Various powder flow properties, such as cohesion, unconfined yield strength,. The entire process is user-controlled and transparent: Diagrams and extrapolations. The Circle Feeder can be used as a material feeder, large industrial feeder, laboratory feeder, powder. Valves & Actuators. UNIT- 3: HANDLING OF SOLIDS (2 HOURS) Sliding and flow of powder, Method for free flowing powder and granules, methods for cohesive powders Bins, Vacuum and conveyor. Whey protein is classified as a combustible powder, and high concentrations can create a. In practice, this group of bulk materials is the most common. T or F A water column is a boiler fitting that reduces the movement of boiler water to provide an accurate. Major Testing: Bulk Density Measurement [ USP<616>] Tapped Density. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. A _______ provides a signal that simulates the signal from load cells at various weights. Magnetism is often overlooked for metal powders. za NNNEL FLOW i. C - For flow, D> y or ff y (a) powder has a yield stress greater than c/ff no flow occurs. As the level of fly ash in the flow channel drops, a resistance to further flow into this channel occurs due to. This was attributed to the fact that the poor flowability of APAP could cause ratholing and high flow variations, especially when the powder. Conducting studies. True. Larger particles are more likely to penetrate the surface than fine particles. Based upon mathematical models, Jenike developed design charts to determine which flow pattern is to be expected during gravity discharge from a bin or hopper. Ratholing is a common flow issue in storage structures. When you have buildup in the silo, the loads associated with asymmetric flow can be detrimental to the structural integrity of the silo as they can lead to wall failure and total silo failure. In all applications, this fluidizer prevents bridging, ratholing, and material hang-ups. It is critical to measure a powder’s flow properties before designing a handling system or solving a flow problem. It is critical to understand the type of hang-up that you may be experiencing. : Fine Powder Flow Phenomena in Bins, Hoppers and Processing Vessels. 8 B), F > 63 and F > 90 had practically equal outlet diameters (1. include modifying the hopper, adding a bin insert, using a flow. Arching or bridging is a flow-arresting situation whereby the powder mass creates a structure (such as a dome or a bridge) above the outlet hole inhibiting flow completely. It may lead to injury and hazardous plant environments, and compromise product safety. pharmaceutical tablets, detergents, ceramics, powder metallurgy etc. outlet dimensions to avoid arching and ratholing. Flow difficulties at the blending step often manifest as slow/no discharge or ratholing. offers powder testing services (flowability, friction, time consolidation, strength as used for comparative tests, silo design for flow and silo design for strength) and. 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. 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. 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. Arching occurs when large particles interlock to form an arch at a hopper outlet and stop flowing due to. Typical powder flow issues found in the hopper are ratholing, bridging and segregation. Eastern/11 a. No flow due to arching or ratholing. 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. 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. 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. On Wednesday, September 21, 2022 at 2 p. Discharging aids. Keep in mind that the mass-flow bin design process is iterative. Fig. Native corn starch did not flow from the hopper, so tablets were not compressed and had a severe ratholing problem. Some of these conditions include:. 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. 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. 23Marinelli will discuss how to design the best kind of bin, silo, hopper, or feeder at Powder & Bulk Solids Texas, October 13-14, as one of two conference sessions he will present. Most problems that manifest on the. , Listowel, Ireland. Problems associated with ratholing are flooding, substantial variation of density in product, and eventually no-flow. Figure 3: Stagnant, cohesive powders can form a stable rathole in funnel flow. The flow properties of a bulk solid can have a significant impact on process efficiency and the success of the end product. 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). 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. Under those conditions, the product flow typically typically is last in, first out. Leading Powder Handling Equipment. The design of a silo is based on the most economical case: gravity flow. Circle Feeder is the premier choice feeder that can prevent the segregation during mass flow discharging. 5). It offers automatic and controlled discharge of virtually any powder type, winning where other systems have failed. Ratholing occurs when only a flow channel located above an outlet discharges product. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. 