Search This Supplers Products:horizontal bead millhigh speed dispersersingle screw extruderpowder mixercooling beltparticle size analyzer
Questions and Answers About Horizontal Bead Mill
time2012/05/06
WHAT IS THE BEST PUMP FOR ME, THEN?
Either lobe type rotary or a gear type rotary. The gear type has a price advantage, while the lobe type will accept larger lumps. If your experience is such that a pump lasts a year or more, then consider going to the abrasion-resistant types of gear pumps, as they are more costly but much longer lived. Abrasion resistant pumps often use tungsten carbide or hardened cast iron wear surfaces and special hard-faced mechanical seals. If your pumps last only a few weeks or months or you cannot keep from feeding them media or steel balls or drum bungs, then buy the cheapest that will fit.
MY STRAINERS PLUG UP AND THE MEN JUST LEAVE THE SCREENS OUT, RATHER THAN CLEAN THEM. IS THERE ANY HELP FOR THIS?
Indeed. First, keep junk out of your premix, bag scraps, cigarettes, etc., which CAN be kept out. Next, see how long it takes on a typical batch to plug your strainer. If you get half a batch out before having to clean the strainer, then get a strainer with twice the open area of screen. Use a basket type or a so-called self cleaning type and make it reachable. Put a pan under it. You can also look at buying a duplex strainer, or pipe in two simplex strainers in parallel so that one strainer can be cleaned without shutting down the mill. If the man doesn't have to make a project out of it, he will clean it with less fuss.
WE RUN OUR SANDNMILLS AT HALF-MAST BECAUSE WE CAN'T GET THE GRIND. THE MILL PEOPLE TELL US WE SHOULD GET 80 GPH AND WE HIT 45 IF WE ARE LUCKY. WHAT'S WRONG?
Running a mill must be learned. Read the foregoing list of variables and work at them ONE BY ONE, your answer will probably be obvious. If this fails, go to the pigment people. Each of them can tell you how to handle their pigments in a sandmill, or give you formulation help. Sometimes the fault is as simple as an improperly cleaned screen, or an operator who is expected to gauge heat with his palm instead of a thermometer. Get someone form the other end of the plant and have HIM check out your variables. We find that firms who take the time to reformulate to take advantage of newer types of media and mill types are the companies who maximize production from their mills. When you change to a new mill or new media, it pays to re-optimize the mill base formula.
WHAT DOES A PUFFY OR BUTTERY PASTE HANGING ON A SCREEN INDICATE?
Almost invariably-too low resin solids. If the vehicle demand of the pigment is not satisfied, it will hang onto anything it can get, and the most available "fluid" is air. Just move up a few points at a time on resin solids, or down on pigment concentration. Take solvent out to compensate.
I GET GRIND MEASUREMENTS THAT ARE OFF THE SCALE FROM THE SCREEN, BUT SOMEHOW WE LOSE GRIND IN THE LETDOWN AREA. WHY? HOW DO I SOLVE THIS PROBLEM?
This is obvious. The mill is not at fault, for it has proven, at the screen, that it can do the dispersing, even though the product is unstable. Again, this is usually too much pigment or too little resin. Solvent will shock it out, or air, or even resin sometimes. If you can't reformulate, then try dropping the paste into some resin while mixing.
ON OUR CLOSED MILL, ESPECIALLY WHEN WE ARE STARTING A BATCH, THE MEDIA SEEMS TO JAM BETWEEN THE TOP DISC AND THE UNDER SIDE OF THE COVER. IT GETS HOT, SOMETIMES ENOUGH TO SMOKE OR EVEN CHAR. WHY?
