Method and apparatus for extrusion of thermoplastic handrail

Abstract

A method and apparatus for extrusion of an article is provided. A die assembly can apply flows of thermoplastic material to an array of reinforcing cables to form a composite extrusion. A slider fabric can be bonded to one side of the composite extrusion. After exiting the die assembly, the slider fabric can act to support the extrudate as it passes along an elongate mandrel, which can cause the base of the slider fabric to change shape from a flat profile to the final internal profile of the article. The extruded article can then be cooled to solidify the material. The die can include cooling for the slider fabric and means for promoting penetration of the thermoplastic into reinforcing cables.

1 . A method of extruding an article of constant cross-section and including a first thermoplastic material, a stretch inhibitor and a web of fabric on one side of the article, the method comprising the steps of:
 a) supplying the stretch inhibitor to a die assembly;   b) supplying the first thermoplastic material to the die assembly in a molten state, the extrusion temperature of the first thermoplastic material being below a melting point of the stretch inhibitor;   c) bringing the first thermoplastic material together with the stretch inhibitor, thereby to embed the stretch inhibitor within the first thermoplastic material;   d) supplying an elongate flexible web fabric of constant width, the extrusion temperature of the first thermoplastic material being below a melting point of the fabric;   e) bringing the fabric up against the first thermoplastic material, the first thermoplastic material, the stretch inhibitor and the fabric thereby forming a composite extrudate; and   f) permitting the extrudate to cool and solidify.   
     
     
         2 . The method as claimed in  claim 1 , wherein step (f) further comprises extruding the extrudate from the die assembly at an intermediate cross-section and at a temperature above the crossover temperature of the first thermoplastic material such that the first thermoplastic material is molten but sufficiently viscous to be stable. 
     
     
         3 . The method as claimed in  claim 2 , wherein the following additional step is carried out, between steps (f) and (g): passing the intermediate extrudate along a path, in which the fabric is supported to support the molten first thermoplastic material, and along which the extrudate is progressively shaped to a final, desired cross-section. 
     
     
         4 . The method as claimed in  claim 3 , wherein the additional step includes supporting the fabric on a support surface of an elongate primary mandrel which determines the profile of the extrudate, wherein the support surface at one end has a profile corresponding to one side of the intermediate cross-section and the profile of the mandrel changes progressively along the length thereof with the other end of the support surface having a profile corresponding to one side of the final cross-section. 
     
     
         5 . The method as claimed in  claim 4 , including applying a vacuum to cause the extrudate and the fabric to be pressed against the support surface of the mandrel. 
     
     
         6 . The method as claimed in  claim 5 , wherein, after formation of the final cross-section, the method includes cooling the extrudate from the exterior thereof to remove sufficient heat to solidify a substantial external layer around the exterior of the extrudate. 
     
     
         7 . The method as claimed in  claim 6 , the method comprising forming a handrail, wherein the fabric comprises an elongate slider fabric, and wherein the stretch inhibitor comprise a plurality of reinforcing cables, wherein the first thermoplastic material comprises a thermoplastic elastomer, and wherein in the additional step the extrudate is formed to a generally C-shape cross-section. 
     
     
         8 . The method as claimed in  claim 7 , wherein the intermediate cross-section has a planar base and side edges extending perpendicularly thereto, and wherein within the die assembly, the method includes folding the fabric to extend along the elongate base and up the side edges of the intermediate cross-section. 
     
     
         9 . The method as claimed in  claim 8 , wherein the mandrel is shaped so as to provide the final C-shape cross-section with an internal T-shape within the handrail comprising a vertical stem and a horizontal portion, with rounded corners at the end of the horizontal section and angular corners between the stem and the horizontal portion. 
     
     
         10 . The method as claimed in  claim 9 , including passing the handrail through a cooling unit, in which the exterior of the handrail is cooled by a liquid coolant, to effect cooling and solidification of the external layer, wherein the liquid coolant comprises water, and wherein during cooling the method includes supporting the handrail on a secondary mandrel that is an extension of the primary mandrel, whereby water cools the exterior of the handrail only. 
     
     
         11 . The method as claimed in  claim 10 , wherein, in step (c), the first thermoplastic material is supplied as two separate flows on generally opposing sides of the stretch inhibitor. 
     
