Comparison of Load-Bearing Capacity: An IIT Roorkee research project

For the last three years, Stelda Packaging has been working with the Department of Packaging Engineering, IIT Roorkee, as part of the MTech thesis, where the students conducted studies to understand the behaviour of CFC boxes under point loads.

The studies, conducted in two stages, found that uneven load, caused due to irregular stacking, is the reason behind damages of boxes and products in transit.

The study also found that boxes sealed with Stelda case sealing machines were more effective in reducing these damages than the regular tapes.

Stelda is an acronym for security, tamper evidence, low damages in the application of tertiary packaging. The range of case sealers and case packers made by Stelda are designed and developed with indigenous expertise in order to address the various challenges in the supply chain, as the name suggests. These machines can handle boxes ranging from 200x200x200-mm to a maximum size of 650x500x500-mm. The Stelda range of case forming and sealing machines offer multiple sealing options such as hotmelt adhesive and a hybrid sealing with a combination of glue and tapes.

In the industry for more than 25 years, the parent organisation of Stelda, Impel Services –Welbound Group has its manufacturing facility in Bengaluru with four major regional offices and 16 sales and service centers. A leading manufacturer and supplier of machines for book manufacturing in South and Middle East Asia, Impel services clients in 300 districts, and has a strong domain understanding of adhesion and surfaces in book binding.

Damages due to uneven loads
CFB boxes are used to transport goods from factories to different distribution points. These are to be ideally designed to carry stack-loads during storage and transit. However, there are many challenges in logistics, leading to building high factors of safety. The challenges include boxes of different sizes and weights getting stacked one above another during distribution. As a result, point loads lead to damages of boxes with products inside.

The box acts as the first layer of protection against the load, but once the deflection of the top surface increases, the load comes on directly on to products, resulting in losses for brands.

The case study
In 2019, Impel sought help from the Department of Packaging Engineering, IIT Roorkee to study the impact of point loads on shipper cartons in transit. The department agreed to take up the project as part of its MTech thesis research programme, and deputed students for this study.

The impact of point loads was studied by simulating the situation using ANSYS structural engineering software. Models of CFC boxes and sealing methods were created by selecting the type of liner material, flutes, hotmelt adhesive and tapes available from ANSYS library.

Both the induced stress and the deflection due to the loads were arrived at. Then these results were compared with lab tests.

The study carried out by IIT Roorkee simulated the stress induced and the deflection generated on the top of a CFB box against a point load using ANSYS structural analysis software.

In the study, tape sealed boxes showed more induced stress than glue-sealed.

The lab tests included box dimensions of 370x200x200-mm. Two sealing methods were used —Stelda hotmelt adhesives, and tape. The boxes were filled with not more than 10 1-litre pouches of edible oil. The imprint load area was 150x100-mm.

The test was to simulate the uneven load encountered during transit damage. The test was done in an accredited lab of an industrial research Institute.

The lab test results found that the tape sealed box has more deflection compared to HMA sealed. As the headroom in boxes are at best at 7-mm, any further deflection of the top of the box would put load onto the products, thereby damaging them. It was also found that at a load of approximately 12 kgs, the deflection of the taped box crossed this 7-mm threshold. It took a load of more than 16 kgs for the Stelda sealed boxes to reach this deflection.

The second lab test
For the second stage of the lab test, Stelda picked C-fluted corrugated boxes of the same dimensions from the same manufacturer, but of two different types of liner material (120-gsm and 150-gsm). The boxes were sealed using two different methods — BOPP taping and Stelda glue sealing.

These four types of boxes were then subjected to two types of point loads — one at the centre and the other eccentric.

The study observed the deflections of the box leading to deformation, by increasing the loads.

The study found that for the same gsm, for a deflection of 7-mm, with the load at the centre of the box, HMA sealed boxes exhibited 50% more resistance to the taped boxes. Meanwhile, 120-gsm of HMA sealed boxes could carry 37% more load than the 150-gsm taped boxes for the same deflection.

The study also found that for the same headroom of 7-mm, with load at the corner of the box, HMA sealed boxes showed more than double resistance to the tape sealed boxes due to cross directional joining of flaps. The 120-gsm of HMA sealed boxes showed more resistance than 150-gsm of tape sealed boxes.

The result justified the obvious trend in increase of load carrying capacity with increase in gsm (keeping the material properties constant) currently followed by brands in order to address challenges due to point loads.

The result
The lab tests concluded that the deflection per load in the case of glue sealed boxes is much lower than the taped ones. The glued boxes can carry more centric/ eccentric loads and resist buckling in or damaging. The 120-gsm Stelda-sealed box performed much better than the 150-gsm box sealed with BOPP tape.

Thus, the study showed that the gsm of the liner can be reduced if we change the process of sealing from taping to Stelda sealing. As a result, the cost of boxes can be brought down by 20% by changing the method of sealing.