ASME B18.13:2017 pdf download

ASME B18.13:2017 pdf download.Screw and Washer Assemblies — SEMS (Inch Series)
1 INTRODUCTION
1.1 Scope This Standard covers general and dimensional data pertinent to the various types of screw and captive washer assemblies, otherwise known as SEMS. SEMS products may include screws, tapping screws, or bolts in sizes No. 0 through 1 ⁄ 2 in. diameters in various grades and materials. The word SEMS is recognized in the United States as a generic term applicable to screw and washer assemblies. Also included in this Standard is Nonmandatory Appendix A illustrating the relative proportions of plain and conical washer SEMS. NOTE: The word lock, which appears in the names of products in this Standard, is a generic term historically associated with their identification and is not intended to imply an indefinite fixity in attachments where the fasteners are used. 1.2 Use and Application The SEMS covered by this Standard are general pur- pose fasteners intended for mass production and other assembly operations where speed and convenience are paramount factors. Further attributes of the various washers, recognized herein, are given in detail for each type of SEMS. Products having washers of styles and shapes not shown in this Standard may be considered SEMS; however, these products must be covered by the purchaser’s drawing, standard, or the supplier’s standards.1.4 Screw Heads 1.4.1 Head Styles. The head styles applicable to the various types of SEMS shall be as depicted in the illustrations and designated in the tables for each type. Where only the slotted head SEMS are illustrated, it should be understood that this Standard also applies to the corresponding cross-recessed head. 1.5 Dimensions All dimensions in this Standard are given in inches unless stated otherwise. 1.6 Options Options, where specified, shall be at the discretion of the manufacturer, unless otherwise agreed upon by the manufacturer and the purchaser. 1.7 Responsibility for Modification Parts made to this Standard can be subject to the effects of hydrogen embrittlement, either from elec- troplating operations or exposure in the environment. The manufacturershallnotbe held responsiblefor modi- fications, such as plating (done by the purchaser to unplated SEMS supplied in the original order), when these modifications are not made by the manufacturer. 1.8 Terminology Fordefinitionsofterms relatingto fasteners orcompo- nent features thereof used in this Standard, refer to ASME B18.12.
SEMS can be made of any screw type with any washer type; however, the method of manufacture is affected by the materials used for the screw and washer and the properties required in the finished part. SEMS are made using two methods of production (a) washer assembly and thread rolling before heat treat (b) washerassemblyand thread rollingafterheattreat This Standard acknowledges these two methods of SEMS manufacture. The material choice in the first method requires skilled selection of the screw and washer materials, since the properties of each have to be realized by a single set of heat treat conditions. The selection of materials depends on the heat treat system involved, the size and shape of the washer and screw, and the austenitizing and quenching of the SEMS unit in oil. The second method is used when the desired properties of the screw and washer cannot be made by the first method of heat treating the screw and washer at the same time.
In this process, a fully heat-treated bolt or screw blank is assembled with a fully heat-treated washer and then roll threaded to form an assembly. Following threading, no further heat treatment of the assembly is required. SEMS manufacturing using Method 2 may not be reheat treated as a corrective action. Unless determined and stated otherwise at the time of order agreement, Method 1 processing is used. NOTES: (1) Due to work hardening, screws thread rolled after heat treat- ment increase in core and surface hardness. This may cause the screws to have hardnesses greater than that allowed by the material specification after thread rolling. To keep the finished screws within hardness requirements, the hardness of the screws before thread rolling will have to be somewhat lower than the final product desired hardness. This can only be deter- mined through experimentation. (2) Method 1 is considered the default method and used where possible. However, if hardness requirements are unattainable with available materials using Method 1, Method 2 automati- cally applies.