8 9 Dissolution can be improved by improved. Even high viscous material can be fed through the feeder and discharger smoothly. This is often not taken into account and can result in arching or ratholing in storage bins or silos, blockage of chutes, flooding of hoppers and other problems that may affect the performance of the plant. Attempts to initiate flow, such as use of vibration on hopper with rubber mallet or increasing powder paddle feeder, did not work. Flow problems, such as ratholing, arching, and erratic flow, can be eliminated with appropriate container geometry. Dimensions to Prevent Arching: Mass Flow Bin. The key to feeding cohesive materials in a screw feeder is with the use of Flow Aids. Conducting studies. g. Ratholes develop most often in conical hoppers that are not steep enough to produce flow at the walls. Flow aids are used to return to a more regulated flow pattern and are relatively inexpensive. Cleveland Vibrator Company offers a range of solutions for manufacturing and processing powder products from bin vibrators, feeders and conveyors to screeners for 10 micron and up. 10). Erratic flow results when ratholes collapse, causing the powder to arch as it impacts the out-let. However, when the fine iron is held inside a coagulation of powder, then it could be held out of the reach of the maximum magnetic force. Traditional powder testing methods cannot force the bridging to occur in a repeatable manner and thus they cannot discriminate flow differences between powders. forms. Powder strength is measured as “yield stress” by shearing particles trapped in the lid pockets against particles in the shear cell. 1. Unstick material and promote even flow. 2 Calculation of the Minimum Required Outlet. Ratholing: can occur in a bin when the powder empties through a central flow channel, but the material at the bin walls remains stagnant and leaves an empty hole (rathole) through the material, starting at the bin outlet (Fig. 5). 89-0. The gyrators also reduce particle segregation to make sure each bag is completely. Test results allow a formulator to determine required hopper outlet dimensions that will prevent flow stoppages, hopper angles necessary to prevent ratholing, and outlet sizes required to achieve. Powder Feeding. Ratholing/ funneling 5 Inconsistent flow 3 Electrostatics Flowability Compaction . c 3 Critical condition for flow. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. Ratholing, another flow arresting situation, is when material directly above the outlet flows but the rest of the powder mass closest to the walls does not, creating a tunnel. This type of flow pattern is indicative of uniform, first-in-first-out flow, where ratholing, erratic flow, segregation, and flooding problems are mitigated. 5D Hopper: A converging sloping wall section attached to the bottom of a silo. Containment. Jenike, who pioneered the theory of bulk solids flow at the University of Utah in Salt. The principles discussed in this chapter can be applied to analyzing new or existing equipment designs. n 1. TheFlowability is the ability of a powder to flow, and it is measured as the time in seconds necessary for a given volume of powder to leave a rotary drum through a slit of a certain size. Eliminate bridging, rat holes, stuck material and uneven flow in chutes and pipes. 2 feet 2. Bulk solids and powder flow properties testing is considered mandatory when designing screw conveyors and screw feeders for handling difficult to manage products. /d. Flow occurs in most powder-based processes, opposed by various cohesive forces. Keep in mind that the mass-flow bin design process is iterative. Membrane adsorbers, bioreactors, and mixing. 11. Equipment for powdered metals, ceramic powders, pigments, chemicals, super-abrasives. Figure 1: Manufacturing pharmaceutical tablets and capsules involves several powder handling steps. Bridging is the name given to the self- created arch that develops just above the outlet of a bulk material silo or hopper as it empties. • Low-maintenance because of few wear points. 1 Funnel flow bins When a fine powder is stored in and discharged from a bin having a funnel flow pattern, ratholing and flooding problems are almost inevitable. Rotoflo is designed to help with material handling ensuring that silo discharge is free-flowing and controlled when handling a number of diverse materials. If you are experiencing issues with dust in your manufacturing facility, it is probably due to open processing. Mass-flow bin. 2 pg 266. The powder influences the silo by the flowability of powder causing bridging and ratholing. The most common and serious problem is no-flow, due to arching or ratholing [6], [7]. Absolute flow factor: FLA = FLR * ρb0. Do you suffer from Bin Rash? When Material gets clogged in Bin, Hoppers and Silos, do you bang your hoppers with hammers? It is not a great solution and it c. Santos et al. A Brookfield Powder Flow Tester, equipped with Powder Flow Pro software for automated instrument control and data acquisition, was used