CA2299487C - Collapsible mandrel - Google Patents

Abstract

A novel construction of collapsible mandrel is described, the outer wall of which comprises a plurality of sections with mating edge surfaces that diverge inwardly on odd-numbered sections and convergently on the alternating even-numbered sections of the mandrel wall, so that the odd-numbered set of sections may be retracted by a predetermined first amount than the even-numbered wall sections by a predetermined, lesser second amount. The collapsible mandrel is useful in a number of applications, such as the production of filament wound containers. In a particular embodiment of the invention, the retractible sections make up the walls of a vertically-oriented cylindrical retractible mandrel which may be used for fabricating large-diameter chimney liners of fibre-reinforced plastic.

Description

COLLAPSIBLE MANDREL
FIELD OF THE INVENTION
This invention relates generally to mandrels and more particularly to an improved retractible mandrel for use as a mold in the molding of large diameter chimney liners fabricated of fibreglass reinforced plastic (FRP).
BACKGROUND OF THE INVENTION
Solid, inflatable and retractible or collapsible mandrels in a wide variety of forms 11) have been used in filament--wound structures, and in other applications in which rigid hollow structures are fabricated by the curing of a resin to solidity.
One collapsible type of mandrel, of rectangular cross-section, for use in the filament winding of large container-like structures is disclosed in U.S.
Patent No.
15 3,754,717 (Daidla). That collapsible mandrel has side walls comprising quarter sections which are hinged at the centre of the upper and lower walls and engageable at the centre of the side walls. A complex arrangement of linkage assemblies is operatively connected to a central hydraulic power cylinder, which effects a collapse of the quarter sections to peel them away from contact with 20 the interior winding surfaces of the completed filament wound structure.
U.S. Patent No. 4,288,277 (Siilats) issued to the present inventor, is directed to a vertically axised mold far large diameter reinforced cylindrical chimney liners.
In that arrangement, a plurality of horizontal spider modules are mounted in 25 mutually axially spaced relation on axially extending support means. The spiders are provided with fluid powered expanders, actuable in radial expansion mode prior to winding the FRP liner onto the mold. A predetermined extent of retraction "allowance" leads to inward radial retraction of the mold from the wound liner upon de-energization of the expanders, to facilitate ready vertical 3() separation of the formed liner from the mold.

The molding system of the Siilats '277 patent represents a significant improvement in the art of in-the-field winding of corrosion resistant liners for chimneys or chemical tanks which are too massive to be fully constructed and shipped to the site of use.
Particularly in the case of large diameter (20' - 30') thin-walled casings for chimney liners, serious difficulties were experienced in stripping the molded liners horizontally from off the mold, such casings being subject to buckling collapse when horizontally oriented.
The molding system of the Siilats '277 patent included a mold usable in the vertical orientation, which could be prepared for a predetermined diameter of liner by modifying the aforementioned axially spaced spider by manually adjusting the radial arms, using pinned sliding joints to achieve a desired radius 1 ~i for the spiders. The outer chordal rib of each spider module was correspondingly adjusted in length to accord with the selected spider diameter.
Each module is then provided with a predetermined replacement outer segment form secured to and complementary to the selected chordal rib length so as to complement the polygonal spider to form the desired circle.
SUMMARY OF THE INVENTION
The present invention represents a simplification and significant improvement to collapsible mandrels generally, and in particular, provides a vertically-oriented cylindrical retractable mandrel which may be used for fabricating large-diameter (15' - 30') chimney liners of fibre reinforced plastic.
Unlike previous arrangements, the liner molding procedure used with the present invention may conveniently be carried out right in the column of the chimney, thereby greatly increasing the ease of assembly and reducing the costs and risks of transportation of the liner.

These and other advant;sges are achieved by forming the mandrel of circumferentially alternatingi plate sections, which are held in their fully expanded position when the mandrel is wound with liner material. The molding surface of the mold comprises a plurality of these plate sections fabricated of rolled steel 'i or aluminum. Conventional hydraulically powered means are included, to permit the alternate radial retraction of alternating sets of plate sections. Thus, the odd-numbered sections, say, are retracted by a selected amount and then the even-numbered plate sections are retracted by a smaller amount in a two-stage overall retraction of the maindrel (molding surface) from the liner.
BRIEF DESCRIPTION OF THE DRAWINGS
1 ~i Figure 1 is a cut-away perspective of an installation of a collapsible mandrel according to the present invention, in use in a chimney liner molding system set up in the column of a chimney..
Figure 1A is an enlarged perspective schematic view of one of twelve radial elements, indicated generally at 1A in Figure 1, shown in more detail than the other like elements, while i:he adjacent radial element has been substantially omitted for clarity. The fully detailed radial element is shown in orthographic elevation in Figure 3.
2~i Figure 2 is a plan view of the liner mold taken along the arrows 2-2 of Figure 1.
Figure 3 is a part-section elevational view of the liner mold of Figure 2, taken on the arrows 3-3.
Figure 4 is an enlarged scrap plan view of the area shown in chain dot line, marked 4 on Figure 2, a chain dot arc being used to represent the periphery of the moveable plates.

