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An extrusion apparatus including a die and a mask are provided such that no slots feed directly into the longitudinal skin forming gap between the mask and the die. In a method of forming a die adapted to improve skin uniformity of extruded cellular ceramic substrates a slotted block of die material

An extrusion apparatus including a die and a mask are provided such that no slots feed directly into the longitudinal skin forming gap between the mask and the die. In a method of forming a die adapted to improve skin uniformity of extruded cellular ceramic substrates a slotted block of die material is provided including central slots adapted to form a cellular matrix of the substrate and peripheral slots located outwardly of the central slots designed to be covered by a skin former mask and adapted to extrude peripheral batch material. An arcuate skin former is cut corresponding to a target shrinkage so as to intersect the slotted block such that skin flow from tangent slots at 90 degree positions of the die is limited to the peripheral batch material.

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1. A method of forming a die adapted to improve skin uniformity of extruded cellular ceramic substrates, comprising: providing a slotted block of die material including central slots adapted to form a cellular matrix of the substrate and peripheral slots located outwardly of the central slots design

1. A method of forming a die adapted to improve skin uniformity of extruded cellular ceramic substrates, comprising: providing a slotted block of die material including central slots adapted to form a cellular matrix of the substrate and peripheral slots located outwardly of the central slots designed to be covered by a skin former mask and adapted to extrude peripheral batch material;selecting a target shrinkage;cutting an arcuate skin former corresponding to said target shrinkage so as to intersect said slotted block such that skin flow from tangent slots at 90 degree positions of the die is limited to said peripheral batch material; and whereinthe method includes determining values for a slot width (W), a slot spacing (S) and a face gap (F), and obtaining ranges of O and I as follows: Omin=a minimum outer slot to mask distance=½W; Imax=a maximum inner slot to pin face distance=S−F−Omin;Imin=a minimum inner slot to pin face distance=½W; andOmax=a maximum outer slot to mask distance=S−F−Imin,wherein said skin former is cut at values of O and I in said ranges. 2. The method of claim 1 wherein said cutting of said skin former produces a circular or oval ramp intersecting a discharge face at a front of the die, and a peripheral die surface located outwardly of said ramp. 3. The method of claim 2 wherein said skin former ramp forms a partial pin having a sloped pin face at the 90 degree positions of the die. 4. The method of claim 1 comprising: calculating first values for O and I, using a first shrinkage, outer dimension of fired substrate, mask radius and pin face radius; anddetermining whether said first values for O and I satisfy said ranges for O and I. 5. The method of claim 1 wherein the step of cutting the arcuate skin former is configured to provide extrusion of a cellular ceramic substrate with a difference between a skin thickness corresponding to the 90 degree positions of the die and a skin thickness corresponding to 45 degree positions of the die is not more than 3.00 mils. 6. A method of forming a die configured to extrude a honeycomb substrate, the method comprising the steps of: cutting a slotted block including an interconnected matrix of slots defined by a plurality of block pins, wherein the matrix of slots include a first set of parallel rows of slots extending in a first direction and a second set of parallel rows of slots extending in a second direction perpendicular to the first direction;wherein cutting the slotted block comprises cutting an arcuate skin former into outer peripheral block pins of the plurality of block pins to define outer partial die pins circumscribing central full die pins, wherein the central full die pins each include a discharge surface partially defining a discharge face of the die, the arcuate skin former including a ramp surface extending outwardly at an angle from a pin face periphery of the discharge face of the die, wherein the pin face periphery includes a first pair of 90 degree positions that each include a line tangent to the pin face periphery and extending in the first direction, and the pin face periphery includes a second pair of 90 degree positions that each include a line tangent to the pin face periphery and extending in the second direction, and wherein a first slot of the first set of parallel slots positioned outwardly of each of the first pair of 90 degree positions does not intersect the ramp surface, and a first slot of the second set of parallel slots positioned outwardly of each of the second pair of 90 degree positions does not intersect the ramp surface; and whereinthe method includes determining values for a slot width (W), a slot spacing (S) and a face gap (F), and obtaining ranges of O and I as follows: Omin=a minimum outer slot to mask distance=½W; Imax=a maximum inner slot to pin face distance=S−F−Omin;Imin=a minimum inner slot to pin face distance=½W; andOmax=a maximum outer slot to mask distance=S−F−Imin,wherein said skin former is cut at values of O and I in said ranges. 