Filtration Test for Master Batch Colorant

All it is doing is indicating that the gear pump is doing its job of passing a known flowrate of fluid regardless of pressure difference across it. It is actually holding fluid back from the 60bar source. A clean filter has a low pressure drop, so the term "theoretically" needs alteration.

It will depend on the reference pressure that the pre filter is being compared to. Normal practice would measure pressure difference (before versus after) across the filter to determine the level of obstruction.

In such a case the target condition would be "almost zero" difference for a clean filter pack.

Having it downstream of the metering pump means that the pump is isolating the material feed pressure from the sensor and the sensor is seeing the back pressure of the combined viscosity pressure of the extruder plus the screen pressure. Viscosity pressure will depend on feed rate and temperature of the melt product.

Many Thanks to both of you for your comments. I still have a question - when we use a very fine filter of 10 micron rating, even it is clean, there will be resistance to the polymer flow across the filter and due to that resistance there should be pressure increase before the screen and substantial drop after the screen. I agree that normally pressure before and after the filter is measured to know the clogging or partial chocking of the filter screen and take action of changing the filter. However, here the equipment is designed to deliver the melt at constant pressure to the gear pump and a rise in the back pressure is an indication of partial chocking of the filter which gives a delta p of start of the test and end of the test after passing the defined quantity of polymer melt through the filter screen. More or less, exactly same situation is there in the commercial melt spinning machine and we observe a starting pressure of the spin pack substantially high when it is fresh in the position with a series of filter packets, which is nearly 60 to 100 bar and no case it is starting with "zero" or 5 to 6 bar. Can any one help me to calculate, back pressure developed, with the pump through-put of 60 cc/min of polyester material (density 1.342 g/cc) across a filter of 33.8 mm dia, having wire mesh screen of 10 micron.?

Once again thanks for taking interest. M.P.Joshi

I am now a little confused. Ihad imagined the filter pack in the flow after the pump, but now you imply that it is before the pump.

If the filter pack is in the flow before the pump, then the pump might be providing negative pressure on the downstream side of the filter and so assisting flow, creating the low pressure that you see.

No dear, "Filter pack" is after the gear pump only. It is like this---

Extruder>>------$----Gear Pump------$--------Filter(@)Pack--->>>-Melt out let

pressure sensors are shown as = $

Sensor before the "Filter pack" is showing "zero" pressure at the start of the test, according to me, which should show as high as 30 to 40 bar due to "10 micron" filter rating which will restrict the melt flow to great extent due to extremely small openings for the melt to flow through.

I would appreciate if some one can suggest calculations for the melt flow pressure before filter pack.

In-let to pump is constant pressure at 60 bar which avoids starvation of the melt flow to the pump, in case extruder feed is interrupted. Thanks.

You seem correct. Zero pressure before filter pack does not make sense!!

Has the "zero" been verified? Maybe the calibration is out of whack.

Are you absolutely certain the filter pack is not back to front and thus measuring pressure at outlet? (I'm sure that eveeryone believes it is, but that might be one casue of this strange result.)

Thanks. Pressure sensor before filter pack is checked several times and confirmed it's working fine. During this test, first base polymer material is fed to the extruder and which confirms initial filling of the fresh filter pack and the melt channel. Then the polymer resin mixed with color master batch starts extruding and we can see the color melt flowing out. This takes only 1 or 2 minutes to happen and then the test is started manually by clicking the "start" button on the computer screen. Delta "P" from start to max. pressure value for the known quantity of colored material passed through filter is the measure of the filter ability of the colored material. To me also, zero pressure at the start of the test does not make any sense! But I find it hard to convince to my colleagues.