Plastic article or earthenware shaping or treating: apparatus – Means applying electrical or wave energy directly to work – Radiated energy
Patent
1996-02-09
1998-07-14
Davis, Robert
Plastic article or earthenware shaping or treating: apparatus
Means applying electrical or wave energy directly to work
Radiated energy
264454, 264458, 264535, 425526, 425535, B29C 4964
Patent
active
057800693
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a blow molding apparatus suitable for molding PET bottles and the like. More particularly, this invention relates to an improvement in the preform carrying mechanism of a blow molding apparatus. This invention also relates to a heating control system used in a blow molding apparatus for radiant heating of preforms to a temperature suitable for blow molding.
BACKGROUND ART
A hollow molding such as a PET bottle is molded by heating a cylindrical preform extrusion molded from a thermoplastic resin to have an opening at one end and a closed bottom at the other and then biaxial stretching the preform after it has been cooled to a temperature suitable for molding. The blow molding apparatus used for this is constituted to carry out these processes on preforms as they are successively carried along a carrying line at a constant feed pitch.
A blow molding apparatus of this type is disclosed in JP-B 1-17855. The apparatus taught by this publication has a preform carrying line closed on four sides and block-shaped carrying units disposed on this line are successively fed at a constant feed pitch. The carrying units are equipped with carrying members for immobilizing the preforms by insertion into their openings, and the preforms are carried by the carrying units with the carrying members inserted therein. Each carrying unit receives a preform at a preform loading section, passes through a heating section and a stretch-molding section, delivers the molding to an offtake section, and then returns to the preform loading section empty. Circular carrying lines are also used.
The carrying system of the prior art blow molding apparatus thus includes a so-called closed carrying line having a large number of preform carrying members disposed at a constant pitch, and the preform carrying members are successively fed at a constant pitch. Each carrying member carries a preform through a heating section and a stretch-molding section located along the carrying line and then returns to the preform loading section empty after passing through the stretch-molding section and delivering the molding to the offtake section thereof. In addition, the carrying members can be rotated in the heating section for uniformly heating the preforms by radiant heat from only one direction.
In the case of using this type of so-called closed carrying line, however, the carrying members have to be returned to their initial position empty after takeoff of the molding. This is not efficient because it results in a proportional operation loss. Further, since the carrying members which travel on the line need to be additionally equipped with rotating systems for rotating the preforms, their systems are complicated. In addition, fasteners are required for constantly fastening the preforms to the carrying members traveling on the line. Moreover, in the prior art the carrying members move and molding air supply etc. is conducted with respect to the preforms held by the carrying member in the stretch-molding section. It is therefore necessary to provide the carrying members with systems for blowing in air. The carrying member systems also tend to increase in complexity in this point.
On the other hand, the heating of preforms in prior-art blow molding apparatuses is generally conducted by positioning the radiant heating element of an infrared heater or the like along the preform carrying line and uniformly heating the conveyed preforms from the side as they are rotated about their axes. Since radiant heating from the outside causes the outer surface of the preform to be heated more rapidly than the inner surface, their temperatures change as shown by the curves A1 (outer surface temperature) and A2 (inner surface temperature) in FIG. 10. As can be seen from these curves, the heating increases the outer surface to a higher temperature. Since the stretch rate of the inner surface is larger, however, the temperature of the inner surface has to be made higher in the ensuing stretch-molding. After heating, therefore, th
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Davis Robert
Frontier Inc.
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