To help my customers solve some problem in the rubber mixing cycle, I often analyze the steps (or phases) programmed in the mixer.
Almost always the capabilities of the automatic mixer control system are only minimally used, this limits the optimization of the cycle and consequently leads to higher costs for the company.
In the DosareX system, mainly 3 criteria are used to determine when to perform a step change or when to terminate a cycle.
These are:
– Time;
– Temperature;
– Energy;
Companies coming from a purely manual management of the mixer, tend to use only one of the variables, ignoring the benefits of a composite use of the 3 parameters.
I want to bring you back an adapted text by P.K. Freakley of the Institute of Polymer Technology at Loughborough University (UK) that was written a few years ago but clearly indicates how energy is a variable that should be actively used to achieve a better cycle.
<<The time variable is the only one that does not depend on other quantities; consequently, it is completely indifferent to raw material conditions, mixer temperature, rotor speed, or anything else.
The temperature of the compound is usually measured by a thermocouple mounted on the discharge door or in the mixer body; it is related to the energy used in mixing and the energy subtracted by cooling.
Although it is affected by the temperature of the mixer chamber, it is still a good indicator of the state of the compound.
When we talk about energy, we refer to the electrical energy consumed by the main motor during the mixing phase minus the energy required to move the empty mixer. Since this value is expressed on a time basis, it is an integral of instantaneous power.
This quantity gives a good indication of mixing performance although it does not take into account the rate of power input (you could work for a long time at low power and consume the same energy compared to working for a short time at high power, nda).
This power rate is directly related to the torque of the rotors at constant speed and is therefore related to the force applied on the components during the dispersive phase.
Time and energy are used to determine when to load the components while temperature is used to determine the time of compound discharge.
In addition, the electrical power of the motor is often used as a criterion for determining when to add other components, particularly oil, which is normally inserted after the peak motor power due to the end of the dispersive phase.
All of these quantities are indirect indicators of the state of mixing, so they must be related to the properties of the components used, the other machines in the line, and the performance of the product to be obtained.
Their value depends on their sensitivity in predicting changes in material behavior and how much they are affected by other factors (e.g., machine temperature).
Ideally they should only be sensitive to material properties.
This characteristic is most displayed by the energy magnitude.
It has been shown that the “first cycle” effect, such that the first four or five batches are different from the following, is greatly reduced by using energy as a criterion.>>
What we can deduce from this writing is that there is not just one variable to use during the mixing cycle but, depending on the phase, a certain variable or a set of them should be used.
Too often I see customers using only time or only temperature when the correct thing is to use the set of the 3 quantities.
As you know the DosareX system provides logic AND/OR use of variables so you can program the phase change when 2 or 3 conditions are reached at the same time or when one condition takes precedence over the others.
You can find an example video of our mixing room control system at this address:
I am not a technologist or a chemist, and it is right that each company has its own experiences and uses its own method, so it is not my intention to tell you how to program the mixing cycles of your mixing room.
My job is to give you all the tools to help you translate your knowledge and experience into an efficient and replicable cycle.
If you have one of our service contracts and can’t remember how to program the mixer steps, give us a call and we’ll help you get the most out of your machine without asking you a dime.
Buona vita
Claudio Tosi
