Hi Kodwo, Frequent Breaking of Press Screw - earlier I shared on operation aspects which may cause the above failure, now let me share from design aspects of press screw. Based on my experiences frequent failure were at it’s key ways and neck areas. 1) Press screw bore diameter fixed to drive shaft is having bigger diameter than its discharge end diameter. The reduction of it’s diameter at driving end towards driven end should be as gentle as possible (reduction of diameter over longer distance) may reduce it’s frequency of breakage. 2) key way to main drive shaft - to have as small tolerance as possible between screw bore and main drive shaft. However, zero tolerance may make you maintenance work difficult. 3) you may keep some records on the pitch of last ribbon of screw compare against pitch of second last ribbon if reduction of pitch in last ribbon contribute to press screw breakage. Thanks.
Hi Kodwo, to add to the various causes of breaking of Press Screw, all motors have overload relay to trip it in case of overloading of the press & low voltage or frequency drop. This should help to prevent or reduce breaking of press screw. If operators simply reset and run without finding out the problem, it will likely cause damages to the Press not only the screw but probably the main shaft as well.
From my experience, very seldom im facing worm screw breaking problem, main shaft more often. Worm screw broke most probably cause by foreign materials drop into digester, especially steel. Housekeeping is very important near digester area, not only can prevent steel from dropping into digester, it also can prevent fire hazard. Foreign materials may from digester itself( stirrer arm or 'v' block). Another possibility may be is the worm screw itself, quality uncertainty during casting at foundry. You can try to change other wormscrew supplier.
Dear Kodwo Koomson, Frequent Breaking of Press Screw - this is a very good question and is a common problem in oil mills. There are few causes, I just share one of it from operational aspects. During start up in the morning, 1) the press cake remained in the worm screws and press cage had harden and required comparatively higher torque to rotate and therefore generate excessive stress to it’s rotational components.Propose remedy actions - empty the press cage during stopping, if possible replace the press cake with wet shells. 2) empty digester during start up may leads to lower digestion retention time and press operator tend to increase the press cone pressure excessively and again generate excessive stress to screw press rotational components. Propose remedy actions - adequate digestion retention time before pressing and preferably with auto cone pressure system on and should not allow press cone in lock position. If press cake is wet, it may due to inadequate digestion retention time or even sterilisation efficiency.
Great insight from you, thanks sir
Hi Kodwo, Frequent Breaking of Press Screw - earlier I shared on operation aspects which may cause the above failure, now let me share from design aspects of press screw. Based on my experiences frequent failure were at it’s key ways and neck areas. 1) Press screw bore diameter fixed to drive shaft is having bigger diameter than its discharge end diameter. The reduction of it’s diameter at driving end towards driven end should be as gentle as possible (reduction of diameter over longer distance) may reduce it’s frequency of breakage. 2) key way to main drive shaft - to have as small tolerance as possible between screw bore and main drive shaft. However, zero tolerance may make you maintenance work difficult. 3) you may keep some records on the pitch of last ribbon of screw compare against pitch of second last ribbon if reduction of pitch in last ribbon contribute to press screw breakage. Thanks.
Hi Kodwo, to add to the various causes of breaking of Press Screw, all motors have overload relay to trip it in case of overloading of the press & low voltage or frequency drop. This should help to prevent or reduce breaking of press screw. If operators simply reset and run without finding out the problem, it will likely cause damages to the Press not only the screw but probably the main shaft as well.
From my experience, very seldom im facing worm screw breaking problem, main shaft more often. Worm screw broke most probably cause by foreign materials drop into digester, especially steel. Housekeeping is very important near digester area, not only can prevent steel from dropping into digester, it also can prevent fire hazard. Foreign materials may from digester itself( stirrer arm or 'v' block). Another possibility may be is the worm screw itself, quality uncertainty during casting at foundry. You can try to change other wormscrew supplier.
Dear Kodwo Koomson, Frequent Breaking of Press Screw - this is a very good question and is a common problem in oil mills. There are few causes, I just share one of it from operational aspects. During start up in the morning, 1) the press cake remained in the worm screws and press cage had harden and required comparatively higher torque to rotate and therefore generate excessive stress to it’s rotational components. Propose remedy actions - empty the press cage during stopping, if possible replace the press cake with wet shells. 2) empty digester during start up may leads to lower digestion retention time and press operator tend to increase the press cone pressure excessively and again generate excessive stress to screw press rotational components. Propose remedy actions - adequate digestion retention time before pressing and preferably with auto cone pressure system on and should not allow press cone in lock position. If press cake is wet, it may due to inadequate digestion retention time or even sterilisation efficiency.