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Final Report: GlassRite: Wine Lightweight Wine Bottles Strength as an Issue in the Manufacture of Lightweight Wine Bottles Project code: MSG009 ISBN: 1-84405-388-1 Research date: July 2007 to February 2008 Date: May 2008
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Wine Bottle Strength May'08

May 20, 2017

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Page 1: Wine Bottle Strength May'08

Final Report: GlassRite: Wine

Lightweight Wine Bottles

Strength as an Issue in the Manufacture of Lightweight Wine Bottles

Project code: MSG009 ISBN: 1-84405-388-1 Research date: July 2007 to February 2008 Date: May 2008

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WRAP helps individuals, businesses and local authorities to reduce waste and recycle more, making better use of resources and helping to tackle climate change.

Written by: Andy Hartley

Front cover photography: View of standard and lightweight wine bottles. WRAP and GTS believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and regulatory requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken in using any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.). The report does not claim to be exhaustive, nor does it claim to cover all relevant products and specifications available on the market. While steps have been taken to ensure accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being inaccurate, incomplete or misleading. It is the responsibility of the potential user of a material or product to consult with the supplier or manufacturer and ascertain whether a particular product will satisfy their specific requirements. The listing or featuring of a particular product or company does not constitute an endorsement by WRAP and WRAP cannot guarantee the performance of individual products or materials. This material is copyrighted. It may be reproduced free of charge subject to the material being accurate and not used in a misleading context. The source of the material must be identified and the copyright status acknowledged. This material must not be used to endorse or used to suggest WRAP’s endorsement of a commercial product or service. For more detail, please refer to WRAP’s Terms & Conditions on its web site: www.wrap.org.uk

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Executive Summary This report has been prepared as part of the WRAP-funded GlassRite suite of projects which are intended to reduce the volume of packaging entering the UK waste stream. The GlassRite projects aim to encourage the lightweighting of glass containers as a means of reducing the tonnage of glass in the waste stream. The GlassRite Wine project has the additional objectives of seeking to promote the bulk importation of wine into the UK to be filled in lightweighted bottles and also of encouraging importers of bottled wine to consider the use of clear glass. This report seeks to demonstrate that lighter, thinner wine bottles can now be manufactured to a strength equal to that of the heavier bottles that are in common usage. The report also seeks to demonstrate that computational aids such as Finite Element Analysis (FEA) can usefully be employed to evaluate new designs prior to their manufacture and identify any potential structural weaknesses. The report provides potential users of glass with an understanding of the factors that influence glass strength. It gives an insight into the improved manufacturing techniques that have allows glass manufacturers to reduce the weight of containers without compromising strength or safety. Glass has many properties that make it an ideal choice for wine bottles and for packaging many other foodstuffs but, whilst it is an inherently strong material, it is also a brittle one. The report seeks to explain how and why a brittle material like glass fails. Glass containers are produced by blowing the glass into metal moulds. The amount of glass used to make the container is a secondary consideration in determining the final strength. The principal consideration is to ensure that the glass that has been used is properly distributed and that no thin spots occur. Preventing manufacturing flaws and minimising surface damage are also important factors that determine a container’s strength. As a means of demonstrating that lighter wine bottles can be manufactured to a comparable strength to their heavier counterparts, a comparison has been made between three 750ml Bordeaux style bottles at weights ranging from 360 to 475g. The comparison has been made using FEA with some physical testing used to validate the process. The results of the analysis demonstrate the usefulness of computational tools in the design process and show that the lighter bottle is perfectly serviceable. Reference is made in the report to some other practical research in which a more direct comparison was made between a typical container and its lightweighted counterpart. The work concluded that, in general, the lighter container was actually the stronger container. The report also demonstrates a wireless sensor technology which offers the opportunity to test the performance of containers in real time in real environments e.g. on the filling line. The technology is not yet in general use but could become an invaluable design tool leading to better understanding of the products lifecycle and thereby help designers make further weight reductions.

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Contents 1.0 Introduction ............................................................................................................................. 2 2.0 Why do Glass Containers Fail? ................................................................................................. 3

2.1 Glass Failure .........................................................................................................................3 2.2 Glass Flaws and Surface Damage ...........................................................................................3 2.3 Stress Inducers .....................................................................................................................5 2.4 Glass Failure Modes...............................................................................................................5

3.0 The Safe Manufacture of Lightweight Glassware .................................................................... 7 3.1 Improved Design Capabilities .................................................................................................7 3.2 Improved manufacturing process control ................................................................................8 3.3 Improved Mould Production ...................................................................................................8 3.4 Improved Machine Operation .................................................................................................8 3.5 Improved Inspection Technology............................................................................................8 3.6 Real Time In-situ Monitoring ..................................................................................................8

4.0 The Performance of Lightweight Wine Bottles ........................................................................ 9 4.1 Finite Element Analysis ..........................................................................................................9 4.2 FEA Comparison of Three Wine Bottles of Different Weights .................................................. 10

4.2.1 Inputs .................................................................................................................... 10 4.2.2 Outputs.................................................................................................................. 10

4.3 Results ...............................................................................................................................11 4.3.1 Internal Pressure and Head load.............................................................................. 11 4.3.2 Impact Loading....................................................................................................... 12 4.3.3 Physical Testing...................................................................................................... 16

