US3727678A

US3727678A - Heat transfer device useful for extruders

Info

Publication number: US3727678A
Application number: US00102627A
Authority: US
Inventors: C Schott
Original assignee: Gloucester Engineering Co Inc
Current assignee: Gloucester Engineering Co Inc
Priority date: 1970-12-30
Filing date: 1970-12-30
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17

Abstract

Heat transfer devices useful for extruders. Jacket sections defining inwardly directed ribs are heat shrunk about extruder barrels. By appropriate sizing, the stresses produced exceed the yield stresses causing metal to self-seal any nicks occurring and to expand adjacent base portions tighter against the inner member or barrel. Arelatively hard barrel concentrates the yielding to the metal of the jacket. Heat shrunk ribs provide good heat transfer paths to electric heaters secured about the exterior of the jackets, as well as defining fluid passages. Free flanges joined by narrow root sections enable joining of adjacent jacket sections by welds with immunity to disturbance in the presence of differential expansion of the assembly. Intercommunication of annular compartments is provided by interruption in the ribs or by covered grooves formed through the free side of the jacket wall.

Description

United States Patent 1 Schott, Jr.

1 1' Apr. 17,1973

[54] HEAT TRANSFER DEVICE USEFUL [73] Assignee: Gloucester Engineering Co., Inc.,

Gloucester, Mass.

[22] Filed: Dec. 30, 1970 [21] App]. No.: 102,627

Primary Examiner-Charles Sukalo Attorney-John Noel Williams ABSTRACT Heat transfer devices useful for extruders. Jacket sections defining inwardly directed ribs are heat shrunk about extruder barrels. By appropriate sizing, the stresses produced exceed the yield stresses causing metal to self-seal any nicks occurring and to expand adjacent base portions tighter against the inner member or barrel. Arelatively hard barrel concentrates the yielding to the metal of the jacket. Heat shrunk ribs provide good heat transfer paths to electric heaters secured about the exterior of the jackets, as well as defining fluid passages. Free flanges joined by narrow root sections enable: joining of adjacent jacket sections by welds with immunity to disturbance in the presence of differential expansion of the assembly. lntercommunication of annular compartments is provided by interruption in the ribs or by covered grooves formed through the free side of the jacket wall.

- 6 Claims, 10 Drawing Figures PATENTE D APR 1 7 i975 SHEET 2 0F 6 FIG 4 PATENTED APR 1 71975 sum u or 6 FIGS PATENTEBAPR 1 7197s SEiEEI 5 UF 6 HEAT TRANSFER DEVICE USEFUL FOR EXTRUDIERS This invention concerns heat transfer assemblies of the fluid compartment type useful for plastic extruders and other equipment where cooling and heating are required.

In plastic extruders a plastic compound is subjected to mechanical working effects and heat, to render it fluid and to force it through an orifice under substantial pressure. Various degrees of heating and cooling of an extruder at various points along its length are desired for start-up and running conditions and for heating the extruder to the extent that the extruder screw may be removed. Variability of the temperature along the extruder length over a wide range will permit a given extruder design to be employed with various plastics materials where physical properties and extruding con ditions vary.

One object of the invention is to provide improved heat transfer assemblies of the fluid compartment type.

Another object of the invention is to provide improved extruders which permit desired temperature control.

Other objects include providing: reliable and lowcost, leak-proof seals for coolingjackets which can perform over a wide operating temperature range; simple jacket constructions which facilitate both efficient cooling and heating and are practical to construct and operate; jacket constructions which absorb distortions of the jackets and prevent warping of the internal member; and jacket constructions of a standard form useful over a wide range of applications.

In one aspect the invention features a heat transfer assembly useful for plastics extruders having a hollow metal outer jacket disposed about an internal metal member and defining therebetween a confining volume for heat transfer liquid. The jacket member has an in tegral liquid-sealing circular rib member protruding toward and deformed by interference shrink fit against and in liquid-sealing relation with a corresponding outer surface ofthe internal member. The unassembled internal diameter of the rib member is less than the outer diameter of the internal member when both are at the same temperature and the rib member is shrunk fit upon the internal member by cooling of the jacket from a temperature hotter than that of the internal member. In preferred embodiments the internal member is an extruder barrel and the jacket defines a cooling passage about the outer periphery of the barrel; the outer surface of the internal member is constructed of metal harder than that of the jacket; the outer surface of the internal member is smooth and the jacket includes additional rib members defining a path for the heat transfer liquid, these also being deformed by interference shrink lit with the internal member; and the assembly has at least one annular electric resistance band heater disposed around the jacket and arranged to transfer heat to the internal member through the shrink-fit rib members.

