A. Marchese, A. Papo and G. Torriano
Summary Chlorinated rubber primers formulated with active pigments, which are claimed to be non‐toxic and non‐polluting, are investigated; they are designed for the protection of…
Abstract
Summary Chlorinated rubber primers formulated with active pigments, which are claimed to be non‐toxic and non‐polluting, are investigated; they are designed for the protection of ships (above the waterline), port installation, industrial plants, bridges, etc.
Previous articles in this series have described some of the techniques that are used to characterise paint film properties. In many instances results from such tests are used…
Abstract
Previous articles in this series have described some of the techniques that are used to characterise paint film properties. In many instances results from such tests are used predictively, that is they yield information on the likely performance of the coating during service. It is however, widely accepted that the most accurate way of determing performance is to actually subject the coating‐substrate combination to the service conditions it will meet in practice, or a close approximation to them. Suitability can then be assessed by periodic inspection and/or by taking measurements of some appropriate parameter which might be expected to change with time. A great many techniques have been developed and refined over the years that are intended to replicate service environments in some simplified and reproducible way; an indication of the range of test methods that can be employed to this end can be seen in a recent article by El‐Sawy. Many of these techniques are suitable for the laboratory and range from simple immersion tests in appropriate solutions through to exposure testing in controlled environment cabinets. Because of the problems of interpreting the results from laboratory simulation testing though, exposure of test panels in the natural environment is also widely practiced. This, the last article in this series, will consider some of the recent literature concerning environmental testing, with particular reference to techniques appropriate for assessing the weather, marine and corrosion resistance of coatings.
For any paint or coating system performance in service is determined by the whole formulation, with each of the individual ingredients contributing either directly or by…
Abstract
For any paint or coating system performance in service is determined by the whole formulation, with each of the individual ingredients contributing either directly or by interaction to the overall balance of film properties. Within these constraints, paint formulators recognise that certain materials have a well defined role to play and in many instances a consideration of a coatings service requirements does largely dictate the initial approach to formulation. One such ‘key’ group of materials are the pigments added to anticorrosive paints to provide protection to metallic substrates under aggressive conditions of exposure. One group of these pigments inhibit corrosion by perturbing in one of a number of ways the chemical reactions that would otherwise occur on the substrate surface in the presence of water. Other types of protective pigments function by improving the barrier properties of the applied paint film so that water cannot readily permeate through and initiate corrosion reactions on the substrate. Pigments in this group typically have a flake‐like particle shape which enables a ‘leafing’ effect to be achieved within the liquid coating after application. The inhibitive types of pigment need to be in close proximity to the substrate to function properly, and accordingly these are normally placed in primer coats only. The flake pigments which reduce moisture permeation through the film are most effective if added in depth, and these are often added to severa or all of the coats comprising a system, or are included as the sole protective pigment in high‐build paints. Recent developments in both of these broad groups of inhibitive and flake pigments will be considered in this article.
The previous three reviews in this series have considered recent developments in the pigments and extenders used in surface coatings; the next two articles will be concerned with…
Abstract
The previous three reviews in this series have considered recent developments in the pigments and extenders used in surface coatings; the next two articles will be concerned with the other essential ingredient, the polymer component. The polymer is the media that binds the other constituents of the formulation together and forms an adherent film on the substrate being coated. This vital component also provides many of the necessary chemical, mechanical and durability properties required for the coating to provide an effective level of performance in its service environment.
M. Deyá, V.F. Vetere, R. Romagnoli and B. del Amo
The efficiency of two anticorrosive pigments containing aluminium polyphosphate was studied. Pigments were analysed by current analytical techniques and characterised by FT‐IR…
Abstract
The efficiency of two anticorrosive pigments containing aluminium polyphosphate was studied. Pigments were analysed by current analytical techniques and characterised by FT‐IR spectrometry. The anticorrosive properties of the selected pigments were evaluated following the electrochemical behaviour of a steel electrode in pigments suspensions. In a second stage, solvent‐borne paints with 30 and 10% v/v of the pigment and PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ratio 0.8 were formulated. Three resins were chosen as film forming materials: an alkyd, an epoxy and a vinyl. The performance of the resulting anticorrosive paints was assessed by accelerated (salt spray cabinet and humidity chamber) and electrochemical tests (corrosion potential, ionic resistance and polarisation resistance). The anticorrosive performance of the tested paints was closely related with pigment composition. The nature of the resin was also of importance; in this sense, epoxy paints showed the best anticorrosive performance. Good correlation has been obtained between accelerated and electrochemical tests.
The rheological properties of a coating are important determinants of storage, application and flow characteristics and, as such, the need for its accurate measurement is an…
Abstract
The rheological properties of a coating are important determinants of storage, application and flow characteristics and, as such, the need for its accurate measurement is an important requirement in formulation development. Measurement of rheology is also an important phase of quality control testing, though frequently less sophisticated, more rapid, characterisation techniques may sometimes be used here. This article will consider some of the literature concerned with techniques of measuring coating rheology.