1 Importance of powder flow in the pharmaceutical industry 6 1. Bridging, ratholing, arching and comparable behaviors are the bane of powder handling and formulating. g. to 11 a. UK-based powder flow solutions firm Freeman Technology offers this video on how particulate materials react when aerated, loosely packed or. In this study, we showed that the. k. 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. 2 Flowability indicators used in industries 7 1. The best way to establish flowability is to compare flow on a Flodex powder flow tester with the tablet configuration to determine whether the powder’s intrinsic flow is close or equivalent to the cross-section of the die. If the powder does not bind sufficiently to another material, it will separate through fluidization if aerated or allowed to free-fall. 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. 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. Rotoflo is designed to help with material handling ensuring that silo discharge is free-flowing and controlled when handling a number of diverse materials. • Prevent ratholing, bridging and damage to the material. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. Mechanical Agitation when used properly will condition the material to a uniform bulk. • Low-maintenance because of few wear points. Air pads may be needed to move the first material and merely gravity or small vibrations can be sufficient for the second. the powder flows at the place of the smallest flow resistance. bridging, ratholing and compacting. 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. 125” to 0. Also in the case of funnel flow, asymmetry is of no help when ratholing has to be avoided. Driveshaft Removal:is a scenario that powder starts. Measuring flow properties leads to proper equipment selection and process reliability. , flow pattern (mass flow or funnel flow), and obstructions to flow (arching, ratholing). , 2018). Why Battery Manufacturers Choose the Circle Feeder. discharge) and its flow rate have been used to measure (USP 1-May-2024) powder flow. This occurs when particles are conveyed in the gas stream at a velocity that is less than the saltation velocity. As a general rule, extremely fine powders (<200 mesh) deaerate and pack readily (dusts, talc, etc. 456 inches. Solve your powder handling problems, whether it is. It is critical to understand the type of hang-up that you may be experiencing. hopper that gives mass flow with one powder may give core flow with another. The 2-in. 10a or M-cell that is. Abstract. Ratholing = funnel flow: discharge. This results in a no-flow. The key to feeding cohesive materials in a screw feeder is with the use of Flow Aids. A bin experiencing ratholing will have limited live (i. Caking of powder can have adverse effects on solubility, mixing, and dispersion resulting in loss of products, delays in launch and consumer complaints. Flowability 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. The obstruction to flow would have a significant impact on the overall CM process as it. (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 bridging occurs when the pressure actually locks the powder granuals together because they simply can not pass though the neck of the case and pressure increases dramatically. Segregation Ratholing (Fig. Before. A mass flow screw feeder prevents preferential flow which can lead to ratholing and arching problems. Powder flow characteristics and vessel design vary tremendously. Ratholing synonyms, Ratholing pronunciation, Ratholing translation, English dictionary definition of Ratholing. Expanded flow: Term used to describe flow in a vessel that combines a core flow converging hopper with a mass flow attached below it. include modifying the hopper, adding a bin insert, using a flow. Rotoflo is designed to help with material handling ensuring that silo discharge is free-flowing and controlled when handling a number of diverse materials. Wall friction, internal friction and bridging properties determine the applicable hopper angle and opening diameter. Arching and Ratholing does not occur. 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. Ratholing is a flow obstruction that can cause erratic discharge from a bin, as well as induce material caking. The hopper design can play a role in this as those with sharp angles and rough surfaces can inhibit powder flow. 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. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. Many factors can lead to ratholing in your hopper, bin, or silo. 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. Arching. 2. Pivotal work on the development of the theory of bulk solids flow began in earnest in the early 1950s, when. The Wolfenbuttel, Germany) is used for measuring the flow properties of bulk solids or powder ( fig. Ratholing. doi: 10. Jenike, who pioneered the theory of bulk solids flow at the University of Utah in Salt. In the present work, the discharge characteristics of non-gravity-driven powder in the horizontal silo were investigated experimentally, with an emphasis on the half cone angle, aeration. g. Bulk solids and powder flow properties testing is considered mandatory when designing screw conveyors and screw feeders for handling difficult to manage products. Ratholing occurs when material in the center discharges completely while material nearer the walls of the hopper remains in place. This can usually be overcome by. To overcome bridging the wall friction must be reduced or prevented from occurring. The powder flow is measured using an X-ray-based mass flow meter (SETXvue XP-300, Enurga, Inc. Due to the cohesive strength of fine dry fly ash, the material is a great source of friction. 