Cushion Impact Analysis
Shock Blocks are engineered for the ultimate in shock absorbtion and impact performance. But don’t just take our word for it, read the text of an independent test report provided below.
The purpose of this testing is to develop cushion curves for molded pulp corner cushions. In addition, the information will be compared to the cushioning abilities of a corrugated container with no additional cushioning.
Testing was conducted according to the Transmitted Shock Characteristics of Foam-in-Place Cushioning Materials, ASTM D4168-95 specification.
Prior to and throughout testing the samples were held at ambient conditions approximately +23°C and 50% relative humidity. The corner protectors and boxes were tested according to ASTM D4168-95 (modified for pulp cushion testing) on the shock test machine using a test block and weights.
The cushions were placed in a 32 ECT C-flute corrugated fiberboard all flaps meet (AFM) box under each base corner of the test block. Cushions were impacted from an equivalent drop height of 12 inches (96 in/sec) and 24 inches (136 in/sec). For the empty box testing the test block was placed directly in the zero clearance box with no additional corner protection. For the corner protector testing the test block was placed in the appropriate clearance box (1/2”, 5/8”) with four corner protectors.
After each set of impacts, the cushions and box were changed, and weights were added to the block to increase the static loading. The transmitted deceleration was measured using an accelerometer placed near the center of the block fixture.
The moisture content of each type of corner was determined. The C500 corners had a moisture content of 8.3%. The C625 corners had a moisture content of 6.5%
Background and Test Procedures
- The purpose of testing was to determine and compare the dynamic cushioning characteristics of the molded pulp corner protectors versus the corrugated fiberboard boxes.
- To conduct the test, the corner protectors were placed in the box under the test block fixture provided by Western Pulp. The test block and box were fastened to the table of the shock test machine in a manner that allowed deflection but restricted excess rebound.
- The impact velocity change was programmed into the shock test machine equivalent to both 12-inch and 24-inch drop heights at 96 in/sec and 136 in/sec respectively.
- The surface area used to calculate the static loading for each of the cushion systems was:
- No Corners - 182.3 square inches (the area of the base of the test block)
- C500 - 18.4 square inches (the area occupied by 4 corner pads)
- C625 - 26.8 square inches (the area occupied by 4 corner pads)
- Metal weights were added incrementally to increase the overall weight of the block thus changing the static loading. Several different static loadings were used for each cushion system to develop the cushion curves. To calculate the static loading the weight of the block and weights was divided by the total surface area of 4 corners that were placed in the bottom of the box. For the boxes with no corners the total area of the bottom of the box was used to calculate the static loading. Refer to the table below for each loading used for the curves.
- The transmitted deceleration levels were measured using a response accelerometer mounted on the fixture. This data shows a typical time domain deceleration versus duration pulse relationship.
- The results of this test sequence were displayed in the form of a cushion curve showing a transmitted deceleration level versus static loading relationship. The data was divided into three separate curves for each type of cushion; an initial impact curve and a curve for the average of the 2nd and 3rd through 5th impacts as suggested by the ASTM D4168 test standard. This test followed the general guidelines of ASTM D4168-95.
Conclusions and Recommendations
The molded pulp corners responded to the first impacts at the static loadings in a similar fashion. There were higher transmitted deceleration levels for the 2nd and average of the 3rd through 5th impacts. The no corner boxes responded to the first impact, 2nd impact and average of the 3rd through 5th impacts at the static loadings in a similar fashion with higher deceleration levels and a limited static loading range over which the box with no corner protection was effective at cushioning the impact. For the first impacts from the 12” drop height the C500 corners provided 4 times more cushioning than the package with no corners from the same drop height. Over all for the 12” drops the corner (C500, C625) pads provided greater protection than the box with no corner pads. The boxes with no corner protectors had a very narrow range of static loading over which they were effective. All of the static loadings were below 1 psi which means that the cushioning properties of the box work for very light weights only. The corner protectors had a static loading range of 0.68 psi to 6.8 psi. The boxes with no corner protectors also had higher deceleration levels than the boxes with the corner protectors at both the 12 inch and 24 inch drop heights. Deceleration levels can be broadly defined as amount of energy transmitted into the product.
This information does not reference Western’s C750 prototype part which is included in the full report.
Testing Provided by Westpak, Inc.
Westpak, Inc. is a full service ISO 9001:2000 Registered, Environmental and Package Test Laboratory. Their founding philosophy is that “integrity is the priceless ingredient in testing.” Learn more about Westpak and the services they offer. Package Drop Testing: The Do’s And Don’s Of Package Impact Performance Tests Read a paper (pdf) prepared by Herbert H. Schueneman, Cp-P, Mh and Mark Escobedo. This paper discusses some of the issues involved with the development and testing of a protective package system. Issues related to impact or shock are specifically addressed. The purpose of this paper is to assist those who design and test protective packages. Many elements go into a protective package system, some of which have a large effect on the ability of the package to do its job. Presented by: Westpak, Inc.