to test this name brand baby formula. If the object is to maintain material flow only, fewer vibrators may be used. The purposes of this investigation were to develop a method to evaluate flow properties of powders from avalanching tests and to detect similarities and relationships between. ‘Rat-holing’ (shown in Figure 2a) is the principle flow obstruction in a core-flow vessel where the powder in the flow-channel above the outlet discharges and leaves a stable. View our Flow Solutions Video! One of the most common problems with bulk material flow is a condition known as ratholing. Erratic flow results when ratholes collapse, causing the powder to arch as it impacts the out-let. Consequently, meas-urement of the wall friction characteristic of a. Figure 3: Stagnant, cohesive powders can form a stable rathole in funnel flow. Figure 10. 26. Topics covered in this lecture include flow problems due to arching and ratholing, flooding issues, limiting discharge rates and segregation problems. m. Pacific, Joe Marinelli, president, Solids Handling Technologies Inc. Generally, flow is limited to a central flow pattern. Silo: A tall bin, where H > 1. Figure 1: Manufacturing pharmaceutical tablets and capsules involves several powder handling steps. Bulk solids and powders frequently encounter various flow challenges, including bridging, ratholing, flooding, and inadequate flow rates, and more. Besides that, powder flow can be determine by the angle of repose make by the powder itself when poured onto a flat surface throughout the hopper. Valves & Actuators. To avoid problems in silos concerning flow, product ageing or decay, silo design is necessary. In most cases, the vessel or bin can be attached to a vibrator, which shakes the vessel to pack the powder together. Typically, they are used when flow by gravity alone will not work or when it is impractical to provide the design that is required for reliable flow. The silo influences the powder via the silo diameter, height and the angle of the hopper. Ratholing of powders can occur in a container (silo, hopper, IBC, mixer vessel) when the powder empties through a central flow channel. However, in powder pressing industries (e. Air Cannons For Solving Tough Material Flow Problems. Flow problems related to food powders, such as arching, ratholing and erratic flow are thoroughly described and reviewed by Marinelli (2005). The flow of powder in a hopper is linked to 3 properties : The powder internal friction : how easy the powder particle can move from each other. 363 14. Ratholing: can occur in a bin when the powder empties through a central flow channel, but the material at the bin walls remains stagnant and leaves an empty hole (rathole) through the material, starting at the bin outlet (Fig. This was attributed to the fact that the poor flowability of APAP could cause ratholing and high flow variations, especially when the powder. , will present "Solids Flow Properties That Affect Your Feeder Design" as part. Critical Rathole Diameters, Df, ft—“D” is the diameter of the opening required to collapse a rathole, while “f” stands for funnel flow. Larger particles are more likely to penetrate the surface than fine particles. Air pads may be needed to move the first material and merely gravity or small vibrations can be sufficient for the second. pharmacopeial methods to characterise powder flow. We can clean your silos, hoppers & vessels. A commercial system to study avalanching in powders was first described by Kaye et al [18]. Typical powder flow issues found in the hopper are ratholing, bridging and segregation. za NNNEL FLOW i. Unload and produce good faster in your production process. The vane lid is used to perform the flow function test. As the level of fly ash in the flow channel drops, a resistance to further flow into this channel occurs due to. Wall friction, internal friction and bridging properties determine the applicable hopper angle and opening diameter. In practice, this group of bulk materials is the most common. Material Flow Solutions, Inc. A mass flow screw feeder prevents preferential flow which can lead to ratholing and arching problems. Resources. In powder technology, the flow conditions are from. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. Only with a not too poorly flowing bulk solid might it be possible that flow obstructions occur somewhat less often in asymmetric funnel flow silos compared to symmetric ones, because lessDetermine wall slopes for mass flow, by measuring the friction that develops between a bulk solid and any hopper wall material. Motor with gear suitable for running at 30 rpm. ), and dry, uniformly-sized larger materials will be free flowing. g. Flow agents are used to enhance the flow behavior of solids by reducing the inter-particle adhesion force. Frequently encountered problems include: bridging, leading to no flow/erratic flow/stoppages; flooding (uncontrolled flow); segregation; and funnel flow/ratholing (flow through the core of the. POWDER FLOW DATA The equipment consisted of a custom-built laboratory scale hopper feeding material in a controlled manner onto a. This results in a no-flow. . Robert Sedlock. 