Abstract:
An extrusion calibrator, to calibrate the exterior profile of a thermoplastic extruded product exiting from an extrusion die, has a modular calibrating cassette of calibrating plates in a surrounding shell. One calibrating cassette is readily interchangeable within the shell for another calibrating cassette of a different extruded product cross-sectional profile. The cassette plates have planar surfaces, free of fluid-conducting pathways, which greatly reduces the time, cost and skill required to establish vacuum and coolant conducting routes through the extrusion calibrator. Fluid conducting routes to conduct vacuum and coolant through the calibrator are established by vacuum and coolant conducting manifolds and channels in the shell interior and by interplate spacings mating with these channels.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to extrusion calibrators, and more specifically, relates to an extrusion calibrator to calibrate the exterior profile of a thermoplastic extruded product exiting from an extrusion die. In particular, this invention relates to an extrusion calibrator having a modular calibrating cassette of wear-resistant plates retained in a surrounding shell, so that one calibrating cassette is readily interchangeable with another calibrating cassette of a different extruded product cross-sectional profile. In this inventive extrusion calibrator, the fluid conducting routes for conducting vacuum and coolant through the extrusion calibrator are established by vacuum and coolant conducting manifolds and channels within the shell interior and by interplate spacings mating with these channels. The plates of the cassette have planar surfaces, free of fluid-conducting pathways, which greatly reduces the time, cost and skill required in establishing the required vacuum and coolant conducting routes through the extrusion calibrator. 
     BACKGROUND OF THE INVENTION 
     In the process of continuously melt-extruding thermoplastic material from an extrusion die, the extruded product exits the die at an elevated temperature and in a relatively soft state, unable to retain the shape imparted by the die. To assure that the final extruded product has the required exterior shape and dimensions, the exterior cross-sectional profile of the extruded product is cooled and calibrated by passing the extruded product through an extrusion calibrator. The extrusion system, thus, includes both the extrusion die and one or more extrusion calibrators. In each extrusion calibrator, the extruded product is cooled as it travels through a passageway generally similar in size and shape to that of the extrusion die. Each extrusion calibrator has ports and channels for the entry and circulation of a coolant medium (generally water) and vacuum ports for withdrawal of steam generated by cooling of the extruded product. As the extruded product travels through the extrusion calibrator passageway, a thin layer of water covers the extruded product outer surface. The water layer tends to cool the outer surface of the extruded product, producing a thin surface “skin” to further hold the product shape. The water layer also tends to lubricate the extruded product as it passes through the extrusion calibrator. The extrusion calibrator passageway may typically have a smaller cross-sectional size than the extrusion die passageway, further to shape the extruded product, which tends to contract as it cools. The extrusion calibrator passageway may also gradually reduce in cross-sectional size along the passageway, again to accommodate contraction of the extruded product on cooling. The amount of taper and the angle of taper will be determined based on the expected shrinkage of the specific plastic used for the extruded product. 
     Besides removing steam generated by the cooling extruded product, the vacuum holds the walls of the hollow or single wall extruded product in place against the interior walls of the passageway as the extruded product travels through the extrusion calibrator, further helping the cooling extruded product to retain its desired shape. The vaporization of water contacting the extruded product traveling through the extrusion calibrator removes a large amount of heat (BTUs) from the extruded product, and the steam is extracted through the vacuum exhaust ports. Such evaporation systems can remove heat from the extruded product at a much higher rate than possible with conventional heat transfer type extrusion calibrators. Because of the time required to cool the extruded product and the speed of extruded product travel required for economical production, a series of extrusion calibrators may be used to cool and shape the extruded product in an acceptable amount of time and at an acceptable throughput speed. Pullers positioned after the last extrusion calibrator control the extrusion speed by continuously drawing the formed extruded product exiting from the last extrusion calibrator. Examples of extrusion calibration systems are shown, for example, in U.S. Pat. Nos. 5,516,270, 5,514,325, 5,316,459, 5,288,218 and 4,468,369. Extruded products made by such processes typically have a uniform hollow cross-sectional shape along their longitudinal axis, including products such as automobile moldings, window parts, and pipe. 
