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MIAT 105 Materials Fasteners Day 1

First lecture in materials on fasteners

MIAT 105 WandM

on 3 July 2013

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Transcript of MIAT 105 Materials Fasteners Day 1

Materials DAY 1

Standard = hex (most common shape), wing, speed nuts.

Locknuts = collar, slotted, crimped
(do NOT re-use)

Castle and Pal-nuts – used with cotter pins.

Other Special types
A common metric unit of pressure or stress equal to one million Pascals or one Newton per square millimeter.

1MPa = 106Pa = 1N/mm2

One MegaPascal equals 10bars or approximately 145.038 pounds per square inch (lbf/in2 or psi) or 20,885.5 pounds (10,443 U.S. tons) per square foot.

1MPa = 10bar = 145.038psi = 20,885.5lbs/ft2
Megapascal (MPa)
Threaded Fasteners
Shims and Shim Stock
The characteristics of splines:

1. The keys are integral with the shaft. → Greater fatigue strength of a spline shaft compared with keyways.

2. Greater carrying capacity because of greater working surface.

3. The centering is good, and more uniform pressure distribution over the height of the spline.

4. Parts mounted on spline shaft are more accurately centered and guided if they slide along the shaft.

5. The technology of manufacturing is complex, and the demand of manufacturing precision is high.
Splines (cont.)
Spline joints consist of spline shaft and hub joint.

They are used as fixed joints between a hub and a shaft, as sliding joints without load and as sliding joints subject to loads.

Types of splines:
- parallel-sided splines
- involute splines
- thin tooth involute splines
1. Flat keys

2. Woodruff keys

3. Wedge Keys Taper keys

3.1. Taper keys
3.2. Tangent keys
Key Types
A key is a fastening inserted into the key way (slot) of two mating parts to prevent relative angular or sliding motion between the parts.

It is mainly employed to transmit torque from a shaft to a hub or vice versa.

Keys are made from drawn steel with a tensile strength of approximately 700 MPa.

They must have a greater strength and hardness than the machine parts to be connected, so that they are not deformed when they are driven in.
Clevis Pins
are a unique type of fastener that can hold two materials together non-permanently.

Unlike bolts and nuts, which press the materials together for holding power, pins can hold the assembly together with no torque pressure.

Roll pin usage
Shift linkage inside trans, speedometer drive gears, pinion gears in steering rack.
Roll Pins
Zinc Plating
- Many steel fasteners are electro-plated with zinc for better corrosion resistance.
- Fasteners that have been zinc plated have a shiny silver or golden appearance referred to as clear or yellow zinc respectively.
- They are fairly corrosion resistant but will rust if the coating is destroyed or if exposed to a marine environment.

Hot Dip Galvanizing
- Galvanizing is another coating involving the application of a layer of zinc.
- Hot dipped galvanizing puts the thickest possible coating on the metal resulting in superior corrosion resistance.
- Due to the thickness of the coating hot dipped galvanized bolts are not compatible with other nuts.
- Galvanized nuts are tapped slightly larger than other nuts to accommodate this coating. - Hot dipped galvanized fasteners are frequently seen in coastal environments.

- Chrome is used in plating fasteners for its appearance.
- It provides similar corrosion resistance to zinc plating.
- The main drawback of chrome is the extremely high cost.
- If more corrosion resistance is required stainless steel may be chrome plated, preventing any corrosion should the chrome be penetrated.
Steel fasteners Coatings
Lock Washers (cont.)
Other special shape types

Use a flat washer under a lock washer on aluminum applications.
Lock Washers
Nut Grade Markings (cont.)
Nuts are graded with strength ratings compatible with their respective bolts.

The grade of nut used must match the grade of bolt it is used with.

For example:
an ISO property class 10 nut will be able to support the bolt proof strength load of an ISO property class 10.9 bolt without stripping.

, an SAE class 5 nut can support the proof load of an SAE class 5 bolt, and so on.
Nut Grades
Nut Types
A nut is a type of hardware fastener with a threaded hole.

Nuts are almost always used opposite a mating bolt to fasten a stack of parts together.

The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts.

In applications where vibration or rotation may work a nut loose, various locking mechanisms may be employed: adhesives, safety pins or lock wire, nylon inserts, or slightly oval-shaped threads.
Cap Bolts/Screws
Socket Cap Screws
Machine Screws
Set Screws
Shoulder Screws
Tapping Screws
Types of bolts & screws
The property classes most often used are
5.8, 8.8, and 10.9.

a property class 8.8 bolt has:

- a nominal (minimum) ultimate tensile strength of 800MPa (116,000lbs)

- a tensile yield strength point of 0.8 times tensile ultimate strength or 0.8 (800) = 640MPa (92,800lbs).

of marking/number indicates a lower grade bolt with low strength.

