CA1080593A - Method and apparatus for the production of wound cylindrical bodies of resin-impregnated glass fiber with a sandwich core - Google Patents

Abstract

METHOD AND APPARATUS FOR THE PRODUCTION
OF WOUND CYLINDRICAL BODIES OF RESIN-IMPREGNATED GLASS FIBER WITH A SANDWICH CORE

Abstract of the Disclosure Process and apparatus for forming cylindrical sand-wich constructions of glass fiber impregnated with synthetic resin, in which the core between the inner and outer shells is a spiral-wound corrugated strip of glass fiber impregnated with synthetic resin such as polyester resin. A strip of glass fibers impregnated with synthetic resin is fed between a pair of coacting endless belts whose adjacent runs are provided with interfingering projections to corrugate the strip. Retainer filaments can be laid over the spiral-wound corrugated strip to hold the same in place until the outer shell of glass fiber impregnated with resin is spiral wound thereover. The corrugating unit and its glass fiber supply and the supply of the retainer filaments, are all mounted for movement as a unit parallel to the axis of the cylindrical member.

Description

1081~593 Tho present inventlon relateA to ~ method an-l apparatus ~or the production of cylindr~cal bodl~R ~uch as condults or vessels, whose wall~ are con~tltuted by cured thermosett~ng resin reinforced by ~plral-wound gla88 fiber, and which have a sandwich core for increa~ed ~trength, It is well known to produce cyllndrlcal bodie~
~uch as conduit~ and ves~el3 from glass-fiber-relnforced synthetic res~n by winding. Such cylindrical bodie~ have enormous fioop strength, thanks to the high tensile ~trength of the glass fibers. Iiowever, because of their low modulus of ela~ticity, they are not ~trong when subjected to oth¢r stresses, as in the case of und~rground storage containers, pipelines, or vessel~ subjected to vacuum or wind pres~ure.
To deal adequately with stresses other than hoop stresse~, it would be necessary to increa~e the wall thick-ness unreasonably; and therefore, $n practice, ~uch cylindri-cal bodies are provided with external reinforcing ribs or sandwich-type construction.
Sandwich-type constructions of this type are gene~ally made by winding the cylindrical inner wall, and then cementing on the outer surface of the inner wall a core material wnich may be a hardened plastic foam, or paper or aluminum honeycomb, l~ght wood or the like. The outer shell is then~wound onto the core; and the inner and outer shells are ~ nded to the core material, the three layers being thus , ~
inte~rated. Such sandwich-type constructlons are light ~n welght but also rather rigid.
The formatlon of such sandwich-type constructlons involving gla3s fiber inner and outer shell~ i3 fraught with . .
difficulty, however, because although the wlnding ~t~elf can : ....
be ~ wholly automated oparation, the applicst~on of th~ core

