WO2009090622A1

WO2009090622A1 - A method of extending the lifespan of a metal cavity mould

Info

Publication number: WO2009090622A1
Application number: PCT/IB2009/050178
Authority: WO
Inventors: Hilton Mark Layman
Original assignee: Mould Technico Cc
Priority date: 2008-01-18
Filing date: 2009-01-19
Publication date: 2009-07-23

Abstract

A method of extending the lifespan of a metal cavity glass bottle mould, includes the steps of machining the entire moulding surface of the mould to remove a surface layer of metal, cladding the machined moulding surface by depositing a layer of filler metal onto the surface in a laser cladding process and machining an exposed surface of the cladding layer so as to remove excess filler metal and return the moulding cavity to its design dimensions. The method includes a method of repairing a metal cavity mould by removing surface defects in the moulding surface of a damaged mould by machining the moulding surface and thereafter cladding the moulding surface. The method extends to the cladding of the moulding surface of an undamaged metal cavity mould.

Description

A METHOD OF EXTENDING THE LIFESPAN OF A METAL CAVITY MOULD

FIELD OF INVENTION

This invention relates to a method of extending the lifespan of a metal cavity mould. It relates also to a metal cavity mould wherein the lifespan of the mould has been extended in accordance with the method.

BACKGROUND TO INVENTION

Metal cavity moulds for use in moulding glass articles such as bottles or the like, have a limited lifespan. A typical cast iron cavity mould for moulding glass bottles in a continuous moulding process, typically operates at a working temperature of approximately 450 °C and produces approximately 750 000 bottles during its lifetime. When a crack forms in such a metal cavity mould, it is discarded and replaced. In many instances, the production line is brought to a halt to allow for the cracked mould to be removed and replaced, after which production resumes, resulting in a loss of production. If the moulding surfaces do not become cracked, the moulding surfaces of such moulds eventually become worn after a period of use to such an extent that the mould is no longer able to produce glass bottles which meet the required dimensional specification and thus need to be replaced. Any reference herein to the "working temperature" of a metal cavity mould must be interpreted to mean the temperature at which the mould is normally used during a moulding operation.

Any reference herein to "design dimensions" of the mould cavity of a metal cavity mould must be interpreted to mean the dimensions of the mould cavity specified for moulding articles having specific dimensions.

It is an object of the present invention to provide for the repair of damaged metal cavity moulds thereby extending the lifespan of such damaged moulds and also to extend the lifespan of undamaged metal cavity moulds.

SUMMARY OF INVENTION

A method of extending the lifespan of a metal cavity mould, the method including:

machining the entire moulding surface of the mould to remove a surface layer of metal;

depositing a layer of molten filler metal onto the machined moulding surface, wherein the layer of molten filler metal has a thickness which is greater than the thickness of the surface layer of molten filler metal removed during machining; and

machining an exposed surface of the deposited layer of filler metal so as to remove excess filler metal, thereby to return the moulding cavity of the mould to its design dimensions.

The method may be applied to the repair of a metal cavity mould, wherein the mould has at least one relatively shallow surface defect in the mould surface, the method including the steps of:

machining the entire moulding surface of the mould to remove a surface layer of metal to a depth sufficient to remove the depression in the moulding surface; depositing a layer of molten filler metal onto the machined moulding surface, wherein the layer of molten filler metal has a thickness which is greater than the thickness of the surface layer of metal removed during machining; and

In another embodiment of the invention, the method may be applied to the repair of a metal cavity mould wherein the mould has at least one relatively deep crack in the moulding surface, the method including the steps of:

machining the entire moulding surface of the mould to remove the surface layer of metal to a depth which reduces the depth of the crack but does not remove the crack entirely;

enlarging the crack by removing metal surrounding the crack;

heating the mould to a temperature at or above the working temperature of the mould;

while the mould is at said temperature at or above the working temperature of the mould, filling in the enlarged crack by depositing molten filler metal into the enlarged crack and allowing time for the mould to slow cool;

annealing the mould by heating the mould to a temperature above the working temperature of the mould and allowing the mould to slow cool;

depositing a layer of molten filler metal onto the machined moulding surface of the mould, to a thickness which is greater than the thickness of the surface layer of metal removed during machining; and machining an exposed surface of a deposited layer of filler metal to remove excess filler metal, thereby to return the mould cavity of the mould to its design dimensions.

