Question from Jesse:
Is the testing you do in your lab an ISTA test?
Thanks for the question, Jesse. It is a question that comes up often when customers send product to our lab for testing. The test protocol used in our lab is different from what is used by ISTA.
To understand the difference, let’s take a close look at our objectives. The ISTA test is a pass/fail test where a certain threshold is met, similar to Underwriter’s Lab. As an example, when you see the UL label on a product, it means that product has passed certain tests, but it DOES NOT indicate how well it performs. The ISTA test criteria was developed based on conventional methods of load containment. So, passing an ISTA test does not guarantee loads will not fail during transportation.
In contrast, we test loads to the point of failure, so the limits of load containment can be quantified. To optimize load containment, it is critical to know how much force will be necessary to cause failure. While our methods are similar, our objective is quite different.
There are several forces that act on a load during transportation. For our purpose, it is critical to apply each one separately so we can quantify its effect on the load. Some loads may be more susceptible to certain type of applied force. We incorporate three testing methods; each simulating a real-world condition. After analyzing the data that we collect from each of these tests, we optimize the load containment, focusing on the specific force that effects the load the most.
Now, let’s take a step back for just a moment and review what those forces are and how we apply them to a test load. Imagine a load about the size of your hand and it weighs one pound. Every time the truck turns, travels uphill / downhill, accelerates or brakes, the forces that act on the pallet would be similar to your hand pressing against the side of the load. If you are turning right, you would press the right side, and the opposite if you are turning left. If you are going uphill or accelerating, you would be pushing against the front of the load. If you were decelerating or going downhill, you would be pushing against the back. Most normal transportation forces generate about .5g max, which means that you would be applying about ½ pound of force (.5 x load weight). If your load weighs 2,000 pounds, that would be 1,000 pounds of side force that the stretch film must contain. That force is applied and removed over a relatively long period of time (not instantaneous). Although if you are riding in that truck, it may seem instant to you. From a previous Ask Steve, I talked about inertia and momentum (a body remains in motion until a force equal and opposite acts upon it). When the driver turns the wheel, steps on the gas, or brakes, the force applied to the load is limited by the traction the tires provide and dampened by the movement of the suspension. Even the most abrupt changes the driver makes take some fractions of a second to transfer to the load. In contrast, trucks backing hard into dock bumpers, rail car coupling, and trailers running up over curbs are examples of impact forces and they are quite different. An impact force can generate 7g or so, and do so in less than 30 milliseconds, less than a blink of your eye. Again, if our load weighs 2,000 pounds, we have just applied 14,000 of side force that the stretch wrap must contain.
Our Transportation Simulator will generate the “normal forces” on the load, up to .84g by tilting the pallet, allowing gravity to create the side force. We begin with a nominal tilt and increase by a couple of degrees until the load fails. Vibration over a range of frequency can be applied during the test to simulate road vibration. We scan the side of the load to create a digital image, so we can identify where movement occurs with each successive test. We also video the test, so each frame can be meticulously analyzed.
For impact, we place the pallet on a sled which is accelerated by gravity over a distance to a point of impact. We can generate over 40g of force with this test in a few milliseconds, although no load will survive that. We start with an impact of about 1.75g and increase to a point of failure. Profile scans and video allow us to analyze data. In addition, we have data loggers that measure impact force and velocity.
The final test is a horizontal acceleration test. In this test we place the pallet on a sled and accelerate it using precise hydraulic controls. This test simulates panic braking where the drive locks up the wheels. We usually begin at about 2.5g and increase from there. As with the other tests, we capture the profile, video, g force applied and accelerate/velocity.
Once the load is fully optimized and we have collected all the data, we publish a comprehensive report of our findings, conclusion, and recommendations. This report also includes all the data we collected.
So, while the test methods we use may be very similar, how we use them is very different, and is a critical tool in optimizing load containment, reducing loss from unnecessary damage while using only the amount of stretch film you need.
As always, thanks for asking!