GB1600427A

GB1600427A - Method of and apparatus for manufacturing an object consisting completely or partly of a foamed thermoplastic material

Info

Publication number: GB1600427A
Application number: GB4415/78A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1977-02-08
Filing date: 1978-02-03
Publication date: 1981-10-14
Also published as: BE863694A; SE7801324L; FR2379370A1; NL7701283A; AR216935A1; IT1092397B; ES470079A1; CH626565A5; JPS5398368A; BR7800707A; ES466674A1; IT7819996A0; IN147437B; DE2803571A1; AU3303978A

Abstract

A mixture of a foamable thermoplastic material and a blowing agent in a mixing and pressing device (1) is brought to a temperature and pressure at which temperature and at which pressure the mixture is liquid. The mixture is then forced via an outflow opening (2) connected directly to one or more filling openings (8), lying in the same plane, of a female mould (5) into the female mould cavity (7). After the filling, the female mould (5) and the outflow opening (2) are pushed towards one another, the female mould (5) being provided with surfaces which cut off the material flow on displacement of the female mould. It is thereby achieved that the object produced has no sprue and that virtually no blowing agent can escape out of the outflow opening (2). <IMAGE>

Description

(54) METHOD OF AND APPARATUS FOR MANUFACTURING AN OBJECT CONSISTING COMPLETELY OR PARTLY OF A FOAMED THERMOPLASTIC MATERIAL (71) We, N.V. PHILIPS' GLOEIL AMPENFABRIEKEN, a limited liability Company, organised and established under the laws of the Kingdom of the Netherlands, of Emmasingel 29, Eindhoven, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a method of manufacturing an object which partly or completely consists of a foamed thermoplastic material, in which a mixture of a foamable thermoplastic material and a foaming agent in a mixing and compressing device is brought to a temperature and pressure at which the mixture is liquid, after which the mixture is transferred via a discharge opening and a feed opening into a mould in which a lower pressure prevails and which has a cavity with a shape which, at least during moulding, conforms to that of the object to be manufactured.

It is known to manufacture objects from, or to encapsulate electrical or electronic components such as electrical resistors, capacitors etc. with, a solid plastics material. Manufacturing or encapsulating is then effected by injection-moulding, a mould cavity, containing a component in the case of encapsulation, being filled with a liquid plastic under high pressure by an injection-moulding machine. The high pressure is then necessary to ensure that the mould cavity is correctly filled.

After the mould has been filled a high pressure must be maintained for a certain time, the so-called "post-compression", so as to allow for shrinkage during solidification of the plastic and thus to ensure that a neatly finished object or encapsulation is obtained. This postcompression has an adverse effect on the cycle time. A further drawback of this known method is that it yields objects with sprues which have subsequently to be removed.

These drawbacks can be circumvented partly by the use of a mixture of a thermoplastic material and a foaming agent. Such use is known from the Netherlands Patent Application 65 08 288, which has been laid open for public inspection. In this known method, first a batch of plastic and foaming agent is prepared in a feed chamber at a pressure and temperature such that the mixture is liquid but hardly any foaming can occur, after which, through a feed conduit which includes a valve, the feed chamber is put into communication with a mould cavity in which a lower pressure prevails.

Owing to the lower pressure in the mould the foaming agent in the plastic material will expand, so that an object of a foamed thermoplastic material is obtained. An advantage of this method is that the postcompression is no longer necessary, because owing to the expanding foaming agent shrinkage during cooling is sufficiently compensated for and the mould cavity always remains completely filled, so that an object with smooth surfaces is obtained.

However, the method has a drawback in that comparatively intricate steps must be taken to remove any residual material in the part of the feed conduit between the location of the valve and the mould after closure. This is done both to prevent the material still contained in the feed conduit, which material would lose its foaming agent after removal of the mould, from entering a following mould as a solid mass of material and to avoid the formation of a sprue on the moulded object.

