Native corn starch did not flow from the hopper, so tablets were not compressed and had a severe ratholing problem. However, determining the physical properties under normal operating conditions is essential. 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. Pivotal work on the development of the theory of bulk solids flow began in earnest in the early 1950s, when. 24hr Emergency Service. 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. g. Case Studies Keep product moving by preventing buildup, bridging and ratholing. 448 m, respectively), corroborating the previous results that demonstrated that shape had more. 2. Why are my powders are not flowing efficiently?Ratholing occurs when discharge takes place only in a flow channel located above the outlet. . powder addition easier. 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. High Shear Mixers and. The reason for this is that when a powder becomes deaerated in the stagnant region of a funnel flow bin, it usually developsFlow function is only half of the solution because it’s a measure of powder cohesiveness: Powder flows if: Ì % = σ1/ffc The external stress arising from gravity, (a. , 1998,. A Mass Flow Approach to Solving Your Sifting Segregation Issues Using a mass flow pattern will not only prevent the flow problems typically experienced by funnel flow (ratholing, flushing, etc. Powder blockage in silos. The gravy mix was scooped into the trough, and the. 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. 1 Test Methods. Exceptions are the ore concentrate or fine powder bins which usually are of the mass flow type. g = gravity constant. 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. Arching. See Fig. 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. 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. Efficiency– As explained earlier ratholing powder flow can be likened to creating a “funnel effect”,meaning silos and hoppers cannot be used to their full storage capacity. The powder flow is measured using an X-ray-based mass flow meter (SETXvue XP-300, Enurga, Inc. 4 Feeders used at discharge of hopper. Figure 3: Stagnant, cohesive powders can form a stable rathole in funnel flow. Free-Flow: The powder flows reliably through very small outlet dimensions under gravity. Ratholes develop most often in conical hoppers that are not steep enough to produce flow at the walls. The finest fraction did not flow through a Hall flowmeter, then. Fine particles and low-density particles tend to float on the liquid surface, making powder addition extremely difficult (7). asymmetric conical. Jenike, who pioneered the theory of bulk solids flow at the University of Utah in Salt. On the other hand, NP0 produced mass flow behaviour even for the narrowest orifice diameter of 2 mm. 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. 2. Cocoa powder storage in silos, hoppers and bins can be fraught with blockage problems such as bridging and 'ratholing' because of its cohesive. Materials interlock or bond together to form an arch above the outlet, blocking any flow. 10. A superb discharge device, it overcomes all the typical powder handling and flow problems of bridging, blockages, mix segregation, flushing and core flow that are commonly associated with butterfly valves. Acceptable flow is required in powder transfer operations such as the emptying of tumble bins and conveyance of powders by gravity or screw feeders. Robert Sedlock. Various powder flow properties, such as cohesion, unconfined yield strength,. 2. Before. 1. Check drier is switched on. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. The flow issue is arguably the most important and pervasive. b. It offers automatic and controlled discharge of virtually any powder type, winning where other systems have failed. Bulk Material. The system is designed to help prevent powder bridging and ratholing in silos and hoppers. 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. 456 inches. Before. The entire process is user-controlled and transparent: Diagrams and extrapolations. Many of these flow issues can be traced back to improper discharger or feeder designs. 9b, although the variation of the blend flow was larger compared to the total powder flow in case study 1. Ratholing of powders can occur in a container (silo, hopper, IBC, mixer vessel) when the powder empties through a central flow channel. This can usually be overcome by. There are two main reasons why no-flow conditions happen: arching and ratholing. Knowledge about bulk density of materials is essential for avoiding ratholing and arching effects in silos and hoppers. In silos and hoppers it’s often the cause of flow problems like ratholing and bridging. 9 b, although the variation of the blend flow was larger compared to the total powder flow in case study 1. 93+0. 4. 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. induce material caking. 