Chromium Plating Process Research Articles

Statistical optimization of process parameters to obtain maximum thickness and brightness in chromium plating

Chromium plating process is the most effective way of protecting the base material against hostile environment or improving surface properties of base material. However, in electroplating industry, electro-platers are faced with many problems and undesirable results on chromium plated materials. Problems such as matt deposition, milky white chromium deposition, rough or sandy chromium deposition, insufficient thickness and hardness are the most common problems faced in the electroplating industry. In this work, an experimental setup for chromium plating process has been constructed and MS58 brass materials have been chromium plated under different process conditions to study their effects on the thickness and brightness of chromium layers. The experimental results are analyzed and optimized based on central composite design of response surface methodology. This paper presents the optimum chromium plating conditions which produce the possible thickest and brightest coatings and detailed information about the interaction between process parameters.

Electrically Mediated Process for Functinal and Decorative Trivalent Chromium Electroplating: An Alternative to Hexavalent Chromium

Research work performed to develop a functional and decorative trivalent chromium plating process from a single, simple to control trivalent-based electrolyte to replace hexavalent chromium plating will be reported. Hexavalent chromium plating has been used for many years to provide hard, durable coatings with excellent wear and corrosion resistance properties. However, hexavalent chromium baths have come under increasing scrutiny due to the toxic nature of the bath, effects on the environment, and workers' health. In this work, Faraday is updating its accomplishments to date to achieve properties comparable to existing hexavalent chromium plating for both functional and decorative applications. Continuing work on the bath chemistry, diffusion layer, hydrodynamics, and electrically mediated process parameters will also be discussed.

Effect of chromium(VI) on the status of plasma lipid peroxidation and erythrocyte antioxidant enzymes in chromium plating workers

The present study was carried out to determine the effect of chromium(VI) on the status of plasma lipid peroxidation and erythrocyte antioxidant enzymes in workers exposed to chromium during chromium plating process. Fifty subjects working in chromium plating process formed the study group. An equal number of age-sex matched subjects working in administrative units formed the control group. The control subjects were residing in the same city but away from the work place of study group subjects. Urinary chromium levels were determined by using a graphite furnace atomic absorption spectrophotometer. The plasma lipid peroxidation and erythrocyte antioxidant enzymes were determined by using spectrophotmetric methods. A significant increase of plasma lipid peroxidation and a significant decrease of superoxide dismutase and glutathione peroxidase levels were noted in the study group as compared with the controls. The level of plasma lipid peroxidation was positively and erythrocyte antioxidant enzymes were negatively and significantly correlated with chromium levels in urine. Multiple regression analysis was assessed the oxidative stress associated with chromium and life style confounding factors such as BMI, coffee, tea, alcohol and smoking. The multiple regression analysis showed that the urine chromium levels >10 micro g/g of creatinine, smoking, consumption of green vegetables and BMI variables were significantly associated with the levels of oxidative stress. The results show that the increased plasma lipid peroxidation and decreased antioxidant enzymes (superoxide dismutase and glutathione peroxidase) observed in chromium-exposed workers could be used as biomarkers of oxidative stress.

Preparation and characterization of Cr–P coatings by electrodeposition from trivalent chromium electrolytes using malonic acid as complex

Cr–P coatings were prepared by electrodeposition from trivalent chromium plating bath using malonic acid as complex. The influences of bath composition on the trivalent chromium electrodeposition process and deposited coating properties were studied. The effects of plating parameters such as current density, bath pH and plating time on structure and morphology of deposited coatings were investigated in detail. XRD, SEM, EDAX and XPS techniques were used to characterize the Cr–P deposited coatings. Results show that the composition, microstructure and surface morphology of the Cr–P coatings depend on bath composition and plating conditions including bath pH, current density, plating time, etc. Results of EDAX and XPS indicate that the deposited coatings contain Cr(s), Cr(III), phosphorus, oxygen and carbon. The optimum bath composition was obtained using malonic acid as complex and the mechanism of Cr–P electrodeposition was analyzed. The optimum plating parameters for good-quality chromium deposited coating are pH 2–3, current density 3–12 dm2, temperature 35 °C and Ti/IrO2 as anode. These results may be of great practical and theoretical significance for further improvement of trivalent chromium plating process.

