Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2000-09-14
2002-08-20
Elve, M. Alexandra (Department: 1728)
Electric heating
Metal heating
For bonding with pressure
C219S069170, C219S118000
Reexamination Certificate
active
06437280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of this invention lies within the printer art and the manufacture of printers. It lies to the extent of utilization within the printer art relying upon print hammers having tips. The print hammers are released against a ribbon and underlying media to be printed upon. The tips of the hammers are made of a hardened material and can be attached or formed on the hammers for continuous long wearing printing. More specifically, this invention relates to the print hammer's tips being formed of a hardened material that is fused to the magnetic steel of the print hammers in a consistent and long wearing manner.
2. Prior Art
Various printer tip designs and configurations have been known in the art. Some of these tip configurations can be seen in
FIGS. 3 and 4
. The foregoing printer tip configurations shown in
FIGS. 3 and 4
are welded or fused to a print hammer.
During the process of welding a tip it is connected to an upper electrode and placed in contact with the magnetic steel forming the spring element or hammer element underlying the tip. Electrodes contacting the two respective elements, namely the tip and the hammerspring, are provided with a current, and welding takes place.
In the foregoing scenario, both the tip which can be formed of a cemented tungsten carbide having a matrix including cobalt binder and the magnetic steel are melted. During the melting process, the cemented tungsten carbide not only melts, but can become deformed as shown in FIG.
4
.
Deformation of a pin or the print tip creates a situation wherein stress can build up at the fillet or angular melt point interfacing the hammerspring and the tip. As can be understood this creates a prospective situation where failure can occur.
In the alternative, if the pin material correctly melts and deforms at the right temperature, then an improved fillet is provided as shown in FIG.
3
. On the other hand, if the temperature is not correct, and other conditions are not met with regard to the variances in the cemented tungsten carbide forming the tip, lines of deformation D and deformation areas as shown in
FIG. 4
occur. These as previously stated become stress areas and are prone to fatigue failures.
Some of the foregoing is based upon the cobalt content in the cemented tungsten carbide. When different amounts of cobalt are in the tip either due to changes in quality control or other process changes, variable results can occur. Further to this extent, when the deformation lines D as in
FIG. 4
are created, a degree of ink migration can take place.
Cemented tungsten carbide typically can have 2% or up to 22% of cobalt. The Condensed Chemical Dictionary Defines cemented tungsten carbide as a mixture consisting of tungsten carbide of eighty five to 95% and cobalt 5 to 15%, it can vary even to further ranges. In the prior art, the cemented tungsten carbide printer tips generally contain 16% cobalt and 84% tungsten carbide to facilitate melting. With the new process of this invention, the cobalt can be decreased significantly because of the fact the fusing, brazing, or connecting process does not require a melting of the cobalt to fuse with the underlying steel of the hammer.
Fundamentally, in prior processes where cemented tungsten carbide is utilized, it must fuse to other metals. This requires a higher percentage of cobalt in the way of a binder to reduce the melting temperature of the cemented tungsten carbide. The net result is to decrease the life of the tip because the cobalt causes softening of the cemented tungsten carbide material.
This invention overcomes the requirement of significant amounts of cobalt in the matrix of the cemented tungsten carbide. A further feature is that by lowering the amount of cobalt in the cemented tungsten carbide, a significantly longer wear life is incurred by the tip.
Another improvement is that by having an increased amount of tungsten carbide, the overall tip maintains a significant degree of formation in its original state rather than being deformed.
Another feature of this invention is that the temperature ranges can be maintained below the melting temperature of the cobalt or melting temperature of the cemented tungsten carbide material.
Another improvement of this invention is that materials can be selected from the family of tungsten, sintered tungsten carbide, alloys of tungsten, composite ceramics, metallic, and noble metallic materials for the formation of the printer tips. The only requirement is that they be hard conductive materials having a melting temperature greater than the melting temperature of the underlying magnetic steel.
As a further improvement the cemented tungsten carbide tips can be plated or coated with a conductive metal prior to being fused. This improves the consistency of the process and helps to accommodate any inconsistencies in the matrix or surface of the cemented tungsten carbide tips.
A further improvement of this invention is that an electrode milling or electrode removal of material can be utilized which significantly shapes the tip to provide for an improved configuration. This improved configuration can be such wherein it centers the tip substantially within the area of the hammerspring while providing shoulders for the decrease of ink migration.
The foregoing improvements over the art will be seen in greater detail hereinafter as set forth in the specification.
SUMMARY OF THE INVENTION
In summation, this invention is an improved printer tip for a hammerspring that is released for impact against a ribbon with an underlying media and a process for manufacturing the printer tip with improved brazing and conformation of the printer tip through an electrode milling process.
More specifically, this invention utilizes a printer tip of cemented tungsten carbide or other hard materials. The printer tip of cemented tungsten carbide is connected to a magnetic spring steel hammerspring by a brazing or fusion process whereby the underlying spring steel is softened or melted to the extent where it receives the printer tip without significant deformation of the printer tip itself. The printer tip retains its integrity as to its relative amount of cobalt in the cemented tungsten carbide. The brazing or fusion of the printer tip to the hammerspring steel is effected by a controlled current between two electrodes, one being on the printer tip and the other on the underlying hammerspring.
The brazing process allows the printer tip to sink slightly into the matrix of the hammerspring. This effects a brazing process or fusion without deformation, or degeneration of the cemented tungsten carbide matrix. Because of the variable constituents of the cemented tungsten carbide matrix, it is possible that an insignificant amount of cobalt could melt without causing deformation or degeneration of the printer tip.
In order to improve the consistency of the fusion process and provide for any inconsistencies in the cemented tungsten carbide, the printer tips can be coated or plated with a conductive metal prior to fusion. The coating of such metals as nickel, nickel alloys, nickel cobalt, cobalt alloys, cobalt, noble metal alloys, noble alloys, copper, silver, silver alloys, chrome, chrome alloys and tin coatings provide for a consistent flow of current, accommodation of variations in the surface or matrix of the cemented tungsten carbide and differences of constituent and surface cemented tungsten carbide content.
Another improved portion of this invention is that the configuration of the tip is maintained with significant integrity which can then be formed by an electrode milling process. The electrode milling process allows for a controlled removal of the material on the tip in order to provide for a well configured tip. The tip can be provided with shoulders which help to diminish ink migration and ribbon wear while at the same time providing for an improved striking tip.
Finally, the brazing or fusion process provides for defining a proper temperature range for the brazing and later shaping of
Bethel George F.
Elve M. Alexandra
Printronix, Inc.
Stoner Kiley
LandOfFree
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