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Tuesday, June 14, 2016

Technical Basics of Bursting Strength

Vintage Mullen Burst Tester
Bursting strength is measured by a test methods where a specimen is held between annular clamps and subjected to pressure from one side. The portion of the specimen exposed between the openings is the test area. The portion of the specimen around the test area is clamped rigidly so that it does not slip as the test area bulges under the increasing pressure during the test. Pressure is applied to the underside of the specimen by a rubber diaphragm which is expanded by hydraulic pressure at a controlled constant rate. The bursting test value is the maximum pressure, above atmospheric pressure, in pounds per square inch (or kilonewtons per square meter or kilopascals) required to produce rupture of the specimen. There are separate test methods for paper burst and board burst.

It is sometimes said that the bursting strength is very closely related to machine direction tensile strength. The basis for this statement lies in the distribution of stresses within the specimen during the test. Prior to rupture, the rigidly clamped specimen stretches due to the stress applied by the expanded diaphragm. The strain is approximately equal in all directions. But, since the paper will not withstand stretch equally in all directions, unequal stresses build up and eventually produce rupture. In most cases, the line of rupture will be perpendicular to the machine direction because the paper stretches least in that direction. At other times, there is no principal rupture line. Consequently, the burst test can be used to determine the machine direction of a specimen whenever a principal line of rupture occurs during the test.

Bursting strength is of importance as a paper mill control test for linerboards for shipping containers. Conformity of the finished shipping containers with the test specifications required by Uniform Freight Classification Rule 41 is dependent on the bursting strength of the finished corrugated paperboard, which is controlled by the bursting strength of the linerboard.
Modern PROFILE/Plus Burst

Common Standards:
ISO 2758 Paper. Determination of bursting strength 
ISO 2759 Board. Determination of bursting strength 

TAPPI T403 Bursting Strength of Paper 
TAPPI T807 Bursting Strength of Paperboard and Linerboard 
TAPPI T810 Bursting Strength of Corrugated and Solid Fiberboard