GB2039879A - Shaping glassware - Google Patents

Abstract

There is described a method of shaping hot glass in a mould wherein the hot glass is caused to contact a material comprising a metallic matrix containing from 4 to 14% by weight of a solid lubricant substantially uniformly dispersed therethrough. Suitable lubricants are graphite, boron nitride and molybdenum disulphide.

Description

SPECIFICATION Shaping glassware This invention relates to the shaping of glassware, and especially to the blowing of hollow glassware in glass-forming moulds.

Broadly speaking, the manufacture of hollow glassware involves the melting of glass batch in a furnace, the conditioning of the molten glass in a forehearth, the separating of the conditioned glass into individual gobs, the charging of these gobs into forming moulds and the forming of the glass in the moulds by pressing, blowing or a combination of these techniques. The gob of glass entering the forming mould must be at a sufficiently high temperature to be readily re4ormed, but at the same time the shaped article which is removed from the mould must be cool enough to be self-supporting.It is necessary, therefore, for the mould itself to extract a certain amount of heat from the glass being formed within it, and this heat-extraction is assisted generally by the blowing of air onto and around the outside of the mould, thus extracting heat from the outside of the mould. Other systems used for this purpose included water-cooling of the mould. The greater the rate at which the mould can extract heat from the blown glass, the sooner the mould can be used again, and hence the greater the number of times the mould can be used per unit of time. In other words, the greater the production.

Blown glassware, for example containers or tableware, is at present formed in moulds made of cast iron, stainless steel, chromium-plated cast iron, and certain alloys. A pre-requisite of a material for use as a mould material is that it should not adhere to hot glass when it is itself hot. Clearly, the blown glassware must be removed without surface imperfections. It is normal practice, when using moulds made from the above materials, to apply a graphite swab to each mould repeatedly during the use of the mould. This lubricates the glass-contacting surface of the mould and allows the formed glassware to be removed from the mould cleanly.

Another problem at present found in the glass tableware industry particularly arises when it is required to obtain products which have smooth external surfaces, i.e. they do not have lines corresponding to the mould split lines. It is normal when making this type of ware to rotate the glass within the mould as it is being blown. This requires the presence of an exceptionally friction-free mouldglass interface. The standard method of accomplishing this is to apply a thin layer of a special paste to the surface of the mould. The mould and paste are then baked and the paste becomes a hard porous layer. During the operating cycle water is applied to the moulds prior to the entry of the glass to be blown therein. The paste takes up a quantity of water and this is turned to steam by hot glass, the steam providing a thin vapour layer between the rotating glass and the mould paste surface.This provides an excellent friction-free arrangement, but since such paste moulds only have an active life of about twenty-four hours they must be frequently repasted.

It is an object of the present invention to provide a method of moulding glassware wherein a frictionfree lubricating interface is provided without recourse either to the use of the usual paste moulds or to the repeated swabbing of the mould surface with graphite, which latter technique additionally presents a hazard to the operator and is of course not uniformly effective due to the possibility of under- or -over swabbing.

It has hitherto been proposed to deal with this problem by providing the surface of the mould, made from conventional materials such as cast iron, with a thin surface coating of a material which includes a lubricant. In one known method an aqueous composition comprising aluminium phosphate and a particulate lubricating material is coated onto glass-forming mould components, e.g. by spraying. In another known method a powder is flame- or plasma-sprayed onto the mould surface to give an adherent layer thereon consisting of from 50 to 85% by weight of nickel, or of nickel and cobalt, and from 50 to 15% by weight of aluminium, graphite, finely divided silica or calcium fluoride.

Such techniques, however, have proved of little value, since in the first instance they show little or no improvement in terms of the speed at which they enable glassware to be produced, and secondly, and probably more importantly, the surface coatings or linings produced on the moulds wear away far too quickly for them to be of much commercial value in the high speed production of glassware. The present invention seeks to overcome the problems mentioned above in a manner which is much more commercially viable.

According to the present invention there is provided a method of shaping hot glass in a mould wherein the hot glass is caused to contact a material comprising a metallic matrix throughout which is substantially uniformly dispersed from 4to 14%, by weight, of a solid lubricant.

The glass-contacting material is preferably in the shape of a forming mould, or at least part thereof (e.g. the bottom-forming plate), and preferably the material is made up into the form of an insert for a standard mould formed, for example, of stainless steel or cast iron. The glass-contacting material preferably has a thickness of the order of 2 to 10mum., suitably 5 to 1 ohm.

The glass-contacting material is suitably made from a mixture of components in which the predominant component is iron, nickel or copper. The solid lubricant dispersed throughout the material is preferably graphite (most suitably colloidal graphite) but may be other lubricants, e.g. boron nitride, molybdenum sulphide. The lubricant makes up from 4to 14, preferably from 6to 10%, by weight, of the glass-contacting material, which may contain more than one solid lubricant.

In one composition for making the glasscontacting material of the present invention the basis of the matrix is iron powder to which 10% approximately by weight nickel and 4% approximately by weight copper in powdered form have been added to improve the thermal conductivity at elevated temperatures and the resistance of the material to scaling. To this component mixture is added a solid lubricant, such as graphite or boron nitride, which is homogeneously dispersed throughout the component mixture during processing of the mixture. Materials suitable for use as glasscontacting materials in accordance with the present invention are commercially available.

