Non-rotating, levitating, cylindrical air-pillow apparatus and method for supporting and guiding an endless flexible casting belt into the entrance of a continuous metal-casting machine

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a plurality of stationary belt-guiding elements defining the cylindrically shaped path;
• said belt-guiding elements being arranged for association with pressurized air for applying pressurized air in belt-levitating relationship against a cylindrically curved inner surface of such a casting belt moving along the cylindrically shaped path;
• and
• further comprising:
• an elongated, stationary air-throttling barrier extending across the cylindrically shaped path for positioning generally transverse to motion of such a casting belt moving along the cylindrically shaped path.

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a plurality of stationary belt-guiding elements defining the cylindrically shaped path;
• said belt-guiding elements being arranged for association with pressurized air for applying pressurized air in belt-levitating relationship against a cylindrically curved inner surface of such a casting belt moving along the cylindrically shaped path;
• wherein:
• the cylindrically shaped path has a constant radius R1;
• said convex outer surface spans an angle “A” of about 180°;
• and
• the constant radius R1 has a length in the range of about 200 millimeters to about 400 millimeters (about 7.9 inches to about 15.8 inches).

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a plurality of stationary belt-guiding elements defining the cylindrically shaped path;
• said belt-guiding elements being arranged for association with pressurized air for applying pressurized air in belt-levitating relationship against a cylindrically curved inner surface of such a casting belt moving along the cylindrically shaped path;
• wherein:
• the cylindrically shaped path has a constant radius R1;
• the cylindrically shaped path includes a cylindrically shaped flexural transition region of variable radius R+;
• the variable radius R+ of said cylindrically shaped flexural transition region progressively increasing in length relative to said length of constant radius R1 for progressively decreasing curvature of said cylindrically shaped flexural transition region for reducing flexure of such a casting belt moving along the cylindrically shaped transition region toward an entrance into a mold space of a continuous casting machine.

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a plurality of stationary belt-guiding elements defining the cylindrically shaped path;
• said belt-guiding elements being arranged for association with pressurized air for applying pressurized air in belt-levitating relationship against a cylindrically curved inner surface of such a casting belt moving along the cylindrically shaped path;
• further comprising:
• a fixed, stationary support for said belt-guiding elements having said belt-guiding elements thereon;
• said support having at least one passage for feeding pressurized air into contact with said belt-guiding elements;
• said support having mounting members for mounting the air-pillow apparatus in fixed, stationary position in a continuous casting machine near the entrance into the mold space;
• said fixed, stationary support having said belt-guiding elements thereon being a member having a convex outer surface;
• said belt-guiding elements being on said convex outer surface;
• said convex outer surface conforming generally with and being spaced inwardly from the cylindrically shaped path defined by said outwardly facing, stationary surfaces of said belt-guiding elements;
• said member being a cylindrical shell;
• end walls and a back member secured to said cylindrical shell enclosing a plenum chamber adjacent to an inner concave surface of said cylindrical shell;
• said belt-guiding elements forming a stationary grid on said convex outer surface;
• said grid having a generally rectangular pattern with belt-guiding elements of the rectangular pattern forming walls of a multiplicity of rectangular depressions on said convex outer surface;
• said convex outer surface defining floors of said rectangular depressions;
• and
• said cylindrical shell having a multiplicity of passages extending therethrough from said concave inner surface to said convex outer surface for providing communication from the plenum chamber through floors of the rectangular depressions for feeding pressurized air from the plenum chamber into said shallow depressions.

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a plurality of stationary belt-guiding elements defining the cylindrically shaped path;
• said belt-guiding elements being arranged for association with pressurized air for applying pressurized air in belt-levitating relationship against a cylindrically curved inner surface of such a casting belt moving along the cylindrically shaped path;
• further comprising:
• a fixed, stationary support for said belt-guiding elements having said belt-guiding elements thereon;
• said support having at least one passage for feeding pressurized air into contact with said belt-guiding elements;
• said support having mounting members for mounting the air-pillow apparatus in fixed, stationary position in a continuous casting machine near the entrance into the mold space;
• said fixed, stationary support having said belt-guiding elements thereon being a member having a convex outer surface;
• said belt-guiding elements being on said convex outer surface;
• said convex outer surface conforming generally with and being spaced inwardly from the cylindrically shaped path defined by said outwardly facing, stationary surfaces of said belt-guiding elements;
• said member being a cylindrical shell;
• end walls and a back wall secured to said cylindrical shell enclosing a plenum chamber adjacent to an inner concave surface of said cylindrical shell;
• and
• said belt-guiding elements being arranged in a predetermined pattern on said convex outer surface of said cylindrical shell.

