Rotary expansible chamber devices – Non-metallic working member – cylinder or partition
Reexamination Certificate
2000-03-09
2002-03-12
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Non-metallic working member, cylinder or partition
C418S048000, C418S178000, C427S355000, C428S457000
Reexamination Certificate
active
06354824
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to wear-resistant hardfacings for movable parts and especially to hardfacings for rotors of progressing cavity pumps.
BACKGROUND OF THE INVENTION
Progressing cavity pumps have been used in water wells for many years. More recently, such pumps have been found well suited for the pumping of viscous or thick fluids such as crude oil laden with sand. Progressing cavity pumps include a stator which is attached to a production tubing at the bottom of a well and a rotor which is attached to the bottom end of a pump drive string and is made of metallic material, usually high strength steel. The rotor is usually electro-plated with chrome to resist abrasion, but the corrosive and abrasive properties of the fluids produced in oil wells frequently cause increased wear and premature failure of the pump rotor. Since it is important for efficient operation of the pump that a high pressure differential be maintained across the pump, only small variations in the rotor's dimensions are tolerable. This means that excessively worn rotors must be replaced immediately. However, replacement of the rotor requires pulling a whole pump drive string from the well which is costly, especially in the deep oil well applications which are common for progressing cavity pumps. Consequently, pump rotors with increased wear resistance and, thus, a longer service life are desired to decrease well operating cost.
Various hardfacing methods have been used in the past to increase the wear resistance of metal surfaces. Hardfacings consisting of a thin layer of metal carbide applied by conventional thermal spraying techniques are the most commonly used due to the extreme hardness of the coating achieved. However, although this type of hardfacing works well when in friction contact with a metal surface, surfaces so coated have a roughness which makes them unacceptable for use in progressing cavity pump applications. The surface roughness of the metal carbide hardfacing is due to the grainy structure of the hardfacing structure which is caused by the individual sprayed-on metal carbide particles. This roughness results in excessive wear of the progressing cavity pump stator which is made of an elastomeric material, most often rubber. Polishing of the metal carbide hardfacing to overcome this problem is theoretically possible, but cannot be done economically due to the extreme hardness of the material. Thus, an economical hardfacing for progressing cavity pump rotors is desired which increases the surface life of the rotor without increasing stator wear. In particular, a hardfacing is desired which provides the surface hardness and wear characteristics of a metal carbide that is substantially insoluble in corrosive solutions found in wells.
Coating a metal component with a thin layer of a ceramic material or another metal is known. One primary purpose of a coating process is to protect the surface of a fragile metal product or substrate from abrasion or thermal degradation (i.e., melting) or oxidation by coating it with a more abrasion resistant and thermal degradation resistant material. Recently, various ceramics having high abrasion resistance or high oxidation resistance characteristics have been used to coat metal substrates. One method for applying a ceramic coating to the substrate is by spraying the ceramic coating onto the substrate.
Early equipment used for the spray-coating process, which typically is called flame spraying, included a wire-type flame sprayer. Flame spraying involves heating a heat fusible material, such as metal, to the point where it can be atomized and propelled through the gun onto the surface to be coated. The heated particles strike the surface and bond to it. In the typical flame spray gun, the acetylene and oxygen act as the fuel and combustion gas, respectively, creating the flame. Flame spraying includes oxyacetylene torch spraying. Examples of coatings produced by the flame spraying gun process are found in Ingham, H. S. & A. P. Shepard, Flame Spray Handbook, Vol. II (Metco Inc.)(2d ed 1964). The protective coatings that can be applied this way are limited to those materials that can be formed into a wire or rod. Commercially available flame spray guns also permit the use of a wide variety of metals, alloys, ceramics and cements which can be ground into a relatively fine powder to coat the object. However, high melting point materials are merely cemented by a matrix of material which can be melted in the flame plume. The typical flame spray gun is designed to apply self-fluxing alloys, self-bonding alloys, as well as oxidation-resistant alloys. The flame spray gun utilizes combustion to produce the necessary heat to melt the coating material. Other heating means such as electric arcs and resistance heaters may also be used in a flame spray gun.
In a plasma spray gun, the primary plasma gas is generally an inert gas such as nitrogen or argon. The gas mixture is heated by passing between electrodes with a high voltage discharge. A powder reservoir is attached to the gun and an a water cooler may be attached to the gun to prevent over-heating. Some metal powders require a triggered vibrator to maintain powder movement from the powder reservoir to the gun. The gun can either be “hand-held” or attached to a lathe for larger work, which rotates the metal component to be coated. Typically, the gun is perpendicular to the surface of the rotating object to be sprayed.
The plasma spray gun is the most versatile thermal spraying technique and produces enough heat to plasticize ceramic powder particles. The high thermal efficiency of the plasma spraying gun makes it possible to spray refractory materials at rates and deposit efficiencies which make the coatings economically feasible. The plasma spray technique can produce plume temperatures of 20,000 to 30,000 degrees and velocities of up to Mach 2.
However, ceramic coatings may be porous and may not afford much oxidation or corrosion protection to the base material. Therefore an undercoat of an oxidation-resistant or corrosion-resistant metal or alloy may be used between the base material and the ceramic coating.
Typically, ceramic coatings having high thermal resistance, have a lower wear resistance, while ceramic coatings having a high wear resistance have a low thermal resistance. The general reason for this relationship is that ceramic coatings having a high thermal resistance typically are more sponge-like and have a higher void content allowing thermal dissipation yet allowing easier abrasion, while ceramic coatings having a high abrasion resistance have a lower void content, thus reducing abrasion while at the same time lowering the heat dissipation properties.
Other melting spraying techniques are High Velocity Oxygen Fuel (HVOF) and Detonation Gun (D-gun).
In the HVOF technique, oxygen and a combustible fuel, either a gas or a liquid, are continuously injected into a combustion chamber and continuously ignited. The combustion gases are directed down a barrel and form a plume at the exit. The metal powder is injected into the plume axially in the barrel. This technique permits more efficient mixing of the metal powder in the plume, and may achieve plume velocities of up to Mach 3. The high velocity results in a coating having low porosity and permeability, and a compression coating is achieved which is more resistant to cracking if the part flexes. However, the lower temperature of the plume limits the use with ceramics.
In the D-gun, oxygen and a combustible gas are injected into a combustion chamber in an explosive mixture with a metal powder. The mixture is detonated and the combustion gases and metal are accelerated down a long barrel. This technique produces a high velocity plume compound to other metal spraying techniques, and a lower temperature than plasma and HVOF spraying.
The present invention is intended to included the use of any suitable thermal spraying technique, but plasma spraying is preferred.
U.S. Pat. No. 4,671,740 issued Jun. 9, 1987 to Ormiston et al. states that
Denion Thomas
Kudu Industries Inc.
Pendorf & Cutliff
Trieu Theresa
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