Method and apparatus for making a blow molded fuel tank

A fuel tank is formed by a blow molding apparatus and method wherein a blow pin provides pressurized gas into an interior of a parison received in a blow mold so the parison may be blown to shape within the mold cavity. When the blow pin is no longer needed, it is retracted from the mold and a pinch plate assembly is used to close off the opening in the molded part created by the blow pin. Thereafter, the mold may be opened and the molded part removed, the pinch plate assembly and moved back to its retracted position, and the blow mold pin may be advanced into the open mold for use with a subsequent parison so that the subsequent parison can be blow molded in the same manner.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for forming a fuel tank, and more particularly a blow molded fuel tank.

BACKGROUND OF THE INVENTION

Generally, in a blow molding process, a parison is extruded in a size and of an amount of material sufficient to create a desired part. The parison is placed into an open mold in which a blow pin may be oriented, and the mold is closed around the parison. Portions of the parison are pinched between halves of the mold as the mold is closed, and the parison is preferably received around the blow pin. A gas under pressure, such as air, is introduced into the interior of the parison through the blow pin to outwardly expand the parison into the mold and conform the parison to the shape of the mold cavity.

After the blowing procedure, the blow pin may be retracted from the mold and the molded part removed from the mold. Flashing is removed from the molded port at a trimming station, and other secondary finishing operations may be performed. A hole in the molded part where the blow pin was received is then closed with a plug or cover welded to the tank. A cover or plug welded over or in the opening may result in a gap in a barrier layer of the fuel tank thereby allowing increased emissions from the fuel tank. Also, there is a potential for failure in attaching the cover or plug to the fuel tank resulting in an increased scrap rate of fuel tanks produced by a blow molding operation.

SUMMARY OF THE INVENTION

A fuel tank is formed by a blow molding apparatus and method wherein a blow pin is communicated with an interior of a parison received in a blow mold so the parison may be blown to shape within the mold cavity by introduction of a pressurized gas from the blow pin into the interior of the parison. When the blow pin is no longer needed, it is retracted from the mold and a pinch plate assembly is used to close off the opening in the molded part created by the blow pin. The pinch plate assembly may also remove flash to reduce or eliminate downstream processing operations. Thereafter, the mold may be opened and the molded part removed, the pinch plate assembly moved back to its retracted position, and the blow pin may be advanced into the open mold for use with a subsequent parison so that a subsequent parison can be blow molded in the same manner.

The pinch plate assembly preferably includes two opposing plates having leading edges movable from an open position spaced from each other to a closed position pinching and sealing between them a portion of the parison or molded part. The above-outlined method and apparatus for blow molding a fuel tank creates a formed part without a hole created by a blow pin. In this manner, a fuel tank formed by the above outlined method does not need to be further processed in a finishing operation to seal or plug a hole formed in the part during the blow molding operation. Flash may also be removed from the formed tank to reduce or eliminate subsequent processing operations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring in more detail to the drawings,FIG. 1illustrates a blow molding apparatus10according to one presently preferred embodiment of the invention. The blow molding apparatus10includes a mold12having a pair of mold halves14,16(only partially shown inFIGS. 1 and 3) which may be moved between open and closed positions to receive a parison and to enable the parison to be blow molded, respectively. The mold halves14,16define a mold cavity18in which the parison is received and formed into its final shape. An opening20in the mold12receives a blow pin22of a blow pin assembly24that provides pressurized gas, such as air, into an interior of a parison to expand it outwardly into the mold cavity18. A pinch plate assembly25includes a pair of pinch plates26moveable between an open position (shown inFIG. 1) wherein the pinch plates26are spaced from each other and a closed position (FIGS. 3 and 4) wherein the pinch plates preferably engage and pinch closed a portion of the fuel tank material as will be discussed in more detail below. InFIG. 1, the pinch plates26are shown in their open position and the blow pin22is shown in its extended position received between the pinch plates26and through the opening20to the mold cavity18.

A carrier arm30may also be received through the opening20, and as shown, extends through the blow pin22so that it also communicates with an interior of the parison. One or more components received on the carrier30are disposed within the interior of the parison so that they are disposed inside the formed or molded fuel tank, eliminating the need for subsequent insertion of the components into the fuel tank, and potentially reducing the number of openings required in the fuel tank.

To form a blow molded fuel tank, a parison of fuel tank material is located between the open halves14,16of the mold12and preferably over the blow pin22and carrier arm30. The mold halves14,16are then closed, preferably pinching desired portions of the parison and also closing the parison around the blow pin22. Pressurized air is introduced from the blow pin22into the interior of the parison to expand the parison outwardly into engagement with the mold12in the mold cavity18and form the parison into its desired final shape. When the blowing operation is finished, the blow pin22and carrier arm30can be retracted leaving behind whatever components were on the carrier arm30within the interior of the blow molded fuel tank.

