Deformation tests were performed by using decreasing gauge numbers of hot dipped galvanized mild steel stampings. With an applied tension of 6000 pounds and a chain angle of 45 degrees, eleven gauge steel plates did not deform, but as tension was increased to 8000 pounds, deformation was visibly apparent. As chain tension increases, not only does load marking become more apparent, but the tie-down assembly becomes susceptible to fracture and failure from shock load, so maintaining a tension under 6000 pounds is not only necessary to prevent load damage, but becomes a vital part of safety and load integrity.
The “Cargo Guard” was designed to accomplish several tasks. Naturally, reducing load damage is the main function, but in addition, the radiused area of “C-Guard” chain contact points allow a more uniform tension throughout the two or three segments of the chain separated by their angles. This uniformity was also observed using strain gauges. The characteristic humps on the “Cargo Guard” are to help locate the chain links during the tie-down, but in fact, serve another purpose. When the chain is drawn down to the proper tension, front to rear slippage is reduced. Instead of the chain links sliding along the corner of a load, the leading edge of the “Cargo Guard” transmits an increased force to that point of contact. Again, this was demonstrated by applying measured side forces to equally tensioned chains, installed with and without “Cargo Guards”. So, the secondary benefit of load integrity essentially becomes primary.
A variety of materials were tested for the cushion portion of the “Cargo Guard”, including nylon, high-density polyethylene, polyurethane and several natural and synthetic rubber compounds. Most worked well as a medium to distribute the tie-down load forces, and conform to the various cargo shapes, but failed in adhesion tests. (Slippage) the optimum compound was found to be a mixture of natural rubber and SBR (Styrene Butadine Rubber) which has excellent adhesion, good temperature characteristics and resistance to lubricant absorbency.