1. Particle size distribution (PSD) estimation by sieving of the two powders was performed according to Ph. • Easy to clean due to detachable components. Getting the powder flow wrong can be highly disruptive to plant performance and productivity, particularly where equipment has to be taken off-line and stripped down for cleaning out blockages. Schulze RST which is equipped with either S-cell that is shown in fig. 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. Bridges of powder can form in your containers preventing flow. 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 . m. m. In addition, a cone-shaped member 360 is mounted thereto and functions to prevent ratholing of bulk powder and to assist the formation of powder mass flow. The powder influences the silo by the flowability of powder causing bridging and ratholing. As a general rule, extremely fine powders (<200 mesh) deaerate and pack readily (dusts, talc, etc. 2. refilling) and unexpected events (e. g. Typical component concentrations in. The phrases “failure to discharge” and “erratic flow in the. 24hr Emergency Service. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. 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]. Arching occurs when large particles interlock to form an arch at a hopper outlet and stop flowing due to shape, pressure, moisture or temperature. 2. AirSweep breaks up material blocks and sweeps the vessel walls clean. 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. Improper design of storage vessels causes problems, such as arching, ratholing, flooding etc. Ratholing is affected by consolidating pressure; thus, large funnel-flow bins have a higher ratholing tendency. Our in-house testing laboratory measures the flow properties of your material so our solutions are robust - your product will flow through your system without hang-up, arching, , ratholing, blocking or other flow issues. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. Most problems that manifest on the. If the powder does not bind sufficiently to another material, it will separate through fluidization if aerated or allowed to free-fall. Bulk solids and powders frequently encounter various flow challenges, including bridging, ratholing, flooding, and inadequate flow rates, and more. 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. 2. described ratholing and powder bridging in a small-scale feeder for fine, cohesive and compressible powders (Santos et al. flowability to avoid problems during blending, compression, filling and transportation (Räsänen et al. Movement speeds up material segregation. Flow aid devices are internal or external devices that are used to assist in discharging materials from a bin, hopper, or silo. These are examples of material flow problems. their manufacture are in powder form. Typical powder flow issues found in the hopper are ratholing, bridging, and segregation. As the silo empties, side material flows into the middle channel. 2 feet 2. 4. Attempts to initiate flow, such as use of vibration on hopper with rubber mallet or increasing powder paddle feeder, did not work. 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 the case of my Allen Mags, the 257 and 6. Increase powder fluidity enables spreading. the powder flows at the place of the smallest flow resistance. In the characterization of the powder flow, all predictions previously formulated were effectively understood. Bridging, ratholing, arching and comparable behaviors are the bane of powder handling and formulating. Rotoflo is designed to help with material handling ensuring that silo discharge is free-flowing and controlled when handling a number of diverse materials. Measuring flow properties leads to proper equipment selection and process reliability. 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. 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. Generally, flow is limited to a central flow pattern. e. 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. Mass flow exhibits a first-in-first-out flow sequence, allowing the product at the bottom (coarser or heavier particles) to discharge first. Flow aids are used to return to a more regulated flow pattern and are relatively inexpensive. Dense phase. If the material is even slightly cohesive, material may stick to the walls and eventually become part of the bin structure. The API AeroFlow® automated flowability analyzer was tested using 6 pharmaceutical excipients. These problems can result in limited live capacity. a. Ratholing. View our Flow Solutions Video! One of the most common problems with bulk material flow is a condition known as ratholing. Ratholing is influenced by the bin/hopper geometry and outlet size the material is being fed through. The flow of powder out of a silo is stopping primarily for 2 reasons ; either formation of arches. Arching = bridging: an arch-shaped obstruction forms above discharge outlet and prevents flow i. In addition, poor flowability can also cause content uniformity concern because of insufficient mixing. Arching occurs when large particles interlock to form an arch at a hopper outlet and stop flowing due to. The corresponding control schemes at different levels for the