Method and apparatus for plating extrusion dies
Method and apparatus are set forth for providing a substantially uniform coating on inner wall portions of a die having slots or openings formed in the face of the die. The die is supported by a fixture for up and down movement while it is immersed in a bath of a desired plating solution. A tube or cylinder positioned on an upper surface portion of the die repeatedly collects a column of plating material in a cylinder from the bath on downward movements of the die, so as to provide fresh or replenishment plating solution to the die. The column of plating solution in the cylinder functions as a hydrostatic head and forces the confined solution into the interior of the die on upward movements, thus promoting coating uniformity along inner walls of the die. The die may be rotated 180 degrees so that each face of the die may be subjected to the hydrostatic force flow of the plating solution, also resulting in a more uniform coating.
Extrusion dies have been found to be useful in forming cellular or honeycomb ceramic substrates for use in catalytic converters utilized in the exhaust system of internal combustion engines. In order for such converters to function efficiently, it is necessary that the cells provide a substantially large surface area for catalytic material to react with the exhaust gases, and that the cell walls have a substantially thin cross-section dimension so as to provide a substantially large open frontal area and thereby reduce back pressure within the exhaust system.
In order to provide increased surface area within the honeycomb structure so as to enhance catalytic activity, the number of cells has been increased and the wall thickness between the cells has been reduced from about 8 mils to 4 mils or less. Accordingly it became necessary to reduce the slot size of the extrusion die from about 0.008″ to 0.0035″ to form such thin walled cellular structures. To protect the extrusion die from the abrasiveness of the extruding ceramic material, it is necessary to provide a hard protective coating on the walls of the die. The coating must be as uniform as possible for the die to function correctly. The reduced slot size of the dies for thin walled structures, made it difficult to provide a uniform coating on the die walls using the known electroless nickel plating process techniques.
In order for the electroless nickel plating process to produce a uniform coating throughout a die, it is necessary that all surfaces of the die receive a constant replenishment of the plating solution with adequate concentration of the solution constituents. As the plating deposit builds up on the die walls, some of the constituents are consumed and therefore the constant replenishment of the solution to all surfaces of the die is needed to ensure that a uniform deposit thickness is obtained. However, with reduced slot sizes the restrictive nature of the small slots in the dies prevented adequate replenishment of plating solution with known devices, resulting in significant non-uniformity of the coating.
Others have experienced non-uniform plating problems, but for different reasons. In U.S. Pat. No. 4,938,840, coating variations were a problem due to variations in accessibility of the plating solution, whereas in U.S. Pat. No. 6,291,025, the problems in plating thickness were due to the interactions of the plating solution components. U.S. Pat. No. 4,842,886 has a problem with controlling the thickness of the plated layer due to unpredictable surface characteristics, and U.S. Pat. No. 4,406,250 is concerned with the deposition rate variation due to the reaction by-products formed in the plating solution.
The present invention has overcome the problem of plating the walls of extrusion dies for forming thin-walled honeycomb structures with a substantially uniform coating, particularly where the slot size may have a width of less than 8 mils, by implementing an improved fixture and plating solution flow techniques.SUMMARY OF THE INVENTION
In its simplest form, the present invention is directed to an improved fixture for supporting a die to be plated in a plating solution, and a novel procedure for enhancing the flow of the plating solution through the die to provide a substantially uniform coating on the walls of the die. The fixture is designed for vertical movement within a plating bath and includes a tube or cylinder above the die for replenishing plating solution and for maintaining a column of such plating solution over the die during the plating process, so as to produce uniform deposit thickness, such as from an electroless nickel plating solution. The cylinder complements a peripheral portion of the die and thus the solution within the cylinder, when under a hydrostatic head, is directed solely downwardly through the die and not permitted to flow outwardly around the die. A further feature of the fixture is that the tube may be removed and the die flipped or rotated 180 degrees while within the bath, so that either the pin side or the feed hole side of the die may be facing upward, again to provide better uniformity of the deposited coating.
It thus has been an object of the present invention to provide an improved fixture for facilitating the production of a uniform coating on wall portions of the passageways in dies for forming thin walled honeycomb structures.
A further object of the invention had been to provide an improved method for flowing plating solutions through a die so as to facilitate a uniform coating of the plating material on inner wall portions of the die.BRIEF DESCRIPTION OF THE DRAWINGS
To better appreciate the present invention it is helpful to look at what preceded it. Referring now to
Referring now to
A confinement tube or cylinder 50 is removably mounted on the clamping rings 36, 38 by means of pins 52 on the tube 50 which engage t-slots 54 formed in an inner surface of the rings 36 and 38, as shown in
As shown in
By thus enabling adequate solution replenishment throughout the plating process, the uniformity of thickness of the deposit of plating solution along internal passageways of the die between the slot entrance and the exit end of the slots is greatly improved over that obtained with the prior art fixture as shown by die 14 in
The confinement tube 50 is removable from the die clamping mechanism 34 by means of the pins 52 on the tube which engage t-shaped slots 54 formed in clamping rings 36, 38, as can be seen in
When it is desired to rotate the die 40 from one fixed position to another, the confinement tube 50 is removed from the clamping mechanism 34 by rotating the tube pins 52 to clear the slots 54 in clamping rings 36,38, and the tube is lifted out of the fixture 32. The locking pin 48 is then removed from an opening 46 in pivoting lever 44, and the die held by clamping mechanism 34 is rotated 180 degrees, while the die remains in the plating bath 56, by means of lever 44. The locking pin 48 is then reinserted in an opposite opening 46 in pivot lever 44. The solution confinement tube 50 is then reinstalled on the fixture 30 by positioning the tube pins 52 into their respective t-slots 54 and rotating the tube to lock it within the slots.
