GB2362156A

GB2362156A - Mould or plunger with a composite structure

Info

Publication number: GB2362156A
Application number: GB0110979A
Authority: GB
Inventors: Lars Christian Herzbach; Christian Schenk; Steffen Thiel
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 2000-05-06
Filing date: 2001-05-04
Publication date: 2001-11-14
Also published as: DE10022114A1; GB0110979D0

Abstract

A mould (1) or plunger used to shape glass or plastics has a composite structure being composed of materials (2,3,4) having different thermal properties. A mould may comprise a base material and at least one heat insulating layer and at least one heat conducting layer, the latter being boron nitride, aluminium nitride and/or graphite.

Description

2362156 Tool for Hot Forming Glass or Plastics The invention relates to a

tool for the hot-shaping of glass or plastics having locally varying thermal behaviour for the purpose of optimising the heat balance during the shaping.

In the hot-shaping of glass parts from a glass gob introduced into a mould, local heat extraction occurs during the production process between the part to be formed and the tool, such as moulds, plungers and rolls.

If for example a glass gob is introduced into a pressing mould with a flat bottom, the glass gob, because of its typical viscosity, does not run evenly over the bottom of the pressing mould but forms a hemispherical accumulation at the centre with the result that a high heat input into the mould occurs at this place and the glass part cools down intensely at this place, whereas the free area of the glass remains relatively hot.

This uneven heat extraction may have an adverse effect on the properties of the glass part, in that schlieren (striae) and/or geometrical surface defects may develop in the glass part. In addition, in the case of pressing tools, the ejection behaviour may be unfavourably influenced. In order to achieve the required properties of the glass part, measures are taken to optimise the heat balance of the tools. According to the prior art, the tools are adapted in a locally varying manner with the aid of design measures for this purpose. For example, cooling bores are provided at the places where the heat of the glass part has to be extracted, whereas other tool regions at which the heat has to be retained are thermally insulated. The different thermal behaviour may also be achieved by different wall thicknesses in the tool and/or by shaped elements which are partially attached to or inserted in the tool and have a different conductivity than that of the tool material. As a result of these design measures on the forming tools, the heat balance required for the particular product is adjusted in a controlled manner.

Such design measures are described, for example, with regard to the provision of cooling bores, in the information publication Informationsschrift 50, "Glas und Glasprodukte" [Glass and glass products] by A.W. Frbhler, published by J. Moers, 1996, pages 212-214 and, with regard to different wall thicknesses and material attachments or inserts, in EP 0 546 236 A2, in the abstract of JP 08165 125 A, and in the abstract of JP 01-143 738 A.

The adjustment of the local heat balance of the tools by the known design modifications on the tool requires elaborate design measures and is costly in terms of adaptation. Moreover, to make matters worse, the number of materials available as contact materials for the hot-shaping of glass is limited owing to the special requirements such as wear resistance, corrosion resistance, antiadhesion properties and high operating temperatures. Furthermore, in the case of the attachments or inserts of materials of different conductivity in the tool, the heat transfer is not optimal, since the attachments or inserts lie against the tool merely in a form-fitting manner and the customary roughness of the surfaces prevents an intimate contact.

In the hot-shaping of plastics, for example in injection moulding, the circumstances are similar. What is particularly important here is the good demouldability and short cycle times.

The object on which the invention is based is to design the tool, referred to at the outset, for the hot-shaping of glass or plastics having locally varying thermal behaviour for the purpose of optimising the heat balance during the shaping, in such a way that the elaborate adaptation of the design of the tool for the purpose of achieving the heat balance can be dispensed with or this adaptation can be amended for the purpose of optimisation, and that there is no restriction of the heat transfer.

This object is successfully achieved according to the invention, starting from the tool referred to at the outset, in that the tool consists of a composite material structure composed' of materials having different thermal properties at predetermined material thicknesses.