4. , 2003). powder becomes deaerated in the stagnant region of a funnel flow bin, it usually develops 2. Cocoa powder storage in silos, hoppers and bins can be fraught with blockage problems such as bridging and 'ratholing' because of its cohesive. to 11 a. When a stable rathole develops, the bulk material remaining in the vessel is stagnant and will not discharge. Buildup in the Silo is an Indication of Ratholing. The finest fraction did not flow through a Hall flowmeter, then. A _______ provides a signal that simulates the signal from load cells at various weights. This type of flow pattern is indicative of uniform, first-in-first-out flow, where ratholing, erratic flow, segregation, and flooding problems are mitigated. The purposes of this investigation were to develop a method to evaluate flow properties of powders from avalanching tests and to detect similarities and relationships between these data and conventional powder flow properties. Powder flow obstruction during hopper/bin discharge, such as arching or ratholing, remains an outstanding risk and cannot be reliably diagnosed using the existing flow function coefficient-based method. Prevent segregation with mass flow. Generally, flow is limited to a central flow pattern. Our comprehensive line of feeding technology can provide: high and low feed rates, batch, continuous, high. The reason for this is that when a powder becomes deaerated in the stagnant region of a funnel flow bin, it usually develops Ratholing: can occur in a bin when the powder empties through a central flow channel, but the material at the bin walls remains stagnant and leaves an empty hole (rathole) through the material, starting at the bin outlet (Fig. In this work, the piping flow of cohesive granular materials in a flat-bottomed silo is investigated using finite element method (FEM). The purposes of this investigation were to develop a method to evaluate flow properties of powders from avalanching tests and to detect similarities and relationships between these data and conventional powder flow properties. Problems with Hoppers • Ratholing/Piping and Funnel Flow • Arching/Doming • Insufficient Flow • Irregular flow • Inadequate Emptying • Time Consolidation. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. These problems can result in limited live capacity. You would think after all these years that our industry would realize that there is a scientific approach to solids handling and therefore silo design. 1 Funnel flow bins When a fine powder is stored in and discharged from a bin having a funnel flow pattern, ratholing and flooding problems are almost inevitable. diam Mini Disk fits in pipes, chambers, chutes, and small hoppers with curvatures as small as 4 in. flow rate through an orifice compressibility index and hausner ratio angle of repose shear cell. m. Eur. powder addition easier. 2. Numerous cement plants are plagued with bulk solids flow problems like bridging, ratholing, and flooding, each of which can negatively impact production efficiency. 8 B), F > 63 and F > 90 had practically equal outlet diameters (1. powder becomes deaerated in the stagnant region of a funnel flow bin, it usually develops 2. 2. Purutyan H. The flow channel drains material in the middle first. Valves & Actuators. This can disrupt your production line. For example, when conveying powders that tend to cake or pack, it will be necessary to feed the aeromechanical conveyor from an infeed hopper of steep-wall design that encourages material flow along the hopper walls and prevents bridging and ratholing of the material. The critical arching dimension, of 5. Joe will describe uses for liners such as TIVAR 88 and 2B stainless steel along with coatings such as electrostatic powder coatings and Plasite 7122 epoxy coating. at the Tech Theatre (Booth 127). The bin activator works discharges not over the full covered area, but only in a small unpredictable area and coarse ratholing. (710, 500, 355, 250, 180, 125, 90 and 63 μm, sieves Retsch) using a sieve shaker (Retsch AS 200 digit, Germany) with a vibratory amplitude of 2 mm [40]. Silos and hoppers are particularly prone to this issue if the. The primary design objective when determining the bin geometry is to ensure that bulk solid or powder will flow with the effects of gravity, and without flow obstructions occurring. The entire process is user-controlled and transparent: Diagrams and extrapolations. The orifice flow behaviours had thus corroborated with the powders' flow properties. This article describes a study scientists conducted to resolve a powder-binding problem that developed during the scale-up—from proof-of-concept scale to pilot. Arching. Aside from funnel flow, powder bridging is another undesirable flow issue which can occur in the hopper (Fig. Where less desirable properties are present, poor powder flow can: lead to challenges during blending (no discharge or ratholing), 4 difficulties when discharging the powder into the hopper 5 or issues regarding weight uniformity in the tablet. When hoppers are designed without consideration of the actual materials being handled, problems inevitably arise. 