feeding-blending system are provided in Table 6. When working with bulk solids, especially in high-moisture environments, the material flow characteristics can change. powder flow problems. ”. Two common flow issues. Caking of powder can have adverse effects on solubility, mixing, and dispersion resulting in loss of products, delays in launch and consumer complaints. The outlet is the smallest flow channel through which the bulk material should move. The field of bulk solids handling was developed due mainly to the work of Dr. To mitigate process variations and disturbances caused by such risk scenarios, closed-loop feedback control is required. Rat-holing causes a funnel flow effect, where the powder flows freely above the outlet but then stops as the compacted powder is held in the silo or hopper. 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. Use the following guidelines for impacting vibrators: Wall Thickness of 0. 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. Chem Eng Sci. When hoppers are designed without consideration of the actual materials being handled, problems inevitably arise. /d. 2. 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. offers powder testing services (flowability, friction, time consolidation, strength as used for comparative tests, silo design for flow and silo design for strength) and. 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. The large open inlet exceeds most materials’ critical arching diameter, preventing bridging and ratholing. This can disrupt your production line. Powder flow characteristics are often. When a stable rathole develops, the bulk material remaining in the vessel is stagnant and will not discharge. 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. m. ; the ratio of tapped bulk density to loose bulk density; where the greater the ratio, the more. Our pneumatic and electric bin and hopper vibrators will: Promote the consistent and controlled material flow of dry or semi-dry bulk materials. Uneven flow, ratholing, segregation or bridging during tablet. Ratholing definition: Present participle of rathole . Ratholing occurs when cohesive bulk materials are stored and conveyed in vessels with a funnel flow discharge pattern. ) (Ganesh et al. Matcon designs and manufactures powder handling equipment that can be used to improve manufacturing processes across a range of applications. reviewing these solutions, however, it’s important to understand. 10a or M-cell that is. The Circle Feeder is used to reliably discharge all types of granular materials. 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. Ratholes develop most often in conical hoppers that are not steep enough to produce flow at the walls. The material that is. 4. Expanded flow silos and stockpiles are recommended for storing large quantities of non-degrading materials and for modifying existing funnel-flow silos to correct problems caused by arching, ratholing and flushing. Note that this method does not work well if the bulk material is a powder that can compact easily. 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. Arching. za NNNEL FLOW i. . 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. The two most common flow problems experienced in a silo, bin or hopper are arching (bridging) and ratholing. Valves & Actuators. The depth of the trough into which the powder is filled is 12 mm and. Jenike shear testing has determined the following characteristics given below. . In addition to potential ratholing, powders, like cement or flour, can become aerated when filling a bin and, if the silo is not designed with sufficient retention time for the material to become deaerated by the time it reaches the outlet, it will flow out of the silo uncontrollably, like. PRINCIPLES OF MATERIAL HANDLING Primarily concerned with the storage and movement of material Used in. Prevent bridging and ratholing. Apparatus. Material builds up on the vessel walls, restricting the flow and the vessel’s full storage capacity. 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. Hoppers designed for mass flow with high-quality surface finishes can address these issues. As the level of fly ash in the flow channel drops, a resistance to further flow into this channel occurs due to. flow channel empties, flow stoppages will occur when powder along the walls remains stagnant. Keep in mind that the mass-flow bin design process is iterative. The flow of powder from hoppers is usually assumed to take place in open atmosphere. This is due to issues related to the flow pattern of most bulk solids: arching in the hopper occurs during mass flow when the arch builds sufficient strength to support the powder above it; ratholing in the storage vessel. to compare flow on a Flodex™ powder flow tester (Teledyne Hanson Research, CA, US) with the tablet configuration to determine whether the powder’s intrinsic flow is close or equivalent to the cross-section of the tablet press die. Breakthrough Products Awards. 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. 770-255-1322. 