EP1526958A1

EP1526958A1 - Mould core of an injection moulding tool

Info

Publication number: EP1526958A1
Application number: EP03735314A
Authority: EP
Inventors: Werner Plass; Manfred Lausenhammer
Original assignee: MHT Mold and Hotrunner Technology AG
Current assignee: MHT Mold and Hotrunner Technology AG
Priority date: 2002-08-09
Filing date: 2003-05-20
Publication date: 2005-05-04
Also published as: DE3735314A1; BR0313544A; MXPA05001385A; CN1700975A; DE20321175U1; WO2004018180A1; AU2003236805A1; US20060121150A1; DE10236522A1; CA2493235A1

Abstract

The invention relates to a mould core (1) of an injection moulding tool for injection moulding preforms in plastic. The mould core (1) consists of a hollow sleeve, closed at one end and having a central axis, an outer surface (3), an inner surface (4) and a hollow cooling tube, positioned in the mould core (1) at a distance from the inner surface (4) of said core and connected to coolant supply conduits and coolant drainage conduits. The aim of the invention is to increase the cooling effect of the mould core (1) in relation to previously used mould cores. To achieve this, the cooling tube extends coaxially in relation to the mould core (1) over approximately the entire length of the latter and is provided with an outlet opening (9) on the outflow side and cooling grooves (11) are configured in the inner surface of the mould core (1), extending approximately crosswise to the central axis (2).

Description

Mold core of an injection mold

The invention relates to a mold core of an injection molding tool for injection molding plastic preforms, the mold core having the shape of a hollow sleeve closed on one side with a central axis, an outer surface, an inner surface and a hollow one in the mold core at a distance from it inner surface arranged cooling pipe in connection with coolant supply lines and coolant discharge lines.

It is known to blow bottles made of more or less transparent plastic from preforms, in particular the known PET bottles (PET = polyethylene terephthalate). Preforms made of PET are produced in large numbers in high-performance injection molding machines. These preforms usually have relatively thick walls, usually from 1.5 mm to 4.0 mm. They are injection molded at relatively high temperatures of around 260 ° C to 310 ° C. The hollow preforms, which are closed on one side, are cooled after the injection molding, on the one hand on the mold core and, on the other hand, after removal from the injection molding machine, in order to prevent their deformation or sticking together. Their thick walls act like a heat insulator that traps the heat in the wall.

In order to increase the production performance of the known injection molding machines, attempts are made to reduce the cooling time with the disadvantage that a lower limit cannot be undershot here without accepting damage to the preforms after the injection molding process.

The cooling of the surface of the molded preforms must be sufficient to allow them to be ejected from the mold without damage. In addition, additional cooling is necessary in order to also dissipate the heat coming from the interior of the walls to the surface. If the cooling in the injection molding machine is not carried out after the injection molding and the preforms after they have been removed from the machine, the temperature of the surface rises undesirably and causes the sprayed preforms to stick to one another, prone to damage to the surface, and bend or discard. Measures have therefore always been taken to improve the cooling of the molded preforms.

In practice, for example, attempts have been made to cool the outer tool part surrounding the preform as well as the mold core. It has been found that the preform is short early on after its injection process shrinks inwards onto the core, with the result that there is a small gap between the outer tool part and the product itself, the preform, which makes the heat transfer from the outer, cooled tool part to the preform considerably more difficult and practically one Cooling has no effect. Therefore, the focus has been increasingly on cooling the mandrel. In practice, a cooling tube has been inserted into the mandrel in such a way that it occupies practically the entire interior of the mandrel, with the exception of a gap-shaped annular space around the cooling tube and within the inner surface of the mandrel. Through supply lines connected to the open lower end of the cooling tube, coolant, preferably water, has been introduced into the cooling tube and the water is allowed to wet the inner surface of the mandrel in a cooling manner, after which the water is discharged through discharge lines. In fact, the mold core could be cooled somewhat via its inner surface. However, it has been recognized that this cooling could still be improved and the entire production of preforms could thus be improved, in particular made more powerful.

The object of the present invention is therefore to provide a mandrel of the type specified in the introduction, the cooling effect of which has been significantly increased compared to previously used mandrels.

