GB2299865A - Leak testing containers formed on blow moulding machine - Google Patents

Abstract

A leak testing apparatus for testing containers formed on a blow moulding machine in which containers are formed by blow moulding a parison by the introduction of a gas through a core rod in which the parison is supported, includes: (a) means (6,8) for introducing a gas under pressure into a container (7) via a core rod (2,3,4) of a blow moulding apparatus (1) whilst said container is supported on the core rod (2,3,4); (b) means for measuring the pressure and the pressure decay in the container as a function of time; and (c) indicating means for indicating whether the pressure in the container reaches a predetermined level or whether the pressure decay from the container per unit time is greater than a predetermined amount, pressure less than the predetermined level or pressure decay per unit time greater than a predetermined amount being indicative of a hole in the container.

Description

LEAK TESTER This invention relates to an apparatus and method for the testing of leaks in containers, particularly those made by injection blow moulding.

Containers can be formed by injection blow moulding either in single stage or two stage processes. In single stage blow moulding1 a container preform is injection moulded and is immediately thereafter transferred to a blow mould within which the container is formed. In two stage blow moulding1 a preform Is separately Injection moulded and is thereafter cooled. It is subsequently reheated for blow moulding. The leak testing method and apparatus of the present invention may be utilized in either system. In fact it can be utilized in any blow moulding apparatus. However, it is principally suited to single stage injection blow moulding and the invention is hereafter described with reference to such methodology and apparatus. It should be appreciated, however, that the invention is not so limited.

Conventionally, single stage injection blow moulding apparatus includes a central turret which transports a parison/bottle sequentially to respective treatment stations. The first such treatment station in conventional apparatus is an injection station. At the injection station, melted plastic resin is injected Into a parison cavity and around a core rod. The core rod is connected to the central turret and this turret rotates to transport the parison to second and third stations usually being a blow mould station and an ejection station respectively.

Once the parison has been injection moulded, the turret of the apparatus Is rotated so that the formed parison is located at the blow station. The blow station comprises a blow mould in the shape of the desired container and the core rod to which the parison is attached includes a central aperture through which air may be passed under pressure so to blow the heated parison into the blow mould. Air is passed through the core rod expanding the parison against the cavity of the blow mould which in turn cools the formed bottle. Blowing and curing of the bottle takes place within the blow mould. The turret is then further rotated so that the formed bottle is transferred to the ejection station at which point the formed bottle is ejected from the turret apparatus.The process is generally conducted with the parison and the formed bottle being disposed horizontally in and through each of the stages.

The time for an entire cycle varies according to a number of factors including the size of the bottle being formed1 the nature of the resin being used and the wall thickness desired. The time limiting step is the Injection moulding of the preform and this generally takes somewhere between about 9 to 18 seconds.

Whilst Injection blow moulding using such apparatus is very reliable, contamination in the polymer is quite common and can produce holes of sufficient size to cause a problem to customers. it is thus necessary for all bottles to be tested for possible leaks.

in the past it has been convention practice to test for leaks in the formed containers after they have been ejected from the blow mould apparatus. Usually, the containers are sequentially passed through a separate testing apparatus positioned adjacent to the ejection station. The formed containers are mechanically handled so to stand upright (having been formed and ejected whilst lying horizontally) and are then conveyed through a testing apparatus.

There are various forms of leak testing apparatus presently available.

They generally Include means to introduce a gas into the individual containers sequentially at measured pressures higher than atmospheric pressure and separate means to thereafter measure the pressure decay as a function of time.

The accuracy of such testers Is largely dependent on the time available to test each separate container. The smaller the hole in the bottle the slower will be the loss of pressure and the longer it will take accurately to detect. With a multi cavity injection blow moulding apparatus having for example 12 cavities operating In a standard cycle of about 15 seconds the leak testing apparatus must test each formed container in little more than 1 second Conventional leak testing apparatus is also bulky as separate mechanisms are required for the handling of the bottle from the horizontal to the vertical disposition and to convey the bottle to the leak testing station. Further, the apparatus must include means to accurately locate the formed containers under the testing unit for air tight connection of an air Injection nozzle Into the outlet opening of the bottle.

The aim Df the present invention is to provide an apparatus and method for the testing of bottles formed by blow moulding which overcomes some of the deficiencies of prior arrangements as hereinbefore described.

The present invention achieves this aim W through apparatus adapted to test containers for leaks whilst the container is still attached to the blow moulding apparatus.