5.0 Other Comparative Studies of Lightweighted Container Strengths....................................... 16 6.0 Conclusions ............................................................................................................................ 17 Appendix A: Modelling Results........................................................................................................... 18 Appendix B: Physical Testing Data & Results..................................................................................... 24 Figures Figure 1 The Blow and Blow glass forming process. .........................................................................................4 Figure 2 The Press and Blow glass forming process. ........................................................................................4 Figure 3 Residual Stress in a glass container. ..................................................................................................5 Figure 4 Tensile stresses produced in hollow items by squeezing......................................................................6 Figure 5 External impact (a) and internal pressure failure (b). ..........................................................................7 Figure 6 “Wireless” monitoring of a filling line using a mock bottle with series of sensors. ..................................9 Figure 7 Combined pressure and head load for wine bottle A. ........................................................................ 11 Figure 8 Impact simulation conditions. .......................................................................................................... 13 Figure 9 Impact loading for wine bottle A...................................................................................................... 13 Figure 10 Comparison of physical testing and finite element analysis (shoulder strikes only). ........................... 15 Figure 11 Glass Distribution of the three wine bottles investigated................................................................... 18 Figure 12 Combined pressure and head load for container A (lightest weight). ................................................ 19 Figure 13 Combined pressure and head load for container B (intermediate weight). ........................................ 20 Figure 14 Combined pressure and head load for container C (heaviest weight)................................................ 20 Figure 15 Impact loading for container A....................................................................................................... 21 Figure 16 Impact loading for container B ..................................................................................................... 22 Figure 17 Impact loading for container C. ..................................................................................................... 23 Tables Table 1 Physical dimensions of wine bottles investigated................................................................................ 10 Table 2 Maximum stresses from combined pressure and head loading. ........................................................... 12 Table 3 Maximum tensile stresses for impact stresses for the three wine bottles investigated........................... 15 Table 4 Summary of the physical impact testing. ........................................................................................... 16

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1.0 Introduction This report seeks to provide those involved in the purchase and specification of wine bottles with information relating the strength of glass bottles. It aims to demonstrate that modern glass manufacturing methods can produce lighter, thinner wine bottles which have a comparable strength to those heavier versions that have traditionally been used by the wine trade. Wine bottles are a major contributor to the UK’s waste stream and WRAP’s Glassrite suite of projects aims to reduce this impact. Reducing the weight of packaging is one means of achieving this objective and this report seeks to promote lightweighting activities by providing clear evidence that lightweight bottles are safe to use and not more prone to failure than their heavier counterparts. To be commercially viable, glass containers must be produced at high speeds by automated machines. Forming a hollow item such as a glass container is inherently more complicated than making a solid product. The glass forming process essentially entails introducing a relatively small amount of molten glass into a mould and then blowing the glass outwards to fill the mould space. Calculating how much glass to place into the mould is not difficult; the challenging task is to ensure that glass is distributed appropriately within the mould and that no unwanted thin spots occur which create areas of weakness. Glass is a strong material but due to a lack of crystalline structure it is brittle. The container manufacturer will be aware of the conditions and environment to which the container will be exposed and the stresses that it is expected to withstand. The manufacturer will also be aware that the glass forming process will inevitably have resulted in microscopic surface damage and may have introduced other flaws into the body of the glass. One of the most challenging aspects of glass container production is ensuring that the glass is properly distributed in the mould. In the absence of good control over glass distribution the glassmaker has to resort to making thicker-wall containers, in the hope that even the thin spots have sufficient glass to ensure that the container will not fail in use. The development of the Narrow Neck Press and Blow (NNPB) manufacturing process allowed glassmakers to produce lighter, stronger bottles as it greatly increased the control they had over glass distribution. The process was initially used for the high volume beer market and resulted in dramatic weight reductions. By adopting the new technology, companies were easily able to achieve weight reductions of 20% with no loss in strength or any need for a radical change to the container’s shape. As an example, the Ukrainian-based Gostomel Glass Factory (GGF) adopted the technology and was able to report “The new production lines will allow GGF to decrease the weight of beer bottles from the current range of 340g to 380g to ultra lightweight bottles weighing 280g to 240g (a substantial saving in raw materials) while retaining the 15 bar pressure rating.”. Spirit bottles have also been lightweighted. Until recently the tall round 70cl industry standard was being produced at around 450g. The same bottle is now available for general use at 298g. The Co-op1 was able to claim to be the first company to adopt the new “sub-300g environmentally friendlier” bottle by using it for their own-brand whisky. Having gained control of glass distribution the container designers are now better placed to benefit from computer modelling technology. Finite Element Analysis (FEA) is one of the most widely used modelling tools finding applications in many areas of advanced engineering. FEA enables a designer to test a new container for a range of performance indices such as vertical loading, bursting pressure and impact resistance without the need for expensive prototypes.

1 Spirit of Innovation: Co-op Roll Out World's Lightest Whisky Bottle, http://www.wrap.org.uk/wrap_corporate/news/spirit_of.html

Adnams beer bottle

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Coca-Cola is perhaps the most high profile company to acknowledge the value of FEA in container design. The Coke bottle is an iconic shape and the marketing implications of any change to the profile would be profound. However, the Coke bottle has been redesigned with the aid of FEA. The new bottle is seen by Coca-Cola as part of their commitment to corporate social responsibility.

The Ultra Glass contour bottle is designed to improve impact resistance, and reduce weight and cost. The innovative Ultra Glass bottles are 40 percent stronger, 20 percent lighter and 10 percent less expensive than traditional contour bottles. Use of the Ultra Glass design has eliminated 52,000 metric tons of glass – resulting in a CO2 reduction of 26,000 tons or

the equivalent of planting 8,000 acres of trees.2

2.0 Why do Glass Containers Fail? Glass technologists frequently claim that their material is “inherently strong”, yet common experience teaches us that the material is fragile. How can the claim of strength be reconciled with contradictory the experience of fragility? An answer to this quandary is provided by gaining a better understanding of the mechanism of glass failure. A better understanding of glass properties will also help glass users identify possible problems in handling and in specifying glass containers. 2.1 Glass Failure Glass containers fail when sufficient stress is applied. The glass invariably fails by cracking i.e. splitting apart. Glass in pristine condition will be able to resist large stresses. Unfortunately, any flaws will significantly reduce the ability of a glass container to withstand stress. However, the application of stress to a glass flaw does not necessarily equate to failure. It is only those stresses that are acting to pull the glass apart (tensile stresses) and exacerbating flaws and tiny cracks that will cause failure. Stresses (compressive) that act to close a flaw such as surface crack will not cause failure. The failure of a glass item could be described by the following simple expression:

