The Impact of Shape on Glass Weight
- A round / balloon shape could be said to be the strongest and lightest glass container. The necessities of packaging dictate a flat base for stability and straight sides for a label. Given the above, a VB Stubby in its proportions and shape would be close to the best container for production.
- As the design moves beyond this optimum shape to one which may be taller, wider or more contorted (shaped) a greater amount of glass (weight) is needed to enable a minimum wall thickness needed to achieve the required strength and performance through the container’s working life.
- Taller container proportions can significantly impact glass weight. For the same capacity a tall cylinder or shaped design has more surface area than a short design of the same type i.e. more glass is required.
- A more contorted design can create a greater potential for faults to be created in the forming process. The faulty containers will be rejected by the cold end inspection. The reject / loss rate has the greatest impact on production efficiency.
- Most beverage containers are round (cylindrical). Containers containing gaseous products i.e. beer, carbonated drinks and sparkling wines have to have a round cross section to contain the pressure within. These bottles are said to be “pressure rated”
Glass container parts and functionality
From the top of the container down:
- Internal Bore - The internal form of the finish and neck of a container. As stated above the form of the bore is determined by the external configuration of the container finish and neck. The bore is most important when it is used in combination with the closure to seal the bottle. The minimum size of the bore determines the size of the filling tube and through that the speed of the filling process.
- Finish - That part of the top of the container, which interacts with the Closure to effect the sealing of the container and its contents. A single finish specification may have a number of variants with differing bead configurations to suit various container designs; these do not affect the functionality or the specification of the finish. The functional sizes of each finish are specified by single letter definitions.
- Neck Ring Bead - Set below the finish, the bead is an integral part of the glass container manufacturing process. It is used to support the parison when it is placed in the final blow mould and to move the finished container from the blow mould position to the primary conveyer. The bead can also be used in conjunction with a closure to effect Tamper evidence in the finished package.
- Neck Diameter - In combination with the shoulder, the neck of a bottle most often defines the image and style of a container. Traditional styles based on hand made bottles are recognised and often preferred by our customers and consumers. A straight conical neck profile can be used to support a label.
- Root of Neck
- Shoulder - Connecting the body and the neck of a container the shoulder also provides definition of the container image. It can be used as an area for embossing supporting the brand of a proprietary container or a label if it has a flat conical form.
- Body - Defines the Over All (OA) diameter of the container and the majority of the capacity.
- Contact to Label Panel Transition
- Label panel - A section of the container, flat in one direction, which will accept a pliable printed label - can be cylindrical or conical - on the heel, body, shoulder or neck of the bottle. The label on the panel can be protected from bottle to bottle contact to prevent scuffing by recessing the panel slightly from the overall diameter.
- Bottle to Bottle Contact Flat
- Heel or Insweep - To ease the transition between the sides of a container body and its flat base, modern designs incorporate an in-sweeping or radiused heel section. The use of a heel allows for a lower glass weight and its form is most important in the design of pressure rated containers.
- Bearing Surface Radius - The flat junction of the heel and the base on which the container rests. This section of the container is most subject to thermal shock and abrasion in production and filling. A series of small ridges called stipples are moulded over the bearing surface to minimise any damage to the container.
- Push up / Punt - All containers incorporate a raised central section (push up) in the base to prevent damage through contact and abrasion. This, as in the heel design, is most important in the design of pressure rated containers.
- Standard Engraving - Raised (embossing) or recessed (debossing) detail on the glass surface. It is used for purposes of process control, identification, legal requirement, aesthetic image and product branding. Normally engraving is not higher or lower than the surface by more than half a millimetre. A label can be applied over debossing. Raised engraving must be kept clear of any equipment and bottle-to-bottle contact during all stages of the manufacturing, filling and distribution process. Paper and self-adhesive labels cannot be applied over detailed embossing. Engraving can cover the entire surface of a container with a texture commonly termed Stipple, Knurl or Machine Knurl.
Pressure containing closures - These closures are designed to contain high pressures inside the container. They are mostly used for sealing pasteurised beers and carbonated beverages.
Used for beer and other carbonated beverage bottles. Crown seals are a low cost steel closure using a moulded polymer lining to provide a seal on the finish. Internal and external surfaces are lacquer coated and caps can be printed.
In the capper, a fluted construction in the cap skirt allows it to be crimped into a groove under the lip of the crown finish by the downward action of a ‘bell’ shaped capping tool.
Crown seals can contain carbonated products at the elevated temperatures of a brewery pasteuriser. A “pry off” crown seal requires deformation by a bottle-opening tool for its removal by consumers. Crown seals are not resealable.
Used for beer and other carbonated beverage bottles. Twist crown construction is as per a crown seal.
In the capper the downward action of the ‘bell’ shaped tool crushes the skirt’s fluting onto multiple fine threads on the glass finish, which forms threads in the cap.
Twist crown seals are removed by the consumer twisting them anticlockwise as per a screw cap. Twist crowns are not resealable.
Aluminium roll on closure - Soft drink
Used for carbonated beverages. Pressure rated roll on caps are sealed by polymer liners, which can be flowed in, moulded in, or placed as a wad in the aluminium shell (on the underside of the cap). Internal and external surfaces are lacquer coated and both can be printed.
Commonly known as ‘Roll on’, ‘Alcoa’, ‘ROPP’ or Pilfaseal closures.
The caps are applied as a plain cylindrical ‘shell’ that is positioned on and over the finish. In the capper a top and side seal is effected on the finish by a ‘redraw’ tool, which reshapes the top of the shell into tight contact with the contours of the glass, finish.
The side seal is needed for carbonated products because the pressure in the container causes the top panel of the cap to ‘Dome’ upwards eliminating the top seal.
The screw threads in the cap are formed by spinning rollers, which shape the cylindrical wall of the closure to form threads matching those of the glass finish.
Tamper Evidence - Most caps have an extra roller running horizontally, which tucks a band at the lower edge of the cap under the lower edge of the finish. A Tamper Evident system is created by either horizontal or vertical perforations in the band, which are broken when the band is expanded as the cap is removed.
Plastic pressure rated cap
Used for carbonated beverages. Pressure rated plastic caps are sealed by polymer liners, which are placed in the plastic shell. The top surface of a cap can be printed.
Plastic caps are screwed onto the glass finish in the capper. The internal shape of the cap forms the polymer liner to effect the top and side seal required for pressure retention.
A moulded plastic break away band at the base of the cap locks under the base of the glass finish to effect tamper evidence. Slots in the threads of the cap help allow escape of the free gas in the container headspace before the thread has fully disengaged to prevent the gas propelling the cap off the finish during opening.
There are many other closures used on food, sauce and non-carbonated products. Most of these are not suitable for carbonated beverages, as they can’t contain the pressure within the container.
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It is important to view some of these websites for a better understanding of the glass making process: