temperature higher than the temperature of threshold (TS).   8 Ammunition comprising a main explosive charge (6) contained in a first space (lb) and an initiating explosive charge (7) contained in a second space (la), characterized in that it comprises   furthermore a device in accordance with one of the claims   1 to 5, this device separating said first and second spaces (la, lb).   9 Ammunition according to claim 8, characterized in that the device for separating two spaces comprises a thermal insulating coating (10) on its face (llb) adjacent to the space (lb) containing the main explosive charge (6).   Ammunition in accordance with one of the claims   cations 8 or 9, characterized in that the space (la) containing the explosive initiating charge (7) is delimited on the one hand by one of the plates (2 a) of the device for separating two spaces and d on the other hand by a thermal conductive wall which is in contact with this plate (2 a).