Glass Flaw + (High) Tensile Stress = Failure 2.2 Glass Flaws and Surface Damage The strength of a glass bottle can be reduced by flaws generated during its manufacture and by surface damage sustained in subsequent use. Flaws can be introduced into glass bottles during manufacturing, some of which are serious and can compromise the strength of the finished product. Some of these flaws are due to poor process control e.g. thin walls; others are due to contaminants being introduced into the furnace such as inclusions from broken ceramic often found in the cullet supply and which can pass through the manufacturing and end up embedded in a bottle’s sidewall or base. Fortunately, the rigorous inspection process which every bottle undergoes is able to detect the great majority of these flaws before the bottle leaves the glass factory. Bottles are formed in metal moulds. Two basic forming processes are used to produce bottles; the “blow and blow” and the “press and blow” methods. Both processes employ two moulds to form an article; the blank mould and the blow mould. The blow and blow process is shown in Figure and essentially uses a small metal plug to begin the process and form the neck and relies solely on air pressure to form the bottle. The press and blow process is shown in Figure and involves pressing a metal plunger into the glass prior to the start to the “blowing” stage. The press and blow process is more complex but gives better control over glass distribution. Both processes involve glass to metal contact which results in the bottle suffering a small amount of surface damage and whilst under normal conditions the bottle will be perfectly safe and serviceable, it will have lost some of its strength.

2 Package Design, http://www.thecoca-colacompany.com/citizenship/package_design.html

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Figure 1 The Blow and Blow glass forming process.

Figure 2 The Press and Blow glass forming process.

Once formed the bottles passes through an annealing process which involves controlled heating and cooling stages and which is intended to remove the internal stress generated during forming process. Ideally annealing the glass will remove all the internal stress but in practice some will remain. Thicker glass needs to spend more time in the annealing oven and the annealing time is thus determined by the maximum wall thickness of the container. Lightweighted containers, being thinner and in general having a more uniform glass distribution than their heavier counterparts, require less annealing and are thus less prone to being poorly annealed. Consequently, glass manufacturers include tests for annealing in their quality control regime of tests. Fortunately, any residual stress is easily identified by simply viewing the container under polarized light and any stress present can be quantified by comparison to standard strain discs. Figure shows a jar that has some residual stress in the shoulder and base (the stressed areas appearing yellow/orange under polarized light).

Gob dropped

into blank mould

Neck formed

Blank blown Blank blown

Blank shape

Blank transferred

to blow mould

Final shape blown

Finished bottle

Finished jar

Final shape blown

Blank transferred

to blow mould

Blank shape

Blank pressed

Plunger presses blank shape

Gob dropped

into blank mould

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Figure 3 Residual Stress in a glass container. Once annealed the bottles progress through several inspection stations before being palletised for despatch to the customer. All of these stages involve some form of glass to glass or glass to metal contact which adds to the surface damage. Whilst glass is not unique in that it suffers from surface flaws, it is unusual in having a non-crystalline structure, which makes it particularly susceptible to tensile failure. Other materials are essentially composed of many interlocked grains which present a barrier to crack propagation. Glass lacks this internal grain structure and thus allows cracks to develop unhindered. 2.3 Stress Inducers In normal use, glass containers will be subject to a variety of stresses which could act on a glass flaw to produce breakage. These stresses include:

Impacts bumps and knocks from filling and general use

Squeezing sideways pressure from rollers on filling lines

Loading vertical pressure from stacking

Residual stress internal manufacturing stresses that should be removed by annealing

Bursting internal pressure from carbonated drinks - which is of particularly relevance to champagne and sparkling wine production that involves re-fermentation

Thermal rapid expansion due to hot filling

2.4 Glass Failure Modes Glass fails by cracking and forces that act to close a split (compressive) will not cause failure but those that act to pull apart the split (tensile) may cause failure. Forces acting on hollow items such as containers can simultaneously produce both compressive and tensile stresses. A force that produces compressive stress on the outer surface also produces tensile stress on the inner. Figure shows a container that is being placed under an external compressive load; it is being squeezed as might occur between the rollers on a filling line. The squeezing action is tending to compress the container into an elliptical shape. The outer surface at the compression point is being flattened whilst the inner surface is being stretched i.e. is being put under a tensile stress. At 90 degrees to the applied load the converse situation applies. Here the outer surface is being stretched whilst the inner surface is being compressed. Points were the glass is under high tensile stress and thus tending to being pulled apart are known a “hinge points” and are the positions that are most prone to failure.

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Thus, as the outer surface of a container is more likely to contain a flaw than the inner, a container that is crushed may fail at a point 90 degrees to the application of the pressure.

Figure 4 Tensile stresses produced in hollow items by squeezing.

When glass fails it leaves behind characteristic features on the fracture surfaces which can provide clear evidence as to origin and cause of failure. Trained observers can reconstruct items and, with their specialist knowledge of crack propagation, can trace failure patterns back to the point of origin. The origin of a glass fracture may not coincide with the point at which the container was struck or stressed; however, the experienced observer can usually determine the actual cause of a failure which may be a combination of a glass fault and an applied stress. With the evidence provided by the fragments an investigator can often determine if a failure was due to a design fault or the misuse or abuse of the failed item. Figure shows two examples of failure, one being a typical external impact, the other the result of internal pressure as might occur with a sparkling wine bottle. More examples of typical failure patterns can be found in the publication “The American Society for Testing and Materials (ASTM) Designation: C 1256 – 93 “Standard Practice for Interpreting Glass Fracture Surface Features”.

Squeeze

Inner surface being stretched (tensile)

Hinge Point

Outer surface being stretched (tensile)

Hinge Point

Outer surface being compressed

Inner surface being compressed

Squeeze

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Figure 5 External impact (a) and internal pressure failure (b). 3.0 The Safe Manufacture of Lightweight Glassware Given that glass is a brittle material and can fail when it suffers a sharp blow or is simply dropped, is lightweighting a prudent step? Glassmakers are confident in their ability to reduce the weight of containers whilst retaining (and in some cases improving) structural strength. The “lightweighting process” is viewed as the natural outcome to the progressive application of new and improved technology to the manufacturing process. In recent times significant advances have been made in better design, forming and inspection and testing techniques all of which have all contributed to the safe production of lighter glassware. A brief description of these improvements is given in the following sections. 3.1 Improved Design Capabilities The contribution to the lightweighting process of computer-assisted design (CAD) tools has been significant. Glass container designers were some of the first users of CAD technology. Initially the use of these programmes was confined to producing images for customers and more detailed technical information to assist with mould production. Further increases in computer power and the ready availability of user-friendly packages eventually made the use of Finite Element Analysis (FEA) a practical reality for glass container designers. Several software packages are now commercially available. Some consider the actual forming process and how the glass moves during forming, which helps the designer direct more glass into potential weak spots; others consider the performance of the finished container. FEA enables the designer to model the strength implications of any design feature and reduce the need for the costly step of actually producing prototype glass containers for testing and subsequent bottle redesign that may be necessary.