The metal cavity mould may be specifically adapted for use in moulding glass articles. More particularly, the metal cavity mould may be specifically adapted for use in moulding glass bottles.

The metal cavity mould may be of cast iron and the filler metal which is deposited onto the machined moulding surface, may be of a metal having a relatively greater hardness than that of the cast iron of the metal cavity mould.

The filler metal which is deposited onto the machined moulding surface, may be of a metal having a relatively lower thermal conductivity than that of the cast iron of the metal cavity mould.

The layer of molten filler metal may be deposited onto the machined moulding surface by one of a laser cladding, laser cusing and an arc welding process.

The invention extends to a metal cavity mould, wherein the lifespan of the metal cavity mould has been extended in accordance with the method described and defined hereinabove.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are described hereinabove by way of a non-limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a schematic perspective view of a metal cavity mould with a base plate connected thereto;

Figure 2 shows a schematic exploded top plan view of the metal cavity mould and base plate of Figure 1 ; Figure 3 shows a sectional side view of the metal cavity mould of Figure 1 , sectioned along section line Ill-Ill of Figure 1 ;

Figure 4 shows a sectional side view of the metal cavity mould of Figure 1 , sectioned along section line Ill-Ill of Figure 1 , illustrating the mould having a surface defect in the form of a relatively deep crack in the moulding surface thereof;

Figures 5A to 5F show an enlarged sectional side view of detail R of Figure 4, illustrating, in sequence, the manner in which the crack in the moulding surface of the mould is repaired in accordance with the method of the invention;

Figure 6 shows a sectional side view of the mould of Figure 4 in its repaired state;

Figure 7 shows a sectional side view of the mould of Figure 1 , sectioned along section line Ill-Ill of Figure 1 , having a surface defect in the form of a shallow depression in the moulding surface thereof;

Figures 8A to D show enlarged sectional side views of detail S of Figure 7, illustrating, in sequence, the manner in which the depression in the moulding surface of the mould, is repaired; and

Figure 9 shows a sectional side view of the mould of Figure 7 in its repaired state.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 to 3 of the drawings, a metal cavity mould for use in moulding glass bottles, is designated generally by the reference numeral 10. The metal cavity mould 10 is of SG600 cast iron and has a mould surface 12 defining one half of a mould cavity 14 in which the sides and neck of a glass bottle is moulded. A base plate 16 also of SG600 cast iron is located relative to the metal cavity mould for forming the base of a glass bottle. Under typical operating conditions, the mould 10 is used for moulding glass bottles in a continuous moulding process at a working temperature of approximately 450 °C. Moulds of this type have a typical lifespan of approximately 750 000 bottles. At the end of its lifespan, the mould begins to show signs of wear and tear. The moulding surface 12 is often pitted and cracks may appear in the moulding surface due to metal fatigue and/or overheating. Depressions may also form due to loss of material as a result of wear. The general practice is to discard moulds which have cracks in the moulding surface and which become worn to an extent wherein the mould is no longer able to produce bottles which meet the required dimensional specification.

In accordance with the invention, the lifespan of the mould 10 can be extended by, broadly, machining the entire moulding surface 12 of the mould 10 by using a milling cutter, to remove a surface layer of metal. Thereafter, the machined moulding surface is clad by depositing a layer of molten filler metal onto the machined moulding surface wherein the layer of molten filler metal has a thickness which is greater than the thickness of the layer of molten filler metal removed during machining. Finally, the exposed surface of the deposited layer of filler metal is again machined so as to remove excess filler metal, thereby to return the moulding cavity to its design dimensions.

The lifespan of an undamaged cast iron metal cavity mould for moulding glass bottles, can be extended by following the steps of the broad method described hereinabove.