     Automated EDM, Inc., the assignee of this application, has previously made available an extrusion calibrator, that was assembled from a series of thicker plates of a harder metal, such as steel, alternating with a series of thinner plates of a softer metal, such as aluminum. The thicker plates were each constructed with an aperture sized and shaped to a cross-sectional profile of an extruded product exiting from an extrusion die. The thinner plates were also each constructed with an aperture matched to that of the thicker plates. The thinner plates also were constructed with channels for introduction and circulation of coolant and vacuum. The thinner and thicker plates were assembled in alternation and retained by threaded rods inserted through the assembled plates. The apertures together defined the extrusion passageway and were shaped using wire electrical discharge machining (WEDM) to construct the passageway through the assembled plates. The vacuum and coolant channels were formed by using computer numerically controlled (CNC) milling technology. Holes for the threaded rods were drilled and reamed. With the plates assembled, the channels on the thinner plates provided pathways for coolant and vacuum circulation from sources exterior to the calibrator to the passageway to contact, cool and extract heat from the traveling extruded product. To provide an extrusion calibrator for an extruded product of a different cross-sectional profile requires the manufacture of an entirely new calibrator. Changing a calibrator of one passageway cross-sectional profile to one of a different profile requires disassembling and reassembling all vacuum and coolant access lines. If more than one extrusion calibrator of this earlier design is used in series, such as attached to a baseplate, all of the calibrators must be removed from the baseplate in order to change the passageway profile of the series of calibrators. 
     SUMMARY OF THE INVENTION 
     The present invention is an extrusion calibrator to calibrate an exterior profile of a thermoplastic extruded product exiting from an extrusion die. An extrusion calibrator of this invention may include a pair of covers, a pair of sidewalls, and a set of wear-resistant plates. Each cover has a vacuum manifold and a coolant manifold formed on a cover surface. The manifolds have at least one vacuum channel and at least one coolant channel, respectively. Each side wall has at least one vacuum channel and at least one coolant channel, respectively, in communication with the vacuum manifold and the coolant manifold, respectively, in each cover. The vacuum channels communicate between the vacuum manifold and a vacuum source and vacuum outlet, respectively, and the coolant channels communicate between the coolant manifold and a coolant source and coolant outlet, respectively. The vacuum and coolant channels may be in parallel arrangement alternating with each other. The vacuum manifold and channels may be of larger cross-section than the coolant manifold and channels. A liquid ring vacuum pump removes moisture from the atmosphere within the calibrator. 
     Each plate has a calibrating aperture dimensioned to an extruded product cross-section exterior. The plates have planar surfaces free of fluid conducting pathways. The plates are oriented to each other, so that the apertures together define an extrusion passageway through the calibrator. The cross-sectional dimensions of the passageway may decrease in the direction of travel of the extruded product through the calibrator, to accommodate shrinkage of the extruded product with cooling and to insure accurate dimensioning and profiling of the extruded product. The plates may be spaced to each other and to the respective manifold and channel, so that one inter-plate spacing (or set of spacings) communicates between the vacuum manifold, vacuum channels and the passageway, while another inter-plate spacing (or set of spacings) communicates between the coolant manifold, coolant channels and the passageway. The oriented plates are retained together into a cassette, for example, by threaded rods inserted through the oriented plates. The pins are generally aligned with the passageway, and the inter-plate spacing may be maintained by precision spacers on the pins. The first and last inter-plate spacings of the cassette may communicate with the coolant route and the other inter-plate spacings may alternately communicate with the vacuum route and the coolant route, respectively. Typically, a route for coolant is positioned as the first spacing, so that a coolant layer will cool the outer surface of the extruded product, producing a thin surface “skin” to further hold the product shape. Also, the coolant layer will lubricate the extruded product as it passes through the extrusion calibrator. The first and last coolant inter-plate spacings may be smaller than the other coolant inter-plate spacings, and the vacuum inter-plate spacings may generally be about equal to the first and last coolant inter-plate spacings. The covers and sidewalls may be assembled to the cassette of oriented plates, so that the covers and sidewalls together form an open-ended shell, with the open ends oriented longitudinally with the passageway. The channeled cover surfaces may each have a recess matched to the width of the cassette, to further locate and retain the covers to the cassette and correctly to position the cover and sidewall channels to the inter-plate spacings. The cover is retained, for example, by threaded screws through clearance holes in the cover and into corresponding threaded holes in the ends of the sidewalls and the plates. The threaded screws and the pins may be counterbored. The threaded holes in the side walls may be symmetrical, so that the sidewalls are reversible about a horizontal centerline in assembly of the extrusion calibrator. 
