Wire coating by withdrawal from a bath of power law fluid

An analysis for withdrawal of cylinders from power law fluids has been presented for predicting the withdrawal speed for a desired film thickness. The theory has been compared with the previously published photographic and flow rate data of a low viscous Newtonian fluid for three values of N_GO and shows close agreement up to N_CA = 0.7. Comparison of the theory with the published experimental data on only one essentially inelastic fluid (n = 0.73) shows close agreement up to N_CA = 0.3. The disagreement at higher speeds is attributable to shear thinning of polymeric solutions.     

超高耐蚀性氯化钾镀镉防护层的制备

介绍了一种具有超高耐蚀性的氯化钾镀镉防护层的制备工艺,包括在金属基体上从内到外依次制备氯化钾镀镉层、铬酸盐低铬彩色钝化层和羟基石墨烯封闭层.在钢铁件上制备的这种防护层在中性盐雾试验中20160 h无白锈生成,27000 h无红锈生成.这为解决金属在热带海洋环境中的强腐蚀问题提供了新的解决方案.     

Conversion coating treatment for AZ31 magnesium alloys by a phytic acid bath

A phytic acid chemical conversion bath was applied to a sample of AZ31 magnesium alloy in this study; a transparent conversion coating formed subsequently on the sample surface. The test results of this coating with a scanning electron microscope (SEM) showed that there exist compact coatings on the surface of treated magnesium alloy. With the analyses of electronic probe microscopy (EPMA) and IR spectrum, a further study of this coating indicated that the coating was mainly composed of phytate and oxide or hydroxid. Furthermore, The electrochemical tests showed that the phytic acid bath conversion treatment enhanced the corrosion resistance of AZ31 magnesium alloys. The optimal pH of the phytic acid bath was 9.00–10.00.     

Studies on wire coating extrusion. II. The rheology of wire coating coextrusion

An experimental and theoretical study of wire coating coextrusion through a pressure-type die was carried out. For the experimental study, the wire coating apparatus employed was the same as that described in Part I of this series (14), except for the newly constructed coextrusion die. The die was provided with three melt pressure transducers along the axial direction, which permitted us to determine the pressure gradient in the die. It was found that a reduction in pressure gradient was realized when a lower viscosity polymer was coextruded with a high viscosity polymer. The materials used for the coextrusion were combinations of low-density polyethylene, high-density polyethylene, polystyrene, and two different commercially available thermoplastic rubbers (UniRoyal TPR-1900 and Shell Kraton G 2701). The use of a high shrinking (crystalline) polymer inside a low shrinking (amorphous) polymer was found to give rise to distorted coatings (non-circular cross section of the coated wire). The interface between the coextruded layers was examined under a magnifying lens, and it was found that under certain processing conditions, the interface was highly irregular. Experimental correlations were obtained to explain the onset of an unstable interface in terms of the rheological properties of the individual components being coextruded, and of the processing variables. It was found that interfacial instability occurs when the shear stress and the viscosity ratio (also elasticity ratio) of the two components at the interface exceed certain critical values. For the theoretical study, using a power-law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymers being coextruded. Solution of the system of equations permitted us to predict the velocity profile and shear stress distributions of two molten polymers inside a pressure-type wire coating coextrusion die. Comparisons were made between the experimental and theoretically predicted volumetric flow rates. The comparison was found to be reasonably good with certain systems. The discrepancy between the experimentally obtained and the theoretically predicted volumetric flow rates was attributed to interface migration and interfacial instability.     

添加剂对无氰电镀铜-锡合金(低锡)镀层性能的影响

通过赫尔槽试验与直流电解试验,研究了添加剂在焦磷酸盐溶液体系无氰电镀铜-锡合金(低锡)工艺中的作用.该体系镀液组成与工艺条件为:Cu2P2O7·3H2O 25 g/L,Sn2P2O7 1.0 g/L,K4P2O7·3H2O 250 g/L,K2HPO4·3H2O 60 g/L,温度25℃,pH 8.5,电流密度1.0 A/dm2.采用扫描电镜(SEM)、X射线衍射(XRD)、能谱(EDS)、中性盐雾试验等方法研究了添加剂对镀层组成结构、外观、耐腐蚀性能及微观形貌的影响.结果表明,焦磷酸盐溶液体系无氰电镀铜-锡合金(低锡)时使用有机胺类添加剂可抑制Sn的析出,使合金镀层致密均匀,耐蚀性能好.镀层结晶主要为Cu13.7Sn结构,镀层中Sn含量为9％～11％.镀液中添加剂的使用量增加,则合金镀层中的Sn含量降低.     