3. , and J. m. 20-36 , wherein there is shown a hopper assembly H which utilizes a hopper 401 and a hermetically sealed cover 402. The energy requirements are very dependent on the bulk solids or powder flowability properties, including cohesion and internal shear angle. Powder flow can also vary from lot-to-lot, which needs to be understood during R&D. Uneven flow, ratholing, segregation or bridging during tablet. 2. • Prevent ratholing, bridging and damage to the material. Some products like dry cell battery. Pumps, Motors & Drives. Arching. the powder blend exhibit ‘Funnel Flow’. critical pressure at the abutment of the dome ê $) in hopper design principles, is the stress that facilitates powder flow Pharmaceutical powder discharge from a hopper Buildup in the silo is an indication of ratholing and potentially asymmetric flow, which can increase pressure loads inside silo walls. Fig. The simplest way of explaining the flow function is with the uniaxial unconfined failure test shown in Figure 4, which measures the. How to prevent solids and powder flow stoppages with proper feeder design FREE | October 18,. The hopper must be designed so the outlet diameter is larger than the outlet rathole critical diameter. Ratholing occurs when material empties out through a flow channel above an outlet. Of course the outlet of the hopper has to be large enough to prevent bridging above the feeder. For powders such as T100 and T100M which exhibit arching and. Powder flow can be defined as the ease with which a powder will flow under a specified set of conditions. Our pneumatic and electric chute and pipe vibrators and vibratory equipment will: Unload dry or semi dry bulk material. Includes supplementary material: sn. Wall friction angle (against SS plate) = ϕ’ = 25º Bulk density = γ = 22 lb/cu ft Angle of internal friction. Particle size distribution (PSD) estimation by sieving of the two powders was performed according to Ph. Compressibility properties Measure a material’s bulk density as a function of consolidation pressure, which is required in the analysis of bridging, ratholing, and hopper angles. : Fine Powder Flow Phenomena in Bins, Hoppers and Processing Vessels. Material hang-up (arching and/or ratholing) problems are generally caused by one of four things: cohesive forces between powder particles or granules, external forces, inter-particle locking, or elastic constraint issues. Powder flow is a critical attribute of pharmaceutical blends to ensure tablet weight uniformity and production of tablets with consistent and reproducible properties. The behavior is irregular and often catastrophic for achieving regular powder flow. However, determining the physical properties under normal operating conditions is essential. Silo discharge solutions for powder bridging and ratholing. 4. Whether powder will flow smoothly or in an erratic manner inside a bin or a hopper depends on the flow pattern inside that equipment. Flow stoppages due to arching and ratholing within ingredient feed hoppers and bins are more than just a nuisance, since these problems will directly contribute to the composition of the final blend for a period of time. 5). Presented at Bulk 2000: Bulk Material Handling Towards the Year 2000, London, 1991. A key variable that will have an impact on the flow is its cohesive strength. Materials interlock or bond together to form an arch above the outlet, blocking any flow. Differences in densities and flow rate cause the materials to separate on a vibrating conveyor belt, upon free-fall into a bin, or when flowing horizontally into a container. , wedge-shaped and transi-usable capacity of the vessel. Before. In this study, we showed that the major principal stress (σ1) at the bin outlet is required for. e. The powder flowability is defined as the ability of a material in the form of particles to flow in a desired manner when used in specific equipment [33]. flowability to avoid problems during blending, compression, filling and transportation (Räsänen et al. the powder flows at the place of the smallest flow resistance. Silo and hopper ratholing is an issue which causes the compaction of materials on silo and hopper side walls, which results in a severely restricted material flow. Bridging, ratholing, arching and comparable behaviors are the bane of powder handling and formulating. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. A Brookfield Powder Flow Tester, equipped with Powder Flow Pro software for automated instrument control and data acquisition, was used to test this name brand baby formula. If the coarser particles stick to the sides of the hopper they can get rancid and contaminate the next batch. Scope. 4 Feeders used at discharge of hopper. Free-Flow: The powder flows reliably through very small outlet dimensions under gravity. 