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a plurality of stationary belt-guiding elements defining the cylindrically shaped path;
• said belt-guiding elements being arranged for association with pressurized air for applying pressurized air in belt-levitating relationship against a cylindrically curved inner surface of such a casting belt moving along the cylindrically shaped path;
• further comprising:
• a fixed, stationary support for said belt-guiding elements having said belt-guiding elements thereon;
• said support having at least one passage for feeding pressurized air into contact with said belt-guiding elements;
• said support having mounting members for mounting the air-pillow apparatus in fixed, stationary position in a continuous casting machine near the entrance into the mold space;
• said fixed, stationary support having said belt-guiding elements thereon being a member having a convex outer surface;
• said belt-guiding elements being on said convex outer surface;
• said convex outer surface conforming generally with and being spaced inwardly from the cylindrically shaped path defined by said outwardly facing, stationary surfaces of said belt-guiding elements;
• said member being a cylindrical shell;
• end walls and a back wall secured to said cylindrical shell enclosing a plenum chamber adjacent to an inner concave surface of said cylindrical shell;
• said belt-guiding elements being arranged in a predetermined pattern on said convex outer surface of said cylindrical shell;
• said belt-guiding elements are elongated;
• said elongated belt-guiding elements are in spaced parallel relationship;
• said spaced parallel elongated belt-guiding elements extend along said cylindrically shaped path in a circumferential direction generally parallel with movement of such a casting belt moving along the cylindrically curved path;
• and
• spaces between said spaced parallel elongated belt-guiding strips define channels having a width not exceeding about 150 times a thickness of such a casting belt moving along the cylindrically shaped path;
• such thickness is in a range from about 0.3 mm (about 0.012 of an inch) to about 2 mm (about 0.079 of an inch);
• and
• said cylindrical shell has passages extending therethrough providing communication between the plenum chamber and said channels.

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a convex cylindrically shaped path wherein the convex cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a multiplicity of spaced, stationary elements having spaces therebetween;
• said spaced, stationary elements having stationary belt-guiding surfaces;
• said belt-guiding surfaces being laterally spaced across said convex, cylindrically shaped path;
• said belt-guiding surfaces facing outwardly along said convex, cylindrically shaped path for guiding such a casting belt moving along said path with a cylindrically curved moving inner surface of the moving belt facing said belt-guiding surfaces;
• and
• said air-pillow apparatus having at least one passage for feeding pressurized air into said spaces between said elements for providing pressurized air in levitating contact with said cylindrically curved moving inner surface of the moving belt.

Air-pillow apparatus for guiding a moving, flexible, tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a multiplicity of spaced, stationary elements having spaces therebetween;
• said spaced, stationary elements having stationary belt-guiding surfaces;
• said belt-guiding surfaces being arranged along a convex, cylindrically shaped path;
• said belt-guiding surfaces facing outwardly along said convex, cylindrically shaped path for guiding such a casting belt moving along said path with a cylindrically curved moving inner surface of the moving belt facing said belt-guiding surfaces;
• said air-pillow apparatus having at least one passage for feeding pressurized air into said spaces between said elements for providing pressurized air in levitating contact with said cylindrically curved moving inner surface of the moving belt;
• said tensed belt exerts a first force component of predetermined magnitude directed toward said air-pillow apparatus;
• said pressurized air feeding into said spaces between said elements is controllable for providing controlled pressurized air in levitating contact with said cylindrically curved moving inner surface of the moving belt for exerting on said cylindrically curved moving inner surface a second force component having a magnitude which is at least about 90% of said predetermined magnitude of said first force component;
• said second force component is directed away from said air-pillow apparatus and is in opposition to said first force component;
• said pressurized air feeding into said spaces between said elements is controllable for providing controlled pressurized air in levitating contact with said cylindrically curved moving inner surface of the moving belt for exerting on said cylindrically curved moving inner surface a second force component having a magnitude which is in a range between about 99% and 100% of said predetermined magnitude of said first force component;
• said second force component is directed away from said air-pillow apparatus and is in opposition to said first force component;
• said mold space extending substantially flat from the entrance along a generally straight downstream direction;
• said mold space having an upstream direction opposite to said downstream direction;
• said convex, cylindrically shaped path spanning an included angle of about 180°;
• said convex, cylindrically shaped path having a radius R1 having a length in the range of about 200 millimeters to about 400 millimeters (about 7.9 inches to about 15.8 inches);
• and
• said controlled pressurized air in levitating contact with said cylindrically curved moving inner surface of the moving belt exerting a force component in the upstream direction which is about 250 newtons per millimeter of belt width.

