Attachment of rings to articles

Attachment of a ring, particularly a metal ring (2), to an article which has walls or skirts (1) of fibre-reinforced resin material. The ring has a plurality of external grooves (3, 4, 5, 6). The skirt comprises, for each groove in sequence, a first (32, 36, 37, 40) and second (33, 38, 39, 41) layer of fibre-reinforced resin material. The fibres in the first layer have a substantial orientation in directions parallel with the axis of the ring and extend from the skirt into the respective grooves. Overlying the first layer is a second layer comprising hoop windings from the skirt towards the groove. The second layer lies at least partly in the groove to lock the first layer in the groove. This layering is repeated for each groove and finally successive hoop windings (45, 46, 47, 48) are wound over the entire article. This is useful for attaching end rings to rocket motor cases or for attaching rings to pressure vessels to define an aperture.

This invention relates to the attachment of rings in articles which have 
walls (also referred to herein as skirts) of fibre reinforced resin 
material. One possible application of the invention is to the attachment 
of an end ring to the body wall of a rocket motor case. However, the 
invention may be applied to other articles such as pressure vessels which 
are open at only one point, ie, an aperture defined by the ring, and tubes 
which are open at opposite ends with a ring attached at either or both of 
the opposite ends. The invention is primarily concerned with the 
attachment of metal rings but could be applied to the attachment of rings 
of other materials. 
GB No. 1402133 describes a corrugated structure and a method of making such 
a structure. The corrugated structure is built up on bridge supports of a 
first ply of tensioned parallel filament strands extending across all of 
the bridge supports along the axis of the structure. A second ply of 
parallel filament strands is applied transverse to and over the first ply 
so that the first ply is deflected into a generally concave parabolic 
configuration between and suspending from the bridge supports. 
According to one aspect of the present invention a composite article 
comprises a ring, a plurality of external circumferential grooves in the 
ring, a skirt attached to the ring, first and second layers of fibre 
reinforced resin material comprising the skirt, the first layer having 
fibres with a substantial orientation in directions parallel with the axis 
of the ring and the second layer overlying the first layer and comprising 
a hoop winding, each groove in turn starting with the groove nearest to 
the skirt has a respective first layer having fibres with a substantial 
orientation in directions parallel with the axis of the ring extending 
from the skirt to within the respective groove and a second layer 
comprising a hoop winding and extending from the skirt and substantially 
fitting the groove. 
According to another aspect of the invention, a vessel has a ring 
component, a fibre-reinforced resin wall forming a body of revolution, an 
opening on the axis of generation of the body, the opening being bounded 
by the ring component, a plurality of external circumferential grooves in 
the ring component, the wall comprising a plurality of layers, a layer for 
each groove in turn starting with groove nearest to the skirt which 
extends to within that groove the layer including fibres having a 
substantial orientation in directions which are generally axial of the 
vessel, a hoop winding of resin-impregnated fibre material to lock each of 
the said layers in a respective one of the grooves. 
According to a third aspect of the invention a rocket motor case has a 
cylindrical wall of fibre-reinforced resin material, at one end a metal 
end ring, a plurality of external circumferential grooves in the end ring, 
the cylindrical wall comprising a first layer which includes fibres with a 
substantial orientation in directions parallel with the axis of the ring 
extending to within each groove in turn, and a respective hoop winding 
overlying the polar wound layer within the groove to retain the polar 
wound layer. 
According to a fourth aspect of the invention, a method of securing a ring 
in a circumferential wall which comprises providing a ring, first and 
second external circumferential grooves in the ring, a layer of 
fibre-reinforced resin overlying the first groove, a second layer of 
fibre-reinforced resin applied by hoop winding to lock the first layer in 
the first groove, a third layer of fibre-reinforced resin overlying the 
first and second grooves, a fourth layer applied by hoop winding of 
fibre-reinforced resin to lock the third layer in the second groove, a 
fifth layer applied by hoop winding over the fourth layer, the layers 
constituting at least part of the said wall. 
