The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-019057, filed on Feb. 6, 2018, the contents of which are hereby incorporated by reference in their entirety.
The present invention relates to a process of producing a hollow resin-molded article using a thermoplastic resin and to a fuel tank.
In an automobile fuel tank produced using a thermoplastic resin (hereinafter referred to as resin as appropriate), a tank body containing fuel expands due to the evaporation of the fuel. To inhibit such expansion of the tank body, an outer surface of the tank body can be covered with a cover made of fiber-reinforced plastic.
Japanese Patent Application Publication No. 2009-1048 and Japanese Patent Publication No. 5608287 describe examples of such a tank body with an outer surface covered by a cover.
In either process described in Japanese Patent Application Publication No. 2009-1048 and Japanese Patent Publication No. 5608287, a premolded cover is arranged on a mold and then blow molding of a parison is performed. This process presses a high-temperature parison onto the cover arranged on the mold to mold a tank body made of the parison. When the high-temperature parison is pressed onto the cover, a portion of the cover that contact the parison melts, so the cover and the tank body (parison) are fusion-welded to each other. As a result, the rigidity of the fuel tank can be increased.
However, when blow molding the tank body with two sheet-like parisons, the tank body has a portion where the two sheet-like parisons overlap with each other, so that the tank body has an increased thickness in such a portion. In such a portion where the overlapped parisons have a large thickness, the cooling efficiency is reduced and thus the parisons are inhibited from being cooled. In addition, when the cover covers such a portion where the overlapped parisons have a large thickness, the cooling efficiency is further reduced due to the cover. In other words, the time for drawing heat is increased. Japanese Patent Application Publication No. JP 2009-1048 and Japanese Patent Publication No. 5608287 are silent with respect to such consideration.
The present invention has been made in view of the above background, and it is an object of the present invention to shorten the time for molding the thermoplastic resin.
To solve the above-described problem, an aspect of the present invention is a process of producing a hollow resin-molded article using a mold comprising a pair of mold halves, the method including steps of: arranging a cover on an inner wall of each of the pair of mold halves, the cover being premolded and having a shape corresponding to the inner wall; introducing a thermoplastic resin fusion-weldable to the cover into an inner space between the pair of mold halves so as to form a pair of sheets of thermoplastic resin each facing the cover arranged on the inner wall of corresponding one of the pair of mold halves; blowing air into an intermediate space between the pair of sheets of thermoplastic resin to cause each of the pair of sheets of thermoplastic resin to contact the cover arranged on the inner wall of corresponding one of the pair of mold halves, and thereby fusion-welding each of the pair of sheets of thermoplastic resin to the cover arranged on the inner wall of corresponding one of the pair of mold halves; closing the pair of mold halves; and cooling down the covers and the pair of sheets of thermoplastic resin in a state where the pair of mold halves is closed. The covers and the pair of mold halves are configured such that, in the step of arranging the cover, there is an uncovered portion of the inner wall of each of the pair of mold halves that is not covered by the corresponding cover, and that, in the step of closing the pair of mold halves, there is a mold contact portion of each of the pair of sheets of thermoplastic resin that directly contacts the uncovered portion of the inner wall of corresponding one of the pair of mold halves and the mold contact portions of the pair of sheets of thermoplastic resin are fusion-welded to each other in an overlapping manner.
Another aspect of the present invention is a fuel tank including: a tank body formed of a plurality of sheets of thermoplastic resin; and a cover arranged to cover the tank body, the cover being fusion-weldable to a surface of the tank body by heat. The tank body has an overlapping portion where two of the plurality of sheets of thermoplastic resin are overlapped with each other and fusion-welded to each other. The overlapping portion has a portion not covered by the cover.
Other aspects of the solution will be described in the description of embodiments as appropriate.
According to the present invention, the time for molding a thermoplastic resin can be shortened.
Next, an embodiment for carrying out the present invention will be described in detail with reference to the drawings as appropriate.
As shown in
As described above, the cover C is disposed to inhibit the tank body T from expanding due to the evaporation of the fuel in the tank body T. In
As shown in
It should be noted that the tank body T is molded from two sheet-like parisons (thermoplastic resin).
As shown in
The fuel tank F illustrated in
Incidentally, of the constituent elements shown in
The standoff portion 100 includes a fusion-welded portion 101 where the parison of the upper bottom surface is overlapped with the parison of the lower bottom surface.
The standoff portion 100 includes bulge portions 102 that are formed of the parisons pushed out inside the tank body T.
Tank body T has a larger thickness at the fusion-welded portion 101 and the bulge portions 102 than other portion of the tank body T because two parisons are overlapped with each other in the fusion-welded portion 101 and the bulge portions 102. For this reason, the cooling efficiency in the fusion-welded portion 101 and the bulge portions 102 can be reduced. In addition, if the fusion-welded portion 101 and pinched-off portion 200 thus structured are covered with the cover C, the cooling efficiency is further reduced.
