US3518722A - Guide for incompletely solidified polymeric article - Google Patents

Description

July 7, 1970 RYAN ET AL GUIDE FOR INCOMPLETELY SOLIDIFIED POLYMERIC ARTICLE Filed Oct. 31, 1967 III/II IAI/IA/IIl/Ill/I/ I III/III I11 I III! III! United States Patent 3,518,722 GUIDE FOR INCOMPLETELY SOLIDIFIED POLYMERIC ARTICLE Daniel J. Ryan, Chester, and James L. Discavage, Prospect Park, Pa., assignors to FMC Corporation, Philadelphia, Pa., a corporation of Delaware Filed Oct. 31, 1967, Ser. No. 679,392

Int. Cl. B29f 3/00 U.S. CI. 18-12 5 Claims ABSTRACT OF THE DISCLOSURE A guide for directing a relatively thick, hot and only partially solidified polymeric article through a substantially right-angled turn in a quench bath. The guide basically comprises a plurality of horizontally extending members which are spaced apart and arranged in a circular are having a vertical tangent and a substantially horizontal tangent. Use of the guide facilitates the making of an article of uniform thickness.

This invention relates to apparatus for making relatively thick, indefinitely elongated polymeric articles of substantially rectangular cross section and especially to apparatus for forming such articles which are subsequently further elongated to produce longitudinal molecular orientation. In its more particular aspects, the invention relates to apparatus for producing high strength, oriented polymeric strapping useful as a substitute for steel band strapping. Still more particularly, the invention constitutes an improvement over the apparatus described in the U.S. patent to Ryan et al. No. 3,276,076.

The general procedure followed in manufacturing polymeric strapping comprises extruding the molten polymeric material (such for example as polypropylene) through a substantially rectangular die into a bath of cold water known as a quench bath, wherein the material is solidified to form an article having the appearance of a strap but which lacks great tensile strength. This article or strap is then subjected to stresses which substantially elongate the same and cause the molecules thereof to become oriented longitudinally. This orientation may be accomplished by stretching the strap or by rolling the same between rolls which cause it to elongate but prevent widthwise spreading. To minimize the amount of power required to elongate the strap, it is normally heated prior to orientation. As is well-known, molecular orientation greatly increases the tenacity and tensile strength of 0 the strap. The various operations of extruding, quenching,

heating and orientation are carried out as a continuous process, the final product being collected in roll form of substantial length. An entire production line from the point of extrusion to the point of windup may be fifty feet or more long and economic reasons normally dictate that the line extend generally horizontally. This horizontal orientation applies also to the quench bath which may extend for ten feet or more in order to assure complete solidification of the strap interior. However, in order to permit easy access to the extrusion nozzle or die and avoid complicated design problems and custom built extrusion equipment, it is desirable to extrude the molten polymer in a vertically downward direction from a point somewhat above one end of the quench bath. Thus, in order for .the strap to proceed to the far end of the quench bath it is necessary for it to make a turn at the forward end of the bath while the interior thereof is still in a highly plastic or at least not fully solidified condition. With a thin strap or sheet this initial turn in the forward end of the quench bath does not create any special problems but when the final oriented strap is over about twenty mils 3,518,722 Patented July 7, 1970 "ice thick it does, as will be seen, and it is towards this area of the strap production apparatus that the present invention is directed.

While specific reference will be made herein to strapping and while the invention is particularly useful in making strapping or other molecularly oriented articles, it also has utility in the production of heavy gauge polymeric articles such as sheeting which is not normally molecularly oriented.

It is an object of the present invention to provide an improved guide for directing a relatively thick and only partially solidified polymeric article about a turn in a quench bath.

A further object of the invention is to provide a guide for a relatively thick and only partially solidified polymeric article which is easily laced and which enables uniform cooling of the article as it progresses about the guide.

Other and further objects, features and advantages of the invention will become apparent as the description of a pre ferred embodiment thereof proceeds.