This object is achieved according to the invention in that the cooling tube extends coaxially to the mandrel over its almost entire length and is provided at the downstream end with an outflow opening and that cooling grooves extending approximately transversely to the central axis are provided on the inner surface of the mandrel. As in the practice already used in operation, the cooling tube extends practically into the entire interior of the mandrel and ends only "at the front" at the closed end of the mandrel shortly before the end of the interior in such a way that the cooling water which flows through the cooling tube reaches it leaving its front end through an opening in the cooling tube and coming into contact with the inner surface of the mandrel. The mandrel is closed like a bag at the front, and its inner surface forms the outer wall of the coaxial, gap-shaped annular space between the cooling tube and the mandrel. At the back, that is, downstream of the cooling water , this annulus is connected to the coolant discharge line mentioned.

The mold core is cooled to a certain extent by the contact of the cooling water with its inner surface, but this cooling effect can be improved according to the invention on the one hand by increasing the inner surface of the mold core. This is achieved by additionally introducing cooling fins into the otherwise closed inner surface of the mandrel. In a particularly favorable manner and surprisingly, the cooling effect is additionally increased, on the other hand, by the fact that the cooling fins or cooling grooves located on the inner surface of the mandrel not only extend lengthways but also run transversely to the central axis. "Cross" means vertical only in a special case, you can choose the direction of extension of the Think each cooling groove obliquely to the central axis of the mandrel. The cooling grooves do not need to follow a straight line on the way of their extension, but can somehow be curved or undulating. It should only be noted that the majority of the cooling grooves do not run in the direction of the central axis, but at an angle to it.

It has been shown that cooling grooves running "transversely" to the central axis are correspondingly flowed to during operation, with the result that the coolant is subjected to not inconsiderable turbulence on its way after leaving the cooling tube from its opening front to rear along the gap-shaped annular space The cooling effect of the respective mandrel thus increased as a result of an increase in surface area by enlarging the otherwise smooth, closed inner surface of the mandrel, that is to say it contains ribs, grooves, grooves or the like, but on the other hand turbulence occurs in the coolant flow in the course of its flow path, and it is precisely this turbulence that significantly increases the cooling effect.

In an advantageous further embodiment of the invention, the cooling grooves have a pointed and / or round profile in cross section. Profile here means the cross section through a cooling groove, which can be “round”, for example the bottom of a U; or “pointed”, such as the lower end of a pointed V. If, for example, a V-shaped profile is also considered two flanks intersecting at an acute angle, it may be particularly preferred to select this angle from the range between 10 ° and 70 °, preferably from the range between 20 ° and 50 °, or to select it at 40 °. This information does not mean that the considered angle of the profile must lie in these areas. This information only means that successful attempts with such angles have already been carried out in practice.

Instead of the flanks with "pointed" profiles, it is also possible to use curved surfaces for the production of round profiles, as is known, for example, from round threads.

So it is also expedient if the cooling grooves run helically according to the invention. In other words, the cooling grooves extend like a thread. This can have any type of geometry, provided that only the smooth surface, if no cooling grooves were provided, is enlarged. The radial geometry of the cooling grooves can preferably be designed as a trapezoidal thread or a sawtooth thread. It is advisable to choose a radial geometry for enlarging the surface and producing the turbulence. From a manufacturing point of view, it is also favorable if the cooling grooves run smoothly. Practical trials have already shown that it can be manufactured cheaply if rings, grooves, threads or all of these designs are brought together. The water flowing over these cooling grooves is subjected to strong turbulence, with the result of good turbulence and thus a great cooling effect. A particularly drastic improvement in the cooling effect is obtained if, according to the invention, the cooling grooves extend over that surface area of the mandrel on which the preform is injected. Lines and holders are provided in the rear area of the mandrel, so that the preform to be sprayed is kept away from this rear area of the mandrel. It is therefore not necessary to provide a special feature for cooling there. According to the invention, however, the cooling grooves are provided in the entire surface area, that is to say the area of the outer surface of the mandrel on which the plastic of the molded preform is seated and touches. According to the invention, the cooling grooves are provided at least over this surface area on which the preform is injected. It is not excluded that the thicker areas of the holder of the mandrel can also be provided with cooling grooves. However, surprising successes in increasing the cooling effect have already been achieved if cooling fins are provided on the inner surface of the mandrel only in the area of the preform that is seated.

