Cake Strength Research Articles

Characterisation of spray dried soy sauce powders made by adding crystalline carbohydrates to drying carrier

This study aimed to reduce stickiness and caking of spray dried soy sauce powders by introducing a new crystalline structure into powder particles. To perform this task, soy sauce powders were formulated by using mixtures of cellulose and maltodextrin or mixtures of waxy starch and maltodextrin as drying carriers, with a fixed carrier addition rate of 30% (w/v) in the feed solution. The microstructure, crystallinity, solubility as well as stickiness and caking strength of all the different powders were analysed and compared. Incorporating crystalline carbohydrates in the drying carrier could significantly reduce the stickiness and caking strength of the powders when the ratio of crystalline carbohydrates to maltodextrin was above 1:5 and 1:2, respectively. X-ray Diffraction (XRD) results showed that adding cellulose or waxy starch could induce the crystallinity of powders. Differential Scanning Calorimetry (DSC) results demonstrated that the native starch added to the soy sauce powders did not fully gelatinize during spray drying.

Flowability Properties of Labisia Pumila Herbal Powder

This paper investigates the flowability properties of Labisia pumila (L. pumila) powder. Material properties of the powder and their influence on flowability were discussed. L. pumila, a popular Malaysian herb with therapeutic and medicinal functions was compressed into tablets using a stainless steel cylindrical uniaxial die with 13 mm diameter and compaction pressures of 7 to 25 MPa. Two feed weights, 0.5 and 0.7 g were used to form tablets. Compaction strength and density increased as compaction pressure increased resulting in tablets porosity reduction. Cohesion index, flow stability and caking strength were also determined to enhance the understanding of flowability properties of the L. pumila powder.

Stamped and pressed coal cakes for carbonisation in by-product and heat-recovery coke ovens

Coking of coal blends using high volatile coals with poor coking abilities to produce a high quality coke for blast furnace application can be achieved by compacting the coal blend prior to the carbonization process. Here densification up to a relative material density of 80%, i.e. a compact density around 1100kg/m3, has proven to be advantageous. Coal is compacted by stamping, if the so-called stamp charging process applied. Compacting of the coal by pressing is used in case of the cokemaking with so called heat-recovery ovens.Stamped and pressed coal cakes require over the cake volume uniform high density and mechanical stability. Besides the aspects of the coal selection, the efficiency of the process is mainly determined by the operating parameters compacting time and compacting energy for coal cake making and by the sufficient cake mechanical stability to ensure trouble-free charging the ovens.At the Department for Mechanical Process Engineering & Solids Processing of the Technical University Berlin the two sub-processes of densification and strengthening during stamping and during pressing are theoretically and experimentally investigated using specially developed lab-scale compacting test units for stamping and for pressing and a coal cake strength test device.Describing cake density in terms of coal properties for a given coal and measured compacting energy input then leads to a compacting equation with the so-called Stampability as the integral model parameter for the stamping process. For the pressing process the cake density can be calculated with the measured compacting pressure and the Compressibility factor, respectively. Investigations were carried out to provide evidence of a significant influence of coal type, coal surface moisture, coal granulometric properties on the densification process.In order to investigate the mechanical strength properties of the stamped and pressed coal cakes, a specific strength tester has been developed, combining the possibilities of investigating compressive/tensile strength as well as shear strength.Based on the tests on the densification behaviour and cake strength for a given coal, the stability criterion of a coal cake with the required density and height can now be calculated.

An experimental and numerical study of packing, compression, and caking behaviour of detergent powders

This paper presents an experimental and numerical study of the packing, compression, and caking behaviour of spray dried detergent (SDD) powders with a two-fold aim: an experimental process of observation and evaluation of the packing, compression and caking behaviour of SDD powders, and a numerical approach based on discrete element modelling (DEM). The mechanical properties, including the stress–strain response and the corresponding porosity change as a function of consolidation stress in a confined cylinder, the stress–strain response during unconfined shearing and the cake strength as a function of consolidation stress, were evaluated and compared for different SDD powders using an extended uniaxial tester (Edinburgh Powder Tester – EPT). The experiments using EPT showed excellent reproducibility in the measurement of packing, compression and caking behaviour and were therefore very useful for describing the handling characteristics of these powdered products including screening new products and different formulations. It was found that the sample with higher moisture had lower bulk porosity but higher compressibility and cake strength. The porosity, compressibility and cake strength were found to vary across different size fractions of the same sample. The larger sieve-cut samples had higher initial bulk porosity, compressibility and cake strength. It is revealed that moisture plays a significant role in packing, compression, and shearing behaviour of the powder. Three-dimensional DEM modelling using a recently developed elasto-plastic adhesive-frictional contact model showed that the contact model is able to capture the detergent behaviour reasonably well and can be used to model complex processes involving these powders.

