Analysis of sponge resilience test method (GB/T6670-2008)

The national standard GB/T6670-2008 has replaced GB/T6670-1997 'Determination of Resilience of Flexible Foam Plastics' and changed to 'Determination of Resilience of Flexible Foamed Polymer Materials by Falling Ball Method', using two measurement methods, namely Method A and Method B. Detailed Determination of Resilience of Flexible Foamed Polymer Materials by Falling Ball Method Contents: 1. Test Scope: 1.1 Two methods for determining the resilience of flexible foamed polymeric materials are specified. 1.2 It is suitable for the determination of the ball rebound performance of flexible foamed polymeric materials. 2. The following terms and definitions apply to this standard. 2.1 Open-cell flexible foam materials: flexible foam materials with closed cell volume less than 25%. 2.2 Closed-cell flexible foam: a flexible foam with a closed cell volume greater than 25%. Principle: A steel ball with a certain quality and diameter is dropped from a fixed height to the surface of the sample, the height of the steel ball bounced is measured, and the percentage of the ratio of the bounce height of the steel ball to the falling height is calculated. Method A, test equipment and main parameters: sponge falling ball resilience tester, including a transparent tube with an inner diameter of 30mm to 60mm, a diameter of 16mm±0.5mm steel ball with a mass of 16.8g±1.5g, released by magnet or other device. There is no rotation during the fall, and it is always in the center position. The drop height is 500mm±0.5mm. The top of the ball should be 516mm from the surface of the sample. Therefore, the origin of zero springback is the diametrical distance of the steel ball above the surface of the specimen. If the tube is not vertical, it may cause measurement errors, and the steel ball contacts the inner wall of the tube during the fall or rebound process, and the measurement result is invalid. Use a spirit level or similar device to calibrate the hard reference surface to ensure level, and place the transparent tube and rack vertically. 3. Manual reading equipment: Mark the scale line on the back of the tube in an orderly percentage, with a large scale every 5% (25mm) and a small scale every 1% (5mm), and the angle is 120°arc. This full circle scribe is an integral part of the instrument and it can rule out parallax errors. Automatic reading device: An instrument that electronically displays the rebound height of the steel ball, which has been confirmed to be the same as the manual reading. The height of the rebound can be calculated from the speed of the rebound of the steel ball or the time interval between the first and the second contact of the steel ball with the surface of the foam, and the installed electronic equipment should display the height of±1% (5mm) accuracy, the tubes of this device do not need to be scaled. Method B, test equipment and main parameters: the same equipment as method A, a foam falling ball resilience tester, with manual reading equipment and automatic reading equipment. Digital display of the falling ball rebound tester, the accuracy of the instrument is that the relative error is less than 1.5%, the main parameter steel ball diameter is the same as that of method A, and the steel ball mass is 16.3g (0.5g lighter than the 5.1 steel ball). The important different parameters are: the drop height of the steel ball is 460mm±0.5mm. So that the rebound value measured by method A and method B cannot be directly converted. Test sample (polyurethane material): 1. The sample should have parallel and flat surfaces up and down. 2. The sample area is 100mm±100mm, the height should meet 50m. If the thickness of the specimen is less than 50mm, it shall be superimposed to 50mm, but no adhesive shall be used. For model products, the upper skin should be removed. Note: For soft materials, if the error of the results is large, a thicker sample can be used without being limited by the thickness of 50mm. For ultra-low-density materials, there may be problems with the test results due to the sample itself. For multi-layer sheet samples, it is easy to slip between layers, and it is best to choose a larger area of ​​the sample to overcome. Number of samples: 3 samples were tested in each group. The three samples can be taken from the same block or from different blocks in the same batch. State adjustment: After the material is made, it can be tested for at least 72 hours. If it can be proved, the difference between the results obtained 16h or 48h after production and the results obtained after 72h of production is not more than±10%. The samples are allowed to be tested 16h or 48h after production. Before the test, the sample should be conditioned for more than 16h in any of the following environments. 23℃±2°C, (50±5) % relative humidity; 27℃±2°C, (65±5) % want to humidity; in the case of testing 16h after production, the state adjustment time can include part or all of the post-production placement time. When testing for quality control, the sample can be placed for a short period of time after production (down to the shortest 12h), and according to any of the above environmental regulations, a short state adjustment time (down to the shortest 6h) is used after adjustment. test. Test steps and results: 1. Preload state adjustment: The open-cell flexible foam material should be preloaded state adjustment before the test. The method is to compress the sample to 75% to 80% of the original thickness at a speed of 0.4mm/s to 6mm/s, and to precompress the sample twice to adjust the prestressed state of the sample, and then allow the sample to have a 10min±5min recovery period. Note: The prestress state adjustment does not apply to the closed-cell flexible foam materials mentioned in 3.2. Test method A: 1. According to the conditions specified in Chapter 8, start the test immediately after the state is adjusted. 2. Put the sample on the datum surface, adjust the height of the tube, so that the zero rebound is 16mm above the surface of the sample±0.5mm. Secure the tube to ensure that there is light contact between the tube and the specimen that does not cause any visible pressure. 3. Put the steel ball on the release device, then release the steel ball, and record the integer value of the maximum rebound height. If the ball hits the inner wall of the tube during the fall or rebound, the test result is invalid. This happens mainly because the tube is not vertical or the surface of the specimen is not uniform. To reduce visual errors, the tester's line of sight should be level with the rebound reading scale line on the tube.
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