Molding system with retracting mold

A molding system for molding large diameter chimney liners of fibreglass reinforced plastic (FRP) utilizes a vertically oriented cylindrical mold for use in combination with a working platform mounted on a vertical ram. The mold is of modular construction, having a plurality of axially spaced-apart spiders, each spider being segmented into a plurality of adjoining tri-angulated segments to form a polygon, to the outer sides of which are attached chordal segments to complete the circular form of the spider. Vertically axially extending ribs interconnect the spiders, with a flexible skin being applied thereabout. The provision of expansion means on the spiders increases the diameter of the mold to its working diameter, so that, upon completion of molding a liner, the action of the spider expansion means is reversed, causing contraction of the mold sufficient to facilitate ready axial separation of the mold and liner. The modular construction of the mold, including radial adjustability of the spider segments permits the mold to be built up to different selected diameters so that liners having a size range between 20 feet and 30 feet diameter may be readily fabricated using one basic mold.

This invention is directed to a molding system for molding large diameter 
reinforced cylindrical liners, including an improved mold, and an 
arrangement of elements for use therewith in producing the liners. 
The use of chimney liner fabricated of fibreglass re-inforced plastic (FRP) 
has recently encountered a large upswing in view of increased coal 
utilization stemming from current oil shortages. 
Such FRP liners are attractive to use because of their resistance to 
sulphur dioxide and other acidic combustion by-products, as well as 
possessing an inherent insulation value to maintain more constant the 
temperature of flue gases. 
However, with the need to provide FRP liners ranging in diameter generally 
between 20 and 30 feet, (6 to 9 meters), having a thin-walled 
construction, difficulties are experienced in stripping the molded liners 
horizontally from off the mold. 
Current molding practices encompasses horizontally extending molds of about 
30 feet (9 meters) axial extent mounted upon stub axles extending from the 
ends of the mold to phenolic bearings spaced about 50 feet (15 meters) 
apart. This axle extension permits a stripping clearance at the axial end 
of the mold, for removing the liner axially at least partially from off 
the mold. 
This type of arrangement, wherein the mold is segmented in order to 
facilitate transportation, results in a mold having a total of about 2500 
component parts, and weighing in the order of 20 tons (18,000 kilograms). 
In addition to the foregoing requirements, such an arrangement also 
requires the provision of two stripping jacks, for raising the mold and 
liner, to permit the insertion of a liner stripping dolley beneath the 
liner, and two intermediate mold support stands to facilitate removal of 
one of the mold support bearings for completing removal of the liner 
axially from off the mold, with the aid of a tractor. 
This prior system is costly to provide, requires a large working area and a 
building of about 70 feet in width, 40 feet in height and 120 feet in 
length (approx. 21.times.12.times.36 meters), and is time consuming, 
cumbersome and on occasions somewhat dangerous in use. The necessary 
collapsing of such existing molds to permit liner withdrawal is achieved 
by the provision of an axial hinge securing adjacent peripheral segments 
of the mold, with hydraulic actuators providing inward retracting collapse 
of the mold wall. 
Certain of the disadvantages attributed to this type of prior art 
arrangement are: 
1 retraction clearance is not uniform, owing to the limited number (two) of 
support segment portions: 
2 hang-up of the liner on the mold can create consequent damage and danger: 
3 necessity for installing steel stiffener rings about the liner prior to 
withdrawal of the liner from the mold requires manipulation of the liner 
and the mold in order to locate the rings in segments about the liner, 
with a complex jacking requirement in order to support the mold as the 
liner is withdrawn. 
The adoption in this present invention of a mold having vertical 
orientation provides particular advantages in the case of large diameter 
thin walled casings that are subject to buckling collapse when 
horizontally oriented, as the vertical orientation minimizes transverse 
(diametrical) distortion forces acting on the casing. 
The vertically axised mold per se is inherently self supporting and may be 
made of relatively light construction, owing to its vertical orientation. 
The effects of winding tensile forces may be minimized as opposed to the 
prior art arrangements, wherein winding forces tend to supplement the 
diametrical liner collapse forces due to self-weight. 
The provision of modular spiders having fluid powered expanders actuable in 
radial expansion mode prior to winding the liner on the mold serves to 
provide a predetermined extent of retraction "allowance," ensuring a 
substantially uniform radial retraction of the mold inwardly from the 
wound liner upon de-energization of the expanders, to facilitate ready 
vertical separation of the mold and the formed liner. 
