Grinding Processes and Magnetic Particles

Are you really trying to ask us if the product being ground is picking up ferromagnetism from contact with your grinding wheels?

WHat is your process? Blanchard, centerless, infeed, throughfeed, or between centers, vibratory bowl, creep feed or crush grinding?

Is there a magnetic chuck or worktable?

Is this electrical powered equipment?

How are you measuring magnetism?

Or is your question related to the "stones" picking up iron or steel and thus being 'magnetic.'

What is your material?

What is your "stones?"

Please describe the problem in terms of process.

Thanks.

milo

Please state your question.....it is not clear what the problem is, or what you want to do.

Our products are different types of spices. In grinder(electricaly powered) there are 60 offcenter blades or hammer plates.

To increase weight of raw material suppliers are mixing stones in product which difficult to separate it 100%. stones are basically those construction stones.

Some part of stones are going through the process how we can separate those 100%.

#1 Stop purchasing product from cheating suppliers - and tell them why you now buy from their competition. If you ever go back to them it should be dependant upon their making good on what they cheated you out of plus the losses to you in production as well as damage to your equipment from their stones and changing of your production process to correct the problem they created.

#2 The stones will not be magnetic unless they are lodestone - not likely. Friction on rocks will not make them magnetic. Use the fact that the stones are more dense than the spices and use puffs of air to separate them. This is similar to separating wheat from its chaff except the heavy stuff in your case is what gets thrown away.

Whilst the stones are unlikely to be magnets, they may be attracted to magnets, depending on their composition. As a child I was surprised at how much our dirt track gravel stuck to magnets. A magnet may remove some of the stones, however as there are no guarantees as to the stones' magnetic properties it's still better to rely on the density difference.

First use suitable sieves to separate out undersized and oversized contaminants. You particularly need to get rid of undersized contaminants, as they'll behave more like the spices in the density based separation (eg rock dust blows around more easily than rocks, even though they have the same density).

Then you can either blow the spices away from the stones, or throw the mix into the air with uniform velocity (eg by dropping/pouring them onto a rapidly spinning wheel) causing the denser stones to travel further than the spices as air resistance slows the spices down more.

How this clay particals some times get attracted to magnet.

Density sometimes not help us.

If you use air it creates problem in envirenment.

If you use blower its difficult to regulate.

Milo - you asked me so many genvine questions please show interest in this problem.

Good evening Sandeep. I had no idea about your process, so I have stayed back. You have been given several good answers already, but I understand your airquality concerns.

I especially like the spinning wheel (centrifugal) idea to fling off the rocks.

When I was in college I worked at a screening station for iron ore, and in addition to using the screens of various sizes, we used the speed of the conveyor belts to throw off the heavy stones farter down a chute while the fines fell into the bin directly below the end of the head pulleyclosest chute.

I do not know your batch size, but if it is boxes that people can lift you could make a nice screen using what we call 1/4" hardware cloth To capture the coarse stones larger than 1/4". My wife and I made a two person one to screen mulch to turn it into fine garden soil. We set it on a wheel barrow, dump some unprocessed mulch onto the screen, then pick it up and shake it , the fines fall into the wheelbarrow, we take the coarse to another whell barrow or cart and dump it elsewhere.

You can staple two or more pieces to get the proper opening size for your spice material.

For your spice mix, I would then take this screened material and experiment with different means of further separation, the spinning wheel already suggested, ( Hint- old phonograph for trials!) inclined conveyor belt of different speeds to learn of the "throw" is practical, or perhaps you could use a vibratory bowl feeder. See photo below! different settings could cause either the spices or the heavies to climb the helix.

Your commercial problem is really corrupt suppliers. Even if the spices are purchased at auction, you should inspect, and refuse to buy contaminated product. What if the "stones" are contaminated with lead, arsenic, mercury, pcb's, fertilizer, or fecal contamination?

I realize you don't have the same commercial rules that we enjoy, but this case really sounds like you are being forced to take it or leave it, and you think you can't afford to leave it. However, you can't afford to take it either.

Over here we have the same issue with oil contamination in brass chips. The buyer of the brass chips determines the oil/moisture content of the load returned, then adjusts the price that he pays based on the amount of unwanted oil/ moisture. More oil/ more moisture = less $ per pound of chips.

Here is picture of vibratory bowl

Here is info on supplier from India:

Company Information:
Name: Elscint Automation
Address: W-191 Bhosari MIDC,
City: Pune
ZIP: 411026
Country: India
Phone: +91-20-27122059
FAX: +91-20-27122994
http://www.elscintautomation.com

Thanks for the callout Sandeep. Keep us informed.

milo

Hi again Sandeep.

1) The clay particles may contain iron impurities, which could allow them to be attracted to a magnet. You'd have to test a sample.

2) I'm not sure what you mean by "Density sometimes not help us".

Construction stones are almost certainly denser than just about any spice (correct me if I'm wrong), in which case you just need the right density sorter. Size screening is IMPORTANT for any air-resistance based sorter, as smaller size will mimic lower density. This may mean that you have to sort the same spice in different lots so that you don't have small stones in with large seeds, for example.

If you pre-wash the spices you may be able to use water as the sorting medium - even if the spices sink, the right flow rate should pick up the spices but not the stones. Below is a rough diagram of how it could be done.

With a little ingenuity this could be modified for air use, driven by a vacuum rather than a blower so as to make air quality control easier (the exhaust air could be filtered). Airflow could be adjusted by using different diameter updraft tubes, by adjusting power to the vacuum motor, and/or by "wasting" some of the vacuum by way of a controlled leak. For continuous processing you might have to use a hybrid of vacuum plus blower so as to reduce the suction at the outlet and allow the spices to exit.

3) For a more regulated blower, use an air compressor and a pressure regulator. As long as you have a enough pump and air tank capacity this should give very good regulation.

4) If the problem is not equipment damage, but rather contamination of your end product, you may be able to remove the stone fragments by using a fine sieve.

5) Appropriate vibration applied for sufficient time should cause the rocks to settle to the bottom of the spices. For spices other than seeds this may be more effective after the grinding process, or at least a preliminary break-up process (e.g. rocks could get trapped in pieces of cinnamon bark and not settle out).

6) Other separation possibilities include electrostatic attraction of the spices (CAUTION: beware of organic dust - explosion hazard), inductive attraction of the rocks, and paramagnetic repulsion of the spices. These are all only theoretical possibilities, in case nothing else works, and would require experimentation.

7) All these suggestions assume you have no way of stopping your unscrupulous suppliers adding rocks in the first place.

P.S.: My earlier suggestion of a spinning throw wheel was meant to refer to a vertical wheel, effectively acting as a minimalist throw conveyor. I had considered a horizontal wheel, but decided a vertical wheel would give better control and use less space.