Search results

The purpose of this paper was to improve the frictional wear resistance properties of piston skirts caused by the low viscosity lubricant by studying the tribological performance of three novel coating materials.

Comparative tribological examinations were performed in a tribological tester using the ring-block arrangement under two viscosity lubricants, the loading force was applied as 100 N, the speed was set to 60 r/min and the testing time was 180 min.

Under low viscosity lubricant, the friction coefficient and wear of the three coatings all increase, and the friction coefficient and wear of the PTFE coating are the largest, while the MoS₂ coating has the lowest friction coefficient and wear. Under low viscosity lubricant, the friction coefficient of the MoS₂ coating is 2.1%–5.4% and 20.0%–24.3% lower than that of the SiO2 and PTFE coating, respectively. The friction coefficient and wear fluctuation rate of the MoS₂ coating is the smallest when the lubricant viscosity decreases, which indicates that the MoS₂ coating has excellent stability and adaptability under low viscosity lubricant.

To reduce the piston skirt wear caused by low viscosity lubricant in heavy-duty diesel engines, the friction and wear adaptability of three novel composite coating materials for piston skirts were compared under 0 W-20 low viscosity lubricant, which could provide a guidance for the application of wear-resistant materials for heavy-duty diesel engine piston skirt.

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.

The purpose of this study is to determine the material extrusion (MEX) printability envelope of a new kind of low-viscosity powder-binder feedstocks using rheological properties.

Formulation of 13 feedstocks (variation of solid loading 60–67 Vol.% and thickening agent proportion 3–15 Vol.%) that were characterized and printed at different temperatures.

Three rheological models were successfully used to define the viscosity envelope, producing stable and defect-free printing. At a shear deformation rate experienced by the feedstock in the nozzle ranging from 100 to 300 s^–1, it was confirmed that metal injection molding (MIM) feedstocks exhibiting a low viscosity between 100 and 150 Pa s could be printed using an extrusion temperature as low as 85 °C.

MEX can be used in synergy with MIM to accelerate mold development for a new injected part or simply as a replacement for MIM when the cost of the mold becomes too high for very small production volumes.

Correlation between the rheological properties of this new generation of low-viscosity feedstocks and MEX printability has been demonstrated for the first time.

The use of alternative oils for the lubrication of automobile engines has a potential of ecological and technical advantages. It requires the detailed knowledge of several thermophysical and viscosimetric properties in a large temperature range.

For 11 different oils, the density, the heat capacity, the thermal conductivity, the viscosity at ambient pressure and the pressure‐viscosity at maximal 1,000 bar have been measured. The latter has been measured with a newly developed apparatus which is described in detail. Two hydrocarbon‐based factory‐fill oils and nine alternative oils have been tested. Five of the alternative oils are based partly or completely on esters, the other four on polyglycols, one of them additionally on water.

Data for thermophysical and viscosimetric properties are given in form of diagrams and tables. The consequences for the cooling capacity and the film forming behavior are discussed. The latter is only slightly better for the factory‐fill oils, compared to the alternative oils.

The pressure‐viscosity is measured at up to 1,000 bar, which is lower than the maximum pressure in the tribological contacts of an engine.

The published data can be used to calculate tribological contacts which are lubricated with alternative engine oils or with actually used factory‐fill oils. This might help to decide if esters or polyglycols are superior as engine oils.

The results of this test program might be helpful for engineers who are interested in using alternative lubricants in tribosystems.

ONE WINTER MORNING, many years ago, we observed with interest a road tank wagon belonging to one of the large oil companies being towed round a piece of waste land by a stable companion, in an endeavour to bring its reluctant engine to life. The vehicle with the dead engine bore a slogan in large letters which read : “Use Pratts for Easy Starting”.

The interaction between the silver powder and organic vehicle largely determines the rheological behavior of silver conductive paste. This study aims to prepare silver conductive paste with an organic vehicle system consisting of ethyl cellulose (EC) and terpineol/butyl carbitol acetate solvent mixtures. The study also aims to measure the rheological behaviors of the silver conductive pastes with different solvent mixtures, EC molecular weights and silver content, to investigate the interaction among the polymer, solvent and silver powder and determine the main factors affecting the thixotropic index and maximum silver content.

