Metal working – Method of mechanical manufacture – Impeller making
Reexamination Certificate
2002-09-09
2003-06-17
Vidovich, Gregory (Department: 3726)
Metal working
Method of mechanical manufacture
Impeller making
C029S426400, C029S426500, C029S407100, C156S583200, C156S345420
Reexamination Certificate
active
06578265
ABSTRACT:
The invention relates to a method and a device for removing a plate made from a material that can be heated by electromagnetic induction, generally a metal sheet, and retained on a supporting member by a heat-fusible adhesive substance that will at least soften when heated, i.e. loses its mechanical characteristics to a large extent under the action of heat.
BACKGROUND OF THE INVENTION
The plate made from a material that can be heated by electromagnetic induction and which can be removed by the method and device proposed by the invention may be a substantially flat or curved plate and may have several flat parts adjoining one or more curved parts, formed by folding or bending, and such a plate is preferably made from metal or metal, alloy having good properties for heating by electromagnetic induction.
The adhesive substance retaining such a plate on a supporting member must be one which is heat-fusible in that it will at least soften under the effect of heat and, for the purposes of the invention, this adhesive substance might not or need not necessarily be brought to the liquid state by fusion.
By supporting member is meant any base of any nature, for example metal or composite, which is sufficiently rigid to be capable of supporting a plate us defined above which is retained on this base by a layer or film of a heat-fusible adhesive as defined above and thus having a so-called “plastic range” in its temperature range, which is a minimum of approximately 20° C. higher than the range of its vitreous transition temperature, i.e. a temperature range at which the bonding forces of the adhesive substance may be reduced by 80%. The adhesive may be a glue which is initially applied to the base in a gel, paste or liquid state or alternatively a heat-fusible film adhesive, for example a thermoplastic material or even a thermosetting network or alternatively may be a thermoplastic or thermosetting resin in the matrix of a base having a composite structure, for example resin used to impregnate reinforcing fibres of one or more surface layers of a stratified composite structure constituting the supporting member for a plate to be removed using the method and device proposed by the invention.
By way of example, the supporting member may be a second plate or sheet of metal or any other sheet, optionally a coating sheet, as would be the case for example with a member such as an aircraft door, consisting of two metal plates or panels bonded one against the other, the method of the invention enabling one metal plate or panel to be removed with a view to repair without damaging the other, by acting on the heat-fusible adhesive substance between the two plates or panels. The base may also be the core, for example a material with a honeycomb structure, of a sandwich panel, for example the floor of an aircraft, wherein one of the two skins on either side of the core is specifically the metal plate to be removed by means of the method and device proposed by the invention.
The base or supporting member may also be a composite structure constituting the inner core of a rotor blade, for example of a helicopter, this internal core, with the spar or spars and the filler body or bodies of the blade being enclosed by a stratified external shell forming in particular the lower surface and upper surface skin of the blade, which meet along the leading edge and the trailing edge of the blade, in which case the plate to be removed by the method and device proposed by the invention may be a protective cap at the leading edge of the blade.
Although the method and device proposed by the invention may be used in numerous applications, this method and this device are described in a context in which they apply to the removal of a protective cap from the leading edge of a rotor blade, in particular of a helicopter, since this application is of particular interest to the applicant.
It is known that the leading edge of helicopter rotor blades is protected, in particular against erosion and impact by foreign bodies, by a cap which is generally made from metal sheet (titanium or stainless steel; or even nickel or aluminium), bended to produce a substantially U-shaped form and which is bonded onto the underlying structure of the blade, which may be metal and/or composite, so that the leading edge and the lower surface and upper surface of the blade adjacent to it are covered, at least over a part of the blade span. During the service life of the blade, it is necessary to remove the protective cap from the leading edge to replace it with a new cap, generally as a result of three types of circumstances: as a result of damage to the blade due to impacts on its leading edge and its protective cap; as a result of damage to the protective cap due to erosion; and, in the case of a composite blade, when superficial layers of the composite structure of the blade have started to come unstuck (peeling of the stratified lower and upper surface skin in the region of the leading edge).
At present, the protective cap is manually stripped from the leading edge in a manner that will be described with reference to
FIG. 1
, which depicts a composite helicopter rotor blade shown by reference
1
, at the end of its aerodynamically profiled part, which is attached by a blade neck
2
of varying section to a blade foot
3
, having two bores
4
by means of which the blade
1
is joined by two pins to a rotor hub or a linking member for connection to this hub in a known manner. The leading edge
5
of the blade
1
as well as the adjacent parts of the upper (surface
6
and the lower surface (not visible in
FIG. 1
) of the blade
1
are covered by a metal cap
7
which protects the leading edge, this metal sheet being substantially U-shaped and bonded onto the underlying composite structure of the blade
1
by an adhesive substance as defined above.
The operation of removing the cap
7
firstly consists in using a tool of the wood shears type to make a nick or cut to initiate the removal at the start of the operation, guided substantially along the length of the cap
7
, i.e. along the span of the blade
1
, starting at a transverse edge (along the chord of the blade
1
) of the cap
7
, for example from the edge
8
of the cap
7
turned towards the blade foot
3
so as to create a narrow tongue which will be the start of a longitudinal strip
9
of the cap
7
, and then inserting the end
10
of this strip
9
into the slot of the shaft
12
of a tool
11
similar to a key such as used for opening a sardine can, the handle
13
of which is manipulated by an operator who turns the tool
11
on itself, about the longitudinal axis of its shaft
12
, so as to wind the strip
9
in a spiral about itself around the shaft
12
of the tool
11
, by means of which the operator is thus able to make a mechanical tear of the strip
9
by a cold-peeling process.
This manual tearing operation for cold-peeling a longitudinal strip
9
off the cap
7
, performed step by step on adjacent strips to remove the entire cap
7
, is a delicate operation endangering the operator because each strip
9
wound in a spiral about the tool
11
of the sardine tin key type can behave in the manner of a spiral spring and can release suddenly, whilst the face of the operator needs to be very close as he visually checks the process of tearing back a strip
9
, the metal of this strip
9
being held on the underlying composite structure of the blade
1
by a greater or lesser amount of adhesive as it progresses, and as far as possible without tearing the superficial layers of the stratified composite structure of the shell of the blade
1
. Regardless of all the precautions taken during this manual operation, bearing in mind the surface treatments applied to the composite blades during manufacture and the adhesion forces built up by the adhesive substances used, consequential damage is often caused to the superficial Myers of the composite shell of the blade
1
underneath the cap
7
.
EP-A-0 854 208 also discloses a method and a device for removing a cap or a metal shield
Amari André
Boschet Patrick
Brunner Daniel
Eurocopter
Jimenez Marc
Rudnick Piper
Vidovich Gregory
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