GB2153738A - Glass fibre reinforced cement products - Google Patents

Abstract

In the manufacture of glass fibre reinforced cement products by casting there is provided a mould core 11 which is covered on the outside with a close fitting layer 22 of sheet plastics material, such as polyethyelene, clamped beneath the core. This assembly is lowered into a mould outer 5, and the reinforced cement mix is then poured into the mould cavity 21 and vibrated. When the mix has cured sufficiently to be self-supporting but whilst it is still green, the core 11 may be removed, leaving the lining or plastics material in place so that the core may be re-used long before the product is fully cured. <IMAGE>

Description

SPECIFICATION Mould and method for the manufacture of glassreinforced cement products The invention relates to the manufacture of glassreinforced cement products.

Glass-reinforced cement products, i.e. products made from a mix rich in cement with a proportion of glass fibre as a reinforcement, are gaining acceptance in a number of fields, such as pre-formed land drainage units, owing to their high strength to weight ratios, which gives rise to ease of handling and installation. Such units have hitherto normally been made by a spray process, but this has led to difficulties in control of wall thickness and to waste of material, thus losing much of the advantage arising from the choice of material. Casting has more recently come into serious consideration as a method of manufacture in this medium.However, this is a comparatively slow method of manufacture, in that the units have to be left to cure for a considerable time in the moulds, before the latter can be re-used, so that there is a high capital cost involved in providing a number of moulds. In view of the comparatively thin wall thicknesses involved, the moulds have to be made to fairly strict tolerances, which further adds to the cost.

It is an object of the invention to provide a method which leads to economy in the use of moulds.

In accordance with a first aspect of the invention, there is provided a method for the manufacture of glass-reinforced cement products by casting, in which a mould core is covered on the outside with a close-fitting layer of sheet plastics material, a cement mix reinforced with glass fibre is poured and vibrated into a mould cavity defined between the sheet and a split mould, and the core is withdrawn while the mix is still in a green state but substantially self-supporting, to allow the mix to cure between the sheet and the mould.

The core may then be re-used with a further mould, while the original mould ana the lining support the green and curing casting.

The sheet plastics material may be in the form of a tube which is clamped beneath the core when the latter is lowered onto a casting base.

Means may be provided for releasably attaching the core to the casting base.

In accordance with a second aspect of the invention, there is provided a split outer mould and a core co-operable with the outer mould to form a mould cavity, the core having means thereon to trap a layer of plastics material so as closely to cover the outer surface of the core.

The invention will be further described with reference to the accompanying drawings, which show a preferred form of the invention, and in which Figure 1 is a plan view of a form of mould and casting base in accordance with a preferred form of the invention Figure 2 is a section taken on the line A-A of Figure 1; and Figure 3 illustrates to a larger scale, a detail of Figure 2 taken from within the circle B of Figure 2.

Turning first to Figures 1 and 2, a casting base 1 is formed of square section tubing and is generally rectangular in plan view, as shown in Figure 1. A gantry 2 extends over a central zone of the casting base 1, and is rigidly mounted thereon. A mould support structure 3 is solidly mounted on the casting base and an exterior portion 4 thereof supports a mould outer 5 which is split into three parts as indicated by the jointing flanges 6 shown in Figure 1. The mould outer 5 is reinforced by upper and lower angled flanges 7 and 8 respectively and the lower flange 8 is also used to secure the mould outer 5 to an L section pallet 9 which rests on the exterior portion 4 of the support structure 3.

A mould core is shown formed by a skin portion 11 and a central tube 12 joined by a base 13. The skin portion 11 is provided with strengtheners 14 in the form of inwardly directed radial flanges. The base 13 is provided with a tongue 15 which projects through a locating aperture in a block 16 on the support structure 3, and a wedge may be inserted in a slot 17 in the tongue 15 to lock the core to the support structure 3 and casting base 1.

