INTRODUCTION TO
MANUFACTURING
Case Study: Thermometers- By: Bitisa Kandel
INTRODUCTION
A thermometer is an instrument for measuring the temperature of a system. Temperature
measurement is import to a wide range of activities, including manufacturing, scientific
research, and medical practice. Over the years there has been many different variations of
thermometers like digital thermometers, electronic ear thermometers, forehead thermometers
but for this case study we will be looking at glass and mercury thermometer. [I]
[VI]
[V]
MATERIALS USED AND MATERIAL CONSIDERATION
Thermometers consist of these basic elements:
Spirit-filled liquid (Mercury) kerosene or ethanol may also be used which responds to
changes in heat and cold. Due to environmental concerns, contemporary thermometers
are manufactured less with mercury and more with a spirit-filled hydrocarbon liquid.
A glass tube to house the temperature-measuring liquid.
Black ink to colour in the engraved scale marks with legible numbers.
A wax solution used to engrave the scale marks on the glass tube an engraving engine
that makes permanent gradations on the glass tube
A hydrofluoric acid solution into which the glass tube is dipped to seal the engraving
marks. [II]
[VI]
Why is mercury used:
It has high coefficient of expansion. Hence, the slightest
change in temperature is notable when it is used in a
thermometer. It also has a high boiling point which makes
it very suitable to measure higher temperatures. With
changes in temperature, the mercury expands and
contracts, and the temperature can be read from the scale.
[IV]
Why is glass used:
Glass has a very low coefficient of thermal expansion. This is the reason
why thermometer bulb or for a matter-of-fact entire thermometer is made up of glass. Due to
low coefficient of thermal expansion, when the thermometer undergoes a large temperature
change it will have minimal change in dimensions for which we will get an accurate reading
of the temperature. [III]
MANUFACTURING PROCESS
Thermometer manufacturers start with glass
blanks with bores down the middle; these are
usually received from glass manufacturers. The
bulb reservoir is formed by heating one end of
the glass tube and pinching it closed. The bulb is
sealed at its bottom, leaving an open tube at the
top.
Next, with the open end down in a vacuum chamber,
air is evacuated from the glass tube, and the
hydrocarbon fluid is introduced into the vacuum until
it penetrates the tube about 1 inch. Due to
environmental concerns, contemporary thermometers are manufactured less with mercury
and more with a spirit-filled hydrocarbon liquid.
After the bulb reservoir is formed
and the liquid inserted, the unit is
heated and sealed. Next, the scale
markings are added. This is done
using engraving, in which the bulb is
dipped in wax, the marks engraved, and the bulb dipped in hydrofluoric acid to seal the
marks on the glass. [II]
SUITABILITY OF MANUFACTURING PROCESS
With the variety of different thermometers there are many ways of manufacturing of each those
thermometers. I chose this method of manufacturing because the manufacturing process other are
more complex compared to the glass-mercury thermometer.
REFERENCE:
I. Britannica, Thermometer measuring instrument, written by editors of encyclopedia Britannica, Last
updated 11th Nov 2020, https://www.britannica.com/technology/thermometer
II. How products are made, Thermometer, http://www.madehow.com/Volume-1/Thermometer.html
III. Quora, why are thermometers and electric bulb made of glass, written Saptarshi Majumder, 20th June
2016
https://www.quora.com/Why-are-thermometers-and-electric-bulb-made-of-glass
IV. The Times of India Why is mercury used in thermometers despite being the poorest conductor of heat?,
11th Feb 2007,http://timesofindia.indiatimes.com/articleshow/1590334.cms?
utm_source=contentofinterest&utm_medium=text&utm_campaign=cppst
Images:
V. https://ie.rs-online.com/web/p/glass-thermometers/2068878/
VI. https://www.sciencedirect.com/topics/nursing-and-health-professions/mercury-thermometer
VII. https://www.chemistryworld.com/podcasts/mercury/3005860.article
