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Sherlock Ohms

The Adventure of the Clogged Fins

July 2, 2009

Contributing Writer Harshwardhan Gupta

I was once called in the late 90s to Mumbai (formerly Bombay) to solve a problem of a large motor of a hammer mill repeatedly burning out. The mill was used for grinding spices, and was originally supplied with a 15 horsepower, 2-pole DOL start 3-phase AC motor. The mill was regularly used to grind a variety of spice blends, and worked perfectly for about 12 odd weeks, after which, it just burned itself out after a long, grinding day (without ever tripping the overload relay, a fact that was missed all along by everyone). The mill only ran one 10-hour shift a day.

The attending engineers reasoned that the motor must have burned out due to overloading, so they replaced it with a 25 hp motor. This one worked fine till it too met the same fate after about 15 weeks. The same reasoning was applied again and the motor was replaced by a 35 hp one. This one lasted for about 18 weeks, and then a 50 hp one gave up after about 22 weeks.

The next was an incredible 75 hp giant, and that one was about to meet the same fate, when I was called in. I stepped into the mill room, which was hot and redolent with the fragrances of every exotic Indian spices like black peppercorn, cloves, cardamom, bay leaf, dried red chillies, mace, nutmeg, black cumin, saffron, ‘cheedphal’, ‘nagkesar’, coriander seeds, star anise, turmeric, black stone flower, allspice, sesame, etc.

The mill room was pretty clean and well-ventilated, and yet the smell of the spices was overwhelming and there was a barely detectable, fine particulate mist of spice powder everywhere in the air in the room. The mill had a large cyclone separator attached to the output end, and the separator had a huge fine cloth sock filter attached to its exhaust to catch all the fines escaping from the cyclone separator. With the mill running, the cloth sock has swelled up like a giant Casper ghost, reaching a height of 15 feet.

The giant motor smelt hot! I gingerly touched the running motor and almost got seared. It was as hot as an Indian griddle used to make bread. I then dangled a piece of fluff between the large cooling fins on the body of the motor to judge the air-flow from the cooling fan, but could not detect any air-flow at all. I re-checked by other methods and that only confirmed my observation.

Suspecting clogged air-passageways, I asked the operator to stop the mill and open the fan cowling of the motor. And lo and behold, the entire space below the edge of the cowl, where it overlapped the cooling fins, was completely blocked with very fine, very oily, caked-up spice dust. So this was the culprit, not the so-called overload.

I asked the operator to take a wire-brush and clean out the air passages thoroughly, and re-assemble the cowl; and further advised him to open out the cowl every week and clean out the air-passages, a fairly easy task.

After an hour of running at ‘full load’, the motor soon cooled down, and ran absolutely cool from then on. I further advised my client to replace that giant with the original 15 hp motor, and save a lot of Rupees in his power bill.

Essentially, the motor’s fan would suck-in the extremely fine, very oily spice dust floating around in the room, and the necessary cooling action would progressively reduce, and finally stop altogether - so the burnouts. Case dismissed.

About the Author:
Harshwardhan Gupta lives in Pune, India, has a B.Tech from IIT Bombay and runs his own machine design studio. He has designed many Word’s Firsts in various custom machines.

Posted by Sherlock Ohms on July 2, 2009 | Comments (21)

July 22, 2009

In response to: The Adventure of the Clogged Fins
Doug commented:

Now you piqued my curiosity - what is the story about the Rolls Royce and ice cream?
Please let me know.

July 22, 2009

In response to: The Adventure of the Clogged Fins
R. Mullins commented:

Without seeing the actual equipment I can only assume interfacing an increasingly larger motor must have been a tremendous challenge by itself. Not to mention the increasing cost of the motor and power requirements. Also based on the description of the fine dust floating in the air I'm surprised a dust explosions hasn't removed all the equipment! By the time they had more than doubled the original HP rating someone should have suspected some other culprit than the motor. Amazing!

July 22, 2009

In response to: The Adventure of the Clogged Fins
William Ketel commented:

It was indeed good diagnostic work. A means to prevent the problem would be to use an external cooling air source. A simple way to observe the clogging developing would have been a motor temperature monitor display with an alarm.
BUT didn't anybody notice that the motors were getting excessivly hot?

July 22, 2009

In response to: The Adventure of the Clogged Fins
Joe commented:

This is pretty tame stuff. Any decent tech with a thimble-full of curiosity would have opened the first motor to find the root cause. Even if the spice house didn't have the staff, the motor should have been returned to the manufacturer.

July 20, 2009

In response to: The Adventure of the Clogged Fins
Todd commented:

It is obvious that the UAW wasn't there, since the dust causing the motor problem wouldn't have been in the plant due to the workplace rules the UAW fought for for so many years.
The cases of emphysema that the dusty work environment will cause in the workers is another "benefit" of not having all those pesky rules.

