GB2106094A

GB2106094A - Moulding of glassware

Info

Publication number: GB2106094A
Application number: GB08122805A
Authority: GB
Inventors: Sidney Maurice Budd
Original assignee: United Glass Ltd
Current assignee: OI Glass Ltd
Priority date: 1981-07-23
Filing date: 1981-07-23
Publication date: 1983-04-07

Abstract

Glassware is moulded in moulds formed from or lined with porous material and saturated with water during the moulding operation. The porous material is suitably sintered metal, e.g. sintered steel, brass or bronze, having a plurality of interconnecting pores. Alternatively the porous material may be carbon fibre-reinforced carbon.

Description

SPECIFICATION Moulding of glassware The present invention relates to a method for the moulding of glassware, and to glassware moulds.

There are basically two processes for manufacture of glassware, such as bottles and tableware. The first and most common involves a two-stage manufacturing process, and for this purpose two sets of moulds are required. One set, usually referred to as the blank mould, is used in the first stage of moulding, that is converting a gob of molten glass into a moulded form known as a parison or pre-form. The other set, the blow mould, converts the parison during the second stage into the final moulded article. The second process of manufacturing glassware involves a single stage process, e.g. a pressing technique, and in this case a press mould and plunger are used.

In order to fashion molten glass its initial temperature generally needs to be well in excess of 1 000 C, and, equally, in order that the finished glassware should not deform on completion of the moulding operation when it is removed from the mould, its temperature should be not greater than 600"C. It is clear, therefore, that during the moulding process a considerable amount of heat must be extracted from the glass, and in order to maintain rapid and extended production it is necessary that this heat be continuously removed from the mould. For this reason the moulds used are usually of metal, e.g. cast iron, so that the heat can be conducted rapidly into the metal and removed by blowing cooling air onto the mould during that part of the cycle when it is not in contact with glass.The mould material, as well as being conductive to heat, needs to have reasonable strength, since the stresses imposed upon the mould during continuous operation are considerable, and premature breakage of the mould could occur if a relatively weak material were used. A major disadvantage however in using metal moulds is that the material is hard, and can damage the finished glass surface by contact with the glass, particularly if thermal stresses are simultaneously set up in the glass.

In the case of tableware contact of glass with a metal mould also produces a mottled surface effect which is unacceptable for quality ware. This has been overcome by operating the final blow moulding in what is known as a paste mould, while simultaneously rotating the ware. The paste mould consists of a cast iron mould treated with a carbonaceous resinous mix which is subsequently fired in to give a porous graphitic lining. This mould is maintained saturated with water, and under these circumstances a satisfactory finish to the glass can be produced. However, the pasting process has a disadvantage in that after a few hours continuous production the paste starts to wear off and a poor quality surface finish to the glass is obtained.

We have found that the rate of heat transfer from hot glass at a porous material interface, where the material is saturated with water (i.e.

the amount 'of water applied to the surface prior to contact with the glass is sufficient to displace all the air contained in the material by virtue of its porosity, and provide a wet surface), substantially exceeds the heat transfer both at a solid dry interface and at a solid wet interface, and according to the present invention there is provided a method of moulding glassware wherein the moulds are formed from porous material and are saturated with water during the moulding operation.

The present invention also provides a mould for making glassware, said mould being formed from porous material.

Such method and apparatus are applicable to both methods of manufacturing glassware mentioned above (e.g. the blank and blow moulds of the press mould and plunger may be of porous material) and produce glassware of much enhanced strength and improved appearance.

Moulds in accordance with this invention may be formed from a number of materials.

Sintered metals, for example, can be used, and in this connection sintered steels, brass and bronzes are all suitable, provided that they have pores which are inter-connecting.

Other materials include carbon fibre-reinforced carbons, which are prepared by impregnating carbon fibre cloth or felt with a carbonaceous material and subsequently igniting the material to convert it into carbon. Further treatment by way of chemical vapour-deposition of carbon and high temperature treatment.to graphitise the carbon is preferred since this will result in an increased porosity as well as a substantial increase in thermal conductivity.

By suitable choice of the grade of carbon fibre cloth the finished product may possess a substantial strength, enabling it to be used confidently for glass manufacture. Carbon fibre-reinforced carbon is generally more preferable than sintered metal since it is not damaging to the glass surface after it has been formed.

The invention also relates to a mould for glassware wherein said mould is lined with carbon fibre-reinforced carbon or with sintered metal, instead of with the conventional paste previously used to line moulds. This provides a satisfactory product which has a life of several weeks compared to a few hours with conventional paste.

It has also been found that a carbon fibrereinforced carbon or sintered metal mould lining, and a plunger made of similar material, may with advantage be used for the manufac ture of pressed ware where both plunger and mould are sprayed with water between each pressing cycle. In this case the quality of the glass surface is substantially improved upon glass ware produced using normal cast iron or steel mould parts.

Claims

1. A method of moulding glassware wherein the mould is formed from or lined with porous material and is saturated with water during the moulding operation.

2. A method according to claim 1, wherein said porous material is sintered metal having a plurality of inter-connecting pores.

3. A method according to claim 2, wherein said sintered metal is sintered steel, brass or bronze.

4. A method according to claim 1, wherein said porous material is carbon fibrereinforced carbon.

5. A method according to claim 4, wherein said carbon fibre-reinforced carbon is prepared by impregnating carbon fibre cloth or felt with a carbonaceous material and subsequently igniting the material to convert it into carbon.

6. A method according to claim 5 wherein said carbon is graphitised by way of chemical vapour-deposition and high temperature treatment.

7. A mould for glassware, wherein said mould is formed from or lined with porous material.

8. A mould according to claim 7, wherein said porous material is sintered metal having a plurality of inter-connecting pores.

9. A mould according to claim 8, wherein said sintered metal is sintered steel, brass or bronze.

10. A mould according to claim 7, wherein said porous material is carbon fibrereinforced carbon.

11. A mould according to claim 10, wherein said carbon fibre-reinforced carbon has been formed by impregnating carbon fibre cloth or felt with a carbonaceous material subsequently igniting the material to convert it into carbon.

12. A mould according to claim 11, wherein said carbon has been graphitised by way of chemical vapour-deposition and high temperature treatment.

13. A method of moulding glassware, substantially as herinbefore described.

14. A mould for glassware substantially as hereinbefore described.