Investigation into the thickness of LLDPE rolls used to manufacture liquid bulk containers

Introduction

A manufacturer of a liquid bulk containers was experiencing splitting of their containers leading to significant losses (material transported, as well as financial).

One Eighty sampled several of the quarantined rolls of LLDPE and performed various tests to determine the possible cause of the failure.

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Investigation

Background
Liquid Bulk Containers transform a standard shipping container into a non-hazardous bulk liquid transportation system and offers a reliable solution for transporting bulk liquids.

These containers are manufactured from heat welded liner low density polyethylene (LLDPE) tubes (3.8m in diameter). Due to the inertness of the LLDPE various liquids can be transported without fear of contamination.

These liquids can be anything from vegetable oils and beverages to fuels and pharmaceuticals.

These containers are only used once and once emptied, the LLPDE is recycled.

Experimental approach
One Eighty used several techniques to test the rolls but one specific test showed a unique trend for all the data that was recorded and plotted. This test was ASTM 5199 – Standard Test method for Testing the Nominal Thickness of Geosynthetics.

Sample Preparation:
100mm wide strips were cut of the end of the rolls in question. The strips were labelled and matched with the corresponding roll number.
These strips were laid flat and 16 samples were cut (100mmx100mm) from the strips – 8 from the “top” and 8 from the “bottom” of the strip.
The objective was to compare the results of sample no 1 on each of the strips to determine the consistency in the thickness of the material on the diameter of the roll. A total of 1696 samples were measured for thickness.

 

What We Found

Results

The results showed that 8.3% of the samples were less than 0.914mm in thickness (Product specification for this LLDPE).

It was also found that 1.8% of the samples tested were of a thickness of below the average minus 2 times the standard deviation. The average thickness of these samples was measured to be 0.840mm.

By comparing the position of the samples of each of the rolls with the individual rolls, it was found that there is a band of thinner material running along the length of the roll.

Closer inspection of the splitting incidents recorded showed that they occurred in the regions were the thinner material was recorded.

Conclusion

  1. The rolls in question (although the average thickness was above the nominal thickness of 0.914mm) had a definite weaker region running in a band along the length of the roll.
  2. Due to the pressure exerted on the bladder by the internal liquid, there is a higher likelihood of failure present in these rolls.

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