Electroless Ni-B plating for electrical contact applications

Electroless Ni-B plating has been tried on steel substrate in an effort to employ low-cost starting materials for electrical contacts or connectors. By selected conditions of heat treatment in a high vacuum environment the plating can acquire Cr-equivalent hardness without the effluents of the hard chromium plating process. The surfaces were characterized under scanning electron microscope and by XRD. The fabricated materials were tested under corrosion conditions by polarization measurements. Semispherical nickel plated steel joints were tested in a computer controlled contact make-break apparatus, under simultaneous application of a mechanical and a low-voltage electrical load for 20,000 cycles. After heat treatment the plating acquires a crystalline structure with very good adhesion to the substrate material. Corrosion decreases and increased hardness is obtained. The surface is also characterized by good electrical properties during aging accelerated tests.

Numerical 3D BEM Simulation Of TheChromium Layer Thickness Distribution OnParts In A Rack Plating Configuration

A three dimensional Boundary Element Method (BEM) approach is used to compute the current density and plated layer thickness distribution on parts of complex shape in a rack plating configuration. Results are shown for a decorative chromium plating process. Simulations take into account electrode polarisation characteristics and the plating efficiency. The entire plating tank configuration is considered, including dimensions and position of anode baskets or rods, the number of parts on the rack, and the position of the rack in the tank. For decorative chromium plating, simulated results reveal that parts located at the outer positions of the rack receive a current that might double the value received by a central part, hence also the average plated thickness from one part to another might differ by a factor 2. The variation of the plated thickness on a single part is up to a factor 5 or more, with some of the inner zones receiving no layer thickness at all. These results are in agreement with industrial experience. The BEM solver is integrated in the SolidWorks CAD environment, enabling a fast modification of the dimensions of the entire configuration (rack configuration, current thieves, etc.), the surface mesh characteristics (determining the computational accuracy), and the physico-chemical input parameters (polarisation and efficiency characteristics, electrolyte conductivity, imposed DC or bipolar currents, etc.).

Alternative to chromium: characteristics and wear behavior of HVOF coatings for gas turbine shafts repair (heavy-duty)

Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas turbine shafts. However, such a technology presents harmful effects on the environment and the public health and it exhibits, moreover some intrinsic technical limitations. HVOF (high-velocity oxy-fuel) thermal spraying process appears as more environmentally friendly than chromium plating process but exhibits also lower potential production costs when compared to hard chromium deposits. In such a way, HVOF process appears as an alternative to hard chromium plating for shafts repair, by reducing the frequency of maintenance operation and repair and by deferring the need to fabricate or to buy replacement parts for used engines of previous generation. The purpose of this study was to investigate and to compare microstructural properties, wear resistance, and potentials of HVOF sprayed Tribaloy©-400 (T-400), Cr 3C 2–25%NiCr and WC–12%Co coatings for a possible replacement of hard chromium plating in gas turbine shafts repair. It was shown that thermal spray coatings exhibit the adequate properties compared to electrodeposited hard chromium coatings.

Alternative to chromium: characteristics and wear behavior of HVOF coatings for gas turbine shafts repair (heavy-duty)

Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas turbine shafts. However, such a technology presents harmful effects on the environment and the public health and it exhibits, moreover some intrinsic technical limitations. HVOF (high-velocity oxy-fuel) thermal spraying process appears as more environmentally friendly than chromium plating process but exhibits also lower potential production costs when compared to hard chromium deposits. In such a way, HVOF process appears as an alternative to hard chromium plating for shafts repair, by reducing the frequency of maintenance operation and repair and by deferring the need to fabricate or to buy replacement parts for used engines of previous generation. The purpose of this study was to investigate and to compare microstructural properties, wear resistance, and potentials of HVOF sprayed Tribaloy©-400 (T-400), Cr3C2–25%NiCr and WC–12%Co coatings for a possible replacement of hard chromium plating in gas turbine shafts repair. It was shown that thermal spray coatings exhibit the adequate properties compared to electrodeposited hard chromium coatings.

Vacuum Heated Electroless Nickel Plated Contacts

Electroless nickel plating has been tried on steel or brass substrates. By selected conditions of heat treatment in a high vacuum environment the plating can produce chromium equivalent hardness without the effluents of the hard chromium plating process. The resulting surfaces were examined and characterized under an optical and a scanning electron microscope. X-ray diffraction analysis was also performed to investigate recrystallization effects. The fabricated contact materials were also tested under corrosion conditions and linear polarization measurements were performed. To exploit possible utilization of produced coatings as electrical contact or connector materials, semispherical nickel plated steel joints were tested under the simultaneous application of mechanical fretting and a low-voltage electrical load. Their contact resistance was monitored during 20,000 cycle tests. The results show that after a 2-min heat treatment under 800/spl deg/C in a high vacuum environment, the plating acquires a crystalline structure with microhardness exceeding 1100 HV and a very good adhesion to the substrate material, without deteriorating its corrosion wear properties. In addition they exhibit a low and stable electrical contact resistance when operating in adverse environments i.e. fretting conditions or corrosive atmosphere.