Periodically rotating the die 40 in the manner described, further improves the plating thickness uniformity since the direction of flow of the plating solution through the die is alternated. Further, by rotating the die, provides an opportunity for any trapped gas that has built up from the plating process to escape from underneath the die, which aids in solution replenishment throughout the die's internal passageways.
From the foregoing, it can be seen that the improved fixture of the present invention and the procedure for operating the fixture provides for improved uniformity of plating thickness, by not only continually replenishing plating solution to the die, but also by directing and forcing the solution through the die and periodically rotating the die to present an opposite surface of the die to the plating solution.
Although the now preferred embodiments of our invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit and scope thereof as defined in the appended claims.
1. A method of plating interior wall portions of a die which comprises,
- immersing a die within a bath of plating solution,
- moving said die upwardly and downwardly within said bath,
- repeatedly confining a replenished supply of said plating solution above said die during downward movement of said die within said bath, and
- flowing said confined supply of replenished plating solution solely into interior portions of said die during upward movement of the die to produce a substantially uniform plating coating on the interior wall portions of said die.
2. A method as defined in claim 1 including the step confining a column of the replenished plating solution above the die and within the confines of peripheral portions of the die.
3. A method as defined in claim 1 including the step of creating a hydrostatic head of said plating solution within the confined supply of plating solution and forcing said solution into interior portions of the die.
4. A method as defined in claim 1 including the step of periodically rotating the die 180 degrees while still being retained within the bath.
5. A method as defined in claim 1 including the step of periodically flowing the confined supply of replenished plating solution into interior portions of the die from opposite faces of the die.
6. A method of nickel plating interior wall portions of a die having slots for extruding ceramic honeycomb structures which comprises,
- immersing an extrusion die to be coated in a bath of electroless nickel plating solution,
- moving said die upwardly and downwardly within the bath solution,
- forming a separate confined column of plating solution above the die from the bath, and
- creating a hydrostatic head within said separate confined column of plating solution;
- whereby the hydrostatic head forces the confined column of plating solution into the slots of said die to provide a substantially uniform nickel coating on the interior wall portions of said slots.
7. A method as defined in claim 6 including the step rotating the die 180 degrees while retaining the die within the plating solution.
8. A method as defined in claim 7 including the step of flowing the confined supply of plating solution under hydrostatic pressure into the die from opposite faces of the die to provide more uniform coating thickness along the slot length.
9. A fixture for plating interior wall portions of a die member which comprises,
- means for supporting said die member in a plating bath solution,
- means for moving said die member upwardly and downwardly within said plating bath and,
- means for confining a column of said plating solution above said die and for directing the flow of said confined solution solely into interior portions of said die member to provide a substantially uniform coating of plating material along said interior wall portions.
10. A fixture for plating interior wall portions of a die member as defined in claim 9, wherein said confining means includes means for replenishing plating solution to an upper surface of said die member.
11. A fixture for plating interior wall portions of a die member as defined in claim 9, including pivotal means for rotating said die member from one fixed position to another fixed position while said die is in said plating bath.
12. A fixture for plating interior wall portions of a die member as defined in claim 9, wherein said means for supporting said die includes a pair of clamping rings which encircle a peripheral portion of said die member.
13. A fixture for plating interior wall portions of a die member as defined in claim 12, wherein said confining means includes a tubular member removably secured to said support means.
14. A fixture for plating interior wall portions of a die member as defined in claim 9 wherein said confining means includes a cylindrical member removably secured to at least one of said clamping rings.
15. A fixture for plating interior wall portions of a die member as defined in claim 9 including trunnion means pivotally mounting said die support means and wherein said pivotal means includes a lever secured to said die supporting means for rotating said support means and said die about said trunnion means.
16. A fixture for plating interior wall portions of a die member as defined in claim 9 including locking pin means for locking said die in a desired rotated position.
17. A fixture for plating interior wall portions of a die member as defined in claim 13 wherein said clamping rings have recessed t-slots and said cylindrical member has a pair of pins for engagement with said slots for securing said cylindrical member on said clamping ring.
International Classification: C25D 21/18 (20060101); C25B 15/00 (20060101);