Metric (ISO) bolt property class (cont.)
Bolt Terminology
There are two main systems of threaded fasteners in North America:

(English) Inch System
which is regulated by:

SAE= Society for Automotive Engineers
- set the standard for the automotive industry
- no manufacturer may make or use a fastener that is not SAE approved

ASTM = American Society for Testing and Materials
- one of the largest voluntary standards development organization
- guides design, manufacturing and trade in the global economy

ANSI = American National Standards Institute
- set standards for bolt grades
- measures a bolts tensile strength

Metric System

regulated by ISO
ISO= International Standards Organization
- defines strength in terms of tensile and yield strength.
Threaded fastener standards
Mechanical Strength Terms (cont.)
Yield Strength Point (Elastic Limit)
– Maximum stress it can stand and still return to it’s original shape.

Ductile metals do not have a well defined yield point. The yield strength is typically defined by the "0.2% offset strain".

Ultimate Tensile Strength
– stress at which the bolt will receive a permanent set (an elongation from which it will not recover when the force is removed) of 0.2 % offset strain.

Breaking Strength
– the stress at which the bolt fails (about 10% higher than the yield point )

Ultimate tensile strength and Yield strength

are used as a reference for bolt grade/class classification.
Characteristics of fasteners (cont.)
Mechanical Strength Terms
Fastener material can be important when choosing a fastener due to differences between materials in strength, brittleness, corrosion resistance, galvanic corrosion properties, and of course cost.

When replacing fasteners, it is generally best to match what you are replacing.

Replacing a bolt with a stronger one is not always safe. Harder bolts tend to be more brittle and may fail in specific applications.

Also some equipment is designed so that the bolts will fail before more expensive or critical items are damaged.

In some environments such as salt water galvanic corrosion must also be considered if changing fastener materials.
Characteristics of fasteners (cont.)
Where great resistance to weather or corrosion is required, stainless steel, titanium, brass (steel screws can discolor oak and other woods), bronze, monel or silicon bronze may be used, or a coating such as brass, zinc or chromium applied.

Electrolytic action from dissimilar metals can be prevented with aluminum screws for double-glazing tracks, for example.

Some types of plastic, such as nylon or Teflon, can be threaded and used for fastening requiring moderate strength and great resistance to corrosion or for the purpose of electrical insulation.
Characteristics of fasteners (cont.)
Fasteners are manufactured in a wide range of materials from common steel to titanium, plastic and other exotic materials.

Many materials are further separated into different grades to describe specific mechanical strength characteristics, alloy mixtures, hardening processes, etc.
Characteristics of fasteners
US and Metric Thread Sizes
Thread Classes define the amount of tolerance and allowance associated with a particular thread.

Classes 1A, 2A, 3A
- apply to external threads.
Class 2A is the most commonly used.

Classes 1B, 2B, 3B
- apply to internal threads.
Class 2B is the most commonly used.

1 = loose fit
2 = normal fit
3 = tight fit
Thread classes
– used in USA, Canada, and England

– unified national course

– unified national fine

– unified national extra fine
Fine threads will have higher torque limits but will strip easier.
Fine threads are used for adjustments.
Fine threads are where short length of engagement is available.

– national pipe thread – used for sealing liquids

Metric (ISO)

(e.g. 0.5, 1.0, 1.25, 1.5, 1.75, 2, etc.)
- standard (coarse)
- fine
- (extra fine)
Thread series
(refers to the thread pitch)
Thread Types (cont.)
Wrapping direction
Thread Types (cont.)
Power Screw Thread Types
Thread Types
d — major diameter
d1 — minor diameters
d2 — mean diameter

Threaded fastener terminology
What are Fasteners? Machine elements that connect or join various parts of a machine.

There are different fastener types which include-

: This type permits the parts to be readily disconnected without damaging the fastener,
e.g. bolt and nut (bolted joint).

: For this type, the parts can be disconnected, but some damage usually occurs to the fastener,
e.g. cotter pin.

: When this type of fastener is used, the parts will never be disassembled,
e.g. rivets and welding.
Fastener types
Threaded Inserts
Solid Pin usage
- Use a solid pin (as a safety element) when you want to protect parts from over loading.

- Solid pins shear easier than roll pins.
Solid pins (cont.)
Manufacturers use several different nut markings to denote grade identification.

Some are marked on the top and some are marked on the sides.

Grade 8 nuts are always marked but grade 5 nuts sometimes are not.
Nut Grade Markings
A = Overall Length
B = Length of Thread
C = Length of Thread
D = Diameter and Pitch of Thread
E = Diameter and Pitch of Thread
F = Center Relief Diameter
Studs (cont.)
Bolt/Screw = a rod with a head on one end and external threads on the other end.