Pressure Failure Forked pattern

Impact Failure Star pattern

a) outer surface (by impact) a) inner surface (by pressure)

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3.2 Improved manufacturing process control Glassmakers can never achieve perfect glass distribution within a mould and must incorporate a safety factor to ensure that glass thickness does not fall below a safe level at any point. The safety margin is needed because of the uncertainty in ensuring good distribution. Today’s glassmakers have much more control over the forming process. The glass forming process begins when a discrete portion of molten glass (a gob) is fed to the mould. A consistent gob weight is a prerequisite for a uniform product. Advances in the control of the parameters which determine gob weight have reduced the variations in the amount of glass that is fed to the mould. Better control is also exercised over the movement of the plunger used in the Narrow Neck Press and Blow (NNPB) process which results in better glass distribution within the mould. The improved level of control at these two critical points gives the glassmaker confidence that the a safe glass distribution has been achieved with the result that a lower safety margin is required and less glass need be used. 3.3 Improved Mould Production The cast iron moulds used for forming the glass containers are negatives of the required shape with allowances for thermal expansion at the glass forming temperature. Improved machining technology to manufacture the moulds now enables the moulds to be produced to much tighter tolerances. 3.4 Improved Machine Operation The glass forming machine performs a complex sequence of actions in order to produce a wine bottle or jar (see Figure 1 The Blow and Blow glass forming process. Modern forming machines use electronic timing mechanisms which give more precise control over the timing of individual events than was possible with old mechanical timing technology. This improvement in process control again helps the manufacturer to work to tighter tolerances and a lower safety margin and thus allowing the use of less glass. The cast iron moulds used to shape the containers need continuous and rapid cooling. Best practice now involves controlled internal mould cooling which gives much better control than the older external blow cooling method. 3.5 Improved Inspection Technology Every container produced is subject to a range of quality checks during the manufacturing process. Increasingly these tests are performed in-situ, by technology based on high speed imagery which is able to identify and reject any manufacturing faults including: thin walls, inclusions, crizzles (small cracks) and dimensional variations. A number of containers are also routinely tested to destruction to assess impact resistance, vertical load and bursting pressure the latter being of particular importance to highly carbonated sparkling wines. Thus the quality system ensures that any lightweighted container meets the same exacting standards that were applied to its heavier predecessor. 3.6 Real Time In-situ Monitoring Developments in telecommunications and data logging now enable the glass manufacturer to gather information about the stresses that the glass container will be subjected to during its working life. One such system involves producing an exact perspex replica of the container within which are installed various load, temperature, and accelerometer impact sensors. The model container is then introduced into the production line and is able to send back information in real time on the conditions that prevail (Figure ). The information gathered can be used to refine the design of the container or alternatively can identify those points in the production, filling and distribution system at which the container is at risk. To date three UK glass manufacturers have acquired this technology but no operational details have yet been made available.

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Figure 6 “Wireless” monitoring of a filling line using a mock bottle with series of sensors. The data received from the sensing equipment relating to impacts is not directly comparable with the standard pendulum impact testers found in quality laboratories, but it is arguably more representative of actual operating conditions. The laboratory equipment places a container against an immovable V-backstop and subjects it to a standard blow. In reality a container will receive only glancing blows from fixed objects and bump into other (moveable) containers on the filling line. It is also important to recognise that for a moving container the energy of the impact is proportional to the container weight so lighter containers will receive smaller knocks causing less damage. 4.0 The Performance of Lightweight Wine Bottles As a means of demonstrating that lighter wine bottles can be manufactured to a comparable strength to their heavier counterparts, the performance of 3 existing wine bottles has been evaluated. The bottles chosen had weights ranging from 360 to 475g and the analysis was designed to determine their relative ability to withstand the stresses that such bottles could reasonably be expected to encounter in normal use. The bottles selected were three 75cl Bordeaux style wine bottles of varying weight and glass thickness. The performance of the bottles was compared by mathematical modelling using a standard Finite Element Analysis (FEA) package. The bottles were also subjected to standard impact testing as would be applied in the glass factory as a means of validating the FEA output. 4.1 Finite Element Analysis Finite element analysis is a computational method that is increasingly finding application in glass container design. The technique makes it possible to evaluate strength and performance of a glass container on a computer before final design decisions are made. In the absence of FEA (or other numerical analysis), decisions on safe wall thicknesses and the radii of curved surfaces were based on experience supplemented by hand calculations. For a complex structure, the simplifying assumptions required to make any calculations possible often led to a conservative and over heavy design. A considerable factor of ignorance could remain as to whether the design would be adequate for all expected loads.

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4.2 FEA Comparison of Three Wine Bottles of Different Weights The FEA study was undertaken by Rockfield Software which has recognised expertise in the field of FEA and which is used by some UK glass manufacturers in their development work. In order to perform a FEA the following details were required: 4.2.1 Inputs Detailed engineering drawings of the bottles – these were provided by the participating companies and remain confidential. Glass Distribution – this was determined by actual measurements of the glass thickness. The details and dimensions of the wine bottles are given in Table 1 and Appendix A: Figure shows the glass distribution of the samples.

Table 1 Physical dimensions of wine bottles investigated.