The adoption of selectively adjustable spider modules permits use of the 
basic mold to encompass a significant range of liner sizes, with minimum 
cost or lost time required to provide preliminary setting up of the spider 
frames, and to provide the requisite complementary parts necessary to 
complete the desired mold comprising supplementary module segments 
together with axial ribs and a tensioned mold cover. 
In preparing the subject mold for a predetermined diameter of liner, the 
axially spaced spider modules are each modified by manual adjustment of 
the radial arms using pinned sliding joints to achieve the desired radius 
for the spiders. The outer chordal rib of each spider module is 
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. Axially extending wooden ribs are then secured about the spiders 
extending between the outer segments to provide a substantially complete 
stiff cylinder frame. 
Using the cylindrical, rotatable mold as on a lathe, with one or more 
cutting tools mounted upon and reciprocating axially with the work table 
and operating against the surface of the mold the desired true cylindrical 
surface can be readily generated. 
A plastic or other flexible wrapping diaphragm is then passed around the 
cylinder, having at least one of the ends thereof secured to a tensioning 
roller, by means of which a desired degree of pre-tension is applied to 
the wrapping. In order to condition the prepared mold preparatory to the 
commencement of fabricating a liner thereon, fluid pressure is applied to 
a manifold interconnecting the fluid powered expanders of each spider. The 
pressure fluid expands the spiders radially by a predetermined retraction 
clearance, thereby increasing the loading of retraction springs. The 
expanders are then isolated from the fluid supply, to maintain the mold in 
expanded condition, and the molding operation then proceeds with the 
application of a suitable slip agent, prior to the building up of the FRP 
liner, using known FRP molding techniques. 
While vertical mold systems are known, such as Mede, U.S. Pat. No. 
3,255,976, June 14th, 1966, and Luckett et all, U.S. Pat. No. 3,928,104 
Dec. 23rd, 1975, the present arrangement provides particular and unobvious 
advantages in the fabrication of liners having the recited 
characteristics. Thus, by mounting the rotatable mold platform below 
ground level such that the top of the mold is more or less flush with the 
ground, an FRP applying work station is arranged on a worktable vertically 
displaceable on a ram oscillating vertically, parallel with the axis of 
the platform. The worktable also includes one or more tool stations, 
having a lathe tool, milling or suitable grinding tools for preparing the 
surface of the mold to the required cylindrical form by machining of the 
vertical ribs upon rotation of the mold and vertical oscillation of the 
tool with the work table. 
The handling of mold components the separation of the fabricated liner from 
the mold, and the disposition of the liner, is facilitated by a 
track-mounted gantry crane spanning the pit. 
A simple, low cost, bogey-mounted cover positioned beneath the crane on 
tracks located between the crane tracks can obviate the need for a 
permanent building. 
Thus, for on-site fabrication one low cost embodiment provides sliding 
disposable covers located beneath a gantry crane, operating in 
co-operation with a simple low cost turntable located in a work pit below 
ground level.

Referring to FIGS. 1 and 5 the arrangement 10 comprises a pit mounted 
turntable 11 having an adjacent ram 12 mounted in a hydraulic cylinder 14, 
the ram 12 extenting substantially parallel with the polar axis of 
turntable 11 having control means (not shown) to oscillate the work table 
15 upwardly and downwardly at desired rates in the work pit 16. The 
subject mold 18 is assembled on turntable 11, co-axially therewith. 
The turntable 11 has a central post 26 carried on thrust bearing 13, having 
a driving gear 17 connected by chain 19 to variable speed motor 21. The 
working surface 23 of turntable 11 is supported on a plurality of casters 
25 running on a circular track 27. A magnetic brake 29 working on the 
under surface of working surface 23 provides accurate control of the 
turntable. 
The worktable 15 is centered in co-axial relation with the ram 12 having 
one filament feed and wet box working station 20 mounted thereon, and is 
provided with a tool station 22 for finishing the peripheral surface of 
the axial ribs 44 of mold 18 to a cylindrical form. The lathe turning 
effect is achieved by rotation of the turntable 11 bringing the tool at 
station 22 into cutting relation with the ribs 44, and oscillating the 
work table 15 as required to complete the operation. 
Referring also to FIG. 2 the mold 18 has a central post 26 on which a 
number of axially spaced spiders 30 are mounted by way of a sleeve 32. 
Each spider 30 has a plurality of radial arms 34 of tubular form secured to 
the sleeve 32, each arm 34 having an extension 36 extending therefrom and 
secured by bolts 37, the radially outer ends of extensions 36 being 
interconnected by chord ribs 38 which are selectively extensible by 
adjustment means, permitting selective adjustment in length to the chord 
ribs 38 as dictated by the selected radial positioning of the chord ribs 
38 when the radial arm extensions 36 are adjusted to a desired mold 
diameter. 