STUD = rod with threads on at least one end.

May have a hex head in the middle

May not have threads on both ends

May be two different threads on opposite ends

May have two different diameters
Head style
One-piece screws with a cylindrical shoulder under the head to serve as a bearing or spacer.
Shoulder Screws
Set Screws – Point Types
Used to hold a part in position only.

Provide fast, permanent location of parts on shafts.

Usually have an Allen head.
Set Screws
Generally a smaller fastener (less than 1⁄4 inch in diameter) threaded the entire length of its shank that usually has a recessed drive type (slotted, Phillips, etc.).
Machine screws are also made with socket heads in which case they may be referred to as socket head machine screws.

Sized from 0 – 12
Threads per inch are also specified
Example of 6-32 : 6 = size 32 = threads per inch

Screws are described as 4-40, 6-32, 8-32, 10-32, 10-24, etc. (for numeric sizes, odd numbers are rare),
or 1/4"-20, 1/4"-28, etc. (for inch unit sizes), with the first number giving shaft diameter (numeric or inches).
Machine Screws
Metric bolts use the ISO strength property classes

Property Class numbers
1st # - tensile ultimate strength in MPa divided by 100

2nd # - 10 times the ratio of tensile yield strength to tensile ultimate strength
Metric (ISO) bolt property class
Bolt measurements and codes (cont.)
Characteristics of fasteners (cont.)
Mechanical Strength Terms
This is an example of a
down bolt

This happens because of tightening the bolt past its
Elastic Limit
Fasteners most commonly made by steel are sometimes heat treated for improving their mechanical strength characteristics.

Low strength fasteners are made of low carbon mild steel.

High strength fasteners are made of carbon steel with added carbon for heat treating.

Heat treating can be to Temper (toughen) a metal with heat and then quench it.

Heat treating can be to Anneal (soften) a metal with heat it and then cool slowly.
Characteristics of fasteners (cont.)
The pitch of metric threads varies according to the diameter, but not absolutely regularly.
Metric Thread depending on fastener nominal size (nominal diameter)
US Thread depending on fastener nominal size (nominal diameter)
These consist in a pair of mating bodies of a rectangular cross-section. Each of these bodies has one inclined side face, the inclination proportion (taper) is 1:60 up to 1:100.

Tangential keys are used if very great rotational forces have to be transmitted in both directions of rotation.
With their inclined surface turned towards each other, they are driven into inclined keyslots and hub keyways.
Tangent keys
Solid Pins are chiefly used as dowels for precise mutual location of members, and, to some extent, to transmit relatively small loads.

Do not interchange with roll pins
Solid pins (dowel)
May be Double Up For Heavy Duty Applications

Use one standard inside another for additional strength. Install the smaller pin inside the larger pin, then insert into the application.
Roll Pins (cont.)
Used on castle & slotted nuts
Used on linkages
Do NOT replace with nails or anything else
Cotter pins
Intake manifolds
Exhaust manifolds
Rocker arm assemblies
Wind turbine blade root, etc.
Examples of Stud usage
The same type of screw or bolt can be made in many different grades of material.

Bolts of different grades are marked on the head to show what grade bolt they are.

SAE bolts have marks for strength

METRIC bolts have numbers for strength
Bolt Grades/Classes
Mechanical classifications
Thread Types (cont.)
The structure is simple, and it is easy to assemble or disassemble, better centering quantity, used for transmitting load by pressing and shearing of higher speed.

Straight keys are of square or rectangular cross section.
The end may be either rounded or square.
Flat keys
Head style
Drive style
Self Tapping Screws
Includes Sheet Metal, Thread-Forming, Thread-Cutting and Self-Drilling styles in a wide variety of sizes, drives, and head types.

Form their own mating threads when driven in metallic and nonmetallic materials.
Self Tapping Screws
Also known as Hex Head Bolts/Screws.
Includes Standard, Drilled Head, Left Hand Threaded, Self-Sealing, and Military Specification Cap Screws.
Cap Bolts/Screws
Metric System
SAE System
Bolt measurements and codes
Bolts and screws
when tightened in order to provide clamping force or spring tension on the parts being held together.
Below elastic limit, fasteners can be tightened repeatedly.