Dimensions Average Glass Thickness Bottle ID

Weight (g)

Height (mm)

Diameter (mm)

Body (mm)

Shoulder (mm)

Neck (mm)

Base (mm)

A 360 283 75 2.5 1.5 2.6 5.4

B 430 279 77 2.8 3.0 3.5 6.5

C 475 299 76 3.1 2.7 4.0 6.3

4.2.2 Outputs Finite element analysis can be used to predict the performance of a container to a range of operating conditions. For the purposes of this demonstration the bottles were modelled for: Combined internal pressure and head loading Containers are filled, capped or corked and then transported usually in palletised form to the end user. Capping and palletising subject containers to large vertical loads. For the purposes of the modelling exercise a loading force was applied to the top of the container to represent the head load of 4020N (410 kg) which is well in excess of the 1080 to 1370N (110 to 140 kg) typically experienced by wine bottles finished with a cork or screw closure. The model also simulated an internal pressure of 1.21 N/mm2. Pressure testing is not a general requirement in the case of still wine but has been included here to demonstrate the range of simulations that can be achieved with FEA. Pressure testing is however needed for products such as sparkling wine, where carbon dioxide is held in bottle under pressure.

Pendulum impact at the shoulder Containers are subject to impacts during filling, transportation and use. The standard test comprises a simple pendulum which is used to deliver a calibrated impact to the shoulder or heel of a container, these being the natural contact points. For the purposes of the modelling exercise an impact of 100 cms per second was simulated in the shoulder location.

Vertical Load due to Stacking

Industry Standard impact tester

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4.3 Results Detailed results for all the modelling work are given in Appendix A. A single example of each simulation is included in this section for the purposes of illustration. The outputs are provided in the form of graphical presentation in which the predicted and target stresses are plotted alongside the container’s profile. 4.3.1 Internal Pressure and Head load This simulation replicates conditions of a uniform internal pressure of 1.209 N/mm2 (175 psi) and a simultaneous vertical load of 4000N. Details of the individual simulations are give in Appendix A and that for container A is also reproduced below (Figure ) for the purposes of clarification. The output from the simulation shows the tensile stresses generated on the outside and inside surfaces of the wine bottle. The blue line represents the tensile stress generated by the simulated test conditions, and the red line represents the maximum allowable stress at that the bottle should be designed to withstand (“target stress”). The target maximum stress set used assumes good handling, i.e. little surface damage. Different areas of the container are given different allowable stresses, depending upon their location and likelihood for damage. These areas, or “zones”, (e.g. the punt (bottle bottom), the shoulder and the neck) are identified automatically by the software, and the appropriate allowable stress from the chosen set of limits is displayed along that area.

Figure 7 Combined pressure and head load for wine bottle A.

Glass profile

Predicted Stress

Failure Indicator

Line

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The position and the maximum stresses experienced by each of the three sample bottles under the simulated test conditions are given in Table 2.

Table 2 Maximum stresses from combined pressure and head loading.

Inside Surface Outside Surface

Position Stress (N/mm2) Position Stress (N/mm2)

Bottle ID

Model Safe Limit

Safety Margin

(%)

Model Safe Limit

Safety Margin

(%) A

(360g) Heel 38

190 80 Shoulder 35 135 74

B (430g)

Heel 47 190

75 Shoulder 24 135 82

C (470g)

Heel 34 190 82 Shoulder 18 135

87

As the bottles are all of a similar size, shape and glass thickness, a similar performance was to be expected under pressure and head loading. In general the results do show that thicker bottles are stronger, but the more important finding is that the lightest bottle is still comfortably below the maximum allowable stress level and little extra strength is provided by the addition of more glass. Indeed bottle B is seen to be more prone to failure at the heel than bottle A despite being some 70g heavier; the additional glass not being used to strengthen the weak point. Bottle A (Appendix A: Figure) was the lightest and has somewhat thin shoulders which are causing a stress peak at this point on both inside and outside surfaces However, the stress is still below the acceptable level. Bottle B (Appendix A: Figure ) has stress levels well below the acceptable limits in all areas but does show a slightly high value at the heel which is consistent with the results from the physical pendulum testing (Appendix B). Bottle C (Appendix A: Figure 1) similarly shows stress levels well below the acceptable limits in all areas. This bottle has a more pronounced punt, but the glass thickness around the heel is well distributed and the stress levels do not show a large peak. 4.3.2 Impact Loading The impact loading simulation was designed to replicate the action of the industry standard American Glass Research (AGR) pendulum tester impacting on the shoulder region with a hammer speed of 100cms/s. The simulated test set up is shown in Figure (the V-Bar is the part of the test rig against which the bottle sits as it is being struck) and an example of the simulation output (bottle A) is shown in Figure .

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Impactor @100 cms/s V-Bar Support

Figure 8 Impact simulation conditions.

Figure 9 Impact loading for wine bottle A. Inside Surface: Section Angle = 0º (through impact point)

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Outside Surface: Section Angle = 43º (through hinge point) Details of the individual simulations are given in Appendix A Figure , Figure & Figure and that for container A is also reproduced below (Figure ) for the purposes of clarification. The output from the simulation shows the tensile stresses generated on the outside and inside surfaces of the wine bottle. The output from the analysis are in the form of “stress maps” which show the maximum tensile stress generated on the outside and inside surfaces of the containers during the impact incident (i.e. the stresses shown are the maximum at any given point during the very short period of the strike, so would not in practice occur simultaneously). The maximum tensile stress will be developed on the inside of the bottle immediately behind the impact point. As the glass surface on the inside of the bottle should be in near pristine condition it should be well able to absorb the impact energy. Pristine glass typically is able to withstand 650 N/mm2. The stress map produced for the outside surface is of interest not only at the point of impact but also for the position of any hinge points which are also possible failure points and which could be strengthened by small design changes if necessary. It is prudent to assume that the outside surface will have suffered some wear and tear and a value of around 70 N/mm2 is accepted as normal for lightly scratched surfaces. The maximum tensile stresses predicted by the finite element analysis are given below in given in Table 3. The results have also been compared with those of the physical testing in Figure and are seen to be consistent with the thinner bottle developing higher stress levels for a given impact and thus faring less well with the pendulum testing. The full data sets are given in Appendix A and a summary of maximum stresses developed is given below in Table 3.

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Pendulum Results vs. Predicted FEA Maximum Stressshoulder position only

100

150

200

250

300

350

400

450

500

100 150 200 250 300 350

Impact Resistance (cm/s)

Max

Ten

sile

Str

ess

((N/m

m2)

Table 3 Maximum tensile stresses for impact stresses for the three wine bottles investigated.