The rheological behaviors of silver conductive pastes with different solvent mixtures, EC molecular weights and silver content were investigated using viscometer.

The shear thinning became significant with increasing EC molecular weight. The EC solvation with higher molecular weight in solvent is better than that of EC with lower molecular weight. This leads to a stronger interaction between the silver powder and EC with higher molecular weight and consequently good silver particle dispersion. The relative viscosity of silver conductive paste at 10 s⁻¹ increases significantly with increasing silver content, but the relative viscosity at 100 s⁻¹ is much less sensitive to the silver content. The viscosities at low and high shear rate can be increased by increasing the silver content and EC molecular weight, respectively.

The interaction among the polymer, solvent and silver powder was investigated for the silver paste with high solid content. The main factors affecting the viscosities at high and low shear rates, thixotropic index and maximum silver content were determined.

Industrial cellulose nitrate, sometimes called pyroxylin, collodion cotton or nitrocotton, is made by treating cellulose in the form of cotton (inters (threads) or woodpulp with a large excess of mixed nitric and sulphuric acid controlled to fine limits as regards strength of acid and the time and temperature of the nitration. Following a water washing process, the nitrocellulose is partially dried and the remaining water displaced by the selected damping medium — industrial methylated spirit, isopropanol or butanol. For certain purposes the nitrocellulose is damped with water.

THE function and behaviour of a lubricant on certain parts of an internal‐combustion engine is so complex that the knowledge on this subject is still very incomplete. After several years of experimentation both with specially designed apparatus and with actual engines, the authors of these notes have reached certain conclusions which they will here endeavour to record. Some of the conclusions must, nevertheless, be regarded as opinions only, since lubrication in all its forms is not yet an exact science. For instance, the exact means by which oil lubricates a piston‐ring reciprocating within a cylinder remains very obscure. The action of the lubricant at the rings and in some bearings, such as at the gudgeon‐pin, does not lend itself to mathematical treatment because the conditions are not constant. The alternate sliding and stopping is not a strictly continuous process, and neither the “fluid” nor the “boundary” theories of lubrication can be satisfactorily applied.

Increasingly stringent European market requirements for improved heavy duty diesel engine performance, such as fuel economy and durability, continue to highlight the need for higher performance engine lubricants. To meet this need, new additive technology is being used in combination with higher quality base‐stocks and has resulted in a growing trend towards the use of oils of lower viscosities than those used in the past. Such a trend has led to some concern over the ability of low viscous oils to maintain adequate engine wear protection, not only during extended service operations but also under the more severe conditions of low temperature engine start‐up. This paper describes the results of a recent study to evaluate the effect of base oil composition and viscosity grade on the low temperature performance of a modern Euro II diesel engine with respect to wear, using the technique of Thin Layer Activation. Engine test results showed that the use of full synthetic SAE 5W40 grade oils based on Polyalphaolefin provided enhanced low temperature cylinder liner wear protection.

This work aims to provide additional insights regarding the practicability of using conventional materials in the fused filament fabrication (FFF) process.

Two different acrylonitryle butadiene styrene (ABS) grades are studied and compared, aiming to check to what extent the regular ABS developed for conventional polymer processing, with a different rheology than the one provided for the FFF process, can also be used in this process (FFF).

The rheological results show that a general-purpose ABS (ABS-GP) melt is much more viscous and elastic than ABS-FFF. It is clear that using ABS-GP as feedstock material in the FFF process results in poor coalescence and adhesion between the extruded filaments, which has a detrimental effect on the mechanical properties of the printed specimens. Despite its lower performance, ABS-GP can be a good choice if the objective is to produce an aesthetical prototype. If the objective is to produce a functional prototype or a final part, its mechanical performance requirements will dictate the choice.

This work provides insightful information regarding the use of high viscosity materials on the 3D printing process.