The dynamic rupture strength, measured in joules, is the puncture strength. It shows how important corrugated board and cartons are. Puncture strength is much harder to figure out than bursting strength because it has to do with both the box board paper and the corrugated layer. The strength to puncture and the strength to burst are related in a straight line. In practice, the bursting strength can be used to get a good idea of the puncture strength.
Why is it important to detect the puncture strength of paperboard?
A corrugated board’s puncture strength is the amount of work it takes to push a certain shape of corner cone through the board. This work is the total amount of work needed to poke, tear, and bend the board into a hole, which is measured in J. When the paperboard is used or moved after being made into cartons or other containers, it will inevitably be changed. So that the paperboard doesn’t break when this happens, it needs to have enough impact strength. The impact resistance of corrugated board is a good way to figure out how strong it is when it is hit.
Things that affect how strong corrugated board is when it’s punctured
The puncture strength of paperboard is mostly affected by force and speed, distance, force area, the angle of the fixed paperboard, and other things.
- When the same thing hits the paperboard at high and low speeds, the high-speed hit is more powerful.
- When the same object is hit with the same force, the intensity of penetration is less when the object is far away than when it is close.
- The power of the paperboard to break through gets stronger as the force gets stronger.
- For objects with the same mass and shape, resistance isn’t taken into account, and the penetration force is lower when the force area is bigger.
- If the same object is hit from the same distance and at the same speed, the penetration force of the fixed paperboard can be higher than that of the fixed paperboard. For the paperboard that is not fixed by the fulcrum, the intersection of straight lines between the fulcrum and two points or the straight line between two points is not taken into account.
The difference between the piercing strength and bursting strength of corrugated boxes
The bursting strength of a carton is the maximum pressure per unit area that increases evenly perpendicular to the surface of the sample. This pressure is measured in kPa. It shows how resistant corrugated board is to all kinds of damage and is part of its static strength. Usually, Mullen is used to measure it. Absolute breaking strength is the value you get from the instrument itself. The bursting strength shows how well the carton can manage being handled, loaded and unloaded, hit, and torn during the circulation process. It is one way to measure the overall performance of the carton.
The piercing strength is the vertical impact load that can be put on the corrugated board plane at one time. The sample is pierced through the piercing head, anti-friction sleeve, and single pendulum, which is measured in energy Joule (J). It shows how sharp objects can damage corrugated board when they hit it and is part of its dynamic strength. The carton puncture strength tester is used to test the strength of different types of paperboard, like carton board, corrugated board, etc.
There is a close relationship between the puncture strength and the base paper’s fiber willfulness, hardness, tightness, and moisture content, as well as the corrugated board’s bonding strength and thickness. While the bursting strength affects the puncture strength, random items can also change it. Random things have a direct effect on the choice of corrugated base paper, the wear of corrugated production equipment, the choice of corrugated rod model, and the bonding forming.
Puncture strength and puncture resistance:
There is a link between the strength of bursting and the strength of bursting of corrugated board. In general, corrugated board with good bursting strength has a better bursting strength. There is a linear link between the two, but they are also different in some ways. The bursting value of corrugated board shows the bursting strength value in an indirect manner. So, in general, one of the two options is to measure the resistance to bursting and the strength against getting holes.
Science and technology are always getting better, and packaging and shipping are gradually improving too. For corrugated boxes, the index of puncture strength is not as important as it used to be. This is done to save resources and make packaging more efficient.
But its bursting value is especially high for special cartons like the A-A double corrugated carton. When the pressure in the instrument reaches 4600 kPa, it is easy to pop the film. There are some limits to how well paperboard can keep from bursting. The standard says that the most paperboard can resist bursting is 5500 kPa, and the puncture strength is just enough to make up for this. The two are also different in some ways.
The difference between bursting strength and puncture strength
The carton is destroyed by the sudden impact of the puncture strength, which can happen at any time. Sharp tools, edges, and corners often hit the carton.
The bursting strength squeezes the carton in a certain spot, which causes the carton to break in this spot. It is common for the carton to break because it has been pushed out from the inside or the outside.
Both are used to protect goods in a safer way, but there is a difference in the source of the destructive power. The bursting resistance of paperboard depends on the bursting resistance of the base paper, which is related to the surface paper, lining paper, and medium paper, but has nothing to do with the corrugated paper in the middle. The test shows how well the corrugated board holds up when sharp objects hit it. The puncture strength shows how hard the carton is hit when it is being used or transported.
How to adjust and calibrate the cardboard puncture strength tester?
In the measurement range, when the center of gravity of the pendulum cone is at its lowest point, the corner cone must be within 5 mm of the level that goes through the pendulum’s axis of rotation. If it’s not in the range that’s allowed, the lifting paperboard puncture strength tester’s balance thallium needs to be changed.
Adjusting the zero point: Take off the heavy thallium and sample splint from the pendulum, move the pointer to the maximum value, put the pendulum in the start test position, press the release button, and the pendulum will swing. At this point, the pointer should be pointing to the zero point. If not, use the zero point adjustment screw on the pendulum to change it. When different weights of heavy thallium are used to replace the old ones, the zero point needs to be set up again.
