WO2000030831A1

WO2000030831A1 - Method for the manufacture of elastic tubular elements with helical profile and mould suitable for implementing said method

Info

Publication number: WO2000030831A1
Application number: PCT/EP1999/008903
Authority: WO
Inventors: Evans Santagiuliana
Original assignee: Taplast Spa
Priority date: 1998-11-24
Filing date: 1999-11-22
Publication date: 2000-06-02
Also published as: ITVI980227A1; AU3034100A; IT1302465B1

Abstract

The invention is a moulding method for the manufacture of elastic tubular elements (S) with helical profile, comprising the following operations: positioning of a mould (1) into an injection moulding press, said mould (1) comprising a die (4) and a punch (2) in the shape of a truncated cone, whose side surfaces have helical profile; injection of plastic material (M) in the mould (1) to obtain a hollow elastic moulded element (C) in the shape of a truncated cone and with the side surface shaped according to the helical profile of the punch (2) and of the die (4) and with closed small base (Ca); extraction of the punch (2) from the moulded element (C) through rotation on its longitudinal axis (3); opening of the die (4); extraction of the moulded element (C) from the mould (1); cutting of a through hole in the small base (Ca). The extraction of the punch (2) from the moulded element (C) starts when the die (4) is closed and continues when the die is open, and is facilitated by blowing a pressurized aeriform substance between the punch (2) and the moulded element (C).

Description

METHOD FOR THE MANUFACTURE OF ELASTIC TUBULAR ELEMENTS WITH HELICAL PROFILE AND MOULD SUITABLE FOR IMPLEMENTING SAID METHOD.

The invention concerns a method for the manufacture of elastic tubular elements with helical profile and a mould suitable for implementing said method.

It is well known that dispensing pumps directly applied to the container are widely used to measure and dispense liquid and/or creamy substances, like for example soaps, cosmetic creams, detergents and similar products. These pumps comprise a pumping piston that is applied to the dispensing mouth of the container and that must be axial ly compressed by the user to dispense the product.

After each dispensing operation, elastic means make the piston return to its original position. A particular type of measuring pump for dispensing liquid or thick substances from their containers is described in patent n. VI97A000035, the holder of which is also the applicant for the present patent.

In accordance with the indications given in the above mentioned patent, the piston return means comprises a cap in the shape of a truncated cone, provided with external helical grooves that give it the aspect of bellows and make it particularly elastic in the axial direction.

The bellows is obtained through blowing or through injection moulding, by using plastic materials with elastic properties suitable for preventing the permanent deformation of the bellows that is subjected to repeated compressing and extending actions.

In accordance with the known blowing technique, a plastic tubular element with circular section is positioned inside a shaped die that is then closed by means of a pair of opposing plates delimiting the tubular element in correspondence with the bases. Pressurized air is blown inside the tubular element and, in combination with the heating to which the tubular element is subjected, deforms the tubular element making it adhere to the walls of the die and assume its shape.

The bellows obtained through the blowing technique present the advantage that they have a balanced molecular structure, since the moulding effort is developed radially and in the same degree in all directions, thus obtaining an isotropic product. As a consequence of this, the obtained bellows has uniform elastic behaviour in all its sections.

The blowing technique, however, presents some drawbacks, like for example very slow production cycles and the fact that only moulds with a limited number of impressions can be used on the press.

For these reasons, instead of the blowing technique, the known injection moulding technique is preferably adopted, which makes it possible to use a greater number of impressions on the press and ensures quicker moulding cycles. One of the problems connected with the manufacture of elastic tubular elements with profile in the shape of bellows through the injection moulding technique is represented by the fact that the extraction of the male from the mould is particularly difficult, especially when plastic materials with high elastic memory coefficient are used. It is for this reason that the known elastic tubular elements in the shape of bellows obtained through injection moulding using known moulds, too, are manufactured with plastic material compounds that combine the desired elastic properties of the product with the required technical feaseability and in particular with the possibility of extracting the punch from the moulded element without damaging it.

Therefore, the moulds of the known type that are presently used do not permit the moulding of elastic tubular elements in the shape of bellows with materials having a high rubber content, since after the moulding operation the high elasticity of the material would result in damage to the moulded element during the extraction of the punch.