     An extrusion calibrator according to this invention may comprise an open-ended exterior shell and a cassette of wear-resistant calibrating plates. The shell has a vacuum route and a coolant route formed on the shell interior surface, the routes communicate between a vacuum source and outlet, and between a coolant source and outlet, respectively. The cassette plates together define an extrusion passageway between the shell open ends. The passageway is dimensioned to the extruded product cross-section exterior profile. The plates may be spaced to each other and to the respective route, so that a first inter-plate spacing (or set of spacings) communicates between the vacuum route and the passageway, while another inter-plate spacing (or set of spacings) communicates between the coolant route and the passageway. 
     Generally, an extrusion calibrator of this invention, which uses a cassette having a single passageway is suitable for calibrating a generally hollow extruded product. An alternative embodiment of a cassette may be used to calibrate a hollow extruded product that has a nonhollow segment, such as an exterior flange. To calibrate such an extruded product, the cassette may comprise mating upper and lower cassette portions, each formed of upper and lower plate portions. The upper and lower plate portions, respectively, may be spaced and retained into the upper and lower cassette portions, respectively, by means of threaded rods through holes, in the same manner as for the unitary cassette. The mating sides of each cassette portion each are shaped with a part, generally about half, of the cross-sectional shape of the passageway. Constructing the cassette in this manner allows for easier shaping of the passageway to accommodate the non-hollow segment of the extruded product to be calibrated. 
     Accommodating the extrusion calibrator to an alternate extruded product cross-section exterior profile involves removing the shell from a first cassette and installing the shell about a second cassette having an extrusion passageway dimensioned to the alternate extruded product cross-section exterior profile, while the shell remains connected to vacuum and coolant sources and outlets, respectively. When the shell is comprised of a pair of covers and a pair of sidewalls, exchanging the cassette involves removing the covers (and optionally the sidewalls) from one cassette and installing the covers and sidewalls to a second cassette, while the vacuum and coolant sources and outlets remain connected to the covers, respectively. 
     Also, according to this invention, two or more calibrators may be attached in series to a single base plate, so that their passageways are generally axially aligned to each other. The base plate may be retained to the calibrator cover by means of counter-bored shoulder bolts. To position the shoulder bolts, a few threaded screws are removed from the lower cover and the shoulder bolts pass through holes in the base plate and in the lower cover to screw into threaded holes in the plates and/or the sidewalls. 