In the case of the tool according to the invention, therefore, the heat balance is optimised by materially bonded composite material structures. The heat balance is achieved in this case by the local thermal properties of the tool, preset by appropriate materials.at predetermined thicknesses, and no longer exclusively by elaborate design modifications. The materially bonded composite material structure leads to an atomic bonding of the individual materials, so that the heat transfer at the interface is optimal. Similarly, the mechanical properties, in particular the strength, are also optimal.

In the hot-shaping of plastics, the extraction of heat can be adjusted locally, with the result that the demouldability of the plastics part is improved. Furthermore, a higher heat flow can be achieved, with the result that lower cycle times are attainable.

According to a development of the invention, the composite material structure of the hot-shaping tool is constructed in a way that there are applied, in a materially bonded fashion, to a tool base body made of a base material, at predetermined locations of the base body, material layers having different thermal properties, which adjust the heat extraction from the glass melt or plastics melt in a process-specific manner. This design allows uncritical, simple local presetting of the thermal properties. In this case, it is advantageous if the material layers are formed by at least one heat-insulating layer and/or at least one heat-conducting layer. This design assists the local presetting of the thermal properties.

In order to produce the composite material structure, various appropriate measures are available to a person skilled in the art. According to a first development of the invention, the composite material structure of the materials having different thermal properties is constructed by the method of hot isostatic pressing (HIP) in an enclosure, it being possible, in addition, to design the enclosure in a manner close to the final contour of the hot-shaping tool. This method of producing a composite material structure is advantageous whenever homogeneous, dense and firmly adhering tool composite material structures are required.

According to a second development, the composite material structure of the materials having different thermal properties is constructed in a way that there is partially applied, by thermal spraying, to a material layer having a first thermal property a second material layer having a second thermal property. This method is advantageous with relatively thin material layers (up to about 2 mm) and also as an inexpensive alternative to the HIP method.

According to a third development, the composite material structure of the materials having different thermal properties is constructed in a way that appropriate material elements are joined together by design measures such as screwed connections, soldering, welding and shrinkage. In this case, it is advantageous for the defined thermal behaviour if the elements of the composite material structure which are to be joined, with bridging of the voids between them, by heat-conducting layers, consist for example of h-BN (hexagonal boron nitride) or AIN graphite, or those which are to be joined, with bridging of the voids between them, by heat- insulating layers, consist for example of Quarzal, Si02.

The invention is explained in more detail with the aid of exemplary embodiments depicted in the drawings, in which:

Fig. I shows a diagrammatic longitudinal sectional representation of the principle of the construction of a hot-shaping tool in the form of a pressing tool having locally varying thermal behaviour for the purpose of optimising the heat balance during the shaping by means of a composite material structure composed of materials having different thermal properties using only a heat-insulating layer, Fig. 2 shows a diagrammatic longitudinal sectional representation of a hot-shaping tool, formed by a composite material structure, in the form of a pressing tool analogous to Fig. 1, having a layer of particularly high insulation and a layer of very good conduction, Fig. 3 shows a diagrammatic longitudinal sectional representation of the formation of the composite material structure for the pressing tool according to Fig. 1 by hot isostatic pressing, Fig. 4 shows a two-part diagrammatic longitudinal sectional representation of a symbolically represented hot-shaping tool consisting of two different materials, the one material being applied by thermal flame spraying to the other material to form a composite material structure, and being subsequently enclosed by flirther materials, and Fig. 5 shows a diagrammatic longitudinal sectional representation of a hot-shaping tool according to Fig. 1, in which the materials are brought together to form a composite material structure by design modifications, in this case a screwed connection.

Figure 1 shows a diagrammatic sectional representation of one example of a design of a hot-shaping tool 1 having locally varying thermal behaviour for the purpose of optimising the heat balance during the shaping by means of a composite material structure composed of materials having different thermal properties at predetermined material thicknesses. A pressing tool having a heatinsulating layer in the composite material structure has been chosen as an example.

