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92THE DISTRIBUTOR’S

92THE DISTRIBUTOR’S LINKLARRY BOROWSKI DUCTILITY TESTING from page 12Additional requirements for the testing apparatus are:a. The block shall be made of hardened steel.b. The block shall have a hole(s) that are between.020” and.040” (for Inch sizes), and .50mm to 1.0mm(for metric sizes) larger than the given nominal majordiameter of the screw.c. The given wedge angle of the block face should berelative to the axis of the hole in the block.d. The block can contain a single hole or any numberof holes, and it can also have a common hole used forboth inch series and metric series screws. Below is onesuch block created by Greenslade & Company, Inc., whichcontains most of the common sizes of tapping screwscombining inch and metric into a single block.[2] Insert the screw into the proper sized hole of theDuctility Testing Block.[3] Strike the head of the screw with a hammer orother suitable device until it conforms to the angledsurface. That is until the bearing surface of the head isflat against the angled surface. It may take more than oneblow with a hammer to bend the screw head.[4] Remove the screw from the Ductility Testing Blockand observe the condition of the head. Note that it hasbeen bent, and that it is not completely separated fromthe shank. Even if there is a significant crack at the headto shank junction, but the head remains attached to theshank, the test for ductility was successful.Besides Ductility Testing being a required performancetest, it is also a relatively easy and inexpensive test toperform in order to ensure that the tapping screws beingsold or used are good. Ductility test failures can alsoindicate other problems besides the core hardness beingtoo high or the case hardness being too deep. A failurecan also be a result of the recess in the head being toodeep leaving very little material at the head to shankjunction, or the under head fillet radius could be too smallcreating a high stress point at the head to shank junction.It is always important to perform all required dimensionaland mechanical tests on a screw before passing it ontoto the end user. A single test or check is not sufficient toprovide enough information regarding the quality of thefastener.Besides the standards referenced above, the followingstandards also provide details of this test along with otherdimensional and performance related requirements. Someof which are FIP1000, ISO 898-1, ISO 7085, SAE J1237,SAE J78, etc. Again, be sure you are working to the correctspecification before assuming all self-tapping screws havethe same angular deformation requirement.LARRY BOROWSKI | GREENSLADE & COMPANY INC