电压对电刷镀三价铬镀层性能的影响

在45钢表面电刷镀得到三价铬镀层,镀液组成和工艺条件为:Cr₂(SO₄)3·6H₂O 0.4 mol/L,甲酸铵0.5 mol/L,氨基乙酸0.5 mol/L,H₃BO₃ 0.6 mol/L,NaH₂PO₂·H₂O 0.3 mol/L,pH=1.5,温度50℃,镀笔移动速率15 cm/s。研究了电压对镀铬层显微结构、表面粗糙度、厚度、显微硬度和耐磨性的影响。随电压增大,镀层厚度增大,显微硬度和耐磨性均先提高后降低。电压为14 V时,镀层的表面平整,粗糙度为2.387μm,显微硬度为602 HV,耐磨性最好。     

Studies on wire coating extrusion. I. The rheology of wire coating extrusion

Wire coating extrusion was studied, both experimentally and theoretically, using a pressure-type die. For the experimental study, a wire coating apparatus of laboratory scale was constructed, consisting of a pay-off device, extruder, cross-head and pressure-type die, cooling trough, and take-up device. The materials used were low- and high-density polyethylenes and thermoplastic rubber. The following measurements were taken during the experiments: (1) the axial pressure profiles in the die, (2) melt flow rate, and (3) take-up speed. The measurements were then used to determine the effect of the rheological properties of the polymers on the performance of the wire coating operation. It was found that a reduction in axial pressure gradient and a reduction in the recoverable elastic strain of a molten polymer at the die exit can be realized as the speed of the wire is increased. For the theoretical study, using a power-law model, the equations of motion were solved numerically to predict the volumetric flow rate as functions of the pressure gradient in the die and the rheological properties of the polymer being extruded. Solution of the system equations permitted us to predict the velocity profile and shear stress distributions of a molten polymer inside a pressure-type wire coating die.     

High speed platinum deposition from a sulphamate formulation

A sulphamate based bath was identified as being suitable for high-speed platinum plating. The bath offers current efficiency approaching 70–80% and the deposits are bright in appearance. SEM examination showed that the grains are fine and XRD analysis indicates their grain size to be at the nano level. Cyclic voltammetric studies of the deposits indicate increased surface area. The properties of deposits obtained from sulphate and sulphamate formulations are compared.     

Finite element analysis of wire coating

A general-purpose finite element program has been used to simulate the flow of polymers through wire-coating dies. The analysis includes Newtonian and power-law fluids. The effect of normal stresses was examined through a simple viscoelastic constitutive equation, Nonisothermal wire coating was studied to obtain the temperature field within the melt. The effect of a slip condition at the solid boundaries was also examined. The determination of the coating melt free surface was carried out through an iterative procedure. The finite element solution provides details about the existence and extent of recirculation regions, about hot spots due to viscous dissipation, and also captures the stress singularities present at the impact of the melt with the wire and at the exit from the die. Pressure distribution, maximum temperature rise, haul-off wire tension, maximum wire tension, and stresses at the wire surface and die wall are also presented.     

Development of coating materials from liquid wax esters for wood top-based coating

Of late, UV-curable products are gaining attention in the wood industry because of the effectiveness and efficiency of this method. UV-curable surface coatings are widely used because of their excellent properties and because they are environmentally friendly products. In this study, immobilized Candida antarctica lipase B was used to catalyze formation of liquid wax esters, such as adipate esters, via a solvent-free process. The adipate esters formed were then used as UV-curable reactants in the wood coating formulations, consisting of epoxy acrylate, additives, and a photoinitiator. The performance of the products was evaluated by coating them onto glass tiles (using gel content, hardness, and scratch resistance tests) and wood panels (using adhesion, impact, and heat resistance tests). The coated film from this formulation performed well during the evaluation tests. The gel content exhibited more than 90% polymerization, while the pendulum hardness gave a value of 55.25%. Both analyses were significant in determining the effect of irradiation cycles. A scratch test was also carried out to verify the resistance of the coating. The maximum weight load which can be resisted by the wax esters formulation is 4.5 N.     

