GB2145364A

GB2145364A - Releasing tubular article from mould

Info

Publication number: GB2145364A
Application number: GB08418288A
Authority: GB
Inventors: Giancarlo Bonissone; Piero Mulas
Original assignee: FIP Formatura Iniezione Polimeri SpA
Current assignee: FIP Formatura Iniezione Polimeri SpA
Priority date: 1983-07-26
Filing date: 1984-07-18
Publication date: 1985-03-27
Also published as: IT8312591A0; IT8312591A1; GB2145364B; GB8418288D0; IT1171214B

Abstract

A thermoplastic tubular article (10) provided, at least at one end, with an external rib and an internal groove is released from a mold consisting of a pair of radially opposed and radially movable semi-shells (21,22), defining the outer central surface of the article up to the vertex of its external rib, an annular component (40) which is axially movable and defines the outer surface of the article from the outer annular rib vertex as far as to its end and an axially sliding pin (50), defining the inner surface of the article. The article is released in three stages, namely retracting the annular component (40), withdrawing the pin (50) until cylindrical portions of the article on either side of the groove rest on an end, cylindrical portion of the pin (50) and then completely withdrawing the pin (50) and removing the semi-shells (21, 22). <IMAGE>

Description

the said tubular article, is defined by an edge annular component 40 which is axially sliding, for instance under the action of hydraulic means such as jacks or the like. The radial inner surface 41 of edge annular component 40 defines the outer surface portion of the tubular article enclosed between the vertex of rib 16 and the edge of the article; the radially outer surface of the said edge annular component 40 is housed in a corresponding annular step 26 and 27, provided for in the two semi-shells 21 and 22.

The edge annular component 40 slides axially above a cylindrical pin 50, whose diameter is preferably equal to the outer diameter of the edge annular portion 13 of the tubular article 10.

Pin 50 is substantially formed by two cylindrical parts having different diameters, wherein the diameter of the outer part 51 (at right in the figure) is equal to the external diameter of the edge cylindrical portion 13 of article 10, whereas the second or inner part 52, of smaller diameter, follows the inside profile of the internal surface of tubular article 10.

Therefore, there is provide between the two parts 51 and 52 of pin 50 a step 53 which is used to define, inside the mold, the edge 19 of article 10. The inner part 52 of pin 50, of smaller diameter, extends as far as to the symmetry plane 11 of tubular article 10. In the cylindrical inner part 52 of pin 50, of smaller diameter, is further provided an annular rib 54 which internally defines the profile 15 of waving 14.

In order to control the temperature of article 10 during the ejection stage, the edge annular component 40 is provided with a heating circuit 60, made for instance with a resistor. A further heating element 61 is located inside pin 50 and extends from rib 53 towards the outer end of the said pin so as to heat the waving 14 as well as the end cylindrical tract 13 of article 10 in combination with the heating element 60.

Therefore the waving 14 of art. 10 and its end cylindrical portion 13 are heated both inside and outside by the heating elements 60 and 61.

On the other hand, a cooling element is located near the cylindrical surface of the terminal element 52 of pin 50, the purpose being to facilitate the cooling of the central part 12 of the sleeve 10, right after its molding, and also to cool (as will be seen), the cylindrical edge 13 of the sleeve during the intermediate stage of the ejection process. The said cooling element can advantageously consist in a pipe coil filled with a cooling fluid.

In a way known per se, the axial movement of the edge annular element 40 of the mold is linked to pin 50. To this purpose, pin 50 is provided with a stop collar 70 that cooperates with the two annular pawl surfaces 71 and 72, which define the edges of an annular groove 73 provided in the inner cylindrical surface of the annular end component 40. Thus component 40 is free to move, in respect of pin 50, by an axially measured quantity equal to the length of groove 71 minus the axial length of rib 70.

The ejection process according to the invention, and consequent working of the above said device is as follows: In the position shown in Figure 1, the tubular article mold 10 is realized by the two semi-shells 21 and 22, the surfaces 52 and 53 of pin 50, and finally the surface 41 of the edge annular component 40.

The four above said components of the mold stay in the position shown in Figure 1 until the cavity defined by them is filled with the thermoplastic material. At this point, the ejection process according to the invention is started.

