Method for improving leak testing of hollow plastic containers with a mouth hole

Abstract

Method for improving the leak testing of hollow plastic containers (5) provided with a mouth opening, in which method a mold (3) with several cavities and an auxiliary mold (4) are used, into which the plastic containers (5) produced in the mold (3) are transported for further removal with the aid of a manipulator for further processing, characterized in that in the method onto the inside of simultaneously produced plastic containers (5) through the mouth opening before carrying out the leak test, a compressed air blowing at a constant temperature is directed simultaneously into all plastic containers (5) as an equal volume flow in order to stabilize their internal air temperature.

Description

[0001] The present invention relates to a method for improving the leak testing of hollow plastic containers provided with a mouth opening, in which method a mold with several cavities and an auxiliary mold are used, into which the plastic containers produced in the mold are transported for further removal by means of a manipulator for further processing.

[0002] Hollow plastic containers with a mouth opening, such as bottles and canisters, can be manufactured, for example, from a tube blank by blow molding in a mold having a mold cavity corresponding to the desired bottle shape, to which an auxiliary mold is attached, which guides the finished bottles away from the point where the bottles are blown. The finished containers from the auxiliary mold are placed on a conveyor track, and their leak tightness can be tested, for example, as described in patent FI 100825 B, using a manipulator above the auxiliary mold with a testing / gripping head that can be guided into the mouth opening of the container to be tested in order to seal the mouth opening in the manner required to perform the leak tightness test.

[0003] In a multi-cavity bottle production process, when bottles are transferred from the main mold to the auxiliary mold, significant fluctuations in the internal air temperature of the bottles can occur between the different cavities. Even within the same cavity, the temperature can vary considerably between different production cycles. The latter situation is the most severe in terms of leak testing, as adjusting test parameters under changing conditions is virtually impossible. When using an integrated leak detector, the bottles are inspected and removed from the auxiliary mold.

[0004] For a successful leak test, the container's mouth is tightly closed and pressurized to a slight overpressure, and leaks are detected as a pressure drop. Leak testing considers the change in pressure in a closed bottle as a function of time. Since time is generally very limited in the bottle manufacturing process, the measurement of pressure and time must be very precise. For the above measurements to be performed reliably, the measurement conditions must be stable.

[0005] The most important factor for a reliable pressure measurement is that the air inside the cylinder maintains a uniform temperature during the measurement process. When the air inside the cylinder heats up due to the hot cylinder, the air expands, causing an increase in pressure in the enclosed space. According to the general equation of state of gases, in a closed state, (pressure x volume) / temperature ((pxV) / T) is constant.

[0006] US 4 019 370 A relates to a leak test for plastic bottles. In this test, plastic bottles from a molding machine are transported on a conveyor belt through a leak testing device, where a predetermined number of bottles are temporarily stopped. Reciprocating top test heads and side ejectors are located on one side of the conveyor path. On the opposite side, the bottles are supported by a movable side flap, which is moved into a release position when a defective bottle is to be ejected. The test heads are lowered until they are hermetically sealed to the bottle mouths, and a constant amount of compressed air is fed into each bottle from a reservoir. The resulting pressure of the bottle-reservoir system is an index of bottle integrity.

[0007] The object of the present invention is to provide a solution that eliminates the above-mentioned problem caused by temperature fluctuation.

[0008] The object is achieved by means of a method according to the invention as defined in claim 1. Advantageous design features of the method according to the invention are the subject of subclaims 2 and 3.

[0009] In order to achieve the object, the method according to the invention is characterized in that, in the method, a compressed air bubble with a constant temperature is directed onto the inside of simultaneously produced plastic containers as an equal volume flow into all plastic containers before carrying out the leak test in order to stabilize their internal air temperature.

[0010] The elements for carrying out the compressed air blowing can, for example, be arranged in connection with the manipulator to move with it, or fixed in connection with the deburring station, to which deburring station the auxiliary mold brings the finished plastic containers.

[0011] In the following, the invention is explained in more detail in connection with the arrangement shown in the attached drawings according to the prior art. Fig. Figure 1 shows a prior art arrangement for carrying out a leak test on plastic containers provided with a mouth hole, and Fig. 2 shows the arrangement of Fig. 1 used test / gripper head.