8 lb/min Feed Density Index (FDI) 24. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. Powder blockage in silos. However, in powder pressing industries (e. Powder Feeding. Eliminate bridging, rat holes, stuck material and uneven flow in chutes and pipes. Mechanical Agitation when used properly will condition the material to a uniform bulk density and eliminate bridging/ratholing resulting in the material filling the flights of the feed. The large inlet exceeds most materials' critical arching diameter, preventing bridging. 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. Common problems include ratholing, arching in silos during discharge, blockage of pipes during powder transport,. There are many consequences of flow problems. 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. The hopper must be designed so the outlet diameter is larger than the outlet rathole critical diameter. include arching (when the powder forms a cohesive bridge over the outlet) and ratholing (when the powder flows out only from the. May be formed by 1. Cohesive Arching Ratholing (Piping) B. Powder Hand Process 4:293–299. 8 feet 12. The frequency of the vibration needs careful consideration as it could affect the flow ability of the powder. 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. 2017). 2 pcf Spring Back Index (SBI) 1. Figure 10. The simple cure is to use Ball powder. Finally. Air displacement as the product flows from the container can cause segregation, leading to an inconsistent end product. 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. Flow issues can hurt your facility so let us fix your ratholing problems. 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. However, flow aids are sometimes used when they are unnecessary and. A key variable that will have an impact on the flow is its cohesive strength. 1. Hoppers. One of the recommended types of flow aids is called Mechanical Agitation. The bulk material continuously in motion. A better approach to predicting flow behavior is to take the characteristics of wall friction (φ w ). The most common causes of these issues are: Improper storage; Poorly selected binder that is too cohesive with the API;. The API AeroFlow automated flowability analyzer was tested using 6 pharma. 2. These flow problems can result in powder caking, production delays, increased operator intervention, or product losses. the types of flow problems that can occur and the flow patterns. Flow function test. 1. Because of this flow pattern, funnel flow silos that are not emptied. 4. Mass Flow also allows the most efficient outlet. 5). The typical problems encountered are either a cohesive arch or ratholing. The total powder flow can be controlled in the level 1 closed-loop operation as indicated in Fig. Mass flow develops when all the material in a silo is in motion whenever any is withdrawn. 2. Keep product moving by preventing buildup, bridging and ratholing. hopper that gives mass flow with one powder may give core flow with another. powder ratholing, bridging, agglomeration) occur. Discharge of powder from a hopper or bin is a common operation in solid dosage form manufacture. censorious. Our pneumatic and electric chute and pipe vibrators and vibratory equipment will: Unload dry or semi dry bulk material. Of course the outlet of the hopper has to be large enough to prevent bridging above the feeder. 4. 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. Purutyan H. 5 % Hang-Up Indices CONSOLIDATION TIME 0 HR 16 HR Arching Index (AI) 1. To find out more about Rotoflo, contact [email protected] Consumer Products Industry Challenges. Circle Feeder is the premier choice feeder that can prevent the segregation during mass flow discharging. This creates a non-flow regime whereby a discharge aid is needed to re-initiate powder flow from the silo. The unique design can feed sticky, fluffy, lumpy, flaky, and fibrous materials without issues of bridging and ratholing in the hopper. Eastern/11 a. 2. pharmacopeial methods to characterise powder flow. Even high viscous material can be fed through the. Mass flow is the ideal flow pattern where all powder moves downwards towards the opening, and is often recommended by powder consultants for consistent and reliable flow. 59 2 Effective Angle Intl Friction 53. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. Our pneumatic and electric bin and hopper vibrators will: Promote the consistent and controlled material flow of dry or semi-dry bulk materials. PBS: Why is the handling and processing of. Preventing Flow Stoppages in Powder Handling Processes. Powder Mix Segregation. 1. If you are experiencing issues with dust in your manufacturing facility, it is probably due to open processing. ratholing (when the powder flows out only from the center leaving the rest of the material static against the walls). Such hoppers are sensitive to arching and ratholing. To overcome bridging the wall friction must be reduced or prevented from occurring. 