WO2004101255A1

WO2004101255A1 - Centring mould assembly

Info

Publication number: WO2004101255A1
Application number: PCT/NL2004/000340
Authority: WO
Inventors: Ralph Kruidering
Original assignee: F.T. Engineering B.V.
Priority date: 2003-05-16
Filing date: 2004-05-17
Publication date: 2004-11-25
Also published as: NL1023453C2

Abstract

Mould assembly consisting of two mould sections (33, 34), each provided with centring means that interact with one another. The mould assembly is in particular intended for an injection moulding device with which centring of the mould sections with respect to one another is achieved not by the rigidity of the injection moulding device but by centring means (38, 42) on the mould sections themselves. The centring means (40) on one of the mould sections can be moved with respect to the mould section concerned. By centring the mould sections (33, 34) outside the injection moulding device with the aid of a central centring pin (45) and then securing the movable centring means (40) concerned, accurate centring can be obtained when installing in the injection moulding device.

Description

Title: Centring mould assembly

The present invention relates to a mould assembly comprising two mould sections, each having end faces, a mould cavity being delimited between said sections when said end faces are in the position moved towards one another along a central axis, said end faces being provided with centring means that interact with one another, comprising, in one end face, cavities that extend radially with respect to said central axis and become narrower into the depth of the end face concerned, and, in the other of said end faces, corresponding projections extending radially with respect to said central axis. More particularly, but not exclusively, the present invention relates to a mould assembly to be used in an injection moulding device of relatively lightweight and compact construction. This can be either a vertical or a horizontal injection moulding device. According to the present invention, the mould sections are each provided with end parts, a mould cavity being delimited between them when said end parts are in the position moved towards one another along a central axis, said end faces being provided with centring means interacting with one another, comprising, in one end face, cavities extending radially with respect to said central axis and becoming narrower into the depth of the end face concerned and, in the other of said end faces, corresponding projections extending radially with respect to said central axis. That is to say, the present invention relates mainly, but not exclusively, to mould assemblies that can be used in combination with injection moulding devices with which the frame construction of the injection moulding device is not essentially responsible for the mutual centring of the mould sections. Such injection moulding devices can be of short or low construction. Moreover, it is easily possible to change the mould assemblies. After all, particularly complicated adjustment operations in order to centre the mould sections with respect to one another on the injection moulding device are not necessary.

IP 4-216025 discloses an injection moulding machine that closes horizontally and has centring projections effective in the diametric direction and cavities corresponding to these. These are arranged in a ring so as always to give a tight fit.

The aim of the present invention is to enable centring of the end faces after the mould parts have been fitted on the injection moulding machine.

This aim is realized with a mould assembly as described above in that a projection and/or said cavity is made in an auxiliary part that is adjustable with respect to the end face concerned. As a result, the assembly, which in a first step is outside the injection moulding device, can be centred in an optimum manner and when the two mould sections are in said optimum position the adjustable centring means can be secured in a desired position with respect to the mould section concerned. Consequently, a mould assembly obtained in this way can be used in an arbitrary manner in any injection moulding device. This means that the projections and cavities, respectively, can be moved to some extent with respect to one another. That is to say, a projection can be moved relative to another projection and/or the same applies for the cavities.

The projections and cavities interacting with one another can be of any conceivable shape. Preferably, cylindrically shaped projections (rollers) and corresponding cavities are used.

According to another advantageous embodiment, the cavity is tapered in a N-shape. The number of centring means can also be as desired. Preferably, three centring means are used arranged as far as possible around the periphery of the mould section concerned.

The original centring of the mould sections with respect to one another can be effected using the bore present in the mould sections. Such a bore is, for example, present for an aerosol can, punching member and the like. A pin can be inserted into this bore, as a result of which the sections concerned are aligned precisely with respect to one another. In this position the centring described above can be carried out. Such a pin can optionally be a pin of variable diameter. One embodiment thereof comprises a pin with a relatively thin wall section inside which a fluid is present, and when pressure is applied to the fluid the wall section expands to some extent, as a result of which a clamped fit is provided.

