Properties and Selection of Engineering Materials

SUBMITTED TO:Dr. JAYANT JAIN

PRESENTED BY: SANDEEP SIKRI(2012 AMD 2608)

Indian Institute of Technology, DelhiDepartment of Applied Mechanics

MATERIALS FOR SCREWDRIVER

INTRODUCTION

A screwdriver is a hand-tool for turning (driving) screws (and sometimes bolts or other machine elements with a mating drive system).

A typical screwdriver comprises: •A cylindrical handle •An axial shaft •Blade•Tip

The handle and shaft allow the screwdriver to be positioned and supported .

By rotating the handle, torque is applied to the tip via the screwdriver's shaft.

A screwdriver is typically identified by its tip, which is shaped to mate with a screw.

The head of screw has a particular contour, or surface shape.

Screwdriver tips are available in a large variety of shapes and sizes.

HISTORY

The earliest screwdrivers of which written evidence remains were used in Europe in the late Middle Ages. They were probably invented in the late 15th century either in Germany or France.

These earliest screwdrivers had pear-shaped handles and were made for slotted .

The screwdriver remained inconspicuous, however, as evidence of its existence throughout the next 300 years was based primarily on the presence of screws.

Metal screws and nuts seem to have been used as fasteners in the fifteenth century, screw heads were either square or hexagonal. Screws with slots in their heads were found in armor in the following century.

The modern screwdriver descends directly from a flat-bladed bit used in a carpenter's brace circa 1750. Woodworkers were using hand screwdrivers in the early 1800s, and they became more common after 1850.

These early screwdrivers were flat throughout the length of their shaft; the current design of a rounded bar that is flattened or shaped only at the working end makes the tool much stronger and takes advantage of the round wire used in its manufacture.

The oldest and most common type of screwdriver is the slotted screwdriver, which fits a screw with a single slot in the head.

There are perhaps thirty different types of screwdrivers available today in a variety of sizes, all with different purposes and all designed to fit into special screws.

VARIOUS TYPES OF SCREWDRIVERS

Robertson ScrewdriverIn 1908, square-drive screws were invented by Canadian P. L. Robertson. Robertson screw is considered the "first recess-drive type fastener practical for production usage. A square-drive head on a screw can be better than a slot head because the screwdriver will not slip out of the screw's head during installation.

Phillips Head ScrewdriverIn the early 1930s, the Phillips head screw was invented by Henry Phillips. The rounded, tapered slots of the Phillips head were deliberately designed for the screwdriver to "cam out” (pop out) of the screw head recess under high torque .This prevents stripping damage to the screw threads.

Torx ScrewdriverThe torx screwdriver, widely used for automobile repair and other applications, was designed to take the torque that a Phillips screw can while eliminating the cam-out problem. It has six edges in a star pattern on its flat point, and hence it is also called as star screwdriver.

Material Selection for Screwdriver

Steps Involved:

FUNCTION --- Screwdriver(Torque is applied)

OBJECTIVE --- Minimization of mass “m”

CONSTRAINTS --- Torsional stiffness “S” Strength

FREE VARIABLES --- Cross sectional area Choice of material

DESIGN REQUIREMENTS FOR SCREWDRIVER

Material Indices

Mass = m = A L

Objective function:

Where :

= Density of material

A = Cross sectional area

L = Length

Constraint on Torsional stiffness:

We know that Torsion Equation is :

Where :

T = Applied torqueJ = Polar moment of InertiaG = Modulus of rigidity = Angular twist L = Length = Max. shear stress r = Radius

Constraint on Strength:

E vs Graph using CES

vs Graph using CES

From above Graphs we came to know that Low/ Medium Carbon Steel,Ni alloy,Chromium alloy are the materials which are good candidates for screwdriver.

MATERIAL M1 M2

Low carbon 1.95 11.06 Steel

Medium carbon 1.85 9.26steel

Cr alloys 1.72 9.38

Ni alloys 1.68 8.95

310X)//()( 32/1 mMgGPa

POSTSCRIPTLow carbon steel or medium carbon steel is best suited material for Screwdriver.

Carbon dominates the hardness but destroys the toughness. Torque value can be increased as the silicon content is higher.

Nickel addition assists in compensating hard steel for toughness.

Chromium combined with molybdenum to form carbides are beneficial for wear-resistance.

Also,Nickel or chrome plating on low carbon steel is also a good option for the material of screwdriver.

REFERENCEShttp://en.wikipedia.org/wiki/Screwdriver http://en.wikipedia.org/wiki/Screw

http://en.wikipedia.org/wiki/Torx

http://www.madehow.com/Volume-1/Screwdriver.html

http://www.ezlok.com/TechnicalInfo/MPCarbonSteel.html

http://www.denofgeek.com/tv/20081/a-short-history-of-the-sonic-screwdriver http://wenku.baidu.com/view/8a3c3c6daf1ffc4ffe47ac0f.html

http://books.google.co.in/books?id=R2YEAAAAMBAJ&pg=PA82&redir_esc=y#v=onepage&q&f=false

http://www.britannica.com/EBchecked/topic/529926/screwdriver

http://www.steeltalk.com/high_carbon_steels.php

http://the-working-man.com/screwdriver-history.html http://www.wisegeek.com/what-is-a-magnetic-screwdriver.htm

http://www.interlloy.com.au/our-products/carbon-steels/1045-medium-tensile-carbon-steel-bar/

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