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Over the last few years, the share of powder coatings used for the protection of aluminium extrusions and claddings for architectural uses in competition with conventional liquid paints and as an alternative to anodising has sharply increased. In 1987, about 47 million m2 or 135 thousand tons of aluminium used in outdoor architecture have been powder coated in France, Germany, Italy and United Kingdom. This paper gives a thorough description of the latest developments of the polyester powder coating systems used for aluminium extrusions and claddings in Europe, underlining the criteria of the choice of the weathering resistant powders, the importance of metal pretreatment and of the coating process itself as well as of the quality control in this industry. A comparison with competitive coating technologies is also given.

The title of this article would indicate that it's going to knock powder, or try to talk you out of using powder or even investigating powder. On the contrary, it is intended to help you investigate powder for your application by guiding your interest to certain areas where powder may be troublesome or unsuitable if misapplied.

Selective laser sintering (SLS) is a solid freeform fabrication process whereby a part is built layerwise by scanning a powder bed. The processability of metal powder varies depending on the state of the powder prior to SLS. A powder thermal pre‐treatment was developed which involved degassing the powder at an elevated temperature in a vacuum. Without powder thermal pre‐treatment, the powder may flow poorly and may “ball” or form molten clumps during the laser exposure rather than wetting into the present and previous layer. These effects result in SLS parts with poor surface finish, mechanical properties and density. The purpose of this study was to identify for titanium alloy powder the mechanisms responsible for the improvements obtained after powder thermal pre‐treatment and to optimize the thermal excursion.

This paper aims to describe a new process for suppressing the formation of orange peel, which is a polymer laser sintering (LS) process error.

The target for controlling the suppression of orange peel is securing the contact between the molten polymer and the surrounding powder. The authors set the powder bed temperature closer to the melting temperature than that for a typical LS. Alternatively, the authors use a low-power laser to irradiate the powder bed surrounding the parts being built. The surface finish of the built parts was evaluated using a three-dimensional scanner.

Both approaches were effective in suppressing orange peel. From the viewpoint of reusability of the used powder, the process that includes low-power laser irradiation is practical. The presence or absence of contact between the surrounding powder and the molten polymer determines whether the orange peel is formed.

The authors have not tested orange peel suppression for complex shapes.

The authors have demonstrated a concrete process that can suppress orange peel formation even for powders with low melt-flow rates. Furthermore, a mechanism for the formation/suppression of orange peel based on the experimental results was proposed.

More than two decades after their frist start the thermosetting powder coatings became in 1985 a technically viable product and a commercial success. Powder coatings are 100% dry paints that contain no solvents. They are generally applied to metal substrates by means of electrostatic spray equipment that provides each powder particle with a small electric charge, which in turn makes it stick to the substrate. The coated objects then go into a high temperature oven (usualy 150 to 200°C), where the powder coating melts and reacts chemically while sintering together to a continuous smooth finish of a thermoset film.

The purpose of this paper is to report a new method, the dissolution‐precipitation process, to prepare nylon‐coated metal powders for the indirect selective laser sintering (SLS) process.

The nylon‐12 coated carbon steel powders were prepared by the dissolution‐precipitation process. The powder characteristics are examined by scanning electron microscope (SEM) and laser diffraction particle size analysis. The effect of the applied laser energy density on the three‐point bend strength and dimensional accuracy of the SLS specimens are studied. The influence of nylon‐12 content on the bend strength are also investigated.

The SEM and laser diffraction particle size analysis results indicate that the steel particles are well coated by nylon‐12 resin. The bend strength of the SLS specimens increases with increasing the applied energy density until it reaches a maximum value, and then further increasing energy density will cause the decrease in the bend strength. The bend strength of the SLS specimens increases with increasing the nylon‐12 content over the investigated range. The dimensional errors in the X‐Y‐and Z‐directions are all increased with the increase in energy density.

This paper only concerns the preparation and SLS of the coated powders. Further investigations are planned into post‐processing, such as binder decomposition and high‐temperature sintering, of the green parts made from the coated powders.

This paper provides a useful method for preparing nylon‐coated metal powders for making metal parts by the indirect SLS process.

A non‐contact infrared temperature sensor was used to monitor the temperature–time relation of a point on the powder bed during laser sintering. The results were translated into a temperature–distance relation of the monitored spot with respect to its distance from the laser beam. The effect of particle size of polycarbonate (PC) powder on the temperature–distance relation was studied. The maximum temperature attained at the monitored spot was found to increase with decreasing size of the PC particles. The phenomenon was probably caused by the higher packing density of the smaller particles, and more laser energy was absorbed near the powder bed surface. The temperature–distance relations of some common additives such as graphite, quartz, silica and talc were also studied, and graphite was found to give the highest temperature distribution. PC/graphite composite powders were blended and sintered under similar conditions. The surface temperature of the powder bed increased greatly with the addition of a small amount (up to 2 per cent) of graphite powder. The result was attributed to the higher absorptance of CO₂ laser energy by the graphite powder.

Since the development of electrostatic powder spraying, powders based on epoxy resins have been the ones predominantly used. These powders have worked well in many cases and can be used for decorative as well as functional coatings. These coatings due, to the chemical nature of epoxy resins, are ‘thermosetting’. This means they not only undergo a physical change when heated, that causes them to melt and flow but they also undergo a chemical change that causes them to increase in molecular weight or ‘crosslink’. Once this happens they cannot be remelted if heated a second time. Due to the wide use of epoxy powders many people associate powder coating with thermosetting powder.

A solid freeform fabrication (SFF) technique is described where powder is deposited layer‐by‐layer using electrophotographic printing. In the electrophotography process, powder is picked up and deposited using an electrostatically charged surface. A test bed was designed and constructed to study the application of electrophotography to SFF. It can precisely deposit powder in the desired shape on each layer. A polymer toner powder was used to build small components by thermally fusing each layer of printed powder using a hot compaction plate. The feasibility of 3D printing using this approach was also studied by printing a binder powder using electrophotography on to a part powder bed.

The purpose of this paper is to acquire thermal conductivities of both fresh and preheated polyamide 12 powder under various conditions to provide a basis for effective and accurate control during the laser sintering (LS) process.

A Hot Disk® TPS 500 thermal measurement system using a transient plane source (TPS) technology was employed for thermal conductivity measurements. Polyamide 12 powder was packed at different densities, and different carrier gases were used. Tests were also performed on fully dense laser sintered polyamide 12 to establish a baseline.

Polyamide 12 powder thermal conductivity varies with packing density and temperature, which is approximately one-third bulk form thermal conductivity. Inter-particle bonding is the primary factor influencing polyamide 12 thermal conductivity.

Limited ranges of density were tested, and the carrier gas needed carefully control to prevent powder oxidation. Thermal properties obtained were not tested in the LS process.

This experimental result could be used to enhance thermal control during the LS process.