According to an advantageous embodiment of the invention, one of the end faces has a so-called venting ring and more particularly a sprung venting ring. This can be moved with respect to a mould section located within it. Thus, it is possible to perform injection/compression technique. That is to say, mutual centring already takes place before a mould closes completely. In this position a quantity of plastic is injected and as the mould closes further this plastic is distributed and subjected to pressure while the mould parts remain centred.

The invention also relates to a method for centring two mould sections, wherein each of said mould sections is provided with centring means on the end faces and at least one of said centring means on one of said end faces can be moved with respect to said end faces, comprising centring said mould sections outside an injection moulding device by moving and securing said movable centring means with respect to the end face concerned.

Furthermore, the invention relates to a method for the injection moulding of an article, comprising installing two mould sections in an injection moulding device, wherein one section is installed such that it can be moved in a direction perpendicular to the closing movement of said injection moulding device, wherein said mould sections are centred with respect to one another before device, the method described above for centring the two mould sections being used.

The invention will become more clearly apparent on the basis of an illustrative embodiment shown in the drawing, hi the drawing:

Fig. 1 shows, highly diagrammatically, an injection moulding device in which the mould assembly according to the present invention is used;

Fig. 2 shows the end face of each of the mould sections; and Fig. 3 shows centring of the mould sections with respect to one another. An injection device in which the mould assembly according to the invention can be used is shown in Figure 1. This injection moulding device is indicated in its entirety by 1 and consists of a top frame 2, that is joined to the base plate 4 by, for example, three columns 3 in a relatively "weak" manner, i the construction shown here, the injection moulding device has been set up vertically, that is to say the mould sections move in the vertical direction with respect to one another.

The operating means for the movable mould section comprise a crankshaft 5 that is driven in some way or other by a motor and controller that are not shown in more detail. The crank of crankshaft 5 is connected to a drive rod 6, which is provided close to the free end with a joint 9, to which auxiliary rods 7 and 8 are fixed in a pivoting manner. Auxiliary rod 7 engages on the joint 10 of piston 14, whilst auxiliary rod 8 engages on joint 11 at the end of the piston rod of ram 13. This piston rod can assume various positions. There is a stationary mould section 34 and a movable mould section 33. The movable mould section 33 is provided with a venting ring 50 that can be moved with springs 51 with respect to the core 52 of the mould section 33. In addition, the construction is such that in the non-loaded state ring 50 protrudes above the central part 52. When the moulds close, the venting ring 50 is pressed downwards against the force of the springs 51.

The end faces of the movable mould section 33 and in particular of the venting ring 50 and stationary mould section 34 are shown in Fig. 2. These are indicated by 35 and 36, respectively. Here, end faces are understood to be the faces that are juxtaposed when the mould sections close.

A variant of the cavity 42 is shown in Fig. 2A. This is made in a N-shape. It will be understood that other cavity shapes that provide a centring effect are possible. As indicated above, the construction of the vertical injection moulding device is non rigid as such. As a result of the presence of the double thrust bearing 15, the movable mould section 33 can, in principle, be moved into different positions with respect to the top mould section, in a direction that differs from the direction of closure that is indicated with the axis 37. There are centring means to ensure that the mould sections 33 and 34 close correctly.

The stationary mould section 34 is provided with three recesses 38 in which cylindrical rollers 39 have been fitted in a permanent manner. The movable mould section is provided with three cups 40 that are to be fixed to the relevant movable mould section with the bolts 41. With this arrangement the construction is such that the cups 40 can be moved into a number of different positions because the opening for the bolts 41 is larger than the diameter of the bolts 41. The cups 40 are provided with seats 42 that correspond to the size of the cylindrical rollers 39.

With this construction consisting of rollers 39 and seats 42, accurate mutual positioning is achieved during closing of the mould sections. Centring can optionally be obtained in combination with a venting ring or other construction.

