The Falling Dart Impact Tester tests the impact resistance of plastic films. It covers the determination of the energy that causes Polyethylene Film to fail under specified conditions. This is with the impact of a free-falling dart. This energy is in terms of weight (mass) of the dart falling from a specified height. Which would usually result in 50% failure of specimens tested. Therefore, this test very important.
Most importantly, the Falling Dart Impact Tester is useful for films whose impact resistance requires masses of approximately 50gms to 2 kg to fracture them. For example: Using Method A, the unit employs a dart with a 38mm diameter hemispherical head. It drops from a height of 660mm.
Understanding the impact resistance of packaging materials is critical as packaging will be subject to external impact. Especially during loading and unloading of packages. This machine is useful for R&D and laboratories. Also in packaging industry, film manufacturing. And especially for quality control and inspection. This machine determines the strength of the packaging materials.
Test Method A
It employs a dart with a 38.10 ± 0.13-mm (1.500 ± 0.005-in.) diameter hemispherical head dropped from a height of 0.66 ± 0.01 m (26.0 ± 0.4 in.). This test method can be used for films whose impact resistances require masses of about 50 g or less to about 6 kg to fracture them.
Test Method B
It employs a dart with a 50.80 ± 0.13-mm (2.000 ± 0.005-in.) diameter hemispherical head dropped from a height of 1.52 ± 0.03 m (60.0 + 0.25, −1.70 in.). Its range of applicability is from about 0.3 kg to about 6 kg.
Falling Dart Impact Tester Apparatus
The Falling Dart Impact Tester is manufactured to use common components for each Test Method.
The Specimen Clamp
- A two piece annular specimen clamp having an inside diameter of 125 ± 2.0mm.
- The lower half of the clamp has been mounted rigidly to the base of the Falling Dart Impact Tester.
- The upper half of the clamp has been designed to maintain positive and plane contact with the lower half when in contact.
- Pneumatically operated clamps firmly hold the test specimen in place during the test operation.
- Rubber gaskets have been employed to give a cushioning effect to minimise thickness variation effects.
- 60 Grit sandpaper may be adhered to the rubber with double sided tape to prevent slippage of films greater than 0.10mm.
Dart Release Mechanism
- An electromagnetic release mechanism, which is capable of supporting up to 2kg weight, has been used.
- The electromagnet is located through a centre-locating hole found on the moveable head, ensuring all drops are from the same position.
- The Falling Dart Impact tester has a moveable head allowing the operator to adjust the drop height up or down the supporting Post. The distance between the surface of the dart head and the surface of the specimen is considered to be the drop height. In Test Method A, the drop height is 0.66 ± 0.01m and in Test Method B the drop height is 1.50 ± 0.03m. “A” has been marked on the shaft at the correct positioning height for Test Method A.
- The centring device holds the dart vertically above the centre of the test specimen.
- A micrometer accurate to ±0.0025mm with a range from 0.0025 to 1mm may be used to measure the specimen thickness.
- Cushioning and Shielding Device
- A shielding device may be used to avoid damaging the dart or the operator during the fall so long as it does not disturb in any way the specimen or the dart.
- A felt-cushioning pad has been installed to protect the surface of the dart after penetration of the specimen.
- A small O ring is used to hold the selected weights in place on the neck of the dart.
- For Test Method A, the hemispherical dart head is 38.0 ±0.06mm in diameter with a 6.5 ±1mm dia. shaft which has a steel tip for use in the electromagnet.
- For Test Method B, the hemispherical dart head is 50.0 ±0.08mm in diameter with a 6.5 ±1mm dia. shaft which has a steel tip for use in the electromagnet.
- The head and stem of the darts are constructed from aluminium, with the stem being long enough to accommodate the incremental weights.
The weights are constructed from brass before being nickel-plated. Each weight has a centre hole of 6.6 +1.0 –0.0mm.
Weights supplied for Test Method A:
- 2 x 5gram
- 8 x 15gram
- 8 x 30gram
- 8 x 60gram
Weights supplied for Test Method B:
- 2 x 15grams
- 8 x 45gram
- 8 x 90gram
- Optional weights are available if required at 120gram or 180grams.
