Leak Tester

Abstract

A method for in-line leak testing of blow moulded containers wherein a conveyor line is fed with a continuous stream of blow moulded containers from a blow moulding machine, at least one measuring head is temporarily connected to a first blow moulded container. The measuring head is moved in order to follow the movement of said first blow moulded container which is pressurized by a source of pressurized gas, the source of pressurized gas is disconnected, said at least one measuring head is used to measure the pressure decay therein. The pressure decay is compared with stored data for the pressure decay of acceptable containers and an accept or non-accept signal is generated which implies proceeding or disposal of said first blow moulded container. The measuring head is moved against the moving direction of the conveyor line to a subsequent blow moulded container, and the process is repeated.

Claims

1. A method for the in-line leak testing of blow moulded containers comprising: feeding a conveyor line with a continuous stream of blow moulded containers from a blow moulding machine, wherein at least one measuring head is temporarily tightly connected to a first blow moulded container, said at least one measuring head is moved in order to follow the movement of said first blow moulded container; pressurizing said first blow moulded container by a source of pressurized gas whereafter the source of pressurized gas is disconnected; measuring, with said at least one measuring head, the pressure decay in said first blow moulded container while following the movement of said first blow moulded container; comparing said measured pressure decay with stored data for the pressure decay of acceptable containers and an accept or non-accept signal is generated which implies proceeding or disposal of said first blow moulded container such that the at least one measuring head thereafter is moved against the moving direction of the conveyor line to a subsequent blow moulded container, is tightly connected to said subsequent blow moulded container, is moved in order to follow the movement of said subsequent blow moulded container and is used to perform in-line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal for said subsequent blow moulded container.

2. The method according to claim 1, wherein the measuring head is moved to an idle position before it is moved and tightly connected to the subsequent blow moulded container.

3. The method according to claim 1, wherein the idle position is located close to the entry point of the fed containers.

4. The method according to claim 1, wherein measuring heads are arranged in a group comprising two or more measuring heads, moving in unison to test two or more blow moulded containers simultaneously.

5. The method according to claim 1, wherein the blow moulded container has a volume of at least 0.5 L.

6. The method according to claim 1, wherein the measuring head is tightly connected to the blow moulded container for less than 3 seconds.

7. The method according to claim 1, wherein the rate of leak tested bottles is at least 100 per minute.

8. The method according to claim 1, wherein the blow moulded containers are not fed in a tight sequence on the conveyor line due to deviations in the blow moulding machine and the distance between two or more measuring heads is adapted to random gaps between the containers.

9. The method according to claim 4, wherein the position of the group of measuring heads is adapted to block gaps occurring in the sequence of containers on the conveyor line due to batch wise production of the containers.

10. The method according to claim 1, wherein the block gaps occurring in the sequence of containers on the conveyor line are used to move the group of measuring heads against the moving direction of the conveyor line, or to move the group of measuring heads close to the idle position, or to move the group of measuring heads to the idle position.

11. The method according to claim 1, wherein the speed of the conveyer belt is automatically reduced to allow sufficient time for measurement, if the point at which the measurement can be initiated, is so far from the entry point and so close to the discharge point from the leak-testing station that the time for measurement becomes critically small.

12. The method according to claim 1, wherein after the accept or non-accept signal is generated at least one measuring head is moved to and hold at an idle position and the remaining heads are tightly connected to subsequent blow moulded containers which are measured with higher sensitivity compared to when all measuring heads are tightly connected to blow moulded containers.

13. The method according to claim 1, wherein all measuring heads are tightly connected for a prolonged time period to subsequent blow moulded containers on the conveyor line in order to perform a leak testing with higher accuracy compared to when the blow moulded containers are fed in a tight sequence on the conveyor line.

14. The method according to claim 13, wherein said leak testing with higher accuracy reduces the number of false generated non-accept signals.

15. A device (10) for in-line leak testing of blow moulded containers comprising: a conveyor line fed with a continuous stream of blow moulded containers from a blow moulding machine; at least one measuring head arranged to move in parallel with the blow moulded containers and to temporarily tightly connect with a first blow moulded container and movable in order to follow the movement of said first blow moulded container, wherein the measuring head is equipped to pressurize the first blow moulded container and to measure the pressure decay in said first blow moulded container while following the movement of said first blow moulded container; a control unit equipped to compare the measured pressure decay with stored data for the pressure decay of acceptable containers and to generate an accept or non-accept signal which implies proceeding or disposal of said first blow moulded container wherein the at least one measuring head is equipped to be moved against the moving direction of the conveyor line to a subsequent blow moulded container, tightly connected to the subsequent blow moulded container, moved in order to follow the movement of said subsequent blow moulded container, used to perform in-line leak testing of said subsequent blow moulded container and to generate an accept or non-accept signal said for the subsequent blow moulded container.