With reference to Figures 4 to 6 of the drawings, the manner in which the lifespan of a metal cavity mould can be extended by repairing a crack in the moulding surface of the mould, is illustrated. In order to inspect the moulding surface for cracks, a developing solution is sprayed onto the moulding surface and an ultraviolet light is directed onto the moulding surface which shows up any cracks which may have formed in the mould surface. In Figure 4 of the drawings, a relatively deep crack 18 is shown in the moulding surface 12. In order to repair the crack, the entire moulding surface 12 of the mould 10 is machined in a milling process using a milling cutter 20, to remove a surface layer 0.5mm thick to thereby remove surface deformities in and carbon deposits on the moulding surface. In Figures 5A to 5F, the moulding surface 12 which corresponds to the design dimensions of the mould cavity 14, is represented by the reference letter "A", whereas the moulding surface after a surface layer of metal has been removed in the milling process, is represented by the reference letter "B". The mould is then heated to the working temperature of the mould, i.e. to approximately 450 °C and while at this elevated temperature, the crack 18 is ground open to remove a surface layer of metal surrounding the crack. The ground crack is then bevelled to an angle of approximately 60° (see Figure 5C).

While the temperature of the mould is maintained at 450 °C, the bevelled crack is filled in by depositing molten filler metal 20 into the crack (see Figure 5D). Typically, this involves depositing molten filler metal into the cracks in a stick welding operation using a 3mm diameter nickel welding rod. The weld area is then peened to remove porosity in the weld and thereafter ground smooth while the temperature of the mould is maintained at 450 °C. The mould is thereafter allowed to slow cool in ambient air to room temperature. Thereafter, the mould is annealed by heating the mould to a temperature of approximately 600 °C and allowed to slow cool in ambient air to room temperature. After the mould has slow cooled, the machined mould surface is clad by depositing a cladding layer of molten filler metal onto the machined moulding surface of the mould (see Figure 5E), to a thickness which is greater than the thickness of the surface layer of metal removed during machining. The surface of the cladding layer of the deposited molten filler metal is represented by the reference letter "C" in Figure 5E and 5F. The metal selected as the filler metal for forming the cladding layer in this instance, is selected so as to have a relatively greater hardness than that of the cast iron of the metal cavity mould 10 and also to have a relatively lower thermal conductivity than that of the cast iron of the mould. Furthermore, the filler metal for forming the cladding layer must also be metallurgically compatible with the cast iron of the mould. The Applicant has found martensitic Stainless Steel 304 or 316 which exhibits both of these material properties, to be suitable cladding metals.

After the cladding layer has fused to the underlying machined moulding surface, the exposed surface of the cladding layer of filler metal is machined in a milling process to remove excess filler metal, thereby to form a cladding layer 24 returning the mould cavity 14 of the mould 10 to its design dimensions. The cladding layers 24 and 28 provide the mould 10 with increased hardness and resistance to wear thereby extending the lifespan of the mould. In typical examples, the cladding layers may be V∑mm - 1 mm thick.

With reference to Figures 7 to 9 of the drawings, the manner in which the lifespan of a metal cavity mould can be extended by repairing a relatively shallow surface defect in the form of a depression which has been formed due to localised wear in the moulding surface, as illustrated. In Figure 7 of the drawings, a shallow depression 26 is shown in the moulding surface 12. In order to repair the mould, the entire moulding surface 12 of the mould 10 is machined in the milling process using a milling cutter 20, to remove a surface layer of metal to a depth sufficient to remove the depression 26 in the moulding surface. In Figures 8A and 8B, the moulding surface 12 which corresponds to the design dimensions of the mould cavity 14, is represented by the reference numeral "K", whereas the moulding surface after a surface layer of metal has been removed in the milling process, is represented by the reference numeral "L". The machined mould surface is thereafter clad by depositing a cladding layer of molten filler metal onto the machined moulding surface of the mould (see Figure 8C), to a thickness which is greater than the thickness of the surface layer of metal removed during machining. The surface of the cladding layer of the deposited molten filler metal is represented by the reference numeral "M" in Figure 8C and 8D. As for the repair of a crack in the moulding surface as described hereinabove, the metal selected as the filler metal for forming the cladding layer, is selected so as to have a relatively greater hardness than that of the cast iron of the metal cavity mould and also to have a relatively lower thermal conductivity than that of the cast iron of the mould. Furthermore, the filler metal for forming the cladding layer must also be metallurgically compatible with the cast iron of the mould. In this instance, the Applicant has found martensitic Stainless Steel 304 or 316 which exhibit these material properties, to be suitable cladding metals.

