glass bottles in production line

Quality Defects in Glass Bottle and Jars

MC Glass bottle is glass bottle manufacturer in China with over 20 years factory experience. We provide designed glass bottle and custom packaging service knowing how to manufacture glass bottle and glass jar with premium quality.

There are many advantages to use glass as a packaging material for foods and beverages. Glass is impermeable to gases and moisture vapor. This property is important for all food and beverages. Glass material is visible. The consumer can immediately see the color of the product before buying it. Although glass bottle is a common packaging material can be recycled and reused in daily lift. In the production process, finishing mold, chain marks, there are many defects need to be avoided. Quality defects can be categorized per type, area of the container where they usually occur and gravity on consumers’ health.

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Type of glass bottle defects

  • Cracks
  • Splits
  • Checks
  • Seams
  • Non-glass inclusions
  • Dirt
  • Spikes, bird cages, glass filaments
  • Freaks
  • Marks

Area of the bottle where they occur

  • sealing surface and finish area: off-set finish, bulged finish, broken finish, corkage check, neck ring seam, dirty or rough finish, bent or crooked finish.
  • neck: seam on necking parting line, bent neck, long neck, choked neck, dirty neck, punched neck, tear on neck.
  • shoulder: checks, thin shoulders, sunken shoulders.
  • body: stringy glass appearance, blank and blow mold seam, bird cage, checks, sunken sides, bulged sides, washboards.
  • heel and base: flanged, thin, thick, heavy, rocker bottom, slug bottom, baffle marks, heel tap, slug bottom, swung baffle.

Gravity of glass bottle defects consequences on people

  • Critical defects: defects which can cause serious physical damage to the final consumer of the product or when containers are handled.
  • Major (or Primary or Functional) defects): defects which prevent the container from being used or which could cause a deterioration of the product due to an inefficient closure system.
  • Minor (or Aesthetic) defects: defects of only aesthetic nature which do not affect functionality of container or do not constitute a hazard for the consumer or when containers are handled.

The following Table A reports types and a short description of the main defects and possible corrective

Actions aiming to eliminate these defects during production

Critical defects Description Corrective actions
1. Unstuck or stuck pieces of glass inside bottle Glass pieces (smaller or bigger than bore size) free or stuck inside container.
This is the most critical defects
Decrease glass or plunger temperature
Tighten the plunger adaptor to the rod of piston
Increase the exhaust hole size
Change the plunger
Optimize cooling air flow to plunger
2. Glass spikes inside A thorn of glass in the body or in the bottom of container Remove glass remains in flow head
Reduce plunger time inlet
Change shears
Decrease the speed of the machine
Slightly delay the vacuum inlet
Remove glass particles when mold is changed
3. Bird cage/bird swing A filament or a surface of glass connecting two sides of container Same as 2)
4. Finish defects (split, checks, broken, chipped, off set, bulged, unfilled, crooked, overpress susceptible of breakage, tear) Cuts, checks, incomplete filling, excessive material, tear initiations, etc., in the finish area Adjust gob temperature
Shorten plunger contact time
Change neck ring
Dehumidify blow air
Optimize mold closing time/speed
Increase gob weight or modify shape
5. Filaments A hair like string of glass inside bottle Same as 2)
6. Cracks Small fractures mainly in heel area Increase glass temperature
Increase machine speed
Stabilize Leher temperature
7. Freaks Completely distorted shape which make the container completely unusable Correct set up parameters
8. Uneven glass distribution affecting strength Thin spot in the bottle well below the acceptable thickness Decrease glass temperature
Eliminate glass temperature differences
Decrease the gob shape
Load correctly the gob
Increase hardness of parison
9. Internal dirt Foreign materials in the bottle, normally introduced during warehousing or transportation, e.g., dust, dirt, cobwebs, spiders, flies, mosquitoes, small butterflies, interlayers crumbs, etc. Introduce GMP in warehousing, packaging and transport
10. Blisters Thin skin deep blisters near or on external surface Dehumidify blow air
Main major defects
1) Dimensions out of tolerances
2) Capacity out of tolerance
1. Out of round or off gauge bore size

2. Out of shape bottle

Reduce glass temperature, reduce the hot ring temperature, reduce machine speed, clean the neck ring, verify air blow pressure, change the blow mold.
If uneven or bad distribution of glass is causing off spec capacity: correct glass temperature, verify any temperature gradient in the gob, verify cooling speed rate of blank molds
3) Seams on top or on the side of finish Visible junction line of the two half mold Adjust feeder temperature, change neck ring, reduce pressing pressure
4) Washboards A wavy condition of horizontal lines in the body of the bottle Eliminate any temperature gradient in the gob, correct shape of gob, verify setting of drop guide, verify blank design
5) Skin blisters on the body Small bubbles in the body glass Increase the level of glass in the furnace, increase the temperature on the feeder plunge, decrease the temperature of blanks and plungers
6) Small inclusion of non glass material Small pieces of refractory or not melted batch materials Causes: pieces of refractory material of the furnace falling into molten glass. Contaminated batch materials. Contaminated cullet. Flame impinging on furnace refractories.
7) Rocker bottom A sunken centre portion at the base of the bottle which makes bottle unstable when placed on a flat surface Reduce glass temperature, reduce takeout time, increase cooling time
8) Flanged bottom A rim of glass around the bottom at the parting line Adjust feeder temperature, correct bottom plate height, check blank/baffle matching
9) Orange peel appearance of external surface Orange peel-like external surface Correct the shear cut, change plunger and neck ring, reduce the oil spray, improve polishing of mold and neck ring
10)- Dirty on external surface Carbonized crumbs of foreign material on external surface Reduce oil spray on shears, clean blank and/or blow mold, reduce Sulphur content in the cullet


References And Bibliography

  • Glass containers defect – Causes and remedies – Copyright EMHART GLASS – TW0738/1191 (no date)
  • Packaging Technology – Chapter 8 – Glass containers
  • Glass in packaging – C.S. Purushothaman – CSP – TRG – AIDS – August 2008 – 1 – Power point presentation
  • Bruni Glass defects on bottles – available in

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Soda lime glass bottle are made from a mold, which has two parts. So, the appearance of the bottle surface you can find the part line of the mold. When the mold is dirty or used many times, the bottle surface will be not so good looking. The finishing mold material is alloy. The bottle-made process is complicated so find a qualified supplier can help you to focus on your product itself and the branding of the product. Just pass sourcing glass bottle job to us. MC Glass Bottle Products Company is China glass bottle manufacturer can streamline all the bottle making processes, decoration, packaging and logistic to your hand.

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