     
         12 . The method as claimed in  claim 11 , wherein the following additional step is carried out, after step (c): supplying a second thermoplastic material to the die assembly in a molten state as a separate flow, and bringing the flow of second thermoplastic material up against the first thermoplastic material on a opposing side relative to the fabric, the first and second thermoplastic materials defining separate layers in the extrudate. 
     
     
         13 . The method as claimed in  claim 12 , wherein the first and second thermoplastic materials have different hardnesses. 
     
     
         14 . A method of extruding an article of constant cross-section and including a thermoplastic material and a web of fabric on one side of the article, the method comprising the steps of:
 g) supplying the thermoplastic material to a die assembly in a molten state;   h) supplying an elongate flexible web of fabric of constant width;   i) extruding the thermoplastic material out of the die assembly to form an extrudate of intermediate cross-section, while maintaining the thermoplastic material at a temperature above the crossover temperature of the materials such that the material is molten but sufficiently viscous to be stable; and   j) bringing the fabric up against the thermoplastic material to complete the article of constant cross-section.   
     
     
         15 . The method as claimed in  claims 14 , further comprising passing the intermediate extrudate along a path, in which the fabric is supported to support the thermoplastic material, and along which the extrudate is progressively shaped from the intermediate cross-section to a final, desired cross-section, before cooling and solidification of the article. 
     
     
         16 . The method as claimed in  claim 15 , including supporting the fabric on a support surface of an elongate primary mandrel which determines the profile of the extrudate, wherein the support surface at one end has a profile corresponding to one side of the intermediate cross-section and progressively changes along the length of the mandrel to a profile corresponding to one side of the final cross-section. 
     
     
         17 . The method as claimed in  claim 16 , wherein a vacuum is applied to cause the extrudate to be pressed against the support surface of the mandrel. 
     
     
         18 . The method as claimed in  claim 17 , including passing the article through a cooling unit, in which the exterior of the article is cooled by a liquid coolant, to effect cooling and solidification of the external layer. 
     
     
         19 . A method of forming a handrail by continuous extrusion, the method comprising the steps of:
 k) combining together a thermoplastic elastomer in a molten state, a stretch inhibitor and a reinforcing slider fabric, to form a handrail of a desired cross-section, the thermoplastic material being above a crossover temperature of the elastomer, so as to be in an initially molten state but sufficiently viscous to be stable; and   l) cooling the handrail along the length thereof from the exterior to solidify a substantial external layer around the exterior of the handrail and subsequently cooling and solidifying the interior of the handrail to prestress the handrail thereby to provide improved lip strength.   
     
     
         20 . The method as claimed in  claim 19 , wherein step (b) comprises passing the handrail continuously through an elongate cooling unit which includes a mandrel along which the handrail passes, and applying cooling fluid to the handrail from the outside so as to cool the exterior thereof, and wherein the mandrel defines and internal T-shaped slot for the handrail. 
     
     
         21 . An apparatus for extruding an article of uniform cross-section, the apparatus comprising:
 a die assembly having a first inlet for a thermoplastic material, an entrance slot for introducing an elongate fabric for bonding to one side of the thermoplastic material, an outlet die for forming an extrudate comprising at least the thermoplastic material with an intermediate cross-section, and a primary mandrel extending from the outlet die and having a support surface for supporting the extrudate while still in a molten state, with the fabric abutting the mandrel for relative sliding movement, the support surface at one end adjacent the outlet die corresponding to the profile of one side of the intermediate extrudate and progressively changing along the length of the primary mandrel to the final profile, at the other end thereof, the final profile corresponding to a desired final cross-section for the extrudate.   
     
     
         22 . An apparatus as claimed in  claim 21 , wherein the mandrel includes a plurality of openings and a bore along the length thereof in communication with the openings, for application of a vacuum to cause the extrudate to be pressed against the support surface of the mandrel. 
     
