Test method for minimum tightening torque of screw caps

In the ASTM standard catalog, the test standard for the minimum tightening torque of the screw cap is ASTM D 3810-1997 (2002) 'Test Method for Minimum Application Torque of Type IA Child Safety Cover' (Test Method for Minimum Application Torque of Type IA Child-Resistant Closures). This test method is mainly to determine the minimum tightening torque value to verify the use time of the child-proof feature of the screw cap. The minimum tightening torque value affects the fully degraded opening torque value, which must be greater than the expected maximum reverse ratchet torque during use. The minimum tightening torque test method can be used both to compare the child-resistant properties of two or more types of crimp caps, and to analyze the effect of factors such as liner material, cap material, and container type on the child-resistant properties.

The test sample is a screw-on child safety cover pretreated under certain environmental conditions. At each time interval and at each torque level, the minimum torque value of five samples was detected as a data point. The data points must be chosen to ensure that there is no longer a large change in torque degradation for a minimum duration of four weeks. For example, a large change in torque occurred on the third day of the test, but the torque may still change during the rest of the time. The time points of detection data can be selected from the 1st day, the 1st week, the 2nd week, the 3rd week and the 4th week.

Test conditions Time, temperature and humidity have a great influence on torque detection. To ensure the repeatability of the test, specific test conditions must be determined. Table 1 is a selection of some special environmental conditions. Before testing the lid-container system, each part must be left to stand alone in the specified environmental conditions for at least 48 hours, without stacking the parts on top of each other to ensure adequate circulation in the surrounding environment.

Detection steps

① First determine the tightening torque of three levels, and select the smallest level of tightening torque to test first. Some recommended opening torque ranges for different tests are as follows: 0.90 N·m-.13 N·m; 1.58 N·m-1.31 N·m; 2.15 N·m-2.37 N·m; 2.71 N·m-2.94 N m.

② Simulate the process environmental conditions such as container cleaning, hot filling and capping, and place the lid-container system under simulated environmental conditions to wait for the test. It is required that the torque detection test must be completed within 2 hours after environmental pretreatment. The detection of the tightening torque and opening torque must be done by one operator, thereby reducing operating errors.

③Using a platform torque tester, tighten all the screw caps smoothly and slowly at the same speed.

④Tighten the five caps with the minimum tightening torque in each level, then immediately use the platform torque detector to open the caps smoothly and slowly at the same speed, and record the opening torque value.

⑤In the storage environment, increase the tightening torque levels in turn, and tighten five bottle caps with the average tightening torque in each level. Then open the screw cap, as shown in ④. ⑥ When there is no obvious change in the opening torque, write down the tightening torque level or the opening torque level at this time. The measured fully degraded opening torque for a certain level must be greater than the expected maximum reverse ratchet torque.

Precautions

In the test report, the screw structure of the screw cap, the material of the inner and outer caps, the coating material of the inner cap, the container material and structure must be clearly described. When the minimum tightening level corresponding to the minimum opening torque level is determined, the torque control level on the packaging production line can be determined.

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