Container Inside Surface (N/mm2) Outside Surface (N/mm2)

A (360g) 447 51

B (430g) 317 27

C (470g) 280 24

Figure 10 Comparison of physical testing and finite element analysis (shoulder strikes only). The pattern of stress distribution is seen to be broadly the same for all the bottles. At the point of impact the bottle suffers a concentrated region of stress on the inside of the bottle due to the impact, as that surface is the one being stretched. On the outside of the bottles the highest stresses occur at the “hinge points” (see Figure 4) which are nominally located on either side of the impact site. The actual hinge point positioning depends upon the geometry, thickness and impact location. The results of the analysis are seen to be in broad agreement with the physical testing with all maximum stresses being within the acceptable range for a working bottle for both internal and external surfaces. Bottle A (Appendix A: Figure was the lightest and displayed the highest tensile stresses on inner surface. The impact was simulated at the shoulder location, where the glass was relatively thin and thus it was to be expected that this container would not perform as well as the other two containers, which had thicker walls at this point. Laboratory pendulum testing confirms this result (Appendix B). This container also showed the highest stresses on the outside surface, again due to the fact that the hinge points fell within the thinner area of glass. Two sets of hinge points are apparent in Bottle A. This is can be associated with containers having significant curvatures at the shoulder. It can also be seen that principal hinge points occur at the top of the shoulder on Bottle A. Bottle B (Appendix A: Figure 16 ) has its principal hinge point somewhat lower in the bottle and it has a barely discernable secondary hinge point coinciding with the upper shoulder region. This bottle performed least well for stress in the heel region.

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Lightweight Wine Bottles 16

Bottle C (Appendix A: Figure ) has the largest average wall thickness and displays the least stress. The two sets of hinge points are clearly defined, coinciding with the top and bottom of the shoulder region. 4.3.3 Physical Testing Physical testing of the three bottles was undertaken by GTS. Testing was confined to impact testing and glass distribution. As the bottles were production items they had already undergone extensive testing and were thus known to be fit for purpose. The full data sets of the physical testing are given in Appendix B and a summary is given below in Table 4.

Table 4 Summary of the physical impact testing.

Heel impacts (cm/s) Shoulder impacts (cm/s) Bottle ID

Minimum Maximum Average Minimum Maximum Average

A (360g) 120 260 188 120 220 169

B (430g) 120 200 141 180 >320 263

C (470g) 200 240 223 170 >320 >290

The American Glass Research (AGR) pendulum tester is the industry standard and used worldwide but no formal minimum standards are set for individual products, e.g. wine bottles, against which they could be judged on a “pass/fail” basis. In practice glass manufacturers and testing laboratories are aware of the strength required by individual products and are guided by experience in deciding a safe level. In the case of bottles to be used for non-carbonated wine a minimum value of around 80 cm/s is considered to be an appropriate minimum. Based on a minimum strength value of 80cm/s all three bottles are seen to be comfortably within the limit. The results do display a broad correlation with weight with the heavier, thicker bottle C displaying the greatest strength but nonetheless bottle A is perfectly serviceable and some 24% lighter than bottle C. The physical testing also confirms some of the results of the FEA work by confirming that the design of bottle B has produced a (relatively) weak heel and that the shoulder on bottle A would be somewhat weaker than the other bottles. 4.4 Practical Experience of Lightweighting Wine Bottles During the course of the project a number of lightweighting initiatives were completed and bottles are now available for use in the on and off trade. Ideally developing a new bottle will begin by the formation of a project team which will include representatives of all the members of the supply chain including: the glass manufacturer, the packer filler and the customer. The lightweighting process will then be able to progress rapidly as there will be early and open involvement of all interested parties who will be able to ensure that the product meets all of the customer’s requirements whilst not encountering any unforeseen difficulties during manufacture and filling processes. This approach adopted by the consortium that produced the lightweight bottle initially for use by Tesco and latterly for the Co-op and proved to be very effective and contributed over 3,500 tonnes to the project’s target. 5.0 Other Comparative Studies of Lightweighted Container Strengths A literature search revealed that other researchers have attempted to compare the performance of established containers with their lightweighted equivalents. Jaime S.B.M. et al3 compared the mechanical performance of lightweight glass packages produced by the Narrow Neck Press and Blow and the same regular weight glass packages produced by the conventional process Blow and Blow.

3 Packaging Technology and Science, Volume 15, Number 4, July/August 2002, pp. 225-230

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Lightweight Wine Bottles 17

Several parameters including glass thickness distribution, mechanical performance (impact, vertical load and thermal shock strength) and the performance of lightweight glass packages under transport simulation were monitored. The study found that the lightweight glass containers had a more uniform thickness distribution in comparison with the regular weight containers and a better performance (about 33% improvement) in relation to the impact strength, especially in the heel, even when evaluated after line simulation. The lightweight glass container also gave a better performance with respect to vertical load strength, both before and after line simulation. Both containers withstood the temperature difference of 42°C that such packages are supposed to resist according to thermal shock specification. However, due to the better thickness distribution of lightweight glass packages, they were able to withstand a 5 to 10°C higher maximum temperature difference of than the regular weight containers. 6.0 Conclusions The weight of a wine bottle is not necessarily a good indicator as to its strength. A strong bottle will have the glass well distributed; have no thin spots and few surface defects. Glass is an inherently strong material but being brittle it is susceptible to failure when subjected to high tensile stresses. Small surface defects act to weaken glass and are usually the focal point of breakages. Good manufacturing methods that minimise these defects will produce a stronger bottle. Most wine bottles are manufactured to designs appropriate to older forming technology and practices which could now be revised to be lighter and yet sufficiently strong. Most glass manufacturers have added some lighter wine bottles to their portfolio and these may be available if requested. Some wine brand owners are still apprehensive about lightweighting, feeling that a move to a lighter version would cheapen their image. However, others including Adnams and Coca Cola have used lightweighting to put out a positive environmental message. Whilst lighter wine bottles are generally only marginally cheaper to purchase than heavier versions they do reduce transport costs, and even small dimensional changes may translate into an increase in the number each pallet can hold. Modern manufacturing methods permit container manufacturers to produce wine bottles that are significantly lighter than was previously possible, without compromising safety. Computational techniques such as Finite Element Analysis (FEA) can reliably be used to ensure that new design concepts will produce a safe, strong wine bottle without the need for extensive proto-typing. The technique is not able to predict the actual strength of a container design but rather to determine which areas of a container are potential weak spots and some physical testing will still be required. The results of the FEA simulations of three nominally similar wine bottles were able to able to establish that the designs would produce bottles with the required strength characteristics. The simulations were also able to identify any (relative) weak points in the design which were confirmed by physical testing. Remote sensing technology now offers the chance to monitor the performance of a container throughout the supply chain and identify those areas in the system where containers are prone to damage. New products can more rapidly be brought through the design, development and production stages if a guided by project team with members drawn from all stages in the supply chain.