7. The method of claim 6, further including the step of selecting a target shrinkage, wherein the step of cutting the slotted block includes cutting the arcuate skin former to correspond to the target shrinkage. 8. The method of claim 6, wherein the ramp surface comprises a circular or oval ramp surface. 9. The method of claim 6, wherein the step of cutting the slotted block provides a peripheral die surface located outwardly of the ramp surface. 10. The method of claim 6, wherein the ramp surface partially defines a plurality of the outer partial die pins. 11. The method of claim 6 comprising: calculating first values for O and I, using a first shrinkage, outer dimension of fired substrate, mask radius and pin face radius; anddetermining whether said first values for O and I satisfy said ranges for O and I. 12. The method of claim 6, wherein the step of cutting the arcuate skin former is configured to provide extrusion of a cellular ceramic substrate with a difference between a skin thickness corresponding to the 90 degree positions of the die and a skin thickness corresponding to 45 degree positions of the die is not more than 3.00 mils. 13. A method of forming a die configured to extrude a honeycomb substrate, the method comprising the steps of: cutting a slotted block including an interconnected matrix of slots defined by a plurality of block pins, wherein the matrix of slots include a first set of parallel rows of slots extending in a first direction and a second set of parallel rows of slots extending in a second direction perpendicular to the first direction;wherein cutting the slotted block comprises cutting an arcuate skin former into outer peripheral block pins of the plurality of block pins to define outer partial die pins circumscribing central full die pins, wherein the central full die pins each include a discharge surface partially defining a discharge face of the die, the arcuate skin former including a ramp surface extending outwardly at an angle from a pin face periphery of the discharge face of the die, and the arcuate skin former further including an outer peripheral die surface extending outwardly from the ramp surface and circumscribing the ramp surface, and wherein the pin face periphery includes a first pair of 90 degree positions that each include a line tangent to the pin face periphery and extending in the first direction, and the pin face periphery includes a second pair of 90 degree positions that each include a line tangent to the pin face periphery and extending in the second direction, and wherein a first slot of the first set of parallel slots positioned outwardly of each of the first pair of 90 degree positions is offset outwardly from the ramp surface and intersects the outer peripheral die surface, and a first slot of the second set of parallel slots positioned outwardly of each of the second pair of 90 degree positions is offset outwardly from the ramp surface and intersects the outer peripheral die surface; and whereinthe method includes determining values for a slot width (W), a slot spacing (S) and a face gap (F), and obtaining ranges of O and I as follows: Omin=a minimum outer slot to mask distance=½W; Imax=a maximum inner slot to pin face distance=S−F−Omin;Imin=a minimum inner slot to pin face distance=½W; andOmax=a maximum outer slot to mask distance=S−F−Imin,wherein said skin former is cut at values of O and I in said ranges. 14. The method of claim 13, further including the step of selecting a target shrinkage, wherein the step of cutting the slotted block includes cutting the arcuate skin former to correspond to the target shrinkage. 15. The method of claim 13, wherein the ramp surface comprises a circular or oval ramp surface. 16. The method of claim 13, wherein the ramp surface partially defines a plurality of the outer partial die pins. 17. The method of claim 13 comprising: calculating first values for O and I, using a first shrinkage, outer dimension of fired substrate, mask radius and pin face radius; anddetermining whether said first values for O and I satisfy said ranges for O and I. 18. The method of claim 13, wherein the step of cutting the arcuate skin former is configured to provide extrusion of a cellular ceramic substrate with a difference between a skin thickness corresponding to the 90 degree positions of the die and a skin thickness corresponding to 45 degree positions of the die is not more than 3.00 mils.