Technical Services

Drop tests and Field Performance


Free-fall drop and shock tests are used to evaluate sack construction.

Manufacturers of multi-wall packaging have years of cumulative experience in flexible containers and can offer unique wisdom in designing a new package or ways in which current packages can be designed to be even more cost efficient. Drop tests and field performance are usually relied upon to help predict the effectiveness of a package for a specific product and the typical distribution conditions encountered.

Drop test results reflect a number of variables including sack construction, flow of the product, ply nesting, uniformity or lack of uniformity of packaging materials, etc. They also serve as a major historical method by which to evaluate prospective sack constructions.

Here is a brief summary of the two types of drop tests:

 

Flat Drop

A sack is dropped on its face or back; the major impact is focused on sack length (MD paper direction).

 

 

Butt Drop

A sack is dropped on its end; the major strain is on sack seam closures and sack width (CD paper direction). Field performance frequently involves test shipments of newly designed sack constructions with careful attention being paid to the distribution system characteristics such as whether the product is palletized, shrink or stretch wrapped, shipped as less than carload lots (LTL) or in full carloads, the number of times handled in the distribution system, warehouse/storage conditions, etc.

 

 


A technician uses a spectrophotometer to identify unknown sack contaminants.

Modern tear test equipment with digital read out.

Testing of Incoming Raw Materials
With hundreds of raw materials purchased for inventory, the manufacturer of multi-wall packaging must keep a watchful eye on quality control for each component of a package. Random audits of incoming raw materials – with emphasis on suppliers not consistently providing materials equal or superior to those needed to manufacture sacks with nearly zero defects – are essential for converters of sack packaging to ensure excellence in manufacturing.

Tests done on raw materials range from simple tear and tensile tests on paper to sophisticated analysis done with gas chromatography and spectrophotometry.



Some companies have developed testing methods such as this device to test the relative extent to which sack closure is sift-proof.

Registering Complaints

If you have a complaint to register with a sack manufacturer, the following general guidelines are suggested:

  • Set aside as many damaged sacks as possible which illustrate the precise difficulty. At the same time, obtain some undamaged sacks from the same shipping unit to help in analysis. Contact your supplier, explain the difficulties experienced and advise the sack manufacturer of the exact markings on the shipment and the date on which it was received. Provide all available bill of lading information to help identify the lot of sacks in which the trouble occurred. 
  • If the difficulty persists, request the sack manufacturer to send a representative for consultation. If time allows, send the manufacturer some typical samples and describe at which point in packing or handling the problem occurs so the representative will be better informed and able to address the problems when on site.

Control charts helps monitor the production process.

Reporting Damaged Sacks

If properly reported, damaged paper shipping sacks can be traced to specific causes so future difficulties may be avoided wherever they occur. When reporting damage, the following should be supplied:

  • The name of the commodity and the quantity packed per sack, the name and address of the product manufacturer and the sack manufacturer's symbol or trade-mark appearing in the certificate on the sack.
  • The total number of sacks in the shipment and the number damaged.
  • If damage occurred at top or bottom closures, describe the type of each closure (sewn or pasted) and explain the nature of the damage. Photographs are frequently helpful if taken closely enough to the damage to illustrate it specifically.
  • Does damage indicate snagging or tearing? If so, explain whether the tear was crosswise or lengthwise. For example, were lengthwise pasted seams intact?
  • Were sacks exposed to weather or do they show evidence of damage by foreign material such as oil, etc.?
  • Describe the condition of the railroad car, truck or vessel used in the transportation of sacks. Were there loose boards in walls or floors? Nails or other hardware in evidence? Were sacks loaded together with cargo packed in containers other than sacks?
  • If delivered by rail, did empty space in the car indicate shifting of the load? If so, to what extent did the load shift? If unloaded from a vessel, what type of slings were used?
  • If palletized, did the pallet contribute to sack failure or damage?
  • Several sacks showing damage should be set aside and mailed to the supplier for examination. A few typical samples frequently reveal to the sack packaging expert the likely cause of damage.