In accordance with the present invention there is provided a leak testing apparatus for testing containers formed on a blow moulding machine in which containers are formed by blow moulding a parison by the introduction of a gas through a core rod on which the parison is supported, said leak testing apparatus Including: (a) means for introducing a gas under pressure into a container whilst said container is supported on a core rod of a blow moulding apparatus; (b) means for measuring the pressure and the pressure decay in the container as a function of time; (c) indicating means for indicating whether the pressure in the container reaches a predetermined level or whether the pressure decay from the container per unit time is greater than a predetermined amount thus being indicative of a hole in the container; wherein said gas introducing means is connected to the container through the core rod on which the container is held.

The apparatus of the present invention is suitable for use with any apparatus In which a container is formed by blow moulding through a core rod used to support the parisonicontainer and through which air or gas is passed to blow mould the container.

Once the bottle has been blown and cured, the passageway in the core rod used to blow mould the container can be used for the introduction of a second gas by the leak testing apparatus. As previously stated, the invention has particular application In Injection blow moulding apparatus and it is preferred that the blown bottle be blown and transferred to the ejection station of the injection blow moulding apparatus before it is tested. in this way, the formed container is entirely disengaged from the blow mould and disposed independently. This facilitates more accurate testing.

Preferably, the leak testing apparatus is used in conjunction with an injection blow moulding apparatus which Incorporates a central turret having at least three core rods - one for each of the respective injection blow mould and ejection stations.

The apparatus preferably operates on a cycle such that whilst a parison is being injection moulded at the first station, a bottle is being blow moulded at the second station and a formed bottle is being tested for leaks and then ejected at the third station. Additional core rods and stations can be incorporated for additional treatment steps as is known in the art. In this preferred embodiment, the leak tester apparatus is connected to each of the respective core rods and separate control means is provided so to regulate the gas from the gas introduction means so that gas under pressure is delivered only to the respective core rods when positioned at the ejection station. A three way valve or other sultable mechanism can be utilized.

Preferably, the control means is set so to permit the introduction of the leak testing gas substantially Immediately after the transport of the formed container to the ejection station. In this way, the optimum time period is available for testing and ejection of the formed container prior to the rotation of the core rod to the injection station. In a multi-cavity apparatus the leak tester should be connected to all of the core rods and the control means regulated so that the gas from the gas introduction means is delivered only into each of the core rods located at any time in the ejection station position.

When the apparatus is utilized with multi-cavity injection blow moulding apparatus it is thus possible to simultaneously test a number of containers whilst they are still on their respective core rods positioned at the ejection station.

whilst it is possible to incorporate separate means for measuring the pressure decay from each of the containers simultaneously, this is usually not required as the discovery of holes In formed containers is sufficiently rare that if a hole is detected in any one of a set of containers (e.g such as a set of 12 containers in 12 cavity tool) then all of the containers in the set for which a leak has been detected may be discarded. Alternatively, of course if separate pressure measuring means are utilized for each core rod and container, it is possible to discard only that container or those containers found to be defective.

The means used to Introduce the high pressure gas into the respective containers may be of any pneumatic type as known in the art. A test facility may be conveniently added to the pneumatic circuit.

A small orifice1 in the order of 0.5 mm in diameter may be incorporated in the pneumatic circuit in such manner that it can be opened or closed. As soon as a container moves into position to be tested. the hole is opened and the air from the system is deliberately leaked. This will mean that the pressure In the container will not reach the predetermined level and If the apparatus Is operating correctly, the indicating means should register a leakage. This simple expedient allows the apparatus to be easily tested at any time.

The means for measuring the pressure decay as a function of time may take many forms also as well known in the art. To reduce bulk it is however preferred that the pressure measurement means incorporate a digital integrated circuit pressure sensor in which an operational amplifier is used to bias the integrated circuit to set the pressure level at which the sensor will trip.

The indicating means can operate so to immediately stop the blow moulding apparatus once a leak is detected (this is particularly useful in identifying possible problems in the apparatus itself such as in the mould1 which might be causing the defects in the containers to occur). Alternatively, the indicating means may be operatively attached to a mechanism for separately collecting the container or set of containers in which a hole has been detected.

