5 to 400 kNTJ-125
Direct Compression Fixture
Flat, parallel platens taking the ring crush holder centrally. Parallelism is what decides whether the ring collapses evenly or on one side, and it matters more here than platen size.
SpecificationsTesting standard
TAPPI T822
Ring crush of paperboard (rigid support method)
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
TAPPI T822 stands a strip of paperboard on edge in a circular groove so it forms a ring, then crushes it between platens and reports the maximum force. The ring and the rigid support stop the strip buckling so it fails in genuine edgewise compression. It is intended for board between 0.28 mm and 0.61 mm thick. The current revision is TAPPI/ANSI T 822 om-22.
At a glance
- Test type
- Compression — the specimen is squeezed
- Published by
- TAPPI
- Edition
- TAPPI/ANSI T 822 om-22
- Material
- Paper, board & corrugated
- Runs on
- Series 7200 and Series 9000
What the test does
A strip of paperboard is stood on edge in a circular groove in a sample holder, so that it forms a ring. The holder is placed between the platens of a compression machine, and the driven platen approaches the fixed one at a uniform speed until the board collapses. The maximum force is the ring crush value.
The groove is the whole idea. Paper stood on edge as a flat strip buckles long before it crushes, so the ring form and the rigid support constrain it laterally until it fails in genuine edgewise compression rather than as a slender column.
What it measures, and why it matters
Ring crush correlates with the edgewise compressive strength of the paper, and edgewise compressive strength is what holds a stacked corrugated box up. The chain runs from the component papers, through the combined board, to the finished container: ring crush of the liner and medium feeds the edge crush of the board, which feeds the compression resistance of the box.
That is why the number is bought and sold. Containerboard is specified on ring crush in North America, and a mill that misses the figure has produced a grade the converter cannot use, regardless of how the paper looks or how it runs.
The method has a stated thickness window: it is intended for paperboard between 0.28 mm and 0.61 mm thick. Outside that window the result is progressively less a measure of compression and more a measure of buckling, and the number stops meaning what the specification assumes it means.
Specimen, and the edges that carry the load
The cut edges are the loaded surfaces. Everything about specimen preparation follows from that one fact.
- Material
- Paperboard, principally containerboard components
- Thickness window
- 0.28 mm to 0.61 mmOutside it the result becomes progressively a measure of buckling rather than of compression.
- Specimen
- A strip of specified width and length, cut square
- Edges
- Clean and square — they are the loaded surfacesA ragged or crushed edge collapses first, and the recorded force describes the knife rather than the board.
- Direction
- Machine and cross direction, both recorded
- Conditioning
- In the standard atmosphere for testing paper and boardCompressive strength falls with rising moisture more sharply than tensile strength does.
- Treat the groove holder as a consumable
- DakGroove width is specified. A worn, widened groove stops restraining the strip and results drift downward over months in a way that looks like a change in the board.
Loading and rate
- Loading
- The driven platen approaches the rigid platen at a uniform speed until the specimen collapses
- Rate
- As specified in the method; the figure sits in the purchased text
- Reported
- Maximum force before collapse
- Platens flat, clean and parallel
- DakThe specimen is short and stiff, so a small tilt loads one side of the ring first and it collapses there before the rest.
What the ring does, and what the number means
Ring crush value—
The maximum force the ring carried before collapse
Reported as a force, and where required as a force per unit length of specimen.
Why a ring and not a flat strip—
A flat strip on edge buckles long before it crushes
The ring form plus the rigid support constrain the strip laterally, so it fails in edgewise compression rather than as a slender column.
The chain to box compression—
Component ring crush → board edge crush → box compression
- component
- liner and medium, tested here
- board
- the combined corrugated board, tested by edge crush
- box
- the finished container, tested by compression
Ring crush is the first link and the reason containerboard is bought and sold on it in North America.
How the test runs
- 01Confirm the board thickness lies between 0.28 mm and 0.61 mm.
- 02Cut strips to the specified width and length, square and with clean edges.
- 03Take specimens in both directions and from across the reel.
- 04Condition in the standard atmosphere and test in it.
- 05Check the groove in the holder for wear before the run.
- 06Stand the strip in the groove so it forms a ring.
- 07Place the holder centrally between flat, parallel platens.
- 08Approach at the specified uniform speed until the board collapses.
- 09Record the maximum force.
- 10Report the mean by direction, with the number of specimens.
Grips and fixtures for this method
Self-identifying
Load Cells
Ring crush values run from tens to a few hundred newtons. A cell sized for a heavy compression frame turns a 200 N peak into noise, so the cell is chosen for the specimen.