     
         23 . An apparatus for extruding an article of uniform cross-section, the apparatus comprising:
 a die assembly having an entrance for introducing a stretch inhibitor, a first inlet for a thermoplastic material, an entrance slot for introducing an elongate fabric for bonding to one side of the thermoplastic material, a combining zone including a duct for combined extrusion flow with the entrance opening into the combining zone and first and second primary manifolds connected between the first inlet of the die assembly and the duct, for supplying the thermoplastic material into the duct as a first flow from the first primary manifold on one side of the stretch inhibitor and as a second flow from the second primary manifold on the other side of the stretch inhibitor, for embedding the stretch inhibitor within the combined extrusion flow, the fabric being brought up against the combined extrusion flow after embedding the stretch inhibitor therein, and an outlet die forming an extrudate comprising at least the thermoplastic material and the stretch inhibitor.   
     
     
         24 . The apparatus as claimed in  claim 23 , which includes a second inlet for providing a second flow of thermoplastic material, and a respective second manifold connecting the second inlet to the duct downstream of the combining zone, on a side remote from the entrance slot, for supplying the second flow to the other side of the extrudate. 
     
     
         25 . The apparatus as claimed in  claim 24 , which includes an elongate primary mandrel which determines the profile of the extrudate, wherein the support surface at one end has a profile corresponding to an intermediate cross-section of the extrudate upon exit from the outlet die, and the profile of the mandrel changes progressively along the length thereof with the other end of the support surface having a profile corresponding to one side of a final cross-section of the extrudate. 
     
     
         26 . The apparatus as claimed in  claim 25 , wherein the mandrel includes a plurality of openings in the support surface of the mandrel and a bore in communication with the openings for connection to a vacuum source, the vacuum source for applying a vacuum to the extrudate and to cause the fabric to be pressed against the support surface of the mandrel. 
     
     
         27 . The apparatus as claimed in  claim 26 , which includes a cooling unit for rapidly cooling the exterior of the handrail after the handrail leaves the primary mandrel. 
     
     
         28 . The apparatus as claimed in  claim 27 , wherein the cooling unit comprises an elongate tank, a secondary mandrel for supporting the handrail co-extensive for the primary mandrel and a fluid source for applying a cooling fluid to the exterior of the handrail. 
     
     
         29 . The apparatus as claimed in  claim 28 , wherein the fluid source includes a plurality of nozzles positioned above the secondary mandrel. 
     
     
         30 . The apparatus as claimed in  claim 28 , wherein the fluid source includes at least one nozzle positioned near an entrance of the cooling unit, the nozzle for cooling and skinning the handrail as it enters the cooling unit, and further comprising at least one roller upstream from the nozzle and at least one roller downstream from the nozzle for shaping the external profile of the handrail. 
     
     
         31 . A method of extruding an article of constant cross-section including a thermoplastic material and a stretch inhibitor, the method comprising the steps of:
 m) supplying a stretch inhibitor to a die assembly;   n) supplying the thermoplastic material to the die assembly in a molten state at a temperature below the melting temperature of the stretch inhibitor; and   o) passing the stretch inhibitor and the thermoplastic material through an element of restricted flow cross-section, to generate back pressure tending to cause penetration of the thermoplastic material into the stretch inhibitor.   
     
     
         32 . The method as claimed in  claim 31 , wherein the element of restricted flow cross-section comprises a comb section having a plurality of slots. 
     
     
         33 . The method as claimed in  claim 32 , wherein the comb comprises a plurality of vertical slots and at least one horizontal slot, and wherein the stretch inhibitor comprises a plurality of cables, the method comprising passing the plurality of cables through one horizontal slot of the comb assembly. 
     
     
         34 . The method as claimed in  claim 33 , further comprising supplying an elongate flexible web of fabric to the die assembly beneath the flow of the thermoplastic material and the stretch inhibitor, and maintaining the temperature of the fabric below its melting point. 
     
     
         35 . The method as claimed in  claim 34 , including providing the die assembly with an extrudate support block for supporting the extrudate with the fabric, and cooling the extrudate support block. 
     
     
         36 . The method as claimed in  claim 35 , further comprising providing thermal separation between the extrudate support block and other elements of the die and providing heat to the die to heat the extrudate above the extrudate support block. 
     
     
         37 . A die assembly for extruding an article including a thermoplastic elastomer and a stretch inhibitor, the die assembly comprising:
 p) a first inlet for a thermoplastic elastomer;   q) an entrance for the stretch inhibitor;   r) a combining zone wherein the stretch inhibitor is embedded in the thermoplastic elastomer; and   s) an element of restricted flow cross-section, through which the thermoplastic elastomer and the stretch inhibitor pass, whereby the element of restricted flow cross-section generates back pressure to promote penetration of the thermoplastic elastomer into the stretch inhibitor.   
     