Air-pillow apparatus for guiding a moving, flexible tensed, heat-conductive casting belt along a cylindrically shaped path wherein the cylindrically shaped path is suitable for guiding such a casting belt moving toward an entrance into a mold space of a continuous casting machine, said air-pillow apparatus comprising:

• a multiplicity of spaced, stationary elements having spaces therebetween;
• said spaced, stationary elements having stationary belt-guiding surfaces;
• said belt-guiding surfaces being arranged along a convex, cylindrically shaped path;
• said belt-guiding surfaces facing outwardly along said convex, cylindrically shaped path for guiding such a casting belt moving along said path with a cylindrically curved moving inner surface of the moving belt facing said belt-guiding surfaces;
• said air-pillow apparatus having at least one passage for feeding pressurized air into said spaces between said elements for providing pressurized air in levitating contact with said cylindrically curved moving inner surface of the moving belt;
• further comprising:
• a support having an exterior of generally convex, cylindrical shape;
• said spaced, stationary elements being on said exterior of said support;
• said spaced stationary elements being a grid on said exterior of said support;
• said grid extending along said convex, cylindrically shaped path;
• and
• said belt-guiding surfaces being outwardly facing surfaces of said grid.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, and wherein tensile stress in the tensed moving casting belt accords with operating practice known in the art for such a continuous casting machine, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a tensed moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• and
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of the tensed moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by the tensed revolving casting belt.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of a moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by a tensed revolving casting belt;
• further comprising:
• an air-pillow shell having a convex, generally cylindrical exterior and having an interior;
• said multiplicity of stationary elements being on said exterior;
• the air-pillow apparatus including walls secured to the air-pillow shell defining a plenum chamber communicating with said interior of the air-pillow shell;
• the air-pillow apparatus including members for mounting the air-pillow apparatus in a continuous casting machine near the entrance into the mold space;
• said air-pillow shell having at least one passage therethrough from the plenum chamber to said exterior;
• said source of pressurized air is said plenum chamber in association with said at least one passage through said air-pillow shell;
• in which:
• said pressurized belt-levitating air pressing outwardly against a cylindrically curved moving inner surface of a moving casting belt exerts a force component in an upstream direction on a moving casting belt which is about 250 newtons per millimeter of belt width;
• and
• said force component in an upstream direction results in a tensile stress in a moving casting belt of about 10,000 newtons per square centimeter of cross section of the moving casting belt, which is a tensile stress approximating a customary tensile stress previously used in such a continuous casting machine.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of a moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by a tensed revolving casting belt;
• further comprising:
• an air-pillow shell having a convex, generally cylindrical exterior and having an interior;
• said multiplicity of stationary elements being on said exterior;
• the air-pillow apparatus including walls secured to the air-pillow shell defining a plenum chamber communicating with said interior of the air-pillow shell;
• the air-pillow apparatus including members for mounting the air-pillow apparatus in a continuous casting machine near the entrance into the mold space;
• said air-pillow shell having at least one passage therethrough from the plenum chamber to said exterior;
• said source of pressurized air is said plenum chamber in association with said at least one passage through said air-pillow shell;
• in which:
• said stationary elements on said exterior air-pillow shell define isolated regions among said stationary elements;
• said isolated regions among the stationary elements when said air-pillow shell is enwrapped by a moving casting belt become isolated belt-levitating chambers positioned below the working surfaces of said stationary elements;
• said isolated belt-levitating chambers have a width, measured in a direction transverse to a moving casting belt, which is less than about 150 times said predetermined thickness of the moving casting belt;
• said air-pillow shell has a plurality of passages therethrough;
• said passages communicate individually with said isolated belt-levitating chambers;
• and
• said passages fixedly throttle pressurized air flowing therethrough from the plenum chamber to said stationary elements for providing said pressurized belt-levitating air.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of a moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by a tensed revolving casting belt;
• further comprising:
• a stationary support having a convex exterior;
• said stationary elements being on said convex exterior;
• said working surfaces of said stationary elements defining a cylindrically shaped path;
• said cylindrically shaped path having a constant radius R1 along a major circumferential portion of said cylindrically shaped path commencing near said return portion of said loop;
• and
• said air-pillow apparatus being configured for defining a minor circumferential portion of said cylindrically shaped path having a varying radius R+ progressively increasing along said minor circumferential portion of said cylindrically shaped path in a direction toward said entrance for progressively reducing curvature of said minor circumferential portion of said cylindrically shaped path in a direction therealong toward said entrance;
• thereby progressively reducing flexural stress in a casting belt moving along said minor portion of said cylindrically shaped path toward said entrance.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of a moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by a tensed revolving casting belt;
• further comprising:
• a support having a convex exterior of generally cylindrical shape;
• said multiplicity of stationary elements being on said convex exterior;
• said stationary elements protruding above said convex exterior defining isolated depressions among said stationary elements;
• said working surfaces of said stationary elements being at a height “h” above said convex exterior;
• said height “h” being in a range between about 25 microns and about 2.5 millimeters;
• said source of pressurized air comprising passages communicating individually with said isolated depressions;
• said passages individually fixedly-throttling pressurized air feeding individually into said isolated depressions for providing pressurized belt-levitating air in said isolated depressions;
• and
• a cylindrically curved moving inner surface of such a casting belt moving along said cylindrically shaped path being in adjacent relationship with respect to said working surfaces and in cooperation with said working surfaces throttling leakage of pressurized belt-levitating air from said isolated depressions;
• whereby screeching noises are substantially avoided.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of a moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by a tensed revolving casting belt;
• further comprising:
• an air-pillow shell having a convex, generally cylindrical exterior and having an interior;
• said multiplicity of stationary elements being on said exterior;
• the air-pillow apparatus including walls secured to the air-pillow shell defining a plenum chamber communicating with said interior of the air-pillow shell;
• the air-pillow apparatus including members for mounting the air-pillow apparatus in a continuous casting machine near the entrance into the mold space;
• said air-pillow shell having at least one passage therethrough from the plenum chamber to said exterior;
• said source of pressurized air is said plenum chamber in association with said at least one passage through said air-pillow shell;
• in which:
• said stationary elements on said convex exterior of said air-pillow shell comprise an array of elevated air-throttling, belt-levitating plateaus having thereamong a complementary array of depressed regions which are air-exhaust channels;
• said working surfaces are outer surfaces of said belt-levitating plateaus;
• said air-pillow shell has a plurality of passages therethrough individually terminating at centers of said working surfaces of said belt-levitating plateaus;
• and
• said passages fixedly throttle pressurized air flowing therethrough from the plenum chamber to the centers of said working surfaces of said belt-levitating plateaus.

