TL;DR
Uneven container walls usually trace to the plunger arriving at the wrong point in the cycle. Check the plunger timing against the section timing diagram and verify the plunger air cylinder operation.
What you might see
- containers with uneven wall thickness
- gob not centered on the blank mold
- plunger contact time out of specification
- reject rate elevated for parison shape defects
Likely causes
Plunger air cylinder worn, reducing stroke speed and causing late plunger contact
Plunger timing cam or controller setting shifted from the design value
Plunger guide worn, causing radial deflection during the press stroke
Plunger tip damaged or worn, creating an off-center parison
Required tools
- Section timing diagram for current container
- Caliper for container wall thickness measurement
- Heat-resistant gloves and face shield
- LOTO kit
Safety first
- Glass gobs are above 1000 degC. Use heat-resistant gloves and face shield when near the blank mold area.
- Lock out the gob delivery and section drive before any manual inspection inside the section.
- Thermal radiation from the hot end. Use appropriate PPE throughout.
Procedure
- 1
Stop the affected section and lock out the gob delivery and section drive.
Warning: Glass IS machines involve high-temperature glass gobs above 1000 degC. Use heat-resistant gloves and face shield when working near the blank mold or gob delivery area. - 2
Read the current plunger timing setting from the section controller and compare to the design timing diagram for this container.[1]
- 3
Observe the plunger stroke using the slow-motion or strobe mode if available. Confirm the plunger reaches full contact at the correct timing point.[1]
- 4
Measure the plunger stroke length manually after locking out the section. The stroke should match the specification for the mold in use.
- 5
Inspect the plunger guide for radial play by hand. Visible radial movement indicates a worn guide.
- 6
Inspect the plunger tip for chips, wear, or deposit buildup that could offset the gob.
- 7
After correcting the timing or replacing the plunger, run 50 trial containers and check wall thickness uniformity.
Sources
Bucher Emhart Glass Bucher Emhart NIS / FlexIS IS (Individual Section) Machine general technical documentation, Bucher Emhart Glass
General IS machine operation and maintenance documentation, plunger mechanism timing and inspection procedures (general)
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