16. The device for in-line leak testing of blow moulded containers according to claim 15, wherein the measuring head is connected to a source of pressurized gas wherein the connection can be opened and closed by an automatic valve.

17. The method according to claim 1, wherein measuring heads are arranged in a group comprising three or more measuring heads, moving in unison to test three or more blow moulded containers simultaneously.

18. The method according to claim 1, wherein the blow moulded container has a volume of at least 2 L.

19. The method according to claim 1, wherein the measuring head is tightly connected to the blow moulded container for less than 2 seconds.

20. The method according to claim 1, wherein the rate of leak tested bottles is at least 600 per minute.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Below, the present invention is described in form of a few non-limiting embodiments illustrated by figures, in which:

[0029] FIGS. 1A-1G show schematically a side view of a leak-testing station with one measuring head in a number of situations, chronologically arranged;

[0030] FIGS. 2A-E show schematically a side view of a leak-testing station with three measuring heads in a number of situations, chronologically arranged;

[0031] FIGS. 3A and 3B show schematically a side view of a specific feature of the leak-testing station shown in FIG. 2; and

[0032] FIG. 4 shows a diagram illustrating functionality of the embodiments.

DETAILED DESCRIPTION

[0033] The terms “right”, “left”, “right-most” and “left-most” as used herein, are only in relation to the drawings, not intended to be general statements.

[0034] FIG. 1A shows a schematic side view of a device according to the disclosure in the form of a leak-testing station 10. A container 11 is about to enter the leak-testing station 10 on a conveyor belt 12. A measuring head 13 with connections to a source of pressurized gas (not shown) is suspended from a rail 14 via a carrier wheel 15 and a connection arm 16 which is shown as telescopic but may have any functional configuration. A pressure sensor 17 is arranged within the measuring head 13; it may as an alternative be arranged outside the measuring head 13 but in fluid connection therewith. The container is visualized as a bottle, but can have other forms as long as it exhibits an opening accessible from above. The only contact areas between the leak-testing station and the container are on the top between measuring head and container and at the bottom between conveyor belt and container. The side walls of the container are not touched in order to avoid scratches and similar defects. The connection between the connection arm 16 and the rail 14 can also have any functional configuration.

[0035] As shown in FIG. 1, the pressure head is in an idle or stand by position, i.e. to the far right in the drawing and slightly elevated (telescope retracted) so as to allow the container to move into a position below the pressure head without bumping into it.

[0036] While not shown, the far right point of the conveyer belt is in communication with an upstream conveyer belt or the like feeding containers to the test station 10.

[0037] In FIG. 1B the container has moved to a position within the testing station, has been detected and the pressure head has initiated a movement in the same direction with the same approximate speed and initiated a lowering of the head towards the opening at the container top. The small vertical arrow indicates that the measuring head is moving downwards.

[0038] In FIG. 1C the measuring head is tightly connected to the opening of the container and at this point the container is immediately filled with air or other gas from a pressurized source thereof, via the measuring head to a predetermined pressure.

[0039] In FIG. 1D, the pressure source has been disconnected and the measurement of pressure decay is initiated. As indicated by the comparatively short distance travelled from the position of the container in FIG. 1C, the pressurizing of the container is a quick operation. In fact, it may be even quicker than visualized by FIGS. 1C and 1D.

[0040] FIG. 1E shows the point at which the measurement is to be terminated. As shown, the leak-testing station has a width that is more than sufficient for measurements that are initiated at the entry point of the containers, which is beneficial for reasons explained below.

[0041] FIG. 1F shows that the measuring head has been disconnected from the container and is no longer moving away from the entry point while the container naturally continues to the left.

[0042] FIG. 1G shows the measuring head returning back to the entry point or idle position, which it can safely do since in this particular case no further container is about to enter the leak-testing station.

[0043] FIG. 2A shows an embodiment of a leak-testing station according to the disclosure comprising three measuring heads 13, all parked at the entry point. A container A is about to enter the station.

[0044] In FIG. 2B, a moment later, two containers A, B have entered the leak-testing station, A being tightly connected to the left-most measuring head and in the process of being pressurized, B about to be connected to the second measuring head while the third measuring head is still idle.

[0045] In FIG. 2C a third bottle C has entered the leak-testing station and is about to be connected to the third measuring head. As shown, the distance between container B and C is larger than the distance between container A and B, reflecting a small “interruption” in the feed of containers and the third measuring head has been adapted to this increased distance. In the meantime, measurement is being performed on container A while container B has been pressurized.