Almost certainly you are pumping your paste in too fast behind the solvent. If the media bed is full of solvent, it is like damp beach sand, and has little flow. It is just extruded ahead of the paste-solvent interface, and it never becomes homogeneous with the more lubricant paste. When it gets into that dead area at the top, it becomes a relatively dry, non-fluid mass with low heat loss, so it just gets hotter and hotter. When you start such a mill on paste, start it dead-slowly allowing the media to mix with the paste rather than being pushed ahead of it. This takes a few seconds longer but is worth the time. This will help keep you from blowing out your screens also, because that dry media jams itself into the screen tightly, and before you catch it the pressure is up.
MY SCREENS BREAK FREQUENTLY, MORE SO THAN IN OTHER PLANTS. WHAT DO I LOOK FOR?
Careless handling, usually. If a screen is perfectly round, the media just rolls slowly around in it. If there is a dent, a crease, or some irregularity, it can't roll on, and will wear right into the obstruction. Wash your screens carefully, and put them in a safe place. If you must soak them, do it in a small bucket or tank where only the one will fit and another cannot be thrown on top of it. Another possible cause is running with too thin pastes and too much sand. If the top media is drained dry and is thrown about, it will wear into the screen. An abrasive media or too large a media in thin pastes can also accelerate screen wear.
WE ARE BOTHERED BY VARYING AMOUNTS OF DISCOLORATION AND GRAY-OFF. WHAT SHOULD WE LOOK FOR?
"Varying amounts" gives us a hint. Discoloration is usually one of three things. First, poor or incomplete washup between batches; second, too long rinsing with solvent; or, third, an outright abrasive media. We can include steel shots with the last, not that they are abrasive, but, at best, they do discolor anything light or clear. So let's eliminate. If you were using an abrasive media, you would notice discoloration much of the time. Sand would not be this abrasive, and amorphous glass beads are not abrasive.
Incomplete washup can be isolated simply by seeing what color your contamination is. If you just finished a red and your discoloration is red, then your washing technique is at fault. If your discoloration is graying or hazing, then look at the rinsing angle.
If the operator rinses out the mill with solvent, and just keeps running the agitator, there will be some metallic discoloration from the vessel walls and the agitator. This is less noticeable with glass than with anything, but even smooth glass beads, especially dense ones, if they are just agitated in solvent and allowed to settle to the bottom of the mill, will grind away at each other and the mill. Higher density ceramic beads will be much worse. Since this is an operator error, the amount of discoloration will vary depending on just how long he rinses. Just jog the agitator, don't keep it running while rinsing. The media washes in a snap. The color is in the pump and piping.
MY OUTPUT RATE VARIES. THE MEDIA GOES UP AND DOWN. WHY?
This is a pump feeding problem. The pump will feed exactly the same amount constantly, but only if it can get to it. Your suction lines to the pump are too small, too long, or of crushed hose. Possibly you are forgetting to clean the strainer. Make sure you have a good gasket in your quick-couplings, and that there are no air leaks in the suction line of the pump, even tiny ones.
WE GET ALL KINDS OF FIGURES ON VISCOSITY FOR OUR MILLS. WHAT RANGE OF VISCOSITIES CAN WE HANDLE IN MOST SMALL MEDIA MILLS?
This is one of those things that can't be limited. Go back to the section on formulation. If a paste is too highly pigmented, it will fight the mill with dilatancy, even though it is apparently thin. If the resin solids are too high the grind will be slow, and the mill will flood at moderate rates, again even though the material is highly fluid. Some pastes work well at 50 KU and sandmills on sand are running successfully at well over 120 KU. The figures you hear of 70 or 80 KU up to 95 or 120 KU are not limits, they are just coincidentally where most successful formulations happen to fail. If in doubt, go to your pigment people; they can give you a good starting formula.
HOW HOT SHOULD I RUN MY MILL? I DON'T WANT IT BLOWING FUMES INTO THE ROOM.
Run it as hot as the material will allow. We touched on this earlier. If you don't, you won't get the rate up, and may not even get the grind. If you have a closed mill, fumes are no trouble. If you have an open mill, KEEP THE FUME GUARD ON! The fumes will condense rapidly and just fall back into the trough. Do not guess at the temperature. Put in a thermometer where the material flows over it all the time, and put the safe top temperature on the batch card for the operator.