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Lightweight Wine Bottles 18

Appendix A: Modelling Results The results of the finite element analysis conducted on the three bottles are given below. Bottle Geometry Based on technical drawings and the detailed wall thickness measurements made by GTS, Rockfield were able to construct a glass profile for each item. Figure shows the profiles of these bottles.

Figure 11 Glass Distribution of the three wine bottles investigated. Bottle A Bottle B Bottle C Height (mm) 283 279 299 Diameter (mm) 75 77 76 Weight (g) 360 430 475

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Lightweight Wine Bottles 19

Internal Pressure and Head Loading The results for simulated internal pressure and head loading are shown in Figures 12 to 14. The simulation replicates conditions of a uniform internal pressure of 1.209 N/mm2 (175 psi) and a simultaneous vertical load of 4020N (410 kg). These graphs show the tensile stresses generated on the outside and inside surfaces of the containers. The blue line represents the tensile stress generated by the simulated test conditions, and the red line represents the maximum allowable stress at that the bottle should be designed to withstand (“target stress”). The target stress set used assumes good handling, i.e. little surface damage. Different areas of the container are given different allowable stresses, depending upon their location and likelihood for damage. These areas, or “zones”, (e.g. the punt (bottle bottom), the shoulder and the neck) are identified automatically by the software, and the appropriate allowable stress from the chosen set of limits is displayed along that area

Figure 12 Combined pressure and head load for container A (lightest weight).

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Lightweight Wine Bottles 20

Figure 13 Combined pressure and head load for container B (intermediate weight).

Figure 14 Combined pressure and head load for container C (heaviest weight).

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Lightweight Wine Bottles 21

Impact loading

Figure 15 Impact loading for container A Inside Surface: Section Angle = 0º (through impact point) Outside Surface: Section Angle = 43º (through hinge point)

Impact

High Stress

Stress Point

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Lightweight Wine Bottles 22

Figure 16 Impact loading for container B Inside Surface: Section Angle = 0º (through impact point) Outside Surface: Section Angle = 116.5º (through hinge point)

Impact

Stress Point

Stress Point

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Lightweight Wine Bottles 23

Figure 17 Impact loading for container C. Inside Surface: Section Angle = 0º (through impact point) Outside Surface: Section Angle = 47º (through hinge point)

Impact

Stress Point

Stress Point

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Lightweight Wine Bottles 24

Appendix B: Physical Testing Data & Results Results of the physical testing carried out at the GTS technical facility are given below. Caution must be exercised in making comparisons between modelled and physical data as the latter is greatly influenced by the degree to which the test samples have been handled prior to the testing.

Sample Number

Impact Strength

(cm/s)

Sample Number

Impact Strength

(cm/s)

A1 150 A11 150A2 150 A12 140A3 240 A13 170A4 170 A14 120A5 230 A15 190A6 150 A16 220A7 170 A17 180A8 120 A18 160A9 260 A19 180A10 240 A20 180Min 120 Min 120Max 260 Max 220

Average 188 Average 169Std Dev 49.4 Std Dev 28.1

Sample Number

Mould Number

Sample Number

Mould Number

B1 160 B11 180B2 120 B12 280B3 120 B13 250B4 140 B14 >320B5 150 B15 220B6 130 B16 300B7 140 B17 220B8 200 B18 >320B9 130 B19 280B10 120 B20 260Min 120 Min 180Max 200 Max >320

Average 141 Average >263Std Dev 24.7 Std Dev >46.2

90° To Mould Seam90° To Mould Seam90° To Mould Seam90° To Mould Seam

Mould SeamMould Seam

Mould SeamMould Seam

HEEL IMPACTS SHOULDER IMPACTS

Bottle A Bottle A

90° To Mould SeamMould Seam

90° To Mould Seam

Position of Failure

Mould Seam90° To Mould Seam90° To Mould Seam

Mould Seam

Mould Seam90° To Mould Seam

Mould Seam90° To Mould Seam

Mould SeamMould Seam

Position of Failure

90° To Mould SeamMould Seam

90° To Mould Seam

Mould SeamMould Seam

Position of Failure

90° To Mould Seam

Position of Failure

90° To Mould Seam

Bottle B Bottle B

Mould SeamMould Seam

90° To Mould Seam 90° To Mould Seam

90° To Mould Seam90° To Mould Seam

No FailureMould SeamMould SeamMould SeamNo Failure

Mould Seam

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Lightweight Wine Bottles 25

It should be noted that as the bottles are of different designs and the natural contact (impact) points vary it is difficult to draw direct comparison between the 3 bottle types.

Sample Number

Impact Strength

(cm/s)

Sample Number

Impact Strength

(cm/s)C1 200 C11 170C2 220 C12 300C3 230 C13 310C4 220 C14 >320C5 230 C15 >320C6 220 C16 >320C7 220 C17 230C8 230 C18 290C9 220 C19 >320

C10 240 C20 >320Min 200 Min 170Max 240 Max >320

Average 223 Average >290Std Dev 10.6 Std Dev >50.6

HEEL SHOULDER HEEL SHOULDER HEEL SHOULDERMin 120 120 120 180 200 170Max 260 220 200 >320 240 >320Average 188 169 141 >263 223 >290Std Dev 49.4 28.1 24.7 >46.2 10.6 >50.6

90° To Mould SeamMould Seam

Mould Seam Mould Seam Mould Seam Mould Seam

Mould Seam 90° To Mould Seam90° To Mould Seam

Position of Failure

Bottle C

.