It can be seen from the above that mutual position of the rollers 39 and seats 42 is of essential importance for the accuracy of closing of the mould sections. hi Fig. 3 it is shown how this mutual position is fixed. The mould sections 33 and 34 are placed some distance apart, preferably outside the injection moulding device. A pin 45 is then inserted through the central opening 43 in the stationary section and the central opening 44 in the movable section. This pin either has accurately the same diameter as the openings concerned or is provided with means by means of which the diameter thereof can be increased to some extent. Such means can comprise applying pressure in the interior of the pin, as a result of which the pin locally expands to some extent. i the case of the construction with which it is possible to increase the diameter of the pin, it is furthermore possible to provide accurate centring of mould sections that are provided centrally with a sleeve of relatively small wall thickness that is movable with respect thereto. Such a sleeve can be an ejection sleeve or stamper holder. Such a sleeve is accommodated in the relevant component of the mould section in the longitudinal direction with very small tolerance (usually a few μs). By using a pin which has a diameter that can be enlarged, this small tolerance will be removed, as a result of which the parts will make tight contact with one another and accurate centring is possible. The mould sections are moved towards one another, h addition, the bolts 41 are loosened, that is to say cups 40 are able to make a limited mutual movement with respect to the movable mould section. As they move downwards, the rollers 39 of the stationary mould section 34 will provide correct positioning of the cups 40 as a result of the presence of the centring pin 45. The bolts 41 are then tightened and accurate mutual centring is achieved by combination of the rollers 39 and seats 42.

In the abovementioned manner it is possible to place the mould sections or the assembly consisting of the mould sections in any type of injection moulding device with which mutual movement of the supporting parts of the injection moulding device for the mould sections is possible in a direction perpendicular to the direction of closure. Further measures are then not needed. As a result it is possible to change moulds particularly quickly. Moreover, it is possible to make the injection moulding device of more compact construction because it is no longer necessary to have the injection moulding device open much farther for centring operations. After all, the mould section concerned can easily be removed for maintenance and then replaced. The mould assembly can be used either in vertical or in horizontal injection moulding devices. A wide variety of types of articles, and more particularly disc-shaped optical information carriers, can be produced using such injection moulding devices.

After reading the above, modifications that are obvious and fall within the scope of the appended claims will be immediately apparent to those skilled in the art.

Claims

1. Mould assembly comprising two mould sections (33, 34), each having end faces, a mould cavity being delimited between said sections when said end faces are in the position moved towards one another along a central axis (37), said end faces being provided with centring means (38 - 42) that interact with one another, comprising, in one end face, cavities (42) that extend radially with respect to said central axis (37) and become narrower into the depth of the end face concerned, and, in the other of said end faces, corresponding projections (39) extending radially with respect to said central axis, characterised in that a projection and/or said cavity is made in an auxiliary part (40) that is adjustable with respect to the related end face.

2. Mould assembly according to Claim 1, wherein one of said mould sections is provided with a movable fixing (15), which in one direction is not coincident with said central axis (37), for fixing to an injection moulding device (1).

3. Mould assembly according to one of the preceding claims, wherein said cavities and said projections are made cylindrical.

4. Mould assembly according to one of the preceding claims, comprising three projections/cavities each positioned 120° apart.

5. Mould assembly according to one of the preceding claims, wherein said auxiliary part (40) is adjustable in the peripheral direction of the related end face.

6. Mould assembly according to one of the preceding claims, wherein said mould sections are provided with a bore (43, 44) extending along said central axis (37).

7. Mould assembly according to one of the preceding claims, wherein one of said end faces has a ring (50) that surrounds a mould section (53).

8. Kit, comprising a mould assembly according to Claim 6 as well as a pin (45) to be fitted through said bores with a tight fit.

9. Kit according to Claim 8, wherein the diameter of the pin in said bores is variable.

10. Method for centring two mould sections, wherein each of said mould sections is provided with centring means on the end faces and at least one of said centring means on one of said end faces can be moved with respect to said end faces, comprising centring said mould sections outside an injection moulding device by moving and securing said movable centring means with respect to the related end face.

11. Method according to Claim 10, wherein said mould sections each have a bore (43, 44) extending along a central axis (37), wherein said mould sections are centred with respect to one another by inserting a centring pin (45) in said bore.

12. Method for the injection moulding of an article, comprising installing two mould sections in an injection moulding device, wherein one section is fitted such that it can be moved in a direction perpendicular to the closing movement (37) of said injection moulding device, wherein said mould sections are centred with respect to one another before device using the method according to one of Claims 9 or 10.