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1.
A number of high-velocity oxygen-fuel flame (HVOF) systems have evolved during the last 9 years. The most advanced is now
challenging the coating qualities produced by the very successful detonation (D-Gun) process. The fundamentals of these various
processes are described and compared. A mathematical analysis of an established HVOF gun is profiled. Gas and particle temperatures,
velocities, pressures, and Mach numbers are calculated and plotted at various points within the gun and spray stream. Significantly,
all measured values were in close agreement with calculated and predicted values. Flow patterns and shock-wave phenomena are
also described and compared with actual observations. 相似文献
2.
An analysis of a low temperature high velocity air fuel (LTHVAF) thermal spray process is presented using computational fluid
dynamics (CFD). The originality of the process lies in the injection of liquid (water) upstream of the powder injection to
control to gas temperature and, therefore, the heat transfer to the injected particles. First, computation fluid dynamic techniques
are implemented to solve the mass, momentum, and energy conservation equations in the gas phase. A turbulence model based
on the renormalized group theory (RNG) is used for the turbulent flow field. The gas dynamic data are, then, used to model
the behavior of the liquid droplets and particles in the gas flow field. The calculated results show that the liquid flow
rate should range between 20 and 30 kg/h to achieve the optimal gas characteristics for particle treatment. They also show
that particle velocity and temperature are strongly affected by particle size. At the gun exit, the particle velocity and
temperature range between 700 and 300 m/s and between 900 and 400 K, respectively, for Cu and Ni particles with size distributions
of 1 to 50 μm. As expected, the smaller particles have higher velocity and temperature. The metal coatings (Nickel and copper)
produced by the LTHVAF spray process are characterized by low oxide content, low residual stresses, high deposition rates,
and good bonding to the substrate. 相似文献
3.
High velocity oxygen fuel (HVOF) thermal spray technology is able to produce very dense coating without over-heating powder particles. The quality of coating is directly related to the particle parameters such as velocity, temperature and state of melting or solidification. In order to obtain this particle data, mathematical models are developed to predict particle dynamic behaviour in a liquid fuelled high velocity oxy-fuel thermal spray gun. The particle transport equations are solved in a Lagrangian manner and coupled with the three-dimensional, chemically reacting, turbulent gas flow. The melting and solidification within particles as a result of heat exchange with the surrounding gas flow is solved numerically. The in-flight particle characteristics of Inconel 718 are studied and the effects of injection parameters on particle behavior are examined. The computational results show that the particles smaller than 10 μm undergo melting and solidification prior to impact while the particle larger than 20 μm never reach liquid state during the process. 相似文献
4.
Liquid-fuelled high-velocity oxygen–fuel (HVOF) thermal spraying systems are gaining more attentions due to their advantage of producing denser coatings in comparison to their gas-fuelled counterparts. The flow through a HVOF gun is characterized by a complex array of thermodynamic phenomena involving combustion, turbulence and compressible flow. Advanced computational models have been developed to gain insight to the thermochemical processes of thermal spraying, however little work has been reported for the liquid-fuelled systems. This investigation employs a commercial finite volume CFD code to simulate the flow field through the most widely used liquid-fuel HVOF gun, JP5000 (Praxair, US). By combining numerical combustion and discrete phase models the turbulent spray flame is captured and the development of supersonic gas flow is revealed. The flow field is thoroughly examined by adjusting the nozzle throat diameter and combustion chamber size. The influence of fuel droplet size on the flame shame shape and combusting gas flow is also examined. 相似文献
5.
6.