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material is ordinarily performed manually and at a slow rate.
According to one aspect of the present invention there is provided a process for producing a cylindrical member of sandwich construction, com-prising forming a cylindrical inner shell, rotating said shell about its axis, applying a strip of corrugated glass fiber impregnated with synthetic resin onto said shell by continuous spiral winding with the corrugations of the glass fiber strip at an acute angle to the axis of the shell and with the edges of adjacent windings in abutment, and integrating said shell and strip into a hardened unit.
Preferably, an outer shell is formed on the wound strip by winding on it synthetic resin impregnated glass fiber.
The corrugated core material can flex out of its plane in such a direction as to make possible the winding of the strip of corrugated material about the inner shell of the sandwich construction; and so it is possible to apply a core continuously to the inner shell by spiral winding the strip of corrugated material thereabout, thereby making it possible to produce the sandwich construction by a continuous winding technique.
An additional discovery is that the corrugated core material of glass-fiber-reinforced synthetic resin, can be continuously produced in the same equipment that produces the entire sandwich construction, so that only a single apparatus is required.
Thus, according to another aspect of the present invention there is provided apparatus for forming a cylindrical member of sandwich construction, comprising a rotary drum for receiving an inner shell, and forming means including means to form a glass fiber stripJ means to impregnate said strip with synthetic resin, means to corrugate said strip, and means to spirally wind the strip of corrugated glass fiber impregnated with synthetic resin on the inner shell with the corrugations disposed at an acute angle to the shell's axis and with the edges of adjacent windings in abutment.
To form the corrugated strip of core material, a strip of parallel 108~593 glass fibers, such as glass fiber roving, can be continuously drawn through a bath of liquid synthetic resin so as to impregnate the glass fiber with resin prior to the corrugation thereof. Alternatively, the impregnated glass fiber can be supplied in the form of a strip of fibers previously impregnated with synthetic resin that has been sufficiently crosslinked that it is no longer tacky to the touch, that is, a so-called "pre-preg". In either case, the glass fiber impregnated with resin is passed through a corrugating unit which is preferably a pair of coacting endless belts with interfingering corrugating projections thereon, which may be heated or not, and which are mounted for bodily movement parallel to the axis of the cylindrical member to be formed, with the length of the endless bands preferably disposed at a small acute angle to the axis of the cylindrical member, as viewed in plan, and tangentially to the surface of the cylindrical member, so that the cor-rugated material emerging from between the bands can move in a straight line directly to the point of application by spiral winding to the cylindrical member that is undergoing formation. The linear speed of the endless bands ;.
is equal to the circumferential speed of rotation of the member undergoing formation; and the linear speed of the entire unit for forming the corrugated core, parallel to the axis of the member undergoing formation, is so related to the peripheral speed of rotation of the member undergoing formation and the width of the strip of corrugated material, that the strip is deposited on the inner shell in :, .

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'':' ~080593 spiral configur~tion with acl~acent c0118 of the ~trlp sub-~tantially edgewlse abutting each other.
Other objects feature~ and advantage~ of the present invention will become apparent from a conslderation of the following description, taken in connection with the accompanying drawings, in which:
Figure l is a fragmentary cross-sectional view of a sandwich construction produced by a method and apparatus according to the present invention;
Figure 2 is a diagrammatic side elevational view, looking parallel to the axi~ of the cylindrical memher to be formed, and showing one embodiment of apparatus according to the present invention; and Figure 3 is a top plan view of the apparatus shown in Figure 2.
Referring now to the drawings in greater detail, and first to Figure l thereof, i~ will be ~een that the cylindrical member to be produced according to the present invention con-sist6 of an inner shell l, a corrugated core 2, and an outer shell 3, these components being bonded together in an integral mass, either by a separate adhesive or by the synthetic resin that is an integral part of each component It is also to be understood that each of these three components is of glass-fiber-reinforced synthetic resin, preferably polyester refiin, and that i~ is preferred that the resin be the same for all :~
~h~ components.
Turning now to Figure 2, the apparatus for forminq ~,h~! ~ylindrical member on a rotatiny drum, comprises a cor-~ug~ing unit 4 mounted on a base which is movable rectilinearly on trac~ that are parallel to the axis of the cylindrical member to be formed, which latter member i8 in turn mountecl for rotation about its h~ rl7~0ntal axi~ on a motor-drlven supporting ~tand ~r by a motor ~ in a conventional manner.
The corrugatlng unit'4 lncludes a pair of coactlng endless belts 5 and 6 which have transverse rlbs thereon who~
outer surfaces are of sinusoidal configuration to impart the desired curvature of corrugation, and which interfinger so that glas~ fibers passing lengthwi~e therebetween are given a corrugated configuration. An infinitely variable drive 7 causes the two belts to circulate in a direction such that their coacting or adjacent runs move upwardly to the left as seen in Figure 2, in a direction toward the periphery of the cylindrical unit to be formed, which is to say tangentially thereof. Depending on the degree of crosslinking to be induced in the resin prior to application of the core material to the cylindrical member, the belts 5 and 6 can be heated for that purpose. ,~
~ continuous strip of plural glass fibers, in the form of rovin~'or the like, is wound up on a roll 8 carried by corrugatin~ unit 4, to supply glass fiber strip to the region betwee~ the belts 5 and 6. In the embodiment of Figs. 2 and'3, the strip on roll 8 is "pre-preg", that is, previously impregnated with thermosetting resin that is crosslinked to the extent that it is dry to the touch, pref-erably polyester resin in admixture with a known hardening catalyst therefor.
The corrugated glass fiber strip emerges from co~rugating unit 4 and is wound on the inner shell 1 as the ~atter is rotated,counterclockwise as seen in Fig. 2, the carriage 9 ~upporting the corrugating unit for moving slowly along its ~upporting railq 9' upwardly as seen in Fig. 3. At th~s point, the inner shell 1 can be unpolymerized, or can . .