According to another aspect of the invention a portion of the projection ofa rib member is in permanently deformed condition as a result of stresses in excess of the elastic limit produced from the interference fit, preferably the projection extending from a base, and as a result of dislocation of metal of the projection, the

base being extended toward and pressed against the internal member, contributing to the effectiveness of the seal. The metal of the rib can be formed into and sealed against surface irregularities occurring in the area of the seal.

According to another aspect of the invention the jacket is formed by a plurality of jacket sections with internal ribs of unassembled internal diameter less than corresponding portions of the barrel or internal member and the jacket sections are shrunk fit onto the internal member or extruder barrel with the ribs pressing tightly upon the outer surface of the barrel in heat transferring relation therewith and the heaters, in the form of annular bands surrounding portions of the jacket, are arranged to transfer heat through the ribs to the extruder. Adjacent sections of the jacket have mating radial flange portions at corresponding ends which are welded together and each of which is joined to its jacket section through a root portion of thickness less than the general wall thickness of the jacket, whereby differential expansion of adjacent sections of the jacket may be accommodated with bending of the flanges and without disturbance of the relationship of the ribs upon the barrel.

In another aspect annular compartments are defined between adjacent ribs of the jacket and liquid passages are provided connecting selected compartments. In one form the passages comprise openings in adjacent ribs spaced circumferentially from each other to define a circuitous path for coolant flowing successively through the compartments while in another form grooves machined in the outer wall of the jacket permit cross over of any numberof compartments, openings being provided into the groove from the selected compartments and a cover plate applied over the groove.

Other objects, features and advantages will become apparent from the following description of a preferred embodiment of the invention, taken together with the attached drawings thereof, in which:

FIG. I is a side elevation, partially in cross-section and partially in diagrammatic form, of an extruder constructed in accordance with the invention;

FIG. 2 is a perspective view of an extruder jacket of FIG. 1 before it is assembled around the barrel, with a portion of the jacket broken away;

FIG. 3 is a cross-sectional view of portions of the jacket before the jacket is assembled around the barrel;

FIG. 4 is a diagrammatic view of the flow paths established by the jacket around the barrel;

FIG. 5 is an enlarged crosssectional view of the ribs and end construction ofajacket section with an indication also of the relative size of the barrel;

FIG. 6 is an enlarged cross-sectional view of portions of the jacket and barrel adjacent an end seal; and

FIG. 7 is an enlarged cross-sectional view of a portion of the end seal adjacent a surface irregularity of the barrel;

FIG. 8 is a diagrammatic cross-sectional view,

FIG. 9 is a partially cut away perspective view and FIG. 10 is a detail of another preferred embodiment of the invention.

Referring to FIG. 1 an extruder comprises a hopper 12 arranged to feed plastic pellets to a barrel 14. In the barrel a threaded screw 16 is rotated by a motor 18, to work the plastic from solid to molten form, and propel the molten plastic toward barrel end 20. At end 20 the barrel has an orifice 22 communicating with a die or other plastic forming apparatus (not shown).

The major thickness of the barrel is typically of 4140 Alloy steel with a durable X aloy(trademark of Xaloy Incorporated) lining at the bore of the barrel.

The portion of barrel l4 beyond hopper 12 is divided into a number of zones, each having an

annular cooling jacket

34, 36, 38, 40 and 42 (to be discussed in greater detail below) surrounding the barrel. Each jacket is separately operable and arranged to receive a cooling fluid, for example, ethylene glycol, from a fluid heat transfer system 44 through pipes 46, to permit circulation of the fluid to cool barrel 14, and to return the fluid to heat transfer system 44 through pipes 48. Annular electric band heaters 24 are disposed about the jackets, the temperature of each of which is controlled at heat control panel 28 over leads 30 and 32. The extruder is further provided with a sixth cooling jacket 52, and a sixth band heater 50, each of which is separately operable, around the portion of barrel 14 which surrounds the drive shaft 54 of screw 16 adjacent motor 18.

