Real-time analysis is not possible because measurement times are too long The measurement technology is predominantly manual and ill-suited to automation or the process environment. Two cements with the same Blaine number may exhibit different performance characteristics. It is very well-established within the cement industry but has a number of important and widely recognised limitations: Correlations developed in the laboratory are being used to set more precise, relevant specifications for milling that, in combination with on-line analysis, deliver better product at lower cost.īlaine number is a surface area based parameter, quantified using an air permeability technique. Laser diffraction data correlate more sensitively with performance attributes such as strength and cure quality, and the technology is suitable for real-time measurement. The traditional measure for fineness is Blaine number, but increasingly cement producers are switching to laser diffraction particle size measurement. Milling circuits reduce the resulting clinker to fine cement. Composition is controlled by manipulating both the feed to the kilns and the reaction conditions, principally temperature. The successful implementation of either approach demands detailed understanding and control of the factors influencing product performance.Ĭement performance is a function of composition and fineness (particle size). Tightening and/or automating process control is an important strategy for reducing waste and energy consumption, as is the use of replacement materials, such as fly ash or blast furnace slag, in the final product. The scale of cement manufacture and its energy intensive nature are strong incentives for process improvement, to which the industry continues to respond. D 1 or D 99).Cement producers have found that switching from a conventional fineness measurement technique to laser diffraction particle size analysis provides more sensitive cement characterisation and better parameters for tuning product performance. The beginning and end of the distribution are commonly defined by D 10 and D 90, although other D values can be used to define the cumulative distribution as well (e.g. D 50 defines the point where 50 % of the particles are smaller and 50 % bigger than that certain diameter. In either direction, the cumulative curve always ranges from 0 % to 100 %, with the middle point D 50 being the most commonly reported result of particle sizing by laser diffraction. This is done either from the smallest to the biggest diameter (called the "undersize curve") or in the opposite direction (called the "oversize curve"). To get this distribution, values for all previous classes are added to the next. For this reason, usually the cumulative distribution is analyzed. spikey, flat, etc.), so peak values are rather unreliable. However, there might be more peaks or the peak might be weakly defined (e.g. The D mode value defines the position of the highest peak. The basic particle size distribution might have one or more peaks for size classes, which indicate the most common particle sizes. The sample de-agglomerates (breaks down into smaller sized particles) as particles collide with each other or with the wall of the dispersion unit.Ī typical result of a laser diffraction measurement is shown in Figure 11. In dry mode the powder is put into motion either by compressed air or by gravity, creating a dry flow which is positioned in front of the laser beam. The liquid dispersion unit is usually equipped with a mechanical stirrer with adjustable speed and with a sonicator with adjustable duration and power. The sample keeps circulating until the measurement is done. In liquid mode the particles are dispersed in a liquid and pumped into a glass measurement cell which is placed in front of the laser. it should be measured in liquid mode if the final product is a liquid dispersion and in dry mode if the final product is a powder. Usually a sample should be analyzed in a state relevant to its application, i.e. This means that each particle should be visible as a single particle in front of the laser, moving through either liquid medium or air. In order to get a clear diffraction, it is necessary to have a proper dispersion of the sample.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |