My task was to develop a device that rotated
the cap at a very low rpm. Optimum speed of rotation required was 3 rpm. The
caps were circular and roughening process needed a device that will hold the
cap and rotate it continuously at very low rpm of 3 so that roughening tool
will roughen it uniformly. There
were a few devices available in the market which would run at 3 rpm, but were
very costly. My aim was to develop such a device that was cost effective.
Initial working thoughts
The project would involve an electric motor as a basic driving
element. Usual motors available in the market rotate at 1440 rpm. One such motor
of ‘Bharat Bijlee Ltd.’ was available in spare with us. To achieve a reduction
to 3 rpm, I thought of frequency controlled drives which was a simple option.
However, using such drives again would prove costly. The company wanted a much
cheaper alternative, as this was one of many operations involved and it was not
worth spending more amounts on this development. High spending on this would
add to final cost of filter that would increase selling price of filter. Filter
market is very competitive having cut throat competition and therefore cost
reduction becomes essential. Hence, I did not go ahead with frequency
Principle of Working
After some study, I decided that the best
option to reduce the rpm was using a motor rotating at 1440 rpm with a suitable
speed reduction unit to rotate job at 3 rpm. Upon search in local market, I
found that ready made local make reduction gear boxes were available in the
market. These gear boxes offered gear ratios of 1:40, 1:60 and 1:80. I wanted
to achieve reduction to 3 rpm from 1440 rpm. Therefore, speed was to be reduced
by 1/480. Reduction gear box with 1:80 was offering the highest reduction. With
given size of gear box, the teeth pitch in gear box reduces with an increase in
speed reduction and its load bearing capacity reduces. Upon further study, I
found that reduction gear box of 1:60 would be an optimum choice. Therefore, I
procured a local made gear box with gear ratio of 1:60. This ensured that the
rpm was reduced to 1440/60 that is 24 rpm.
However to achieve a rpm of 3, an additional
speed reduction of 1/8 was essential. I thought of using another reduction gear
box, but this solution was not suitable this time. I started thinking different
options and one option which came to my mind was ‘use of pulleys’. This speed
reduction could be achieved through incorporating pulleys. Upon survey in
market, I found that V pulleys of diameters 2.5″ and 20″ were readily
available. Three different V belts are available – “A” section V belt, “B”
section V belt and “C” section V belt. For the kind of prevailing load, “B”
section V belt was the most appropriate. Using pulleys of diameter 2.5″ and
20″, I could further reduce the rpm by 1/8. In turn the desired rpm of 3 could
be achieved. This solution was discussed with the plant manager and the
owner of the company and they were impressed with the solution suggested.
Components to be Assembled:
1. Electric motor
3. V belt
4. Reduction Gear Box
I did the entire assembly by myself taking the
entire responsibility of the project. Speed reduction system could be obtained
by first reducing speed to 1/8 by using pulley. 1440 rpm of motor was hence
reduced to 180 rpm by pulley. With an input of 180 rpm to reduction gear box of
1:60, output of 3 rpm could be achieved.
Motor was fixed on a fabricated stand and was
connected to the smaller pulley (diameter 2.5″) using its shaft. Smaller pulley
was then connected to the larger one (diameter 20″) using B section V belt.
Larger pulley was connected to the input shaft of reduction gear box. Output
shaft of the reduction gear box was connected to the cap which would in turn
rotate at 3 rpm. Reduction gear box was fixed on a stand using a mix of
fabrication and use of nut and bolt. Figures 2.1 and 2.2 show photographic view
of the developed device.
Once the product was assembled, I carried out trials
on 10 caps. The results that I got were as per company’s expectations. A
detailed report of design, manufacturing and cost analysis was submitted to the
plant manager. The final product is now a permanent fixture in company’s
My work was appreciated not only by plant
manager but also the owner of company. This was my first practical experience
in a manufacturing company. I learned to do root cause analysis of any failure.
I also got immense knowledge about motors and reduction gear boxes. On doing
the cost analysis of our product, we found that our product was costing INR
9,000.00 which is almost three times cheaper than the readymade motor available
in market. One more reason for me to be happy was that the entire project was
completed within the stipulated time period.