     
         38 . The die assembly as claimed in  claim 37 , including a second combining zone and an inlet for a second thermoplastic polymer, wherein in the second combining zone, the second thermoplastic polymer is combined with the flow of the first thermoplastic polymer and the stretch inhibitor, on one side thereof. 
     
     
         39 . The die assembly as claimed in  claim 38 , including an inlet slot for an elongate web of fabric, for bonding to one side of the thermoplastic polymer. 
     
     
         40 . The die assembly as claimed in  claim 39 , including an extrudate support block, the die assembly being configured so that the fabric passes over the extrudate support block and supports the extrudate. 
     
     
         41 . The die assembly as claimed in  claim 40 , including at least one of:
 t) cooling for the extrudate support block; and   u) heating for elements of the die assembly remote from the extrudate support block.   
     
     
         42 . The die assembly as claimed in  claim 41 , wherein the extrudate support block includes at least one inlet and at least one outlet for cooling fluid and limiting heat transfer from other elements of the die assembly to the coolant support block. 
     
     
         43 . A method of extruding an article of constant cross-section including thermoplastic material and a stretch inhibitor, the method comprising the steps of:
 v) supplying stretch inhibitor to a die assembly;   w) supplying the thermoplastic material to the die assembly in a molten state at a temperature below the melting temperature of the stretch inhibitor, so that the stretch inhibitor is embedded in the thermoplastic material;   x) supplying an elongate web of fabric to the die assembly and causing the fabric to bond to one side of the thermoplastic material; and   y) at least one of:
 cooling the die assembly in contact with the fabric; and 
 providing at least some thermal isolation of an element of the die assembly in contact with the fabric, to reduce heat transfer to the fabric. 
   
     
     
         44 . The method as claimed in  claim 43 , wherein the die assembly includes an outlet for an extrudate formed from the thermoplastic material and including the stretch inhibitor, and wherein the fabric is brought up against the extrudate adjacent the outlet, to support the extrudate while the extrudate cools and solidifies. 
     
     
         45 . A die assembly for extruding an article including thermoplastic material and a stretch inhibitor, the die assembly comprising:
 z) a first inlet for a thermoplastic material;   aa) an entrance for the stretch inhibitor;   bb) a combining zone wherein the stretch inhibitor is embedded in the thermoplastic elastomer;   cc) an inlet slot for an elongate web of fabric; and   dd) an element of the die assembly that contacts the fabric during passage through the die assembly and that includes at least one of:
 cooling for the element; and 
 thermal separation form other elements of the die assembly to reduce heat transfer to the fabric. 
   
     
     
         46 . The die assembly as claimed in  claim 45 , wherein the die assembly includes an outlet for an extrudate formed from the thermoplastic material and including the stretch inhibitor, and wherein the inlet slot is located adjacent the outlet such that the fabric is brought up against the extrudate to support the extrudate while the extrudate cools and solidifies. 
     
     
         47 . A die assembly for extruding an article including thermoplastic material and a cable array for inhibiting stretch, the die assembly comprising:
 ee) a cable mandrel for supplying cables;   ff) at least one first runner plate secured to the cable mandrel, the at least one first runner plate connected to a first inlet for receiving a supply of a first thermoplastic material, the at least one first runner plate including channels for directing flow of the first thermoplastic material to embed the cables supplied by the cable mandrel; and   gg) at least one second runner plate secured to the at least one first runner plate, the at least one second runner plate connected to a second inlet for receiving a supply of a second thermoplastic material, the at least one second runner plate including channels for directing flow of the second thermoplastic material onto the first thermoplastic material.   
     
     
         48 . The die assembly of claimed in  claim 47 , further comprising a comb plate secured between the at least one first runner plate and the at least one second runner plate, the comb plate including slots of reduced flow cross-section to create a back pressure in flow of the first thermoplastic material. 
     
     
         49 . The die assembly of claimed in  claim 48 , wherein each of the cable mandrel, the at least one first runner plate, the comb plate and the at least one second runner plate are configured to be disassembled from one another to facilitate cleaning. 
     
     
         50 . (canceled) 
     
     
         51 . (canceled)