The principles discussed in this chapter can be applied to analyzing new or existing equipment designs. Process Control & Automation. 3. 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. , 2003). Keep in mind that the mass-flow bin design process is iterative. Generally, flow is limited to a central flow pattern. Our pneumatic and electric bin and hopper vibrators will: Promote the consistent and controlled material flow of dry or semi-dry bulk materials. Mechanical Agitation when used properly will condition the material to a uniform bulk. Potential issues with powder flow from containers due to improper design include ratholing, arching, or erratic flow. These issues are most likely due to improper storage, a poorly selected. Additionally, when vibrators are used, the Magnetic. Bulk solids and powder flow properties testing is considered mandatory when designing screw conveyors and screw feeders for handling difficult to manage products. For each bulk powder the low powder percentage retainedFlow and discharge of powders in process vessels are well known to give rise to significant handling problems in a range of processes, for example in the pharmaceutical, mineral, chemical and food industries. 400 Business Park DriveRatholing is a scenario that powder starts. a more practical non-invasive method to visualize dynamic powder flow is needed that can help to quantify the efficacy of a given unit operation (such as in silos/bins) used in. Valves & Actuators. 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. 26. As occurrences of bulk powder flow issues are strongly affected by the flow pattern during discharge. Depending on their makeup, products in powder or bulk form are prone to cling to surfaces, especially if they’re high in fat or moisture. Powder flow characteristics are often. If the material is even slightly cohesive, material may stick to the walls and eventually become part of the bin structure. The finest fraction did not flow through a Hall flowmeter, then. 10). As a general rule, extremely fine powders (<200 mesh) deaerate and pack readily (dusts, talc, etc. 19 5 Inst Flow Function - Prorated 0. As the silo empties, side material flows into the middle channel. In silos and hoppers it’s often the cause of flow problems like ratholing and bridging. It is only possible to compare materials using the same reference stress. bulk solid materials exhibit in bins and silos. Poor flowability of powders in a hopper means that flow obstruction due to arching occurs or uneven flow causes ratholing. In all applications, this fluidizer prevents bridging, ratholing, and material hang-ups. The Influence of External Variables on Powder Flow Freeman Technology on YouTube. Valves & Actuators. The rate of addition and surface motion can either worsen or improve powder addition. If your effective is 20’ after 3 days at rest the rathole dimension is 18. In powder technology, the flow conditions are from. 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. , wedge-shaped and transi-usable capacity of the vessel. Ratholing of powders can occur in a container (silo, hopper, IBC, mixer vessel) when the powder empties through a central flow channel. Figure 1: Manufacturing pharmaceutical tablets and capsules involves several powder handling steps. A silo for wood dust and gypsum powder regularly gave flow problems. The flow pattern of a powder in a storage container or system is dependent on the powder itself as well as the container design. 5). To improve the flowability of powders, flow aids or lubricants such as magnesium stearate are often incorporated in. UK-based powder flow solutions firm Freeman Technology offers this video on how particulate materials react when aerated, loosely packed or. Before. In systems not designed with the material type in mind, powders and bulk solids can. ), and dry, uniformly-sized larger materials will be free flowing. In practice, this group of bulk materials is the most common. Lower the total height requirement. Air displacement as the product flows from the container can cause segregation, leading to an inconsistent end product. Multi-Craft Services. Jenike, who pioneered the theory of bulk solids flow at the University of Utah in Salt. Powder & Bulk Processing. Eastern/11 a. Valves & Actuators. 8 9 Dissolution can be improved by improved. The powder's flow pattern has a major effect on the development of certain flow problems, especially flooding. "ratholing" can occur, that is, the diameter at which. was used to control the flow of powder. Robert Sedlock. The primary focus of this chapter is to provide guidance in designing bulk solids (powder) handling equipment to provide consistent, reliable flow, and the required product uniformity by minimizing segregation. Apparatus. 2 pg 266. No flow due to arching or ratholing. Despite being a simple test of compressibility, it can be useful for identification of powder flow behavior. Provided here is a review of shear-cell testing and how the technique can be used to predict arching, ratholing and other behaviors. What Can Cause A. 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. Material builds up on the vessel walls, restricting the flow and the vessel’s full storage capacity. Uneven flow, ratholing, segregation or bridging during tablet. 1 Test Methods. Predicting powder flow behavior is important to successful solids-handling processes. Comparison of the flow properties of eight commercial dairy powders5. 