Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Corrugating
Patent
1991-05-02
1992-08-18
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Corrugating
2642094, 4253261, 425336, 425393, 425396, 4253791, B29C 4790
Patent
active
051397307
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method and an apparatus for manufacturing ribbed pipe.
BACKGROUND OF THE INVENTION
Finnish Patents 60 825, 74 654 and 77 405 disclose manufacturing lines for ribbed pipes, wherein a formable mass brought into a plastic state is extruded by means of a die between movable forming means pressed against one another to achieve continuous production of ribbed pipe. With these prior art solutions, ribbed pipe products having a good quality and being commercially successful are achieved.
In prior manufacturing lines for ribbed pipes, cooling of the pipe has been arranged to be two-sided, i.e. both the forming means disposed against the exterior surface of the pipe and the interior mandrel supporting the pipe through the corrugator are cooled. However, slight waviness has been found on the inner surfaces of ribbed pipes thus produced, despite the mandrel arrangement suggested by Finnish Patent No. 74 654. It has been found that this is caused by depressions at the rib flanges, resulting from the fact that the rib flanges are cooled at different rates at different points, i.e. faster at the rib flange surfaces pressed into the grooves of the forming means than at the foot of each rib flange. Uneven cooling will result in uneven shrinkage of the material, which is manifested as said waviness on the inner surfaces of the pipe.
SUMMARY OF THE INVENTION
The object of this invention is to develop the manufacturing process for ribbed pipe further so that the above stated disadvantages are avoided. To achieve this, the method of the invention, wherein a formable mass in a plastic state is extruded into a substantially cylindrical forming space of a corrugator, said forming space being delimited by forming means, i.e. moulds, movable in the production direction of the apparatus and having grooves on the inner surface thereof for forming rib flanges, and a stationary mandrel forming the inner surface of the pipe, and wherein the mass formed as a pipe in the forming space is cooled, is characterized in that the ribbed pipe is cooled from the inner surface of the pipe with the mandrel which extends an essential length externally of the forming space constituted by the forming means of the corrugator.
The invention is based on the conception that when on the one hand rapid cooling is provided for the pipe from the interior, whereby the inner surface thereof will naturally be cooled rapidly and uniformly and be compacted as a glassy surface against the mandrel, and on the other hand cooling from the mold side is reduced or totally eliminated, flawless ribbed pipe is produced, as long as the softening of the pipe caused by the reduction in the cooling of the molds is compensated at the point when the pipe leaves the corrugator by supporting the pipe by means of an extended mandrel. The decrease in the cooling of the molds does not require any special operations; shortening of the corrugator as such already reduces the cooling effect, and the cooling can still be reduced or totally eliminated by modifying the cooling cycle in the molds and the temperature thereof. Measures of this kind are obvious to a person skilled in the art.
The most significant advantage of the invention is naturally that the production of ribbed pipes having a flawless inner surface is made possible. Additional advantage is provided by the fact that when in the known apparatus the length of the corrugator in the region where the forms are shut is of the order of 2.5 m, it may have a length of only 1 m when realized in accordance with the invention. When the size, complexity and weight (about 20 tons) of a normal corrugator are taken into account, reducing the size in this way has several advantageous multiplied effects. While a normal kernel has a length of about 0.5 m, a kernel length according to the invention is 1 to 3 m.
The apparatus of the invention, which is adapted to receive formable mass in a plastic state and which comprises a corrugator having a substantially cylindrical forming space deli
REFERENCES:
patent: 3292213 (1966-12-01), Donald
patent: 3613162 (1971-10-01), Talsma
patent: 3994646 (1976-11-01), Hauck
patent: 3998579 (1976-12-01), Nordstrom
patent: 4721594 (1988-01-01), Jarvenkyla
patent: 4867928 (1989-09-01), Jasrvenkyla et al.
patent: 4983347 (1991-01-01), Rahn
Agren Lennart
Holso Eino
Holso Paul
Jarvenkyla Jyri
Scharwachter Dieter
Thurlow Jeffery
Uponor N.V.
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