Referring now to the drawing:

FIG. 1 is a side elevation of an apparatus for making a relatively thick polymeric article and showing the guide of the present invention; and

FIG. 2 is a plan view of the guide.

Since the invention is directed to that part of the operation that takes place prior to molecular orientation of the finished product (if indeed, a molecularly oriented product is to be produced) only that portion of the overall apparatus involving the extrusion die and quench bath has been shown. The molten polymer is extruded vertically downward from a conventional extruder 10 through a substantially rectangular die 12. After passing between opposed quenching and sizing rolls 14, the extrudate or partially solidified and still hot article 16 falls into one end of a horizontally elongated tank 18 containing cold water, the level of which is indicated at 20. This is the quench bath and as previously mentioned it may extend for ten feet or more in order to permit complete solidification of the article as it passes therethrough. After entering the tank vertically, the article is drawn lengthwise through the bath in a substantially horizontal direction by a pair of feed rolls 22 from which it moves on through the molecular orientation apparatus or is immediately collected in those cases where molecular orientation is not desired or necessary. In this case of a thin film, the transition from the vertical to the substantially horizontal direction may be accomplished by passing it about a roller or the like but when the article is relatively thick, for example when the smaller dimension of the die, this being the dimension determinative of the thickness of the article, is 0.06 inch or more, other means must be resorted to in order to attain an article of uniform thickness, as will presently be explained. At this point it might be mentioned that in the case of a high strength strap formed of polypropylene, the strap is elongated to about eight times its extruded length to obtain the desired degree of molecular orientation and to produce a strap having a thickness of 0.02 inch requires a die opening of 0.06 inch thickness.

In order to fully appreciate the value of the arrangement to be hereinafter described, it should be remembered that when the strap or other article enters the quench bath it is in a highly plastic state and is quite hot. The passage of the extrudate through the quenching and sizing rolls 14 quenches and partially solidifies the outer faces but the interior of the article is still substantially molten when it enters the bath and in fact that interior does not reach full solidification until near the point where the article emerges from the bath. When a relatively thick article such as a strap is forced to change direction from vertical to horizontal, the strap face on the outside of the curve travels through a noticeably longer path than does the inner face. This stretches that face of the strap on the outside of the curve so that as the strap approaches the horizontal direction, the lower face (lower as viewed in FIG. 1) is somewhat longer than the upper face but since the strap is not fully solidified at this point, as it starts to move in a straight line some puckering of the lower face takes place since both faces are now traveling at the same speed. Such a puckering of the lower face of the article means that the article is no longer of uniform thickness at the time it reaches the rolls 22. Furthermore, since the strap is quite hot at the time it enters the bath, some localized boiling of the bath water takes place where it contacts the strap and this can result in gas bubbles adhering to the faces thereof whereby at the locations of the bubbles, cooling is retarded. This uneven cooling results in an article of spotty or blotchy appearance. These objections are largely overcome by use of the apparatus described in the above-mentioned Pat. No. 3,276,076 but the apparatus of said patent is rather difficult to lace up, is relatively expensive and consumes a fairly substantial amount of water in its operation.

In accordance with the present invention, the guide comprises, a plurality of horizontally extending members 24, 26, 28, 30, 32, 34, 36, 38, and 40 which are spaced apart and arranged in a circular are having a vertical tangent lying adjacent the vertically downward path of movement of the article 16 and a substantially horizontal tangent at the bottom of the arc. Preferably the guide members are in the form of open ended tubes and are secured at opposite ends to a pair of plates 42 and 44 which have, as shown in section in FIG. 2, openings aligned with the tubes so that the bath water may circulate through the tubes to keep them cool. Plates 42 and 44 are secured in a suitable manner to the upper edges of side walls 46 and 48 of the tank so that the members 24, 26, etc. are positioned within the tank in the manner shown in FIG. 1. The strap 16 or other article is laced around the guide by weaving it in and out through the various horizontal members, the strap passing about the outside of member 24, the inside of member 26, the outside of the following member and so on. As the strap passes around the outside of the member 24, one face is wiped clear of gas bubbles and as it passes around the inside of member 26 the other face is wiped clear. The localized boiling of the bath Water is substantially confined to the immediate vicinity of the place where the extrudate enters the bath so that rubbing of one face of the article against member 24 and the other face against member 26 is all that is normally necessary to remove the gas bubbles. The number of the members 24, 26, etc. through which the strap is laced depends upon the thickness of the strap. Thus an especially thick strap may be laced alternately around opposite sides of all of the members, a thinner strap around only the first few as shown in the drawing and an even thinner one may be laced around the inside of only member 26 and then proceed around the outside of the remaining members 28, 30, 32, 34, 36, 38, and 40.