It will be noted that by means of the invention the wall or skirt is 
secured to the ring by the material of the wall being locked into the 
grooves of the ring by turns of a hoop winding. While there may be a bond 
between the material of the wall and the surfaces of the grooves, any 
transmission of load by the bond will be additional to that occuring 
because of the interlock.

The rocket motor case shown in FIG. 1 consists essentially of a tube having 
a generally cylindrical wall 1 made of fibre-reinforced resin with a metal 
end ring 2 secured in each end. The two ends of the motor case are similar 
to one another and for convenience the following description will, for the 
most part, refer only to one end. The motor case being described by way of 
example has an external diameter D which is approximately three times the 
length L of the end ring. 
It will be seen from FIG. 2 that the metal end ring 2 is formed with four 
grooves 3, 4, 5 and 6 each of which is bounded by an inboard rounded wall 
portion 7, a flat bottom 8 and a radial outboard wall 9. The grooves are 
separated by ribs 11, 12 and 13 and the outboard groove 6 is bounded on 
its outboard side by a flange 14, the ribs and flange having progressively 
greater external diameters. As will be explained below, the cylindrical 
wall 1 in the vicinity of the end ring 2 is made up of a plurality of 
layers of three different kinds, the first kind being a laid layer having 
the fibres extending primarily longitudinally ie, parallel with the axis 
of the motor case; under this there may be a layer produced by polar 
winding, and thus also having the fibres extending primarily 
longitudinally, and then a layer produced by hoop winding. 
FIG. 5 shows an end ring suitable for use in a motor case. The end ring is 
similar to that shown in FIGS. 1 to 4 and where the parts are the same the 
same reference numberals have been used. The inboard rounded wall portions 
7 are formed from part of a circle with a radius r whose centre is a the 
base 15 of the radial outboard wall 9 as shown for one of the grooves, 5. 
The flat bottom 8 of each groove is curved to meet the inboard wall 
portion 7 with a radius a and is curved to meet the radial outboard wall 9 
with a radius b. Radiis a and b can conveniently be the same. The outer 
diameter of the ring progressively increases away from the skirt and thus 
the diameters d.sub.1, d.sub.2, d.sub.3, d.sub.4 for successive grooves 3, 
4, 5, 6 progressively increase. Also the distance of the flat bottoms 8 of 
successive grooves 3, 4, 5, 6 are progressively further from the axis of 
the ring and thus the distances p, q, r, s from the axis progressively 
increase. 
The production of the motor case will now be described in detail with 
reference to FIGS. 2, 3 and 4. 
Referring first FIG. 4, there is shown a steel mandrel 20 on which is 
formed a plaster of Paris former 21 having a tapered end portion 22 
against which a tapered portion 23 of the inner wall of the end ring 2 is 
positioned. The end ring is securely located by means of a clamping ring 
24 which is locked to the steel mandrel 20 by means of set screws 25. The 
clamping ring 24 has a rebate 26 which fits within the end rings 2 and the 
radially extending wall of the rebate 26 has a relieved portion 27 to 
provide a slot 28 between the relieved portion and the outer end of the 
end ring. The clamping ring carries a cylindrical row of projecting 
locking pins 29. 
When the end rings have been assembled on the mandrel in the manner 
described, two layers of rubber are applied to the portion of the former 
21 between the end rings 2. These layers are provided by strips of uncured 
rubber sold by Goodyear Rubber Company under the designation HYCAR MM 
40/20, the strips being positioned so that the outer strips centrally 
overlie the joints between the inner strips. An apoxy adhesive, preferably 
that sold by Ciba-Geigy under the designation XD911, is applied to the 
exposed surfaces of the end ring 2 and a first polar cover 31 is then 
polar wound on to the assembly which will lie within the groove 3 to a 
point 16 before the end of the radial outboard wall 9. The polar cover 
comprises two wound layers of carbon fibre 0.254 mm thickness per layer of 
GRAFIL EXAS (sold by Courtaulds) pre-impregnated with a resin system with 
the following ingredients in the proportions shown: 
Epikote 828: 100 parts by weight 
Epikote 1031: 100 parts by weight 
Epikure NMA: 180 parts by weight 
BDMA: 1 part by weight. 