According to the invention there is provided a method of manufacturing an object which completely or partly consists of a foamed thermoplastic material, in which a mixture of a foamable thermoplastic material and a foaming agent in a mixing and compressing device is brought to a temperature and pressure at which the mixture is liquid, after which the mixture is transferred via a discharge opening and a feed opening into a mould in which a lower pressure prevails and which has a cavity with a shape which, at least during moulding, conforms to that of the object to be manufactured, wherein the discharge opening and a feed opening of the mould, which openings are disposed in one plane, are brought into direct communication with each other and, at least after filling, the mould and the discharge opening are moved relative to each other in a direction parallel to said plane, the mould having a surface adjoining the feed opening, which surface, in the relative movement between the mould and the discharge opening, acts as a slide valve to shut off the discharge opening so that the flow of material therethrough is cut off, and the mould being followed in said relative movement by a further member which has a surface that acts as a slide valve to shut off the discharge opening, which member is contiguous with the mould.

With the method in accordance with the invention the pressure in the feed opening of the mould now remains so high that virtually no foaming agent can escape. This is the result of the mould and the member contiguous therewith acting as slide valves to cut off the flow of material through the discharge opening.

Steps which are necessary in the known method for clearing the feed conduit and preventing the formation of a sprue may be dispensed with when the method in accordance with the invention is used. The method in accordance with the invention enables objects to be moulded very rapidly, because post-compression is no longer necessary. The objects have a highly satisfactory shape owing to the fact that the foaming agent in the mould provides the necessary expansion to ensure that the mould cavity remains correctly filled during cooling.

The method in accordance with the invention is very suitable for filling a continuous succession of moulds one after the other. For this purpose the further member may be constituted by a further mould having a feed opening for communication with the discharge opening and having a surface which acts as a slide valve to shut off the discharge opening.

A plurality of said moulds can readily be moved past the discharge opening in a continuous succession, so that a continuous production of moulded objects is obtained.

The feed opening of the mould or each mould is constituted by an open side of the moulds the discharge opening being surrounded by a plate which is thermally insulated therefrom and which, in the relative movement between the mould or moulds and the discharge opening, acts as a slide valve to shut off the feed opening of the mould or each mould in succession.

In this way a wide feed opening is obtained so that even with comparatively rapid relative movement between the mould and the discharge opening the mouid cavity remains long enough in communication with this opening to ensure proper filling.

The plate which surrounds the discharge opening then serves as a closure for the feed opening after the mould has passed the discharge opening.

This plate mav be cooled, so that in a comparatively simple manner the heat can be removed from the mould.

Under certain conditions it may be desirable. in order to ensure a prolonged communication between the discharge opening and the mould cavity to give the discharge opening an elongate shape in the direction of movement of the moulds so that a preceding and a following mould are partly filled simultaneously.

When objects are to be manufactured of high-viscosity thermoplastic materials and in particular when the objects moreover have an intricate shape with many corners and narrow ducts, filling the mould cavity may present problems.

These problems occur in particular when the mould cavity contains inserts to be encapsulated, which inserts are likely to be dislodged or displaced as a result of the high flow rates in the narrow ducts.

In order to mitigate these problems the or each mould may have one or more movable walls which, after an amount of material has been injected into the mould cavity, is or are positioned in conformity with the desired shape and size of the object to be moulded.

Initially the movable wall .or walls can be positioned to increase the volume of the mould cavity so that the plastic can readily be injected into the mould cavity. The movable mould wall or walls can subsequently be moved to the correct position for the desired shaped and size of the object to be moulded, the expanding foaming agent then ensuring a correct filling of the mould cavity and thus a smoothsurfaced object.

The method in accordance with the invention is very suitable for encapsulating electrical or electronic components. As this is nearly always carried out in very large quantities, the fact that with the present invention encapsulation is possible in a continuous process is of considerably significance.

The invention further provides an apparatus for carrying out the method in accordance with the invention, the apparatus comprising a mould, a mixing and compressing device for mixing a foamable thermoplastic material and a foaming agent and bringing the mixture to a temperature and pressure at which it is liquid, which mixing and compressing device can communicate with a feed opening of the mould via a discharge opening, the openings being disposed in one plane, transport means for moving the mould and a further member which is contiguous with the mould past the discharge opening in such a manner that first the feed opening communicates with the discharge opening and then a surface of the mould in which the feed opening is formed and a surface of said further member act as slide valves to shut off the discharge opening, the latter opening being surrounded by a plate which, after passage of the feed opening past the discharge opening, acts as a slide valve to close the feed opening.