Generally, it may be stated in this context that in principle any material, such as metal or ceramic, may be employed for the heat balance which is to be adjusted. Moreover, the materials having different thermal properties and layer thicknesses are varied, preferably by means of a mathematical simulation of the heat balance, for the specific case of a hot-forming tool, in such a way that the process-specific heat.balance of the tool required in the particular application is made available.

In this regard, for the specific application, materials are selected which are required, in respect of their thermal properties (thermal conductivity, thermal expansion, specific heat capacity), for the purpose of optimising the heat balance. Moreover, heat-insulating materials are disposed behind the actual contact material, which exhibits the properties required in glass contact, such as corrosion resistance, wear resistance and anti-adhesion properties, at the places to be thermally insulated. As a result, the heat extraction is minimised and the contact temperature between glass and forming material increased. Materials of particularly good thermal conductivity are disposed at those places where the heat has to be removed.

In the example according to Fig. 1, the hot-shaping tool 1 consists of a pressforming shell 2 made of a suitable base material. This base material is preferably a material for casting, GGG 40, with the material No. 0. 7040. Other materials, such as ST 52 with the number 1.0580, 1.4923, 1. 2787, may also be employed as the base material. Materially bonded to the base material of the pressing tool 2 is a heat-insulating layer 3 made of a material of poor thermal conductivity, for example an Si02 ceramic. Other materials of poor conductivity, such as A1201, Zr02 and Si3N4, may also be used. The composite material structure of the composite hotshaping tool 1 finally also has a glass contact material 4, which may be for example a Stellite 21 from the Finn Deloro Stellite in K6blenz. These contact materials differ according to whether glass or plastics is to undergo shaping. Since higher temperatures prevail in the case of glass shaping, high-temperature corrosion-resistant steels, for example those with the material numbers 1.4923 and 1.2787, and nickel- or cobalt- base alloys, for example Stellite, Inconel alloys and Nicrofer alloys, or coatings of, for example, nickel-tungsten or Cr203, are employed, depending on the application. In the case of plastic shaping, the lower temperatures mean that materials having smaller alloy contents, for example those with the material numbers 1.2311, 1.2767, 1.2343 and 1.273 8,. are sufficient.

The chemical composition of the aforementioned materials with the material numbers specified can be found in the relevant material databases, which are accessible to everyone.

The materials used in the basic example according to Fig. 1, i.e. Stellite 21, Si02 ceramic and GGG 40, have the following chemical composition and thermal conductivities:

Thermal conductivities:

Stellite 21 about 15 W/mK Si02 ceramic about I W/mK GGG 40 about 34 W/mK at 5001C Chemical composition:

Stellite 21: Cr: 27%; Mo: 5.5%; Ni: 2.5%; Si: 1%; Fe: 3%; Mn: 1%; C: 0. 25%; remainder: Co Si02: > than 99.8% GGG 40: C: 3.5-3.8%; Si: 2-3%; M11max 0.4%; P.,,, 0.1%; S.a,,: 0.01%; Mg: 0.06-0.12%; Fe: remainder Fig. 2 shows a diagrammatic sectional representation of another embodiment of the hot-forming tool 1, consisting, according to the invention, of a composite material structure, in the form of a pressing tool having a pressing mould 2 corresponding to Fig. 1, with an associated plunger 5 and a cover 6, which closes off the pressing mould at the top. The pressing mould contains a molten glass gob 7. During ejection, the glass 7 is pushed upwards against the cover 6.

The base material of the pressing mould 2 has two layers embedded in it. A heat-insulating layer 8 is provided in the lower part of the pressing mould, which is exposed directly to the heat of the glass gob 7, and which consists for example of an Si02 ceramic having a thermal conductivity of 1 WlinK. This heat-insulating layer 8 ensures that the heat extraction at the hot places of the shaping tool is reduced. In the upper part of the pressing mould 2 on the other hand, there is provided a heat-conducting layer 9, which may consist for example of nickel having a thermal conductivity of 80 W/mK or of a material with the number 1.2768 having a thermal conductivity of 25 W1m& This heatconducting layer 9 ensures the necessary heat extraction during ejection. The interior of the pressing mould consisting of a composite material structure having different thermally effective materials is lined with a layer 4 made of one of the above-described contact materials so as to give a composite material structure.