Salts of aluminium and calcium such as stearates, octoates and naphthenates, are used to impart structure to oleoresinous paints. Alternatively, aluminium alcohoiates can be used…
Abstract
Salts of aluminium and calcium such as stearates, octoates and naphthenates, are used to impart structure to oleoresinous paints. Alternatively, aluminium alcohoiates can be used as reactive intermediates which form salts by reaction with the medium. The use of these materials is generally restricted to flat or semi‐gloss paints and storage instability is sometimes encountered. A chlorinated rubber paint which contains titanium, kaolin, talc, a chloroparaffin plasticiser, and a solvent blend of hexyl acetate and xylene, is rendered thixotropic using a 1% level of aluminium stearate addition. The product is suitable for applying as thick corrosion‐resistant coatings to metals.
Alexandre Lamoureux and Bantwal R. (Rabi) Baliga
The purpose of this paper is to first present the key features of hybrid numerical methods that enable cost-effective simulations of complex thermofluid systems, and then…
Abstract
Purpose
The purpose of this paper is to first present the key features of hybrid numerical methods that enable cost-effective simulations of complex thermofluid systems, and then demonstrate the formulation and application of such a method.
Design/methodology/approach
A hybrid numerical method is formulated for simulations of a closed-loop thermosyphon operating with slurries of a micro-encapsulated phase-change material suspended in distilled water. The slurries are modeled as homogeneous mixtures, with inputs of effective properties and overall heat-loss coefficients. Combinations of an axisymmetric two-dimensional (2D) control-volume finite-element method and a segmented-quasi-one-dimensional (1D) model are used to achieve cost-effective simulations. Proper matching of the solutions at the interfaces between adjacent axisymmetric 2D and quasi-1D zones is ensured by incorporating and heuristically determining suitable lengths of pre- and post-heating (and also pre- and post-cooling) sections.
Findings
In the demonstration problem, which would strictly require full three-dimensional simulations of the fluid flow and heat transfer phenomena, the proposed hybrid 1D/2D numerical method produces results that are in very good agreement with those obtained in a complementary experimental investigation.
Originality/value
The hybrid numerical methods discussed in this paper allow cost-effective computer simulations of complex thermofluid systems. These methods can therefore serve as very useful tools for the design, parametric studies, and optimization of such systems.
Details
Keywords
Coatings science represents one of the best examples available of the importance of an interdisciplinary approach. The organic chemist must provide polymers, solvents, and many of…
Abstract
Coatings science represents one of the best examples available of the importance of an interdisciplinary approach. The organic chemist must provide polymers, solvents, and many of the additives used in paint formulation. The organic chemist also must provide some of the pigments. The inorganic chemist must also provide pigments and extenders. How these components come together to form a paint and how that paint may be successfully applied to a surface is the realm of the physical chemist. The metallurgist is very much involved in making receptive the metal surfaces onto which coatings are placed. The cellulose chemist similarly has a contribution to make where wooded substrates are involved. The physicist is involved in the colour considerations associated with coatings, and one would be remiss to omit from this list, which admittedly is not complete, the empiricist. Many of the observations on which paint technology is based have been made empirically and to this day are without complete scientific basis. It is for this reason if for no other that scientific studies in the paint industry are extremely important.
Stephan Klomberg, Ernst Farnleitner, Gebhard Kastner and Oszkár Bíró
The purpose of this paper is to present a new computational fluid dynamics model for large electrical machines to simulate the heat transfer at specific components to the…
Abstract
Purpose
The purpose of this paper is to present a new computational fluid dynamics model for large electrical machines to simulate the heat transfer at specific components to the appropriate ventilation method. The most damageable parts for overheating in generators are the end winding bars, pole windings and stator ducts.
Design/methodology/approach
The reduced model introduced is basically derived from the state-of-the-art pole section model (PSM) and enables faster computations for heat transfer and cooling simulations of electrical machines. The fundamentals of the two methods and the grid generation are described. Two PSMs and four different reduced models are presented and compared among each other to tune the reduced model.
Findings
As a topic of outstanding interest in large hydro generators, the heat transfer at the end winding bars is solved with the aid of the reduced model. This slot sector model (SSM) has been validated and the computation time has been reduced enormously in comparison to the state-of-the-art PSM.
Research limitations/implications
The heat transfer has been carried out only for the end winding region of large hydro generators. The effect of the reduced model on the pole sections and stator ducts has not been investigated. Nevertheless, the reduced model is also valid for large motors.
Practical implications
This reduced model can finally be used for parametric studies with different cooling schemes and boundary conditions in the design process.
Originality/value
The comparison of various SSMs to PSMs shows an acceptable accuracy of the reduced model in combination with a rather low computation time. Due to modeling one slot only, the MFR-MP approach is an adequate and fast analyzing method for this kind of model structure.