The bulk material is handled ‘bulk’. A LEGO piece is a brick but 1,000 poured into a bag of bulk material. Corn starch, sand, flour, powder-coat powder, pebbles, cat food, cap’n crunch, coins, screws, styrofoam beads, lead shots and glue worm bulk materials.
There are lots of applications where you have to move a lot of things Selective Sintering 3D Printer, Animal Feeder, DIY Injection Molder, Toner Based PCB Maker, Home Powder Coating, Automatic LEGO / Domino / Ya-sorting or Assembler, Automatic Gardener, Airsoft Managing Parts – Balls College science classes cover solid and fluid, but rarely bulk materials.
Most hackers just pray that it works and tap the bin when it doesn’t. Art works well, but the term slander is “bin rash”, The long-term consequences of this Tapping A 300 ton bin, including a sledgehammer (video), shows that they don’t always get it right. At the same time, this is a fun area that you can experiment with using kitchen items. So come with us for a short series on the basics of bulk material management.
Arching, Ratholes, and Slurping
A common bin contains a cone or pyramidal Funnel With a cylindrical or rectangular bottom Vertical Section above it. Called joint Buttocks. The funnel is an end OpenOften with a control The gate.
Bulk components have a slightly integrated strength compared to solids, but of course it varies across different materials. Lead shots, for example, have a slightly integrated force and flow easily. The flour has a high adjustment strength, and is difficult to pour. An element flows only when the balls across a part of the element exceed the combined energy of the element.
Imagine that there is a small amount of wet sand in the bin just above the gate and we open the gate. Will the sand fall? The sand is now the opening bridge, and the force is just like any other bridge. We want the bridge to fail reliably.
Usually the first little bit will fail and fall out. But as it does, it can leave behind a curved surface. If the arched material could bridge the opening, it would not flow at all. Leave a hole with a round roof, fall out a little, and stop the flow. There are elements Arched.
When the bin is smooth and the funnel has a steep angle, the material flows Mass flow. All material flows, and the flow in the cylindrical section is only vertical. The top surface of the material will go down without rearranging until it reaches the buttocks. For many materials, a smooth interior wall and a conical angle of more than 60 degrees is a good design rule for mass flow.
Instead of slipping on the wall-material interface, if the funnel is too blunt or the walls are too rough, the material can be assembled somewhere internally. This Funnel flow. The material has its own form, sharp funnel inside, and only material flowing inside the funnel. Funnel flow is not inherently bad, but there are more potential problems. (Useful page for flow problems here).
It could be Rat hole – The material flows, but makes holes almost vertically on the opening. Most of the material is not moving, and when the hole reaches the surface, the flow stops, you get a Stable chariot. Even if the rathol is not stable, the outer material is not moving so you can make a small bin. Worse, the stuck material may rot or decompose or become hard compacted.
A couple design tips. The corners of the rectangular bins have more walls to ‘support’ the element, so often hang up in the corners. Use a round bin if you like. Also, the diameter of the rathol will be slightly larger than the opening ear. Sometimes slit opening works are better than round holes.
It can do this when the material is dumped Liquefy, Not fragments but becoming independent particles. Drop one teaspoon of flour from the height of the chest. It turns into a cloud of dust instead of being read as a pile.
Feeding into a rathol can cause liquefaction by dropping new stock directly. Worse, it could tear some part of the rathole wall. It is said to crash all at once, at high speeds Flood – New material and as a liquid the hole falls down and discharges at high speed.
It can break down gates or bean feed, and if mixed too finely with too much air, there is a risk of shortness of breath or even an explosion. And it can lead to isolation.
Most bulk components contain particles of different sizes and often contain different components: gravel below, mixed nuts, a jar of mixed screws. The Brazil nut effect, where a jar of mixed nuts ends with Brazil nuts at the top and peanuts at the bottom, is a form of Separation.
Mix salt and dried peas and pour the mixture through a funnel on a plate. The mixture forms a conical pile. Roll down the pile of peas and finish at the edge of the plate. Feeding from a small central pipe or chute separates the larger components near the walls. If the grasshopper is emptied by funnel flow, the last ingredient is mostly salt. The pea lags behind.
One remedy is to have part of a long cylinder with mass flow and keep the surface of the material above the buttocks. Then the material is moved in the same order it came from, whether it is from the wall or the center. Inserts can help get out of segregation issues. An upward pointing cone on the standoff inside the funnel forces the components from the center to mix, and a baffle plate below the inlet can change the inlet character from a central point to a much smaller feed. Sometimes reducing the creek can help.
Throwing potato chips in an empty two-meter bin guarantees that it will break, but relatively light misuse can also break the particles, as the capon shows the dust under the crunch box. Probably a few centimeters of tan color powder was loaded into the bag at our morning cereal factory – it must have been wasted during transit.
Some elements develop a static charge when it moves and it can interfere with movement. Acrylic or polycarbonate laser-cut bins are often a culprit. A simple test – rub a balloon into your hair, then hold it against the material you want to remove in bulk. If it’s a material pick, fix it to a grounded metal bin.
Some materials are abrasive. Sandpaper is after all adhesive sand on paper. In addition to hard bin materials, intentionally inducing funnel flow can protect the walls. A large funnel only makes a good grasshopper capable of an abrasive blunt enough for funnel flow.
Next week, we’ll take a closer look at the properties of bulk material, and a week later, we’ll look at equipment to move bulk solids around. It has been a whirlwind tour of some terms and problems that can only be presented by leaving bulk material in a bin. Hopefully, this has at least helped to name a few of the lessons you’ve learned from playing in the kitchen or sandbox.
To summarize, TL; DR for most bin designs is:
- Use a round bin with smooth interior walls.
- Place the funnel section walls over a 60 degree bend.
- The bigger the opening, the easier your life is. Slit may be better.
- This is a warning sign if the surface is inclined internally.
- Watch for isolation.
See you next week!