4. Since funnel flow will result in a first-in, last-out flow sequence, any side-to-side segregation that occurred when the equipment was filled will often be exacerbated 7. Particle size also affects wetting. In arching, the material forms an arch (or a bridge) above the outlet that prevents further flow. Ratholing. downtime and degraded product quality. The reason for this is the strength (unconfined yield strength) of the bulk solid. The powder has relatively low cohesive strength. Powder & Bulk Processing. Mass flow exhibits a first-in-first-out flow sequence, allowing the product at the bottom (coarser or heavier particles) to discharge first. Powder flow obstruction during hopper/bin discharge, such as arching or ratholing, remains an outstanding risk and cannot be reliably diagnosed using the existing flow function coefficient-based method. 36 3 Wall Friction Angle 24. Thousands of plants around the world use AirSweep flow aid systems to solve bridging, ratholing, and other material flow problems. There are many consequences of flow problems. Even high viscous material can be fed through the. The cell has a fixed shearing rate of 7 mm min −1 and external and internal diameters of 164 and 120 mm, respectively. 5). 7” to 0. Arching occurs when large particles interlock to form an arch at a hopper outlet and stop flowing due to. Boateng AA, Barr PV. Magazine Events News & Notes Videos Podcasts Webinars White Papers Breakthrough Products Awards. Minor powder flow issues during R&D can turn into major headaches once scale-up to production begins. When the flow channel empties and material flow ceases, it can form a stable rathole that may collapse and block the opening. In plug flow bins, the material flows in the centre of the bin, into which the sides slough as the material is drawn from the bin. ) the powders are filled into closed cavities; this is followed by compaction using rigid punches and finally the product is ejected from the die. The large open inlet exceeds most materials’ critical arching diameter, preventing bridging and ratholing. Due to the pressure, some solids tend to be more cohesive , when powders become cohesive, they can form archs or rathole , 2 phenomena very detrimental to the flow of powder and. Unload and produce good faster in your production process. Thus, it will not be separated. (For an illustration of arching and ratholing, see the online version of this article at If a stable rathole forms in a hopper,They also prevent ratholing of hoppers and prevent lump formation. Powder rheology is the study of the behaviour of powders as bulk assemblies, consisting of solids, liquids and gases. May be formed by 1. was used to control the flow of powder. The powder influences the silo by the flowability of powder causing bridging and ratholing. Ratholing occurs when material empties out through a flow channel above an outlet. 2. g. Another method to improve flow is. All figures are courtesy of the authors. Apparatus. Mass Flow also allows the most efficient outlet. Dense phase. At the heart of our valves is Matcon's world-famous Cone Valve Technology delivering efficient and flexible powder handling solutions, serving a range of. The large inlet exceeds most materials' critical arching diameter, preventing bridging. 3b) occurs in case of funnel flow if only the bulk solid above the outlet is flowing out, and the remaining bulk solid - the stagnant zones – is consolidated and forms the rathole. This creates a non-flow regime whereby a discharge aid is needed to re-initiate powder flow from the silo. . caking and powder flow speed dependency (PFSD) test, of spray-dried bee pollen enriched milk powder (packed in ALP, BOPP/LDPE, and PET/Al. Under the silo a screw feeder with a varying pitch. Also in the case of funnel flow, asymmetry is of no help when ratholing has to be avoided. In advance of her appearance at this year’s Powder Show Toronto running from June 4-6 at the Toronto Congress Center in Canada, Tracy Holmes, the president of Jenike & Johanson, Ltd. powder flow problems. 400 Business Park DriveRatholing is a scenario that powder starts. Ratholing; c. Storage Silos 101. Flow stoppages due to arching and ratholing within ingredient feed hoppers and bins are more than just a nuisance, since these problems will directly contribute to the composition of the final blend for a period of time. ) but it. That’s why. For example, a Flodex may show a neat API powder has flowability of 26mm, with a round tablet design of 12mm in diameter. and host "True or False: Bulk Solids Edition" from 1:29 p. Ratholing occurs when discharge takes place only in a flow channel located above the outlet. Process Control & Automation. It allows users to measure the dynamic flow and shear properties of powders as well as quantifying bulk properties such as density, compressibility and permeability. For example, testing on a Flodex™ may show that a neat API powder has flowability of 26 mm, with a round tabletDischarge of powder from a hopper or bin is a common operation in solid dosage form manufacture. Powder strength data at each consolidating stress are plotted on the graph in Figure 4 to produce a graph called a “flow function. Caking of powder can have adverse effects on solubility, mixing, and dispersion resulting in loss of products, delays in launch and consumer complaints. 