SOP: Measurement of Verticality of Glass Containers
GIFSQ — Global Institute for Food Safety & Quality
Principle
In a cylindrical bottle, the centre of the finish is intended to lie in the vertical plane through the joining faces of the body mould, vertically above the centre of the base. The horizontal distance by which the finish departs from this position is the non-verticality (sometimes called verticality or obliquity). It is measured indirectly with a dial gauge, by rotating the bottle on a lathe, or by the ISI assembly for aerated-water bottles.
Apparatus required
- Dial gauge
- Self-centering chuck of a lathe (for the rotation method)
- Flat plate with pillar, “V” block, and dial indicator (for the ISI aerated-water bottle assembly)
Procedure
Indirect measurement (general method)
↓
Measure the horizontal distances A₁ and A₂ between the side of the top of the bottle neck and the lowest vertical part of the body, on two opposite sides
↓
For symmetrical bottles, the deviation from verticality in the two directions is + (A₁ − A₂) and + (B₁ − B₂)
↓
For unsymmetrical bottles, measure the design values of A₁, B₁, etc., and calculate the deviations
Rotation method
↓
Locate the base of the bottle in a self-centring chuck of a lathe and rotate it
↓
The centre of the finish moves in a circle whose radius equals the non-verticality
ISI procedure for aerated-water glass bottles
↓
The bottle passes the verticality test when: the bottle stands on its base with the sealing surface parallel to the base, and a vertical line through the centre of the circle formed by the inside neck opening passes through the centre of the circle described by the bottom (resting) surface
↓
Fill the bottle with water and place it on its base on the flat plate of the test assembly
↓
Adjust the “V” block mounted on the pillar so that it contacts the outer diameter of the bottle and its measuring point contacts the outer edge of the bottle neck
↓
Rotate the bottle, keeping the body always in contact with the “V” block
↓
Note down the maximum deflection on the indicator — the variation in verticality of the bottle is half of the total deflection shown
Interpretation
- The verticality tested by the ISI method should not vary more than 2.5 mm.
- An empirical tolerance limit of 0.13 mm per cm of bottle height is found satisfactory — e.g., a 27.5 cm bottle may be up to 3.58 mm out of line; since the bottle is positioned half-way up its height at filling, the effective deviation at the filling head is half of this (1.79 mm), which any machine can tolerate.
- The deviation formula (A₁ − A₂) is read from OCR-garbled print — verify the divisor against the physical book before publishing (a ½ factor may be present in the original).
References
Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.
Specifications for Aerated Water Glass Bottles, Crown Cork Type, IS: 1107-1974.