Either lobe type rotary or a gear type rotary. The gear type has a price advantage, while the lobe type will accept larger lumps. If your experience is such that a pump lasts a year or more, then consider going to the abrasion-resistant types of gear pumps, as they are more costly but much longer lived. Abrasion resistant pumps often use tungsten carbide or hardened cast iron wear surfaces and special hard-faced mechanical seals. If your pumps last only a few weeks or months or you cannot keep from feeding them media or steel balls or drum bungs, then buy the cheapest that will fit.
MY STRAINERS PLUG UP AND THE MEN JUST LEAVE THE SCREENS OUT, RATHER THAN CLEAN THEM. IS THERE ANY HELP FOR THIS?
Indeed. First, keep junk out of your premix, bag scraps, cigarettes, etc., which CAN be kept out. Next, see how long it takes on a typical batch to plug your strainer. If you get half a batch out before having to clean the strainer, then get a strainer with twice the open area of screen. Use a basket type or a so-called self cleaning type and make it reachable. Put a pan under it. You can also look at buying a duplex strainer, or pipe in two simplex strainers in parallel so that one strainer can be cleaned without shutting down the mill. If the man doesn't have to make a project out of it, he will clean it with less fuss.
WE RUN OUR SANDNMILLS AT HALF-MAST BECAUSE WE CAN'T GET THE GRIND. THE MILL PEOPLE TELL US WE SHOULD GET 80 GPH AND WE HIT 45 IF WE ARE LUCKY. WHAT'S WRONG?
Running a mill must be learned. Read the foregoing list of variables and work at them ONE BY ONE, your answer will probably be obvious. If this fails, go to the pigment people. Each of them can tell you how to handle their pigments in a sandmill, or give you formulation help. Sometimes the fault is as simple as an improperly cleaned screen, or an operator who is expected to gauge heat with his palm instead of a thermometer. Get someone form the other end of the plant and have HIM check out your variables. We find that firms who take the time to reformulate to take advantage of newer types of media and mill types are the companies who maximize production from their mills. When you change to a new mill or new media, it pays to re-optimize the mill base formula.
WHAT DOES A PUFFY OR BUTTERY PASTE HANGING ON A SCREEN INDICATE?
Almost invariably-too low resin solids. If the vehicle demand of the pigment is not satisfied, it will hang onto anything it can get, and the most available "fluid" is air. Just move up a few points at a time on resin solids, or down on pigment concentration. Take solvent out to compensate.
I GET GRIND MEASUREMENTS THAT ARE OFF THE SCALE FROM THE SCREEN, BUT SOMEHOW WE LOSE GRIND IN THE LETDOWN AREA. WHY? HOW DO I SOLVE THIS PROBLEM?
This is obvious. The mill is not at fault, for it has proven, at the screen, that it can do the dispersing, even though the product is unstable. Again, this is usually too much pigment or too little resin. Solvent will shock it out, or air, or even resin sometimes. If you can't reformulate, then try dropping the paste into some resin while mixing.
ON OUR CLOSED MILL, ESPECIALLY WHEN WE ARE STARTING A BATCH, THE MEDIA SEEMS TO JAM BETWEEN THE TOP DISC AND THE UNDER SIDE OF THE COVER. IT GETS HOT, SOMETIMES ENOUGH TO SMOKE OR EVEN CHAR. WHY?
Almost certainly you are pumping your paste in too fast behind the solvent. If the media bed is full of solvent, it is like damp beach sand, and has little flow. It is just extruded ahead of the paste-solvent interface, and it never becomes homogeneous with the more lubricant paste. When it gets into that dead area at the top, it becomes a relatively dry, non-fluid mass with low heat loss, so it just gets hotter and hotter. When you start such a mill on paste, start it dead-slowly allowing the media to mix with the paste rather than being pushed ahead of it. This takes a few seconds longer but is worth the time. This will help keep you from blowing out your screens also, because that dry media jams itself into the screen tightly, and before you catch it the pressure is up.