1CUB~5~93 be polymerized and coa ed with a sepaxate adhe~lve layer, thereby to secure adherence thereto of the corrugate~ core 2.
A ~pool 10 and roller 11 are mounted on corrugating unit 4 for movement therewith, and are rotatable ln a clock-wise directlon as seen in Pig, 2. Filaments 12 are unwound from spool 10 and pass under roller 11 and are laid over the core 2 as it i8 applied to the inner ahcll 1, thereby pre~s-ing the corrugated material into firm bonding contact with shell l, to hold the core material in place until spinning of the outer ~hell can be effectuated in a known manner.
It is to be noted that it i8 not necessary to use a separate adhesive layer between core 2 and outer shell 3, because outer shell 3 is spun directly on the core and so the resin that impregnates the glass fiber of outer shell 3 can also bond outer shell 3 to core 2.
In the event that the glass fiber strip on roll 8 i~ not previously impregnated, it will be impregnated as withdrawn from that roll by passing the strip through a ~ath of liquid synthetic resin. ~Iowever, this is not shown because it is well kno~.in the art.
The ~ethod and apparatu~ according to the present ~ -invention thus have, among others, the following advantages:
1. Cylindrical bod~es can be produced ent~rely by mec~anized winding techniques.
ii~ 2. The thickness of' the core material can be varied at will; and so bodies of different rigidity can be produced.

3. The core material is quite light in weight, which gxeatly reduces the weight of the finished product,

4. The material of the core i8 the same as that 10~30593 o~ the shell~, whlch lmproves bondllig and avold~ lnher~nt structural etresses,

5. The core maklng and applying apparatu~ can be mounted on the same apparatu~ a~ the w~nding devlcQ~, and 80 only a ~ingle apparatus need be provided.

6. The winding of the ~nner ~hell, the core and the outer shell can succeed each other immediately, and 80 there is no delay or other production difficulty In order to enable those skilled in this art to practice the invention, the following illustrative example~
are given:

E_PLE 1 The cylindrical side wall of a vessel three meter~
in diameter iB to be produced. As a first step, an inner shell four millimeters thick is laid down on the drum of a winding machine~ The quantity of resin used is such as to provide a resin layer 0.2 mm thick on the outer surface of the inner shell. The resin is polyester resin, admixed with 2% methylethyl ketone peroxide a~ catalyzer. Glass fiber roving, in the form of a strip 33 centimeters wide and 0.3 mm thick, containing 50% by weight of this resin, is led through the corrugating unit. The glass fiber that is introduced through the corrugating unît i~ a "pre-preg" consisting of polyester re~in containing kaolin, magnesium oxide and col-loidal 5102~ w~th 0.5% by weight tertiary butylperbenzoate a~ catalyzer. The temperature of the corrugating unit is 120C, whlch produces a hardened corrugated core in the course of one-minute. The length of the corrugating unit i~
3 mlllimeters, measured in the direction of movement of the coacting belt runs;~and BO the corrugated core material ~m~rge~ from the corrugating unit;at .a speed of 3 meters per minute, which i~ also the peripheral ~peed o~ rot~tlon of the lnner shell 1. The corrugated ~trlp le~vlng the corruqnting unit i8 preYsed by means of two parallel braked nylon fila-ment~ 0.6 mm ln diameter, to the surface of the lnner ~hell 1.
The frame 9 moves along its tracks at a ~peed of 33.1 cm per rotation of lnner ~hell 1, whereby the ~trip ls l~id down in edgewi~e abutting ~p~ral configuration.
The lenqth of the cylindr~cal body i8 5 m~ters and 80 the winding wlth core material requires a theoretical 15.2 rotations; but taking into consideratlon an initial and final waste, an actual 16.5 rotations are required. The appl~-cation of the corrugated band thus requires 40 minute~. Hard-ening of the inner shell at room temperature take~ place in one hour. Thereafter, the outer shell made of the same material as the inner shell is wound onto the previously prepared cylindrical body with the core material thereon, in a known manner. The whole construction i~ thereafter heated to harden for a time well known in the art, and i8 then removed from the machine for further proce~sing.
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The same procedure is followe~ as in Example 1, except that the previously hardened inner shell is covered with an adhesive layer of polye~ter resin to a thickness of 0,3 mm, As a startin~ material, glass roving of a width of 33 centimeters and~a~thickness of 0,2 mm, not previously impregnated with E~sin ~ iB fed through an impregnating bath upstream of the aorrugating unit, the hath containing poly-ester resin admixed with 2% benzoylperoxide as catalyzer.
Squeegee rollèrs control the amount of re3in that remains on the strip as it emerges from the bath, after which the procedure recited in ~xample 1 is followed.