A new environmental bulk powder caking tester

Bulk powder transformations, such as caking, can lead to numerous problems within industry when storing or processing materials. The extent of bulk powder caking may vary significantly due to a number of factors, such as time, environment and mechanical conditions. However, there are few caking testers available for rapidly conditioning a sample and monitoring time-dependent consolidation behaviour whilst providing a final measure of caking. In this paper a new bulk powder tester is introduced. The tester is placed within a temperature controlled chamber and has conditioning air at a desired relative humidity percolating through a powder bed to rapidly expose a sample to desired equilibrium moisture content. The temperature and relative humidity at the inlet and exit of the powder bed are recorded. The height of the sample is logged as a function of time during consolidation in order to analyse powder bed response to environmental conditions. Finally, the caking tester has been developed to easily open to expose the caked sample without causing significant disturbance. A sensitivity study with a hygroscopic powder has been performed to evaluate the ability of the caking tester to differentiate caking propensity of the material exposed to various conditions. It is shown that at different environmental and mechanical conditions the caking tester can differentiate caking behaviour with both the in-situ creep measurement and cake strength, which is measured at the end of the trial. Using this approach, the cake strength is shown to depend on sample consolidation, while the extent of consolidation is related to the environmental and mechanical conditions to which the sample is exposed.

Glass transition and flowability/caking behaviour of maltodextrin DE 21

Maltodextrin DE 21 is a spray dried amorphous powder that is commonly used as an ingredient in the food industry. The powder or an ingredient mix containing the powder can form very strong cakes if exposed to certain consolidating pressures and climatic conditions. In particular, it was believed that the glass transition can influence its caking behaviour. Consequently, the focus of this study was to investigate the influence of exposing maltodextrin DE 21 powder to temperatures around its glass transition and to measure its flowability or cake strength using a ring shear tester. To enable this work, the influence of water content on the onset glass transition temperature was measured along with the sorption isotherm of the powder. The ring shear testing showed that the maltodextrin powder readily formed a very strong cake over time when it was exposed to temperatures that were at or above its onset glass transition temperature. Maintaining the powder temperature at 4°C below its glass transition should prevent the powder from caking.

Characteristics of soy sauce powders spray-dried using dairy whey proteins and maltodextrins as drying aids

This study investigated the effect of adding whey protein isolate (WPI) as a complementary drying aid of maltodextrin (MD) on spray drying of soy sauce powders. Soy sauce powders were prepared by spray drying soy sauce liquid adding 5%, 10% and 15% of WPI respectively together with MD as the drying aids. Tests were conducted to evaluate the powder properties relevant to the caking issue of the soy sauce powders. Results showed that addition of just 5% WPI could significantly increase the product yield for the spray drying process. At the same time, the caking strength of the spray dried soy sauce powders were significantly reduced during storage with WPI addition. XPS results indicated that WPI have preferential migration to the surface of the soy sauce powder. The over-expression of WPI on powder surface after spray drying might explain the improved stability for soy sauce powders during the caking test.

Comparison of a Uniaxial Force Displacement Tester with a Ring Shear Tester for Assessing Powder Cake Strength

This article highlights the use of a novel easy to use uniaxial force displacement tester (FDT) for measuring powder cake strength. A comparative study was undertaken of the FDT with a standard ring shear tester (RST) for measuring the cake strength of a powder. The powder used in the study was maltodextrin DE 21 which is an amorphous powder which readily cakes at temperatures at or above its glass transition. The powder was first equilibrated at 50% relative humidity over a five month period and it was then exposed to temperatures at and above its glass transition. The powder cake strength was measured using both the FDT and RST and the measured results were compared. The results showed that the cake strengths measured by the FDT correlated well with those of the RST. This demonstrated that the FDT is a realistic, easy to use method for assessing the cake strength of a powder.

