The Art of the Fold

As a user exploring paper folding endurance tester, you'll discover that different testers employ distinct mechanical mechanisms to subject paper samples to repeated folding. Understanding these variations in folding mechanisms is crucial for selecting a tester that aligns with the types of paper you're testing and the specific standards you need to meet. This article breaks down the key differences in how various paper folding endurance testers achieve the repeated folding action.
 

One of the most significant distinctions lies in the type of folding action. You might ask: "How does each tester actually fold the paper?"

MIT Folding Tester: This is a widely used type that employs a reciprocating folding head with a slot through which the paper strip passes. The head oscillates back and forth, causing the paper to be folded sharply over two folding surfaces with a defined radius of curvature. A constant tension is applied to the paper strip during the folding process. Standards like TAPPI T 511 and ASTM D2176 describe the MIT folding endurance test.
 

Schopper-Type Folding Tester: This type uses a different mechanism where the paper strip is held under tension between two pairs of oscillating rollers. The rollers move in opposite directions, creating a folding action. This method is generally used for thinner papers (typically less than 0.25 mm). TAPPI T 423 describes the Schopper-type folding endurance test.
 

Köhler-Molin Folding Tester: This tester also uses a reciprocating folding action but with a different geometry of the folding surfaces compared to the MIT tester. It's another method for assessing the folding endurance of paper.

You might also be curious about the folding angle. You might ask: "Is the paper folded at the same angle in all testers?" The folding angle, the angle through which the paper is bent during each fold, can vary between different tester types and can sometimes be adjusted within a specific tester to simulate different stress levels. Standard test methods usually specify the required folding angle.
 

Another key difference is the applied tension. You might ask: "Is the tension on the paper the same for all tests?" The tension applied to the paper strip during the folding process is a critical parameter that influences the test results. Different standards and tester types specify different tension levels. For example, the MIT tester allows for adjustment of the tension within a specific range (4.9 - 14.72 N as per TAPPI T 511).
 

The folding speed also varies between different testers. You might ask: "Do all testers fold the paper at the same speed?" The rate at which the folds are performed (number of double folds per minute) can affect the test results, particularly for viscoelastic materials like paper. Standard test methods usually specify the required folding speed.
 

Finally, the type of paper for which each tester is best suited can differ. MIT testers are generally used for a wider range of paper thicknesses and strengths, while Schopper-type testers are often preferred for thinner papers. The specific standard you need to comply with will often dictate the appropriate tester type for your material.
 

Understanding these differences in the folding mechanisms, folding angle, applied tension, folding speed, and suitability for different paper types is crucial for selecting the right paper folding endurance tester for your specific application and ensuring compliance with relevant industry standards. The choice of tester will directly impact the comparability and reliability of your folding endurance test results.