In the present embodiment, as shown in
As shown in
Taking this into account, as shown in
Incidentally, a distance d from a center portion of the pinched-off portion 200 to an end of the cover C, which is shown in
Incidentally, in the present embodiment, the standoff portion 100 and the pinched-off portion 200 are not covered entirely by the cover C. However, the fuel tank F may be configured so that the tank body T has at least a portion not covered by the cover C in each of the standoff portion 100 and the pinched-off portion 200. In other words, the fuel tank F may be configured so that the tank body T has at least a portion that is directly in contact with the mold 12 in each of the standoff portion 100 and the pinched-off portion 200. For example, each of the standoff portion 100 and the pinched-off portion 200 may be covered by a portion of the cover C having holes in a spotted pattern.
As described above, the cover C is disposed to inhibit the tank body T from expanding due to the evaporation of the fuel in the tank body T. However, as described above, the standoff portion 100 and the pinched-off portion 200 have a larger thickness than another portion of the tank body T. Therefore, the tank body T is inhibited from expanding due to the evaporation of the fuel despite that the standoff portion 100 and the pinched-off portion 200 are not covered by the cover C.
Next, a description will be given of a process for producing the fuel tank F according to the present embodiment with reference to
Referring to
The dice 11 discharges a pair of parisons P (thermoplastic resin; see
An air supply device not shown supplies compressed air via the air pin 13 into a space between the pair of parisons P. As a result, the pair of parisons P expands. The expanded pair of parisons P are pressed against the pair of molds 12, whereby a resin tank body T is molded (blow molded).
Incidentally, in the embodiment shown in
First, as shown in
As shown in
Incidentally, the temperature of the pair of molds 12 is a normal temperature (approximately 26° C.).
As shown in
When the pair of parisons P contacts the cover C, a portion of the cover C that is in contact with the corresponding parison P melts. As a result, the tank body T (pair of parisons P) and the cover C are fusion-welded to each other. The melting point of the reinforced plastic of which the cover C is made is 130° C. Incidentally, this blow molding step also serves as the next cooling step.
In the blow molding step, after the compressed air is supplied for a predetermined time period, the supply of the compressed air is stopped. Then, the air pin 13 is withdrawn out of the pair of parisons P by being lowered down. The hole that has been formed in the tank body T by the presence of the air pin 13 is automatically closed because the pair of parisons P are in a plastic state. In this state, the standoff portion 100 and the pinched-off portion 200 are directly in contact with the pair of molds 12, which facilitates drawing heat from the pair of parisons P and thus shortens the time for cooling down.
This state shown in
It should be noted that, in the present embodiment, the compressed air is supplied for a predetermined time period, and, after the supply of the compressed air is stopped, the cooling step is started. However, the blow molding step and the cooling step may be carried out concurrently. In other words, the supply of the compressed air may be continued until the pair of parisons P (tank body T) and the cover C, which have been fusion-welded to each other, have been cooled down.
When a predetermined time period has elapsed and the surface temperature of the cover C has dropped down to a temperature of approximately 70° C. or less, the fuel tank F (cover C and tank body T) is extracted by opening the molds 12 in the directions indicated by the outlined arrows in
As described above, each of the standoff portion 100 and the pinched-off portion 200 has an overlapping portion where a portion of the parison P molded in one of the molds 12 and a portion of the parison P molded in the other one of the molds 12 are overlapped with each other. Such an overlapping portion has a larger thickness due to the overlapping of the pair of parisons P and thus the cooling speed of the pair of parisons P is slower than another portion where the pair of parisons is not overlapped with each other. Moreover, if the cover C covers such an overlapped portion, the cooling speed further decreases because the total thickness of the overlapping portion is increased due to the thickness of the cover C. Moreover, as the cover C itself has thermal insulation properties, the cooling efficiency decreases.
Configuring the cover C so as not to cover the overlapping portions of the pair of parisons P allows the overlapping portions having a larger thickness to directly contact the molds 12. This structure facilitates drawing heat from the pair of parisons P to shorten the time for cooling down. As a result, the production time of the fuel tank F can be shortened.
In addition, as the cover C does not entirely cover the pair of parisons P, the fuel tank F including the pair of parisons P is reduced in weight and cost.
Moreover, in the present embodiment, the cover Cis not present on the standoff portion 100 and the pinched-off portion 200. With this structure, the cover C can be configured so as not to be present on the overlapping portion where the plural parisons P are overlapped with each other in blow molding due to the structure of the molds 12.
In particular, the application of the embodiment to the fuel tank F achieves weight reduction and cost reduction of the fuel tank F while inhibiting expansion of the tank body T by the cover C. In addition, the tank body T has a large thickness of the overlapping portions where the pair of parisons P is overlapped with each other. For this reason, the expansion of the tank body T is inhibited even the overlapping portions are not covered by the cover C.
As shown in
Moreover, the pair of molds 12 may have suction holes through which air in the space between the pair of molds 12 is suctioned. Then, when the cover C is being arranged on the molds 12, the cover C may be fixed to the pair of molds 12 by the air suctioned through the suction hole.
Number | Date | Country | Kind |
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2018-019057 | Feb 2018 | JP | national |