The L section pallet 9 on the outer mould is shown as being provided with a welded-on fillet 18 (see in particular Figure 3) which provides a rebate on the article to be cast between the core 11 and the mould outer 5. It is also envisaged that other forming devices may be attached to the mould outer 5 to provide required rebates or thinned areas. The rebate formed by the fillet 18 is intended to match with the projection formed at the upper side of the corresponding similar moulding so that the mouldings will nest together.

In operation in accordance with the invention, a tube 22 of polyethylene or like plastics material is draped over the outside of the core member 11 and clamped beneath it. The plastics tube 22 will be cut to suitable length and, using a suitable lubricant on the core member 11, slid over it and clamped with a steel or plastics band and simple over-centre device or tensioner to an upstanding rim 23 to the support structure 3 on which the core seats.

This band will be accessible after the core is removed, so that it can be released when the outer 5 with its pallet 9 is removed from the machine.

The plastics tube 22 can be simply held in position at the top of the core by folding inwards over the edge and wedging down with a former of hollow section tube rolled to suit the inside diameter of the core.

The core 11 is then lowered by means of a lifting arrangement (not shown) mounted on the gantry 2 into a central position coaxial with the mould outer 5 and located and locked in position by the tongue 15 and a wedge through the slot 17. The lower end of the plastic tube 22 is thus clamped beneath the base 13 to the support structure 3, and the tube is held tight against the skin 11 by the upper wedge arrangment and forms a lining to the mould cavity 21 between the core skin 11 and the mould outer 5.

The cement-rich mix, with added chopped glass the core and mould are agitated by means of a vibration motor indicated in phantom by the reference numeral 25 in Figure 1.

A form of removable wedge arrangement (not shown) will be provided to fit at the top of the mould during the initial filling and vibrating stage to make sure that the outer mould is centred on the core, and this could be plastics or steel blocks of the correct wall thickness fitted at three or four positions around the top of the outer, and which would be removed before the mould is completely filled.

Once the vibrated mix has set sufficiently hard, but while it is still green, the mould core assembly may be released and withdrawn by means of the lifting mechanism and will slip easily upwards inside the plastics tube 22 so that the inner surface of the casting is not damaged by the withdrawal of the core. The core is then removed and may be put into a separate mould outer and the procedure repeated, so that the core is being re-used while the casting is still green. This leads to efficiency in the use of cores.

It is to be noted that the outer 5 may be made from glass-reinforced plastics, which is cheaper than the conventional steel.

Various modifications may be made within the scope of the invention. For example, the radial flanges 14 may be replaced by axtially extending ribs, e.g. three in number. Also these ribs may be used as anchoring points for attachment of hoisting cables, chains or the like attached to a single cable from the overhead hoist. The tube 12 could also then be omitted.

Claims (7)

1. A method for the manufacture of glass-reinforced cement products by casting, in which a mould core is covered on the outside with a closefitting layer of sheet plastics material, a cement mix reinforced with glass fibre is poured and vibrated into a mould cavity defined between the sheet and a split mould, and the core is withdrawn while the mix is still in a green state but substantially self-supporting, to allow the mix to cure between the sheet and the mould.

2. A method as claimed in claim 1, in which the sheet plastics material is in the form of a tube.

3. A method as claimed in claim 2, in which the tube is clamped beneath the core when the latter is lowered onto a casting base.

4. A method as claimed in claim 1, 2 or 3, in which means is provided for releasably attaching the core to the casting base.

5. A method for the manufacture of glass-reinforced cement products substantially as hereinbefore described with reference to the accompanying drawings.

6. A mould for use in a method as claimed in any of the preceding claims, comprising a split outer mould and a core co-operable with the outer mould to form a mould cavity, the core having means thereon to trap a layer of plastics material so as closely to cover the outer surface of the core.

7. A mould for the manufacture of glass reinforced cement products by casting substantially as hereinbefore described with reference to the accompanying drawings.