July 13, 2009

In response to: The Adventure of the Clogged Fins
Bjorn commented:

Good thing it wasn't a UAW plant, otherwise you would still be arranging work orders for the guy to come remove the cover for you. But with the extra motor purchases and the nice long distance travel to point to dirt, the price to fix the problem was about the same. I wish I could troubleshoot unplugged computers not working or out of gas cars that are not running. Gratz on the job!!

July 12, 2009

In response to: The Adventure of the Clogged Fins
Rahul Krishna commented:

I know Harsh is a Designer Par Excellence and this is a perect example of his habit of going deep into details & out-of-box thinking. This story is somewhat similar to the story of Rolls Royce Car & Ice Cream which many HR Trainers refer to in their trainings.Congratulations !!!

July 9, 2009

In response to: The Adventure of the Clogged Fins
Diamond commented:

This is an example of lack of thought for "waste management" (the unwanted heat generated by the motor) in industry. The cooling fins were put on the motor for a reason. No one gave them much thought, even after failures started to occur. The heat waste from the motor was dealt with just as the waste thrown in a trash dump or put at the end of your driveway to be taken away. No one gives waste management much thought until problems occur. Even when the problems occur, the first thought was not to properly deal with the waste (heat in this case), but to power through it. When waste products (heat, sound, garbage) are not dealt with properly, they will cause problems. Garbage is widely recognized for what it is, waste to be hauled away. The same needs to be recognized for heat and noise. They need to be effectively dealt with or there will be problems. Just as when you fill your stomach with too much food, there will be a waste management issue. Good work on your part to recognize that the heat waste was not being properly dealt with.

July 9, 2009

In response to: The Adventure of the Clogged Fins
Giovanni commented:

Well an enclosed motor, air tight, would be a better choice for this type of enviroment. But good troubleshooting.

July 8, 2009

In response to: The Adventure of the Clogged Fins
Loren Rademacher commented:

Given that the motors must have been of the totally enclosed fan-cooled type, but eventually ran as totally enclosed non-vented; and given the technical savvy (or lack thereof) of the plant personnel - perhaps an actual TENV motor would have been another solution that would not have relied on the operator to keep it clean.

July 8, 2009

In response to: The Adventure of the Clogged Fins
Umesh commented:

Great. It is unfortunate that we manufacturer design machines without getting into ground reality or thinking about the site conditions. Congrats.

July 7, 2009

In response to: The Adventure of the Clogged Fins
Vinay Kaul commented:

Someone wrote about common sense - 'that most uncommon thing which by some strange perversion in the English language is called common sense'.
Good to see you are using all your sensory faculties in diagnosis. I will on some other occasion share with you a few similar anecdotes from my experience.
regards
Hope you remember me from IIT Bombay days?

July 6, 2009

In response to: The Adventure of the Clogged Fins
T V R Swami commented:

Nice & Good, thanks for sharing.Many a times environmental / external influences on to the machines either neglected or not easily observable.

July 6, 2009

In response to: The Adventure of the Clogged Fins
Ajay Phatak commented:

Good stuff!

July 6, 2009

In response to: The Adventure of the Clogged Fins
Bhupesh Chavan commented:

Basics is always important.This is another example which confirms.

July 6, 2009

In response to: The Adventure of the Clogged Fins
Renish commented:

Good thinking Harshwardhan

July 5, 2009

In response to: The Adventure of the Clogged Fins
amitabh commented:

Dear Harsh
Thanks for sharing.You are a great designer ,with a lot of common sense!!!!!!!!!

July 5, 2009

In response to: The Adventure of the Clogged Fins
Shriram Sane commented:

Many times the problems have got simple solution, but we go for difficult ones leading to more difficult situations. Proper analysis was carried out by Mr. Gupta. Congratulations!

July 5, 2009

In response to: The Adventure of the Clogged Fins
Bala commented:

Great stuff, thanks for sharing.
Finding the cause and eliminating it, elementary my dear Watson; easier said than done.
I am sure your clients would have spent thousands of rupees blindly, great saving.

July 5, 2009

In response to: The Adventure of the Clogged Fins
P.Raghunath commented:

Hi nice to see your suggestions.
I will be in touch , i am working at Tetra Pak arabia.
Thanks
P.Raghunath
Education & Training

Tetra Pak Arabia

Address:P.O.Box 9454,Jeddah 21413
Kingdom of Saudi Arabia
Telephone: + 966 2 2688187 Mobile: +966 565373900
p.raghunath@tetrapak.com
www.tetrapak.com

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July 5, 2009

In response to: The Adventure of the Clogged Fins
Ramesh Manghirmalani commented:

Excellent Thoughts

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