目的 研究不同超音速火焰喷涂条件下WC-12Co粒子在45#碳钢基体上的沉积变形行为。方法 基于Johnson-Cook塑性材料模型与Thermal-Isotropy-Phase-Change热材料模型,采用LS-DYNA进行建模分析。结果 不同喷涂参数下,WC-12Co粒子在45#碳钢基体上的沉积行为存在明显差异。沉积过程中,粒子等效塑性应变幅度高于基体;粒子边缘位置等效塑性应变幅度高于粒子中心轴线位置;粒子初始速度与初始温度的增加有助于提升结合界面温度与粒子扁平化程度;粒子初始温度与粒子初始速度对接触界面能量变化影响程度基本一致,单位粒子初始速度与温度提升的能量贡献比 分别为0.78以及0.76,二者的能量贡献比近似相同;适度的基体预热( =500 K)可以促进粒子变形,加深沉积坑深度,增大粒子与基体的结合面积,有助于提升粒子与基体之间的结合强度。基体过冷( =300 K)将导致粒子“翘曲”,降低粒子与基体之间的结合面积,基体过热( =600 K)将导致二者结合处于不稳定状态,易引起粒子剥落,二者均不利于粒子与基体的有效结合。结论 一定范围内提升粒子初始速度、温度与基体初始温度,可以提高粒子扁平化程度,增大粒子与基体结合面积,提升粒子与基体的结合性能,进一步提高涂层质量。 相似文献
7.
Mathematical modelling of the heat transfer between a WC-Co coating and a copper substrate during high-velocity oxygen-fuel
(HVOF) spraying was undertaken. The modeling included the investigation of temperature variation, coating solidification,
melting and solidification in the substrate interfacial region, and specific features of the substrate-coating thermal interaction. 相似文献
8.
S. Gu D. G. McCartney C. N. Eastwick K. Simmons 《Journal of Thermal Spray Technology》2004,13(2):200-213
A computational fluid dynamics (CFD) model is developed to predict particle dynamic behavior in a high-velocity oxyfuel (HVOF)
thermal spray gun in which premixed oxygen and propylene are burnt in a combustion chamber linked to a long, parallel-sided
nozzle. The particle transport equations are solved in a Lagrangian manner and coupled with the two-dimensional, axisymmetric,
steady state, chemically reacting, turbulent gas flow. Within the particle transport model, the total flow of the particle
phase is modeled by tracking a small number of particles through the continuum gas flow, and each of these individual particles
is tracked independently through the continuous phase. Three different combustion chamber designs were modeled, and the in-flight
particle characteristics of Inconel were 625 studied. Results are presented to show the effect of process parameters, such
as particle injection speed and location, total gas flow rate, fuel-to-oxygen gas ratio, and particle size on the particle
dynamic behavior for a parallel-sided, 12 mm long combustion chamber. The results indicate that the momentum and heat transfer
to particles are primarily influenced by total gas flow. The 12 mm long chamber can achieve an optimum performance for Inconel
625 powder particles ranging in diameter from 20 to 40 μm. At a particular spraying distance, an optimal size of particles
is observed with respect to particle temperature. The effect of different combustion chamber dimensions on particle dynamics
was also investigated. The results obtained for both a 22 mm long chamber and also one with a conical, converging design are
compared with the baseline data for the 12 mm chamber. 相似文献
9.
采用超音速火焰(high velocity oxygen fuel,HVOF)喷涂技术在Q235钢基体上制备了FeCrSiB合金涂层.利用X射线衍射仪、扫描电子显微镜、电化学工作站等设备对涂层的显微组织结构和耐腐蚀性进行了研究.结果表明,采用HVOF喷涂技术制备的FeCrSiB涂层结构致密,孔隙率为0.65%,与基体结合良好.FeCrSiB涂层在3.5%NaCl溶液、1 mol/L HCl溶液和1 mol/L NaOH溶液中都经历了活性溶解-钝化-过钝化的过程,且该涂层在3.5%NaCl溶液和1 mol/L HCl溶液中的耐腐蚀性能要优于镀铬层,在1 mol/L NaOH溶液中的耐腐蚀性能低于镀铬层. 相似文献
10.