     An extrusion calibrator may be made by the following method. A pair of covers are constructed, so that each cover has a vacuum manifold and a coolant manifold formed on a cover surface. Each manifold is constructed with at least one vacuum channel and at least one coolant channel, respectively. The vacuum manifold connects between a vacuum source and outlet, and the coolant manifold connects between a coolant source and outlet. A pair of sidewalls are constructed, so that each side wall has a vacuum channel and a coolant channel, respectively, in communication with the vacuum manifold and the coolant manifold, respectively. A set of wear-resistant plates are constructed, so that each plate has a calibrating aperture dimensioned to an extruded product cross-section exterior. The plates are oriented to each other in a cassette, so that the apertures together define an extrusion passageway through the calibrator, and so that the plates are spaced to each other and to the respective channels. The sidewalls and covers are assembled to the oriented plates, so that the sidewalls and covers form an open-ended shell retaining the oriented plates. The passageway is longitudinally aligned with the open ends. At least one inter-plate spacing (or set of inter-plate spacings) between adjacent plates is in fluid-tight communication solely between the vacuum manifold, vacuum channels and the passageway, while at least one other inter-plate spacing (or set of inter-plate spacings) between adjacent plates is in fluid-tight communication solely between the coolant manifold, coolant channels and the passageway. The plates may be oriented to each other by inserting threaded rod through the plates. The rods are generally aligned with the passageway. The plates may be spaced to each other and to the respective manifold channel by spacers maintained on the rods between adjacent plates. The covers may be constructed to remain connected to vacuum and coolant sources and outlets, respectively, during exchange of a first cassette for a second cassette having an extrusion passageway of a different cross-sectional profile. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a matched set of extrusion calibrators of this invention arranged in series and fastened to a baseplate. 
     FIG. 2 is a side perspective view of the set of extrusion calibrators shown in FIG.  1 . 
     FIG. 3 is front perspective view of the set of extrusion calibrators shown in FIG. 1, showing a threaded alignment rod and inter-plate spacing washers removed from the threaded holes through the cassette of wear-resistant plates and showing the cover plate and threaded screws removed from the cassette and the sidewalls, with the vacuum and coolant manifolds and channels on the inside cover surface. 
     FIG. 4 is perspective view of a cover of the extrusion calibrator of FIG. 1, showing the vacuum and coolant manifolds and channels. 
     FIG. 5 is a plan view of the cover of FIG.  4 . 
     FIG. 6 is a cross-sectional view of the cover of FIG. 4, taken along the line  6 — 6  in FIG.  5 . 
     FIG. 7 is a plan view of a sidewall of the extrusion calibrator of FIG. 1, showing the coolant and vacuum channels, with the threaded screw holes seen in phantom. 
     FIG. 8 is an end view of the sidewall of FIG. 7, showing the coolant and vacuum channels, with the threaded screw holes. 
     FIG. 9 is a top view of a cassette of calibrator plates with associated sidewalls, taken along the line  9 — 9  of FIG. 1, showing the alignment of the inter-plate spacings with the sidewall vacuum and coolant channels. 
     FIG. 10 is a plan view of the extrusion calibrator, showing the cover manifolds and channels, the sidewall channels, the inter-plate spacings and the extrusion passageway. 
     FIG. 11 is a perspective view of an alternate embodiment of an extrusion calibrator of this invention, showing a horizontally split cassette, in which the upper and lower cassette portions assemble to form a central passageway, for a hollow extruded product, with a side segment for a solid flange. 