In one embodiment of the apparatus in accordance with the invention the further member is constituted by a further mould having a feed opening for communication with the discharge opening and having a surface which is arranged to act as a slide valve to shut off the discharge opening.

A further embodiment of the apparatus in accordance with the invention comprises an endless guide along which a plurality of moulds can be moved past the discharge opening in a continuous succession by the transport means, the plate which surrounds the discharge opening extending along said guide from one sid of the discharge opening to the opposite side thereof.

In a further embodiment of the apparatus the discharge opening has an elongate shape in the direction of movement of the mould or moulds. Thus, the period in which the mould cavity communicates with the discharge opening is prolonged.

The plate which surrounds the discharge opening may be adapted to be cooled.

In a further embodiment of the apparatus in accordance with the invention. each mould has a movable wall for varying the volume of the mould cavity and the guide comprises means for moving the movable walls of the moulds.

Examples of the method and apparatus according to the invention will now be described in more detail with reference to the accompanying drawings, in which Figures 1, 2 and 3 are diagrammatic partsectional side elevations of three embodiments of an injection-moulding apparatus for carrying out the method according to the invention, Figure 4 is a diagrammatic plan view of the embodiment shown in Figure 3, Figure 5 is a diagrammatic part-sectional elevation of an embodiment similar to that of Figure 2 but comprising moulds with movable walls, Figure 6 is a plan view of one of the moulds of the embodiment of Figure 5.

Figure 7 is a sectional view of an embodiment of an injection-moulding apparatus according to the invention which is very suitable for encapsulating electrical or electronic components, Figure 8, 9 and 10 are perspective views of parts of the apparatus shown in Figure 7, Figure 11 is a view of three of the moulds of the apparatus shown in Figure 7, and Figure 12 is a diagram illustrating the various stages in the movement of the moulds.

In Fig. 1, the reference numeral I denotes a mixing and compressing device for plastics. The construction thereof will not be discussed in more detail because it may be of conventional type. The device 1 has a discharge opening 2 which is surrounded by a cooling plate 3 which is thermally insulated therefrom. Underneath the discharge opening Z and the cooling plate 3 a guideway 4 is located, along which moulds 5 can be moved. The moulds 5 have a height such. that their top surfaces engage the cooling plate 3 and the discharge opening 2 respectively. If necessary the cooling plate 3 can be lightly urged resiliently towards the guideway 4 or vice versa.

Each of the moulds 5 has a mould cavity 7 and a feed opening 8. In the mixing and compressing device 1 a thermoplastic material, such as polypropylene, nylon or polyphenylenesulphide, mixed with a foaming agent, is brought to a temperature and pressure at which this mixture is liquid.

A known foaming agent such as azodicarbonamide may be used. It is also possible to introduce a pressurized gas into the liquid plastic.

Underneath the discharge opening 2, which is continuously open, a mould 5 is slid so that at a given instant the feed opening 8 comes beneath the discharge opening 2 and a quantity of thermoplastic material is forced into the mould cavity 7. The mould may move continuously or may be stopped briefly if desired. As the mould 5 advances, the discharge opening 2 is shut off by the top of the mould 5, acting as a slide valve, to interrupt the flow of plastic. The plastic remains pressurized and at a high temperature in the device I until the feed opening of the next mould 5 is beneath the discharge opening. The filled mould is now advanced along the guideway, the plate 3 closing the feed opening 8 and further cooling the mould through contact with said mould. During cooling the thermoplastic material in the mould will shrink, but this is substantially completely compensated for by the expansion of the foaming agent, so that the mould cavity always remains correctly filled and an object of smooth shape and correct size is obtained. If desired, an insert to be encapsulated with plastic, for example an electrical component, may be inserted in each of the mould cavities. The moulds can be moved along the guideway 5 either continuously or intermittently, the feed opening of a mould each time allowing the plastic to flow into the mould cavity from the discharge opening for a given period. Because a foaming agent has been added to the plastic, the plastic in the mould need not be "postcompressed" until the plastic has set. This means that a fast cycle time is obtained.

When there is no feed opening beneath the discharge opening, the latter opening is always closed by the top of a mould. If desired, members which move along with the moulds and which top surfaces disposed in the same plane as the top surfaces of the moulds may be interposed between the moulds, so that these members can also shut off the discharge opening 2.