Optional machine models:
F0008-M1: Falling Dart Impact Tester - A Method
- 2x Aluminium Dart Head - 38mm (50g)
- Drop Height - 660mm
- Brass Weights - 2x5g, 8x15g, 8x30g, 8x60g
F0008-M2: Falling Dart Impact Tester - A & B Method
- 1x Aluminium Dart Head - 38mm (50g)
- 1x Stainless Steel Dart Head - 50mm (280g)
- Drop Height: 660mm & 1500mm
- Brass Weights - 2x5g, 8x15g, 8x30g, 8x60g, 2x15g, 8x45g, 8x90g
1. Kinetic Energy option to suit ASTM D4272 (IDM-F0008-OP1)
It refers to ASTM D4272: Total Energy Impact of Plastic Films. The Falling Dart Impact Tester is mounted on top of the Kinetic Energy option. There is a catch box and two optical filter sensors measuring the fall time difference after breaking the film and passing through which is displayed on an instrument panel as time.
2. Dart Rebound protection Tube
Test Specimens for the test
A Film has been arbitrarily defined as sheeting having nominal thickness not greater than 0.25 mm (0.010 in.). An alternative technique provides for testing specimens in successive groups of ten. One missile weight is employed for each group and the missile weight is varied in uniform increments from group to group. The test specimens should be large enough to extend outside the specimen clamps at all points. A cutting template of suitable size is available. The test specimens should also be should be free from pinholes, creases etc unless such imperfections are relevant to the test.
Staircase Method of Dart Testing
The standard technique is the staircase method. By this technique, the missile weight employed during the test is decreased or increased by uniform increments after the testing of each specimen, depending upon the result (fail or not fail) observed for the specimen.
Falling dart test significance and use
Test Methods A and B are used to determine the weight of the dart when 50% or more of the specimens under test fail. The information from either test method cannot be compared directly to the other.
The results gained from Tests Methods A or B are greatly affected by the quality of film under test. Limitations of gaining data from these test methods can vary due to the sample quality ie: uniformity of film gauge, die marks, contaminants etc. Test results can usually be used to determine the field performance of the specimen under test. The impact resistance of plastic film, while partly dependent on thickness, has no simple correlation with sample thickness. Hence, impact values cannot be normalised over a range of thickness without producing misleading data as to the actual impact resistance of the material. Data from these test methods are comparable only for specimens that vary by no more than ± 25% from the nominal or average thickness of the specimens tested.
Importance of drop impact resistance testing of plastic films
Several impact test methods are used for film. It is sometimes desirable to know the relationships among test results derived by different test methods. Test Methods A and B are used to establish the weight of the dart when 50 % of the specimens fail under the conditions specified. Data obtained by one test method cannot be compared directly with the other test method nor with those obtained from tests employing different conditions of missile velocity, impinging surface diameter, effective specimen diameter, material construction and finish of the dart head, and film thickness. The values obtained by these test variables are highly dependent on the method of film fabrication.
Dart Drop Test Procedure
a) Assemble the supporting Post to the base unit and square to each other by using the screws located at the base of the Post, and align the BLACK mark on the Post to the top of the base plate
b) Connect Power and Air Supply, attaching black pneumatic tube to regulator.
c) Connect the electromagnet cable supplied to the socket located at the back of the machine.
d) Screw moveable head into place using two thumbscrews. Electrical cable can be “hidden” within the channels of the supporting Post via the cover strip.
e) Level the base using Adjustable Feet in each corner of base and the bulls’ eye level.
f) Set relevant test height in relation to Test Method A or B. Align the BLACK mark on the moveable to either the A or B marks on the Post, to set relevant height – Test A or Test B respectively.
g) Turn machine ON using the On/Off Switch
h) When in rest position, the upper half of the clamp is raised. If clamp does not raise, check air supply and power supply.
i) Select the relevant Dart in relation to Test Method A or B.
j) Place desired sample in place and lower upper clamp.
k) To lower upper clamp, simultaneously press the two hold buttons located on the front panel of the base plate. By using two hands you create a safety barrier.
l) Draw a circle on the specimen where it reaches the inside wall of the clamp using minimal pressure of a ball point pen so as not to damage the specimen. This will show any slippage that may occur during the test. If slippage occurs, this is reason to reject the results. Slippage may increase as the weight of the dart increases.
m) Insert the dart and required weight into the dart release mechanism. The magnetic is active constantly while power is on.
n) To release the Dart, depress Foot Switch.
o) To release the sample for examination, press the reset button and the upper clamp will lift.
p) Turn of the Falling Dart Impact Tester once you have finished with it using the ON/OFF switch located on the left hand side.