Epikote and Epikure are Trade Marks of Shell Chemical Company. A layer 32 
of longitudinally aligned carbon fibre sheet which extends from a point 
approximately 2.5 L from the outboard end of the end ring 2 to a point 
overlying the groove 4 is then accurately positioned over the polar 
winding to lie within the groove 3. A hoop winding 33 (FIG. 2) is then 
commenced from a point midway between the end ring towards one end. At a 
distance of approximately 1.25 L from the locking pins 29 the winding is 
halted and the polar wound layer 31 is cut across the cutting slot 28 
using a sharp knife. Hoop winding is recommenced slowly towards the end of 
the assembly and at a point just on the outboard end of the inboard end of 
the ring 2 the tension on the fibre is raised and two turns are wound into 
the first groove 3 pressing both the polar wound layer 31 and the 
longitudinally aligned layer 32 into the groove. The winding tension is 
then reduced somewhat and a further twelve turns are wound into the groove 
3, traversing backwards and forwards within the groove to consolidate the 
fibre within the groove. The winding tension is then reduced substantially 
and winding is continued until the groove 3 is filled to within 1 mm of 
the top of the rib 11. The projecting portion of the polar winding 31 is 
then cut off at a level just below that of the top of the rib 11. Hoop 
winding is continued until the groove 3 is filled level with the top of 
the rib 11. The procedure is then repeated at the other end of the motor. 
The steps described and consisting of the winding of a polar wound layer 
34, 35, the laying down of a longitudinally aligned layer 36, 37 and the 
production of a loop wound layer 38, 39 are then repeated for each of the 
grooves 4 and 5, the polar wound and longitudinally aligned layers being 
locked in the grooves 4 and 5 respectively by the hoop windings. For the 
fourth groove 6 the procedure is substantially the same except that the 
winding of the polar layer is omitted, the groove being occupied by a 
longitudinally aligned layer 40 and a hoop winding 41. In all cases the 
longitudinal layers of sheet or polar wound layers (31, 32, 34, 36, 35, 37 
and 40) terminate within the respective groove. The hoop winding 41 is 
commenced at approximately 2.3 L from the end and the laid sheet 40 in 
which the fibres are longitudinally aligned is locked into the fourth 
groove. The longitudinally aligned layers extend from points which are 
respectively 2.3 L, 2.15 L and 1.5 L from the outboard end of the end ring 
2, the inboard end 30 of the outermost longitudinally aligned layer 40 
being visible in FIG. 3. The hoop winding by which the groove 6 is filled 
is continued back (layer 45) to the start 2.3 L from the end. The fibre is 
cut and repositioned 2.15 L from the end and is wound to the end and back 
to 1.5 L from the end (layers 46 and 47). This is repeated at the other 
end of the motor. 
The motor is completed by winding four hoop layers 48 over the entire 
length of the motor. The resin is then cured whereafter the clamping rings 
24 are removed and the steel mandrel 20 knocked out of the finished motor 
case. Then the plaster former 21 is washed out using boiling water. 
FIG. 6 shows the end ring of FIG. 5 attached to a skirt to form a rocket 
motor case. This is similar to that shown in FIG. 2 and made according to 
the same method. 
There may be only one layer having fibres with a substantial orientation in 
directions parallel with the axis of the ring and this may conveniently be 
a laid sheet of fibre reinforced material with the fibres orentated 
parallel with the axis of the ring or may conveniently be a polar winding 
of fibure reinforced resin material. Both types of layers may also be 
present as described in the embodiments. 
While several forms of the invention have been shown and described, other 
forms will now be apparent to those skilled in the art. Therefore, it will 
be understood that the embodiments shown in the drawings and described 
above are merely for illustrative purposes, and are not intended to limit 
the scope of the invention which is defined by the claims which follow.