Bottle C

90° To Mould Seam

90° To Mould Seam Mould Seam Mould Seam

Bottle A Bottle C Bottle C

Mould Seam No Failure No Failure

HEEL IMPACTS SHOULDER IMPACTS

No Failure No Failure No Failure

Mould Seam

Position of Failure

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Lightweight Wine Bottles 26

Wall thickness measurements and check weight calculation

Bottle ID A (Light) Bottle weight 360 g

Notes Glass thickness measurements made at 15mm intervals starting +15 mm from baseAlso on 2 axes for base - 5 measurements each axis (includes centre = 9 measurement - centre common)

Q2 A (Light) Simplified calculation of weight360 (Flint) From To Height Thickness Diameter

Measuement Body 0.0 176.0 176.0 2.50 74.6Point A B C Dbase Shoulder 176.0 219.5 43.5 1.47 52.515 3.60 3.36 3.49 3.3130 4.05 3.89 3.84 3.72 Neck 219.5 283.2 63.7 2.61 2645 3.59 3.38 3.42 3.2360 2.77 2.56 2.67 2.42 Bottom 5.41 74.675 2.42 2.30 2.35 2.1690 2.30 2.15 2.22 2.02105 2.44 2.16 2.17 2.00120 2.44 2.12 2.21 2.08 Glass Volumes Height Thickness Diameter Volume Wt135 2.31 2.07 2.18 2.07 (mm) (mm) (mm) (mm3) (g)150 2.02 1.81 1.98 1.88 Body 176.0 2.5 74.6 99629 249165 1.88 1.74 1.84 1.75180 2.08 1.89 1.85 1.75 Shoulder 43.5 1.5 52.5 10219 26195 1.53 1.46 1.52 1.43210 1.42 1.51 1.42 1.43 Neck 63.7 2.6 26.0 12225 31225 2.18 2.15 2.11 2.03240 2.43 2.24 2.27 2.35 Bottom 5.4 74.6 23649 59255 3.45 3.18 3.46 3.49270 xxx xxx xxx xxx total 283 364

crown

Bottle base measurements (mm)A >> C 5.26 5.79 centre 5.74 5.15

4.94B >>D 5.46 5.6 5.66 5.2

Bottle ID B (Medium) Bottle weight 432 g

Notes Glass thickness measurements made at 15mm intervals starting +15 mm from baseAlso on 2 axes for base - 5 measurements each axis (includes centre = 9 measurement - centre common)

Simplified calculation of weightWall thickness measurements (mm) From To Height Thickness Diameter

Measuement Body 0.0 171.0 171.0 2.84 77Point A B C Dbase Shoulder 171.0 211.0 40.0 3.01 55.515 2.81 3.56 3.73 3.1630 2.63 3.69 3.43 2.80 Neck 211.0 280.0 69.0 3.50 2745 2.62 3.02 2.88 2.6060 1.62 2.50 2.33 2.01 Bottom 6.54 7775 2.20 3.26 4.03 3.5390 2.54 3.58 3.40 3.37105 2.45 3.24 3.29 2.93120 2.40 3.03 3.07 2.63 Glass Volumes Height Thickness Diameter Volume Wt135 2.25 2.77 3.12 2.36 (mm) (mm) (mm) (mm3) (g)150 2.05 2.68 3.21 2.20 Body 171.0 2.8 77.0 113177 283165 1.81 2.70 3.66 1.83180 1.99 2.94 4.04 2.06 Shoulder 40.0 3.0 55.5 19852 50195 2.35 3.23 4.45 2.54210 2.96 3.07 3.43 3.05 Neck 69.0 3.5 27.0 17842 45225 3.11 3.45 3.69 3.32240 3.35 3.76 3.85 3.49 Bottom 6.5 77.0 30448 76255 xxx xxx xxx xxx270 xxx xxx xxx xxx Total 280.0 453

crown

Bottle base measurements (mm)A >> C 5.61 7.00 centre 7.05 6.18

7.06B >>D 6.02 7.05 6.93 5.94

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Lightweight Wine Bottles 27

Bottle ID C (Heavy) Bottle weight 475 g

Notes Glass thickness measurements made at 15mm intervals starting +15 mm from baseAlso on 2 axes for base - 5 measurements each axis (includes centre = 9 measurement - centre common)

Rockware 3219 Simplified calculation of weight475 (Green) From To Height Thickness Diameter

Body 0.0 152.4 152.4 3.09 76.1A B C D

Shoulder 152.4 203.4 51.0 2.72 54.115 3.44 3.90 3.89 3.2030 3.05 3.36 3.50 2.85 Neck 203.4 299.3 95.9 3.98 2645 2.41 2.67 3.12 2.3860 1.97 2.67 3.05 2.18 Bottom 6.26 74.675 2.49 3.65 4.11 2.6790 2.66 3.64 4.08 3.06105 2.71 3.44 3.78 3.14120 2.73 3.31 3.70 3.10 Glass Volumes Height Thickness Diameter Volume Wt135 2.62 3.13 3.54 2.97 (mm) (mm) (mm) (mm3) (g)150 2.45 2.90 3.29 2.63 Body 152.4 3.1 76.1 107893 270165 2.30 2.68 2.98 2.39180 2.33 2.68 2.84 2.33 Shoulder 51.0 2.7 54.1 22368 56195 2.94 3.12 3.13 2.88210 3.40 3.33 3.24 3.25 Neck 95.9 4.0 26.0 26383 66225 4.40 4.42 4.33 4.24240 4.30 4.25 4.32 4.32 Bottom 6.3 74.6 27346 68255 4.20 4.09 4.26 4.24270 3.90 3.67 3.63 3.72 total 299 460

Bottle base measurements (mm)A >> C 5.89 6.84 centre 6.56 5.85

5.92B >>D 6.59 6.84 6.71 5.10

Page 31: Wine Bottle Strength May'08

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