The present invention also provides a method for testing for leaks in containers which have been formed on a blow moulding machine in which the containers have been formed by blow moulding a parison by the introduction of a gas through a core rod on which the parison has been supported, said method including: (a) introducing a gas under pressure into a container for a predetermined time whilst said container is supported on a core rod of a blow moulding apparatus; (b) measuring the pressure andlor the pressure decay in the container as a function of time; (c) discarding the container if the pressure in the container fails to reach a predeterrnined level or if the pressure decay exceeds a predetermined amount being indicative of a hole in the container; wherein the gas is introduced into the container through the core rod on which the container is supported.

Preferably, air is Introduced at a low pressure into the container for a fixed time (t,). The pressure inside a container without a detectable leak will reach a pressure higher than atmospheric pressure (p1) after tl. If the pressure does not reach p1 after t1 this is indicative of a leak and the container is discarded. If the pressure reaches p1 then the pressure inside the container is sampled after a further short period of time t2 (preferably in the order of 2.0 to 5.0 seconds). In a container without a detectable leak, the pressure will not drop below P2 after t2. If the pressure falls below the predetermined level p2 after t2 the container is discarded.

A preferred embodiment of the invention is hereinafter described by wav of example only with reference to the following drawings, in which: Figure 1 Is a schematic drawing of an injection blow mould apparatus; and Figure 2 is a graph illustrating the typical variation of pressure against time in a pressurized container.

With reference to Figure 1, there is shown a turret 1 to which there is attached three separate core rods 2, 3 and 4. Turret I rotates so that the respective core rods are positioned sequentially in the positions marked as "injection station", "blow station" and ejection station". At the injection station, melted plastic resin is injected around core rod 2 and into a parison cavity (not shown). In conventional injection blow mould equipment as shown, the injection moulding of the parison at the injection station takes somewhere between about 9 to 18 seconds. This is the time limiting step in the formation of containers on this apparatus. Once the parison has been injection moulded, the turret rotates so to move core rod 2 holding the formed parison into the position of the blow station.

Air is passed through the centre of the core rod so to blow the parison Into the shape of the blow mould 5. The blow moulding of the parison into a container usually takes somewhere between 3 to 5 seconds. It however remains located at the blow station until the turret rotates to bring the next parison from the injection station into the blow station position. When this occurs, the formed container is moved from the blow station to the ejection station. In conventional equipment, the formed container is thereafter Immediately ejected and moved to an independent leak tester. In the present invention, the leak testing apparatus 6 is connected by flexible condults 8 to each of the respective core rods. When the formed bottle 7 reaches the ejection station, It is not immediately ejected but retained on the core rod.A pump in unit 6 is used to introduce air Into the container at a pressure preferably between 1.5 to 5.0 psi. Most preferably, the container 7 Is pressurized to about 2.5 psi. This pressure has been found sufficlent to detect holes of between 0.25 to 0.5 mm in diameter in a test period of about 2.5 seconds. Air is introduced for a fixed period of time at a relatively slow rate so that the introduced gas will not damage the formed container. Preferably, this fixed period (t) is in the order of 1.5 seconds. As the injection blow mould apparatus is time limited by the injection moulding of the parison, there is a significant period of time available for the testing of the formed container at the ejection station. Anything up to about 18 seconds.Generally, not all of this time period is required and a period of approximately 2% seconds is all that is generally required. A pressure of Pl is applied to a container known to have no leaks so to determine what the pressure should be within the bottle after t2 if no leaks are present. This pressure Is then the predetermined level P2. After time t2 the pressure inside the container is sampled and if it is below P2 the indicating means within leak tester 6 (which is connected to an appropriate switching device) is activated so that bottle 7 is ejected and conveyed to a station for discarded bottles rather than a separate station for the containers found to have no leaks. The typical variation of pressure against time Is shown in Figure 2.

In a multi cavity system, leak tester 6 is connected to the core rods for each of the respective cavities and the indicating means within leak tester 6 can be used to indicate a leak within any one of the containers or alternatively, separate indicating means may be operatively attached to each core rod.

It will be appreciated that the present invention offers significant advantages over conventional apparatus. First, the present Invention provides a method and apparatus which can readily leak test bottles of any shape.

Conventional equipment can only test in the vertical plane. Once the bottles have been ejected from the ejection station, they must be transported into a leak tester.

A bottle without a base upon which the bottle can stand is very difficult to test with such apparatus. Bottles which have oval cross sections are very difficult to arrange In a single line so to be accurately aligned under a testing head. In conventional apparatus, the machine has to index each bottle so that they are accurately aligned. The present invention can leak test any shape of bottle successfully.