In the moulds shown in Fig. 1 the feed opening 8 is formed by a duct in the top wall of the mould, and the plastic left in this duct forms a sprue on the moulded product. If such a sprue is undesirable, moulds of the construction shown in Fig. 2 may be used. In these moulds the top wall has been dispensed with completely, so that in this case the feed opening is constituted by the fully open top of the mould. This has the advantages that the product will no longer exhibit a sprue and that the discharge opening 2 communicates with the mould cavity during substantially the entire period that the mould is passing underneath the discharge opening. Thus, a correct filling is now also ensured while the moulds are rapidly advanced.

With an open-topped mould the upper side of the moulded object slides along the underside of the cooling plate 3. It has been found that this side of the object nevertheless has a very satisfactory appearance and that owing to the foaming action the mould cavity always remains correctly filled, also during cooling, and shrinkage is hardly perceptible. Moreover, the product now will not exhibit a sprue.

In order to prolong the communication between the discharge opening 2 and mould cavity 7 the discharge opening may have an elongate shape in the direction of movement of the moulds, as is schematically shown in Figs. 3 and 4. In this case the elongate discharge opening 12 has a length such that filling of a mould commences during filling of the preceding mould. This means that the discharge opening communicates with the mould cavity for an even longer time, so that a very satisfactory filling is ensured and the moulds can be moved at a higher speed, so that the production rate increases.

In the case of products with intricate shapes and with narrow passages, filling the mould cavity may present problems.

Problems may also arise when the mould cavity contains an insert which is likely to be dislodged or displaced by the high flow rate of the plastic. In order to circumvent these problems the moulds may be equipped with movable wall portions. This is schematically shown in Figs. 5 and 6. In this embodiment each of the moulds is provided with two fixed walls 15 and 16 and two movable walls 17 and 18. Such a mould is first positioned underneath the discharge opening 2, where it is partly filled with foamed plastic, the walls 17 and 18 occupying a slidout position as shown in full lines in Fig. 6.

Filling of the mould cavity is now easy because sufficient room is available for the plastic. After the mould has passed the discharge opening, the walls 17 and 18 are slid inwards to the correct position corresponding to the desired shaped and size of the object to be moulded. as is indicated by the broken lines. After this, the plastic is allowed to cool and set, the expanding foaming agent again ensuring that the mould cavity is and remains correctly filled.

Figs. 7 to 12 schematically shown an apparatus for encapsulating electrical or electronic components with a foamed thermoplastic material, the compressing and mixing device being omitted. This apparatus comprises a stationary section 20 (also see Fig. 8) in which are formed a bore 21 for the discharge opening of the mixing and compressing device, as well as openings 22 and 23 for the supply and drainage of cooling water. Furthermore, recesses 24 are formed in the stationary section 20 for the attachment of yokes 25 which carry outer and inner continuous guideways 26 and 27 (see Fig. 9) which comprise cam surfaces and which together form an endless guide for the moulds of the apparatus.

To the stationary section 20 an annular cooling plate 28 consisting of a plurality of parts (see Fig. 10) is secured in such a way that openings 29, 30 and 31 therein cooperate with the openings 21, 22 and 23 in the section 20.

A shaft 34 which carries a plate 35 is journalled in the stationary section 20. This plate 35 carries an inner ring of substantially radially extending fixed mould walls 36 (Fig.

11), between which radially movable mould walls 37 are slidably interposed. On their sides which face the axis of the shaft 34 the movable mould walls 37 each carry a roller 38 which runs on the cam surface of the inner guideway 27 (see Fig. 11).

The plate 35 furthermore carries a ring of arms 40, which are pivotably connected to the plate 35 by pins 41. Each of the arms 40 carries two mould walls 42 which, in the position of the arm 40 shown at the top of the drawing in Fig. 7. extend substantially radially of the plate 35, and between which a radially movable mould wall 43 is slidably interposed, which wall is provided with a roller 44 which runs on the cam surface of the outer guideway 26. Each movable wall 43 faces one of the inner movable walls 37 and together with this wall and the associated fixed walls 36 and 42 forms a mould having a mould cavity 50.

Each of the arms 49 furthermore comprises a cam follower 45 which is adapted to co-operate with a cam track in the form of a groove 46 so as to swing out the arm, as shown in Fig. 7, to open the respective mould.