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. reviewing these solutions, however, it’s important to understand. 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. A key variable that will have an impact on the flow is its cohesive strength. Ratholing. 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. 24hr Emergency Service. 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. Particle size distribution (PSD) estimation by sieving of the two powders was performed according to Ph. While bulk solid and powder handling is extremely common in industry, even some of the most basic fundamentals of material handling remain poorly-understood – largely because our education generally only. :4167–4181. Process Systems 1. In this study, we showed that the major principal stress (σ1) at the bin outlet is required for. 11. 89-0. 1 Shear strength. The typical problems encountered are either a cohesive arch or ratholing. Many consumer products, such as detergent or soap, can be prone to poor flow due to arching or ratholing during routine storage and handling. Problems with Hoppers • Ratholing/Piping and Funnel Flow • Arching/Doming • Insufficient Flow • Irregular flow • Inadequate Emptying • Time Consolidation. Attempts to initiate flow, such as use of vibration on hopper with rubber mallet or increasing powder paddle feeder, did not work. Gravity Flow. 125” to 0. However, flow aids are sometimes used when they are unnecessary and. refilling) and unexpected events (e. doi: 10. Ring Shear Tester to measure the flow properties of powders and bulk solids such as internal friction, strength, caking, cohesion, wall friction and bulk density. In most cases, the vessel or bin can be attached to a vibrator, which shakes the vessel to pack the powder together. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. In the pharmaceutical industry, powder flow assessment methods are of great interest for the development and manufacture of solid dosage. 3. 1. Jenike shear testing has determined the following. Irregular flow; d. Breakthrough Products Awards. Figure 10. This method may be used for all powders, dairy and non-dairy products. Arching = bridging: an arch-shaped obstruction forms above discharge outlet and prevents flow i. Ratholing is a flow obstruction that can cause erratic discharge from a bin, as well as induce material caking. Flow obstructions occur when the forces opposing motion exceed the forces promoting. Boateng AA, Barr PV. 2. forms. capacity — as low as only 10–20% of the bin’s rated stor- age capacity. Your benefits of a HETHON Feeder. The material forms a narrow passageway above the feed auger or outlet, while the remaining materials in the storage structure are stationary and can begin caking to. Ratholes develop most often in conical hoppers that are not steep enough to produce flow at the walls. 2. Solution: Reduce Movement. Ratholing is a common flow issue in storage structures. The flow of powder out of a silo is stopping primarily for 2 reasons ; either formation of arches. 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. Bulk Material. g. Flow agents are used to enhance the flow behavior of solids by reducing the inter-particle adhesion force. If a mass-flow bin is required based on the flow char-acteristics of the powder or bulk solids, the next step is to determine an appropriate outlet size and feeder. Major Testing: Bulk Density Measurement [ USP<616>] Tapped Density. (For an illustration of arching and ratholing, see the online version of this article at If a stable rathole forms in a hopper,Powder flow is critical to a range of pharmaceutical manufacturing processes. Chem Eng Sci. Ratholing. Finally. 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. This results in a no-flow. 2. 2. , 1998,. Materials interlock or bond together to form an arch above the outlet, blocking any flow. If the object is to maintain material flow only, fewer vibrators may be used. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. their manufacture are in powder form. 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. 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. , flow pattern (mass flow or funnel flow), and obstructions to flow (arching, ratholing). High cohesive strength may result in the formation of a stable rathole. If you are experiencing issues with dust in your manufacturing facility, it is probably due to open processing. The 2-in. 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]. Many of these flow issues can be traced back to improper discharger or feeder designs. Some products like dry cell battery. Provided here is a review of shear-cell testing and how the technique can be used to predict arching, ratholing and other behaviors. e. 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. Powder blockage in silos. If you are experiencing issues with dust in your manufacturing facility, it is probably due to open processing. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. Arching and Ratholing does not occur. Problems associated with ratholing are flooding, substantial variation of density in product, and eventually no-flow. High batch accuracy with difficult-to- handle material. 