Illustrated Sourcebook of Mechanical Components Part 7 potx

Grommets, Spacers & Inserts 14-11 A C B \ I 7 D two general types. The first uses modified external threads that form an interference with the parent material, and provide locking action. The second type has many varia- tions, but is characterized by standard external and in- ternal threads, with various types of pins or keys to lock the bushing to the parent material. Some of the most widely used variations are: A two-piece insert with a locking ring and two keys fits into mating grooves in upper external threads, The ring is pressed into place after the insert is screwed into tapped hole; it cuts through enough threads of parent material to provide a positive lock. A counterbore in the tapped hole is required for the ring, but assembly and replacement can be made with standard tools. Another solid bushing insert has bo integral keys which act as a broaching tool when insert is installed flush with the parent material. Locking pins are pressed into the base of the tapped hole through the grooves in the external thread. Still another, a solid bushing, has standard internal and external threads and an expandable upper collar with serrations in the outer surface to lock the insert in the parent material. Factors that affect selection type: These factors must be considered in selecting the best Shear strength of parent material SOLID INSERTS FOR PRE- TAPPED HOLES have many variations. Among the most pop- ular are: (A) modified external threads for interference and lock- ing action; (B) two-piece unit with key ring for locking actfon; (C) integral keys give locking action: (D) expandable collar with external wrrations. Operating temperature Load requirement Vibratory loads Assembly tooling-serviceability and ease of installation Relative cost Shear strength of parent material below 40,000 psi gen- erally calls for threaded inserts. This includes most of the aluminum alloys, all magnesium alloys and plastic materials. But other factors must be considered. High operating temperature effects the shear strength by reducing strength of the parent material; an insert with a IaTger shear area may be required. Bolt loading frequently makes it necessary to use threaded inserts. For example, if the full pull-out strength of a 125,000-psi bolt is required, it is probable that the parent material will need a threaded insert to increase the shear area and thus reduce the effective shear stress. Vibratory loads may reduce bolt preload, and require a threaded insert to increase the effective shear area. Or vibration may cause creep, galling, and excessive wear, and inserts with both external and internal thread-locking fea- tures will be needed. The pullout capacity of an insert is a function of pro- jected shear area, and should equal the tensile strength of the bolt. This means pull-out strengrh should be greater than torque-applied tensile strength of the bolt. In wire thread inserts the projected shear area per coil 14-12 500 r 400 - + L 300 - f 200 - .t- 0 0 V RELATIVE EVALUATION-5 TYPES OF THREAD INSERTS !A-self-tapping insert; B-wire thread insert; C-solid bushing for pre-tapped holes; D-solid bushings for pre-fapped holes and external interference threads; E-self-fapping insert) 0 400 - 4- + 300 - z 3- a + C E O 2- El D c v) Lo v1 0 L) D - al m 0 w 0 8 200 - c A E - 100 E I 0 COST OF PART is price quoted for TOOL COST for each type is based on lots of 1000. manufacturer’s prices for tooling a evaluation. EASE OF ASSEMBLY is a qualitative standard tapping head. 0 ;ii Iiii $4 23 .+ O2 =I 0 0 NUMBER OF ASSEMBLY OPERA- TIONS covers complete installation of an insert, including drill, counterbore, tap, ream, install and reinspect. d n )!I, 0.4 0.5 0.6 0:7 018 d19 1.0 Effective Shear Area, sq in. A USEFUL RELATION is effective shear area to D/L ratio. It determines required insert length or pull-out strength. Solid curves are for self-tapping inserts; dotted curves for wire thread inserts. is relatively small; only way to increase the total projected shear area is to increase the number of coils. On the other hand, in solid and self-tapping inserts the projected shear area Can be increased by a larger OD as well as by more threads, while maintaining the same bolt diameter. One way to determine adequacy of pull-out capacity is to plot the ratio of the internal diameter vs insert length as a function of the effective shear area developed in the parent matcrial. The accompanying curves for three sizes of sclf-tapping and wire thread inserts were derived from tats in which the insert was pulled out of the parent ma- terial. Similar curves could be developed to determine the length needcd for any othcr type of insert. For exnmplc, assume that a +-28 bolt with an ultimate strength of 5000 Ib is to bc uscd in a material with a shear strength of 20,000 psi. The required shear area is 5000 lb/20,000 psi = 0.25 sq in. From the accom- panying curves, the D/L ratio is 0.57; insert length, L = 0.25/0.57 = 0.438 in. Similar calculations, using the same curves, can deter- mine whebher length df bhe insert is sufficient to give a required amount of creop resistance: The creop strength of the parent material is substituted for shear strength in the above calculation. Also, if