Dear Lynn,

we at Alexanderwerk have a very positive record on processing of material for powder coating. A roller screw feeder configuration as with Bepex will lead to too high a prepressure and likely to plastification of the raw material. In this respect our system is different as we overcome gas backpressure in the system not by screw speed or tamping, we vent by a venting chamber and additional features to stay in control of product flow nto the rollers. Feel free to get in touch with me for a free trial to prove my word.

Kind regards

Hendrik Thomsen ■

Hi Hendirk,

Thanks for your reply. Indeed the high pressure in the feeder seems to be the cause of the caking around the screw and therefore the cause to the electrical cut out. And yes we do get a "plasticized" vitreous material. But that's what we want. We noticed that when we mill the product after compaction, we obtain more easily the D50 we want when the compacted material is hard and translucent than when it's a softer opaque material.

Thanks ■

Dear Lyn

The compacting problem you mention with a Fluorpolymer is the same problem I had experienced when compacting a Polythylene rich formulation.

When you follow along the time the compacting performance of any product works in cyclical behaviour. This behaviour can be summarised in different steps:

1- Starting the unit previously filled with product with a resting time:

When the compactor stars after some resting time, the compacting performance is better because the product inside the feeding screws and in the feeding hopper has been more deareated. After some time (minutes) the compactor progressively decrease the compacting performance.

2- The performance arrives till a minimum after some time is increasing again the performance due to a progressive reduction on air containing inside the product that feeds the roller after some additional time the performance increase till a maximum value.

3- From the maximum performance value the compactor decrease progrevelly its performance again till the minimum of point 2 and starts again cycle from 2 till 3 in a continuous manner.

The mentioned behaviour in product not sensitive to temperature and in not plastic deformable products allows an enough reliable process.

The problems arise when we have products with melting points not enough far away from product and compactor temperature. The maximum recommended product temperature is 30 –50 ºC bellow the product melting point.

In polymers field there is not a clear melting point and exist another critical factor affecting to the compacting properties. This parameter is the TG. Temperature of vitreous transition where the product starts to becomes plastic deformable, in many polymers this temperature is close or bellow the product temperature. You can determine the TG by DSC ( Differential Scanning Colorimetry)

Is very probable that your Fluorpolymer has a TG close or bellow the product compacting working temperature. If this is the case, these products when compacted on Step 3 the product is more stressed and becomes plastic deformed, this deformation creates a lot of inter-particle friction that generates head and the polymer becomes melted but at lower temperature.

In this melted or quasi melted situation the friction between the product and the screws and the rollers increase enormously and make the compacting process fully out of control exceeding the maximum rollers or screw electrical power consumption and stopping the unit. The particles mechanical behaviour in this situation is more close to extruder or a kneading situation than to compacting. Usually I said that it I compare this situation as a fire that when starts is very difficult to stop if is not quickly extinguished

My broad compacting experience on roller compactors in the plastic additives field and with PE says me that if you introduce a control process loop that controls the speed of the rollers and screws measuring on line the current compact performance parameters, the system may becomes reliable, another complementary actions has to be probably performed as cooling down the screws and rollers and may be also cooling down the product and the hoppers.

I lead the development of a patented method for compacting using vacuum deareation and we successfully cope with this kind of problems in deep detail.

Nevertheless from my point of view as a powder agglomerating specialist with a broader outlook I will probably recommend another more reliable technologies than roller compacting for size enlargement of your polymer.

In addition we have developed a proprietary new technology that is able to agglomerated very fine particles. For example we have been fully successfully in to recover the wasted ultrafine particles (D50 = 6 ) that are isolated from the Powder Coatings process after milling. The product recovered after these one step proces has the particle size required for powder coating ( D50 = 40 ) with a high yield ( > 98%). A pilot plant is ready for testing.

As a consultant we can help you in the direction you prefer, to improve the compacting performance of your Pharmapactor, recommend another potentially suitable size enlargement technologies or to test the mentioned proprietary technology in our pilot unit.

Kind Regards

Joan Iglesias ■