O. C. Brandt 《Journal of Thermal Spray Technology》1995,4(2):147-152
High-velocity oxygen fuel (HVOF) thermal-sprayed carbide coatings are distinguished by high hardness, low porosity, and good
wear resistance compared to other thermal spray technologies. However, for many engineering applications the ductility and
fatigue resistance are the most important material properties. In the use of HVOF systems, these properties are influenced
by many boundary conditions. This paper presents the effects of different spraying parameters on the fatigue resistance of
samples coated by the HVOF process. 相似文献
11.
Dynamic analysis of particle temperaturein HVOF spray 总被引:1,自引:0,他引:1
0 IntroductionInthermalsprayingprocess,thetemperatureoftheparticlesisoneofthemostimportantfactorsofwhichcontrolthequalityofthermalsprayedcoatings[1,2].Manypropertiesofathermalsprayedcoating,suchasmicrostructure,levelofprimaryphaseretention,phasedistributi… 相似文献
12.
为开发出以航空煤油为燃料的新型高速燃气喷涂枪,需设计出高效的煤油雾化喷嘴.文中提出了一种双气流空气助力雾化喷嘴,并运用计算流体动力学(CFD)模拟技术计算了该喷嘴的气流场,分析了喷嘴主、辅气出口截面积比对雾化气流场分布的影响规律,发现主、辅气出口截面积比增大,气流的喷射锥角相应增大,最大速度减小.综合考虑喷射锥角和气流速度对雾化效果的影响,确定主、辅气出口截面积比在1.01~1.34范围内喷嘴雾化效果较好.利用高速摄像系统对优化喷嘴的喷雾形态进行了试验分析,发现拍摄到的喷雾形态和计算机模拟结果一致,具有良好的雾化效果. 相似文献
13.
An experimental study of the gas-dynamic aspects of the high-velocity oxyfuel (HVOF) thermal spray process has been performed
using commercially available HVOF equipment (Hobart-Tafa JP-5000, Ho-bart-Tafa Technologies, Inc., Concord, NH). Optical diagnostic
techniques, including microsecond-expo-sure schlieren and shadowgraph imaging, were applied to visualize the hot supersonic
jet produced by this equipment without particle injection. Rapid turbulent mixing of the jet with the surrounding atmos-phere
was observed, which is an issue of concern in coating quality due to the possibility of oxidation of sprayed particles. This
mixing appears to be a function of the ratio of densities of the hot jet and the cold atmosphere as well as a function of
the velocity of the jet, rather than one of combustion-chamber pres-sure or barrel length. The supersonic core of the HVOF
jet dissipates rapidly due to the mixing, so that the jet is no longer supersonic when it impinges on the target surface being
sprayed. Secondary issues also observed in this study include strong jet-noise radiation from the HVOF plume and the entrainment
and induced bulk motion of the surrounding air. 相似文献
14.
The application of thick high-velocity oxyfuel (HVOF) coatings on metallic parts has been widely accepted as a solution to
improve their wear properties. The adherence of these coatings to the substrate is strongly influenced by the residual stresses
generated during the coating deposition process. In an HVOF spraying process, due to the relatively low processing temperature,
significant peening stresses are generated during impact of molten and semimolten particles on the substrate. At present,
finite-element (FE) models of residual stress generation for the HVOF process are not available due to the increased complexities
in modeling the stresses generated due to the particle impact. In this work, an explicit FE analysis is carried out to study
the effect of molten particle impingement using deposition of an HVOF sprayed copper coating on a copper substrate as an example
system. The results from the analysis are subsequently used in a thermomechanical FE model to allow the development of the
residual stresses in these coatings to be modeled.
This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials
Park, OH, 2006. 相似文献
15.