3 and Fig. 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. In this case, the hopper walls are steep and smooth enough to ensure flow along them. Ratholing is a flow obstruction is a no-flow condition obstruction that can cause erratic that prevents material discharge discharge from a bin, as well as from a bin. Different process problems, such as arching, ratholing, and segregation could arise during silo operation due to its poor design or extreme operating conditions. Avoid silo problems, such as bridging, funnel flow, ratholing, arching, segregation and product decay. In order to achieve mass flow, tion hoppers) are shown in Figures 5 and 6, respectively. Flow problems related to food powders, such as arching, ratholing and erratic flow are thoroughly described and reviewed by Marinelli (2005). 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. Unload and produce good faster in your production process. If you’re in supplement processing and need expert advice or equipment related to powder handling, supplement or food production, call Right Stuff Equipment at 303. 3 Calculation of Minimum Required Outlet. The simple cure is to use Ball powder. To ensure issues don’t persist or escalate, it’s important to fix the issue as. 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. 3. AirSweep breaks up material blocks and sweeps the vessel walls clean. , answered a few questions from Powder & Bulk Solidson common powder handling and flow issues and how operators can take steps to fix or prevent. the types of flow problems that can occur and the flow patterns. ratholing, flooding, and inadequate flow rates, and more. Ratholing. 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. The aim is to provide a dynamic picture of the piping formation, so as to explore the variation of field. Its unique construction fulfills allows for quantitative dosing steadily and evenly. Ratholing occurs when material in the center discharges completely while material nearer the walls of the hopper. steeper than. If the material is even slightly cohesive, material may stick to the walls and eventually become part of the bin structure. As a general rule, extremely fine powders (<200 mesh) deaerate and pack readily (dusts, talc, etc. 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. There are many consequences of flow problems. Prevent segregation with mass flow. Conducting studies throughout R&D and scale-up can help identify and isolate where in the process a formulation issue began. In this study, we showed that the major principal stress (σ1) at the bin outlet is required for. These are examples of material flow problems. Mass-flow bin. downtime and degraded product quality. Mass flow eliminates ratholing and maximizes the pers with planar geometries (e. Core or Ratholing Flow: The material starts flowing from the top surface in the form of a cylinder at the central portion of the hopper and all the material surrounding this central hole upto the wall is stagnant. In a silo, hopper or bin, the powder is exposed to various pressure. At this point,. and host "True or False: Bulk Solids Edition" from 1:29 p. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. E & FN Spon, London and New York, pp 131–141Bin Activators are equipment conically shaped that aid dry bulk material flow from storage silos, or hoppers. Posted by Control Concepts USA on September 13, 2022 7:13 pm. The reason for this is the strength (unconfined yield strength) of the bulk solid. Thus, reliable information of flow properties of the pulverized coal concerned is required for reliable flow from the hopper, which is essentially crucial in handling and processing operations [8], [9]. 1. c 3 Critical condition for flow. Wall friction angle (against SS plate) = ϕ’ = 25º Bulk density = γ = 22 lb/cu ft Angle of internal friction. 1. This can disrupt your production line. adhesive nature of a material could influence the feedability of materials over time through screw layering or bridging/ratholing, limiting the powder flow through. Flow aids are used to return to a more regulated flow pattern and are relatively inexpensive. Increase powder fluidity enables spreading. When the flow channel empties and material flow ceases, it can form a stable rathole that may collapse and block the opening. Silo design for gravity flow; most economic. This type of flow pattern is indicative of uniform, first-in-first-out flow, where ratholing, erratic flow, segregation, and flooding problems are mitigated. powder flow problems. W. Silos and hoppers are particularly prone to this issue if the. Powder is moist. The depth of the trough into which the powder is filled is 12 mm and. Hopper and feeder design is critical to ensuring proper material flow when handling and storing powders and bulk solid materials. 