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Difference between Flat Crush Test and Radial Crush Test of Paper Tubes / Paper Cores.


1) Horizontal Flat Crush (Commonly known as Flat Crush).

In this method, the Core sample is pressed (Horizontally) between 2 flat platens and the point of failure is recorded.
This test is perfect if the Core Pipe is used as a Packing Medium. i.e. a Product is packed inside the Tube and multiple tubes are stacked together.
This will create a Tube-to-Tube pressure and will generate flattened cores.

2) Radial Crush (Commonly known as Radial Crush).

In this method, the Core sample is pressed (Horizontally) between 2 curved (profiled) platens and the point of failure is recorded. These platens are made snug-fit as per each different core size. The jaws cover 1/3rd of the surface from the top and 1/3rd of the surface from the bottom. The 2 sides are left with 1/6th and 1/6th surface open.

This test is perfect if the Core Pipe is used as a Winding Medium / Carrier.
i.e. a Product is wrapped / wound on the outer surface of the tube. The winding tension creates a compressive force that acts radially inwards on the tube and try to implode (collapse inwards) the tube.

99.9% of the times, all Paper Cores / Tubes are used as Winding Medium or Carriers. And the only test that can meticulously replicate the field condition is a “Radial Crush Test on a Pneumatic Machine”. Unfortunate due
to lack of availability of proper equipment and specially because of lack of knowledge and initiatives, the industry in general is still practicing age old methods of test.

To Summarize :
FLAT CRUSH is good if you are using the Paper Tube for packing and the tube-tube contact will create and line-contact. In this case, Flat Crush is important and can replicate the field conditions.
RADIAL CRUSH is good if your Paper tube is used as a yarn carrier. The Yarn which is wound on the tube with tension creates a 360 Degree contact and presses the tube from all directions.
Hence flat crush will not be a good measure.

Radial Crush covers atleast 66.66% of the surface and still gives a much better co-relation with the field condition.

The Radial Crush values will be about 3-4 times more than the Flat Crush values.
Think about it yourself, what direction do the forces act when your wind it with yarn.

Line-Contact (Flat Crush) or 360Deg-Contact (Radial Crush) ?.


Radial Crush Test is more practical as it is more co-related with the field condition.
It is also possible that 2 different types of tubes give same amount of Flat Crush, but one particular tube gives a slightly better Radial Crush.


The tube that gives better Radial Crush will perform better in the field and you will face less rejections and losses with that tube.


NOTE : The P series of Core Compression Testers (P500D / P1000D  / P2000D) work on proprietary TTC standards and does not confirm to ISO Standards. As per ISO Standards only the Flat Crush is allowed and that also on a mechanical screw based model. Our M Series Core Compression Tester (M500D) is suitable for this purpose.

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