Figure 5 is an enlarged scrap section elevational view showing the hydraulic actuator, the return spring and a pair of movement limiting bolts thereof, taken on the arrows 5-5 of Figure 4.
Figure 6 is an enlarged scrap plan view of the area shown in chain dot line marked 6 in Figure 4, showing the hydraulic actuator and, in a scrap cross-section, the location of the two limiting bolts.
Figure 7 is a partial plan view of a mandrel according to the invention, having a rectangular cross-section.
Figure 8 is an enlarged scrap section elevational view of the area indicated as "8" on Figure 7, showing the manual actuator arrangement for retracting extension arms of the apparatus.
1 ~i DESCRIPTION OF THE PREFERRED EMBODIMENT
(i) Radially RetractiblE: and Expandible Cylindrical Mold As best seen in Figures 1 and 1A, a retractible mandrel/mold 10 according to the invention is set up in the column of a chimney 12.
The walls and outer molding surfaces of mold 10 are formed of a plurality of 2~i convex alternating "A"-type plate sections and "B"-type plate sections.
The radial distance of the P,-group of plate sections and each of the B-group of plate sections from a rigid centre core cylinder 14 are respectively adjustable by means of equiangularly spaced radially extending frames 15, each comprising an inner radial frame 15A bolted to core 14 and an outer radial frame 15B
bolted along its outer side to one of the convex plate sections making up the molding surface and fitting at its ininer side telescopingly into inner radial frame 15A.

Rigidity of the assembly of frames 15 is maintained by transverse bracing sections 16 extending between corresponding points on adjacent radial frames 15A.
Referring to Figures 4 and 5, each radial frame15 has an expansible actuator means 18 connecting its inner portion 15A with the telescoping outer portion 15B. Bracket 20 carries the actuator means and is secured to each outer arm portion by bolts 22. The e~;pandable actuator means contains a fluid actuated short stroke piston and cylinder expander actuator 26 having the piston 28 1 () abutting the bracket 22 in thrust transmitting relation therewith. A
return spring 30 interconnects the arrangement, to provide return action to outer frame portion 15B in opposition to the expansion action of actuator 26. The range of expansion and contraction is limited by bolts 24 through apertures in each inner arm portion 15A. It will be understood that as an alternative to the provision of springs 30 the actuator 26 can be made double acting.
In operation, the mold 10 will be set up in its fully expanded form for a pre-determined diameter of FRf' liner. Forthe specific arrangement shown in Figure 1 and subsequent drawings, in which there are twelve convex plate sections, each associated with a collapsible vertical frame 15, there need be delivered to the chimney site only a carE: portion 14, twelve inner frame sections 15A, twelve outer frame sections 15B, and six each of the "A" plates and "B" plates. These differ from each other in tlhe sense of vertical edge surfaces, the "A" plates having edges which diverge radially and the "B" plates edges which converge 2',5 radially, so that the alternating A and B plates can be fitted together in a cylindrical surfiace the "B" plates radially withdrawn when desired by a lesser amount than the "A" plates, without causing any plate-to-plate impact. There will also be delivered to the sitE: the hydraulic rams and bolstering cross-pieces as described above.
At the site, inner frames '15A are bolted to core 14, then the bracing 16 is installed. Outer frames 15B are slipped into the corresponding accommodating horizontal channels of frarnes 15A and the convex A and B mold forms are bolted to the frames 15B. Conveniently, hydraulic jacks may be inserted at the top and the bottom of each frame, with a'/Z" stroke for the "B" plates alternating with a '/4" stroke for the "A" plates.
I) For chimney liners, an outer diameter of 15' or 22' will be typical. In the fully expanded form of the mold, adjacent pairs of plate sections A and B meet flush along their edge surfaces SA and SB in mating relationship, as indicated in Figure 2. By conventional fluid connection means, all of the pistons 28 are 1 () maintained at the same maximum pressure. Each hydraulic actuator 26 of the mold has its own associated line going to a central pressurizer.
The mold 10 is maintained in its fully expanded state in the chimney by isolating the expander actuators 26 from a hydraulic fluid supply. The molding operation 1!i then proceeds with the application of a suitable slip agent, prior to the building up of the FRP liner, using known FRP molding techniques. As best illustrated in Figure 4, once the liner is substantially cured, one of the two alternating sets of convex structural plates, say B, is retracted (in the direction of arrows R
from the interior surface 11 of the cured liner, by about'/z inch. This is effected by 20 bleeding off a suitable amount of fluid pressure from the actuators associated with the B plates, thereby decreasing the loading on return springs 30.
Subsequently, the A set of convex plate sections are simultaneously withdrawn by a smaller radial amount, say 1/4 inch, so that formerly mating surfaces SA
and SB are disengaged. V'Uith all plate sections A and B now clear of the fully 25 formed FRP liner, the liner can be pulled vertically away using a suitable crane and the molding apparatus disassembled and withdrawn through a chimney side portal.
The molding surface sections A and B are replaceable and interchangeable for 30 connection to the outer frames 15B. These may be of variable circular curvature and size to allow the same core cylinder 14 with associated radial frames 15 to be used with outside frame diameters in the range of from about 15'to about 22', with appropriate extensions or retractions of the telescoping radially outer extensions 15B. To set up the mold 10 for a pre-determined diameter of FRP
liner, the radial extension arms 15B of each frame are set manually to a desired value by adjustment of securing bolts 24.
It will be seen that the present invention provides a low cost chimney liner molding system characterized by a two-stage radial retraction and by adjustability of radial extension arms and replaceable circumferential plate sections which allow mandrel/molds of a range of diameters to be used in the molding of chimney liners.
(ii) Collapsible MandrE~ls for Other Applications The structural and operational principles of the cylindrical mold described above can also be used more generally in a collapsible mandrel useful, for example, in the production of filament wound containers. In the rectangular mandrel shown in Figure 7, a mandrel in the form of a rectangular channel is formed by alternate plate sections P and corner sections C which in the fully expanded state of the mandrel meet along flush mating edge surfaces SP and SC.
Mandrel sections P and C ;are, respectively, centrally fixedly attached to radial arms 17P and 17C symmetrically disposed in a horizontal plane about a vertically extending axial support by attachment to telescoping outer arm portions 17'P and 17'C. The operative connection between an arm 17C and its 2~i telescoping extension 17'C is shown in detail in Figure 8. Brackets 21 and are respectively secured to arm portions 17C and 17'C by bolts 25 and 27. The relative telescopic extension of 17'C from 17C is adjusted by the turning of bolt 27 in plate 21 against the retracting force of return spring 31 interconnecting brackets 21 and 23.
Collapse of the mandrel is effected by partial retraction of the bolts 27 on the radial arms connecting to plate sections P; followed by a lesser adjustment (shorter radial contraction, forthe radial arms connected with the corner sections C. On larger mandrels, a hydraulic system rather than a manual bolting system could be used, entirely anallogous to the embodiment of radially retractable and expandable cylindrical mold described above.
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Claims (7)

