US3353212A - Temperature modifying provision for extrusion apparatus - Google Patents

Description

Nov. 21, 1967 A, W, NELSON ET Al. 3,353,212

TEMPERATURE MODIFYING PROVISON FOR EXTRUSION APPARATUS Filed Oct. 23, 1965 United States Patent O TEMPERATURE MODFYiNG PROi/'ISIN FOR EXTRUSIGN APPARATUS Aiden W. Nelson, West Mystic, and Alhert P. Brown,

Gales Ferry, Conn., assigncrs to Crompton & Knowles Corporation, Worcester, Mass., a corporation of Massachusetts Filed Oct. 23, 1965, Ser. No. 503,152

1 Claim. (Cl. 18-12) ABSTRACT F THE DHSCLGSURE The disclosure pertains to an extruder with a cylinder having outer ring-like iins in spaced planes substantially normal to the cylinder axis, and a hood around and extending substantially over the length of the cylinder, with the hood having on opposite sides of the cylinder inlet and outlet openings and providing a through-passage between these openings. The hood ilares from the inlet opening outwardly to an intermediate part-circular section of the hood to which the tins on opposite sides of the cylinder substantially extend, and flares from this intermediate hood section inwardly to the outlet opening, with air forced into the hood through the inlet opening being with minimum turbulence led to and forced at maximum velocity through the maximum constricted paths between `adjacent fins `at the intermediate hood section for most effective and uniform cooling of the cylinder.

This invention relates to extrusion apparatus in general, and to cooling provisions therefor in particular.

Extruders for different plastics and rubber customarily have provisions for heating and cooling the cylinders. In order most eiiectively to cool extrusion cylinders, recourse is frequently had to closed water cooling systems. However, while these cooling systems are highly efective, they entail Considerable cost in equipment and maintenance and also require the purchase of water from the already heavily tapped and dwindling water sources. In order to avoid these and other drawbacks of water cooling systems, recourse has been had to air cooling systems which provide for blowing air at heat-exchange fins on the outer peripheries of extrusion cylinders. To obtain higher cooling capacity of these air systems, hoods have been placed around nned extrusion cylinders with sufficient clearance therefrom to provide substantial passages therebetween in which air forced past the fins will be in heat-exchange Contact with the latter, with such contact being most effective at the fin tips. However, while the provision of such hoods around extrusion cylinders has increased the cooling capacity of air systems, their cooling capacity is still much below that of water cooling systems, so much so that for quite a few extrusion operations air cooling systems are inadvisable and water cooling systems preferred despite their drawbacks.

It is the primary aim and object of the present invention to provide for extrusion cylinders an air cooling system the cooling capacity of which is not only quite considerably greater than that of prior air cooling systems, but reaches substantially the average cooling capacity of water cooling systems and, hence, is fully adequate for most extrusion operations, including many which heretofore were preferentially water-cooled.

It is another object of the present invention to provide for extrusion cylinders an air cooling system in which the heat-exchange between the finned cylinders and the cooling air is vastly improved over that in previous air cooling systems, yet the volumetric iiow rate of the cooling air need not be greater, and may even be smaller, than that of the air in these previous systems.

It is a further object of the present invention to provide for extrusion cylinders an air cooling system in which the cooling air is directed and forced around the cylinders in such wise to brush the largest possible surface area of the iin formation on the cylinders with the formidable force required to prevent the formation thereon of a thin air layer which has been recognized as such and also as a very effective heat insulator, thereby to admit the cooling air into direct and most intimate contact with the fin surfaces for optimum heat-exchange therewith.

Another object of the present invention is to provide for extrusion cylinders an air cooling system which by a hood formation around an externally iinned cylinder provides an air path therebetween which is largely confined to the spaces between adjacent iins and is thus constricted to an extent where forced air will pass at such high velocity as to brush the iin surfaces with the aforementioned formidable force.

A further object of the present invention is to provide for extrusion cylinders an air cooling system in which the aforementioned hood formation is so arranged around a inned cylinder that the air passage therebetween not only provides the aforementioned constricted air path between the tins, but is otherwise of adequate cross-sectional area to pass forced air in suicient volume for effective cooling of the cylinder.