Air-pillow apparatus for use in a continuous casting machine having at least one endless, flexible, tensed, heat-conductive casting belt revolvable along a closed loop wherein a tensed moving casting belt travels in a downstream direction along a mold space from an entrance into the mold space to an exit therefrom and returns from the exit to the entrance along a return portion of the closed loop, said return portion of the closed loop being positioned away from the mold space, said air-pillow apparatus comprising:

• a multiplicity of stationary elements;
• said stationary elements having working surfaces defining a cylindrically shaped path extending from said return portion of the closed loop toward the entrance into the mold space for guiding a moving casting belt along said cylindrically shaped path with a cylindrically curved moving inner surface of a moving casting belt being adjacent to said working surfaces;
• a source of pressurized air for feeding pressurized belt-levitating air to said stationary elements for pressing outwardly away from the air-pillow apparatus against a cylindrically curved moving inner surface of a moving casting belt for carrying at least about 90% of an overall downstream-directed component of force exertable upon the air-pillow apparatus by a tensed revolving casting belt;
• further comprising:
• an air-pillow shell having a convex, generally cylindrical exterior and having an interior;
• said multiplicity of stationary elements being on said exterior;
• the air-pillow apparatus including walls secured to the air-pillow shell defining a plenum chamber communicating with said interior of the air-pillow shell;
• the air-pillow apparatus including members for mounting the air-pillow apparatus in a continuous casting machine near the entrance into the mold space;
• said air-pillow shell having at least one passage therethrough from the plenum chamber to said exterior;
• said source of pressurized air is said plenum chamber in association with said at least one passage through said air-pillow shell;
• in which:
• said stationary elements on said convex exterior of said air-pillow shell comprise an array of protruding air-throttling barriers having thereamong a complementary array of depressions;
• said air-pillow shell has a plurality of passages therethrough individually terminating at centers of said depressions;
• and
• said passages fixedly throttle pressurized air flowing therethrough from the plenum chamber to the centers of said depressions.