Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Measuring a weight or volume
Patent
1991-07-23
1993-09-28
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Measuring a weight or volume
264 405, 264 51, 2643287, 425 4R, 425140, B29C 6722
Patent
active
052484599
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and an apparatus for manufacturing a molded resin foam, wherein pre-expanded resin pellets or granules are filled in a mold cavity and subjected to expansion molding under heating to produce energy absorbers such as automobile bumper core materials, planks, containers, shock-absorbing packaging materials, e.g. side pads, etc. More particularly, the invention is concerned with the production of a molded resin foam, in which the weight of the pre-expanded resin pellets to be charged to the mold cavity is made constant, whereby foam products are yielded with minimized differences in weight.
BACKGROUND ART
As represented by bead molding technique of expandable styrene beads in a mold cavity, the expansion molding of pre-expanded pellets of a resin such as styrene resins, olefine resins, e.g. polyethylene, polypropylene, etc. or the like has hitherto been known widely. This comprises the charging of pre-expanded resin pellets into a mold cavity and meld-bonding them by steam heating followed by cooling to yield a molded product conforming to the mold contour. With this method, the charging procedure is generally conducted in such a manner that when the pre-expanded pellets are discharged from a feed-stock silo attached to a molding machine through charging equipment into the cavity of mold, the mold is not completely closed, but the mold sections are spaced apart at a clearance or gap, which is called a cracking (hereinafter the term "cracking" will be used), on the order of 0-20 mm, usually 2-8 mm and thereafter, the pre-expanded pellets are charged through the charging equipment into the mold cavity by blowing compressed air into it, thus taking advantage of suction and entrainment actions of the pre-expanded pellets.
In this case, spacing the cracking is aimed at filling the prefoamed pellets equally and homogeneously in the mold cavity by releasing the air blown therein. The mold is constructed so that even if the cracking width is larger than the diameter of the prefoamed pellets, the prefoamed pellets, when charged, ay not leak out of the mold. In spite of the fact that if the apparent density of prefoamed pellets varies, the weight of the resulting molded products will naturally vary, the method usually carried out does not take account of controlling the difference in apparent density thereby to decrease the difference in weight of the molded products. Hence, it is a common practice that the difference in weight of molded products is taken for granted. As a consequence, by taking account of the difference in weight of the molded products when produced according to the current molding method in advance, the standard in weight or expansion ratio of the products is made broad to some degree, whereby quality control (in weight) is performed.
In a situation where the weight of molded foam is measured and found to be off the standard, a worker on-site knows that the manipulation of the cracking width of the mold enables the rectification of the weight of product (expansion ratio) and he may cope with the situation on the basis of his skill by manual operation of the cracking. However, it is virtually impossible to make such adjustment frequently, even if a few times might be possible. Furthermore, in cases where prefoamed pellets disperse more than usual, the frequency of manual operation to the cracking width is increased, and consequently, in the status quo, there is practically no way of taking countermeasures.
No matter how preferable it is to enhance the quality of products by narrowing the current prevailing range of standard of product weight, the manufacturing method now in practice still has limitations as it is.
For instance, in the application of a foam material to an automobile bumper core material or the like, in which the foam serves to absorb the energy upon collision, the difference in expansion ratio of the foam directly leads to a difference in energy absorption magnitude and causes significant differences in that function with the resul
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Fukasawa Yukio
Fukui Hisatoshi
Tojo Shiro
Kanegafuchi Chemical Industry Co. Ltd.
Kuhns Allan R.
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