Particularly suitable glass-contacting materials are those containing, by weight, 70-80% iron, 7.5-10.5% nickel, 5-7% copper, 5-7% boron nitride and 2-4% molybdenum disulphide; and those containing by weight, 80-90% iron, 3-4% copper, 8-10% graphite and 2-3% molybdenum dissulphide. Specific examples include (i) a composition containing 75.5% iron, 9% nickel, 6.5% copper, 6.5% boron nitride and 2.5% molybdenum disulphide; and (ii) 84.5% iron, 3.6% copper, 9% graphite and 2.7% molybdenum disulphide.

A further series of materials suitable for use in the present invention are produced by powder metallurgy and comprise copper and/or nickel as the primary metal; a solid lubricant, such as graphite, boron nitride or molybdenum disulphide; and at least 0.5% by weight phosphorus, introduced as a phosphor -copper alloy or compound, the phosphorus content of the alloy or compound suitably being between 5 and 20% by weight.

The glass-contacting materials of the present invention preferably take the form of mould inserts, and the accompanying drawing is a diagrammatic cross-section through a glass-forming mould, showing the insert in place. In the drawing, two cooperating mould halves 1 and 2, their line of separation being indicated at 3, have a glass-contacting surface the major part of which is formed by two-semicylindrical inserts 4 and 5 retained within recesses 6 and 7 respectively provided in castings 8 and 9. The mould shown in the drawing is used for the manufracture of glass tumblers.

The following Examples are given for the purpose of illustrating the invention.

Example 1 A composition comprising, by weight, 94% iron powder, 4% copper powder and 2% of a phosphorcopper alloy (containing mainly copper) was well mixed. To the powder mixture was added 10% (by weight of the powder mixture) of colloidal graphite and the whole was throughly mixed to disperse the graphite throughout the mixture. This was then formed into the required shape and sintered.

Example 2 Using the basic technique described in Example 1, a sintered material may be produced from a powder mixture comprising, by weight, 98% nickel and 2% phosphor-copper alloy, to which is added a further 10% (by weight on the powder mixture) of colloidal graphite.

Example 3 Again using the technique of Example 1, a sintered material may be produced from a powder mixture consisting of, by weight, 86 parts copper, 13 parts tin, 1 part phosphor-copper alloy and 10 parts graphite.

Example 4 Again using the technique of Example 1, a sintered material may be produced from a powder mixture containing, by weight, 94 parts iron powder, 4 parts copper powder, 2 parts phosphor-copper alloy and 8 parts graphite.

Mould inserts of the form shown in the drawing were manufactured from the powder mixture described in Example 4 and were used in a production run for the manufacture of glass tumblers. The glass temperature was on the order of 1150 - 1155"C and the mould temperature were 540-560"C. The moulds were in use for a period of over 445 hours. It was possible fully satisfactorily to operate the glass forming machine (an HE 28 machine) at speeds in excess of 9% faster than would have been the case if the modified moulds had not been used. Furthermore, the quality of ware produced was such that the number of tumblers which had to be rejected was reduced by 10%, compared with production without the modified moulds.

The invention thus provides a technique which enables very acceptable glassware to be produced at very high speeds. This is particularly surprising in view of the fact that cast iron has a higher thermal conductivity than the glass-contacting materials of the invention, as a result of which it would be expected that the moulds of the invention would not be so efficient as conventional moulds at extracting heat from the hot glass being blown therewithin.

Claims (15)

1. A method of shaping hot glass in a mould wherein the hot glass is caused to contact a material comprising a metallic matrix throughout which is substantially uniformly dispersed from 4to 14%, by weight, of a solid lubricant.

2. A method as claimed in claim 1 wherein said glass-contacting material comprises a major proportion of iron, nickel or copper.

3. A method as claimed in claim 1 or 2 wherein the solid lubricant is graphite, boron nitride or molybdenum disulphide.

4. A method as claimed in any of claims 1 to 3 wherein the said material contains from 6 to 10%, by weight, of solid lubricant.

5. A method as claimed in any of claims 1 to 4 wherein the said material comprises predominantly iron, together with nickel, copper, boron nitride and molybdenum disulphide.

6. A method as claimed in claim 5 wherein the said material comprises, by weight, 70-80% iron, 7.5 to 10.5% nickel, 5 to 7% copper, 5 to 7% boron nitride and 2 to 4% molybdenum disulphide.

7. A method as claimed in any of claims 1 to 3 wherein the said material comprises predominantly iron, together with copper, graphite and molybdenum disulphide.

8. A method as claimed in claim 7, wherein the said material comprises, by weight, 80 to 90% iron, 3 to 4 copper, 8 to 10% graphite and 2 to 3% molybdenum disulphide.

9. A method as claimed in any of claims 1 to 3 wherein the said material comprises predominantly copper and/or nickel, a solid lubricant and at least 0.5% by weight of phosphorus.

10. A method as claimed in claim 9 wherein the phosphorus is introduced into the material as a phosphor-copper alloy or compound the phosphorus content of which is between 5 and 20% by weight.

11. A method as claimed in any of claims 1 to 10 wherein the said material is in the form of a bottom-forming mould for a hollow glass articie.

12. A method as claimed in any of claims 1 to 10 wherein said hot glass is blown to the internal shape of the said material.

13. A method as claimed in claim 1, substantially as hereinbefore described.

14. A glass forming mould wherein at least part of the glass-contacting surface is formed of a material comprising a metallic matrix throughout which is substantially uniformly dispersed from 4 to 14%, by weight, of a solid lubricant.

15. Glassware formed in a mould as claimed in claim 14.