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. Generally, flow is limited to a central flow pattern. It was shown that a very small reduction of pressure changed the critical orifice diameter significantly. Larger particles are more likely to penetrate the surface than fine particles. , flow pattern (mass flow or funnel flow), and obstructions to flow (arching, ratholing). Calculation of a Hopper Geometry for Mass Flow An organic solid powder has a bulk density of 22 lb/cu ft. The rate of addition and surface motion can either worsen or improve powder addition. Powder rheology is the study of the behaviour of powders as bulk assemblies, consisting of solids, liquids and gases. Acoustic cleaners eliminate this issue, ensuring mass flow of material is maintained and production is achieved at maximum efficiency. On Wednesday, September 21, 2022 at 2 p. Abstract. powder becomes deaerated in the stagnant region of a funnel flow bin, it usually develops 2. Moreover, ratholing will not occur in mass flow, as all of the material is in motion. A proven and practical scientific approach for designing bins and feeders based on a material’s flow properties. Boateng AA, Barr PV. This was attributed to the fact that the poor flowability of APAP could cause ratholing and high flow variations, especially when the powder. Here, flowability and magnetization were measured for a dual-phase steel powder in size fractions from 20 ⩽ D / μ m ⩽ 40 to > 200 µm. Mechanical Agitation when used properly will condition the material to a uniform bulk density and eliminate bridging/ratholing resulting in the material filling the flights of the feed. 1. , wedge-shaped and transi-usable capacity of the vessel. Why are my powders are not flowing efficiently? In ratholing, a vertical flow channel develops above the hopper outlet and, once emptied, remains stable. 2 Flowability indicators used in industries 7 1. In: Brown CJ, Nielsen J (eds) Silos – fundamentals of theory, behaviour and design. 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. They all refer. Comparison of the flow properties of eight commercial dairy powders5. (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. Figure 1: Manufacturing pharmaceutical tablets and capsules involves several powder handling steps. 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. For powders such as T100 and T100M which exhibit arching and. Andrew W. True. 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. A bin experiencing ratholing will have limited live (i. 0 feet Ratholing Index (RI) 10. ), and dry, uniformly-sized larger materials will be free flowing. POWDER FLOW DATA The equipment consisted of a custom-built laboratory scale hopper feeding material in a controlled manner onto a. : Fine Powder Flow Phenomena in Bins, Hoppers and Processing Vessels. 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. 26. Keep in mind that the mass-flow bin design process is iterative. Silo discharge solutions for powder bridging and ratholing. 20-36 , wherein there is shown a hopper assembly H which utilizes a hopper 401 and a hermetically sealed cover 402. It offers automatic and controlled discharge of virtually any powder type, winning where other systems. Critical Rathole Diameters, Df, ft—“D” is the diameter of the opening required to collapse a rathole, while “f” stands for funnel flow. b. Some products like dry cell battery. The requirement that the funnel-flow bin be capable of self-cleaning can usually be met by making the hopper slope 15 deg. Flow obstructions occur when the forces opposing motion exceed the forces promoting. powder flow is uncontrolled due to randomly collapsing of rathole (Royal and Carson. ) the powders are filled into closed cavities; this is followed by compaction using rigid punches and finally the product is ejected from the die. Systems supplied by PTSA often include silos, hoppers, and other storage vessels. The large open inlet exceeds most materials’ critical arching diameter, preventing bridging and ratholing. Provided here is a review of shear-cell testing and how the technique can be used to predict arching, ratholing and other behaviors. The two most common flow problems experienced in a silo, bin or hopper are arching (bridging) and ratholing. Powder Rheology. Particle size also affects wetting. Ratholing is influenced by the bin/hopper geometry and outlet size the material is fed through. Despite being a simple test of compressibility, it can be useful for identification of powder flow behavior. 1 Importance of powder flow in the pharmaceutical industry 6 1. If your effective is 20’ after 3 days at rest the rathole dimension is 18. 71 Funnel / core flow. When your bottom line depends on moving product efficiently through your plant, obstructions. Ratholing occurs when material empties out through a flow channel above an outlet. A brief introduction to the flow properties of bulk solids, and common instruments and tests used to measure them, is given first, followed by a detailed summary of the research works. Many of these flow issues can be traced back to improper discharger or feeder designs. , Listowel, Ireland.