Cooling a screw type extruder

[mschro]

I have a screw type extruder that heats up from the friction of the material being processed. Some of the material being processed has a low melting point. I want to cool the last flight of the screw extruder enough that the temperature at the end of the extruder remains below the melting point of all the material being processed. I am considering cooling the screw by continually circulating a cooling fluid through a hole bored into the shaft of the screw, into a cavity cast into the last flight, back through a second hole in the shaft, through a heat exchanger (if needed), and into a tank.

Through testing, I know that the approximate required temperature drop on the end flight to be 50 deg F.
What I am trying to determine is the ideal:

1) pump size and flow rate
2) heat exchanger size
3) coolant to use (water, cutting fluid, oil)

This is way outside my area of expertise so any help would be greatly appreciated.

 

[desertfox]

Hi mschro

I doubt we will be able to sort out all that here on a internet site, however we would need to know how hot the flight gets not just the drop in temperature you require.

desertfox

 

[mschro]

The flight is about 300 deg F

 

[desertfox]

Hi mschro

I should have expanded on my post, we would need drawings, wall thicknesses of the parts involved , area's of parts were trying to keep cool its just to big to do over the internet. Have a look at this simple heat conduction through a tube and you will understand the complexity

http://www.freestudy.co.uk/heat and combustion/outcome1t1.pdf

desertfox

 

[macmet]

Could you lubricate the extruder or add a lubricant to the material to reduce friction? Might be a lot easier.

I worked with a lab size extruder and we found by adding more lubricant to the material the temperature dropped significantly. It was a good solution for us as this lubricant burnt off later on the process and was cheap.

 

[mschro]

That's a good suggestion, but in this case the material can't have anything added to it.

 

[CH5OH]

what about shimming the last barrel? (reduce the friction,greater clearance?

 

[mschro]

We manufacture the screw extruder ourselves. In our other applications until now, a low melting point of the material being processed has not been a problem. We are committed to a design as described above. I guess I was hoping someone had run across a similar type scenario and could guide me toward the appropriate formulas. It’s looking like it might be a little more complex than I was expecting.

 

[CH5OH]

though I dont have operating knowledge with extruders,just a few remarks:
-an extruder works on the principle that for a given proces flow, the rotating energy of the screws is converted mostly into heat.Only minor part of its energy is used to pump and mix the proces flow.What comes out of the extruder is homogeneous liquid state.after the extruder the flow is cooled down below melting point again.So I am a bit confused
about wanting to stay below melting point within the extruder.
-to cool down via the screws is a bit complicating the things (seals,limited contact cooling surface...)why not cool the barrels?
-to have some proces control and flexibility, I would:
1.install VFD on drive motor
2.taper screws towards the end, as well as the last barrel.
install some power pistons on barrel train.
with these two measures heat and flow can be adjusted,while processing (rpm, end clearance between barrel and screws)