Cooling jackets

34, 36, 38, 40, 42 and 52 are substantially identical and for simplicity only end jacket 42, which incorporates the different features of all of the jackets, will be discussed in detail. As can best be seen in FIGS. 2, 3 and 4jacket 42, which is constructed of low carbon steel, is substantially tubular in shape, has a smooth outer surface 56 and has its inner surface machined to provide a plurality of circular ribs 60 (54 inch wide, w, approximately 0.3 inch deep, d, and spaced apart by 2 inch,s,)at the inner periphery, projecting radially inward. Each rib is interrupted, providing cross spaces 62 between the ends 64 of ribs 60. Spaces 62 on adjacent ribs 60 are diametrically opposite each other.

At its outer -or sealing end 66 (FIGS. 3,4 and jacket 42 has a rib 61 of the same radius R;, as rib 60, and projecting 0.004 inches, d,, radially inward from rib 61 is a sealing land 68 (0.062 inches wide,w,). Spaced 0.50 inches,L, from'the inner end 70 (left end, FIG. 5) ofjacket 42 is a middle joint 71 in which a rib 72, 0.25 inches wide, projects 0.3 inches radially inward to alignment with the

ribs

60,61. In this joint region outer surface 56 has annular groove 74, (0.125 inches wide and 0.625 inches deep radially), cut to provide a deformable flange section 76 having a root portion 77 (approximately 0.3 inches thick)and curved curved (V4th circle) annular welding groove 78 cut in the outer corner thereof. The inner corner is chamfered as shown. The end of this flange is butted against a corresponding flange of the next adjacent jacket 40, the welding grooves forming together a semicircular groove in which a welding bead 79 is laid.

Ribs

60, 61 and 72 define annular cooling fluid passages 84 between the jackets and barrel l4 and spaces 62 define longitudinally extending passages which connect adjacent passages 84.

Jackets

36, 38 and 40 have middle joints 7] at both of their ends, while

jackets

34 and 42 have one sealing end 66 at one end and a middle joint 71 at the opposite end. Jacket 52 has two sealing ends 66.

Each jacket section has a fluid inlet passage (FIG. 4) communicating with a pipe 46 and the passage 84 between the nearest two ribs to one end of the jacket and a fluid outlet passage communicating with a pipe 48 and the passage 84 between the nearest two ribs to the other end of the same jacket.

The inner surfaces of

ribs

60, 61 and 72 lie at a radius R; from axis of symmetry A (i.e. 4.931 inch) which is smaller than the outer radius R of barrel l4 i.e. 5 inches. For assembly,

jacket sections

34, 36, 38, 40, 42 and 52 are heated in an oven to a temperature higher than the temperature of barrel 14, eg to 600F, until the metal from which the jackets are constructed expands sufficiently for the effective inner radius of the jackets to become greater than R The jackets are then slipped over barrel 14 in the proper sequence and moved into their respective positions and permitted to cool with the ends of adjacent jackets firmly in place against each other. As the jackets cool they become interference or shrunk fit (see later discussion for details of this fit) around barrel 14 and after they cool, adjacent grooves 78 are welded together and

heaters

24 and 52, leads 30 and 32,

pipes

46 and 48 and motor 18 assembled in place. After the jackets have cooled, the inner surfaces 80 of

ribs

60, 61 and 83 are in tight contact with barrel 14 under all operating conditions.

Referring now to FIGS. 6 and 7, the effects of the shrunk fit on the projection 68 at end seal 66 are illustrated. Since the 4140 alloy steel from which barrel 14 is constructed is harder than the low carbon steel from which the jackets are constructed, substantially all permanent deformation caused by the stresses resulting from the interference fit occur in the jacket. I have found that the stress generated between the barrel 14 and the sealing land 68 is approximately 8,000 pounds per inch of circumference and that under such conditions the metal in lands 68 deforms beyond the yield point of the metal. For example, if the outer surface of barrel 14 has an irregularity 86 (FIG. 7) therein such as a nick in the outer surface of the barrel, metal from a sealing land flows into and seals against the irregularity 86. Furthermore, the stress to which the sealing lands are subjected is sufficient to cause plastic flow (of the steel) to occur in rib 61. In FIG. 5, at the right hand side, dotted lines 80a and 82a show the relative locations of

