Patent EA-003015-B1 (EA)
Title: Method of producing centrifugally cast, glass fiber reinforced plastic tubes
Inventor: CARLSTROM BORGE
IPC: B29C31/00
Filed: 2000-01-19
Abstract: 1. Method of manufacturing centrifuged glass fibre-reinforced synthetic material pipes wherein liquid, curable resin, which can contain a filler, together with glass fibres and additives for the curing process, possibly also with sand, is introduced into a rotating mould and the temperature of the mould is between 40 degree C and 75 degree C as the raw materials are introduced, characterised in that the heating capacity of the mould is so high that the raw materials do not cause the temperature of the mould to drop more than 10 degree C and warm water is used to heat the mould, once the exothermal reaction of the resin has commenced, warm water is sprayed on to the mould in order to maintain the temperature of the mould at least at 60 degree C until the pipe is removed. 2. Method of manufacturing centrifuged glass fibre-reinforced synthetic material pipes wherein liquid, curable resin, which contains a filler, together with glass fibres and additives for the curing process, possibly also with sand, is introduced into a rotating mould and the temperature of the mould is between 40 degree C and 75 degree C as the raw materials are introduced, characterised in that the resin used for the layers in the outer region of the pipe has a gel time which is equal to or greater than the gel time of the resin used for the inner region of the pipe, the resin used has a filler content of at least 40%, and warm water which has a temperature of at least 60 degree C is used for the curing process. 3. Method according to claim 1 or 2, wherein the pipe has a plurality of layers, characterised in that with the exception of the cover layers outside and inside the reactivity of the resin in the other layers is set such that it is higher in the layers before the inner cover layer than in the layer after the outer cover layer. 4. Method according to any one of claims 1 to 3 ,wherein the pipes are manufactured in a continuous manner, the new immediately after the old, characterised in that shortly prior to removing the pipes warm water is sprayed onto the mould so that the mould maintains the same temperature which is necessary when manufacturing the new pipe. 5. Method according to any one of claims 1 to 3, characterised in that the temperature of the warm water and the duration of the spraying process is such that the temperature of the mould remains at least at 70 degree C until the pipe is removed. 6. Method according to any one of claims 1 to 5; characterised in that polyester resin and/or styrene are added to the filler-polyester resin mixture in a mixer at the front in the lance of the injection machine. 7. Method according to claim 6, characterised in that more polyester resin is added to the layers on the inner side of the pipe than on the outer side. 8. Method according to claim 6 or 7, characterised in that an accelerator to the polyester resin is added at the front in the lance of the injection machine to different layers, in order to increase the reactivity in these layers or an inhibitor is used to reduce the reactivity. 9. Method according to any one of claims 6 to 8, characterised in that a mixture accelerator/polyester resin is added to the sand layers in the middle of the pipe in order to increase the reactivity of the filler mixture there. 10. Method according to any one of claims 1 to 9, wherein at least two catalyst pumps are used with different catalysts, characterised in that a catalyst or a catalyst mixture which has a lower light-off temperature is used in one pump and a catalyst or a catalyst mixture which has a higher light-off temperature is used in the other pump and that in order to extend the gel time the catalyst or the catalyst mixture which has the higher light-off temperature is used. 11. Method according to any one of claims 1 to 10, characterised in that the glass fibre content in the inner region of the pipe is higher than in the outer region and with the exception of the inner cover layer all the layers in the inner region of the pipe contain filler. 12. Method according to any one of claims 1 to 11, characterised in that the glass fibres in the inner region of the pipe are of a greater length than the glass fibres used in the outer region of the pipe. 13. Method according to any one of claims 1 to 12, characterised in that in the outer region of the pipe in the layers in which there is no sand, in parts short glass fibres are used and in parts long glass fibres are used. 14. Method according to any one of claims 1 to 13, wherein isocyanate is mixed into the resin for the inner cover layer, characterised in that first a greater part of the cover layer without isocyanate is introduced and then the remainder of the cover layer with isocyanate in a quantity of 4 to 6 %.wt is added and subsequently the finished pipe is treated on the inner side with isocyanate. 15. Method according to any one of claims 1 to 14, for the manufacture of centrifuged synthetic material pipes, wherein the raw materials are introduced from an injection machine into a rotating mould, characterised in that the mould and the injection machine can move in the same plane, that the injection machine operates from a fined position and the injection machine is mounted on a carriage which is displaced horizontally with respect to the movement of the centrifugal machine. 16. Centrifuged, glass fibre-reinforced synthetic material pipes comprising a plurality of layers consisting of cut lengths of glass fibres, polyester resin with filler and sand and also inner and outer cover layers, layers glass fibre-reinforced on the outer and inner part with polyester resin and filler and also in the middle a core part with sand, polyester resin, filler and glass fibre, characterised in that the core part contains at least 7% glass fibre and at least 25% polyester resin maximum 25% filler. 17. Centrifuged, glass fibre-reinforced pipes with a plurality of layers consisting of cut lengths of glass fibres and polyester resin with filler and glass fibres and a core part with sand, characterised in that the content of glass fibres in the inner part of the pipe is on average higher than the average of the glass fibres in the outer part wherein filler is also present in the inner part in all the glass fibre-reinforced layers, in which the glass fibres are orientated in the peripheral direction. 18. Pipe according to claim 17; characterised in that where the glass fibres in the pipe are orientated in the peripheral direction, the filler content in the polyester resin is at least 40%. 19. Pipe according to claim 17 or 18, characterised in that glass fibres whose length is greater than the length of the glass fibres in the outer region of the pipe are provided in the inner region of the pipe. 20. Pipe according to any one of claims 17 to 19, characterised in that in the outer region of the pipe in the layers in which there is no sand in parts with short glass fibres are provided and in parts long glass fibres are provided. 21. Apparatus for manufacturing centrifuged, glass fibre-reinforced synthetic material pipes, wherein the raw materials are introduced from an injection machine into a rotating mould, characterised in that the injection machine (L) can move in a fixed position, but that the centrifugal machine (M-1, M-2) is mounted on a carriage (W) which can be moved in a transverse manner with respect to the injection machine in the same plane, the heating capacity of the mould is so high that the raw materials do not cause the temperature of the mould to drop more than 10 degree C and warm water is used to heat the mould. 22. Apparatus according to claim 21, characterised in that spraying devices are provided by means of which warm water is sprayed onto the moulds, wherein the spraying devices are in fixed positions and cannot move with the moulds and that a device is provided by means of which the water is collected under the carriage in a fixed container. 23. Apparatus according to claim 21 or 22, characterised in that the carriage moves in a closed space, wherein only orifices for the introduction of the raw materials and the removal of the pipes and also for doors, pipes and ventilation connectors are provided.