Adjusting the pointer friction force of a paperboard puncture strength tester is easy: put the pointer at zero, lift the pendulum to the starting test position, press the release button, and the pendulum will swing. At this time, the pointer should not be more than 3mm away from the zero point. If it is more than 3mm away, oil should be put on the pointer bearing to lubricate it, or the pressure on the pointer spring should be loosened so it can be adjusted.
For calibration of pendulum shaft friction: When no heavy thallium is added, let the pendulum swing freely for at least 100 times before stopping.
The calibration of the anti-friction ring resistance of the paperboard puncture strength tester: After setting the pointer to zero, line up an aluminum plate with a 61mm-long hole in the middle, press the hole of the plate with the hole of the sample pressing plate in the middle of the pressing plate, then release the puncture head holding the anti-friction ring and look at the resistance of the anti-friction ring, which shouldn’t be more than 0.8kg/cm (0.078j). If it doesn’t meet the requirements, you can adjust it by tightening or loosening the three jacking screws on the triangular puncture head.
The calibration of the total moment of the pendulum of the paperboard puncture strength tester: Add a small shaft to the back of the pendulum’s counterweight hole, install a vertical downward screw at the end of the small shaft, put the pendulum in the position to be released, push the lower end of the screw against one end of the balance (or on the scale plate), release the pendulum, and add weights to the other end of the balance until the upper plane of the pen is level with (i.e., the balance reaches balance).
How to use the puncture strength testing machine
The 175mm sample is placed between the clamping plates and applied to the clamp with a fixed force. The sample shall be clamped in the middle. If the tester is equipped with a clamping force measuring device, the force can be recorded. Adjust the pendulum and add weight thallium when necessary to select an appropriate range of work, which will keep the test results in the range of 20 ~ 80%.
Put the anti-friction ring behind the corner cone, turn the pointer to the highest scale value, lock the pendulum at the start of the test, and press the release button, the pendulum swings, and the corner cone passes through the sample completely. Read the total work equivalent to that used to pierce the sample and overcome the friction of the tester from the corresponding scale, accurate to 1 grid. If the measurement range of scale reading is 122.4kg • cm (12j), it shall be accurate to 1kg • cm (0.1j); If the measurement range is more than 122.4kg • cm (12j), the accuracy is 2kg • cm (0.2j).
If the friction effect is greater than or equal to 1%, the work loss caused by equipment friction shall be measured in advance to compensate the test results.
In each packaging unit, cut 8 samples from different paper samples. Half of the samples are measured longitudinally parallel to the swing plane of the pendulum, and the other half are measured transversely parallel to the swing plane of the pendulum.
When the longitudinal direction is parallel to the swing direction of the pendulum, the measured value is called the longitudinal puncture strength.
The measurement results are represented by the arithmetic mean of all measured values on the front, back, longitudinal and transverse sides, and the maximum and minimum values are reported. The calculation result is accurate to 0.1kg • cm. If it is expressed in J, the value less than 12j is accurate to 0.1j, and the value greater than 12j is accurate to 0.2j.
How do you roughly figure out how strong corrugated board is?
From the raw materials used, you can figure out how strong corrugated board is when it bursts. It is equal to the sum of the bursting strengths of each layer of carton board multiplied by the coefficient of 0.95, which has nothing to do with the corrugated layer.
For example, here’s how to figure out the bursting strength of a single corrugated board and a double corrugated board:
Single corrugated board (bursting strength) BST = (face paper BST + lining paper BST) 0.95
BST = (face paper BST + sandwich paper BST) * 0.95 = BST of double corrugated board.
Because there is a space between each layer of corrugated board, it can absorb more shock, but each layer is also easier to break. So, in the above formula, the answer that you get when you multiply the total breaking strength of each layer of corrugated board by the coefficient of 0.95 is correct. The bursting strength has nothing to do with the corrugated layer because, on the one hand, the bursting strength of the corrugated layer is much lower than that of the carton board; and on the other hand, because the bursting strength is the static bursting strength, the buffer of the corrugated layer is larger, which greatly lowers its bursting strength, so it can be ignored.
How to convert the bursting strength and puncture strength of cartons?
The puncture strength and bursting strength are linearly related. In practice, the approximate puncture strength can be obtained according to the bursting strength. The calculation formula is as follows: pet = 0.0054bst + 2.16358
Third floor: y = 2.09 × X + 23.5 fifth floor: y = 2.27 × X + 62.4
X represents the bursting strength of corrugated board (kgf / cm ^ 2), and cm ^ 2 refers to square centimeter
Y represents the piercing strength of corrugated board (KGF • cm)
Finally, the unit should be converted.
Conversion ratio: 1kgf = 9.8N, 1 in = 2.54cm, 1 lb = 0.454kgf, 1J = 1n • M
For example, a = B, according to the known breaking strength of 7 kgf / cm2,
Calculation of puncture strength:
2.27 × 7+62.4=78.29（kgf•cm)
78.29 × 9.8/100≈7.67（N•m）=7.67（J）