ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Manufacturing Technical Objects
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Throughout history objects have been invented to make mankind's life easier. We refer to these inventions as technical objects.
Technical objects can be broken down into sections:
1) Materials
2) Technical Drawings
3) Manufacturing
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Materials
The choice of materials used for a given technical object depend on various factors or constraints (outside/external forces that limit or even deform the technical object)
Constraints
1) Compresion: When a material is put under pressure or it is squeezed in some form.
Symbol used:
Example: Crushing a can
or a column of a house
2) Tension: When a material is pulled apart or elongated.
Symbol used:
Example: kite string
3) Torsion: When a material is twisted
Symbol used:
Example: Wringing out a piece of clothing
4) Deflection: When a material is being bent
Symbol used:
Example: Fishing rod
5) Shearing: forces that tend to cut the object
Symbol used:
Example: Scissors
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Deformations
The material undergoing any of the constraints will deform in 3 possible ways:
1) Elastic deformation: Temporary change. If the force is removed, it will return to its original state/form.
2) Plastic deformation: Permanent change. If the force is removed, the object will NOT return to its original state/form.
3) Fracture: The constraint is so much that it will break the object. Tech lab 1
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ST Manufacturing a Technical Object HMH 2015.notebook
Properties
April 24, 2015
Because not all materials behave in the same way, engineers use different words to describe their properties. Depending on a given constraint, an engineer will choose the material needed according to its properties, listed below.
From book pg 388
Mechanical Properties
Definition
Example (with high amounts of the property listed)
Hardness
Ability to resist indentation or abrasion
Diamond
Elasticity
Ability to return to their Rubber
original shape after undergoing a constraint
Resilience
Ability to resist shocks without breaking
Plastic
Ductility
Ability to be stretched without breaking
Gold
Maleability
Ability to be flattened or Lead
bent without breaking
Stiffness
Ability to retain their shapes when subjected Wood
to various constraints
Corrosion Resistance
Ability to resist the corrosive substances such as salt water
Electrical Conductivity
Ability to carry electrical Copper wire
current
Thermal Conductivity
Ability to conduct thermal Copper wire
energy
Stainless Steel
Degradation describes the decrease in some of a materials' properties in a given situation (environment) Ex: Wood can be considered very elastic when fresh. As it dries out, it loses it's elasticity and becomes more brittle. or
Ex: A car that is left near a beach will tend to rust faster than if it stayed in a dry cold area. In order to save a material from the environment that is breaking it down, we may use some sort of protection. Ex: Paint, or Rustproofing (for the examples above)
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Wood
Hardwood
Ex: Oak or maple
Softwood
Ex: Pine or Spruce
The variation in the wood depends on:
1) Species
2) Speed of growth vs. injuries
3) Water content in the wood
Because wood is hard, elastic, resilient and tough, it has a great use in housing and furniture, while still being easy to shape in addition to having a low thermal and electrical conductivity. Past
Whole pieces used
and easy to find
Today
Particles, because not as easy to find
Most of the wood we use today is usually considered modified wood. It is made by pieces of wood, residues or leftover wood, generally held together with glue, plastics or preservative. It will most likely fall under 1 of the following: Modern Wood
1) Plywood
2) Particle board
3) Fibreboard
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Degradation and Protection of wood
Because it is organic it can be broken down quickly. Fungi, plants, and other animals can use wood as sustenance. The wood can be easily painted, varnished or treated with protective coatings.
We can treat the wood in 2 ways to prevent the breakdown:
1) Dipping it in a basic solution containing copper
2) By heating it up ($$$)
The wood is then known as treated wood.
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Ceramics
Ceramics are inorganic materials generally made of oxides and other compounds that are heated up so that the moisture is removed, and in the process forces the bonds to rearrange and become stronger. Ex: Coffee mugs, bricks, floor tiles...
Depending on the ingredients, and the way it is baked will determine the product's properties.
Properties
Low electrical conductivity
Low thermal conductivity
High level of hardness
High resistance to corrosion
Fragile
Uses
insulator
dishes
building materials
special pipes
Degradation and Protection
As a whole, ceramics are very durable, little care is given to their protection against the following:
Certain acids and bases can break down the bonds that make up the ceramic's strength therefore making it weak over time.
