Expansible chamber devices – With lubricating means – Portion of expansible chamber device includes solid...
Reexamination Certificate
1999-02-01
2001-04-10
Look, Edward K. (Department: 3745)
Expansible chamber devices
With lubricating means
Portion of expansible chamber device includes solid...
C092S168000, C092S223000, C417S554000
Reexamination Certificate
active
06212997
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to thin film coating of materials including metal or steel machine components and, more particularly, to coating of metal or steel parts which are intended for assembly and moving contact with parts made of non-metallic or non-ferrous materials.
BACKGROUND OF THE INVENTION
Steel and metal products and machine components are commonly plated or coated for corrosion protection, hardness, friction reduction and appearance. Platings such as chromium, nickel, copper, gold, etc. are commonly applied by an electroplating dipping process. For close tolerance and wear surface applications, these processes are difficult to tightly control to achieve uniform coatings which have the desired physical properties such as hardness, durability and resistance to cracking.
Modern metal coating processes such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) provide improved coating uniformity, strength and hardness. These types of metal coating processes are widely applied to cutting tools and machine components which bear heavy mechanical loads and are in moving contact with other steel or metal components. Metal coatings are applied to steel or metal parts to withstand contact with or cutting of other steel or metal parts. These types of coatings, having extreme hardness and strength, have to the inventors' knowledge not been used in applications where mechnical contact is made with softer non-metallic materials.
Machine components which are in moving contact with components or parts made of non-ferrous
on-metallic materials have also been plated, such as chrome plating of plunger and housing components of reciprocating pumps, which slide against packings made of leather, plastic, rubber or other materials. A common failure of this type of arrangement occurs when cracks form in the chromium plating layer. The cracks form due to volume contraction which occurs when the as-deposited chromium hydrides decompose to molecular hydrogen and chromium metal during post-plating bake-out. Post plating grinding can also produce foreign chrome particles which can damage a seal. Eventually small particles of the chromium layer imbed in the packings. The packings then act as a tool holder of the particles which cut into and score the plated component as it continues to slide against the packings, forming abrasions in the plated surface. The scored abrasions on the plated surface in turn damage the packings, ultimately causing the seal between the packings and the plated surface to fail. Also, as the packings are damaged, they are more likely to collect oxide particles, such as titanium dioxide, from fluid material such as paint being transferred through the pump. These particles can have hardness comparable to chrome and further contribute to scoring of the plunger. Failure of the seals in a reciprocating style pump causes loss of output pressure and loss of containment of the pumped fluid and contamination of other pump components.
In analyzing these type of seal failures, it is most intuitive to suspect the relatively softer non-metallic material, of which the packings are made, as the failing component. However, the inventors have discovered that the above described failure process starts with the failure of the plating or coating of the steel or metallic parts which bear against the packings.
FIGS. 3-6
are micrographs of a chrome plated surface of a reciprocating pump plunger component designed for sliding/sealing contact with a non-metallic packing such as V-rings made of Teflon. In
FIGS. 3 and 4
, chrome particles are indicated at CP, and linear scores S are clearly seen running in the direction of reciprocation of the part past a seal.
FIG. 5
shows an unused surface of a pump plunger chrome plated to prior art design specifications. Cracks CC are shown in the coating, along with chrome particles CP.
FIG. 6
shows a plunger surface after 500 cycles of operation in sliding contact with a packing, exhibiting cracks CC, chrome particles CP within the cracks, and two score lines S.
FIG. 7
shows a mixture of particles P, including chromium and titanium dioxide, imbedded in a Teflon V-ring used as a packing in a reciprocating pump. Linear score marks S are visible in the glass fibers F embedded in the Teflon ring.
FIGS. 8 and 9
show chromium particles CP embedded in a Teflon packing ring. And
FIG. 10
shows a titanium dioxide particle P from paint trapped in a score S in a glass fiber in a V-ring of a pump packing. These micrographs support the inventive discovery that a source of seal failure in combined machine components of metallic and non-metallic materials is the metallic component such as the plating layer on a reciprocating plunger.
In testing, a reciprocating pump in which the plunger is chrome plated to design specifications and in accordance with quality controls, seal failures have occurred at as few as 100,000 pump cycles. The thickness of chrome plating, on the order of approximately 0.004-0.008 inches, requires substantial pre-grinding of the plunger stock to arrive at post-plating tolerances. A post plating grind is also required. Both grinding operations add significantly to manufacturing costs.
SUMMARY OF THE PRESENT INVENTION
The present invention overcomes these and other disadvantages of the prior art by providing chromium nitride coated machine components which are placed in moving contact with non-metallic components, for increased lifespan of the non-metallic components. In accordance with one particular application of the invention, there is provided a reciprocating pump which has a plunger which is actuated to linearly reciprocate within a housing and to bear against one or more non-metallic packing seals.
In accordance with one aspect of the invention, there is provided a reciprocating type fluid pump having a hydraulic section including a housing and a plunger driven to reciprocate at least partially within the housing and to pass through an opening in the housing, the housing having a fluid intake port and a fluid exit port, a ball check operatively associated with the fluid intake port, and a packing seal positioned about a periphery of the opening in the housing through which the plunger passes, the packing seal being made of a non-metallic material and dimensioned to extend into the opening in the housing through which the plunger passes so as to make contact with the plunger as the plunger passes through the opening as it reciprocates at least partially within the housing, and at least one additional seal between the plunger and the housing spaced from the opening in the housing, the plunger having an external surface area configured to bear against and make sliding contact with the packing seal about the periphery of the opening through which the plunger passes as it reciprocates at least partially within the housing, an internal passageway within the plunger which extends generally axially from one end of the plunger to an exit point spaced from the one end of the plunger, and a ball check operatively associated with the internal passageway of the plunger, the external surface of the plunger which contacts the packing seal being coated with chromium nitride, whereby the chromium nitride coating is in continuous contact and sliding with the packing seal, whereby a hydraulic seal is formed between the plunger and the packing seal.
These and other aspects of the invention are herein described in particular detail with reference to the accompanying Figures.
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Karbowniczek Joseph J.
McCollough Mark W.
Calfee Halter & Griswold LLP
Lazo Thomas E.
Look Edward K.
Nordson Corporation
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