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| Author | Topic: Segments of single screw |
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sangitafood Member Posts: 4 |
posted May 04, 2010 12:53 PM
  
Just bought a single screw extruder wenger model x-130 but it is without screw segments. Extruder to be used for producing fish floating feeds. Could anybody guide me about screw segments design of wenger x-130 suitable for fish feeds. I have 6 barrel heads, however. If I could get help about the drawings, better as I could get it made from vendors. IP: Logged |
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Tom C Moderator Posts: 985 |
posted May 04, 2010 01:09 PM
Contact Wenger I'm sure they can help supply parts. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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sangitafood Member Posts: 4 |
posted May 05, 2010 02:30 AM
That's fine. We did that in past month and were quoted exhorbidantly high prices which we find difficult to bear. Our local technical consultant has asked us he can get it locally done in mumbai. However, one doubt remains about the clearance between screw and the barrel liner inner walls. For food processing extruders, we are told clearances should be high, e.g 2-3mm on diameter (i.e max. 1.5mm on one side radially). On plastic extruders, they do not provide more than 0.5mm on this size of screw (130mm). Could u help here please? This is our maiden project on trial basis and if we suceed, then we do not mind buying enw machine directly from them. Help us please... IP: Logged |
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Tom C Moderator Posts: 985 |
posted May 05, 2010 09:38 AM
Sounds like you have justification for paying the price to Wenger for the correct engineering. I don't know the normal clearances used on food equipment, however I have seen the 0.5mm clearance used. One problem is galling of the stainless parts which is more likely to happen with tighter clearances. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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sangitafood Member Posts: 4 |
posted May 08, 2010 01:19 PM
Well, when producing pellets for fish consumption atleast, the extruders normally use hardened alloy steel liners in barrel (this is not stainless) and screws are also made from nitride hardened steel (again, it is not stainless). They use this becauuse not much could be done to harden normal stainless and they have less life. Since the materials used in this case are dis-similar, seizeing usually does'nt occur, but for a normal extruder, radial clearance of 0.25mm or 0.5mm on dia. on 130mm dia. is sufficient, as far as plastic processing is concerned. However, many food technologists differ here, and they say clearances should be more, and they say nearly 2-3mm on 130mm OD screw which sounds bit odd to plastic processor, who normally goes for rebuilding when the screw is worn out greater than 0.75mm, not waiting to afford to wear till 3mm! Hence, I am confused here. I cannot imagine an extruder running with clearance of 2-3mm on dia. and giving normal outputs and quality! The problem is compound since if i keep high clearance, and after trial i find that i need less clearance, then i cannot add the already removed material and the mistake can prove costly.. IP: Logged |
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Tom C Moderator Posts: 985 |
posted May 08, 2010 01:32 PM
Screws have over the flight pumping losses when clearances are high. The problem is worse with high discharge pressure and low material viscosity. If the visosity is high, or the material is "chunky" those pumping losses may be minimal, as the chunks fill in the gaps. Mixing is also improved with large clearances. A lot depends on the condition of the material you are putting in, and the condition you expect out.
------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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sangitafood Member Posts: 4 |
posted May 12, 2010 09:12 AM
Sounds useful comment and some justification for high clearance screws. Well, yes, the material is viscous (dough like, you know how a dough is formed when it is mixed with water). Material exhibits plasticity like a polymeric mass (thermoplastic) but with very high viscosity. May be, the high viscosity of material helps to provide lubrication between the clearance by not allowing metal-to-metal contact, while maintaining the flow rate... but that's was quite useful comment from your part.. anymore? IP: Logged |
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