Общий каталог Yamawa 2021 - страница 681

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11. Differences between UN and UNJ threads Intro The minor diameter of both the external and internal screw threads of a UNJ thread are larger than that of a UN thread. This design is to SP enhance the bending and shearing strength of an external thread as per the diagrams below.UNJ screw thread (MIL-S-8879, AS8879 and ISO3161) is one of the Unified screw threads standard and was established for fastening parts of commercial and military aircrafts with threaded components called “Air-fastener”. UNJ threads have only one combination of 3A class external threads and 3B class internal threads per size and both are the smallest tolerance for Unified threads to ensure that air fasteners are securely fastened for excessive loads. SL The external screw threads of a UNJ have rounded root with radius of specific tolerance for added strength. Yamawa (YMW) tapsmanufactured for UN threads can be used to produce internal UNJ threads per MIL-S-8879, AS 8879 and ISO 3161. Internal threads require a minor diameter bore larger than those recommended for UN threads. This larger minor diameter prevents interference of external and internal threads within the tolerance for UNJ standards. Tapping conditions must be highly accurate to produce an internal screw thread within a 3B class of thread. Thread results can be influenced PO by tapping conditions such as feed mechanism of tapping, machine, etc.Tapping machines with synchronized tapping attachment are strongly recommended. ST ROLL CARBIDE LONG Note: External threads shall be Unified form, in accordance with ASME HAND B1.1 (Class 3A), altered at the TAPS root so that the flanks of the adjacent threads are joined by a continuous smoothly blended curve tangent to the flanks. The EG (STI) root radius tangent to the flanks shall be within specific values determined by the AS8879 norm. SPECIAL THREADS, GAUGES (1) Feature of UNJ threads: Larger minor diameter (larger core diameter) and rounded root make the external screw threads of a UNJ stronger than a UN thread. Internal THREADMILLS UNJ threads require a minor diameter bore larger than those recommended for UN threads while staying within the tolerance of the minordiameter for UNJ standards. (2) Example: Limit size for minor diameter of Unified internal threads 1/4-20UNC (2B) Min: 0.1960” (or 4.979 mm) - Max: 0.2070” (or 5.257 mm) DIES 1/4-20UNJC (3B) Min: 0.2013” (or 5.114 mm) - Max: 0.2121” (or 5.387 mm) CENTER DRILLS Technical info 682