    
    
     DESCRIPTION OF THE INVENTION 
     A first embodiment of an extrusion calibrator  20  of this invention will now be described with reference to FIGS. 1 through 10. FIG. 1 shows a pair of extrusion calibrators  20  arranged in series and fastened to a baseplate  22 . Each extrusion calibrator  20  includes a pair of upper and lower covers  24 , a pair of right and left sidewalls  26  and a set of wear-resistant calibrating plates  28 . Each calibrating plate has an aperture  30 , which is sized and shaped to the external cross-sectional profile of an extruded product (not shown) to be cooled and calibrated through the extrusion calibrator  20 . The calibrating plates  28  are oriented to each other and retained in a cassette  32  by precision ground rods  34  with threaded ends inserted into aligned holes  36 . The required inter-plate spacings  38  between the plates  28  are sized and retained by spacing washers  40  aligned on the rods  34 . The rods  34  retain the plates  28  and washers  40  in alignment by means of internally threaded ends  42 , which may be counterbored into the outer faces of the first and last plate  28  of each cassette  32 . The orientation and alignment of the plates  28  into the cassette  32  can perhaps best be seen with reference to FIG.  3 . The apertures  30  of the individual plates  28 , when assembled into the cassette  32 , form an extrusion passageway  44  through which the extruded product exiting from the extrusion die (both not shown) will travel. The passageway  44  is visible through the first plate  28  of the cassette  32  of the first calibrator  20  in FIG. 1, and through the first plates  28  of the cassettes  32  of the first and second calibrators  20  in FIG.  2 . Once the cassette  32  has been assembled, the upper and lower covers  24  are positioned to the cassette  32 . Note that the length of the covers  24  is equal to the length of the assembled cassette  32 . Each cover  24  has a longitudinal recess  46  sized and shaped to retain and locate the top (bottom) of the cassette  32 . One side edge of each cover  24  is drilled with a pair of access ports  48  and the opposite cover  24  edge is drilled with a single access port  50 . In the embodiment shown in FIGS. 1-10, the pair of access ports  48  provide access for vacuum exhaust, while the single access ports  50  provide access for coolant inlet, as will be later described in greater detail. With the covers  24  thus positioned, the sidewalls  26 , which are equal in length to the cassette  32  and to the covers  24 , are slid into place. The covers  24  are retained to the cassette  32  and to the sidewalls  26  by clearance and counterbored holes  52  through each cover  24  and corresponding threaded holes in edges of the plates  28  and the sidewalls  26 . Threaded screws  54  through the holes  52  may be counterbored to the level of the cover  24 . The two extrusion calibrators  20  are positioned and retained to the baseplate  22  by threaded shoulder bolts through precision holes in the baseplate  22  and the lower cover  24 . To secure the baseplate  22  to the lower cover  24 , a few threaded screws  54  are removed from holes  52  in the lower cover  24 , and threaded shoulder bolts are inserted through the holes in the baseplate  22  and lower cover  24  and are screwed into threaded holes in edges of the plates  28  and/or sidewalls  26 . The shoulder bolts are not visible in FIG. 3, but are attached in the same manner as will be later herein shown and described with reference to FIG.  11 . The shoulder bolts may be counterbored in the baseplate  22  holes. 
     The route through the calibrator  20  for the circulation of vacuum and coolant will now be described with reference to FIGS. 3-10. FIG. 3 is a front perspective view of the set of extrusion calibrators  20  shown in FIG. 1, showing a threaded alignment rod  34  and inter-plate spacing washers  40  positioned in alignment above the cassette  32 . FIG. 3 shows in the first plate  28  the threaded holes  36  through the cassette  32  and shows the cover  24  and threaded screws  54  removed from the cover holes  52  and from the holes  56 ,  58 , respectively, in the edges of the cassette  32  and the edges of the sidewalls  26 , with the vacuum  60  and coolant  62  manifolds and vacuum  64  and coolant  66  channels on the inside cover  24  surface. In the embodiment shown in FIGS. 3-10, the vacuum manifold  60  is shown as communicating between two vacuum access ports  48  and four vacuum channels  64  on each cover  24 . The coolant manifold  62  is shown as communicating between one coolant access port  50  and five coolant channels  66  on each cover  24 . The vacuum channels  64  are shown as wider than the coolant channels  66 , and the vacuum  64  and coolant  66  channels are shown as alternately interfitting with each other. It will of course be understood that the number of access ports and channels and their relative size and arrangement to each other are a matter of engineering choice and may be varied to suit the needs of a particular application. The vacuum  64  and coolant  66  channels in the cover  24  are sized and arranged to communicate with corresponding vacuum  68  and coolant  70  channels in the sidewalls  26 . The vacuum channels  