Each chord rib 38 is provided with a complementary segment 39 generally a 
wooden former, of arcuate segment so as to complete the desired circle in 
dimension and form. A series of slots 42 spaced around the perimeter of 
formers 39 receive axial ribs 44 which extend generally for the full 
length of the mold 18 in interconnecting relation between the spiders 30. 
In the instance of the adjoining segments of FIG. 2 it will be seen that 
the pairs of adjacent radial arms 34 provide a radial passage within which 
the ends of an outer skin 50 are entered, being guided on rollers 52 
carried by respective ones of the chord ribs 38. A filler piece 54 bridges 
the peripheral gap in the skin 50 adjacent rollers 52. A tensioning roller 
53 receives the split ends of the flexible skin 50. Axial spacers 54 
interconnecting the respective arms 34 maintain the spiders 30 in axially 
spaced apart relation. 
Referring to FIGS. 3 and 4, each radial arm 34 has an expansible actuator 
means 56 connecting the radially outer portion of arm 34 with the radially 
outer extensions 36. Angle brackets 58, 60 secured to the respective arm 
portions by bolts 61 contain a fluid actuated short stroke piston and 
cylinder expander actuator 62 having the piston 64 abutting the bracket 60 
in thrust transmitting relation therewith. A return spring 66 
interconnects the arrangement, to provide return action to extension 36 in 
opposition to the expansion action of actuator 62. It will be understood 
that as an alternative to the provision of springs 66 the actuator 62 can 
be made double acting. 
The limited radial expansion provided to the radial arms 34 of each spider 
segment constitutes a mold contraction allowance. 
In operation, to set up the mold for a predetermined diameter of FRP liner 
the radial extension arms 36 of each spider 30 are set manually to a 
desired value by adjustment of securing bolts. This also requires 
adjustment of the length of the chord ribs 38, using bolts 42 in selected 
apertures 40. Selected complementary segments 39 having an outer arc of 
curvature for the desired liner size are installed, and axial ribs 44 
installed. 
The actuators 62 are connected to a source of fluid pressure (not shown) so 
as to take-up the mold radial contraction allowance, as the actuators 62 
expand outwardly, thereby increasing the tension in return springs 66. 
The actuators 62 are then sealed, by way of a suitable control valve, to 
maintain them locked in the expanded condition. 
The mold 18 may then be peripherally profied, using the cutting tool at 
tool station 22 on platform 20 in conjunction with oscillation up and down 
the rotational displacement of the mold to provide a desired degree of 
smoothness and cylindrical surface to the radially outer edges of ribs 44 
and wooden formers 39. The outer skin 50 is then installed in tensioned 
relation about the framework of the mold, and the mold is in condition for 
use. 
With the mold thus prepared, the system is operated using one working 
station 20 having filament feeds and one or more wet boxes, as is well 
known in the art, to build up a pattern of FRP material in desired 
patterns by controlling the rate of rotation of the turntable and mold 
driven by motor 24, together with vertical oscillation by way of ram 12, 
in synchronized relation with rotation. 
Upon termination of liner fabrication, which generally includes automatic 
self-curing, the liner is secured to the gantry crane, the mold contracted 
by releasing fluid pressure from the expansion actuators 62 to permit the 
retraction springs 66 to contract the mold radially. The provision of 
spring tension to the outer skin further assists the contraction of the 
mold when the expansion actuators are depressurized. The gantry crane 
lifts finished liner from the mold pit and removes the liner clear of the 
working area, and work on a succeeding liner can commence immediately, or 
the mold changed to a different desired size. 
Between the tracks 65 of the gantry crane, which straddles the installation 
containing the mold on its turntable, and the working table mounted on its 
ram, all within the pit, there is located a narrower track 68, also 
straddling the installation, carrying a pair of half covers 70 which draw 
together and provide protection from the elements. These withdrawable 
half-covers comprise a low cost substitute in place of a building, so that 
the present invention may be used on location, with a minimum of capital 
investment, the structure generally being sufficiently light to be rolled 
back by hand to uncover the pit, to provide access for the gantry crane, 
the cost of the structure generally not warranting transport to a new 
location of the plant, as it may comprise timber and plastic sheeting. 
It will be seen that the present invention provides a very low cost 
installation comprising an excavated pit to receive the hydraulic ram, 
turntable and driving motor therein, having a low cost track and thrust 
bearing to support the turntable.