MY SCREENS BREAK FREQUENTLY, MORE SO THAN IN OTHER PLANTS. WHAT DO I LOOK FOR?
Careless handling, usually. If a screen is perfectly round, the media just rolls slowly around in it. If there is a dent, a crease, or some irregularity, it can't roll on, and will wear right into the obstruction. Wash your screens carefully, and put them in a safe place. If you must soak them, do it in a small bucket or tank where only the one will fit and another cannot be thrown on top of it. Another possible cause is running with too thin pastes and too much sand. If the top media is drained dry and is thrown about, it will wear into the screen. An abrasive media or too large a media in thin pastes can also accelerate screen wear.
WE ARE BOTHERED BY VARYING AMOUNTS OF DISCOLORATION AND GRAY-OFF. WHAT SHOULD WE LOOK FOR?
"Varying amounts" gives us a hint. Discoloration is usually one of three things. First, poor or incomplete washup between batches; second, too long rinsing with solvent; or, third, an outright abrasive media. We can include steel shots with the last, not that they are abrasive, but, at best, they do discolor anything light or clear. So let's eliminate. If you were using an abrasive media, you would notice discoloration much of the time. Sand would not be this abrasive, and amorphous glass beads are not abrasive.
Incomplete washup can be isolated simply by seeing what color your contamination is. If you just finished a red and your discoloration is red, then your washing technique is at fault. If your discoloration is graying or hazing, then look at the rinsing angle.
If the operator rinses out the mill with solvent, and just keeps running the agitator, there will be some metallic discoloration from the vessel walls and the agitator. This is less noticeable with glass than with anything, but even smooth glass beads, especially dense ones, if they are just agitated in solvent and allowed to settle to the bottom of the mill, will grind away at each other and the mill. Higher density ceramic beads will be much worse. Since this is an operator error, the amount of discoloration will vary depending on just how long he rinses. Just jog the agitator, don't keep it running while rinsing. The media washes in a snap. The color is in the pump and piping.
MY OUTPUT RATE VARIES. THE MEDIA GOES UP AND DOWN. WHY?
This is a pump feeding problem. The pump will feed exactly the same amount constantly, but only if it can get to it. Your suction lines to the pump are too small, too long, or of crushed hose. Possibly you are forgetting to clean the strainer. Make sure you have a good gasket in your quick-couplings, and that there are no air leaks in the suction line of the pump, even tiny ones.
WE GET ALL KINDS OF FIGURES ON VISCOSITY FOR OUR MILLS. WHAT RANGE OF VISCOSITIES CAN WE HANDLE IN MOST SMALL MEDIA MILLS?
This is one of those things that can't be limited. Go back to the section on formulation. If a paste is too highly pigmented, it will fight the mill with dilatancy, even though it is apparently thin. If the resin solids are too high the grind will be slow, and the mill will flood at moderate rates, again even though the material is highly fluid. Some pastes work well at 50 KU and sandmills on sand are running successfully at well over 120 KU. The figures you hear of 70 or 80 KU up to 95 or 120 KU are not limits, they are just coincidentally where most successful formulations happen to fail. If in doubt, go to your pigment people; they can give you a good starting formula.
HOW HOT SHOULD I RUN MY MILL? I DON'T WANT IT BLOWING FUMES INTO THE ROOM.
Run it as hot as the material will allow. We touched on this earlier. If you don't, you won't get the rate up, and may not even get the grind. If you have a closed mill, fumes are no trouble. If you have an open mill, KEEP THE FUME GUARD ON! The fumes will condense rapidly and just fall back into the trough. Do not guess at the temperature. Put in a thermometer where the material flows over it all the time, and put the safe top temperature on the batch card for the operator.