Dewatering and Utilization of Fly Ash Slurries Using Geotextile Tubes

About one billion metric tons of coal ashes are produced annually around the world, among which 700 million tons are fly ash wastes that must be disposed of. The practice of wet fly ash disposal has increased environmental concerns due to fly ash leachate, ground water contamination, and the limitation of pond capacity. Therefore, alternatives to the current disposal methods should be addressed. Geotextile tube dewatering is an efficient dewatering method that can decrease the volume of fly ash slurry and at the same time provides containment of dry fly ash. In this study, pressure filtration tests were conducted to evaluate the dewatering performance of Class C fly ash with seven woven geotextiles having a wide range of hydraulic properties. Anionic polymer flocculant was used to evaluate the effect of polymer conditioning on dewatering performance. In addition, the increase in filter cake strength due to flocculants was evaluated. Lastly, chemical analysis of the effluent was performed to quantify the concentration of contaminants present in the geotextile tube effluent. The results of this study indicate that hydraulic properties of the geotextile do not have a significant effect on the dewatering performance of fly ash. It was found that polymer conditioning significantly increased the strength of the filter cake, making fly ash filled geotextile tubes suitable for use in geotechnical engineering applications. It was also found that geotextile tube dewatering does not retain fly ash trace elements that can leach out with effluent, meaning that proper safety measures must be taken in fly ash reutilization projects.

Characterization of Cohesive Cake Formation and Stickiness of Starches at Various Water Levels in the Presence of Palm oil and Palm Oil Fractions

A key feature of the biscuit manufacture is the combination of the raw ingredients. Different oils are likely to change the quality of dough. The factors important in agglomeration of starch materials are poorly understood and therefore work was carried out to try and establish the behaviour of oil and water on the material properties of starches. An understanding of particle-particle behaviour in the presence of oils and water is relevant to a food production process such as biscuit making, that requires preparation and mixing of these ingredients at ambient conditions. The way these powders pack and flow could have a significant impact on the final quality of the product. Powder flow analyser was used to measure the caking and cohesion properties for different type of starches. Besides the powder type as a variable, three levels of water and four types of oils at 5 % (d.b) concentration were also tested. The presence of water with the powder plays an important role for the way the cereals powders pack and flow. Although tapped bulk densities did not vary much the water had a great impact on the powder caking strength and cohesion index. For samples without oil, the results showed that these parameters were increased significantly as the water level increased for all starches. Plasticization by addition of water to the food powder is believed to be the major factor contributing to the results obtained. Addition of oil to starches increased the caking and cohesion indices where liquid oils showed the greatest impact compared to solid oils.

Characterization of spray-dried soy sauce powders using maltodextrins as carrier

Soy sauce powders were made by spray drying liquid soy sauce using maltodextrin as the drying aid. Three types of maltodextrin, i.e. DE 5, DE 10 and DE 15, were studied and compared. Each type was incorporated into soy sauce with concentration levels of 20% and 40% (w/v), respectively, as a carrier. The spray-dried soy sauce powders were mixtures of amorphous substances and crystalline salts. Caking related properties including particle size distribution, hygroscopicity, glass transition temperature, flowability and caking strength of the powders were characterized. Soy sauce powders produced from the feed solution of maltodextrin concentration of 40% had a larger particle size dispersion, reduced hygroscopicity, higher glass transition temperatures and smaller cohesive index than their 20% concentration counterparts. Maltodextrin of a smaller DE value produced soy sauce powders with less cohesion, higher glass transition temperature and reduced hygroscopicity. Maltodextrin concentration and DE value greatly influenced the caking strength of the soy sauce powders, with different mechanisms and effects under different storage conditions.

Assessment of powder flow characteristics in incoherent soup concentrates

Soup mixtures represent specific flow characteristics while particles of different sizes and properties form a homogeneous mixture. In such mixtures, particle–particle interactions differ with addition of different fat types. This study was done to present a characterization and comparison of the cohesion index, powder flow speed dependency and caking properties of four different aggregates of fat particles with three different moisture contents, used in various compositions of powdered soup concentrates. ESEM micrographs have shown that different fat types bind particles differently. The moisture content of cream soup concentrates has a significant influence on cake height ratio of all cycles – more moisture causes higher cake height ratios (from rs=0.86 to rs=0.76; p<0.05). Cream soup concentrates cake strength values are also significantly influenced by the mixtures moisture content – higher moisture content samples showed higher cake strength values (rs=0.73, p<0.05). There is a significant correlation between compaction coefficients of all speeds and cake height ratios of all cycles for the cream soup concentrates. Combination of measuring techniques (Powder Flow Analyzer, ESEM and Mastersizer) together with Spearman’s Rank Order Correlation, as a method of non-parametric statistics, provides parturient results in characterization of extremely non-homogenous powder mixtures.