Even a drastic change in temperature will cause the ceramic to break
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Metals and Alloys
Metals are extracted from mineral ores after they have been mined.
good conductors of EE and TE
ductile, and malleable
lustrous
When metals are combined with other elements, other metals or not, it becomes an alloy. An alloy will generally have better properties from that of its predecessors.
Because metals are quite often mixed with iron, these are known as ferrous alloys. Otherwise most other combinations are called nonferrous alloys.
Enhancing Steel's Properties Heat Treatments
Steel is made of Fe and C. Through heating and cooling, quickly or slowly, metals atomic matrix can realign itself, thus giving it different properties. (Eg: hot pan in cold water example)
Stages of Heat treatment
Quench Hardening
1) heat the steel >800oC > This will allow the atoms to rearrange themselves differently.
2) drop it into a cold bath
> This will freeze the atoms in place, and make the steel hard and brittle. Tempering or Annealing
3) heat it up but at <800oC > This will relieve some of the built up stress that makes it brittle. 9
ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Degradation and Protection (metals and alloys)
Metals often easily reacts with oxygen (oxidation), therefore degradin them.
Protected
Unprotected
Simple coatings can be applied to prevent oxidation from taking place.
Metallic coatings
Zinc (boats)
Chrome (knives)
Gold (jewelry)
nickel (mags)
...
Non metallic coatings
Paint
Grease
Glue/Resin
...
or Add other elements to change the chemical properties of the alloy.
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Plastics
Plastic is derived from fossil fuels. Inside fossil fuels are molecules known as monomers. When many monomers come together, they form chains called polymers. Poor conductor of EE and TE
Thermoplastics: become soft when heated to be moulded, retain their shape when cooled (3/4 of all plastics are thermoplastic, some can be recycled, recycling codes pg. 530)
Thermosetting plastics: remains permanently hard, even when heated (harder, more resilient, nonrecyclable, ex. kayaks)
Degradation and Protection
Degrade in quality over time. They "dry out" and then crack or discolor, both of which are irreversible. Since plastic is made up of chains of atoms, they are susceptible to chemical reactions like any other molecule. Some plastics may react clearly with acids, while others would not.
Cause Description Example Protection Method Penetration of a Liquids such as water or solutions Waterproof coating (acid) can penetrate plastics liquid Oxidation O2 and gases with properties similar to O2 can react with polymers in the plastic causing degradation Add antioxidants (ex. carbon black) UV Rays Can damage the bonds that make up the polymers Add pigments that absorb UV rays 11
ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Composites
As the name describes it is a combination of the 1) Matrix (original material) and 2) the reinforcement (additive), put together.
Mixing two materials together can play on the strengths of both ingredients.
Ex:
Plastic
Resilient
Ceramic
Stiff
Composite
Stiff and resilient
Main Matrices and Reinforcements
Description Properties Sought Plastic Matrices Durability, Thermosetting plastics preferred, these plastics are lightness, resilient, also called resins low cost Metallic Matrices Made from metals or alloys Ductility, thermal and electrical conductivity, stiffness Ceramic Matrices Made from ceramics, often glass Durability, heat resistance Fiberglass Made of glass (a ceramic) in the form of fibres (length, diameter and type of glass varies Stiff, corrosion resistant Aramid Fibres Know as "Kevlar" one of few plastics used as a reinforcement Low density, resilient Carbon Fibres Made by carbonizing polymers, mostly polyacrylonitriles stiff, low density, electrical conductivity Composites are a massive industry, they are utilized in:
• Aeronautics (airplane wings)
• Sports (sports tools, making swimming pools, bike helmets)
• Arts (violin bows)
• Mechanical Industry (brakes, body)
• Military and Police (bulletproof vests)
Degradation occurs in 2 forms:
1) Deformation or fracture of the matrix or reinforcements
2) Loss of adherence between matrix and reinforcements
The best way to ensure a composite does not degrade is to ensure the correct matrix and reinforcement are chosen for the constraints on the object Floppy
Pg: 203, 204, 207, 208
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ST Manufacturing a Technical Object HMH 2015.notebook
April 24, 2015
Floppy
Pg: 203, 204, 207, 208
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