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SUMMER 2011

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Distributor's Link Magazine Summer Issue 2011 / VOL 34 / NO.3

14 THE DISTRIBUTOR’S

14 THE DISTRIBUTOR’S LINK Guy Avellon Guy Avellon has been in the MRO and fastener distribution industry for over 30 years. He began his metallurgical engineering career at Republic Steel Research Center in metal coatings and has since held positions as sales engineer; Chief Engineer; Manager of Product Marketing, Product Engineering and Quality and Director of Quality and Engineering. He founded GT Technical Consultants where he performs failure analysis, presents lectures on fastener safety, worked for law firms and designs and audits Quality systems. He is a member of SAE and is Vice Chairman of the ASTM F16 Fastener Committee and Chairman of the F16.01 Test Methods Committee, since 1988. He also received the ASTM Award of Merit in 2005. Guy and his wife, Linda currently reside in Lake Zurich, IL and may be reached at 847-477-5057 or visit his website at http://www.BoltDoc.com. SOCKET HEAD SCREW PRODUCTS Socket head cap screws were made primarily for recessed fastening in manufacturing equipment. Most of the equipment at that time were heavy and consisted of hardened tool steels. The common hex head fastener had too high of a head and was not strong enough to support much of the weight and heavy loads without using very large diameter fasteners. The socket head cap screws (SHCS) had significantly greater strength than the SAE Grade 8 with a much lower profile; the heads could be countersunk into dies and other tight places, and then tightened externally with a special drive key. Besides the standard SHCS, there is the socket flat countersunk head, the socket button head, socket head shoulder screw and set screws. All are made from alloy steels commonly in the AISI group of 4140-4145 to the 4340 series. All threads are Class 3A up to 1” in diameter; larger products are Class 2A. Metric threads are to Class 4g6g. All socket head products made to ASTM standards do not allow for any thread lapse at the root or thread flanks below the pitch line. Quench cracks of any sort are not allowed. The flat countersunk head has, as the name implies, a flat top that will lie flush with the top surface of the plate it is attaching. It provides clamping force from its conical bearing surface of 82°. Due to its flush mounting properties, it is ideal for attaching plates that may have close tolerances or slide against each other. Good for shear; its hardness is 38-44 HRc, which is similar to the standard socket head products, but it only has a tensile strength of 145 ksi for diameters of 0.5” and less and 135 ksi for those diameters greater than 0.5”. The button head also has the same properties and tensile strength as the flat countersunk head. Its smooth head will prevent objects from contacting its head and are used for thin materials when counterboring is not ABOVE: Marking on top of socket head indicating an 8.8 metric BELOW: Flat Head Socket Screw, 304 stainless, metric threads practical. They are frequently used to attach personnel safety guards or shields, which will prevent clothing from accidentally catching onto the head. The button head also shares the same tensile strength with the flat head at 145 ksi for diameters less than and equal to 0.5” and 135 ksi for diameters greater than 0.5”. However due to the head critical nature of all socket products, most tests are performed with machined test specimens. Machined tensile specimens will produce higher readings at 180 ksi and 170 ksi respectively. Metric products are based on 1220 MPa minimum tensile strength, however the loads for the button head and flat head products are based on 980 MPa. Torque values for the flat head products will be slightly higher than the button head screws due to the increased surface area under the 82° conical head which will produce more friction. The flat head and button head cap screws conform to ANSI/ASME B18.3 for inch, B18.3.4M for metric button heads and B18.3.5M for flat head screws. Material specifications for ferrous alloy products are to ASTM A574/574M and ASTM F835/835M. Stainless steel socket head products are listed under standards F837/837M and F879/879M. Set screws are not the traditional threaded fastener; i.e. it is not stretched but compressed to cause fastening. These are much harder at 45-53 HRc and are tightened against shafts or bar stock to keep them from turning or otherwise coming out. The tips vary from a dog-point to a cup-point, oval point, flat point, half-dog point and cone point products. The threads for these set screws are class 3A for inch and 4g6g for metric threads. Dimensions conform to ANSI/ASME B18.3; B18.3.6M and material specifications conform to ASTM F 912/912M, inch and metric. please turn to page 120

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