Simulation of potash cake strength by discrete element method

After potash ore has been mined and processed it is stored and shipped as bulk granular particles. If these particle beds are exposed to a relative humidity that is above 50%, moisture will accumulate in the bed. This causes the formation of concentrated brines on the surfaces of the particles that migrate toward the contact points between particles. If drying occurs crystal bridges at or near the contact points will form between particles. If large numbers of bridges are formed per unit volume of bed, the bed is said to be caked. In this paper, the Discrete Element Method (DEM) is used to analyze the micro-mechanical behaviour of ideal spherical or ellipsoidal particles inside a potash bed and these results can be used to determine the cake strength. Hertz contact compressive stress theory is applied at each contact point between particles to resolve the stiffness matrix in the DEM analysis. The results of the DEM analysis compare well to those obtained using continuum mechanics, especially when Poisson's ratio has a low value. After potash ore has been mined and processed it is stored and shipped as bulk granular particles. If these particle beds are exposed to a relative humidity that is above 50%, moisture will accumulate in the bed. This causes the formation of concentrated brines on the surfaces of the particles that migrate toward the contact points between particles. If drying occurs crystal bridges at or near the contact points will form between particles. If large numbers of bridges are formed per unit volume of bed, the bed is said to be caked. In this paper, the Discrete Element Method (DEM) is used to analyze the micro-mechanical behaviour of ideal spherical or ellipsoidal particles inside a potash bed and these results can be used to determine the cake strength. Hertz contact compressive stress theory is applied at each contact point between particles to resolve the stiffness matrix in the DEM analysis. The results of the DEM analysis compare well to those obtained using continuum mechanics, especially when Poisson's ratio has a low value.

Comparing the caking behaviours of skim milk powder, amorphous maltodextrin and crystalline common salt

This work examined and compared the caking behaviour of three physically and chemically different food powders. The food powders studied were maltodextrin DE21 which is an amorphous powder, common salt which consists of crystalline NaCl, and skim milk powder (SMP) which contains a mixture of components including 51% lactose. The three powders were all exposed to high relative humidities (76% or 100%) over a 1-week period and to a humidity cycle to investigate their caking behaviour and interpret their caking mechanisms. The humidity cycle consisted of 2-day exposure to a high relative humidity (RH) followed by 2-day exposure to low RH of 11% and finally 2-day exposure to the original high RH. At the end of each day, cake strength was measured using a force displacement tester and cake water content was also measured. All three powders sorbed much water when exposed to high relative humidities; however, their cake strengths were very different. Cake strength was influenced by glass transition and the ability of the powders to form sinter bridges. All three powders had similar water content profiles during the humidity cycle with water gain at high RH and loss at low RH. The cake strength profile of the amorphous maltodextrin powder and amorphous SMP were different even though the maltodextrin and lactose glass transition temperatures were reduced below the powder temperature during exposure to high RH. The cake strength of maltodextrin decreased during low RH exposure while it increased for SMP. The cake strength profile of the SMP was similar to the crystalline NaCl. The paper presents an interpretation of the caking mechanisms behind the caking behaviour of each powder.

Handling properties of cereal materials in the presence of moisture and oil

Abstract A powder flow analyzer attached to a Texture Analyser (Stable Micro Systems, UK) was used to compare the flow behaviour of four cereals systems: maize and wheat (in both starch and flour forms), as functions of particle size and distribution, water content and the addition of different types of oil. It was expected that the smaller the particle size the higher the tendency to stick (because of less free volume between the particles), but that was not the case. The results showed that wheat starch used, with bigger particle size than maize starch, had higher cohesion properties and as water content increases the cohesion increases by the same magnitude. This was attributed to the differences in granular shape as well as protein quantity and quality. Caking strength for both starches was influenced by the water content; in particular at 30% water content (w/w), neither cohesion nor caking indices could be measured for wheat starch because of the high stickiness of the particles. Although the two flours had particles of very similar sizes, with differences in the distributions only, maize showed higher cohesion indices compared to wheat flour. These values decreased with increasing water content. The caking property for maize was not significantly affected by water content with values of approximately 100 ± 5. The caking strength increased for wheat flour from 8 to 500 as moisture increased from 12.5 to 30%. This was ascribed to the differences in hydration properties of the two flours. For wheat flour and as the water content increased, gluten started to form and would require more than 30% to form a homogenous, visco-elastic mass. Generally, cohesivity and cake forming ability were affected by water content as well as the physical state of the oil i.e. by the solid/liquid ratios. As water content increases, wheat starch showed the greatest packing and cohesive behaviour, with and without the oil, while maize flour exhibited the weakest packing and cohesive properties.