Vacuum heat treatment of electroless Ni–B coatings

Electroless nickel–boron plating with subsequent rapid heat treatment in vacuum has been tried on steel substrate in an effort to obtain hard engineering coatings. By selected conditions of heat treatment in a high vacuum environment (a type of rapid quenching), the plating can acquire chromium equivalent hardness without the effluents of the hard chromium plating process. The resulting surfaces were examined and characterized under an optical and a scanning electron microscope. XRD analysis was also performed to investigate re-crystallization effects. The fabricated materials were also tested under corrosion conditions and linear polarization measurements were performed. The results show that after a 5-min heat treatment in vacuum, the plating acquires a crystalline structure with very good adhesion to the substrate material, obtained so far by several weeks/months thermal treatment.

Study on the Microstructural Characteristics of Some Metallic Layers Produced Using the Electrochemical Method and Thermal Spraying

The paper presents the comparative analysis of the microstructural particularities and the superficial characteristics (microhardness and wear resistance) of 3 methods of producing composite layers on metallic support. The aim of the research was to study the possibility of replacing the hard chromium plating process by the thermal metallization process, in order to produce layers resistant to wear and corrosion. Samples produced by hard chromium plating (layers deposited by electrolysis), samples loaded by thermal metallization with electric arc and G3Si1 wire, and samples loaded by thermal metallization with oxy-gas flame and detonation (HVOF) using tungsten carbide as filler material were used in this study.Hard chromium plating allows for high wear resistance thin layers to be produced, but the process is cumbersome and polluting. Thermal metallization allows the production of composite layers, of a chemical composition selected according to the operational demands, in much shorter times and at lower costs. In order to ensure a higher adhesion and to reduce the mechanical stresses at the support-hard layer interface, an intermediate layer of nickel was deposited in the case of samples loaded by thermal metallization with wire. In the paper, the microstructures in cross-section were analysed, the chemical compositions were determined on micro-zones related to the diffusion from the support material and the microhardness in the deposited metal and in the thermally affected zones was measured. These studies have shown that composite metallic layers displaying satisfactory mechanical and microstructural characteristics can be produced using alternative methods (thermal metallization) if optimum regime parameters are chosen.

Treatment of chromium plating process effluents with ion exchange resins

The surface treatment industry deals with various heavy metals, including the elements Cr, Zn, Ni, Cd, and Cu. Conventional treatments of effluents generate class I solid residue. The aim of this investigation was to study the viability of ion exchange as an alternative process for treatment of rinse water and to determine the efficacy of two ion exchange systems, System 1: “strong” cationic resin–“strong” anionic resin and System 2: “strong” cationic resin–“weak” anionic resin. Commercial resins and solutions taken from rinse tanks of chromium plating companies were used in this investigation. A two-column system, one for the cationic resin and another for the anionic resin, both with 150 ml capacity was mounted. The solution was percolated at a rate of 10 ml/min. The following solutions were used for regeneration of the resins: 2% H 2SO 4 for the cationic and 4% NaOH for the anionic. The percolated solutions revealed chromium contents of less than 0.25 mg/l, independent of the system used. The “strong” cationic resin–“weak” anionic resin gave excellent regeneration results. The “strong” cationic–“strong” anionic resin presented problems during regeneration, and did not release the retained ions after percolation of 2000 ml of 4% NaOH solution. It is concluded that for this type of treatment, the system composed of “strong” cationic resin and “weak” anionic resin is more appropriate.

Chromium plating process

Chromium plating process

Chromium plating pollution source reduction by plasma source ion implantation

There is growing concern over the environmental and workers' health issues due to the chemical baths and rinse water used in the hard chromium plating process. In this regard the significant hardening response of chromium to nitrogen ion implantation can be environmentally beneficial from the standpoint of decreasing the thickness and the frequency of application of chromium plating. In this paper the results of a study of nitrogen ion implantation of chrome-plated test flats using the non-line-of-sight plasma source ion implantation (PSII) process are discussed. Auger electron spectroscopy (AES) showed the implanted layer thickness to be about 2000 Å. Electron spectroscopy for chemical analysis (ESCA) indicated the formation of chromium nitride phase in the implanted layer. The wear resistance improves after implantation owing to both surface hardening and a decrease in coefficient of friction. Corrosion resistance in saline solution improved moderately after PSII treatment.