After the cladding layer has fused to the underlying machine to moulding surface, the exposed surface of the cladding layer of filler metal is machined in a milling process to remove excess filler material, thereby to form a cladding layer 28 having a thickness returning the mould cavity 14 of the mould 10 to its design dimensions. The cladding layers 24 and 28 provide the mould 10 with increased hardness and resistance to wear thereby extending the lifespan of the mould. In typical examples, the cladding layers may be V∑mm - 1 mm thick.

The Applicant has found that metal deposition processes which are suitable for cladding the machined mould surface, include laser cladding, laser casing and arc welding. In a laser cladding process, a metallic consumable typically provided in the form of metallic powder or metal wire feedstock, is melted and consolidated by means of a laser beam thereby to form a cladding layer which is metallurgically bonded to the underlying machined moulding surface.

In a laser cusing process, a metallic powder compound is melted using a laser, in layers of approximately 0.001 mm. As such, layers of the molten metallic powder are deposited onto the machined moulding surface so as to build up the cladding layer to a desired thickness. The cladding layer forms a metallurgical bond to the underlying machined moulding surface.

In an arc welding process, the filler metal is deposited in a number of passes so as to form a metallurgical bond with the underlying machined moulding surface of the mould.

In a continuous glass bottle moulding process, the feed rate is maintained at a feed rate at which the working temperature of the metal cavity moulds, is not exceeded by a significant amount. If the feed rate is too high, the moulds overheat and are prone to damage. Furthermore, when overheated, the moulds expand excessively, resulting in an enlargement of the mould cavities to an extent wherein the moulds are no longer able to produce glass bottles of the required dimensional specification. By cladding the moulding surfaces with filler metal having a lower thermal conductivity than that of cast iron, the feed rate of feed stock in a glass bottle moulding process can be increased, as the working temperature of the moulds in accordance with the method of the present invention, is reduced compared to the working temperature of an unclad cast iron mould. In particular, the Applicant has found that by cladding the moulding surface with martensitic Stainless Steel 304 of 316, the feed rate of feedstock in a continuous glass bottle moulding process, can be increased by up to 25% compared to the feed rate for similar unclad cast iron moulds, without exceeding the working temperature of the mould.

Claims

CLAIMS:

1. A method of extending the lifespan of a metal cavity mould, the method including:

machining an exposed surface of the deposited layer of filler material so as to remove excess filler metal, thereby to return the moulding cavity of the mould to its design dimensions.

2. The method as claimed in claim 1 , which is applied to the repair of a metal cavity mould, wherein the mould has at least one relatively shallow surface defect in the mould surface, the method including the steps of:

machining the entire moulding surface of the mould to remove a surface layer of metal to a depth sufficient to remove the surface defect in the moulding surface;

depositing a layer of molten filler metal onto the machined moulding surface, wherein the layer of molten filler metal has a thickness which is greater than the thickness of the surface layer of metal removed during machining; and

3. The method as claimed in claim 1 , which is applied to the repair of a metal cavity mould wherein the mould has at least one relatively deep crack in the moulding surface, the method including the steps of:

enlarging the crack by removing metal surrounding the crack;

depositing a layer of molten filler metal onto the machined moulding surface of the mould, to a thickness which is greater than the thickness of the surface layer of metal removed during machining; and

machining an exposed surface of a deposited layer of filler metal to remove excess filler metal, thereby to return the mould cavity of the mould to its design dimensions.

4. The method as claimed in any one of claims 1 to 3, wherein the metal cavity mould is specifically adapted for use in moulding glass articles.

5. The method as claimed in claim 4, wherein the metal cavity mould is specifically adapted for use in moulding glass bottles.

6. The method as claimed in any one of claims 1 to 5, wherein the metal cavity mould is of cast iron and wherein the filler metal which is deposited onto the machined moulding surface, is of a metal having a relatively greater hardness than that of the cast iron of the metal cavity mould.

7. The method as claimed in any one of claims 1 to 6, wherein the filler metal which is deposited onto the machined moulding surface, is of a metal having a relatively lower thermal conductivity than that of the cast iron of the metal cavity mould.

8. The method as claimed in any one of claims 1 to 7, wherein the layer of molten filler metal is deposited onto the machined moulding surface by one of a laser cladding, laser cusing and an arc welding process.

9. A metal cavity mould wherein the lifespan of the metal cavity mould has been extended in accordance with the method as claimed in any one of claims 1 to 8.