It is another object of the present invention to provide for extrusion cylinders an air cooling system in which the hood formation over an externally finned cylinder meets the aforementioned cross-sectional area requirements of the air passage therebetween in moet simple structural manner. This is achieved by arranging the hood formation as a longitudinal, preferably sheet metal, duct having its inlet and -outlet on and over opposite sides thereof and having therebetween a part-cylindrical section and further lead-to and lead-off sections which Hare from the inlet and outlet outwardly to and merge substantially tangentially with the part-cylindrical section, with the latter section surrounding the tins on the cylinder in sufficiently close proximity thereto to define the aforementioned constricted air path. In thus arranging the hood formation, compressed air admitted into the inlet will flow smoothly through the lead-in section and be forced wedge-like into the constricted path wherein the air reaches its maximum velocity, with the air being finally discharged smoothly through the lead-off section, all without creating any substantial turbulence of the cooling air in the passage which might give rise to local hot air pockets therein, and with the high-velocity air in the restricted path brushing the iin surfaces most lforcefully and also having its maximum cooling effect thereon.

It is a further object of the present invention to provide for extrusion cylinders an air cooling system in which the aforementioned part-cylindrical section of the hood embraces the adjacent fins with only slight clearance therefrom so as to be out of physical contact therewith on the one hand, and to confine the constricted path thereat virtually entirely to the space between the fins on the other hand for most forceful and uniform subjection of the n surfaces to the passing high-velocity air.

Another object of the present invention is to provide for extrusion cylinders an air cooling system in which air turbulence in the air passage is kept particularly low, by providing on the linned cylinder in line with the air inlet a bathe which prevents the onrushing air in the lead-in section from clashing head-on with the nearest confronting cylinder part and, instead, directs this air gradually toward the constricted path.

Further objects and advantages will appear to those skilled in the art from the following, considered in conjunction with the accompanying drawings.

In the accompanying drawings, in which certain modes of carrying out the present invention are shown for illustrative purposes: Y

FIG. 1 is a longitudinal section through an extruder embodying the present invention;

FG. 2 is a section through the extruder taken on line 2--2 of FIG. l.

Referring to the drawings, the reference numeral designates extrusion apparatus having .a standard 12 with the usual stock infeed throat (not shown), a cylinder 14, and a power-operated stock screw 16. The cylinder 14 is externally finned yat 18, and is in this instance formed by a cylinder liner and a heat-exchange jacket or jackets 22 surrounding the vliner 20 and providing the fins 18. Each jacket 22 is in this instance formed by two complementary sections 24 and 26 which are suitably secured, as by clamping, to the other periphery of the liner 20. The jackets 22 are adapted to cool, and in this instance at times to heat, the cylinder liner 20, with the usually cast jackets being provided with the fins 18 and with preferably cast-in Calrods 28 for cooling and heating the liner, respectively. The liner 20 is at 30 mounted in the standard 12 and is there open to the infeed throat for delivery of plastic stock into the cylinder region R from where the screw 16 feeds the delivered stock through the cylinder to the die assembly 32 for extrusion therethrough, with the screw working the stock gradually to extrusion plasticity in the course of its forward feed in the` cylinder. The die assembly 32 comprises in this instance a die 34 in a holder 36 in which it is retained by a ring 38.

As shown in FIG. l, the entire cylinder liner 20 between the standard 12 and the die assembly 32 is provided with heat-exchange jackets 22 for modifying the temperature of the cylinder as needed. Thus, heating of the cylinder by the jackets 22 is usually resorted to in starting the apparatus into operation, and may be resorted to during its operation in the extrusion of certain plastics requiring for proper extrusion plasticity more heat than is generated in the plastic stock by virtue of its being worked by t-he screw 16. However, in the majority of plastic extrusion operations it is necessary to cool the cylinder and thus extract heat from the plastic stock generated therein by the working screw in order to prevent over-plastiiication and even burning of the stock. It is to thus cool the cylinder that the tins 18 are provided thereon, and in this instance on the jackets 22 thereof, and to provide, on the cylinder over its finned length a hood 40 through which to force cooling ,air in intimate heat-exchange relation with the fins, with the cooling air being usually at room temperature and forced through the hood by a power-blower 42.

The hood 40 is in this instance in the preferred simple forrn of a longitudinal vsheet metal duct which is open along opposite sides thereof to form an inlet 44 and .an outlet 46. The hood 40 has between the inlet and outlet openings 44 and 46 a part-cylindrical section 48, and lead-to and lead-olf sections 50 and 52 which connect the inlet and outlet openings 44 and 46 with the part-cylindrical section 48 (FIG. 2). The several sections 48, 50 and 52 of the hood, which are continuous and uninterrupted with each other, thus form between the inlet and outlet openings 44, 46 a through-passage 54 of which the part defined by the part-cylindrical section 48 is of the largest cross-sectional area. The opposite ends of the hood 40 are closed by walls 56 thereof which may suitably be clamped between the endmost jackets 22 and the standard 12 and die assembly 32 (FIG. 1). The hood 40 is placed with its parts-cylindrical section 48 in close surrounding relation to the finned cylinder. While the wall of the part-cylindrical hood section 48 may be made to contact the tips of the tins 18 thereat, it is preferred and advantageous to provide slight clearance c between this particular hood wall and the fins, as shown. Also, the lead-to and lead-off hood sections 50 and 52,

which are of smaller cross-sectional area that the partcylindrical hood section 48, are preferably flared outwardly from the respective inlet and outlet openings 44 and 46 to the part-cylindrical hood section 48 and merge substantially tangentially with the latter (FIG. 2).