surfaces

80 and 82 before assembly, while lines 80b and 82b show their respective locations after jacket 42 has partially cooled, assuming no barrel in place. Lines 800 and 820 diagrammatically illustrate the location of the surfaces at the same partially cooled temperature with the barrel in place, and the projection and rib shrunk fit around barrel 14. Land 68 has been deformed outwardly toward rib 60 and plastic flow has occurred, as along lines 88, with the result that except for the region 90 immediately adjacent land 68 the metal in rib 60 is deformed inwardly from its unstressed position toward the surface of barrel 14. The stress eventually drops below the yield point after the deformed portion of rib 60 is raised sufficiently for surface 800 to come into sealing engagement with barrel 14 over a width greater than the width of sealing land 68, this raising contributes positively to the effectiveness of the purely metal-to-metal seal, and also it introduces considerable resistance to relative sliding of the jacket on the barrel during differential expansion, and so protects the projection 68 from being sheared off.

In operation heaters 24 and motor 18 are started and plastic pellets deposited in hopper 12. Since heaters 24 are in direct contact with the outer surface 56 of the cooling jacket, the heat which they generate is rapidly conducted to barrel 143 by ribs 60 and 72 which are in tegral with the jackets and shrunk fit upon the barrel, guaranteeing a good heat conductivity path. The pellets enter barrel l4 and are driven and worked, as they are heated and melted, in the direction of orifice 22. As the working of the plastic continues and as the temperature of the molten plastic increases with its movement toward end 20, the mechanical working of the screw 16 tends to cause undesirable increases in the temperature of the plastic in barrel in some or all of the zones and requires cooling.

(It is extremely important in the extruding process that, for a given material and given settings of the extrusion apparatus and dies, that the temperature characteristics of the apparatus remain as constant as is possible to maintain the desired viscosity of the molten material being processed to insure uniformity in the finished product, for example, thin plastic sheets. in addition, with some vinyls, degradation occurs if the temperature becomes excessive. Thus the cooling jackets are provided to permit localized cooling of the barrel for each zone when conditions warrant.) An attendant may regulate the flow of the cooling fluid from heat transfer system 44 to each of the jacket sections through pipes 46 in order to maintain acceptable temperature within the particular zone surrounded by a jacket.

The fluid enters the jackets at the inlet and first flows circumferentially in passages 84 around and in contact with barrel 114, then longitudinally forward through space 62 toward the outlet end, and is urged circumferentially in reverse direction around barrel 14 in passages 84 by ribs 60. Circumferential flow alternates between flow in the upward and downward directions until the fluid reaches the outlet and is returned to system 44 by pipes 48.

The sealing lands 68, at the outside ends of

jackets

34 and 42 and of jacket 50, which have deformed beyond their yield point, together with sufficiently deformed portions of ribs 60, effectively prevent any leakage of the fluid even if the barrel 14 has irregularities (such as that shown in FIG. 7) in its outer surface, caused, for example, by peening required to remove warps from barrel 14 after it has been formed, since the low carbon steel in lands 68, while under high stress, has deformed into the filled them. Similarly the welds between adjacent jackets in grooves 78 around barrel l4 effectively seal the middle joints 711 to prevent fluid leakage to the atmosphere at normal operating pressures of approximately 60 p.s.i. When differential expansion or contraction of adjacent jackets or welding distortions occur, the flange 76 at the middle joint flex to take up this effect without forcing the ribs to shift on the barrel.

Thus, the jacket of the invention provides a seal which is extremely reliable, but at the same time simple and inexpensive to construct. Furthermore, the grooves cut in the inner surface of the jackets to define the ribs 60 and lands 68, because of their cylindrical, rather than the more conventional helical, configuration may be quickly and inexpensively cut by employing a right angle milling head or an internal shaper, rather than requiring alathe with which the direction of cutting must be reversed for each turn if, for example, a helical groove were to be cut. Constructing the overall jacket from a number of shorter sections simplifies both assembly of the jacket (since the sections are more easily handled than a largerjacket) and the heating apparatus required to expand the sections sufficiently to fit them over barrel 14.