In a collar 51 on the plate 35 recesses are formed which accommodate the lead-out wires 52 of electrical or electronic components 53 to be encapsulated which are disposed one in the cavity 50 of each mould.

The operation of the present apparatus is as follows: By a drive means coupled thereto the shaft 34 is rotated at a certain speed which depends on the products to be moulded, so that all parts connected to said shaft are also moved. As the moulds run between the guideways 26 and 27 the movable mould walls 43 and 37 will perform a specific cycle of movements. Starting from position where the discharge opening 29 of the mixing and compressing device (not shown) is located. the cycle is as indicated in Fig. 12.

During stage I the cavity 50 of one of the moulds communicates with the discharge opening 29 and is filled with an amount of plastic. The movable mould walls 37 and 43 bounding that cavity are then in slid-out positions, so that the mould cavity is larger than the product to be moulded. The plastic can now readily flow into the mould cavity without experiencing significant resistance.

The result is a correct filling of the mould cavity and when, as in the present case, and insert to be encapsulated is contained in the mould cavity, this insert will not be displaced by the stream of plastic.

In stage II the mould walls 37 and 43 are pushed towards each other by the cam surfaces of the guideways 26 and 27. so that the mould cavity 50 is now given the desired shape and size of the object to be moulded.

During stage III the plastic in the mould cavity is cooled by contact with the cooling plate 28, which is cooled by a stream of cooling water which is passed through it.

Shrinkage as a result of cooling is then compensated for by the expansion of the foaming agent so that the mould cavity always remains completely filled and objects of smooth appearance are obtained.

At the beginning of stage IV the cam follower 45 on the arm 40 which carries the relevant outer mould wall 43 engages in the cam track 46, which causes the arm 40 to pivot about the pin 41 so that the mould is opened, as shown at the bottom of the drawing in Fig. 7.

The moulded product can now be removed from the mould in stage V, the arm 40 being retained in the swing-out position throughout this stage.

Finally, in stage VI the mould is closed again, after which a new cycle can start. It will be evident from the foregoing that by means of this machine thermoplastic products can be moulded in a continuous manner. The production rate can then by very high. The products will be of smooth appearance and exact dimensions due to the use of a foamed plastic and to the corrent filling of the mould cavity.

A major advantage also is that during encapsulation of components the plastic injected into the mould cavity has ample opportunity to flow around the component, so that components are not displaced.

No intricate valve need be mounted in the discharge opening of the compressing device, because the mould walls themselves act as a slide valve to shut off the discharge opening and interrupt the flow of plastic until the next mould arrives. As one side of each mould is open and constitutes the feed opening of the mould, and also subsequently slides along the cooling plate, the formation of sprues on the product is completely avoided and furthermore a very good heat transfer to the cooling plate is achieved.

WHAT WE CLAIM IS: 1. Method of manufacturing an object which completely or partly consists of a foamed thermoplastic material, in which a mixture of a foamable thermoplastic material and a foaming agent in a mixing and compressing device is brought to a temperature and pressure at which the mixture is liquid, after which the mixture is transferred via a discharge opening and a feed opening into a mould in which a lower pressure prevails and which has a cavity with a shape which, at least during moulding, conforms to that of the object to be manufactured, wherein the discharge opening and a feed opening of the mould, which openings are disposed in one plane.