the inscrt lcngth is limited, these calculations wiil give the availaMe pull-out strength, which will vary wibh shear arca of the insert. This analysis can be used to dctcniiine cithcr the rcquircd length or pull-out strengbh, and from this, the thickness of the parcnt material for minimum weight and maximum economy. Solid threaded bushings oftcn permit using a shorter bolt than for the wire thread insert with limited shear area. Witth a large number of fasteners in an assembly, weight saving in reduction of parent material is much greater bhan the small extra weight added by the solid insert. Other important factors in sdecting inserts are assem- bly tooling, serviceability, relative cost, and ease of installa- tion. These factors have bcen evaluated in the bar charts prepared by W. Moskowitz of GE’s Missile and Space Vehicle Dept, Philadelphia. Dab are for five types using 10-32 internal thrcads. Part of this information is based on estinwtcs of the operating pcrsonnel concerning the numbcr of assembly qcrations, tolerancus rcquired during installation, and relative ease of installation. Grommets, Spacers & Inserts 14-13 Flanged Inserts Stabilize Multi-Stroke Reloading Press E. E. Lawrence, Inventor Robert 0. Parmley, Draftsman Flanged Insert \ I I I I 1 L 0 Flanged Insert / / Flanged Insert W ILLUSTRATED SOURCEBOOK of MECHANICAL COMPONENTS SECTION 15 12 Ways to put Balls to Work 15-2 15-4 Rubber Balls Find Many Jobs 15-6 Multiple Use of Balls in Milk Transfer System 15-8 Use of Balls in Reloading Press 15-10 Nine Types of Ball Slides for Linear Motion 15-12 Unusual Applications of Miniature Bearings 15-14 Roller Contact Bearing Mounting Units 15-16 Eleven Ways to Oil Lubricate Ball Bearings 15-18 Ball-Bearing Screw Life 15-20 Stress on a Bearing Ball 15-27 Compute Effects of Preloaded Bearings 15-29 Compact Ball Transfer Units 15-39 How Soft Balls Can Simplify Design Balls 15-3 11 BALL-LOCI( FASTENS STUD IN BCIND HBLE . Exponds u8en hqnde is serewedon shoft * *I *1 3, , >> ", ST-BEARjNG TAKES LIGHT LOADS. ' I Balls 15-5 Balls 15-7 HOLLOW SHAFT-SEAL embodies ad- hesive-bonded rubber ball with flow hole. Quick connection of leakproof joint for 7 lubricant or other liquid is gained. Balls 15-9 Balls 15-11 Balls 15-13 5 Sleeve bearing consisting of a hardened sleeve, balls and retainer, can be used for reciprocating as well as osdl- lating motion. Trawl is limited similar to that of Fig. 6. This type can withstand transverse loads in any direction. Ball reciprocating bearing is designed for rotating, re- 6 ciprocating or oscillating motion. Formed-wire retainer holds balls in a helical path. Stroke is about equal to twice the difference between outer sleeve and retainer length. Ball bushing with several recircu- 7 lating systems of balls permit un- limited linear travel. Very compact, this bushing simply requires a bored hole for installation. For maximum load capacity a hardened shaft should be used. 8 Cylindrical shafts can be held by commercial ball bearings which are assembled to make a guide. These bearings must be held tightly against shaft to prevent looseness. Curvilinear motion in a plane is 9 possible with this device when the radius of cumam is large. How- ever, uniform spacing between grooves is important. Circular - sectioned grooves decrease contact stresses. Hamilton Standard * [...]... number of circuits Number of balls per turn is From charts Number of impacts per revolution for a D / d ratio of 5 .71 is 7. 8, Fig 2 -9300 /6 load DIMENSIONS for design problem Nut rotates, but is stationary i n a linear direction P (-:-) = 5 7 1 ~ 17. 9 = = 18 Balls 1 o9 1 O8 I o7 I n t 0 0 c W ‘c I 1 o6 I o5 I 1 - - LIFE-LOAD RELATIONSHIPS for various diameter balls 15-23 15-24 Number of turns is No of. .. by providing more of the friction caused by the rubbing of adjacent balls rolling in the same circuits having fewer turns In one series of tests it was found that the direction One way to reduce the tendency to life of nuts having 'two circuits of 3% jam is to include alternate balls of a turns each was comparable to that of a smaller diameter The larger ones nut having five circuits 'of 1% turns serve... load rating of 9120 Ib This bearing supports a radial load of 2000 Ib at a shaft speed of 1000 rpm According to the catalog, the bearing contains 8 balls of h in diameter Also, this bear? ing is listed as having a mean diametral clearance of c = 0.001 in Without any preload, what is the radial deflec- 15-32 tion and estimated Llo fatigue life? From Eq 3 K = (1.53(1 07) (0.G 875 )0.5 = 1.269 X lo7 From Eq... projection, < These factors play an important part in computing the change in fatigue life of a ball bearing when preloaded For best results, design for 0.5 . rev 7/ 32 = 5 .71 , (Ideal D/d ratio is between 4 and 8.) From charts Number of impacts per revolution for a D/d ratio of 5 .71 is 7. 8, Fig 2. Impacts are the number of balls. Flanged Insert W ILLUSTRATED SOURCEBOOK of MECHANICAL COMPONENTS SECTION 15 12 Ways to put Balls to Work 15-2 15-4 Rubber Balls Find Many Jobs 15-6 Multiple Use of Balls in Milk. turns. In one series of tests it was found that the life of nuts having 'two circuits of 3% turns each was comparable to that of a nut having five circuits&apos ;of 1% turns each.