Application Digest 27512

Fasteners that make the grade

John A. Buda, Product Line Manager, Unbrako Division, SPS Technologies

Design engineers use Grade 8 fasteners in many areas, including automotive, appliance, and light and heavy-duty industrial applications. Some fastener specifiers are under the impression that standard alloy-steel socket-head cap screws are Grade 8. This misperception is understandable, because Grade 8 connotes high strength. Specifications for Grade 8 fasteners appear in SAE J429, whereas ASTM A574 gives the requirements for a standard socket head cap screw (SHCS).

Technically, a Grade 8 fastener possesses an ultimate tensile strength (UTS) of 150 ksi, hardness of RC33 to RC39, and six radial lines marking the head.

In contrast, a standard SHCS has a UTS of 180 ksi through .50-inch diameter and 170 ksi in diameters greater than .50 inch. (SPS manufactures its standard SHCSs to a minimum UTS of 190 ksi through .50 inch and 180 ksi for larger diameters.) Socket head cap screw hardness ranges from RC39 to RC45 through .50 inch and RC37 to RC45 in diameters exceeding .50 inch. A standard SHCS can be made only in the SHCS configuration. Grade 8 socket head cap screws can be specially manufactured.

Substantial variations also exist among metric socket screws. Those manufactured overseas can fall into one of several strength categories. Property class 8.8 metric fasteners offer an 800 MPa (116 ksi) UTS for diameters less than M16 (16-mm-diameter, standard thread), and 830 MPa (120 ksi) for M16 and above. Class 10.9 are alloy steel with 1,040 MPa (151 ksi) UTS.

Metric property classes 8.8 and 10.9 offer cost options for applications not requiring maximum fastener strength. However, design practice with SHCSs in the U.S. traditionally used the inch ASTM A574 strength level or metric class 12.9. Inadvertent replacement of a high-strength 12.9 SHCS with a lower strength 8.8 or 10.9 product could cause problems.

To speak with an SPS applications engineer, call (800) 225-5777.

Programming Diverse Devices

John Swain, Director of Engineering, Bytek Corp.

Programming semiconductor devices is often challenging because of the wide range of package types and pinouts available. Instead of choosing the best device-programming technology, however, the type of programmer already in place often limits the choices.

A new device programmer efficiently customizes products that use programmable devices. The Model 2000 from Bytek Corp. programs embedded microcontrollers, E/EPROMs, PLDs, and other control elements.

Reprogrammable gate arrays allow the unit to handle a wide range of pinouts and package types, including DIP, PLCC, QFP, TSOP, SOIC, and others. It programs as many as 16 devices-8, 16, 32, or 64 bits wide-in block, interlace, block/interlace, or gang operation. It programs gangs of identical devices, sets, and even set-of-sets of devices where each contains unique data.

Multi-matrix technology permits changing device types on the fly without shutting down the machine. The unit operates either as a stand-alone unit or under a PC's control.

Rapid throughput complements operating flexibility. The unit comes with 2M bits of RAM, expandable to 128M bits. It can program, verify, and sumcheck sixteen 1M-bit E/EPROMs in 18 seconds, or sixteen 2M-bit parts in 34 seconds.

For application help on device programming, call Bob Sims, (407) 994-3520.