A bolt is stretched to 70% of its elastic limit when tightened properly.
Fasteners have an elastic limit, then fracture occurs.

of a fastener is the point when it will no longer return to it’s original shape when loosened.
Characteristics of fasteners (cont.)
Outside/inside diameter of the threads with a caliper/micrometer
Measure pitch with thread pitch gauge (threads per inch)
Thread identification
1- Bolt /Screw
2 – Nut / internal threaded part
3 - Washer
A universally accepted distinction between a screw and a bolt does not exist.
a) A bolt is a threaded fastener designed usually (but not strictly) to pass through holes in the mating members and is normally intended to be tightened or released by torquing a nut from the end opposite the head of the bolt.

b) A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating usually with a preformed internal thread or forming its own thread, and of being tightened or released by torquing the head.
Threaded fasteners (cont.)
Bolts and Screws

A BOLT or SCREW, is a type of fastener characterized by a helical ridge, known as an external thread (or just thread), wrapped around a cylinder.
Threaded fasteners
are the most common fasteners and they are referred to by many names like
bolts, screws, nuts, studs, lag screws, set screws, etc
Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a NUT or an object that has the internal thread formed into it.

Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted.
Threaded fasteners
Convenient to assemble or disassemble,

Used for the joints of vertical mandrels and hubs,slacking down the shafts seriously.
Lock pulleys and gears tightly to transmission shafts.

Woodruff keys reach deep into the keyway shaft for a firm grip, yet they can rock in their seat and adjust to an angular spine. They can withstand great strain, so rollover is unlikely.
Woodruff keys
The Height of a Hex nut (D) depends on the nut size (B) and its subtype (e.g. standard (finished), jam, nylon insert lock)

For example :
Hex Metric Nuts :
D = 0.8 x B - for standard nuts
D = (0.5 … 0.6) x B - for jam nuts
D = (1.3 … 1) x B - for nylon insert lock nuts
Dimensions of a typical Hex nut (cont.)
Drive Style
Also known as a Allen head Screws/Bolts include Low Head, Button Head, and Flat Head Screws, as well as special Socket Cap Screws such as Vented, Drilled Head, Self-Locking, and more.
Socket Cap Screws
Grade 8
Grade 7
Grade 5
Grade 3
Grade 1, 2, (4)
Grade refers to strength

SAE J429 defines the bolt grades for imperial sized bolts and screws.

It defines them by grade, which ranges from 0 to 8, with 8 being the strongest.

SAE grades 5 and 8 are the most common
(count lines +2 to get grade)
SAE Bolt Grades
The correct gauge will match the grooves of the bolt
gauge has a different thread pitch than the bolt
gauge has a the same thread pitch as the bolt
Driving taper key
Laid-in taper key
Gib-head taper key
These are long bodies with a rectangular cross-section, inclined back surface and with plane or rounded front surface.

Taper keys are in fact wedges that usually have 1:100. in contrast to flat keys, the working surfaces of taper keys are the top and the bottom.
Taper keys
(a) Slotted, (b) Phillips, (c) Pozidriv, (d) Torx, (e) Hex, (f) Robertson, (g) Tri-Wing, (h) Torq-Set, (i) Spanner
Drive Style
Machine Screws
ASTM standards for bolt steel
SAE grades for steel for fasteners
Metric grades of steel for bolts
Mechanical proprieties depending on bolt/screw strength grade
Thread Thickness
Pitch diameter
Minor diameter
Major diameter
Thread angle
Depth of thread
Helix angle
• Major diameter: The major diameter is the largest diameter of the thread. It determines the nominal size.
• Minor diameter: It is the smallest diameter of the thread. In external thread, it is also called as root diameter.
• Pitch: is the axial distance between any point of one thread and the corresponding point of an adjacent thread.
• Lead: The distance a bolt advances into a nut in one revolution is called lead.
Threaded fastener terminology
Both internal and external
Do not bend or straighten
Use special pliers to remove
INTERNAL retaining rings are installed on the inside of a bore or a housing and fit into a groove
EXTERNAL retaining rings are installed on the outside of a shaft and fit into a groove
Retaining Snap Rings
CROSS Section
TOP View
A = Size across flats (wrench size)
B = Thread major diameter (nominal size)
C = Thread minor diameter
D = Height or Thickness
E = External diameter
Dimensions of a typical Hex nut
Diameter (D) – Pitch (T) x Length (L)
Example: M12 - 1.75 x 25 indicates a 12mm diameter (D) with 1.75mm pitch and a 25mm length (L)
Thread pitch is thread width in millimeters (crest to crest)
Diameter (D) – Pitch (T) x Length (L)
Example: 1-1/2 – 6 x 2 indicates a 1-1/2" diameter (D) with 6 threads per inch and a 2” length (L)
Thread pitch is number of threads per inch
Metric System
SAE System
Bolt measurements and codes (cont.)
p — pitch
s — lead
α — thread angle
h — height of thread engagement
λ — lead (or helix) angle
Retaining Rings
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