By lacing the strap alternately around the entire series of members 24, 26, etc., the lower face of the strap travels about the same distance as the top face as the strap makes the over-all about ninety degree turn. This alone enables the strap to maintain its original uniform thickness. However, a further advantage of the present invention is that the strap is continuously flexed back and forth as it makes the turn and this Working of the material as it is cooling makes for more uniform cooling. The curved guide described in Pat. No. 3,276,076 needs to have water circulated through it to prevent it from heating up due to heat transfer from the strap but with present invention, the strap is in direct contact with the bath water on both sides for most of its travel and particularly when the various members 24, 26, etc. are in the form of open ended tubes with the bath water inside the tubes very little heating of the guide members takes place.

If desired, and especially when making thinner articles, a water cooled presser tube or pipe 50 may be employed to press the article against the top member 24 to provide a drag on the face of the article contacted thereby and to wipe the gas bubbles from that face of the article. In this case the article is directed between tube 50 and member 24 and then around the outside of the various members 26, 28, etc. in a smooth curve. Pipe 50 is non-rotatably supported by a pair of arms 52, only one of which is shown, which is pivotally mounted on opposite side walls of the tank 18. A rod 54 secured to one of the arms 52 is surrounded by a spring 56 which is compressed between and adjustable strap 58 on the rod and a member 60 secured to the side wall of the tank whereby pipe 50 is urged toward engagement with guide member 24. A pair of hoses 62, only one of which is shown is connected to opposite ends of pipe 50 whereby cold water may be pumped through the pipe if desired.

Having thus described a preferred embodiment of the invention, what is claimed is:

1. In an apparatus for making a relatively thick polymeric article of substantially rectangular cross section wherein a partially solidified article is directed vertically downward into one end of a horizontally extending watercontaining tank wherein the article becomes fully solidified and from which it is pulled in a substantially horizontal direction; an improved guide for directing the article within the tank from its initial vertically downward direction to a substantially horizontal direction, said guide comprising a plurality of horizontally extending members, said members being arranged in a circular arc having a vertical tangent and a substantially horizontal tangent, and said members being spaced sufficiently far apart to permit and facilitate the lacing of the article alternately about one member toward the outside of the circular arc and about the next member toward the inside of the are where by to prevent undesirable elongation of that surface of the article facing the outside of the arc.

2. The invention set forth in claim 1 wherein the member located at the top of the circular arc lies adjacent the vertically downward path of movement of the article.

3. The invention set forth in claim 2 wherein said members are open-ended tubes whereby the bath water may circulate therethrough.

4. The invention set forth in claim 1 comprising a pair of spaced plates supporting opposite ends of said members, said plates being secured to the side walls of the tank.

5. The invention set forth in claim 1 comprising spaced plates to which opposite ends of said members are secured, said members being tubes, and said plates have openings aligned with the tubes whereby the bath water may circulate through the tubes.

References Cited UNITED STATES PATENTS 2,799,896 7/1957 Grow et al. 3,276,076 10/1966 Ryan et a1.

THERON E. CONDON, Primary Examiner H. A. KILBY, J R., Assistant Examiner

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