Stability of viscoelastic liquid curtain

Thin liquid sheets occur in several practical applications. In curtain coating, a thin liquid sheet is formed and falls freely over a considerable height before it impinges onto a moving substrate. Precision curtain coating was developed for multi layer photographic films but its use has expanded to many different applications. One of the important limits of this process is the stability of the liquid curtain, which may define the minimal thickness that can be coated at a given web speed.The condition at which a low viscosity Newtonian liquid curtain breaks was first derived based on a simple balance between inertial and capillary forces. There is a critical flow rate below which the curtain becomes unstable. For viscoelastic liquids, the normal stress related to the stretching of polymer molecules as the liquid accelerates down the curtain changes the force balance. Here, the critical condition at which a viscoelastic liquid curtain breaks was determined as a function of the rheological properties of the liquid. The results show that high extensional viscosity liquids create more stable curtains. Liquid additives could be used to push the limits of curtain flow rates to smaller values and consequently to widen the operability window of the process.     

Film casting of viscoelastic liquid

Melt film-casting is analyzed by means of a nonlinear integral constitutive equation that incorporates shear history effects, spectrum of relaxation times, shear thinning, and extension thinning or thickening. Film temperature and thickness profiles are predicted. The effects of shear-thinning, relaxation time, and die-design on the final film thickness are evaluated. Temperature variations are investigated by means of the pseudo-time concept. The process dependence on the rheological characteristics of the viscoelastic fluid, the die-design through the history effects, the conditions at the take-up end, and the film temperature is discussed. Predicted film and temperature profiles of casting of polypropylene are compared with experimental data taken from the literature.     

Sol-gel alumina coating of wire mesh packing

Wire mesh packings have seen increasing applications to multiphase processes in recent years. Despite the high surface area, open structure and thermal and chemical resistance, wire mesh packings have a complex geometry which hinders some chemical applications, including changes of surface properties through application of a uniformly adhesive coating. In this work, the sol-gel deposition method of alumina coating ceramics was investigated for the first time on stainless steel wire mesh by using Dixon rings as example. The kinetics of deposition during the hydrolysis and polycondensation was followed for a range of initial composition of the coating such as the ratios of Al₂O₃ to water, acid content, polyethyleneimine binder content and the number of deposition cycles. Well-adhered alumina with a thickness up to 20 μm was successfully deposited. The molar ratios of acid to alumina and alumina to water of 0.25 and 0.01, respectively, 48 h of the aging time, 96 h of the mixing time and 2.1 g/L of polyethyleneimine binder formed a free of cracks coating of controlled thickness alumina on the Dixon rings.     

酸性氯化铵镀锌层变色问题研究

从镀液硫脲含量以及钝化后的烘烤和封闭工艺这三方面探讨了酸性氯化铵体系镀锌层的变色问题。结果表明,镀锌液中硫脲含量过高和钝化膜干燥不彻底均会导致镀层变色。对钝化膜进行封闭处理可有效防止镀锌试样变色。     

Corrosion protection of stainless steel by a new and low-cost organic coating obtained from cashew nutshell liquid

In this work, the corrosion protection of 316L steel was promoted by an electro-synthesized polymer obtained from the technical cashew nutshell liquid (t-CNSL). Spectroscopic techniques confirmed the polymer formation. The polymer was dispersed in the ethyl acetate solvent and used to form coatings on 316L steel substrates. The coated samples were subjected to electrochemical tests in a saline environment. The coated electrode with poly(t-CNSL) polymer was exposed to the corrosive medium for 24 days, and superior corrosion protection was observed compared with the uncoated sample. The open circuit potential measurements showed that the coated sample possessed a more positive corrosion potential when compared with the uncoated substrate. The electrochemical impedance spectroscopy results indicated that the coated electrode's polarization resistance (R_p) recorded ~1.0 MΩ cm² after 24 days of exposure. A decrease in polarization resistance was observed with the exposure time due to the presence of micropores in the t-CNSL coating. The polarization curves exhibited that the coated electrode with poly(t-CNSL) has lower corrosion current density and less negative corrosion potential than the uncoated steel electrode. Therefore, t-CNSL favors the manufacture of thin poly(t-CNSL) coatings for corrosion protection purposes besides being a low-cost material.     

Isometric nonsteady flow of a viscoelastic liquid in a spinneret capillary

Conclusions Nonsteady flow of a viscoelastic liquid which obeys the DeWitt rheological equation in the capillary of a spinneret for spinning man-made fibres has been studied.It has been found that the flow regimes for a polymeric liquid with constant pressure drop and with constant flow rate differ sharply in their character. In the first case, the flow rate of liquid fluctuates with time from plus to minus values; in the second, the pressure drop in the liquid increases monotonically. A fluctuating process for the profiles of lengthwise liquid velocities unifies the two cases of flow.Translated from Khimicheskie Volokna, No. 5, pp. 32–34, September–October, 1987.