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Paints (surface coatings), primarily used to protect various substrates from the corroding action of acidic and alkaline substances, largely contain polymers as coating formulations. Examples of generally used polymers are: butadiene based (space), epoxy resins and silicone fluids (concrete vinyl polymers and polyurethanes (optical fibres) alkyds and acrylics (electronics) and polyester resins (wood, metal and fibre‐glass reinforcements). The binder‐pigment interaction controls important properties like hardness, flexibility, permeability, adhesion, gloss, and mechanical properties and contributes finally to the success or otherwise of the paint as a protective surface‐coating. Excellence of pigment dispersion and paint performance are thus intimately related.

Discusses the various methods that are used for measuring the viscosity of paints and inks in the laboratory environment and suggests what equipment is most suitable for different applications. Identifies the most common sources of errors in making measurements and emphasizes the importance of calibration in obtaining accurate and reproducible results.

Oil film thickness measurements made in the front main bearing of an operating 3.8 L, V‐6 engine were compared with rheological measurements made on a series of commercial and experimental oil blends. High‐temperature, high‐shear‐rate viscosity measurements correlated with the film thickness of all single‐grade and many multigrade oils. However, the film thickness provided by some multigrade oils were larger than could be accounted for by their high‐temperature, high‐shear‐rate viscosities alone. Although the pressure/viscosity coefficients of some of the oils were significantly different from those of the majority of oils tested, they were not oils which produced unusual film thicknesses. As a consequence, correcting oil viscosities for the esimated pressures acting within the bearing was unsuccessful in improving the correlations. The correlations were improved, however, by accounting for the elastic properties of the multigrade oils. Measurements of oil relaxation times at high temperatures and shear rates showed large differences in elastic properties among the test oils. A good correlation (R2 = 0.73) was obtained from a multiple linear regression of film thickness as a function of both high‐temperature, high‐shear‐rate viscosities and relaxation times.

A brief review of the conditions to which a crankcase oil is subjected during engine operation is given prior to a consideration of the relevance of the current SAE J300 viscosity classification to the needs of today's engines. Regarding the high‐temperature part, it is concluded that the current classification based on the low‐shear‐rate kinematic viscosity at 100°C provides a useful guide to oil consumption and a convenient means of evaluating used oils; it is, however, unsatisfactory as a guide to the fuel consumption and journal‐bearing performance of polymer‐containing oils. Whilst modification of J300 to include high‐shear‐rate viscosity limits could provide a classification relevant to the fuel consumption of such oils, knowledge of the complicated effects of both elasticity and viscosity on load‐bearing capacity, although increasing, is currently incomplete and it will be some years yet before J300 could be usefully modified to provide a guide to the rheological performance of oils in automotive journal bearings.

A series of articles dealing, in as simple a way as possible, with the basic facts of lubrication, lubricants, their selection and prescription, specification, application, and testing. This series is primarily intended for students, engineering personnel who may be unfamiliar with certain aspects and others who, one way or another, are interested in this important subject. Part One in our March Issue dealt with Friction, Lubrication and Wear. Part Two in our July Issue dealt with Mineral Oils and their Additives. Part Three, in our September and October Issues dealt with Lubricating Greases. Part Four commenced in our December Issue and is concluded here. Part Five will deal with Non‐Newtonian Flow, Grease Consistency and Shear Stability.

A series of articles dealing, in as simple a way as possible, with the basic facts of lubrication, lubricants, their selection and prescription, specification, application, and testing. This series is primarily intended for students, engineering personnel who may be unfamiliar with certain aspects and others who, one way or another, are interested in this important subject. Part One in our March 1965 Issue dealt with Friction, Lubrication and Wear. Part Two in July dealt with Mineral Oils and their Additives. Part Three, in September and October dealt with Lubricating Greases. Part Four in December and January covered the Purpose and Significance of Lubricant Tests.

Laser sintering kinetics and part reliability are critically dependent on the melt viscosity of materials, including polyamide 12 (PA‐12). The purpose of this paper is to characterise the viscosity of PA‐12 powders using alternative scientific methods: constrained boundary flows (capillary rheometry) and rotational rheometry.

Various PA‐12 powders were selected and characterised by both techniques. Measurement of molecular weight was also carried out to interpret the viscosity data.

Results demonstrate conventional pseudoplastic flow in all PA‐12 materials. Zero‐shear viscosity has been quantified by rotational rheometry; a notable observation is the striking difference between virgin/used PA‐12. This is interpreted in terms of molecular weight and chain structure modifications, arising from polycondensation of PA‐12 held at the bed temperature during laser sintering.

Accurate zero‐shear viscosity data provide scope for use in predictive computational models for laser sintering processes. Careful sample preparation and equipment operation are critical prerequisites for accurate rheological characterisation of PA‐12 powders.

Differences in flow behaviour and molecular structure allow prediction and deeper understanding of process‐property relationships in laser sintering, giving potential for further optimisation of material specification and in‐process machine parameter control.

This is believed to be the first time that techniques other than melt flow rate (MFR) have been reported to measure the viscosity of PA‐12 in a laser sintering context, noting the effects of pre‐drying and molecular weight, then predicting differences between virgin/used powders in practical sintering behaviour.