Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Reexamination Certificate
2000-12-13
2003-07-08
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
C148S230000, C148S605000, C148S607000
Reexamination Certificate
active
06589363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates in general to stainless steel hydraulic components, and more particularly to a method of using and manufacturing hydraulic components from pre-heat treated stainless steel.
2. Description of the Related Art
Hydraulic components must be produced or finished within very close tolerances, i.e., to precision finished dimensions. Currently, most hydraulic components like check valves, poppet valves, or sliding spool valves are produced from carbon or alloy steel and are subjected to a variety of machining, turning, grinding, or cutting process steps necessary to form the component to its precision finished dimension for the completed product.
In the manufacturing process of such hydraulic components, the typical process usually requires at least one turning or machining step followed by a final heat treatment step to provide suitable hardenability to the hydraulic component. As a result, it is more difficult to establish part finishes, geometrical requirements, and dimensional tolerance constraints. This can result in the requirement for more processing time and cost involved in producing a desired part from a selected carbon steel material.
Stainless steel is a material currently used primarily in corrosive environments. Stainless steel is commonly understood to mean a corrosion resistant alloy steel containing approximately 10.5% or more on a weight percent basis, chromium (Cr). Stainless steel (SS) offers strength (approximately 50% stronger than low carbon steels), heat and corrosion resistance, and low maintenance.
Stainless steel materials are widely used for specific industry applications like fasteners, spindles, nozzles, shafts, springs, surgical instruments, etc. as well as in many aerospace and automotive applications. Cast stainless steel has also been employed in some hydraulic valve applications, like fabricating the body and bonnet, wedge, seat ring, stem gland, bonnet bush, yoke sleeve, etc.
The practice of hard turning pre-heat treated stainless steel material to eliminate the need for post turning heat treatment has been employed for some steam flow applications in the electrical power generation industry. However, this practice to the best of the inventors' knowledge has not been applied to stainless steel materials in the hydraulics industry. One skilled in this art is not likely to consider these materials for hydraulic components due to a number of factors including, but not limited to the size of the hydraulic components, the hardness of the stainless steel material, and the difficulties involved with machinability of heat treated stainless steel materials. It is generally known that hardenability decreases as machinability increases. Also, the higher cost of stainless steel relative to carbon steel makes it cost prohibitive for use in the hydraulics industry.
There still exists a need for improved hydraulic components and an improved method for making the hydraulic components. The improved hydraulic components should be made from stainless steel and be more durable, more corrosion resistant, and exhibit improved leak performance over time. The improved method should eliminate secondary process steps along with the extra costs associated therewith. Such a method would make a stainless steel material a cost-effective alternative after processing costs and life cycle cost are compared to other materials.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved hydraulic component made from a pre-heat treated stainless steel material.
Another object of the present invention is to provide a method for making a stainless steel hydraulic component that offers improved performance, corrosion protection, durability, and low maintenance throughout the manufacturing process and life cycle of the product.
Another object of the present invention to provide a method for manufacturing a stainless steel hydraulic component in a cost-effective manner while providing a superior quality product with a shorter fabrication cycle.
Still another object of the present invention is to provide a stainless steel valve component of the sealing type with improved leak performance over a period of time.
A further object of the present invention is to provide a stainless steel valve component of the sealing type with a constant leakage rate over a period of time.
The above and other objects of the present invention are accomplished with a method that hard turns a selected pre-heat treated stainless steel material to precision finished dimensions.
The method according to the present invention comprises the steps of: selecting a pre-heat treated stainless steel material having a predetermined minimum hardness value; providing the selected heat-treated stainless steel material in a bar stock form; and machining a hydraulic component to a finished dimension in a single machining operation.
The present invention is also directed to hydraulic valve components made of a selected stainless steel material having a predetermined minimum hardness value and a maximum ferrite content.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is described and illustrated.
REFERENCES:
patent: 4588440 (1986-05-01), Simoneau
patent: 5257453 (1993-11-01), Neumann et al.
patent: 5513671 (1996-05-01), Cortopassi et al.
patent: 5802937 (1998-09-01), Day et al.
patent: 26895921 (1993-07-01), None
English abstract of Japanese patent 1318763A, published Jun. 20, 1988.*
Carpenter Technology Corporation, “Guide to Selecting Stainless Steels for Pumps, Valves and Fittings”, 1981.
Rohde Daniel P.
Tackes John N.
Eaton Corporation
Kalka Daniel S.
Kasper L. J.
Yee Deborah
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