1. A hollow collapsible mandrel, comprising:
an axially extending support means;
a plurality of extendible or retractible connection means extending radially outwardly from said support means;
a plurality of mandrel wall sections disposed in radial symmetry about said support means, each said wall section being secured to the outer end one of said connection means; and actuating means for retracting said connection means from and extending them toward fully their extended positions in which said wall sections define the fully expanded configuration of the mandrel, wherein each wall section of one alternating set of said plurality of mandrel wall sections presents a first configuration of opposite edge surfaces and each wall section of the other alternating set of wall sections presents a second configuration of opposite edge surfaces such that in the fully expanded configuration of the mandrel the proximal first and second edge surfaces of adjacent wall sections meet in mating abutment, so that said mandrel may be collapsed inwardly towards the axis of the support means by retracting the connection means associated with said one alternating set of wall sections by a selected amount and then retracting the telescoping connection means associated with said other alternating set of mandrel wall sections by a smaller amount.

2. A hollow collapsible mandrel according to claim 1, wherein said first configuration of opposite edge surfaces comprises bevelled, inwardly diverging planar surfaces and said second configuration of opposite edge surfaces comprise bevelled, outwardly diverging planar surfaces.

3. A hollow collapsible mandrel according to claim 2, wherein said extendible and retractible connection means comprise an inner tubular arm portion and outer tubular arm portion in telescoping relationship for relative longitudinal movement.

4. A hollow collapsible mandrel according to claim 3, wherein said actuating means comprises a screw thread through brackets fixed to said inner and outer arm portions, manually operable to separate the brackets, and spring means connected between said brackets for exerting a retracting force on the telescoping arms of the connection means.

5. A hollow collapsible mandrel according to claim 1 or claim 2, wherein said axially extending support means is a rigid, vertically oriented cylindrical core and said mandrel wall sections are the part-cylindrical, vertically elongate sections of a cylindrical mold of modular form.

6. A hollow collapsible mandrel according to claim 5, wherein each of said extendible and retractible connection means comprises an inner rectangular frame secured to the outer surface of said cylindrical core in coplanar alignment with the axis thereof and an outer rectangular frame secured to the inner surface of one of said modular wall sections in coplanar alignment with said inner rectangular frame, said inner and outer rectangular frames including telescopingly engageable transverse tubing sections at vertical spacings therealong.

7. A hollow collapsible mandrel according to claim 6, wherein said actuating means for each mating pair of inner and outer rectangular frames comprises a hydraulically powered short stroke piston and cylinder expander mounted for thrust transmission between the inner frame and the outer frame, and return spring means for actuating the return of an outer frame portion toward the core, when the hydraulic expander is powered down.