Views: 15 Author: Site Editor Publish Time: 2012-04-18 Origin: Site
The small-media mill is a ball mill. Ball mills with balls several inches in diameter show in the history of paint making, back when pigment particle size reduction was in the grinding foreman's bailiwick. At some time in this history, it was found that the big balls were not necessary, and small balls were more efficient. This progression continued until late ball mills used media in the range of 3/8" to 5/8" diameter. Little by little the pigment makers caught up even with these mills, but they ground away for years with little change.
Several people were at work in the area however, and, intrigued with the mathematics of it, reasoned that as the pigment was getting better, that less energy was needed to disperse it. In several momentous jumps, it was found that plain Ottawa sand, a true ball with many of the physical characteristics of the big balls, had all the mass necessary, assuming that sufficient velocity could be applied. Thus, instead of moving tons of balls, it was found that a few pounds of sand would do much the same work. An early paper by DuPont's Dave Bosse (1) pointed out that a 700 micron (25 mesh) particle of sand, moving at 2,000 feet per minute, could exert sufficient force to do most of the dispersing then (40 years ago) necessary to disperse the pigments then available, in a sensible vehicle system. This same size "ball" could be crowded 64,000 per cubic inch, each little ball doing work at six point, as against 25 such balls 3/8" in diameter in the same cubic inch! With much better pigment and better understanding of vehicle behavior, it is apparent that even better results should be possible today. All small-media mills work on this principle, that if only a small mass is needed, and that many points of contact can be provided in a small volume of media, all that is necessary is a mechanical device to impart velocity to it. Thus, whether they stir, spin, or shake, whether they have bars, discs, cylinders, or no apparent agitator at all, if they lie horizontally or stand vertically, if they give this velocity somehow, they will do the same work. The proof is there - all these machines work, each claiming superiority in some area, but all indeed doing the job.
Most of the original sand mills started as vertical cylinders. So indeed was the original - the bucket of sand - a vertical cylinder. Instead of pouring in a bucket of paste, stirring it, then dumping it out ground (this is the way a ball mill works) someone soldered a screen on the bottom and started pouring paste in the top. When coffee breaks became too demanding, another wise operator talked the maintenance crew into giving him a pump to feed it from a really big premixer. Others went off on the batch track, making big mills which could (and still do) make all their own premixes, and which could just be run until the grind was accomplished, then drained through the bottom. Someone began pumping paint into the bottom and screening it over the top, and the most popular mills operate on this principle now. The late bottom feed mills have a little further refinement of a "closed" top which contains the flashed off volatiles, and handle a wider viscosity range. They all came from the original bucket of sand, however, and they all are controlled by exactly the same principles of physics and mathematics. Certain space and mechanical advantages result from making the machine horizontal, and many, if not most, are now built that way.
The bead mills production industry has begun in China since 1980's. Before that, all technologies of the bead mills includes vertical bead mill, ball mill, pin type conical bead mill, horizontal agitator bead mill etc. advanced bead mills were controlled by the famous manufacturers from Europe. But with the development in China, the engineers have begun to research the bead mills construction to do the new designs which are suitable for our domestic paints, inks, pigments etc. industries.
At first, the simple vertical bead mill or ball mills occupies the majarity of the domestic market. With the paints etc. quality requirement, the horizontal agitator bead mills become more and more popular caused by the advanced construction to ensure better particle fineness. The grinding discs type with different materials such as ceramic grinding discs etc. to ensure high quality requirements.
Until now, there are various kinds of bead mills for the customers choices. To meet with the different production requirements, we also recommend our customers choose the most suitable materials and bead mills construction.