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~ 1080593 In view ot the foregolnq dl~closur~, therefore, it will b~ evldent that the initially reclted ob~ct of th~
pre~ent invention ha~ been achieved.
Although the pre~ent lnvention has been described and illu~trated ln connection with preferred embodiments, it is to be under~tood that modificatlons and variation~ ~ay b~
re~orted to without departing from the ~pirit of ~he lnventlon, as tho~e ~killed ln this art will readlly underfitand. Such modification~ and variation~ are considered to be within the purview and scope of the present inventlon as deflned by the appended claim~.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a cylindrical member of sandwich construc-tion, comprising forming a cylindrical inner shell, rotating said shell about its axis, applying a strip of corrugated glass fiber impregnated with syn-thetic resin onto said shell by continuous spiral winding with the corruga-tions of the glass fiber strip at an acute angle to the axis of the shell and with the edges of adjacent windings in abutment, and integrating said shell and strip into a hardened unit.

2. A process as claimed in claim 1, and forming said shell by spiral winding glass fiber impregnated with synthetic resin.

3. A process as claimed in claim 2, in which said synthetic resin of said shell is the same as the synthetic resin impregnating said strip.

4. A process as claimed in claim 3, and spiral winding on the wound strip an outer shell of glass fiber impregnated with the same synthetic resin as said inner shell and strip.

5. A process as claimed in claim 1, and forming on said wound strip an outer shell.

6. A process as claimed in claim 5, in which said outer shell is formed by spiral winding glass fiber impregnated with synthetic resin.

7. A process as claimed in claim 5, in which said inner and outer shells and said strip are hardened into an integral member.

8. Apparatus for forming a cylindrical member of sandwich construction, comprising a rotary drum for receiving an inner shell, and forming means including means to form a glass fiber strip, means to impregnate said strip with synthetic resin, means to corrugate said strip, and means to spirally wind the strip of corrugated glass fiber impregnated with synthetic resin on the inner shell with the corrugations disposed at an acute angle to the shell's axis and with the edges of adjacent windings in abutment.

9. Apparatus as claimed in claim 8, said forming means comprising a pair of coacting endless belts having interfingering projections on their adjacent runs.

10. Apparatus as claimed in claim 9, said coacting belts being disposed at an acute angle to the axis of said drum when viewed in plan and extending in a direction tangential to said drum.

11. Apparatus as claimed in claim 9, and means to move said coacting belts bodily parallel to the axis of said drum.

12. Apparatus as claimed in claim 8, and means to apply at least one retainer filament onto said corrugated strip as said corrugated strip is applied to said inner shell thereby to retain said strip on said inner shell.

13. Apparatus as claimed in claim 12, and means for moving said forming means and said filament-applying means together as a unit parallel to the axis of said drum.

14. Apparatus as claimed in claim 9, and means for rotating said drum at the same peripheral speed as the linear speed at which said corrugated strip emerges from between said belts.