The Center for Packaging and Unit Load Design (CPULD) at Virginia Tech recently completed its first Crate Design and Performance short course. As part of those lab tests and discussions with practitioners, the experts at the CPULD discovered some interesting lessons that anyone who designs wood boxes or crates should know.
Dr. Laszlo Horvath, the director of CPULD and the main instructor of the course, recently sat down with Pallet Enterprise to discuss what they learned and how it can change how crate manufacturers design their products to improve performance and reduce costs.
PALLET ENTERPRISE: What did you learn from the first class that will inform future classes?
Laszlo Horvath: We learned two things that surprised us. First, is how many people design crates without any calculation tables or guiding principles. They design, spec and build them based on experience. One thing that even participants who have been building crates for a long time admitted is that they don’t know how to really size any of the components.
PALLET ENTERPRISE: So, were they underdesigning it or overdesigning it?
Laszlo Horvath: The answer is both. When they had failures, they were under designing the crate. I showed the attendees different pictures from lawsuits we had seen in the past. Obviously, those all had some mistakes in them. Many of the failures occurred at the joints and corner connections. They were mistakenly nailed to the end grain not the side grain. This is especially true for assemblers who don’t have any wood experience or background.
Also, there is the hidden cost of larger components and overdesigning crates. A lot of crates are overdesigned because there is no way to really know for sure if a crate will work without extensive testing.
PALLET ENTERPRISE: And unlike with pallets where there is Best Pallet ™ and Pallet Design System™ software, there are not robust design and simulation tools to help validate specific designs?
Laszlo Horvath: Correct.
PALLET ENTERPRISE: Have you developed rules of thumb based on wood science that you’re teaching?
Laszlo Horvath: During the course, we went through the military specs and used the military’s principles and calculations to size the components. The Department of Defense defined these parameters for their own rigorous needs, which are way overdesigned for most commercial applications. They have tables that we have adapted to use for most supply chains.
My colleague Dan Hindman, who’s a structural timber engineer, basically showed them how they can calculate and size components.
Because we had members of the military, there were a lot of really interesting findings. Upon further review, we learned that many of the specs date back to the Vietnam War, and they are not really applicable anymore.
PALLET ENTERPRISE: What is something you are planning to add to the courses in the fall?
Laszlo Horvath: One thing we are going to spend more time discussing is dunnage. We will explore more on vibration and shock absorption. In addition to just the crate, we can design the internal holding mechanisms for your product. This helps make sure that the product is not damaged within the crate.
PALLET ENTERPRISE: How did the attendees say the first course really helped them?
Laszlo Horvath: Yeah, one thing that participants discovered is how important nails are to the success of the build. For example, we did a compression test in a lab on a completed crate. And we designed it in a way that in one experiment we loaded it with a smaller load on top because I showed them how less-than-a-truckload delivery system will use their crates. So, crates that they designed for those systems are going through a lot harsher distribution system and sometimes will have similar crates on top. Sometimes it’s going to have smaller boxes on top. So, we had a smaller box, and we crushed the crate so that the whole top broke. But then, we went to the next experiment where we loaded it through the sidewalls. The crate should have been so much stronger. What we found is that the plywood started to bend and then pulled all the nails out from the sidewalls, and the crate failed really, really early.
It was really interesting because we didn’t expect it. The nail that we happened to use was not a particularly great quality nail. We clinched it, but it wasn’t a particularly strong nail. The nail bent backwards when being clinched, so it pulled out of the wood. We had some discussions on that failure. Sometimes the cause was the contents hitting the side wall or moving inside of the crate. We talked about solutions, such as internal bracing or dunnage. When we put screws into the crate, the load capacity went from 1,900 pounds to 20,000 pounds for the same exact crate design.
PALLET ENTERPRISE: What did you learn or discuss about diagonals when it comes to crate design?
Laszlo Horvath: Everybody knows that you have to use diagonals, but it’s like what is really the effect of those diagonals on stability. So, we had a crate without the diagonal bracing, and then we put it into our stability tester that we have. We impacted it, and then you could see that the whole structure collapsed. When we put the diagonal bracing in, the structure was like a brick block afterwards. It didn’t budge at all.
PALLET ENTERPRISE: Did you cover different hinge or corner connecting components?
Laszlo Horvath: Not for this first-class. But, for the next one we are going to do more laboratory demonstrations of different types of fasteners and connecting the corner structure of the crate together in various ways.
PALLET ENTERPRISE: When you talked to attendees, what was their feedback on the course?
Laszlo Horvath: Attendees said the information covered was very helpful, and they would recommend the class to others. Participants particularly liked the feedback they received on their crate designs and processes. This really helped them improve what they are already doing. They also enjoyed the visual analysis and lab tests that helped them better understand the dynamic forces acting on crates, as well as the new guidelines they can use to optimize future designs.
PALLET ENTERPRISE: How often will this class be offered in the future?
Laszlo Horvath: The goal is to offer the class once per year. We are offering it again this fall (See sidebar) because we had so much interest. We actually had to shut down the registration because we ran out of space for the first class. We already have significant interest in this fall class. So, if anyone wants to participate, they should go ahead and register quickly.