[0046] As shown by FIG. 2D, container A has reached a position similar beyond that at which the measurement was terminated in the embodiment of FIG. 1 (FIG. 1E). However, since the measuring head connected to container A cannot return before also the measurements of containers B and C are completed. There is therefore an option to continue to measure pressure drop in container A as well, an option that is sensible to use to the extent that added measuring time also will contribute to added certainty of the measurement and the conclusion on accepting or rejecting the container.

[0047] FIG. 2D shows a situation in which three subsequent containers D, E, F follows containers A, B, C so close that the measuring heads do not have the time to move all the way back to the entry point, but initiate the process at the point illustrated, all three heads moving down to connect the point shown, a distance from the entry point.

[0048] If even additional containers arrive without interruption, a situation may occur in which the point at which the measurement can be initiated, is so far from the entry point and so close to the discharge point from the leak-testing station 10 that the time for measurement becomes critically small. If or when that occurs, the speed of the conveyer belt 12 may be automatically reduced to allow sufficient time for measurement. When an interruption occurs, and the measuring heads again have the time to move back to the entry point, the speed can again be raised to normal.

[0049] Now referring to FIGS. 3A and 3B, if containers arrive in a certain pattern, it may be more convenient to let the right-most measuring head rest in the idle position even when there is a container on the conveyer belt which could be tested by that measuring head, due to the fact that it is more sensible use of the resources to be able to return the other heads earlier, and instead let the left-most measuring heads test the container in question as the first one of the next cycle of movement. This is illustrated by FIG. 3A in the sense that container I is not tested by the right-most measuring head even if it could. Instead, when the testing is done on containers G and H, all the two measuring heads performing the testing on containers G and H returns and all three measuring heads go into action to test containers I, J and K simultaneously.

[0050] FIG. 4 shows a typical pressure versus time curve for leak testing by connecting a blow moulded container to a measuring head and a source of pressurized gas. A maximum pressure is reached at T.sub.0. After the source of pressurized gas is disconnected a pressure decay occurs until T.sub.1 is reached. The straight line shows the pressure decay of a container which can still be acceptable at T.sub.1. Pressure decay is caused by delayed volume increase of the bottle (plastic deformation) and/or unavoidable pressure loss between measuring head and container. The interrupted line shows the pressure decay of a container which has to be rejected already at T.sub.1 due significant leakage of pressurized gas. The pressure decay is further measured until T.sub.2 is reached. The straight line shows a pressure decay which flattens. The container is accepted. The interrupted line shows an unacceptable pressure drop which does not flatten. This container has to be rejected.

[0051] While embodiments of one and three measuring heads are mentioned above, other embodiments are feasible, such as four and even more measuring heads within the same leak-testing station.

[0052] In some embodiments, the blow moulded containers have a volume of at least 0.5 L, or at least 2 L or at least 10 L.

[0053] In some embodiments, the measuring head is tightly connected to the blow moulded container for less than 3 seconds, or less than 2 seconds or even less than 1 second.

[0054] In certain embodiments the rate of leak tested bottles is at least 100 per minute, or at least 600 per minute or at least 1200 per minute.

[0055] In some embodiments, the blow moulded containers are fed in a variable sequence on the conveyor line, e.g. due to deviations in the blow moulding machine, in which case the distances between two or more measuring heads are adapted to the actual (random) gaps between the containers.

[0056] In some embodiments the position of the group of measuring heads is adapted to block gaps occurring in the sequence of containers on the conveyor line due to batch wise production of the containers. Modern blow moulding machines operate frequently with several blow moulding heads in parallel and feed more or less tight blocks of containers onto the conveyor belt. After such a block of containers there is frequently a gap until the next block of containers is fed onto the conveyor belt.

[0057] In particular embodiments, the block gaps occurring in the sequence of containers on the conveyor line are used to move the group of measuring heads against the moving direction of the conveyor line and to move the group of measuring heads close to the idle position or to move the group of measuring heads to the idle position.

[0058] In some embodiments, after the accept or non-accept signal is generated, at least one measuring head is moved to and hold at an idle position and the remaining heads are tightly connected to subsequent blow moulded containers. Such a set-up allows a measurement with higher sensitivity compared to the set-up when all measuring heads are tightly connected to blow moulded containers.

[0059] In a particular embodiment all measuring heads are tightly connected for a prolonged time period to subsequent blow moulded containers on the conveyor line. This set-up allows to perform a leak testing with higher accuracy compared to when the blow moulded containers are fed in a tight sequence on the conveyor line. Leak testing with higher accuracy reduces the number of false generated non-accept signals.

[0060] In some embodiments, the measuring heads in the machine for in-line leak testing of blow moulded containers are connected to a source of pressurized gas wherein the connections can be opened and closed by automatic valves.

[0061] It should be emphasized that the drawings are just illustrative for the purpose of the general principles of the exemplary embodiments, and that actual design of the elements shown can deviate significantly from these simple schematic drawings.