are brought into direct communication with each other and, at least after filling, the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sides which face the axis of the shaft 34 the movable mould walls 37 each carry a roller 38 which runs on the cam surface of the inner guideway 27 (see Fig. 11). The plate 35 furthermore carries a ring of arms 40, which are pivotably connected to the plate 35 by pins 41. Each of the arms 40 carries two mould walls 42 which, in the position of the arm 40 shown at the top of the drawing in Fig. 7. extend substantially radially of the plate 35, and between which a radially movable mould wall 43 is slidably interposed, which wall is provided with a roller 44 which runs on the cam surface of the outer guideway 26. Each movable wall 43 faces one of the inner movable walls 37 and together with this wall and the associated fixed walls 36 and 42 forms a mould having a mould cavity 50. Each of the arms 49 furthermore comprises a cam follower 45 which is adapted to co-operate with a cam track in the form of a groove 46 so as to swing out the arm, as shown in Fig. 7, to open the respective mould. In a collar 51 on the plate 35 recesses are formed which accommodate the lead-out wires 52 of electrical or electronic components 53 to be encapsulated which are disposed one in the cavity 50 of each mould. The operation of the present apparatus is as follows: By a drive means coupled thereto the shaft 34 is rotated at a certain speed which depends on the products to be moulded, so that all parts connected to said shaft are also moved. As the moulds run between the guideways 26 and 27 the movable mould walls 43 and 37 will perform a specific cycle of movements. Starting from position where the discharge opening 29 of the mixing and compressing device (not shown) is located. the cycle is as indicated in Fig. 12. During stage I the cavity 50 of one of the moulds communicates with the discharge opening 29 and is filled with an amount of plastic. The movable mould walls 37 and 43 bounding that cavity are then in slid-out positions, so that the mould cavity is larger than the product to be moulded. The plastic can now readily flow into the mould cavity without experiencing significant resistance. The result is a correct filling of the mould cavity and when, as in the present case, and insert to be encapsulated is contained in the mould cavity, this insert will not be displaced by the stream of plastic. In stage II the mould walls 37 and 43 are pushed towards each other by the cam surfaces of the guideways 26 and 27. so that the mould cavity 50 is now given the desired shape and size of the object to be moulded. During stage III the plastic in the mould cavity is cooled by contact with the cooling plate 28, which is cooled by a stream of cooling water which is passed through it. Shrinkage as a result of cooling is then compensated for by the expansion of the foaming agent so that the mould cavity always remains completely filled and objects of smooth appearance are obtained. At the beginning of stage IV the cam follower 45 on the arm 40 which carries the relevant outer mould wall 43 engages in the cam track 46, which causes the arm 40 to pivot about the pin 41 so that the mould is opened, as shown at the bottom of the drawing in Fig. 7. The moulded product can now be removed from the mould in stage V, the arm 40 being retained in the swing-out position throughout this stage. Finally, in stage VI the mould is closed again, after which a new cycle can start. It will be evident from the foregoing that by means of this machine thermoplastic products can be moulded in a continuous manner. The production rate can then by very high. The products will be of smooth appearance and exact dimensions due to the use of a foamed plastic and to the corrent filling of the mould cavity. A major advantage also is that during encapsulation of components the plastic injected into the mould cavity has ample opportunity to flow around the component, so that components are not displaced. No intricate valve need be mounted in the discharge opening of the compressing device, because the mould walls themselves act as a slide valve to shut off the discharge opening and interrupt the flow of plastic until the next mould arrives. As one side of each mould is open and constitutes the feed opening of the mould, and also subsequently slides along the cooling plate, the formation of sprues on the product is completely avoided and furthermore a very good heat transfer to the cooling plate is achieved. WHAT WE CLAIM IS:

1. Method of manufacturing an object which completely or partly consists of a foamed thermoplastic material, in which a mixture of a foamable thermoplastic material and a foaming agent in a mixing and compressing device is brought to a temperature and pressure at which the mixture is liquid, after which the mixture is transferred via a discharge opening and a feed opening into a mould in which a lower pressure prevails and which has a cavity with a shape which, at least during moulding, conforms to that of the object to be manufactured, wherein the discharge opening and a feed opening of the mould, which openings are disposed in one plane.

mould and the discharge openings are moved relative to each other in a direction parallel to said plane, the mould having a surface adjoining the feed opening which surface, in the relative movement between the mould and the discharge opening, acts as a slide valve to shut off the discharge opening so that the flow of material therethrough is cut off, and the mould being followed in said relative movement by a further member which has a surface that acts as a slide valve to shut off the discharge opening, which member is contiguous with the mould.

2. A method as claimed in Claim 1, wherein the further member is constituted by a further mould having a feed opening for communication with the discharge opening, and having a surface which acts as a slide valve to shut off the discharge opening.

3. A method as claimed in Claim 2, wherein a plurality of said moulds is moved past the discharge opening in a continuous succession.

4. A method as claimed in Claim 1, 2 or 3, wherein the feed opening of the mould as each mould is constituted by an open side of the mould, the discharge opening being surrounded by a plate which is thermally insulated therefrom and which, in the relative movement between the mould or moulds and the discharge opening, acts as a slide valve to shut off the feed opening of the mould or each mould in succession.

