Thread buttress

Figure 4-371. Buttress thread casing and coupling. (From Ref [51].) From API Spec 5A, 35th Edition, March 1981, Ref, [151], p. 25.

Buttress threads are designed to resist high axial tension or compression loading in addition to offering resistance to leakage. 

Figure 4-374. Buttress thread configuration for 16-in. outside diameter and iarger casing. (From Ref. [54].)...

Note Most buttress thread couplings will not develop the highest minimum joint strength unless couplings of the next higher order are specified. (See API Specification 5A for more detailed information.)... 

Buttress Thread Casing Coupling Dimensions, Weights, and Tolerances... 

Buttress Thread Casing Joint Strength. Buttress thread casing joint strength is calculated from formulas 4-318 and 4-319. The lesser of the values obtained from the two formulas governs. 

Moldable holes and inserts can complicate molding and may require extra postmolding operations. Thus, the most economical designs are those that minimize the number of holes. With many plastics, both external and internal threads can be molded, but sharp V threads should be avoided because they can cause the plastic to bridge, resulting in incomplete thread fill. Rounded or modified buttress threads will allow improved thread fill. 

The overall effectiveness of most containers relates to the design of the bottle neck and closure and the material from which the closure and container are made. Where a flexible material is used, a buttress thread (BS 5789, 1979) is recommended. However, if the material is substantially harder, e.g. HDPE, PP, or PVC, a conventional type 60° thread (BS 1918, R3/2 and R4 finishes for glass) can be employed. 

British Standard 5789 1979 applies to plastic containers and closures requiring a buttress-type thread. 

FIGURE 45.3 Bone screws (a) a self-tapping V-threaded (has a cutting flute), and (b) a non-self-tapping, buttress threaded screw. 

This has a polypropylene (PP) seat, with welded tubular-steel legs. Use a Phillips screwdriver to remove the four screws that attach seat to the legs. These self-tapping screws (Fig. 1.5) with sharp, widely spaced threads, are much longer than the typical 4 mm thick seat. When screwed into a moulded cylindrical boss on the hidden side of the seat, the threads cut grooves in the initially smooth plastic. It is supported by four or more buttresses, to prevent bending loads causing failure, where the boss joins the seat. Measure the thickness of the buttresses. 

Fiber, buttress A type of thread used for transmitting load in only one direction. It has the efficiency of the square thread and the strength of the V-thread. 

THREADED CLOSURES - TYPE OF THREADS ACME BUTTRESS MODIFIED OTHER ... 

Moulded-in internal or external threads can be used with PP. The design of threads is important to avoid the possibility of thread jumping. Thread jumping may occur if high torque is applied to the screw. If this happens, the moulded thread is still usually unharmed and can still be used. Acme or buttress type threads can be used to decrease the possibility of thread jiunping. 

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