2002). Flow splitting increases capacity and saves floor space. An extreme case of funnel flow is referred to as “ratholing”. Figure 10. Aside from funnel flow, powder bridging is another undesirable flow issue which can occur in the hopper (Fig. 4. An arching flow p Figure 3. 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. Traditional powder testing methods cannot force the bridging to occur in a repeatable manner and thus they cannot discriminate flow differences between powders. The Circle Feeder can be manufactured with several outlets for “one. Material builds up on the vessel walls, restricting the flow and the vessel’s full storage capacity. There are many factors, e. Numerous cement plants are plagued with bulk solids flow problems like bridging, ratholing, and flooding, each of which can negatively impact production efficiency. High batch accuracy with difficult-to- handle material. flowability to avoid problems during blending, compression, filling and transportation (Räsänen et al. 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. 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. In ratholing, a vertical flow channel develops above the hopper outlet and, once emptied, remains stable. Hoppers designed for mass flow with high-quality surface finishes can address these issues. That’s why. 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. the powder blend exhibit ‘Funnel Flow’. Sometimes, slow mixing paddles can keep bridging and ratholes under control. Use the following guidelines for impacting vibrators: Wall Thickness of 0. The frequency of the vibration needs careful consideration as it could affect the flow ability of the powder. These behaviours are related to the cohesive strength of the powder, which is a function of the applied consolidation pressure. Material flow from a bin or silo is inextricably linked to how the feeder extracts the material from the bin outlet. Our engineers can solve two common types of flow issues. It is therefore imperative to know your powder properties in order to design the desired silo. Valves & Actuators. Santos et al. If you are filling your bin with a material and it drops close to the outlet, the P-Factor should be calculated as follows: P-FACTOR = (1 = m) [w/ (A B γ)] 2h/g where: w = weight flow rate into bin h = height of fall. Consolidations can therefore be undone. 3. The simplest way of explaining the flow function is with the uniaxial unconfined failure test shown in Figure 4, which measures the. 5mm are the only two that so far have had this problem. A brief introduction to discrete elemental method (DEM) which computes and models powder. Flow function test. Despite being a simple test of compressibility, it can be useful for identification of powder flow behavior. Figure 2: The two primary flow patterns that occur in gravity discharge are funnel flow and mass flow. This method may be used for all powders, dairy and non-dairy products. The vane lid is used to perform the flow function test. • The particle size distribution – indicator of powder flow and the segregation potential • Bulk and tapped density – indicator of powder flow, mixing (fill volume) and tablet die filling. Meet hygiene and safety requirements and remove the risk of cross-contamination. What Can Cause A. Once the central flow channel has emptied, all flow from the silo stops. If the material being handled is cohesive,. 400 Business Park DriveRatholing is a scenario that powder starts. The lifting action of the cone breaks up bridged product and prevents material from rat. A silo for wood dust and gypsum powder regularly gave flow problems. Gravity Flow. The silo influences the powder via the silo diameter, height and the angle of the hopper. 2 pcf Bin Density Index (BDI) 40. A proven and practical scientific approach for designing bins and feeders based on a material’s flow properties. 0 HOPPER DESIGN 5. (Powder and Bulk Solids) (regular, part-time and distance learning) • PhD (Powder. 1 is handled? Is the 100-mm diameter outlet of the hopper large enough to prevent an obstruction to flow?Powder flow tester, Software for silo design. 1991; Holdich. 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. Let us explain how the use of vibration or sudden large blasts of air solve material flow problems. For system manufacturers, process engineers, and operators: The timely application of flow enhancing solutions is recommended to prevent quality issues and production interruptions, such as bridging, ratholing and demixing. The energy requirements are very dependent on the bulk solids or powder flowability properties, including cohesion and internal shear angle. 