With the blow pin22removed from the mold12, the pinch plate assembly25is moved to its second position moving the pinch plates26to their closed position shown inFIGS. 3 and 4. When the pinch plates26close, they preferably engage the parison or fuel tank material around the opening left by the blow pin22, and pinch and seal it to close the opening left by the blow pin22. Opposed trim blades34may be provided below the pinch plates26to further pinch material and facilitate its removal, or cut or shear and remove flashing from the seam created by the pinch plates26. Thereafter, the mold halves14,16are opened and the formed fuel tank can be removed from the mold12. To prepare for forming a subsequent fuel tank, the pinch plate assembly is retracted to its open position removing the pinch plates26from the area of the opening20, and the blow pin22is extended into the mold cavity16resetting the apparatus10to the arrangement generally shown inFIG. 1for molding a subsequent fuel tank.

Referring toFIGS. 1 and 2, the blow pin assembly24includes the blow pin22itself which is shown having a generally rectangular shape with a central passage42through which the carrier arm30is received and pressurized air flows during the blow molding operation. The blow pin22is slidably received for reciprocation between extended and retracted positions within a blow pin guide44having a passage46and inwardly extending flanges48which help locate the blow pin22. The blow pin guide44is moveable between first and second positions, and is shown inFIG. 1in its first position wherein a neck50of the guide44is engaged with a lower portion of the mold12surrounding the opening20. In this position, the neck50is received between the pinch plates26and prevents inadvertent actuation of the pinch plates26towards their closed position at least when the blow pin22is within the opening20. InFIG. 3the blow pin guide44is shown in its second position where the neck50is spaced from the mold12and the opening20so that the guide44is out of the way of the pinch plate assembly25.

The blow pin guide44is preferably yieldably biased to its first position, as shown inFIG. 1, and is moved to its second position, as shown inFIG. 3, by at least one actuator52, and preferably a pair of actuators52. In the embodiment shown, the blow pin guide44has inclined ramp surfaces54with a slot56or keyway formed in each ramp surface54. The slot56or keyway cooperates with a key (not shown) carried by a block58driven for slidable movement along the ramp surface54by an arm60of an actuator52. As shown, the apparatus has two actuators52, preferably pneumatic or hydraulic cylinders or servo controlled motors, each having an arm60associated with a separate block58received on a corresponding ramp surface54. As shown inFIG. 1the blocks58are initially at the outer portion of the slots56near the lower end of the ramp surfaces54, and are driven linearly forward towards the neck50by the actuator52, moving the blocks58along the ramp surfaces54and providing a force moving the blow pin guide44downwardly away from the opening20to its second position. To permit the blow pin guide44to return to its extended position, the actuators52retract the blocks58moving them away from the neck50into their position shown inFIG. 1. Hence, through use of the ramp surfaces54and blocks58linear reciprocation of the arms60causes linear movement of the blow pin guide44in a path perpendicular to the movement of the arm.

The pinch plate assembly25preferably includes a pair of pinch plates26having generally opposed leading faces62between which a portion of the parison may be pinched to close and seal off an opening created by the blow pin22. Each pinch plate26is preferably associated with a separate actuator64. The actuators64have arms65that drive the pinch plates26for linear reciprocation between an open position wherein the leading faces62are spaced from each other, and a closed position where the leading faces62are moved into the position shown inFIGS. 3 and 4, so that material surrounding the opening in the fuel tank material left by the blow pin22is pinched or clamped between the leading faces62to close and seal the fuel tank opening. The pinching step is preferably performed while the material of the molded article is semi-solid and capable of flowing easily to form a seam. In one preferred form, a molded article comprising polyethylene would be maintained at a temperature ranging from 70° to 80° C. to allow for sufficient flow of material to form the seam.

The actuators64may be any suitable type, for example without limitation, hydraulic or pneumatic cylinders or servo controlled motors. The leading faces62of the pinch plates26may be generally serrated or undulated to improve and strengthen the seal created when the opening is closed and form a non-linear seam. The non-linear seam provides a longer effective length of the seam to accommodate the circumference of the hole left by the blow pin, to limit or reduce formation of folds or pockets in the seam. This may also improve the barrier properties of the fuel tank in the area of the seam. As best shown inFIG. 3, the leading faces62may be provided on separate plates67attached to the main pinch plates26, or the faces62may be integral with the pinch plates26that are driven by the actuators64. Preferably, the trim blades34are carried by and beneath the pinch plates26to further pinch material outboard of the seam formed by the pinch plates and thereby facilitate flash removal, or to shear off the flash.

Preferably, the pinch plate assembly25includes a guide plate68positioned beneath the pinch plates26so the pinch plates26are received between the mold12and guide plate68. The guide plate68may guide and support the pinch plates26as they move between their open and closed positions.

According to another presently preferred embodiment of a blow molding apparatus, as shown inFIG. 5, a blow pin22′ is preferably diamond shaped in cross-section and thereby leaves a diamond-shaped opening in a fuel tank when the blow pin22′ is removed from the blown parison or molded tank material. The diamond-shaped blow pin22′ and corresponding hole formed in the fuel tank material may facilitate or improve pinching and closing the hole in a uniform manner without creating folds and pockets within the fuel tank material, resulting in a seam having improved barrier properties with a more uniform barrier layer in the fuel tank material.