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. The principles discussed in this chapter can be applied to analyzing new or existing equipment designs. This device mixes with the bulk powder to increase. A mass flow screw feeder prevents preferential flow which can lead to ratholing and arching problems. When your bottom line depends on moving product efficiently through your plant, obstructions. Powder flow inside horizontal silos is essential to ensure the efficient operation of the spacecraft using powder engines under horizontal flight positions. It is critical to understand the type of hang-up that you may be experiencing. It is critical to measure a powder’s flow properties before designing a handling system or solving a flow problem. , Listowel, Ireland. This can disrupt your production line. This chapter provides guidance in designing bulk solid (“powder”) handling equipment to provide consistent, reliable flow and to minimize segregation. More. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. and host "True or False: Bulk Solids Edition" from 1:29 p. Calculation of a Hopper Geometry for Mass Flow An organic solid powder has a bulk density of 22 lb/cu ft. pharmaceutical tablets, detergents, ceramics, powder metallurgy etc. Bridging or arching. shear strength (σ f ), bulk density (ρ b) and add three further factors: hopper wall angle (β c ), outlet size (D crit) and Hausner ratio (H. Powder rheology is used in a wide range of industries to. Flow difficulties at the blending step often manifest as slow/no discharge or ratholing. The corresponding control schemes at different levels for the feeding-blending system are provided in Table 6. T or F A bulk solid is a granular solid, such as gravel, sand, sugar, grain, cement, or other solid material, that can be made to flow. 2 pcf Spring Back Index (SBI) 1. 1991; Holdich. Ratholing. Eliminate bridging, rat holes, and stuck material. Ratholing definition: Present participle of rathole . c. Flow aids are used to return to a more regulated flow pattern and are relatively inexpensive. Knowledge about bulk density of materials is essential for avoiding ratholing and arching effects in silos and hoppers. Posted by Control Concepts USA on September 13, 2022 7:13 pm. To overcome bridging the wall friction must be reduced or prevented from occurring. Shear cell techniques were used to measur e the following powder flow pro-perties: powder flowfuncti on, effective angle of internal fricti on and angle of wall friction. Powder flow is a critical attribute of pharmaceutical blends to ensure tablet weight uniformity and production of tablets with consistent and reproducible properties. Hopper and feeder design is critical to ensuring proper material flow when handling and storing powders and bulk solid materials. 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. With. In order to achieve mass flow, tion hoppers) are shown in Figures 5 and 6, respectively. The hopper design plays a role in this as hoppers with sharp angles and rough surfaces can inhibit powder flow. It offers automatic and controlled discharge of virtually any powder type, winning where other systems have failed. Shear cell techniques were used to measur e the following powder flow pro-perties: powder flowfuncti on, effective angle of internal fricti on and angle of wall friction. Conversely, StarTab hadPoor material flow doesn’t just affect productivity. Matcon design and manufacture a range of unique discharge valves to control the flow of bulk powders and overcome the risk of powder flow problems such as bridging, ratholing and segregation. In arching, the material forms an arch (or a bridge) above the outlet that prevents further flow. Ratholing/ funneling 5 Inconsistent flow 3 Electrostatics Flowability Compaction . the types of flow problems that can occur and the flow patterns. 1. • Minimal power consumption. One of the recommended types of flow aids is called Mechanical Agitation. , which have the potential to cause work stoppages [3]. Ratholing occurs when cohesive bulk materials are stored and conveyed in vessels with a funnel flow discharge pattern. Most flow problems are connected with the funnel flow pattern and can be avoided if the hopper is designed for mass flow (Johanson, 2002, Purutyan et al. 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 hopperBuildup in the silo is an indication of ratholing and potentially asymmetric flow, which can increase pressure loads inside silo walls. Visually detectable local ratholing and cratering in the fluid bed: Compressed air too moist, contains oil; relative humidity is too high inside the room in which the powder is processed. The mass flow hopper section ensures a uniform, controlled. 2 Flowability indicators used in industries 7 1. The total powder flow can be controlled in the level 1 closed-loop operation as indicated in Fig. Flow rate evaluationThe model elucidated the impact of the material descriptors for density; powder flow; particle size; compressibility; permeability and wall friction angle on the feeding process. 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. On June 4, Holmes will offer a presentation, "Help! My Powder or Bulk Solid Won't Flow from my Bin, Hopper or Silo!" at the event's Center Stage (Booth 170) from 10:30 a. , et al. Powder Rheology. Eliminate bridging, rat holes, stuck material and uneven flow in chutes and pipes. Mixing & Blending. Arching. Funnel-flow bins lead to ratholing when the non-flowing solid consolidates sufficiently to remain stable after the channel has emptied out, and to flushing of powders as the layers slough off the top of the non-flowing mass and hit the bottom of the channel, or as aerated material rushes through a rathole. Unload and produce good faster in your production process. Ratholing occurs when material empties out through a flow channel above an outlet. hopper that gives mass flow with one powder may give core flow with another. Ratholing occurs when material in the center discharges completely while material nearer the walls of the hopper. 