14. Figure 3: Stagnant, cohesive powders can form a stable rathole in funnel flow. If the material is even slightly cohesive, material may stick to the walls and eventually become part of the bin structure. Process Control & Automation. 2 pcf Bin Density Index (BDI) 40. At this point, peripheral bulk materials remain in place, so the hopper cannot be emptied. Section 1 Arching and Ratholing Dimensions of the Flow Report indicates the arching and ratholing dimensions of your material as a function of time at rest, temperature, etc, as follows: Arching Dimensions Time at Rest, hours -- In our example, the material was tested to simulate 0 hours storage (continuous flow) or as if the material was put. It is therefore imperative to know your powder properties in order to design the desired silo. W. Powder Hand Process 4:293–299. The material that is. 4. 1. This occurs when particles are conveyed in the gas stream at a velocity that is less than the saltation velocity. A brief introduction to discrete elemental method (DEM) which computes and models powder. Ratholing: can occur in a bin when the powder empties through a central flow channel, but the material at the bin walls remains stagnant and leaves an empty hole (rathole) through. Powder flow obstruction during hopper/bin discharge, such as arching or ratholing, remains an outstanding risk and cannot be reliably diagnosed using the existing flow function coefficient-based method. Problems associated with ratholing are flooding, substantial variation of density in product, and eventually no-flow. The Circle Feeder can be manufactured with several outlets for “one. Sometimes, slow mixing paddles can keep bridging and ratholes under control. No ratholing! The slow rotating vanes move the material radially from the center to the outlet ensuring "first in -first out" mass flow; Slow rotating parts insure gentle product handling and minimum downtime; Turndown ratio up to 10:1; Low maintenanceHopper and Silo Ancillaries. A Brookfield Powder Flow Tester equipped with Powder Flow Pro software for automated instrument control and data acquisition was used to test brown gravy mix. reviewing these solutions, however, it’s important to understand. 1 Shear strength. These problems lead to losses worth thousands of dollars at. (USP 1-May-2024) Changes in flow rate as the container empties can also be. 71 Funnel / core flow. Are they steep enough to prevent ratholing when a powder having an FFC of 7. Jenike shear testing has determined the following. 4. 4. Powder Mix Segregation. Wall Thickness of 0. Keep product moving by preventing buildup, bridging and ratholing. Carson, “Fine Powder Flow Phenomena plastic powder, food products, and pharmaceuticals. Ratholing occurs when material in the center discharges completely while material nearer the walls of the hopper remains in place. The rate of addition and surface motion can either worsen or improve powder addition. Magnetism is often overlooked for metal powders. Vibratory flow-aid devices can also be installed on the infeed hopper to. Material hang-up (arching and/or ratholing) problems are generally caused by one of four things: cohesive forces between powder particles or granules, external forces, inter-particle locking, or elastic constraint issues. Ratholing: can occur in a bin when the powder empties through a central flow channel, but the material at the bin walls remains stagnant and leaves an empty hole (“rathole”) through the material, starting at the bin outlet (Figure 28. In order to achieve mass flow, tion hoppers) are shown in Figures 5 and 6, respectively. Acceptable flow is required in powder transfer operations such as the emptying of tumble bins and conveyance of powders by gravity or screw feeders. Referring now to another embodiment shown in FIGS. The Cone Valve technology within each of the Matcon IBCs overcomes powder bridging due to both the lifting action of the cone and its integral vibration during lift. Bridging or arching. flow, including ratholing, erratic flow, flood-ing and segregation. Maintaining reliable powder flow of each ingredient to a continuous blending system is essential for its performance. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. User Tools. This can disrupt your production line. , useable) capacity, as low as only 10–20% of the bin’s rated storage capacity. 2017). bulk solid materials exhibit in bins and silos. It is critical to understand the type of hang-up that you may be experiencing. This was attributed to the fact that the poor flowability of APAP could cause ratholing and high flow variations, especially when the powder. In this case, powder discharge from hopper is not predictable. b.