The present invention aims at eliminating the above mentioned drawback. In particular, one of the aims of the invention is the implementation of a method for the injection moulding of elastic tubular elements with helical profile, permitting the use of materials with high rubber content and high elastic memory coefficient.

Another aim of the invention is the implementation of a mould suitable for the application of said moulding method.

The goals mentioned above have been achieved through the implementation of a method for the manufacture of elastic tubular elements with helical profile that, according to the main claim, comprises the following operations: - positioning of a mould in an injection moulding press, said mould comprising a die and a punch, both of which have a truncated cone shape with the side surface having helical profile;

- injection of plastic material in pasty state into said mould, said material being suitable for filling the interspace between said die and said punch, in order to obtain a hollow elastic moulded element substantially in the shape of a truncated cone, with the side surface shaped according to the helical profile defined by the coupling of said punch with said die and having a closed base;

- extraction of said punch from said moulded element through the rotation of the punch itself on its longitudinal axis;

- opening of said die;

- extraction of said moulded element from said mould;

- cutting of a through hole in said closed base in order to obtain the elastic tubular element from said moulded element, characterized in that the extraction of said punch from said moulded element starts when the die is closed and continues when it is open, said extraction being facilitated by blowing a pressurized aeriform substance between said punch and said moulded element.

According to a favourite application of the invention, the injection of the plastic material is made in correspondence with the bottom of the die and coaxially to it.

In this way a moulded element is obtained, which is constituted by a hollow body in the shape of a truncated cone, closed in correspondence with the small base in contact with the bottom of the die. The removal, after the moulding, of the small base, for example through a cutting operation, makes it possible to obtain the elastic tubular element.

The injection mould suitable for implementing the moulding method described above comprises:

- at least one punch with male helical profile defining a longitudinal axis and combined with a punch-holding plate;

- at least one die with female helical profile that can be coupled with the male helical profile of said punch and is combined with a die-holding plate;

- rotation means to make said punch rotate on its own longitudinal axis, suitable for obtaining the reciprocal axial shifting of said punch and said die along the same longitudinal axis, and is characterized in that said punch comprises valves for intercepting the pressurized aeriform substance and introducing it in the gap defined between the punch and said moulded element.

To advantage, the injection method object of the invention and the mould suitable for implementing it make it possible to use materials that are more elastic than the known materials currently used for this purpose, and therefore they ensure the manufacture of a tubular element that is more elastic and lasts longer than similar tubular elements. Another advantage is represented by the fact that the injection of the material in correspondence with a central point on the bottom of the die produces a balanced molecular structure, and the moulded element has isotropic features that give it the same axial elasticity in all its transversal sections. The goals and advantages described above will be better highlighted in the description of a favourite application among many of the invention in question, illustrated in the enclosed drawings, wherein:

- Figure 1 shows a complete longitudinal section of the mould suitable for implementing the method object of the invention;

- Figures 2 and 3 are two views of a detail of the mould represented in Figure 1 , in different conditions of use; - Figure 4 shows the mould object of the invention when open;

- Figure 5 shows the mould of Figure 4 when closed;

- Figure 6 shows the mould of Figure 5 during the injection phase;

- Figure 7 shows the mould of Figure 6 at the end of the injection;

- Figure 8 shows the mould of Figure 7 during the extraction of the male; - Figure 9 shows a magnified detail of the mould of Figure 8;

- Figure 10 shows the mould of Figure 8 with extracted male;

- Figure 11 shows the cutting of the moulded element.

The method object of the invention can be implemented by using an injection mould that is also the object of the invention and is represented in assembled view in Figure 1 and in exploded view in Figure 4, in both of which it is indicated as a whole by 1.

It can be observed that the mould 1 comprises a male punch 2 in the shape of a truncated cone with external helical profile, said punch defining a longitudinal axis 3 of the mould 1 ,. and a female die 4, divided in two half-shells 4a and 4b, which has the shape of a truncated cone with internal helical profile coupled to that of the punch 2.

The punch 2 is fixed to the end of a cylindrical body 5 passing through a hole 6 made on a punch-holding plate 7 that is in turn connected to one of the movable plates of an injection moulding press, not represented in the figure. Analogously, the die 4 is housed in a suitable seat 8 belonging to a die-holding plate 9 that is connected to the other movable plate of the same press. The punch-holding plate 7 and die-holding plate 9 are axially shifted against each other along the longitudinal axis 3 by the powering means of the press, in order to close the mould as shown in Figure 5 or to open it as shown in Figure 4.