In practice of the operation already carried out with the mold core described, an outflow opening is provided at the front end of the cooling tube. The cooling water emerges from this and leaves the mold core after flowing through the gap-shaped annular space to the rear. If the outflow opening on the cooling tube is now allowed to have at least one recess extending in the direction of the central axis, it is also found that the cooling water emerges from the cooling tube more easily. The outflow opening at the front end of the cooling tube can be imagined in the simplest case by cutting off the theoretically closed cooling tube so that the area of the outflow opening is perpendicular to the central axis of the mandrel. The outer edge of such an outflow opening would then be circular. If this circular edge is now provided with an additional recess, which extends at least partially in the direction of the central axis of the cooling tube, then the area of the outflow opening increases, with the result that the cooling water can exit there more easily into the gap-shaped annular space. Such a recess at the edge of the outflow opening can be thought of as V-shaped, U-shaped or with another profile, provided that the edge does not only follow the circular line, but is extended by said recess.

When the cooling water flows from the outflow opening of the cooling tube, it is intended to provide the main throttling in the course of the flow path in the region of the gap-shaped annular space in which the preform is sprayed on the outside onto the outer surface. Further to the rear, the coolant discharge lines can even have larger cross sections, so that the coolant relaxes there. There in the rear area, at a greater distance from the molded preform, no cooling, swirling and therefore no large areas are required. The coolant can flow smoothly and relaxed backwards without resistance. Further advantages, features and possible applications of the present invention result from the following description of a preferred exemplary embodiment in conjunction with the attached drawings. Of these show:

1 shows a cross-sectional view of a mandrel with the thinner region arranged at the front and the feed and discharge lines arranged at the rear, and FIG. 2 greatly enlarged and broken off the detail II according to the circle II in FIG. 1.

The preferably titanized mold core has the thicker area for the holder, for example in a core plate, shown at the rear (i.e. below) in FIG. 1, and the thinner area 10 at the front, over which the preform (not shown) is stretched after spraying. The wall of the mandrel 1 shown in dashed lines has the shape (in FIGS. 1 and 2 above) of a closed, hollow sleeve with the dash-dotted central axis 2. The mandrel 1 has an outer surface 3 and an inner surface 4.

At a distance from the inner surface 4 of the mandrel 1, it is almost entirely provided with a cooling tube 5. A gap-shaped annular space 6 is formed between the inner surface 4 of the mandrel 1 and the cooling tube 5 on the outside. In the front area, on which the preform is sprayed during operation, the annular space 6 is slit-shaped, i.e. it has a small radial expansion of preferably 1.5 mm to 3 mm, depending on the space available. Ideally, this gives an 80% backflow, i.e. the outflow is 80% of the inflow. In contrast, the radial extension of the rear annular space 6 ', which is located in the thicker mounting area of the mandrel 1, is provided only for the coolant discharged to drain.

In the lower area of FIG. 1, one can see the coolant supply line 7, which can be located in a core plate as well as the coolant discharge line 8 arranged further ahead or in FIG. 1. The cooling tube 5 is open at the rear, where coolant from the coolant supply line 7 is centered in Direction of the central axis 2 flows upwards and forwards, as well as upwards at the front, where the outflow opening 9 is located on the cooling tube 5.

Even in older operating structures, cooling water was introduced centrally through the coolant supply line 7 into the cooling tube 5 at the top, and was pressed into the mold core 1 from the outlet opening 9 at the front. As a result, the cooling water in the gap-shaped annular space 6, parallel to the central axis 2 of the mandrel 1, flowed downward from the front upward from the area of the outlet opening 9 into the enlarged annular space 6 ', in order to flow out of it, outside the cooling tube 5, via the coolant discharge line 8 to be dissipated.

In the new embodiment shown here, the inner surface 4 of the mandrel 1 is in the front surface area 10 of the mandrel, on which in operation the one in the drawings I preform, not shown, is injected, provided with a screw thread to form cooling grooves 11.

