It is commonly known in the art of container fabrication to fabricate containers by the stretch blow molding process. In the stretch blow molding process, a substantially tubular parison or “preform” is provided, said preform being fabricated from a thermoplastic and having an open end near a mouth and a closed end opposite the open end. The preform is disposed within a mold having a cavity substantially defining the form and contours of a container.
The preform is expanded into the cavity of the mold by the action of a stretching rod inserted into a mouth of the preform, combined with the action of a working fluid injected into the preform under pressure. The stretching rod is advanced into the preform and presses against an opposite interior surface, stretching it longitudinally into the mold. The pressurized fluid causes the preform to inflate, expanding primarily radially.
Conventionally, the pressurized fluid injected during the molding of the container is air that can be heated to facilitate the deformation of the preform. However, it is known to use a liquid as the working fluid, preferably the liquid which is ultimately to be packaged within the container. In this way, the process of forming a container and filling it with a product are effectively combined, realizing great advantages in equipment cost and production efficiency compared to an air-injection stretch blow molding system.
In a combined forming-filling container fabrication process, it is important to ensure that the preform is fully expanded into the cavity of the mold and that all of the contours of the resulting container are fully formed. As full expansion of the preform thereby leading to the container results from both stretching and filling operations, it is necessary to link the launch of the stretching, the liquid supply and filling operations in order to supply the liquid at the right moment according to the position of the stretch rod within the preform.
The stretching and filling operations are realized using an injection head configured to interface with the mouth of the preform and with the stretch rod displacement and to establish fluid communication between a fluid supply and the mouth of the preform.
Usually the injection head comprises an injection valve disposed within the outer shell of the injection head and configured to selectively permit fluid communication through the injection head. In an opened position the injection valve allows the fluid to be displaced from the injection head to the preform whereas in a closed position no fluid is transferred to the preform.
In this example, the supply of the liquid to the injection head step and the injection valve's opening allowing displacement of the liquid from the injection head to the preform, are two independent operations that need to be timely coordinated. This coordination is difficult to maintain over time due to the time response of the different components.
First of all, it has to be noted that the time response of the injection valve is evolving due to the wear of the valve and a necessary reset of this synchronization will have to be made periodically.
Secondly, each single valve has a different time response due to manufacturing tolerance meaning that each time the valve is changed the synchronization has to be reset.
One solution currently implemented in the prior art is to electronically control the launch of the two steps: fluid supply and opening of the injection valve.
Even though this solution looks acceptable it is complex to implement mainly due to the time response of the valve leading to a time shift between the two steps. This shift creates difficulties in the process and possible damages.
Indeed, if the injection valve is opened while the fluid has not been supplied to the injection head, only the water remaining in the injection head will be transferred to the preform which will lead to cooling the preform down and to its breakage.
On the other hand, if the fluid is supplied to the injection head and the injection valve is opened too late, the apparatus will undergo important internal pressure possibly damaging the whole system.
It is therefore an object of this invention to provide an injection head, an apparatus and related method for fabricating and filling a beverage container which accurately provides full and effective time coordination of the liquid's supply step and injection valve's opening without the disadvantageous aspects of the apparatuses known in the art.