Determining a Compression Strength Requirement of Box

Transcription

1 Determining a Compression Strength Requirement of Box Mr. Ram Kumar Sunkara F C B M Distribution Environment and Container Performance The ability of a container to perform in distribution is significantly impacted by the conditions it encounters throughout the cycle. Conditions like stacking time, humidity can not be influenced. Others like, pallet patterns, overhangs, deck board gaps etc. can be influenced. We can estimate the impact of these conditions on container strength. Ram Kumar Sunkara

2 Compression Requirement It is the minimum dynamic compression strength required to provide safe stacking performance throughout the containers expected life. Typical compression strength requirement determination only considers the static warehouse portion of the distribution environment. Ram Kumar Sunkara Environmental Factors - Storage Time Under Load Storage time under load Compression Loss Multiplier 15 days 37 % loss days 41 % loss days 43 % loss days 45 % loss days 48 % loss days 50 % loss 0.50 Ram Kumar Sunkara

3 Formula for calculating Environmental Factors - Storage Time Under Load = * LN(S) Where S number of days under in storage under load Ram Kumar Sunkara Environmental Factors Relative Humidity Under Load % Rh Under Load Compression Loss Multiplier 50 % 0 % loss % 10 % loss % 20 % loss % 32 % loss % 52 % loss % 85 % loss 0.15 Ram Kumar Sunkara

4 Formula for calculating Environmental Factors Relative Humidity Under Load = -8.3*H *H *H *H+0.5 Where H is humidity in % Ram Kumar Sunkara Environmental Factors Pallet Patterns Pallet Patterns C. S Loss in % Multiplier Best Worst Columnar, aligned Negligible Columnar, misaligned % Interlocked % Overhang % Deck board Gap % Excessive handling % Ram Kumar Sunkara

5 Impact of Pallet Patterns Interlock Overhang Box Strength No No 100 % No Yes 68 % Yes No 55 % Yes Yes 51 % Ram Kumar Sunkara Example Box size: 500 x 250 x 330 mm Gross weight: 12 Kgs. 180 days stack time under 80 % Rh. Boxes stacked from floor to ceiling. Stack height: 3 meters. Interlock stack pattern on the pallet. Ram Kumar Sunkara

6 Procedure Determine :- Max. no of boxes stacked above bottom box. Load on the bottom box. Environmental factor. Environmental multiplier. Box compression requirement (BCT) Ram Kumar Sunkara Maximum number of boxes above bottom box Number of boxes above bottom box = (Stack height / Box height) 1 = (3000 mm / 330 mm) 1 = = 8.09 = 8 Boxes Ram Kumar Sunkara

7 Load on Bottom Box Load on bottom box = Number of boxes above bottom box multiplied by gross weight of box. = 8 boxes X 12 Kgs. = 96 Kgs. Ram Kumar Sunkara Environmental Factor Environment Multiplier Stack time of 180 days 0.52 Humidity of 80% 0.68 Interlock stack pattern 0.50 Total Environmental factor = 0.52 x 0.68 x 0.50 = Ram Kumar Sunkara

8 Environmental Multiplier Environmental multiplier = ( 1 / Environmental factor) = ( 1 / ) = Ram Kumar Sunkara Box Compression Requirement BCT = Load X Environmental multiplier = 96 Kgs X = 543 Kgs Ram Kumar Sunkara

9 Example 2 Box size: 380 x 380 x 420 mm Gross weight: 30 Kgs. 90 days stack time under 60 % Rh. Boxes stacked from floor to ceiling. Stack height: 3 meters. Columnar stack pattern on the pallet with one inch overhang. Ram Kumar Sunkara Example 3 Box size: 490 x 295 x 490 mm Gross weight: 18 Kgs. 30 days stack time under 70 % Rh. Boxes stacked from floor to ceiling. Stack height: 3 meters. Interlock stack pattern on the pallet. Ram Kumar Sunkara

10 Impact of box dimensions Although the length and width of box has come into picture in form of perimeter, it lacks the impact of the ratio of length to width. It is known that the 2:1 ratio of length to width gives use optimum board area and therefore we investigated for the impact of changing box dimension from 1:1 to 2:1 on the compression strength. Impact of box dimensions We found that there was a drop on an average 4% in the compression strength when length to width ratio was changed from 1.00 to These observations lead us to investigate the impact of length to width ratio on compression strength of the box. 10

11 Impact of box dimensions Due to introduction of foot print concept in box dimensioning to fit the standard pallet sizes, we are now producing boxes with different heights but having same length and width. When we tested the boxes of same foot print but having different heights, we found that there was impact of height on the compression strength. Impact of box dimensions The compression strength of box is estimated using the formula: BCT = BCT M X CF LW X CF D where BCT M is box compression as calculated using McKee s formula, CF LW is the correction factor for length to width ratio, CF D is the correction factor for the depth. 11

12 Graph of L/W ratio Vs correction factor y = x x R² = Length to Width Ratio The co-relation between the correction factor and L/W ratio can be expressed in formula as follows: CF LW = x (LW R ) x (LW R ) 2, Where LW R is the length to width ratio and CF LW is the correction factor 12

13 Depth factor For the same foot print, the height was increased from 100 mm to 750 mm in multiples of 50 mm and compression strength was measured. The correction factor was taken as 1.00 for box height of 250 mm. As the box height was decreased the correction factor increased to 1.18 and As the height was increased from 250 mm the correction factor decreased to Graph of Height of carton Vs the correction factor y = x R² =

14 Depth factor The co-relation between the correction factor and depth or height of box can be expressed in formula as follows: CF D = 2.7 X (Depth) ASTM D 5639 The formula is based only on a regular slottedstyle (RSC) box with normal shape where all dimensions (l, w, d)do not vary by extreme amounts from each other. The depth must not be less than 1/7 of the box perimeter and no one dimension more than double any other. When dimensions do vary extremely, the following adjustments are suggested. 14

15 ASTM D 5639 Dimension Variations Alter Calculated Strength Depth < 2/3 of width Add 5 % Depth > 1.5 width Subtract 8 % Length > 2.5 width Subtract 8 % 15