In the greatly enlarged detail II according to FIG. 2, one can see the straight lines, which are at a small angle to the central axis 2 and which represent the cooling grooves 11. The preferred embodiment selected here is a helical cooling groove 11, which extends transversely to the central axis 2 and has a pointed profile. The shape of the cooling grooves can also be described with a sawtooth thread with a V-shaped profile, the two cheeks of which represent straight flanks in section. The section through the wall of the mandrel 1 according to FIG. 2 shows this V-shaped profile with the straight flanks.

FIG. 2 also shows the shape of the outflow opening 9 on the cooling tube 5 at the front. If one were only to consider that edge of the outflow opening 9 which runs perpendicular to the central axis 2 and is designated by 12 in FIG. 2, then a part circle 12 would be seen in a plan view in the direction of the central axis 2. In between there are recesses 13 with an oblique cutting line 14. In other words, the outflow opening 9 on the cooling pipe 5 has four recesses 13 extending along the cutting line 14 in the direction of the central axis 2 (towards this). From the side, these recesses 13 appear in a V-shape at the front end next to the outlet opening 9. The cooling tube 5 shown here has four recesses 13 which are evenly distributed on the circumference of the circle 12, namely two recesses which are in line with the paper in FIG and two more in the direction perpendicular thereto, which is why the wall 5 ′ of the cooling tube 5 can be seen on the left in FIG. 2 and the plan view of the section line 14 above.

In operation, cooling water flows through the supply line 7 centrally into the cooling tube 5 upwards and forwards and emerges from the outlet opening 9 at the front in accordance with the arrow 15 in FIG. 2. As soon as the cooling water has flowed forward over the cutting lines 14, it is directed through the curved inner surface 4 of the mandrel 1 along the arrow 16 (FIG. 2) in an arcuate and radially outward direction. The cooling water now touches the inner surface 4 of the mandrel 1 and begins to cool it through intensive contact. The cooling water flows in the gap-shaped annular space 6 from front to back parallel to the central axis 2, ie downwards in FIGS. 1 and 2. On its flow path to the rear, the cooling water passes the cooling grooves 11 running transversely to the central axis 2 and is swirled in accordance with the partially circular arrows 17. In this swirled and turbulent state, the cooling water flows further to the rear (downwards in FIGS. 1 and 2). to then get into the large annular space 6 'for relaxation and flow through the discharge line 8. LIST OF REFERENCES

1 mold core

2 central axis

3 outer surface of the mandrel

4 inner surface of the mandrel

5 cooling pipe

5 'wall of the cooling tube

6 gap-shaped annulus

6 'larger rear annulus

7 coolant supply line

8 coolant discharge line

9 outlet opening

10 front surface area of the mandrel

11 cooling grooves

12 edge of the outlet opening

13 recesses

14 cutting line

15 arrow (flow direction of the cooling water)

16 arrow (flow direction of the cooling water)

17 Swirl direction of the cooling water

Claims

Patent claims

1. mold core (1) of an injection molding tool for injection molding preforms made of plastic, the mold core (1) having the shape of a hollow sleeve closed on one side with a central axis (2), an outer surface (3), an inner surface (4) and a hollow cooling tube (5) arranged in the mold core (1) at a distance from its inner surface (4) in connection with coolant supply lines (7) and coolant discharge lines (8), characterized in that the cooling tube (5) is coaxial with the mold core (1) extends over almost its entire length and is provided at the downstream end with an outflow opening (9), and that cooling grooves (11) are provided on the inner surface (4) of the mandrel (1) approximately transversely to the central axis (2) ,

2. Mold core (1) according to claim 1, characterized in that the cooling grooves (11) have a pointed and / or round profile in cross section.

3. mandrel (1) according to claim 1 or 2, characterized in that the cooling grooves (11) extend helically.

4. Mold core (1) according to one of claims 1 to 3, characterized in that the cooling grooves (11) extend over that surface area (10) of the mold core (1) on which the preform is injected.

5. mandrel (1) according to one of claims 1 to 4, characterized in that the outflow opening (9) on the cooling tube (5) has at least one in the direction of the central axis (2) extending recess (13).