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. Motors & Drives Valves & Actuators Powder & Bulk Solids. Full size image. The reason for this is the strength (unconfined yield strength) of the bulk solid. Material Flow Solutions, Inc. Forty years ago, Jenike [Gravity Flow of Bulk Solids, Bulletin 108, Utah Engineering Station, 1961] and Johanson [Flow Indices in the Prediction of Powder Behavior, Pharmaceutical Manufacturing. 25”; vibrator with 2. Arching/Bridging & Ratholing. This resulted in stagnation of the flow, especially after a weekend. The typical problems encountered are either a cohesive arch or ratholing. These problems lead to losses worth thousands of dollars at. The final potential issue is erratic flow, in which flow alternates between ratholing and arching (see Figure 1). They all have one thing in common: none will predict whether or not a powder will flow in a hopper. Avoid silo problems, such as bridging, funnel flow, ratholing, arching, segregation and product decay. powder ratholing, bridging, agglomeration) occur. 8 feet 12. 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 unique design can feed sticky, fluffy, lumpy, flaky, and fibrous materials without issues of bridging and ratholing in the hopper. R. 1. 5D Bunker: A shallow bin, where H < 1. Modeling of particle mixing and segregation in the transverse plane of a rotary kiln. Consequently, meas-urement of the wall friction characteristic of a. It is critical to understand the type of hang-up that you may be experiencing. 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. Different process problems, such as arching, ratholing, and segregation could arise during silo operation due to its poor design or extreme operating conditions. Powder ratholing: the powder flows only within a channel, the powder around this channel, or rathole, do not flow In clear, there is much less or not at all flow out of the hopper ! Note that other flow issues exist, showing different symptoms but are somehow less common and not detailed in this page. 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. "Rotoflo is the best silo discharger!Ratholing can occur when coal flow takes place in a channel located above the silo, bunker or hopper outlet. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. . b. . At the heart of our Powder Handling System is an IBC fitted with our patented Cone Valve Technology, a unique discharge valve that eliminates typical powder flow problems. Ratholing occurs when only a flow channel located above an outlet discharges product. 5). Everything flowing smoothly =. Powder avalanching in a rotating drum evaluates dynamic powder flow characteristics based on theAn annular shear cell was used for measuring the flow function and effective angle of internal friction, as described by Teunou, Fitzpatrick, and Synnott (1999a). Exceptions are the ore concentrate or fine powder bins which usually are of the mass flow type. In this study, we showed that the. The frequency of the vibration needs careful consideration as it could affect the flow ability of the powder. When bulk solids build up into an arch or dome-like shape over the hopper’s outlet and block the flow, it’s called arching or bridging. When the flow channel empties and material flow ceases, it can form a stable rathole that may collapse and block the opening. The goal of the design process is the determination of the hopper wall inclination necessary for mass flow and the minimum outlet size to prevent flow problems due to arching or ratholing. described ratholing and powder bridging in a small-scale feeder for fine, cohesive and compressible powders (Santos et al. In some cases through the design procedure it is found that a. Powder blockage in silos. 5). Pacific, Joe Marinelli, president, Solids Handling Technologies Inc. to 2:15 p. Ratholing occurs then there is excess build up on the walls of a storage structure, so much so that there is a thin and restricted passageway for materials to flow down the vessel. Powder-container design affects discharge rate, cleanability, and powder flow. Most times it does not present any problems such as ratholing, erratic flow, flooding and segregation, because the discharging material is not cohesive or has a small critical rat-hole dimension. 5). Arching, ratholing, caking, segregation and flooding are some of the commonly encountered flow problems in the handling of fine powders. The Circle Feeder has a variety of features but widely known for its ability to prevent material arching, bridging, and ratholing. Kozicki and Mehos found that when potash powder was agglomerated. 