68  are shown as wider than the coolant channels  70 , and the vacuum  68  and coolant  70  channels are shown as alternating with each other. The alignment rods  34  and washers  40  position the inter-plate spacings  38  of the plates  28  in the cassette  32  to communicate between the vacuum channels  64 ,  68  and the coolant channels  66 ,  70 , respectively, and the extrusion passageway  44 . Note that in the embodiment shown in FIGS. 3-10, the three middle coolant interplate spacings  38   a  are shown as generally equal to the width of the coolant channels  66 ,  70 , while the two end coolant interplate spacings  38   b  are narrower than the coolant channels  66 ,  70 . The four vacuum interplate spacings  38   c  are shown as generally narrower than the three middle coolant interplate spacings  38   a  and generally about equal in width to the two end coolant interplate spacings  38   b.  Also, as can be seen with reference to FIGS. 3-10, the upper and lower covers  24  are identical. If a single calibrator  20  is used, the covers  24  will be completely identical and interchangeable with each other. The right and left sidewalls  26  are identical, reversible about a horizontal centerline and interchangeable with each other. Again, it will be understood that the sizing and arrangement of the interplate spacings  38  in the cassette  32  and of the channels  64 ,  66 ,  68 ,  70  in the covers  24  and sidewalls  26  are a matter of engineering choice and may be varied to meet the needs of a particular application. It should also be understood that, when the extrusion calibrator  20  is fully assembled, the mating faces of the sidewalls  26  to the edges of the plates  28  of the cassette  32  and the mating faces of the covers  24  to the edges of the sidewalls  26  and to the edges of the plates  28  of the cassette  32  are all fluid tight, so that fluid circulation through the extrusion calibrator  20  is conducted through the vacuum manifolds  60  and the vacuum channels  64 ,  68  to the extrusion passageway  44  and through the coolant manifolds  62  and the coolant channels  66 ,  70  to the extrusion passageway  44 . 
     For ease of access, the first plate  28  of the extrusion calibrator  20  may have a beveled leading edge (not shown) at the aperture  30  leading to the passageway  44 . 
     A second embodiment of an extrusion calibrator  80  according to this invention is shown with reference to FIG.  11 . FIG. 11 is a perspective view of the extrusion calibrator  80 , showing a horizontally split cassette  82 , in which the upper  84  and lower  86  cassette portions assemble to form a central extrusion passageway  88 , for a hollow extruded product (not shown), with a side segment  90  for a solid flange extending from the hollow extruded product. Each cassette portion  84 ,  86  is assembled from a set of upper and lower wear-resistant calibrating plates  92 ,  94 . Each upper wear-resistant calibrating plate  92  has a portion of a cut-out  93  and each lower heat conducting calibrating plate  94  has a portion of a cut-out  95 , such that the cut-outs  93 ,  95 , with the edges of the plates  92 ,  94  mated together, form an extrusion aperture, sized and shaped to the exterior cross-sectional profile of the extruded product to be calibrated. Each set of upper and lower calibrating plates  92 ,  94  are separately oriented to each other and retained in an upper and lower cassette portions  84 ,  86 , respectively, by precision ground rods  34  with threaded ends inserted into aligned holes  96 . The required inter-plate spacings  98  between the upper and lower plates  92 ,  94  are sized and retained by spacing washers  40  aligned on the rods  34 . The rods  34  retain each set of upper and lower plates  92 ,  94  and washers  40  in alignment by means of internally threaded ends  42 , which may be counterbored into the outer faces of the first and last of the upper and lower plates  92 ,  94  of each upper and lower cassette portion  84 ,  86 . The orientation and alignment of each set of upper and lower plates  92 ,  94  into each upper and lower cassette portion  84 ,  86  can be seen in FIG.  11 . When individual upper and lower plates  92 ,  94  are assembled into the upper and lower cassette portions  84 ,  86 , and when the upper and lower cassette portions  84 ,  86  are assembled into the horizontally split cassette  82 , the cut-outs  93 ,  95  of the individual upper and lower plates  92 ,  94  form an extrusion passageway  88  through which the extruded product exiting from the extrusion die (both not shown) will travel. As already mentioned, the extrusion passageway  88  has a side segment  90 . The larger area of the extrusion passageway  88  will form a generally hollow extruded product, while the side segment forms a generally solid flange or extension from the hollow extruded product. The suction action of the vacuum exhaust is great enough to pull the hollow extruded product against the walls of the passage way  88 , but permits the extruded product to remain solid in the thinner, smaller-dimensioned side segment  90 . Alternatively, if the cut-outs  93 ,  95  together define an extruded product which is entirely thinner and smaller-dimensioned, the entire extruded product may be solid throughout. 