Provided on the extrusion apparatus around the cylinder 14 and hood 40 is an outer enclosure 60 formed of suitable paneling 62 and having on opposite sides windows 64 for access to the hood 40 when needed, with the windows 64 being normally closed by removable covers 66. The blower 42 may also be in a suitable enclosure 68 and be accessible through a window 70 which is normally closed by a removable cover 72. The inlet 44 of the hood 40 is in direct communication with the discharge end 74 of the blower 42, and the hood 40 is provided with a presently hinged cover 76 vfor closing the outlet opening 46 during heat-up of the apparatus or during operation thereof when cooling of the cylinder is not required.

The cylinder 14 is in this instance advantageously arranged substantially horizontally, with the air passage 54 through the hood 40 thus extending equally advantageously substantially vertically (FIG. 2).

The Ipart-cylindrical hood section 48 in close Vsurrounding proximity to the cylinder ns 1.8 thereat denes in the through-passage 54 constricted paths p which are substantially confined to the spaces s between adjacent fins thereat (FIG. 2). Air forced into the hood inlet 44 by the blower 42 will thus ow without impediment and, hence, without appreciable turbulence, through the leadto-section 50 of the hood and then pass to and through the constricted path p wherein the air velocity will in crease quite considerably and the air, in consequence, brush the tins thereat quite forcefully over their entire surfaces for most effective cooling of the latter, whereupon the air will discharge through the lead-off section 52 and outlet 46 of the hood to the atmosphere. The air thus forced through the hood 40 will be in eiective heat-exchange relation with all the iins throughout their surface areas, with the most effective heat-exchange between the air and fins taking place in the constricted path p in which the air will be at more than the necessary velocity to prevent any heat-insulating air film formation on the fin surfaces. For most uniform cooling of the cylinder, the hood 40 is so formed that its throughpassage 54 is substantially concentric about the plane x in which the cylinder axis a lies (FIG. 2). Further to keep turbulence of the forced air in the through passage 54 to ,an absolute minimum and thereby avoid the formation of local hot air pockets in the passage, there is provided along the bottom of the cylinder 14 a baflle 80 which faces the air inlet 44 and wedge-like deects the onrushing air gradually toward the constricted paths p, thus .avoiding a head-on clash between this air and the very bottom of the cylinder.

The present air-cooling system for an extruder has been found to be highly eicient and far superior in its cooling capacity to prior extruder air-cooling systems. Thus, extensive tests have shown that the cooling capacity of the present system vis about 50% higher than that of prior systems with hoods over iinned cylinders, at comparable extruder sizes and volumetric flow rates of cooling air forced into the hoods.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be conn sidered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claim are intended to be embraced therein.

What is claimed is:

In extrusion apparatus, the combination with -an extrusion cylinder having a longitudinal axis and ring-like heat-exchange tins on its outer periphery lying in spaced parallel planes substantially normal to said axis, of a longitudinal hood surrounding and extending substantiallyl over the length of said cylinder and having inlet and outlet openings on opposite sides thereof, said -hood providing a through-passage between said openings and having between said openings a first part-circular section and second sections on opposite sides of said first section and connecting the latter with said openings, said second sections aring from said openings outwardly to, and merge substantially tangentially with, said rst section, with said through-passage being cross-sectionally congruent about a plane in which said axis lies, and said ns o n opposite sides of said cylinder extending outwardly substantially to said rst section so that the latter defines constricted paths substantially confined to the spaces between said tins thereat; means to force air into said inlet opening; and a baille on said cylinder facing said inlet opening for gradually deflecting forced ,air in said hood toward said constricted paths.

References Cited UNITED STATES PATENTS 2,541,201 2/1951 Buecken et al. 18-12 X 2,574,907 11/1951 Bucken 18-12 2,721,729 10/1955 Van Riper 18-12 X 2,723,422 11/ 1955 Marshall 18-30 2,774,107 12/1956 Davis 18-12 2,893,055 7/1959 Wenzel 18-12 2,952,873 9/ 1960 Porter.

3,167,812 2/1965 Von Bennigsen 18-12 3,216,061 11/1965 Schott.

3,218,671 11/1965 Justus et al 18-12 WILLIAM I. STEPHENSON, Primary Examiner.

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