This invention, in general, relates to a process and apparatus for testing containers. More specifically, this invention relates to a process and apparatus for testing the fluid tightness of containers. This invention is especially, but not exclusively, intended for use in testing containers comprising a container body having an aperture which is sealed by a lid.
In many industries, it is important to test the fluid tightness of containers. For example, in the food industry, it is essential to ensure that containers in which foodstuffs are packed are completely sealed to ensure that the foodstuffs are in good condition, free from molds, bacteria and other pathogenic organisms, so that they will be safe when used by consumers. The pharmaceutical industry similarly requires that containers for medications, especially solutions intended for injection or intravenous administration, be protected from contamination or serious danger to public health may result.
Because fluid tightness of containers is not readily ascertained by visual inspection, various attempts have been made to provide apparatus for testing fluid tightness (hereinafter, for convenience, called "leak detection apparatus.") For example, U.S. Pat. No. 4,862,732 describes a "squeezing apparatus" for testing the fluid tightness of plastic bottles, such as those in which laundry detergents are commonly sold. This apparatus creates a pressure within the bottle by squeezing it by means of a pneumatic cylinder. It monitors the position of the piston of this cylinder; if the bottle does not leak, the piston will stop as soon as the pressure in the bottle increases enough to balance the force of the piston. After equilibrium, continued pressure caused by the squeezing will diminish as pressurized gas within the bottle leaks, and thus the piston of the pneumatic cylinder will move further than in the case of a non-leaking bottle.
The apparatus described in this patent gives good results under commercial conditions with the bottles for which it was designed. However, there are several types of commercial container products which cannot be tested by such squeezing apparatus. For example, yogurt is often sold in frusto-conical or inverted frusto-conical (i.e., with a lid wider than the base) containers having a base, a lid which seals an aperture at the upper end of the container, and sloping sides connecting the base to the lid. If one attempts to test the fluid tightness of such inverted frusto-conical containers using he apparatus described in the aforementioned patent, the sloping sides allow the container to slide upwardly relative to the pneumatic cylinder, thus placing a smaller diameter section of the container adjacent the piston, allowing the piston to move forwardly, and disturbing the reading, since the apparatus interprets the forward movement of the piston as indicating a leak in the container. Also, the plastic material conventionally used to form such containers is much thinner and are fragile than that used in plastic detergent bottles, and such thin plastic often buckles or becomes permanently creased if such containers are tested in the apparatus described in the aforementioned patent. Similarly, some berries are commonly sold in flat, semi-rigid plastic trays formed from thin plastic film and sealed with a foil or plastic membrane lid. These trays are unsuitable for testing in a squeezing apparatus since the tray is too rigid and shallow to be squeezed horizontally, and the lid is too fragile to permit vertical squeezing.
Several forms of leak detection apparatus are known which do not rely on squeezing the container. In one form of such apparatus, the container to be tested is placed within a fluid tight chamber, the pressure within the chamber is changed from atmospheric to above or below atmospheric, and the effect of this pressure change on the container is monitored. For example, U.S. Pat. No. 3,751,972 (Hass) describes a leak detector for testing sealed containers formed of semi-rigid or flexible material. The container to be tested is placed in a chamber which is thereafter pressurized at a pressure distinctly different from the internal container pressure, whereby the container is caused to physically distort. A container dimension is first sensed before the chamber is pressurized to produce a first signal representing the dimension resulting from the difference between container internal pressure and atmospheric pressure, this first sign al being held. When the container is under pressure in the chamber and a predetermined time interval has elapsed, the container dimension is again sensed to produce a second signal representing the dimension as a result of the difference between internal pressure and chamber pressure. The first held signal and the second signal are compared and if the disparity therebetween indicates a significant change in dimension, the container is accepted, whereas if there is little disparity between the signals, the container is rejected.
Similarly, U.S. Pat. No. 5,105,654 (Maruyama et al.) describes an apparatus which is generally similar to that of Hass but in which at least a portion of the container being tested comprises an electrically conductive material, and the chamber is provided with an eddy-current displacement sensor to detect the position of the conductive material of the container.