5. A method as claimed in Claim 4, wherein said plate is cooled.

6. A method as claimed in any of the preceding Claims, wherein the or each mould has one or more movable walls which, after an amount of material has been injected into the mould cavity, is or are positioned in conformity with the desired shape and size of the object to be moulded.

7. A method as claimed in any of the preceding Claims, wherein an electrical or electronic component is inserted in the cavity or the or each mould and is encapsulated therein with a foamed thermoplastic material.

8. An obJect manufactured by the method claimed in any of the preceding Claims.

9. Apparatus for carrying out the method claimed in Claim 1, comprising a mould, a mixing and compressing device for mixing a foamable thermoplastic material and a foaming agent and bringing the mixture to a temperature and pressure at which it is liquid, which mixing and compressing device can communicate with a feed opening of a mould via a discharge opening, the openings being disposed in one plane, transport means for moving the mould and a further member which is contiguous with the mould past the discharge opening in such a manner that first the feed opening communicates with the discharge opening and then a surface of the mould in which the feed opening is formed and a surface of said further member act as slide valves to shut off the discharge opening, the latter opening being surrounded by a plate which, after passage of the feed opening past the discharge opening, acts as a slide valve to close the feed opening.

10. Apparatus as claimed in Claim 9 for carrying out the method claimed in Claim 2, wherein the further member is constitued by a further mould having a feed opening for communication with the discharge opening and having a surface which is arranged to act as a slide valve to shut off the discharge opening.

11. Apparatus as claimed in Claim 10 for carrying out the method claimed in Claim 3, comprising an endless guide along which a plurality of moulds can be moved past the discharge opening in a continuous succession by the transport means, the plate which surrounds the discharge opening extending along said guide from one side of the discharge -opening to the opposite side thereof.

12. Apparatus as claimed in Claim 9 or 10, wherein the discharge opening has an elongate shape in the direction of movement of the mould or moulds.

13. Apparatus as claimed in Claim 9, 10 or 11 for carrying out the method claimed in Claim 5, wherein the plate which surrounds the discharge opening is adapted to be cooled.

14. Apparatus as claimed in Claim 11 or Claim 13 when read as appendant to Claim 11, for carrying out the method claimed in Claim 6, wherein each mould has a movable wall for varying the volume of the mould cavity and the guide comprises means for moving the movable walls of the moulds.

15. Apparatus as claimed in Claims 11, 13 and 14, wherein the cooling plate is annular and is disposed between inner and outer continuous guideways which form said guide and which comprise cam surfaces, the cooling plate and the guideways being carried by a stationary section of the apparatus in which is journalled a shaft carrying a plate on which is mounted a ring of first fixed mould walls which extend substantially radially with respect to the shaft and between which are interposed first movable mould walls having cam followers which cooperate with the cam surface of the inner guideway to move said first movable mould walls radially with respect to the shaft relative to first fixed mould walls, the plate on the shaft also carrying a ring of pivotable arms which each carry two second fixed mould walls which in a closed position of the associated arm extend substantially radially with respect to the shaft and between which is interposed a second movable mould wall having a cam follower which in said closed position of the associated arm cooperates with the cam surface of the outer guideway to move said second movable mould wall radially with respect to the shaft relative to the two associated second fixed mould walls, each second movable mould wall. in said closed position of the associated arm, facing a corresponding one of the first movable mould walls and forming therewith and with the two associated second fixed mould walls and the two first fixed mould walls adjacent said one first movable mould wall a mould having a mould cavity of variable volume, and each of said arms being provided with a cam follower which cooperates with a cam track for swinging-out the relevant arm to open the associated mould.

16. A method of manufacturing objects which completely or partly consist of a foamed thermoplastic material, the method being substantially as herein described with reference to Fig. 1 or Fig. 2 or Figs. 3 and 4 or Figs. 5 and 6 or Figs. 7 to 12 of the accompanying drawings.

17. Objects manufactured by the methods claimed in Claim 16.

18. Apparatus for carrying out the method claimed in Claim 16, the apparatus being substantially as herein described with reference to Fig. I or Fig. 2 or Figs 3 and 4 or Figs. 5 and 6 or Figs. 7 to 12 of the accompanying drawings.