When the mould 1 is closed, an interspace 10 is defined between punch and die, as shown in Figure 5, said interspace 10 being suitable for receiving the material M that, injected through the injection channel 11 , as shown in Figures 6 and 7, makes it possible to obtain the moulded element constituted by a hollow body in the shape of a truncated cone C with closed small base Ca visible in Figure 10.

Rotation means visible in Figure 1 , where they are indicated as a whole by 12, comprising a pinion 13 positioned at the end of the cylindrical body 5 of the punch 2 and a rack 14 engaging with the pinion 13 make it possible to set the punch 2 rotating to separate it from the moulded element C at the end of the moulding phase.

According to the invention, at the beginning of the rotation of said punch 2, between the punch 2 and the moulded element C a gap 15 visible in Figures 8 and 9 is defined, in which a pressurized aeriform substance is blown in order to facilitate the extraction of the punch 2 from the inner surface of the moulded element C itself.

The punch 2 comprises valves 16 for intercepting the compressed aeriform substance and introducing it in the gap 15, said aeriform substance being conveyed with a pipe 17 passing through the pinion 13 and communicating with a duct 18 obtained - in axial position - in the cylindrical body 5.

The valves 16, as shown also in Figures 2 and 3, where they are represented in closed and open position, respectively, comprise a closing element 19 housed into a seat 20 obtained in the area with shorter diameter 2a of the punch 2. The closing element 19 is positioned at the end of a rod 21 slidingly fitted into the duct 18 of the cylindrical body 5 of the punch 2 and its profile having the shape of a truncated cone 19a can be joined to the corresponding truncated cone-shaped profile 20a of the seat 20 to obtain a sealing effect. The large base of the closing element 19 is preferably, but not necessarily provided with a circular protrusion 19b.

Outside the rod 21 elastic means are provided that consist of an helical spring 22 included between a first shoulder 23 obtained in the punch 2 and a second shoulder 24 obtained in the rod 21. Practically, if the mould 1 is in the open position represented in Figure 4, it is brought to the closed position represented in Figure 5 and then the fluid plastic material M is injected in the interspace 10 through the injection channel 11 obtained in the die-holding plate 9, as shown in Figures 6 and 7. This material is constituted by a mixture of rubber substances with high elastic memory coefficient that makes it possible to obtain an elastic tubular element in the shape of a truncated cone and with helical profile, characterized by high elasticity and endurance.

Furthermore, the injection is performed coaxially to the longitudinal axis 3 of the mould in correspondence with the base of the die 4, so that the molecular structure of the material M that is symmetrically introduced into the mould is balanced and an isotropic moulded element C can be obtained.

The circular protrusion 19b provided on the large base of the closing element 19 and positioned in contact with the moulded element C delimits an impression I in the small base Ca of the moulded element, said impression - visible in Figure 9 - being suitable for facilitating the successive cutting of the moulded element, as described below.

To extract the punch 2 from the moulded element C, the former is set rotating by the pinion 13 driven by the rack 14.

As soon as the rotation begins, as shown in Figure 8 and in detail in Figures 2, 3 and 9, pressurized air is blown through the duct 18 to push the closing element 19 upwards according to direction 19c and make it strike against the small base Ca of the moulded element C. The closing element 19 is raised of the distance 19d allowed by the lowering of the punch 2 in the vertical direction 2b. The gap 15 is thus created between the moulded element C and the external profile of the punch 2; the compressed air that flows with direction 25 between the sealing profiles 19a and 20a coming from the duct 18 penetrates in said gap 15 with an enclosing movement in the direction 26, thus facilitating the extraction of the punch 2 from the moulded element C. In this way the separation of the punch 2 from the moulded element C takes place with no damage to the latter.

Immediately after the first detachment of the punch from the moulded element, the two half-shells 4a and 4b of the die 4 separate releasing the moulded element C that, at the end of the extraction of the punch 2, adheres to the punch-holding plate 7, as shown in Figure 10, with the punch 2 housed in the hole 6 of the punch-holding plate 7.

