Method of proof testing glass
A method of proof testing glass containers is disclosed. The method involves applying pressure to a sealed container in two discrete stages as shown in FIG. 1 . In the first stage, the pressure is increased to a peak over at a first rate. In the second stage, the pressure is reduced to zero at a much greater rate.
1. A method of testing the strength of a glass container, comprising:
pressurizing the container, the container failing the test if it breaks;
wherein the container is pressurized to be subjected to a pressure profile which in a first stage increases from a starting pressure to a peak pressure at a first average rate of pressure increase; and
wherein in a second stage decreases from the peak pressure to the starting pressure at a second average rate of pressure decrease which is greater than the first average rate of pressure increase.
2. A method as claimed in claim 1 , wherein the second stage of the pressure profile involves reducing the pressure substantially instantaneously to the starting pressure; and
wherein the starting pressure is atmospheric pressure.
3. A method as claimed in claim 2 , wherein the first stage of the pressure profile involved ramping the pressure substantially linearly to the peak pressure.
4. A method as claimed in claim 1 , wherein pressurizing the container comprises filling the container with water and pressurizing the liquid; and
wherein the pressure is applied by first sealing the container and applying the pressure hydrostatically using the water; and
wherein the container seal is applied using an o-ring which seals under hydrostatic pressure.
5. A method as claimed in claim 4 , wherein the pressure is released in the second stage by opening a hydraulic valve.
6. A method as claimed in claim 4 , wherein the pressure is applied using a mechanical servo driven drive and the pressure is released in the second stage by a pneumatic cylinder.
7. A method as claimed in claim 1 , wherein the container is subjected to a plurality of tests.
8. A method as claimed in claim 1 , wherein the first stage of the pressure profile has a duration of 30-250 ms; and
wherein the second stage of the pressure profile has a duration of 1-10 ms.
9. A method as claimed in claim 8 , wherein the first stage of the pressure profile has a duration of 40-70 ms; and
wherein the second stage of the pressure profile has a duration of 0-2 ms.
10. A method as claimed in claim 1 , wherein the second stage immediately follows the first stage.
11. A method as claimed in claim 1 , wherein the peak pressure is in the range 300-900 Bar.
12. A method as claimed in claim 11 , wherein the peak pressure is in the range 300-700 Bar.
13. A method as claimed in any one of claims 1 , 2 , 3 , 4 , 7 and 10 , wherein the pressure to which the container is controlled using feedback from a pressure sensor.
14. A method as claimed in claim 13 , wherein the container comprises a glass capsule for a needle-less injector.
15. A method of testing the strength of a glass container, comprising:
pressurizing the container, the container failing the test if it breaks;
wherein the container is pressurized and subjected to a pressure profile which in a first stage increases from a starting pressure to a peak pressure at a first average rate of pressure increase over a first period of time of 30-250 ms; and
wherein in a second stage which immediately follows the first stage and decreases from the peak pressure to the starting pressure at a second average rate of pressure decrease over a second period of time of 0-10 ms.
16. A method as claimed in claim 15 , wherein the second period of time is substantially instantaneous; and
wherein the starting pressure is atmospheric pressure.
17. A method as claimed in claim 16 , wherein the first stage of the pressure profile involved ramping the pressure substantially linearly to the peak pressure.
18. A method as claimed in claim 15 , wherein the first period of time has a duration of 40-70 ms.
19. A method as claimed in claim 18 , wherein the second period of time has a duration of 0-2 ms.
20. A method as claimed in claim 19 , wherein the container comprises a glass capsule for a needle-less injector.
21. A method as claimed in claim 15 , wherein the peak pressure is in the range 300-900 Bar.
22. A method as claimed in claim 15 , wherein the peak pressure is in the range 300-700 Bar.