[0012] Fig. Figure 1 shows an arrangement for carrying out the leak test for bottles or corresponding hollow containers made of plastic having a mouth opening according to the prior art, which is described in more detail in patent FI 100825 B, and Fig. 2 shows a test / gripping head 2 used therein. According to the Fig. 1A-1D, the assembly 1 comprises a mold 3, which in the presented embodiment has two mold cavities 9, the shape of which corresponds to the desired shape of the bottle 5. The number of mold cavities 9 can be selected as desired. Also connected to the mold 3 is an auxiliary mold 4, which is used to transport finished bottles 5 away from the blow molding station to a deburring station, from where they can be further transferred to a conveyor. The bottles 5 are located in the mold 3 and in the auxiliary mold 4 such that their mouths open upwards. The assembly 1 also contains a manipulator comprising an inspection / gripping head 2 and a track section 6 located above the bottles 5, along which the inspection / gripping head 2 travels between the deburring station, where the inspection / gripping heads 2 of the manipulator grip the bottles 5, and the stations where the accepted and rejected bottles 5 are removed. Fig. 1A-1D also show a control unit designated by reference numeral 7 for carrying out the required control operations. Fig.1, in phase A, the mold 3 is on the blowing station, where the blow mandrels are located at the bottom of the mold 3, during which the necessary blowing takes place to produce bottles 5 from the blanks 8, which blank can be, for example, the aforementioned tube blank or a so-called preform. At the same time, the previously blown finished bottles 5 are mounted in the auxiliary mold 4, and the sealing cone 11 of each test / gripper head 2 of the manipulator lies tightly against the edge of the mouth of the corresponding bottle 5, and the test is in progress, i.e., the test pressure is introduced into the bottles 5 through a tube 14. The holder 13 of the test / gripper head 2 is then pulled upward to engage the expandable gripper rod 12 with the inner surface of the mouth of the bottle 5.In phase B, the mold 3 and the auxiliary mold 4 are opened, and the testing / gripping part 2 lifts the bottles 5 and guides them along the upper track 6 away from the auxiliary mold 4. The leak test can be continued during this phase if necessary, or alternatively, the entire leak test can be performed in this phase, with only the gripping of the bottles 5 taking place in phase A. In phase B, the mold 3 and the auxiliary mold 4 position themselves where the tube blanks 8 and, respectively, the finished bottles 5 located on the blow molding station are located. In phase C, the mold 3 and the auxiliary mold 4 are closed, with the auxiliary mold gripping the finished bottles 5 and the mold 3 enclosing the tube blanks 8. The tubes 8 are then cut off, and the blow mandrels are lifted from the finished bottles 5 at the auxiliary mold 4.The manipulator, in turn, accepts or rejects the inspected bottles 5 and moves to an intermediate station to await approval for start. In phase D, mold 3 moves to the blow molding station, and auxiliary mold 4 transfers the finished bottles 5 from the blow molding station to the deburring station, where the top and bottom burrs are removed. This deburring simultaneously gives the go-ahead to the manipulator's inspection / gripping head 2, which moves to the deburring station, and the inspection / gripping heads 2 are moved to the mouths of the bottles 5. Phase A then begins again.

[0013] This state-of-the-art arrangement works well per se, but the temperature of the plastic containers can sometimes vary considerably between containers in different mold cavities and between different production cycles in the same mold cavity, with the internal temperature variation of the containers causing pressure fluctuations and thus inaccuracy with respect to the leak test.

[0014] In the method according to the invention, the internal temperature of the plastic containers is stabilized by compressed air blowing, which can be carried out while the plastic containers are in the auxiliary mold. The blowing elements (not shown) can be permanently connected to the deburring station or another suitable location in the production line. The blowing elements can also be arranged in conjunction with the manipulator. It is essential that the blowing elements simultaneously direct compressed air at a constant temperature onto the inside of the plastic containers through their mouth openings in order to stabilize the internal temperature before the leak test is performed.

[0015] The leak test can be carried out, for example, at a deburring station before the plastic containers are removed using a test and transfer manipulator or in conjunction with the removal using a test / gripper head of the test and transfer manipulator, and can be continued during transport if necessary.

Claims

[1] Method for improving the leak testing of hollow plastic containers (5) provided with a mouth opening, in which method a mold (3) with several cavities and an auxiliary mold (4) are used, into which the plastic containers (5) produced in the mold (3) are transported for further removal by means of a manipulator for further processing, characterized by in the method, a compressed air blowing device having a constant temperature is directed onto the inside of simultaneously produced plastic containers (5) through the mouth hole before carrying out the leak test, simultaneously into all plastic containers (5) as an equal volume flow in order to stabilize their internal air temperature. [2] Method according to claim 1, characterized by that the compressed air blowing is carried out before the plastic containers (5) are removed from the auxiliary mold (4). [3] Method according to claim 2, characterized bythat the leak test is also carried out before the plastic containers (5) are removed from the auxiliary mold (4).

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