THE HOTEND ASSEMBLY STRUGGLE

THE PHYSICAL-GEOMETRIC CONDITIONS FOR THE GOOD OPERATION OF A SCREW COUPLING ARE KNOWN FROM THE SCIENCE OF CONSTRUCTIONS.

WE KNOW, IN PARTICULAR, HOW IT WORKS ACCORDING TO THE LAWS OF THE INCLINED PLANE AS IN FIG. 1 (VERY, VERY SIMPLIFIED DIAGRAM):

IN PRACTICE, DURING SCREWING, THE SAME LAWS APPLY TO THE WEDGE.

FORCE F1 INDUCES BY THE INCLINATION OF THE THREAD ∞, THE FORCE F2 THAT OVERCOMING FRICTION BETWEEN THE PARTS, ALLOWS THE MOVEMENT TO F3.

HERE WE DO NOT WANT TO EXCESSLY DEEPEN ACCORDING TO A PHYSICS-MECHANICS TREATY BUT ONLY TO HIGHLIGHT SOME INDISCUTIBLE DEFECTS CONCERNING THE COUPLING OF THE CONTACT SURFACES BETWEEN THE NOZZLE AND THE HEAT BREAKER TUBE THROUGH THEIR THREADED CONNECTION ON THE HEATING BLOCK.

REMEMBERING HOW THE PERFECT CONTACT, (IT MEANS ALSO PERFECT UNIFORM TEMPERATURE) IN ADDITION TO A LIGHT PRELOAD BETWEEN THE SURFACE OF THE NOZZLE AND THE HEAT BREAKER TUBE IS FUNDAMENTAL FOR THE REALIZATION OF THE TRANSITION FROM SOLID TO FLUID OF THE PRINT FILAMENT.

IN FIG. 2 THE ASSEMBLY OF THE RAISE3DPRO2 HOTEND:

IN FIG. 3 THE ACTIONS AND REACTIONS RELATING TO SCREWING THE NOZZLE AND THE HEAT BREAKER ON THE HEATING BLOCK.

YOU CAN NOTICE THE FORCES RESULTING FROM THE SCREWING OF THE NOZZLE AND THE HEAT BREAKER CAN GENERATE REACTIONS Fh AND Fn WHICH, IF NOT COMPENSATED BY A VERY LOW COEFFICIENT OF FRICTION BETWEEN THE SCREW AND THE NUT SCREW, AND BY A TOLERANCE BETWEEN THE SCREW AND THE NUT SCREW EQUAL TO ZERO, GIVE ORIGIN TO A TORQUE Fn x AFh x A1 THAT CAN ONLY BE COMPENSATED BY ANOTHER TORQUE Fp1 (Fp2) x B ON THE INTERFACE SURFACE OF THE NOZZLE AND HEAT BREAKER.

AT A MINIMUM THIS LEADS THAT THIS VERY IMPORTANT COUPLING SURFACE WILL BE SUBJECT TO A PRESSURE OR PRE-COMPRESSION ( ANND CONSENQUENTLY THE TEMPERATURE) THAT IS NOT CONSTANT BUT VARIABLE ON ITS RING AREA.

AS SHOWN IN FIG. 4, IN ADDITION TO AN INTERFACE SURFACE BETWEEN THE NOZZLE AND THE HEAT BREAKER WITH A CONTACT PRESSURE AND A PRETENSIONING NOT CONSTANT, EVEN THE NECESSARY COLLINEARITY OF THE EXTRUSION AXIS AX, WILL BE MORE COMPROMIZED.

AFTER MANY DEMONSTRATIVE EXPERIENCES OF THE PHENOMENON, THIS ASSEMBLY PROCEDURE IS CONSIDERED TO BE THE MAIN CAUSE OF THE HOTEND CLOGGING (BOTH IN THE NOZZLE AND IN THE HEAT BREAKER) AND MALFUNCTIONS, AND THEREFOREOF THE ENTIRE PRINTING SYSTEM.

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