We have the same situation. One is quite inconvenient. ■

One would need to examine the details drawing of the installation to put forward the best advice but a great deal depends on the screw transfer arrangement in this installation. In principle, the capacity is determined by the collecting screw as the elevating screw is unable to move more than is fed to it. The ability of the horizontal screw to move product efficiently is impeded by the water that will tend to swirl out the plastic flakes so that increasing the screw speed could give even less capacity. If anything, the horizontal screw should have a reduced pitch and run slow at a high cross sectional loading into a confined casing transfer section that has a perforated section to allow the escape of water back to the tank.

Arching over the screw could be a problem in this situation of rduced effective density, so the depth of the 'U' in the tank is relevant. A force fed elevator will work quite well with standard pitch flights so, in this case, I would tend to look at the collecting screw and transfer arrangement to enhance capacity. ■

Firstly, does the screw conveyor have a tubular housing close fitting around the screw flight, or does it have a 'U' type housing?

Secondly, what is the feed arrangement to this screw conveyor. Is it a hopper? If so, does the wet PET flake actually flow out of the hopper? Conveyors can only take away what flows into them. ■

After reading your posting and understanding how your hoper is designed it definetely sounds like your PET flakes are bridging and not falling to the auger.

Perhaps the solution is to replace the auger with a small flight conveyor such a little giant grain elevator and leaving the bottom of the hopper open to the trough of the flight conveyor. which will eliminate bridging. ■

There are others more experienced with screw conveyors than I who may join this discussion, but a few observations based on my past experience :-

1) For an inclination of 65 degrees a tubular casing is necessary and you have this.

2) For such an incline it is normal for the screw to have the pitch LESS than the diameter (say pitch/diameter about 0.6). You may need to change the screw as your ratio is 1.

3) For the material to be elevated it must fall into the open part of the screw. However, if the PARTICLE density (not the BULK density) is less than 1 and the hopper is flooded with water the particles will float. Even if the PARTICAL density is greater than 1, when immersed in water the effective weight to 'push' the material into the screw is reduced.

4) The effect of the rotation of the screw is to disturb the water/material mixture so making it more difficult to elevate the material. The lower the speed the less disturbance

5) There is also the effect of trying to elevate water which will flow back, carrying material with it.

I think you will need to carry out some experiments to get the optimum performance with this arrangement. ■

"I have to say the density is less than 1"

If the flakes have a particle density less than 1 they will float in water??

"and horizontal screw push them to inclined scrw"

So you have two screws, a horizontal screw to collect the material and feed it to the inclined screw that elevates it.

"I ordered a screw with half diameter pitch"

I don't have a problem with that, anywhere from 0.5 to 0.7 is probably OK.

"what is your sugesstion re to increase RPM?"

You need to experiment. The higher the speed the more you need to force the material into the pickup area of the incline screw to overcome the tendancy fo the rotation of the screw to throw material out due to centrifugal action. ■