Ammunition and explosives – Having reaction motor – Having separation means
Reexamination Certificate
1999-06-02
2001-01-09
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Having reaction motor
Having separation means
C089S001150, C102S312000, C102S313000
Reexamination Certificate
active
06170400
ABSTRACT:
TECHNICAL FIELD
The invention relates to a cutting device using a pyrotechnic expansion tube for cutting at least one part, along a given cutting line.
Such a device can more particularly be used in the aeronautical and space industries for controlling in a very short time the separation of two structural elements, whilst ensuring the transmission of at times high forces and stresses between said two elements, before the cutting takes place.
PRIOR ART
When two metallic structures, between which forces, stresses or loads pass, have to be irreversibly separated in a very short time and in remotely controlled manner, use is currently made of pyrotechnic cutting devices integrated into the junction zone between the two structures.
When a clean cutting is desired, i.e. with a minimum release of dust, use is generally made of a cutting device including a pyrotechnic expansion tube.
The expression “pyrotechnic expansion tube” designates a tight, deformable, metallic tube in which runs a detonating cord or fuse. A flexible material such as silicone rubber is interposed between the detonating fuse and the envelope. Prior to firing, the envelope has an oblong cross-section, e.g. in the form of an ellipse or flattened circle.
When the detonating fuse is fired, the shock wave propagating at very high velocity along the tube deforms the envelope and tends to give it a substantially circular cross-section.
Conventionally a pyrotechnic cutting device including a pyrotechnic expansion tube is used for cutting metallic parts. It is therefore installed in a space formed between two metallic parts or between two portions of the same metallic part. The part or parts to be cut are previously machined, so as to have a reduced thickness zone along each desired cutting line. The expansion of the envelope caused by the firing of the detonating fuse leads to the cutting of the part or parts along the cutting line corresponding to the machined zone.
Devices for cutting one or two metallic parts by means of a pyrotechnic expansion tube are described in the following documents: U.S. Pat. Nos. 3,486,410, 3,453,960, 3,698,281, FR-A-2 598 796 and EP-A-0 273 061.
The structural elements used in the aeronautical and space industries are increasingly frequently made from nonmetallic materials. In particular, the materials used are often composite materials, i.e. materials formed from long fibres arranged in the form of superimposed sheets in preferred orientations and embedded in a resin matrix.
When such nonmetallic materials are used, it is not at present possible to directly cut them by means of a pyrotechnic expansion tube, as is normally the case with metallic structures.
Firstly, the machining of a reduced thickness zone in a nonmetallic material and in particular a composite material is at present indispensable for localizing and limiting the cutting produced by the pyrotechnic expansion tube, is unacceptable in a nonmetallic material, particularly of the composite type Thus, such a machining would unacceptably reduce the mechanical characteristics of the part prior to its cutting, by cutting the long fibres leading to its characteristics.
Moreover, the cutting of a nonmetallic and in particular composite material using a cutting device would possibly give rise to significant pollution of the environment, as well as to a marked reduction in the mechanical characteristics of the adjoining structures. This reduction would be due to so-called delamination phenomena, i.e. a detachment or separation of the fibre sheets in the vicinity of the cutting line.
For various reasons, when a pyrotechnic cutting device has at present to be integrated into a nonmetallic structure, between the two structural elements to be separated is interposed a metallic structure, whose cutting with the aid of a pyrotechnic expansion tube is controlled. In other words, separation is ensured by cutting one or more metallic parts joined to the nonmetallic material structural assemblies which it is wished to separate. This conventional arrangement makes the structure more complicated and increases costs.
It is also contrary to one of the essential advantages brought about by nonmetallic materials, namely the weight gain. Thus, the addition of metallic parts to the linking zone between the two structural assemblies to be separated leads to a non-negligible weight increase. This weight increase is particularly due to the metallic nature of the added parts and the indispensable presence of fixing members ensuring the connection between the metallic parts and the nonmetallic parts. This is a particularly prejudicial disadvantage in certain applications, such as the space industry.
The pyrotechnic cutting of metallic parts also produces relatively severe shocks. Such a shock is applied to often very sensitive instruments and equipment located in the vicinity thereof. However, the very different mechanical characteristics of nonmetallic materials would permit, if their direct cutting was possible, the separation by producing a much lower shock level. This would be an advantage for the embarked instruments and equipment.
DESCRIPTION OF THE INVENTION
The invention relates to a pyrotechnic cutting device making it possible to directly cut nonmetallic parts and in particular composite material parts by means of a pyrotechnic expansion tube, whilst maintaining the mechanical properties of such parts before and after their cutting and whilst limiting the pollution produced during cutting.
According to the invention, this result is obtained by means of a pyrotechnic cutting device comprising a pyrotechnic expansion tube installed in a space formed between two parts and defined by at least one spacer linking said two parts, so as to cut at least one of the parts along at least one cutting line when the tube is used, characterized in that each part to be cut is of a nonmetallic material, an abutment being fixed thereto, opposite to and facing the spacer, so that one edge of the abutment extends along the cutting line.
The abutment fixed to the outside of the part to be cut, facing the spacer, acts in the manner of an anvil against which bears the corresponding portion of the part during the firing of the detonating fuse. This ensures a relatively clean and well localized cutting, without machining the parts. Therefore the mechanical strength of the parts prior to cutting is not cast into doubt. Moreover, the cleanness of the cut preserves the integrity of the parts after cutting and greatly limits pollution.
By rendering possible the direct cutting of nonmetallic materials and in particular composite materials, the device according to the invention makes it possible to very significantly reduce the weight of the nonmetallic assemblies to be cut with the aid of a pyrotechnic expansion tube. Moreover, the device according to the invention makes it possible to significantly reduce the shock level producing during cutting compared with that produced during the cutting of metallic parts.
In a first embodiment of the invention, each abutment is substantially non-deformable.
Conversely, in a second embodiment of the invention, each abutment is made from a deformable material.
In order to even better preserve the integrity of the cut part and in particular oppose its delamination in the case of a composite material part, a maintaining member made from a deformable material is preferably fixed to each part to be cut, opposite to and facing the pyrotechnic expansion tube. The maintaining member then comprises an edge extending along the cutting line and prolonged on moving away from said edge.
When the device comprises both an abutment and a maintaining member, said two members can be made from the same material as the part to be cut and said material is advantageously a composite material formed from sheets of long fibres embedded in a resin matrix. The assembly is then produced directly by covering during the manufacture of the part.
Moreover, the parts and the spacer can be made from the same nonmetallic material in monolithic form. In other words, the pyro
AEROSPATIALE Soci{acute over (e)}t{acute over (e)}Nationale Indu
Nelson Peter A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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