Referring to H68. 8, 9 and 10, another preferred embodiment is shown in which the ribs form continuous hoops and the compartments defined by the ribs are connected through cross passages provided in the outer wall d3 of the jacket member. To this end, a groove is machined in the outer surface of the jacket axially along the jacket, between any two compart' ments desired to be connected. Holes 92 are then drilled to connect the groove with these compartments. Then acover plate 94 is welded in place over the groove, completing the cross-over passage. By this means very complex flow patterns can be established and can be changed from time to time if desired by opening some passages and closing others.

Other embodiments will occur to those skilled in the v art and are within the following claims.

What is claimed is:

1. in a heat transfer assembly comprising a hollow, rigid metal external jacket member of circular crosssection disposed about a rigid internal metal member of similar cross-section and defining therebetween an annular confining volume for heat transfer liquid, one of said internal and external members having axially spaced-apart annular ribs extending radially into con tact with the other member, each of said members being preformed, said members being presized for heat-shrink fitting together, the preformed radial dimension of said ribs being in excess of the space between said members, and in said assembly said ribs residing under substantial radial compression, there being, in reaction, substantial hoop tension stress in said outer member, and radial compression of said inner member in the region of said annular ribs, the improvement wherein the circular surface: of said member engaged by one of said ribs has a surface discontinuity, said rib having preformed on its engaging surface a land of narrow axial dimension relative to the axial dimension of said rib, and a radial extent greater than that of said rib, said land being presized for compressional stressing beyond its metal yield point by heat-shrink fitting of said members together, in said assemblysaid land lying over said surface discontinuity and in a state deformed beyond its elastic limit, the substance of said land effectively sealing against said] surface discontinuity.

2. The heat transfer assembly of claim 1 wherein said internal metal member is substantially cylindrical, said external member has integral, radially inwardly extending ribs, and said land extends integrally, radially inwardly from its respective rib.

3 The heat transfer assembly of claim 1 wherein said external jacket member comprises a plurality of axially contiguous sections, each defining with respective ribs an annular confining volume portion for heat transfer liquid, said sections joined by radially outwardly extending circular walls joined together at an outer radius, said walls having axially displaceable portions inwardly thereof, said joined walls forming a liquidtight expansion joint permitting one of said sections to thermally axially contract without displacing the other of said sections in the axial direction, whereby said land and ribs are protected from detrimental axial shearing stress.

4. In a heat transfer assembly comprising a hollow, rigid metal external jacket member of circular crosssection disposed about a rigid internal metal member of similar cross-section and defining therebetween an annular confining volume for heat transfer liquid,one of said internal and external members having axially spaced-apart annular ribs extending radially into contact with the other member, each of said members being preformed, said members being presized for heat-shrink fitting together, the preformed radial dimension of said ribs being in excess of the space between said members, and in said assembly said ribs residing under substantial radial compression, there being, in reaction, substantial hoop tension stress in each outer member, and radial compression of said inner member in the region of said annular ribs, the improvement wherein said external jacket member comprises a plurality of axially contiguous sections, each defining with respective ribs an annular confining volume portion for heat transfer liquid, said sections joined by radially, outwardly extending circular walls joined together at an outer radius, said walls having axially displaceable portions inwardly thereof, said joined walls forming a liquid-tight expansion joint permitting one of said sections to thermally axially contract without displacing the other of said sections in the axial direction whereby said ribs are protected from detrimental axial shearing stress.

5. The heat transfer assembly of claim 4 wherein said internal metal member is substantially cylindrical, said external member has radially inwardly extending ribs, contiguous portions of sections of said external member each having an external annular groove of substantial radial depth spaced a short distance from the respective end of said section, the end portion of said section beyond said groove forming said wall, radially outer portion of the walls of said contiguous sections being joined together.

