High mixing is the process of putting pigments, dispersants and carriers into the high-speed mixer for high-speed mixing according to the designed formula.
Practical experience has shown that the pre-wetting of pigments in the high-speed mixing process largely determines the final dispersibility of the masterbatch.
According to pigment dispersion theory, combined with high-speed mixing practice, for different material varieties, different requirements, different uses, after continuous exploration, accumulation of experience, in order to gradually improve the high mixing process, while through the high mixing practice can help improve the formula.
Here we will take a look at the key points to be noted in the high mixing process.
01 High-mixing process carrying material volume and speed
The load capacity of the high-mixing process is related to the volume of the high-mixing material. Too much or too little load will affect the normal operation of the high mix and make it difficult to achieve a good high mix quality. The speed of the high mix is generally divided into two grades: low speed start to reduce the power load; high speed mix warming and discharge, with the exception of special structures.
02 High mixing process temperature and time
Without a certain temperature, the high mixing process can not achieve the initial wetting of the pigments, and the key role of the high mixing process is lost. There are two ways to source heat for the high-mixing process.
(1) Through the high mixer jacket oil heating transfer temperature, need to set the temperature control.
(2) Through the material high-speed stirring friction heat transfer temperature, but the first pot of high mixing time is relatively long to accumulate temperature.
As the high mixer jacket has a thermal insulation effect, the time required for a continuous single high mix later on is more regular. The temperature control of the high mixer is related to the molecular weight and quantity of the dispersing wetting agent. A practical understanding of the ideal high-mixing result of the final material can be achieved by means of a temperature control system.
As most of the wetting and dispersing agent has a softening melting and wetting process, it is with the temperature rise gradually melting wetting pigment, and at the same time covered to the carrier, until the material “stirring cooked” put out, disperse wetting agent actually most difficult to 100% melting, so the theoretical melting point of dispersing wetting agent does not exactly match the high mixing temperature.
The time required for high mixing is the time required for the material to “cook” and for the dispersing wetting agent to melt and coat the carrier. It is related to the mode of temperature transfer, to the composition of the material and to the weather. Most of the dispersing wetting agent molecular weight is relatively small, the more dispersing wetting agent, the shorter the high mixing completion time. The longer or shorter the time, the more time is needed to perfect the recipe and finally reach the high mixing quality standard.
03 High-mixing process observation and automatic control
The high-mixing process requires careful observation and there are two types of observation.
(1) A transparent observation port is provided to observe the changing state of the material at any time, but the transparent window can easily be contaminated and affect the observation effect.
(2) Indirectly through the change in current.
At the beginning of high mixing, due to inertia, the resistance is very high, and the power equipment starts with high load, causing the current to jump high instantly.
After entering the normal uniform operation, as the material is loose state uniform movement, the load of power equipment is very light, the current is then reduced. As the temperature rises, the dispersing wetting agent begins to melt gradually, and the state of adhesion between materials becomes more and more serious, causing the motor load to increase, and the current pointer is gradually rising in a wave-like jitter.
Eventually the current stops fluctuating and gradually increases and the material slabs at the bottom of the barrel. The change in current during the high-mixing process conveys to some extent the information about the change of material in the confined state in the high-mixer. The best time to terminate the high mix is theoretically after the dispersing wetting agent has sufficiently melted and coated the carrier. Experience shows that this time is roughly the short wise interval before the current rises slowly and continuously to the “rotten pot”.
If automatic control is to be designed, it is more difficult to design automatic control based on current variation, but more feasible to design automatic control based on temperature variation.
04 High mix quality judgement
After the high mixing process, if the material is basically in its original loose state and there is a lot of dry powder flying, it is generally judged to be unqualified and needs to be reworked to continue the high mixing. If large lumps are formed, even at the bottom of the drum, commonly known as “rotten pots”, or if the material is loose when it is put into the drum and after a few hours it is stored in large lumps, then it has to be mixed and crushed again.
It is generally considered that the ideal state is one in which there is essentially no dust, where the pigments are wetted and stained onto the carrier, and where even the largest particles can enter the screw granulation smoothly, which is the ideal quality for high blending. Special attention should be paid to the fact that the high-mixing process is a process of wetting the pigments and that the wetting agent replaces the air and water on the surface of the pigment, so that the removal of water should be taken into account to ensure quality.
05 Environmental requirements for high blending
This is the main focus of environmental control and the authorities often monitor companies by testing the dust and odour content as a standard.
Most companies currently install inverted funnel-shaped dust extraction equipment above their high mixing equipment, which draws the vast majority of dust and gas into the pipeline by suction, and transmits and filters the gas for processing and release, and collects and disposes of solid waste.
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