One method used in spray forming and coating technology involves transonic/supersonic gas-droplet two- phase flows through
a de Laval nozzle and subsequent subsonic freejet flow from the nozzle to the sprayed surface. To the first- order approximation,
this complex phenomenon can be treated in a quasione-dimensional manner to simulate the entire converging- diverging nozzle
flow field (with particle injection at the throat) as well as the plume (freejet) region. The basic numerical technique and
computer model solve the steady gas field equations through a conservative variable approach and treat the droplet phase in
a Lagrangian manner, with full aerodynamic and energetic coupling between the droplets and the transport gas handled via source
terms. These analyses are simple and economical to execute. The one- dimensional models are valuable in constructing algorithms
for automated process control. Finally, these one- dimensional models give direction to two- and three- dimensional simulations
and serve as a test bed for models based on particle dynamics and energetics. 相似文献
16.
A simple device was constructed for determining a value for the average combustion gas velocity at the exit plane of a high-velocity
oxyfuel gun. This device was used to measure the velocities of a standard factory-made barrel nozzle and a specially designed
de Laval nozzle as a function of the fuel/oxygen ratio and the total mass flow rate. The Mach number of the de Laval nozzle
was 1.42. The maximum combustion gas exit velocities determined for the standard and the de Laval nozzles were 1100 and 1550
m/s, respectively. The maximum velocity depends on the fuel/oxygen ratio but is independent of the total flow rate. The effect
of increased combustion gas velocity on coating quality is demonstrated. 相似文献
17.
Application of HVOF thermal spraying to solve corrosion problems in the petroleum industry—an industrial note 总被引:1,自引:0,他引:1
L. N. Moskowitz 《Journal of Thermal Spray Technology》1993,2(1):21-29
Commercially available thermal spray coatings have seen limited use in corrosion applications due to the presence of interconnecting
porosity and oxide networks. Use of vacuum chambers or post-treatments can eliminate most defects, but these methods are costly
and impractical on a large scale. The ability to produce such high-quality coatings by thermal spraying in atmosphere and
without post-treatments would offer important advantages as a means of building and repairing process equipment. A modified
HVOF process using unique inert gas shrouding has resulted in highly dense, low-oxide coatings of metallic alloys. These coatings
were extensively evaluated for severe petroleum industry corrosion applications in laboratory and plant testing, with exposures
as long as 5 years. Coatings of corrosion-resistant alloys, such as type 316L stainless steel and Hastelloy C-276, were shown
to act as true corrosion barriers. They were protective to underlying base metals in severe environments and in most cases
exhibited corrosion resistance comparable to the corresponding wrought alloy. The process was scaled up for on-site plant
use and successfully applied to numerous corrosion problems in petroleum industry plant equipment. Significant technical and
economic advantages can be realized by use of thermal spray coatings to solve plant equipment problems. 相似文献
18.
This article reports on a series of experiments with various high-velocity oxygen fuel spray systems (Jet Kote, Top Gun, Diamond
Jet (DJ) Standard, DJ 2600 and 2700, JP-5000, Top Gun-K) using different WC-Co and WC-Co-Cr powders. The microstructure and
phase composition of powders and coatings were analyzed by optical and scanning electron microscopy and x-ray diffraction.
Carbon and oxygen content of the coatings were determined to study the decarburization and oxidation of the material during
the spray process. Coatings were also characterized by their hardness, bond strength, abrasive wear, and corrosion resistance.
The results demonstrate that the powders exhibit various degrees of phase transformation during the spray process depending
on type of powder, spray system, and spray parameters. Within a relatively wide range, the extent of phase transformation
has only little effect on coating properties. Therefore, coatings of high hardness and wear resistance can be produced with
all HVOF spray systems when the proper spray powder and process parameters are chosen.
This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according
to the editorial policy of the Journal of Thermal Spray Technology. 相似文献
19.
20.
The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional
computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and
compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of
acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through
an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate.
The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including
the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent
chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as
source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions
and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances
whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the
global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made
to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared
satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated
injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference
code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal
heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations
compared fairly well with experimental results obtained with the optical DPV2000 system. 相似文献