Engineering Strength and Durability into Transit Cases

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Transit cases lead hard lives.  They bang together in the backs of trucks, are often dropped, and take knocks from all directions. Yet, users expect them to shrug off this abuse, protect their delicate contents and be as light as possible.  Case designers tackle these conflicting requirements in three ways.

1. Material selection

Lightweight polymers are the materials of choice.  Polymers have a good price-to-performance ratio.  They insulate well and are waterproof and chemically inert.  They form in the mold readily keeping manufacturing costs down.  However, as a sheet, polymers bend easily and offer little stiffness for case contents. The solution is to design rigidity into the case as shown in the video “Pelican Rotomold Case Durability”.

2. Rigid design

A sheet of paper is pretty insubstantial, but a few folds turn it into an effective dart. It’s the same principle as the ‘I’ cross-section form of steel beams.  Bending a sheet through 90 degrees creates stiffness along the bend.  The taller the vertical section the stiffer the beam. This is why, while a metal sheet deflects readily, the beam is immensely stiff.

Transit case designers use this approach in engineering high strength-to-weight ratio containers. Deep ribs increase case stiffness many times creating a lightweight yet very stiff case.  Just like the ‘I’ beam girder, walls resist bending.

In the same way, rounding-off corners strengthens them against impacts.  And, it makes the case easier to mold.  Anti-shear blocks around the closure help prevent lids from being knocked off.

3. Recessed fittings

The ribs create recessed areas on each face. In a quality case, the designer places hardware — handles, tie-down rings, latches and hinges — in these regions where exposure to impact damage is minimized.

Hardware should not secure directly to the polymer as it could rip out. A better approach is to have the fasteners go through the case to metal inserts mounted in the interior. This technique spreads the load over a larger area to support higher forces. It’s more expensive, but it helps ensure years of service.

Larger cases are designed to be lifted by pallet or fork truck. These sizes have additional reinforcement to prevent damage where forks are inserted.

Rugged and lightweight

When evaluating a transit case, look closely at how it’s designed. A lightweight but rigid structure will endure abuse while protecting precious equipment for a long time.

Written By

Kelvin Aist has designed and sold cases and packaging solutions his entire career. He frequently blogs for Case Advisor.

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