The multi-component hot-shaping tool consisting of a composite material structure, according to the invention, may be composed of the individual material components in different ways, various possibilities for the composite material structure being explained with the aid of the representations in Figs. 35.

Fig. 3 shows a diagrammatic sectional representation of the construction of the pressing mould 2 according to Fig. 1 from a composite material structure by means of hot isostatic pressing (HIP). This HIP process is known to those in the art and is described for example in the publication by B. Hofer, "Werkstoffverbund dank heil3isostafischem Pressen" [Composite material structure by virtue of hot isostatic pressing], Technische Rundschau., 52/1984. The materials to be joined may be present in this case in the following combinations: powder/powder, solid/powder and solid/solid. The required materials for the layers 2, 3, 4 are placed at the predetermined places in an enclosure 10 and firmly sintered to a compact form during the HIP process with the formation of a composite material structure. The HIP enclosure 10 is subsequently removed and the pressing tool 1 finished. Fig. 3 shows, as an example, a solid/solid composite structure with bars as the basic form, these being assembled to produce the product-specific form.

Fig. 4 shows a composite material structure for a tool for hot shaping, in which there is applied to a body 11 made of a first material a layer 12 made of a second material by the known method of "thermal spraying", indicated by the arrows, with the formation of a composite material structure. As a result, the part of the base body 11 covered by the layer 12 has a different thennal property than the remaining part. Thermal spraying can also be used therefore to apply the heat-optimising layers to the necessary places of the hot-shaping tool for the purpose of optimally adapting the heat balance. It is also possible to use thermal spraying to apply the contact layer 4 of Fig. 1 to the body I I Subsequently, the component is assembled (Fig. 4, right-hand part) according to specification, for example to form the tool according to Fig. 1.

Fig. 5 shows a diagrammatic sectional representation of a further possibility for producing a composite material structure between the material parts 2, 3 and 4 having different thermal properties for a hotshaping tool, the composite material structure being made available in this case by design modifications, such as, for example, by a screwed connection 13 as illustrated, or alternatively by soldering, welding, shrinkage or the like, and it being possible for the composite material structures to be joined by way of heat-conducting layers made of pasty or powdery starting material.

Claims

1. A tool for the hot-shaping of glass or plastics having locally varying thermal behaviour for the purpose of optimising the heat balance during the shaping, wherein the tool has a composite material structure composed of materials having different thermal properties at predetermined material thicknesses.

2. A tool according to Claim 1, wherein there are applied, in a materially bonded fashion, to a tool base body made of a base material, at predetermined locations of the base body, layers of materials having different thermal properties, which adjust the heat extraction from the glass melt or plastics melt in a process-specific manner.

3. A tool according to Claim 2, wherein the layers of material comprise at least one heat-insulating layer and at least one heat-conducting layer.

4. A tool according to any one of Claims 1 to 3, wherein the composite material structure of the materials having different thermal properties is one which has been formed by hot isostatic pressing in an enclosure.

5. A tool according to Claim 4, wherein the enclosure is designed in a manner close to the final contour of the hot-shaping tool.

6. A tool according to any one of Claims 1 to 3, wherein the composite material structure of the materials having different thermal properties is constructed in a way that there is partially applied, by thermal spraying, to a material layer having a first thermal property a second material layer (12) having a second thermal property.

7. A tool according to any one of Claims I to 3, wherein the composite material structure of the materials having different thermal properties is constructed in a way that elements of appropriate material are joined together by design measures such as screwed connections, soldering, welding and shrinkage.

8. A tool according to Claim 7, wherein the elements of the composite material structure are joined together by heat-conducting layers.

9. A tool according to Claim 8, wherein the heat-conducting layers consist of hexagonal boron nitride (h-BN) or AIN or/and graphite.

10. A tool substantially as hereinbefore described with reference to any of the accompanying drawings.