SpecificationsWhat the report has to contain
- Reference to TAPPI T 822 and the revision
- Grade, grammage and thickness of the board
- Confirmation that thickness lies within the 0.28 to 0.61 mm window
- Direction of each set of specimens
- Specimen width and length
- Conditioning atmosphere
- Platen approach rate
- Maximum force for each specimen
- Mean and the number of specimens per direction
- Any specimen rejected for edge damage, and why
What the machine must be capable of
Ring crush values run from tens to a few hundred newtons, so this is low-force work. A compression frame with a load cell chosen for the specimen rather than for the frame is essential; a cell sized for a heavy frame turns a 200 N peak into noise. Force accuracy to ASTM E4 over the working range is the requirement.
Platens have to be flat, clean and parallel, and the approach rate uniform. Because the specimen is short and stiff, small tilts matter: any platen tilt loads one side of the ring first and it collapses there before the rest.
The sample holder is a consumable in practice. Groove width is specified, and a worn or widened groove no longer restrains the strip, so results drift downward over months in a way that looks like a change in the board. No grips and no extensometer are involved — the result is a peak force.
What goes wrong in practice
Worn groove holders are the slow, invisible fault and the one that causes the most argument between mill and converter. Blunt cutters that crush the loaded edge are the fast version of the same problem. Testing outside the 0.28 to 0.61 mm thickness window produces a number that is not comparable with a specification written inside it. And unconditioned specimens, particularly in a humid plant, give results that are low, repeatable and blamed on the furnish.
Ring crush against short-span compression
Two ways to stop paper buckling while measuring how hard it is to crush. They are not the same measurement.
| Ring crush (TAPPI T822) | Short span (TAPPI T826) | |
|---|---|---|
| Buckling is | Restrained by a groove and a ring form | Eliminated by a 0.70 mm free span |
| Specimen | A strip stood on edge as a ring | A 15 mm strip clamped almost end to end |
| Applies to | Board 0.28 to 0.61 mm thick | Containerboard, roughly 100 to 440 g/m² |
| Regarded as | The traditional specification measure | The cleaner measurement of the two |
| ISO counterpart | ISO 12192 | ISO 9895 |
Ring crush accepts some contamination of the result by residual buckling; the short-span test removes the possibility instead. Both are legitimate and both are specified. Neither substitutes for the other on a purchase specification.
Questions we are asked about this test
What is TAPPI T822?
TAPPI T822 is the North American ring crush method for paperboard, using a rigid support. A strip is stood on edge in a circular groove so that it forms a ring, and the holder is crushed between the platens of a compression machine until the board collapses. The maximum force is the ring crush value. The current revision is TAPPI/ANSI T 822 om-22.
Why is the specimen formed into a ring?
To stop it buckling. A flat strip of paper stood on its edge behaves as a very slender column and folds over long before it reaches its compressive strength, so the number that came out would describe the geometry rather than the paper. Curving the strip into a ring and supporting it in a groove restrains it laterally, so it fails by genuine edgewise compression.
What is the 0.28 to 0.61 mm thickness window for?
It is the range over which the ring geometry actually delivers a compression failure. Thinner board still buckles inside the groove; thicker board does not sit correctly and the ring stops behaving as the method assumes. A ring crush figure obtained outside that window is not comparable with a specification written inside it, and the report should say where the board sat.
Why does ring crush matter commercially?
Because containerboard is specified and traded on it in North America. Edgewise compressive strength of the components is what ultimately holds a stacked box up: component ring crush feeds the edge crush of the combined board, which feeds the compression resistance of the finished container. A mill that misses the ring crush figure has produced a grade its converter cannot use, whatever else the paper does well.
What is the commonest cause of drifting results?
A worn groove in the sample holder. The groove width is specified, and it widens slowly with use until it no longer restrains the strip. Results then fall gradually over months, and because the change is slow and the equipment looks fine, the drift is usually blamed on the furnish or the machine before anyone measures the holder. It is a consumable and should be treated as one.
How does it compare with ISO 12192?
ISO 12192 is the international ring crush method for the same property, and the two are direct counterparts. As with the tensile methods, that does not make the numbers interchangeable: specimen dimensions and rates differ, and a result obtained to one document should not be reported against a specification written for the other without saying so.
What machine does it need?
A compression frame with flat, clean, parallel platens and a load cell sized for the specimen rather than the frame — ring crush values run from tens to a few hundred newtons. Force accuracy to ASTM E4 over the working range is the normal requirement. There are no grips and no extensometer: the result is a peak force, and platen parallelism matters more than capacity.
Running TAPPI T822 on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Low — commonly tens to a few hundred newtons | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ASTM E4 over the working range | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | A ring crush holder with a groove of specified width, between flat parallel platens | Our compression anvils, built to the specimen |
| Environment | Standard atmosphere for testing paper and board; board compressive strength falls sharply as moisture rises | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.