Size and Concentration Measurements of Particles Produced in Commercial Chromium Plating Processes

Abstract Optical measurements of particle size and concentration were made at the chromium plating tank and exhaust system at a commercial hexavalent chromium plating facility. Particles were examined at three locations in the exhaust system: 1) directly at the hexavalent chromium plating bath surface, 2) at the exit of a cyclone separator located in the exhaust system approximately three to four meters downstream of the bath, and 3) in the exhaust stack, downstream of the induced draft fan and all abatement devices. Particle diameters at the bath surface ranged from 0.3 to 25 μm. Downstream of the cyclone exit and mesh pad filters, particle top sizes were approximately 5 and 0.7 mm, respectively. On a mass basis, the collection efficiency of all abatement devices was 99.997%. Assuming that droplets in the flow consist primarily of water and chromium, correcting the total particle mass flow against water content gives a chromium emission rate of 64,000 μg/hr, which compares favorably with a value of 77,00...

Environmentally Acceptable Process for Electrodeposition of Hard Chromium From Chromium (III) Electrolyte

SummaryIn engineering applications the hexavalent chromium plating process provides excellent wear and corrosion resistant coatings (50–100 µm). However, this process is based on the highly toxic and environmentally unacceptable chromium (VI) electrolytes.Persistent attempts, over many years, have been made to deposit a thick coating of high quality chromium from environmentally more acceptable chromium (III) electrolytes to replace the chromium (VI) process. The most successful studies have shown that it is possible to produce thick coatings of chromium (III) electrolytes but due to the very slow rale metal deposition, falling to about 1 µ/hr, the process is unsuitable as a commercially viable hard chromium system.The present project has developed a laboratory scale high speed electrodeposition process based on chromium (III) electrolyte. This paper reports on an investigation in to the enhanced plating rate (300 µ/hr) using high flow rates and high current density system.Excellent quality deposits were obtained using this process. The quality, structure and properties of the deposits have been examined and related to the prevailing electrohydrometallurgical condition thereby providing quantitative and qualitative data on which to base the engineering design of an advanced environmentally acceptable plating system.

Utilization of ion chromatography and statistics to determine important acids in chromium plating and electropolishing solutions

Inadequate monitoring of sulfuric and chromic acids in chromium plating solutions and phosphoric and sulfuric acids in electropolishing solutions is a serious problem for the industry resulting in poor quality products and wasted resources. This is especially true for the narrow tolerances required to chromium plate cannon systems. Current online and offline instrumental analysis methods either do not result in acceptable precision or are time consuming. Two similar methods, which are improvements on existing ion chromatographic methods, are presented here that provides acceptable analysis and monitoring of these acids in this chromium plating process coupled with an extensive statistical evaluation of the experimental data. For chromium plating solutions, the resultant means and precisions are 2.50 ± 0. 11 g/l sulfuric acid and 250 ± 5 g/l chromic acid. For electropolishing solutions, these values are 685 ± 4 g/l phosphoric acid and 845 ± 5 g/l sulfuric acid.

Mathematical modeling of the diffusion chromium plating of steels in stationary and moving alloying mixtures

1. Mathematical models of the dependence of the thickness of the diffusion layer on carbon concentration and saturation temperature during the diffusion chromium plating of carbon steels are obtained. 2. The growth rate of the diffusion layer during the chromium plating of steels in a moving mixture is appreciably higher (by a factor of 2.5–4) than that during standard saturation in a stationary charge. 3. The activation energy of the chromium-plating process in a moving mixture is approximately 40% lower than that in the stationary mixture. Its value depends to a lesser degree on the saturation parameters (temperature and time) in the first case than in the second; this suggests a higher stability of the results of diffusion metallizing in a moving mixture.

ＨＥＥＦ硬質クロムめっき浴

ＨＥＥＦ硬質クロムめっき浴

Continuous hard chromium plating

A new continuous hard chromium plating process for plating long steel bars has been developed. The process is an application of the reduced pressure method, where the chromium electrolysis takes place in a separated process chamber under a pressure reduction of about 50 kPa.