It must be pointed out that heating elements 60 and 61 are at work also while the mold is being filled with the thermoplastic material.

The first stage of the ejection process provides for an axial retraction of edge element 40, to the position shown in Figure 2, and to the right of the Figures.

Therefore the outer surfaces of end cylindrical portion 13 and of waving 14 (starting from the vertex of the latter) are free.

These portions are filled with thermoplastic material, whose temperature is maintained at a proper degree by heating elements 60 and 61, until element 40 is moved backward, and is maintained at the same degree by heating element 61 also after element 40 has moved from the position shown in Figure 1 to the position shown in Figure 2.

The relative axial position between element 40 and pin 50 is defined by the collision between the pawl annular element 70 and the face 72 of cavity 73.

In the second stage of the ejection process according to the invention, element 40 continues to be axially retracted to the right of the figures.

Thanks to the said collision condition between collar 70 and surface 72, the axial movement of element 40 is transmitted also to pin 50: the annular rib 54 of pin 50 causes an expansion of the edge portion of tubular article 10, and more particularly an expansion of waving 14 and of cylindrical end tract 13, as shown in Figure 3 by a dotted line.

The said second stage of the ejection process must stop before pin 50 is completely withdrawn from inside the tubular article 10: more precisely, the second stage of the ejection process must end when the cylindrical end tract 13 of tubular article 10 is in correspondence with the cooling element 62 provided in the end tract 52 of pin 50.

The waving 14 and the cylindrical end tract 13, which had expanded at the passage of rib 53, consequent to the high temperature supplied first by elements 60 and 61 and then only by element 61, return elastically to their original position, and contract over the end part 52 of pin 50 thanks to the cooling action of e.g. element 62.

During the said cooling the cylindrical end element 13 finds in the outer surface of end tract 52 of pin 50 a calibrated support enabling it to attain and maintain strict dimension tolerances, which are defined univocally by the dimensional tolerances of end portion 52 of pin 50.

Consequently, the edge wall of the tubular article, astride of waving 14, is perfectly calibrated, due to the fact that its cooling takes place against a calibrated collision surface.

It should be noted that until tubular article 10 is completely cooled there are no temperature differences on any circumferential section of tubular article 10.

Not only does this contribute to prevent ovalizations which on the other hand are already prevented by the presence of cylindrical support 52, but, above all, it prevents the setting up of dangerous residual stresses which would modify the mechanical characteristics of the tubular article from one of its points to another.

Such result is most important in consideration of the fact that tubular article 10 can thus be used for building plants intended for work under high pressure and even for the transport of dangerous materials.

After the cooling of at least the edge of tubular article 10, the third stage of the ejection process takes place; in a quick succession, pin 50 is completely withdrawn from the tubular article, the upper semi-shell 21 is raised, while the rods 30 withdraw the tubular article 10, by now ejected, from the lower semi-shell 22.

It should be noted that during the whole sequence every cross section of the article is mantained, point after point, at the same temperature.

This is made possible by exposing to air, at the same time, every single section of tubular article 10.

The result is a tubular article exceptionally devoid of residual stresses, and provided with extremely strict dimension tolerances.

Also, the device for carrying out the process is of great simplicity, and its components do not exceed the number of known devices. The invention, therefore, permits to attain remarkable advantages with no increases either in the manufacturing costs, or in the cost of installations as compared to the devices made available by the known state of the art.

Claims

1. A process for ejecting a tubular article of synthetic (thermoplastic) material, having at least at one of its ends, a waving in the wall, which causes an external rib and an internal groove; the said article being enclosed in a mold consisting in a first and a second molding elements, surrounding the central portion of the article, and consisting in a pair of radially opposed and radially movable semi-shells, which define the outer central surface of the article up to the vertex of its external rib, a third molding element consisting in an axially movable edge annular element, defining the outer surface of the article at the vertex of the outer annular rib up to its edge, a fourth molding element consisting of an axially sliding pin defining the inner surface of the article and provided with an annular rib apt to define the inner groove of the article;; the said process being characterized in that: - in a first stage, after the article has been formed inside the mold, the edge annular element being the third element of the mold, is moved backward until the outer surface of the article is freed from the vertex of its outer annular rib up to its edge; - in a second stage, the above said pin (being the fourth element of the mold) is axially withdrawn by expanding the edge of the article, until the said pin reaches an axial position in correspondence with which the adjacent cylindrical portions of the article placed astride its waving rest on an edge portion of the cylindrical surface of the pin, which is provided with cooling means.

