Product defects caused by molds are varied, with many reasons behind them. They can generally be summarized as mechanical defects, temperature-related defects, molding process defects, and mold-related defects.
Common mold-related defects include the following six types:
1. Insufficient Capacity:
Why❓
The mold cavity does not match the standard size tolerance.
Design capacity is too low.
Bottles are overweight, leading to lower capacity.
Insufficient blowing of the bottle.
This is what usually we do:
Check the bottle body size tolerance.
Adjust the mold cavity size to increase bottle capacity.
Reduce material weight.
Adjust the positive blowing air pressure and time to ensure proper and unobstructed venting.
2. Excessive Capacity:
Why❓
The mold cavity does not match the standard tolerance, or prolonged use causes excessive wear and enlargement of the mold cavity.
Design capacity is too high.
Bottle deformation.
Bottles are too lightweight.
This is what usually we do:
Check the cavity size tolerance.
Modify the design to reduce bottle capacity.
Adjust process parameters, especially positive blowing air pressure and time.
Control and verify material temperature.
3. Seam Line Coarseness, Sharpness, or Corner Issues:
Why❓
Poor seam line fit.
Old molds with severe wear.
Molds not properly closed, or seam lines have broken glass or debris.
Improper settings for positive blowing air pressure and time causing mold opening.
Damaged mold seam lines or corners.
Asymmetry between the initial mold and final mold axis, resulting in double seam lines or misalignment.
This is what usually we do:
Check the seam line fit tolerance.
Replace with new molds.
Inspect switch mechanisms and remove broken glass and debris.
Reduce positive blowing air pressure and adjust blowing time to prevent premature mold opening due to excessive pressure or delayed mold opening due to prolonged blowing.
Replace damaged molds (frequently damaged areas include the edges and corners of the initial mold, neck edges of the final mold, edges between the final mold and mold bottom, and seam lines).
Correct the alignment between the initial mold and final mold axis.
4. Deterioration of Bottle Surface Smoothness:
Why❓
Prolonged mold use leading to surface oxidation and peeling.
Accumulation of dust on mold cavity lubricating oil or coating.
Poor lubrication.
Changes in material temperature or shape.
This is what usually we do:
Replace molds.
Remove accumulated dust and, if necessary, clean or replace.
Apply lubricating oil or coating to the mold as needed.
Adjust material temperature and shape.
5. Bottle Neck Size Tolerance Non-compliance:
Why❓
Small trumpet mouth diameter, unreasonable design of punch dimensions (straight position and mouth ring).
Flared mouth, excessive material weight, or low punch loading position.
Gap, light material weight, or inadequate punch pressure.
Oval mouth, material expansion, improper mold opening leading to deformation (other process-related reasons).
Bulging neck, excessive forming pressure, inappropriate blowing head and blowing tube, material expansion.
Deformity, poor fit between punch and initial mold, material expansion, inappropriate machine speed (other process-related reasons).
Insufficient threads, mold cavity accumulation of dust, oil stains, broken glass (other process-related reasons).
Other temperature-related, mechanical, or process-related reasons.
This is what usually we do:
Redesign or modify punches.
Adjust material weight, raise punch loading position, and adjust loading time.
Increase material weight and punch pressure.
Properly reduce mold opening speed and aperture, reduce material temperature, and strengthen mold lubrication.
Reduce positive blowing air pressure, adjust blowing head and tube.
Correct punch and initial mold fit, reduce material temperature, adjust machine speed.
Clean mold cavity of dust, broken glass, and oil stains; replace if necessary.
Address other temperature-related, mechanical, or process-related defects.
6. Uneven Thickness:
Why❓
Unreasonable design of initial mold cavity and punch (especially for press-blowing).
Excessive or insufficient stretch.
Machine speed too fast or too slow.
Material weight too light.
Inappropriate material temperature or shape.
Other process-related or mechanical reasons.
This is what usually we do:
Correct initial mold cavity and punch to improve glass separation.
Shorten the excessive stretch by shortening the length of the initial mold cavity or using line pin or blow pins. Use deeper blow pins when the stretch is too short. Simultaneously, appropriately reduce molding machine speed and raise material temperature.
Adjust various molding process times and machine speeds, especially the "reheat" process.
Strictly control material weight.
Control appropriate material temperature and shape.
Address other process-related or mechanical issues.
Designing glass bottles is a complex process. In China, glass mold design is primarily based on experience and manual design, lacking mature design theories. Moreover, there is little industry communication and collaboration among manufacturers.
In the past decade, the United States, Germany, and others have developed software for glass mold design. This software, based on CAD systems, facilitates bottle and mold design and modification to meet requirements. It provides clear and precise two-dimensional engineering drawings and three-dimensional solid models of bottle shapes and mold components, improving work efficiency and accuracy. Therefore, enhancing mold design and manufacturing levels and utilizing computers for glass mold design have become increasingly urgent and necessary.
For more insights into glass mold design and manufacturing, visit De Varo Packaging.
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