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. Flow Function: Line of a powder’s Unconfined Failure Strength versus the Consolidation stress that is applied to it. 4 Flow FactorsArching, ratholing, caking, segregation and flooding are some of the commonly encountered flow problems in the handling of fine powders. If a mass-flow bin is required based on the flow char-acteristics of the powder or bulk solids, the next step is to determine an appropriate outlet size and feeder. The powder has relatively low cohesive strength. a cohesive arch when particles bond together ii. Hoppers designed for mass flow with high-quality surface finishes can address these issues. Identifies suitable test methods and helps to interpret and understand their results. Various powder flow properties, such as cohesion, unconfined yield strength,. Jenike shear testing has determined the following characteristics given below. 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. Improper design of storage vessels causes problems, such as arching, ratholing, flooding etc. Powder strength data at each consolidating stress are plotted on the graph in Figure 4 to produce a graph called a “flow function. Bridges of powder can form in your containers preventing flow. 2. The bin activator works discharges not over the full covered area, but only in a small unpredictable area and coarse ratholing. For powders such as T100 and T100M which exhibit arching and. at the Tech Theatre (Booth 127). Ratholing synonyms, Ratholing pronunciation, Ratholing translation, English dictionary definition of Ratholing. Changing (reformulating) the powder to reduce the cohesive strength and wall fric- tion, however, may reduce the likelihood of ratholing. 3. flow, including ratholing, erratic flow, flood-ing and segregation. Reaching a certain level in the bin where the material has time to consolidate. Membrane adsorbers, bioreactors, and mixing. Process Control & Automation. 4. More than 70% of all products contain ingredients that are handled in bulk solid form at some point during the production process. Ratholing. Under those conditions, the product flow typically typically is last in, first out. The hopper design can play a role in this as those with sharp angles and rough surfaces can inhibit powder flow. 770-255-1322. How to prevent solids and powder flow stoppages with proper feeder design FREE | October 18,. The gyrators also reduce particle segregation to make sure each bag is completely. Thousands of plants around the world use AirSweep flow aid systems to solve bridging, ratholing, and other material flow problems. Some of the most challenging. the relationship is called powder flow function Yield locus and family of yield loci Determination of y and c. Once the central flow channel has emptied, all flow from the silo stops. Magnetism is often overlooked for metal powders. Equipment for powdered metals, ceramic powders, pigments, chemicals, super-abrasives. Air Cannons For Solving Tough Material Flow Problems. W. 4704, or Email Us. The hopper to be designed is conical. Problems such as arching, bridging, segregation, ratholing, and more, resulting from a material with poor flow properties, can cause issues such as:. 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. To ensure issues don’t persist or escalate, it’s important to fix the issue as. Consequently, meas-urement of the wall friction characteristic of a. May be formed by 1. Silo design for gravity flow; most economic. Referring now to another embodiment shown in FIGS. Pumps, Motors & Drives. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. Some of these conditions include:. . Researchers at Purdue University have developed a new technology that solves the caking, bridging, and ratholing that occurs in powder flow from hoppers and bins in agriculture and other industries. 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. Bridging, ratholing, arching and comparable behaviors are the bane of powder handling and formulating. powder becomes deaerated in the stagnant region of a funnel flow bin, it usually develops 2. Arching; b. This was attributed to the fact that the poor flowability of APAP could cause ratholing and high flow variations, especially when the powder. 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. 71 Funnel / core flow. Effective feeder design not only enhances the flow within bins, hoppers, and stockpiles but also. 2. 1. High Shear Microfluidizer. powder becomes deaerated in the stagnant region of a funnel flow bin, it usually develops 2. the powder flows at the place of the smallest flow resistance. Keywords: live bottom, cohesive, powder, hopper design. Bulk solids and powders frequently encounter various flow challenges, including bridging, ratholing, flooding, and inadequate flow rates, and more. Geometry modifications are. Its unique construction fulfills allows for quantitative dosing steadily and evenly. LIW feeder flow rates can be compromised when the sudden change of the powder weight (e. Powder flow can also vary from lot-to-lot, which needs to be understood during R&D. Powder rheology is the study of the behaviour of powders as bulk assemblies, consisting of solids, liquids and gases. 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. "Rotoflo is the best silo discharger! Mass flow develops when all the material in a silo is in motion whenever any is withdrawn. Ratholing occurs when material in the center discharges completely while material nearer the walls of the hopper remains in place. The depth of the trough into which the powder is filled is 12 mm and. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. 1. Pumps, Motors & Drives. adhesive nature of a material could influence the feedability of materials over time through screw layering or bridging/ratholing, limiting the powder flow through.