Stamped coal cakes in cokemaking technology: Part 2 – The investigation of cake strength

Coking of coal blends using high volatile coals with poor caking properties to produce a high quality coke for blast furnace application can be achieved by compacting the whole coal blend before the pyrolysis in the so called stamp charge operation. Using stamp charging not only improves the flexibility of the cokemaking plant using cost efficient raw materials, but also increases oven throughput. Therefore, in recent years, densification of coals has been introduced even to coals with good carbonisation properties when heat recovery ovens are used. At the Department for Mechanical Process Engineering and Solids Processing of the Technical University Berlin, the two subprocesses, densification and strengthening during stamping, were theoretically and experimentally investigated. The research work aims on the development of an integrated mathematical model, allowing the calculation of cake density and strength of the coal cake for a given coal blend and as a function of the stamping energy. In the first part of the paper, investigations on the stampability of coal blends were reported. In this paper, the development of a new strength test device for the systematic investigation of mechanical strength of coal compacts produced by stamping is described. Results from compressive strength tests indicate an elastic–plastic behaviour with failure by plastic fracture. Shear test results show similarity to the yield limit description in soil mechanics.

The Relationship between Cake Strength of Potash Fertilizer and Initial Moisture Content, Particle Size, and Drying Time

In this study, a new correlation for the cake strength of potash as a function of initial moisture content, particle size, and drying time is developed. The correlation is based on the experimental data collected by Wang et al. (2006) and Gillies et al. (2006). For initial moisture content ranging from 0.25% to 6% (w/w), particle size ranging from 0.85 to 3.35 mm, and drying time constant ranging from 7 to 1900 min, the correlation shows that strength is linearly related to the product of the initial moisture content, X i , the inverse square of mean particle diameter, d pm , and , where t c is the drying time constant.

Understanding powder caking: Predicting caking strength from individual particle contacts

The chemical, pharmaceutical and food industries generate an average output of 300,000 tonnes of solid products per company per year. Caking of these products is therefore a major concern to the industry. This paper concentrates on caking due to crystal bridges formed under the influence of humidity. Using the micro–macro approach, it is shown how the bulk strength of caked solids can be predicted from individual particle contacts. The individual particle contact measurements are performed in a new test device, the DAPP system, built for particles in the half-millimetre size range. For the modelling, a contact-dynamics model was adapted to caked systems. It proved important to use the complete crystal bridge strength distribution in the simulation. Under these conditions modelling and validation experiment coincided to a factor of two.

Modelling crystal growth between potash particles near contact points during drying processes. Part II: Analysis, results, and comparison with experimental data

AbstractCaking of bulk granular materials is a serious problem that affects many industries including the mineral processing industry. Caking occurs when bulk materials undergo wetting and drying cycles and it has been thought that it occurs due to the formation of new crystal bridges between individual particles. In the first paper in this series a mathematical model is developed for the crystal formation process that occurs at the contact point between two particles. In Part II, numerical simulations of the model are used to determine the effects of changes for several independent parameters in this model: initial moisture content; rate of evaporation of the salt solution from the particle surface; relative size of the contact region compared to the initial film thickness of salt solution; and supersaturation levels near the contact point. Non‐dimensional graphical curves of these simulations are used to compare the effects of each parameter for the deposition of salt crystals near the contact point. These results, when compared to data for cake strength in potash specimens which were obtained for various initial moisture contents, drying rate, and chemical composition of the particle surfaces, show good qualitative agreement even though cake strength and mass recrystallization near a contact point are different physical phenomena. The numerical results show that the mass of crystal deposition near the contact point will increase with increased initial moisture content and decreased evaporation rate. It is also found that variations in the degree of supersaturation near the contact point causes significant variations in the crystal mass deposition near the contact point.

Comparative Evaluation of Flow for Pharmaceutical Powders and Granules

The objective of the present work was to carry out a systematic evaluation of flow of pharmaceutical powders and granules using compendial and non-compendial methods. Angle of repose, bulk density, tapped density, Carr's compressibility index, and Hausner ratios were evaluated. Additionally, flow was characterized using a powder rheometer in which a sensitive force transducer monitors the forces generated as a result of the sample displacement. The critical attributes such as cohesivity index, caking strength, and flow stability were determined for samples. The samples consisted of different grades of magnesium stearate powder including bovine, vegetable, and food grade, physical mixture powder blend consisting of a model formulation, granules prepared by various methods including slugging, high shear granulator, and fluid bed dryer. Lubricant efficiency was also determined for granules lubricated with various concentrations of magnesium stearate. It was observed that the compendial methods were often non-discriminating for minor variations in powder flow. The additional characterization such as cohesivity, and caking strength were helpful in understanding the flow characteristics of pharmaceutical systems. The flow stability test determined that the powders were not affected by the test conditions on the rheometer. The non-compendial tests were discriminating to even minor variations in powder flow.