- in a third stage, and in quick succession, the pin is entirely withdrawn, the upper semi-shell (being the first element of the mold) is radially removed from the central area of the article, and, finally, raised away from the lower semi-shell (being the fourth element of the mold) by means of suitable sliding rods which cross the wall of the lower semi-shell.

2. A process according to the preceding claim characterized in that, during the article molding stage, the inner and outer surfaces of the article edge, in correspondence with the above said waving, are heated by heating elements provided respectively inside the edge annular element (being the third element of the mold) and inside the axial pin (fourth element of the mold), externally to the position of the annular rib of said pin; said heating being continued, during the first stage of the ejection process, by means of the said heating element provided inside the pin.

3. A process according to the previous claims, characterized in that, starting from the end of the second stage of the ejection process, and up to the beginning of the third stage of the said process, the cylindrical portions of the article, astride the waving provided at its edge, are cooled by means of a cooling element provided inside the axial pin (fourth element of the mold).

4. A process according to the previous claims, characterized in that the said heating of the edge portions of the article is obtained by means of electrical resistances (or oil circulation) provided respectively in the edge annular element (third element of the molding) and in the axial pin (fourth element of the molding).

5. A process according to claims 1 to 3 characterized in that the cooling of the article area astride its annular waving, is obtained by means of a cooling fluid circulating in a corresponding circuit.

6. A device for carrying out the process according to the previous claims, of the type providing for a first and a second molding elements, consisting of two semi-shells, radially opposed and radially movable by a relative motion, defining the outer central surface of the article up to the vertex of its outer annular rib, a third molding element, consisting of an axially movable edge annular element, defining the outer surface of the article from the vertex of its outer rib to its end, a fourth molding element, consisting in an axially removable central pin defining the inner surface of the article and provided with an annular rib apt to define the internal groove of the article, in correspondence with its waving, characterized in that the said pin provides for a cylindrical limit portion provided with cooling means, apt to supply a support to the cylindrical areas of the article placed astride its annular waving, after the partial withdrawal of the pin which is effected in the second stage of the process claimed.

7. A device according to claim 6 characterized in that externally to the annular rib of the said axially movable pin, apt to define the inner surface of the article in correspondence with its annular waving, the said axial pin is supplied with heating means acting during the molding of the article and during the first stage of the ejection process.

8. A device, according to claims 6 and 7, characterized in that in the said third element of the mold, consisting of the edge annular element, there are provided heating means acting during the article molding.

9. A process for ejecting a tubular article of synthetic, thermoplastic material, having at least at one of its ends, an external annular protuberance and a registering internal annular groove, the article being enclosed in a mold comprising a pair of radially-opposed and radially-movable semi-shells surrounding a central portion of the article, which semi-shells define the outer central surface of the article up to the vertex of the external protuberance, an axially-movable, annular end element, defining the outer surface of the article from the crest of the external protuberance up to its end, and an axially-slidable pin defining at least part of the inner surface of the article and provided with an annular rib apt to define the internal groove of the article, the process comprising:: - in a first stage, after the article has been formed inside the mold, the end element of the mold is retracted until the outer surface of the article is freed from the crest of the external protuberance up to its end; - in a second stage, the pin is axially withdrawn, expanding the end of the article, until the pin reaches an axial position in which cylindrical portions of the article on either side of the protuberance rest on an end cylindrical portion of the pin; - in a third stage, and in quick succession, the pin is completely withdrawn, and the semi-shells are removed from the central portion of the article.

10. A process for ejecting from a mold a tubular article of synthetic, thermoplastic material, substantially as herein described with reference to the accompanying drawings.

11. A mold arranged for ejecting therefrom a tubular article of synthetic, thermoplastic material, substantially as herein described with reference to, and as shown in, the accompanying drawings.