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 which in a second stage decreases from the peak pressure to the starting pressure at a second, greater, average rate of pressure decrease, wherein the first stage of the pressure profile involved ramping the pressure substantially linearly to the peak pressure.
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.
3. A method as claimed claim in claim 2 , wherein the starting pressure is atmospheric pressure.
4. A method as claimed in claim 1 , wherein pressurizing the container comprises filling the container with a liquid and pressurizing the liquid.
5. A method as claimed in claim 4 , wherein the pressure is applied by first sealing the container and applying the pressure hydrostatically using the liquid.
6. A method as claimed in claim 5 , wherein the water is used to apply the pressure hydrostatically.
7. A method as claimed in 5 or 6 , wherein the container seal is applied using an o-ring which seals under hydrostatic pressure.
8. A method as claimed in claim 7 , wherein the pressure is released in the second stage by opening a hydraulic valve.
9. A method as claimed in claim 7 , wherein the pressure is applied using a mechanical servo driven drive and the pressure is released in the second stage by a pneumatic cylinder.
10. A method as claimed in claim 1 , wherein the container is subjected to a plurality of tests.
11. A method as claimed in claim 1 , wherein the first stage of the pressure profile has a duration of 30-250 mns.
12. A method as claimed in claim 11 , wherein the first stage of the pressure profile has a duration of 40-70 mns.
13. A method as claimed in claim 1 , wherein the second stage of the pressure profile has a duration of 0-10 ms.
14. A method as claimed in claim 13 , wherein the second stage of the pressure profile has a duration of 0-2 ms.
15. A method as claimed in claim 1 , wherein the second stage immediately follows the first stage.
16. A method as claimed in claim 1 , wherein the peak pressure is in the range 300-900 Bar.
17. A method as claimed in claim 16 , wherein the peak pressure is in the range 300-700 Bar.
18. A method as claimed in any one of claims 1 , 2 , 3 , 4 , 4 , 10 , 13 and 15 , wherein the pressure to which the container is controlled using feedback from a pressure sensor.
19. A method as claimed in claim 18 , wherein the container comprises a glass capsule for a needle-less injector.
20. A method of testing a plurality of containers, comprising:
applying to each container of a plurality of containers a method comprising the steps of:
pressurizing each container 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 which in a second stage decreases from the peak pressure to the starting pressure at a second, greater, average rate of pressure decrease; and
determine if each container break as an indication of test failure, wherein the first stage of the pressure profile involved ramping the pressure substantially linearly to the peak pressure.