Testing                                                                                                                                    Folding Endurance

Folding Endurance

General 

Folding endurance test is the best available criterian for testing the serviceability of paper that is creased or folded repeatedly. This test gives information about certain properties of paper, such as durability, which cannot be obtained by other tests. A strip of paper is continuously folded till it breaks, the number of double folds giving the folding resistance.

Equipment

'Schopper' type, double-fold testing machine is recommended. The machine is driven by motor or countershaft with the help of a friction pulley effecting 90 to 120 double folds per minute. When the machine runs, the slotted folding blade slides back and forth in reciprocating motion between creasing rollers. The clamps are under spring tension which can be varied. The number of times the paper goes through each double fold (back and forth) is counted on a rotating disc known as counter which is designed to count up to 10000 double folds.

Precautions

Before putting test pieces on the machine, see that the machine is in locked position bring the counter to ZERO position, fasten the paper securely in clamps and make sure that it is free from creases and folds.

Report

Report the average, maximum and minimum of the number of double folds that the test pieces are able to sustain up to rupturing point in each direction separately.

The variability of the results on a single- specimen is such that the average of 10 tests may only be relied on to be within 15 percent of the true mean. Two average results cannot be classed as significantly different unless they are 20 percent of their mean apart. If less than 10 tests are taken, these limits shall be extended. Therefore, if necessary, more than one test piece, in each direction, shall be taken from each specimen so that a minimum of ten determinations are made in each direction.

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