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 is influenced by the bin/hopper geometry and outlet size the material is being fed through. It may be necessary to apply several linear vibrators when the entire bin must be cleaned. The solid dosage form (tablets and capsules) is manufactured by either dry-blending of fine powder ingredients or combining the ingredients in a wet granulation step, followed by drying. The material that is. 1. Figure 3: Stagnant, cohesive powders can form a stable rathole in funnel flow. g. 6). Ratholing occurs when material empties out through a flow channel above an outlet. Conversely, StarTab hadPoor material flow doesn’t just affect productivity. Retrofit solutions. flow rate through an orifice compressibility index and hausner ratio angle of repose shear cell. 10a or M-cell that is. pharmacopeial methods to characterise powder flow. Discharging aids. Exceptions are the ore concentrate or fine powder bins which usually are of the mass flow type. 770-255-1322. They all refer. Angle of repose. These issues are most likely due to improper storage, a poorly selected. Some of the most challenging. This device mixes with the bulk powder to increase. 2 pg 266. 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. The rest of powder compacts under vibration and get les flow-able in the time, so if a flow channel is established it will stay on the same place. The core flow pattern can also be described as funnel flow where mainly the core is in movement and the powder pattern resembles that of a funnel. As occurrences of bulk powder flow issues are strongly affected by the flow pattern during discharge. 361 14. 2. Pumps, Motors & Drives. Storage Silos 101. "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. Acceptable flow is required in powder transfer operations such as the emptying of tumble bins and conveyance of powders by gravity or screw feeders. 1. If your effective is 20’ after 3 days at rest the rathole dimension is 18. Generally, flow is limited to a central flow pattern. 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. 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. Impact on filling. 31+0. 5D Hopper: A converging sloping wall section attached to the bottom of a silo. 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. In powder technology, the flow conditions are from. LIW feeder flow rates can be compromised when the sudden change of the powder weight (e. Arching = bridging: an arch-shaped obstruction forms above discharge outlet and prevents flow i. The large inlet exceeds most materials' critical arching diameter, preventing bridging. Follow this guidance to avoid common solids-handling issues, such as erratic flow and no flow. 4 Flow FactorsArching, ratholing, caking, segregation and flooding are some of the commonly encountered flow problems in the handling of fine powders. Ratholing is a term used to describe extreme cases of funnel flow where the material nearer the walls is completely stationary and only the central material is discharged . The flow of powder out of a silo is stopping primarily for 2 reasons ; either formation of arches (arching, bridging) or ratholes. Ratholing can be avoided if you pay attention to calculations. 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. Royal, T. 2. The technology is a microcontroller actuated portable device that can be remotely controlled. 24hr Emergency Service. Resources. 3. Process Control & Automation. Whether powder will flow smoothly or in an erratic manner inside a bin or a hopper depends on the flow pattern inside that equipment. The two most common flow problems experienced in a silo, bin or hopper are arching (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. e. 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. From the test results, you can follow Andrew Jenike's analyses to predict flow behavior in hoppers, e. Even high viscous material can be fed through the feeder and discharger smoothly. Bridging or arching. 5). 2. At this point, peripheral bulk materials remain in place, so the hopper cannot be emptied. For system manufacturers, process engineers, and operators: The timely application of flow enhancing solutions is recommended to prevent quality issues and production interruptions, such as bridging,. Valves & Actuators. Ratholing definition: Present participle of rathole . 6 Therefore, a material that has poor powder flow needs to be pre-processed before attempting direct. 3. Of course the outlet of the hopper has to be large enough to prevent bridging above the feeder. Under the silo a screw feeder with a varying pitch. 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. was used to control the flow of powder. Hoppers. Powder strength is measured as “yield stress” by shearing particles trapped in the lid pockets against particles in the shear cell. Air displacement as the product flows from the container can cause segregation, leading to an inconsistent end product. The critical arching dimension, of 5. The hopper must be designed so the outlet diameter is larger than the outlet rathole critical diameter. Mixing & Blending. A. 24hr Emergency Service. spoilage, flooding, or ratholing are likely to occur, then a mass-flow discharge pattern should be selected. Provided here is a review of shear-cell testing and how the technique can be used to predict arching, ratholing and other behaviors. Such hoppers are sensitive to arching and ratholing.