Leather of upper stretched tightly on the last or worn on the feet is not only subjected to tensile force from different directions, but also subjected to jacking force of vertical direction, so conducting the bursting strength test as a practical and comprehensive index is very necessary to judge the extensibility and resistance to burst of leather. Leather Lastometer is a perfect machine to complete this test.
The round edges of circular test piece is clamped into the machine, during the course of distension exerted by a steel metal ball in specified diameter, against the central part of finished surface, the acting force required and distention height are recorded respectively when cracking occurs on the grain surface and rupture happens on the leather. The bursting force is indicated by N, the elevated height is indicated by mm, and the bursting strength is indicated by N/mm.
leather cracking resistance tester
1 Apparatus
1)Clamp
Used to fix the round edges of a circular specimen flatly, and the central aperture of 25mm in diameter can be movable freely. The area being clamped shall be sustain unmovable when the central areal of test piece is subjected to a force of 800N. The junction area between fixed surface and movable surface shall be distinct.
2)Steel ball and force gauge
Distention force is generated through mechanical action by means of steel ball, which applies to the central area of finished surface and can be measured by a special gauge. The relative speed between steel ball and clamp is (12±2)mm/min, and the diameter of ball is 6.25mm. The error of gauge is not more than 3%.
3)Instrument to determine the travel distance of ball. The accuracy of instrument measuring distention height is to the nearest 0.1mm, and all graduation error is not more than 0.05mm.
The height of test piece distention upwards can be calculated in terms of the relatively moving distance between clamp and steel ball. The moving direction of steel ball shall be normal to the plane of the test piece clamped. The start point of relative movement is when the steel ball just contacts with finished surface of leather indicating value is zero. The thickness shrinkage of test piece resulting from pressure of steel ball doesn’t need to be calculated.
2 Sampling
The circular test piece is 44.5mm in diameter, and two semicircular notches on the side is used to locate on testing machine. It’d better cut sample in one time with a press knife. The test specimen shall be conditioned in advance.
3 Application range of this testing method
1)Suitable for various types of light leathers, especially for boots and footwear uppers.
2)If the surface of test piece is finished and painted leather to simulate grain surface or to act as grain surface rather than the full grain leather, the finished surface can be as grain surface to carry out test.
4 Test Procedure
1)Measure the thickness of air-conditioned test piece using a leather thickness gauge, then clamp the test piece into the testing machine horizontally, leaving the grain surface up, and finished surface just contacting with steel ball. Currently the gauge shall display zero.
2)Actuate the machine, velocity of upward distension is 1r/s, equivalent to 0.2mm/s moving vertically, and pay attention to the cracking whether occurs.
3)When cracking is observed in the process, force value and distention height are recorded as soon as possible, and pressuring for distension is to be continued.
4)When test piece bursts, record the force value and distension height.
Because cracking happens If distension suspends and reading goes down during the test. Get the reading soonest If this situation occurs.
5 Bursting strength is equal to applied force when bursting divided by the thickness of test piece.
6 Expression of results
1)If the test piece is broken due to distension, the height of cracking produced on the grain surface and bursting strength shall be expressed when being broken.
2)If the test piece is not broken due to distension, applied force and distension height shall be expressed when cracking occurs on the grain surface, and distension height also shall be expressed when the most applied force is exerted. No bust shall be marked.
3)If there are a few of test piece to be tested at the same time, every specimen shall have result separately, rather than mean value.
7 Attention
1)The mechanical part shall be calibrated at regular intervals, and the device for distention also shall be calibrated at fixed period. Reading must be calibrated If there is error.
2)Record the readings the earlier the better for both acting force and upheaval height.
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