6. in a heat transfer assembly comprising a hollow, rigid metal external jacket member of circular crosssection disposed about a rigid internal metal member of similar cross-section and defining therebetween an annular confining volume for heat transfer liquid, one of said internal and external members having axially spaced-apart annular ribs extending radially into contact with the other member, each of said members being preformed, said members being presized for heat-shrink fitting together, the preformed radial dimension of said ribs being in excess of the space between said members, and in said assembly said ribs residing under substantial radial compression, there being, in reaction, substantial hoop tension stress in said outer member, and radial compression of said inner member in the region of said annular ribs, the improvement wherein said heat transfer assembly is adapted selectively to conduct heat to and from said internal metal member, there being at least one electrical resistance band heater disposed about the exterior of said external acket member, positioned to conduct heat into the body of said external member thence through said rib and the respective heat shrunk joint into said internal metal member, and means also for selectively introducing cooling liquid into the annular volume defined between said external and internal members.

Claims

1. In a heat transfer assembly comprising a hollow, rigid metal external jacket member of circular cross-section disposed about a rigid internal metal member of similar cross-section and defining therebetween an annular confining volume for heat transfer liquid, one of said internal and exteRnal members having axially spaced-apart annular ribs extending radially into contact with the other member, each of said members being preformed, said members being presized for heat-shrink fitting together, the preformed radial dimension of said ribs being in excess of the space between said members, and in said assembly said ribs residing under substantial radial compression, there being, in reaction, substantial hoop tension stress in said outer member, and radial compression of said inner member in the region of said annular ribs, the improvement wherein the circular surface of said member engaged by one of said ribs has a surface discontinuity, said rib having preformed on its engaging surface a land of narrow axial dimension relative to the axial dimension of said rib, and a radial extent greater than that of said rib, said land being presized for compressional stressing beyond its metal yield point by heat-shrink fitting of said members together, in said assembly said land lying over said surface discontinuity and in a state deformed beyond its elastic limit, the substance of said land effectively sealing against said surface discontinuity.

3. The heat transfer assembly of claim 1 wherein said external jacket member comprises a plurality of axially contiguous sections, each defining with respective ribs an annular confining volume portion for heat transfer liquid, said sections joined by radially outwardly extending circular walls joined together at an outer radius, said walls having axially displaceable portions inwardly thereof, said joined walls forming a liquid-tight expansion joint permitting one of said sections to thermally axially contract without displacing the other of said sections in the axial direction, whereby said land and ribs are protected from detrimental axial shearing stress.

4. In a heat transfer assembly comprising a hollow, rigid metal external jacket member of circular cross-section disposed about a rigid internal metal member of similar cross-section and defining therebetween an annular confining volume for heat transfer liquid, one of said internal and external members having axially spaced-apart annular ribs extending radially into contact with the other member, each of said members being preformed, said members being presized for heat-shrink fitting together, the preformed radial dimension of said ribs being in excess of the space between said members, and in said assembly said ribs residing under substantial radial compression, there being, in reaction, substantial hoop tension stress in each outer member, and radial compression of said inner member in the region of said annular ribs, the improvement wherein said external jacket member comprises a plurality of axially contiguous sections, each defining with respective ribs an annular confining volume portion for heat transfer liquid, said sections joined by radially, outwardly extending circular walls joined together at an outer radius, said walls having axially displaceable portions inwardly thereof, said joined walls forming a liquid-tight expansion joint permitting one of said sections to thermally axially contract without displacing the other of said sections in the axial direction whereby said ribs are protected from detrimental axial shearing stress.

6. In a heat transfer assembly comprising a hollow, rigid metal external jacket member of circular cross-section disposed about a rigid internal metal member of similar cross-section and defining therebetween an annular confining volume for heat transfer liquid, one of said internal and external members having axially spaced-apart annular ribs extending radially into contact with the other member, each of said members being preformed, said members being presized for heat-shrink fitting together, the preformed radial dimension of said ribs being in excess of the space between said members, and in said assembly said ribs residing under substantial radial compression, there being, in reaction, substantial hoop tension stress in said outer member, and radial compression of said inner member in the region of said annular ribs, the improvement wherein said heat transfer assembly is adapted selectively to conduct heat to and from said internal metal member, there being at least one electrical resistance band heater disposed about the exterior of said external jacket member, positioned to conduct heat into the body of said external member thence through said rib and the respective heat shrunk joint into said internal metal member, and means also for selectively introducing cooling liquid into the annular volume defined between said external and internal members.