Nail quality and characteristics have a direct bearing on the durability of wooden pallets. The right nail can extend the life of the pallet, reducing time and money spent on repairing the pallet. A more durable pallet also does a better job of protecting the customer’s product.
In addition, computer software, such as the Best Load™/Best Pallet™ pallet design software, has the capability to analyze inputs for fastener durability and performance characteristics. This fastener analysis can also be done by the Pallet Design System (PDS)™. Both programs are commonly used by pallet companies to simulate real world testing of specific pallet characteristics.
A report by the Virginia Tech Center for Packaging and Unit Load Design examines the features and qualities of nails that contribute to pallet durability. It looks in detail at fastener withdrawal resistance and fastener shear resistance, two pallet damage factors that are directly influenced by the fasteners.
Think of withdrawal resistance as the nail’s ability to secure a deck board to a stringer – to resist withdrawal and the separation of the deck board from the stringer.
Shear resistance is a different quality. Think of shear as a force applied to a deck board to push it or slide it along the stringer. When a forklift impacts a leading-edge deck board, it applies shear force to the deck board.
The center staff used the Best Load program to analyze and compare two nails. They used the fastener durability input and fastener input analysis functions, which allows a user to enter specifications of several nails and compare their durability. They compared 11.5-gauge bulk nails and 12.5-gauge collated nails in standard GMA pallet. The 11.5-gauge nail, made of thicker or larger diameter wire, had better resistance to shear and withdrawal compared to the 12.5-gauge nail. Other features that were compared included wire diameter and thread diameter, thread length and nail length, helix count, MIBANT angle and thread angle, and flute count.
A pallet can be rated according to how quickly it is expected to sustain damage from use – the relative damage rate – as well as the severity of the damage – relative damage severity.
The results of the Best Load comparison showed that a pallet assembled with the 11.5-gauge bulk nails has significantly better durability than a pallet constructed with the 12.5-gauge nails. The pallet built with 11.5-gauge nails would last twice as many trips before needing repairs and also twice as many trips before needing to be replaced. Also, the pallet with 11.5-gauge nails had lower relative damage rate values as well as lower relative damage severity. These values for lower relative damage and damage severity determined that the pallet made with 11.5-gauge nails is 85.6 percent more durable than the pallet made with 12.5-gauge nails.
Besides determining the 11.5-gauge nail would improve pallet durability and double the life of the pallet compared to the 12.5-gauge nail, the study reached other conclusions.
- Better fasteners improve the durability of pallets, which saves time and money used to repair the pallet and better protects the product.
- Fastener withdrawal resistance and fastener shear resistance are major factors in pallet durability.
- Fastener withdrawal resistance is most affected by wire diameter, the difference between thread diameter and wire diameter, and the number of helices per thread length.
- Fastener shear resistance is most affected by wire diameter.
The study tapped into research in the 1980s that developed a model to determine when a pallet needs to be repaired and an economic model to predict the overall durability of a pallet. The earlier study also found a correlation between damage severity and damage rate to the lifespan of a pallet.
Earlier research also demonstrated that fastener withdrawal resistance increases with increasing wire diameter, press out (the difference between thread-crest diameter and wire diameter), and the reduction of thread angle. Thread crest diameter, the number of helices, and thread length also play an important role in determining the overall withdrawal resistance of a nail. In addition, fastener shear resistance increases with increasing wire diameter.
Editor’s Note: To read the complete study, go to: www.unitload.vt.edu/education/white-papers/6-wp-effect-of-fastener-quality-on-pallet-durability.html
