Search results

The results of trial experiments carried out with a computer simulation model of total reflection X‐ray fluorescence, TXRF system to determine optimum conditions for detecting certain elements of interest under various analytical conditions in a given ten‐element standard sample is presented in this paper. Results of these trial experiments show that the detectability of elements improved with increasing applied voltages up to about 43kV (for a Molybdenum anode TXRF spectrometer) and atomic number of elements. Variation of geometry such as the glancing incidence angle of the excitation beam reflected slight increase in minimum detection limit, MDL values as the angle of incidence is reduced from an optimum value of 1.6mradian to 1.0mradian. The nature of the sample support was observed to affect the detectability of the elements as good detection limits were obtained if gold is used as sample holder..

A new time‐domain reflectometry measurement method is described that provides accurate measurements of the average high‐frequency (0.1GHz ‐ 10GHz) dielectric constant of printed wiring board materials and is suitable for “factory floor” use. A parallel‐plate transmission line is used for the sample geometry. Only simple numerical processes are required to extract the characteristic impedance and dielectric constant of the sample from the acquired data. The long‐term measurement reproducibility and short‐term measurement repeatability of the method are described.

With the increased use of surface‐mounted devices, both the component density and the board complexity are greatly increased on many circuit pack assemblies. Good solderability for the components as well as for the printed circuit boards has become one of the most important elements in achieving the ultra‐high efficiency and quality required of an assembly soldering process in today's competitive environment. Solderability evaluation generally uses the ‘dip and look’ method that relies entirely on the individual inspectors' often inconsistent interpretations resulting from the examination of the specimen dip‐tested in a molten solder bath. This method is subjective, so the results can vary from person to person and from day to day. In addition, the sensitivity of such a method is inadequate in discerning the differences in solder wetting characteristics of very small device leads and terminations. Consequently, components with marginal or even bad solderability may pass through inspection and move onto the production line to cause many easily avoidable defects and their subsequent repairs. A sensitive and quantitative wetting balance method has been studied with the purpose of developing a better alternative to the ‘dip and look’ procedure. Special sample holders and test conditions have been developed for testing various types of components and printed circuit board coupons. Examples of solderability testings are provided to illustrate the capability of the instrument when proper testing procedures are followed. More effort is under way to simplify the test procedure, and to establish a practical solderability test standard for the wetting balance method.

The ever‐increasing need for circuit boards places equally heavy demands on the control laboratory to prepare and examine sufficient polished cross‐sections for process analysis. High production facilities require large numbers of polished cross‐sections to meet the demands of industrial or military specifications. Manual sample preparation methods are totally inadequate to provide sufficient numbers of samples fast enough to prevent processing of material that is defective. Additional manual devices, technicians and expanded work areas are not capable of meeting the quantity or time demands imposed by high production. However, a system has been devised that addresses the shortcomings of manual sample preparation and provides an efficient, cost effective means of producing very large quantities of polished cross‐sections in a meaningful turn‐around time.

This paper aims on a methodology to overcome the fact that conventional service life testing of porous journal bearings (PJBs) requires long test times and is not economical.

This paper sketches out a pathway to strongly accelerated life tests for PJBs enabled by high load and elevated temperature, which saves months or even years of testing. The testing time is not only reduced to a few weeks, but the results are also statistically secured via a multiple test rig construction of a custom-made tribometer.

An exemplary bearing-lubricant combination is tested in the mixed lubrication regime, where the coefficient of friction is monitored during the test.

A Weibull curve is fitted to the experimental results to show the survival probability of the combination over time.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0351/

To improve productivity and reach better quality in assembling, measurements and proper process controlling are a necessary factor. This study aims to focus on the monitoring heat-level-based vapour phase reflow soldering (VPS), where – as it was found – different thermocouple constructions can affect the set parameters of the oven and resulting soldering profiles significantly.

The study experiments showed significant alteration of the heating profiles during the process of the reflowing using different construction of k-type thermocouples. In a heat-level-based VPS oven, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) gas and water-resistant, fibreglass, thin PFA and ultrathin PFA-covered thermocouples were tested with ±1 °C precision. The oven parameters were swept according to the heating power; the length of the introduced thermocouple cables was also taken into account. An FR4-based sample PCB was used for monitoring the temperature.

According to the results, due to the mass and volume of the thermocouples’ wires, different transients were observed on the resulting soldering profiles on the same sample PCB. The thermocouples with lower thermal mass result in faster profiles and significantly different heating factor values compared to the thermocouples that have larger thermal mass. Consequently, the length of the thermocouple wires put in the oven has also considerable effect on the heat transfer of the PCB inside the oven as well.

The paper shows that the thermocouple construction must be taken into account when setting up a required soldering profile, while the thermal mass of the wires might cause a significant difference in the prediction of the actual and expected soldering temperatures.

The purpose of this paper is to analyze the moisture measurement techniques presently available, as accurate determination of the moisture content (MC) of grains or any food items at right time is very important for its processing, marketing and storing.