     Once the horizontally split cassette  82  has been assembled by stacking the upper and lower cassette portions  84 ,  86  to each other, the upper and lower covers  24  are positioned to the cassette  82 . Note that the covers  24  and sidewalls  26  for this alternate calibrator  80  of FIG. 11 may be the same as the covers  24  and sidewalls  26  for the calibrator  20  described with reference to FIGS. 1-10, as long as the number of plates  92 ,  94  in each cassette portion  84 ,  86  and the interplate spacings are the same as those of the calibrator  20  of FIGS. 1-10. If the number of plates  92 ,  94  and the interplate spacings are not the same as those of the calibrator  20  of FIGS. 1-10, the various access ports, manifolds, channels and other features and dimensions for the covers  24  and sidewalls  26  for the alternate calibrator  80  will vary accordingly. With the appropriate covers  24  positioned to the assembled horizontally-split cassette  82 , the right and left sidewalls  26  are slid into place. The covers  24  are retained to the cassette  82  by clearance holes  52  through each cover  24  and threaded holes in corresponding edges of each set of plates  92 ,  94 . The covers  24  are retained to the sidewalls  26  by clearance holes  52  through each cover  24  and threaded holes  58  in each sidewall  26 . The clearance holes  52  may be counterbored. As described for the extrusion calibrator  20  illustrated in FIGS. 1-10, the extrusion calibrator  80  illustrated in FIG. 11 may be used in pairs in series and may be attached to a single baseplate  22 . To secure the baseplate  22  to the lower cover  24 , a few threaded screws  54  are removed from holes  52  in the lower cover  24 , and threaded shoulder bolts  55  are inserted through the corresponding holes in the baseplate  22  and lower cover  24  and are screwed into threaded holes in edges of the plates  28  and/or sidewalls  26 . This is the same method of attachment of the baseplate to the embodiment shown and described above with reference to FIG.  3 . The shoulder bolts  55  may be counterbored in the baseplate  22  holes. 
     Typically, the plates, covers, sidewalls and the connecting rods, washers and threaded connectors, screws and shoulder bolts may be constructed of a sufficiently hard metal, including such metals as steel, such as stainless steel, brass, bronze, aluminum, etc. All of the features on the plates, covers and sidewalls, including the access ports, manifolds, channels, apertures, cut-outs and threaded holes may be shaped by machining. This eliminates the need for costly, time-consuming and technically difficult procedures, such as EDM, which had been required for earlier extrusion calibrators, in which the extrusion passageway and the vacuum and coolant routes were constructed from a solid metal block, or in which vacuum and coolant routes were constructed in thinner metal plates interleaved between the wear-resistant plates. 
     According to the features of the extrusion calibrator of the present invention, when it is necessary to provide an extrusion passageway of different size and shape to accommodate calibration of a different extruded product exiting from an extrusion die, removal of the upper cover (and optionally the sidewalls or sidewall portions) allows interchange of a cassette of one passageway for a cassette of the newly desired passageway. The vacuum and coolant connections external to the calibrator remain in place on both of the covers during the change over. 
     It will, of course, be apparent to those of skill in this art that various modifications and equivalents can be made in accordance with the teachings of this invention without departing from the scope of the invention. There is no intention to limit the scope of this invention, other than as required in accordance with the following claims.