Cool it down and Crush it

by Pablo Marroquin, 12.02.2021

Today I woke up, and still in half a Zombie modus I put my slippers on and went to drink a delicious cup of coffee to kick-start my day.  I was still not 100% awake, so my daughter managed to convince me to go jogging with her.  We put our jogging shoes on and went out for a short run.  I came back sweating like crazy.  It was a good start in the day.  Now just keep the momentum…. shave, shower, dress up and we are ready to work.

And let me tell you guys…. I work in one of the coolest places you may imagine.  Triangular is an incredible place to work.  Besides having a fantastic team we also have an incredible product.  At Triangular we run a digital platform to connect customers that want to process materials with the equipment and know-how they need.  Many of the things we use in our daily lives are made with materials we help to process.  I just have to remember a couple of products I used today: the slippers, the coffee, the jogging shoes, the handle of the razor, the anti slip bathroom carpet, my clothes and many of the interior materials of my car.  When I think about it, they have more in common than I originally thought.  To get the raw materials ready cryogenic grinding may be just the right process.

What is cryogenic grinding?

I thought you would never ask!!

Cryogenic grinding is a very special process. In pure technical terms cryogenic grinding is the act of reducing the thermal energy of a material until it reaches its ductile–brittle transition temperature (DBTT)  in order to make the comminution below a desired fineness possible. Let me translate: it is basically freezing a material and then crushing it into small pieces.

There are many reasons why cryogenic grinding is necessary.  One of the most common reasons is to be able to achieve the required fineness.  It is a known fact that size reduction is an extraordinary energy consuming process.  Most of the energy used in size reduction processes is lost as heat and only a fraction of it is actually used to reduce the particle size.  The finer the required particles the more energy you will have to use.  And of course there are “special” materials that simply don’t like to break at normal temperatures irrelevant of how much raw violence you are able to use.  

To help you visualize this drama I will give you two examples.  The first example would be the plain and standard chewing gum.  You can chew as long as you want with all your humanly possible force and the perfide little chewing gum will simply refuse to break down. On the other hand it is exactly what you are expecting it to do.  Who would like to have dust in the mouth after a couple of minutes of active chewing?  

The second nice example would be a rubber ball.  If you hit a rubber ball with a baseball bat or a racket trust me, it won’t break. You may be the strongest person in your neighborhood, it will bounce like crazy when you hit it, but it won’t break.

Have you tried to put a chewing gum in the freezer overnight and the next day just take it out and try to chew it right away?  I am really curious how many of you will try it tonight.

By cooling down materials to cryogenic levels they pass the ductile–brittle transition temperature (DBTT).  DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming. This principle is used to make it possible to micronize materials that under normal circumstances won’t be grindable at all. Like the rubber ball.  If a rubber ball is cooled down using liquid nitrogen it will simply obliterate when receiving an impact.

To cool down a product to cryogenic temperatures for milling is expensive, but it has very important advantages.  Among others we may mention that the processing capacity would be drastically increased.  This translates into a lower energy consumption for each unit of mass produced.  Also a much finer end product may be achieved, increasing the end value of the material.  In the total addition this process may be the only economically viable solution for certain materials.

If the monetary advantages are not enough we may also talk about some of the technical advantages that cryogenic grinding offers.  For example avoiding thermal damage on heat sensitive materials.  Or improving the flowability, because the particles will have better defined shape (for some materials even a very nice cubic shape) and smooth surfaces.  

There is also a safety advantage when using cryogenic grinding.  To cool down the materials the most common method is to use liquid or solid Carbon Dioxide (CO2) or liquid Nitrogen (LN2). This automatically creates an inert gas atmosphere reducing the risk of explosion when processing dust explosive products.

What kind of materials require low temperatures to be efficiently processed?  Well let’s check the products I mentioned: the slippers, the coffee, the jogging shoes, the handle of the razor, the anti slip bathroom carpet, my clothes and many of the interior materials of my car.  These materials may be divided into basically three categories:

• Extremely ductile materials at normal temperature, like thermoplastics and elastomers used in the handle of the razor slippers and jogging shoes.
• Materials with a very low melting point like some types of hot glue or adhesives used in the anti slip bathroom carpets, in clothing and interior of cars.
• Products that would lose important characteristics with an increase in temperature like the essential oils in coffee.
  

Talking about essential oils…. spices may be also processed using cryogenic grinding.  If you want it hot and spicy you need to cool It down and crush it.  I already talked too much about spices and coffee, and that made me hungry.  So I will go and eat something now and drink a good cup of coffee.  Next time I will tell you more details about the technical equipment needed for cryogenic grinding and how the process works.

To be continued…...