Secondly, the apparatus and method of the present invention permits for more accurate testing. As indicated earlier, with a multi cavity tool having say, 12 cavities, running at a cycle time of 15 seconds, the conventional sequential machine must test each container in little more than 1 second. As pressure decay apparatus is dependent largely on the time available, such apparatus can only be relied upon to accurately detect relatively large holes. The smaller the hole one attempts to detect, the slower will be the loss of pressure and thus the longer it will take to accurately detect. The leak tester of the present invention has the whole of the blow time (i.e. between about 9 to 18 seconds) to test for a hole in each container.

Thus, the present invention provides a less bulky, more convenient and more accurate leak testing device than prior self standing apparatus which is suitable for use in a range of different blow moulding applications.

Various modifications, alterations and additions to the apparatus as hereinbefore described will be apparent to those skilled in the art and fall within the scope of the present invention as defined in the following claims.

Claims (15)

Claims

1. A leak testing apparatus for testing containers formed on a blow moulding machine In which containers are formed by blow moulding a parison by the introduction of a gas through a core rod in which the parison is supported; said leak testing apparatus including: (a) means for introducing a gas under pressure into a container whilst said container is supported on a core rod of a blow moulding apparatus; (b) means for measuring the pressure and the pressure decay in the container as a function of time; (c) indicating means for indicating whether the pressure in the container reaches a predetermined level or whether the pressure decay from the container per unit time Is greater than a predetermined amount, thus being indicative of a hole in the container; wherein said gas introducing means is connected to the container through the core rod on which the container Is held.

2. The apparatus as claimed In claim 1 wherein said gas introducing means is connected to the container through the passageway in the core rod used for the blow moulding of the container.

3. An apparatus as claimed in either one of claims 1 or 2 wherein said apparatus is operatively connected to an inJection blow moulding apparatus.

4. An apparatus as claimed in claim 3 wherein the injection blow moulding apparatus includes an injection station at which the bottle parison is injection moulded, a blow mould station at which the parison is blown into a blow mould so to form a container and an ejection station at which the formed container is ejected, wherein the parison/container is formed and transported from the injection station to the ejection station on a core rod.

5. An apparatus as claimed in claim 4 wherein the gas Is introduced into the container under pressure after the container has been transported to the said ejection station.

6. An apparatus as claimed In any one of claims 3 to 5 wherein the leak testing apparatus is permanently operatively connected to each of the core rods of the injection blow mould apparatus.

7. An apparatus as claimed in claim 6 wherein the injection blow mould apparatus comprises multiple cavities for the simultaneous production of more than one container at a time and wherein the leak testing apparatus is operatively connected to the core rods for each said cavity.

8. An apparatus as claimed in claim 8 wherein separate measuring means are Incorporated so to measure the pressure and the pressure decay from each of the respective containers being simultaneously tested and separate Indicating means for indicating which of the respective containers have been found to have a hole.

9. An apparatus as claimed in any one of the previous claims In which the pressure measurement means incorporates a digital integrated circuit pressure sensor in which an operational amplifier is used to bias the integrated circuit to set the pressure level at which the sensor will trip.

10. An apparatus as claimed in any one of the previous claims incorporating a test facility to ascertain whether the apparatus is operating correctly in which the connection between the core rod and the gas introducing means incorporates an orifice which may be opened or closed.

11. A method for testing for leaks in containers which have been formed on a blow moulding machine in which the containers have been formed by blow moulding a parison by the introduction of a gas through a core rod on which the parison has been supported; said method including: (a) introducing a gas under pressure into a container for a predetermined time whilst said container is supported on a core rod of a blow moulding apparatus; (b) measuring the pressure and/or the pressure decay in the container as a function of time; (c) discarding the container if the pressure in the container fails to reach a predetermined level or If the pressure decay exceeds a predetermined amount being indicative of a hole in the container; wherein the gas is introduced into the container through the core rod on which the container is supported.

12. A method as claimed In claim 11 wherein gas is introduced into the container for a period between 1 to 3 seconds and in which the pressure within the container is raised to between 1.5 to 5.0 psi.

13. A method as claimed in either one of claims II or 12 wherein the pressure Inside the container is tested between 2 to 5 seconds after the gas has been introduced Into the contalner.

14. An apparatus substantially as hereinbefore described with reference to the acccmpanyinq drawings.

15. A method substantiallv as hereinbefore described with reference to the accompanying drawings.