There are basically two types of MC measurement techniques – destructive method and non-destructive method. In the time-consuming destructive method, cleaning of the food items is done and shells of food items like peanuts are removed for which man power is required and so the technique becomes costly. A literature review of the existing non-destructive methods has been done, and the methodology of each approach is explained with the figure. The less time-consuming non-destructive technique used to measure MC require less man power, as grains or food items can be directly used without any process like cleaning or crushing so that the technique become economic.

Most of the techniques used magnetic or electric properties to measure the MC indirectly. The problem with existing non-destructive technique is that measurement of MC uses only few numbers or grams of grains or food items at a time.

The farmers’ produce large quantity of grains. The small quantity of grains cannot be the representative sample for whole grains produced by the farmers. Most of the techniques use only small quantity of grains or food items at a time to measure the MC which is not accurate and representative of the produce. Also, the techniques are not simple and easily available. The cost of the techniques or arrangement to measure the MC is not reasonable.

Most of the farmers in the developing countries are financially backward. To store the agricultural produce, MC of the commodities is a key factor influencing the quality of the storage. Measurement of the MC of the seeds is thus very important for the farmers.

This paper is a review of the previous research that happened in this area, and it would help the researcher to know the techniques already been used. To the knowledge of the authors, the review of the existing moisture measurement of seeds/agricultural commodities is available in the literature.

The main purpose of this work is to explore the erosion wear characteristics of additively manufactured aluminium alloy. Additive manufacturing (AM), also known as three-dimensional (3D) manufacturing, is the process of manufacturing a part designed in a computer environment using different types of materials such as plastic, ceramic, metal or composite. Similar to other materials, aluminum alloys are also exposed to various wear types during operation. Production efficiency needs to be aware of its reactions to wearing mechanisms.

In this study, quartz sands (SiO₂) assisted with oxide ceramics were used in the slurry erosion test setup and its abrasiveness on the AlSi10Mg aluminum alloy material produced by the 3D printer as selective laser melting (SLM) technology was investigated. Quartz was sieved with an average particle size of 302.5 µm, and a slurry environment containing 5, 10 and 15% quartz by weight was prepared. The experiments were carried out at the velocity of 1.88 (250 rpm), 3.76 (500 rpm) and 5.64 m/s (750 rpm) and the impact angles 15, 45 and 75°.

With these experimental studies, it has been determined that the abrasiveness of quartz sand prepared in certain particle sizes is directly related to the particle concentration and particle speed, and that the wear increases with the increase of the concentration and rotational speed. Also, the variation of weight loss and surface roughness of the alloy was investigated after different wear conditions. Surface roughness values at 750 rpm speed, 10% concentration and 75° impingement angle are 0.32 and 0.38 µm for 0 and 90° samples, respectively, with a difference of approximately 18%. Moreover, concerning a sample produced at 0°, the weight loss at 250 rpm at 10% concentration and 45° particle impact angle is 32.8 mg, while the weight loss at 500 rpm 44.4 mg, and weight loss at 750 rpm is 104 mg. Besides, the morphological structures of eroded surfaces were examined using the scanning electron microscope to understand the wear mechanisms.

The researchers verified that this specific coating condition increases the slurry wear resistance of the mentioned steel. There are many studies about slurry wear tests; however, there is no study in the literature about the quartz sand (SiO₂) assisted slurry-erosive wear of AlSi10Mg alloy produced with AM by using SLM technology. This study is needed to fill this gap in the literature and to examine the erosive wear capability of this current material in different environments. The novelty of the study is the use of SiO₂ quartz sands assisted by oxide ceramics in different concentrations for the slurry erosion test setup and the investigations on erosive wear resistance of AlSi10Mg alloy manufactured by AM.

The electrical properties related to the hydration of the hydrotalcite‐type lamellar compound Zn2Al(OH)6Cl.nH2O are such as to permit the realisation of a humidity sensor. The sensor is achieved by depositing thick film by the screen‐printing technique. First, the means of forming the material is optimised. Two types of sensor are then realised, one working with direct current, the other with alternating current. The performance of each device is studied by means of specified experiments. The authors create a new measurement cell for calibrating the alternating current sensor. Response time measurements are carried out, and results are interpreted and compared.

The paper aims to present an investigation of heating during vapour phase soldering (VPS) on inclined printed circuit board (PCB) substrates. The PCB is a horizontal rectangular plate from the aspect of filmwise condensation with a given inclination setting.

The paper focuses on the measurement of temperature distribution on the PCBs with a novel setup immersed in the saturated vapour space. The measuring instrumentation is optimized to avoid and minimize vapour perturbing effects.

The inhomogeneity of the heating is presented according to the lateral dimensions of the PCB. The inclination improves temperature uniformity, improves heat transfer efficiency; however, a minor misalignment may affect the flow and result in uneven heating.

The results can be implemented for practical improvements in industrial ovens with the use of intended inclination. The improvements may consequently point to more efficient production and better joint quality.

The novel method can be used for deeper investigation of inclination during and can be complemented with numerical calculations. The results highlight the importance of precise PCB holding instrumentation in VPS ovens.