Successively, as shown in Figure 11 , a through hole is made on the small base Ca of the moulded element C through cutting with the punch 27 and the die 28, said hole being made in correspondence with the central area, in such a way as to obtain the tubular element S having a truncated cone shape and the side surface with helical profile. The cutting is favoured by the presence of the impression I produced in the moulded element C by the annular protrusion 19b present in the closing element 19.

According to the above, it is evident that the moulding method object of the invention and the mould suitable fro implementing it actually achieve all the goals set and described in the introductory part.

Even if the method and the mould object of the invention have been described with reference to the attached drawings, the above are just the basic outlines of the invention and any change which may be necessary upon implementation is to be regarded as completely protected by the present invention, provided that it is based on the same innovative concept described herein.

Therefore, with reference to the above description and to the attached drawings, the following claims are put forth.

Claims

1 ) Method for the manufacture of elastic tubular elements (S) with helical profile, comprising the following operations:

- positioning of a mould (1 ) in an injection moulding press, said mould comprising a die (4) and a punch (2), both of which have a truncated cone shape with the side surface having helical profile;

- injection of plastic material (M) in pasty state into said mould (1), said material being suitable for filling the interspace (10) between said die (4) and said punch (2), in order to obtain a hollow elastic moulded element (C) substantially in the shape of a truncated cone, with the side surface shaped according to the helical profile defined by the coupling of said punch (2) with said die (4) and having a closed base (Ca);

- extraction of said punch (2) from said moulded element (C) through the rotation of the punch itself on its longitudinal axis (3); - opening of said die (4);

- extraction of said moulded element (C) from said mould (1);

- cutting of a through hole in said closed base (Ca) in order to obtain the elastic tubular element (S) from said moulded element (C), characterized in that the extraction of said punch (2) from said moulded element (C) starts when the die (4) is closed and continues when it is open, said extraction being facilitated by blowing a pressurized aeriform substance between said punch (2) and said moulded element (C).

2) Mould (1 ) suitable for implementing the method according to claim 1 , comprising: - at least one punch (2) with male helical profile defining a longitudinal axis (3) and combined with a punch-holding plate (7);

- at least one die (4) with female helical profile that can be coupled with the male helical profile of said punch (2) and combined with a die-holding plate

(9); - rotation means (12) to make said punch (2) rotate on its own longitudinal axis

(3), suitable for obtaining the reciprocal axial shifting of said punch (2) and said die (4) along the same longitudinal axis (3), characterized in that said punch (2) comprises valves (16) for intercepting the pressurized aeriform substance and introducing it in the gap (15) defined between the punch (2) and said moulded element (C). 3) Mould (1) according to claim 2, characterized in that said punch (2) is positioned at the end of a cylindrical body (5) housed in a through hole (6) made on a punch-holding plate (7) of said mould (1 ) opposed to a die-holding plate (9). 4) Mould (1 ) according to claim 2, characterized in that said valves

(16) comprise a closing element (19) housed into a seat (20) obtained in the area (2a) with shorter diameter of said punch (2), said closing element (19) being positioned at the end of a rod (21 ) slidingly fitted into a duct (18) obtained coaxially in the body and in the cylindrical element (5) of the punch (2) itself.

5) Mould (1) according to claim 4, characterized in that said closing element (19) and said seat (20) have sealing profiles (19a, 20a) in the shape of truncated cones joined to each other.

6) Mould (1) according to claim 5, characterized in that, in said closing element (19), the surface facing said moulded element (C) is provided with a circular protrusion (19b) suitable for defining an impression (I) in the closed base (Ca) of the moulded element (C).

7) Mould (1) according to claims from 4 to 6, characterized in that said closing element (19) is made yielding by elastic means (22). 8) Mould (1 ) according to claim 7, characterized in that said elastic means comprise at least a cylindrical helical spring (22) positioned coaxially outside said rod (21 ) and included between a first shoulder (23) obtained in the punch (2) and a second shoulder (24) obtained in the rod (21 ).

9) Mould (1 ) according to claim 2, characterized in that said rotation means (12) of said punch (2) comprise a toothed pinion (13) coupled to said punch (2) and a rack (14) engaging with said toothed pinion (13), said rack (14) being mechanically connected with powering means suitable for moving it longitudinally.