U.S. Pat. No. 5,365,774 (Horlacher) also describes an apparatus which is generally similar to that of Hass but in which the chamber is equipped with a suction cup at the end of a suction pipe. This suction cup is placed above the flexible cover of the container being tested. When the pressure in the chamber is reduced, the cover bulges and blocks the suction cup. If the seal between the cover and the body of the container is ineffective, the lid does not bulge and block the cup, thus enabling the ineffective seal to be detected.
U.S. Pat. No. 5,513,516 (Stauffer) describes a method and apparatus in which a flexible or semi-flexible package is received within a closeable test cavity, and a pressure differential is established between the inside of the container and an enclosed space within the test cavity outside of the container. The closeable test cavity comprises a flexible wall whose shape adapts to the shape of the container, at least when the pressure differential is established. The flexible wall advantageously compensates for variations in head space and shape of the packages, as when the contents are not uniformly distributed within the package. The flexible wall can sealingly contact a portion of the container spaced from a container seal to permit detection of seal leaks. A gas permeable, flexible screen can be employed between the container and the flexible wall to permit leak detection of leaks in the container beneath the flexible wall.
Similarly, U.S. Pat. No. 4,055,984 (Marx) describes a device for detecting leaks in an article having readily deformable walls. This device has conventional arrangements for performing a leak detection by overpressure or by vacuum and has a deformable backup wall for engagement with the walls of the article. The backup wall is, on its face oriented towards the article, so configured that between the backup wall and the article there is obtained a coherent fluid tight space which may be evacuated.
The leak detection devices just described suffer from one serious problem when used in commercial settings. Food packages for retail sale, and similar relatively low cost packages, are normally filled on continuous packing lines which run at high speeds, typically at least 30 packages per minute, and it is highly desirable to conduct the leak detection procedure in-line with the packing line. Removing one or two packages from such a packing line, placing them within a vacuum chamber, resealing and applying a vacuum to the chamber, effecting the desired measurement on the package(s), restoring the chamber pressure to atmospheric, opening the chamber and removing the package(s) will in total take at least several seconds. Thus, it is difficult to carry out the leak detection procedure with a throughput sufficient to keep up with the packing line. Although multiple sets of leak detection apparatus can of course be used with a single packing line, the provision of such multiple sets, together with the necessary apparatus for directing packages to the proper leak detection apparatus, and reassembling the packages into a single stream after leak detection, greatly increases the complexity and cost of the packing line.
U.S. Pat. No. 4,774,830 (Hulsman, assigned to the same assignee as the present application), describes a leak detention apparatus which operates on a rather different principle from those previously described. The Hulsman apparatus is used in detecting defective flange-shaped seals between lid and body portions of a package. A pressure chamber is provided for isolating the external edge of the seal and applying a test pressure thereto. Containment of the pressure chamber includes sealing pressure applied mechanically to the flange-shaped package seal during testing. If the seal is defective, gas flows in one direction between the pressure chamber and interior of the package, thus causing a displacement of the lid of the package, and this displacement of the lid is detected by a position detector disposed adjacent a central portion of the lid, this central portion of the lid lying outside the pressure chamber and thus being maintained at ambient pressure. This Hulsman apparatus is effective in detecting leaks and better adapted than the apparatus previously discussed for use in-line with a packing line, since the Hulsman apparatus does not require removal of each package from the line and placement of the whole container within a pressure or vacuum chamber. The pressure chamber of the Hulsman apparatus is formed by two separate members which can close, clamshell style, on a package which is already resting on a transport conveyor or similar device. However, the Hulsman apparatus does require that the seal be placed within a pressure chamber. In addition, there is some risk of mechanical damage as a fragile lid is grasped between the members forming the pressure. Also, the process will not detect a leak located anywhere except in the lid sealing area, for example, in the lid or in the cup.
Accordingly, it is a primary object of the present invention to provide a process and apparatus for testing the fluid tightness of a container which, like the Hulsman process and apparatus, does not require placement of the entire container within a vacuum or pressure chamber. However, unlike the Hulsman process and apparatus, the present process and apparatus also does not require placing a portion of the lid of the container within a pressure chamber, and it tests the entire container for leaks, not just the lid to cup sealing area.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter when the description to follow is read in conjunction with the drawings.