Engineering

Leaving Cert. Engineering Revision Notes – Index

Polymers Condensation & Addition Polymerization General definitions Thermoplastics vs. Thermosetting plastics Joining Mig & Tig Welding Manual Metal Arc welding Oxy Acetylene welding Submerged Arc & Resistance seam welding Material Testing Material Properties General Definitions & Properties Non-Destructive Testing Destructive Testing Internal Structures of Materials Bonding Structure Defects Cooling Curves… Continue Reading →

Material Testing – Engineering Notes

Material Properties Strength: The ability of a material to withstand forces of compression, tension, shear and torsion. Tensile Strength: The maximum pulling stress a material can withstand without fracture. Torsional Strength: The ability to resist twisting forces. Hardness: The ability to resist abrasion, wear, indentation and scratching. Ductility: Ability of a material to be stretched into… Continue Reading →

MIG & TIG Welding – Engineering notes

MIG welding Semi automatic process. A consumable bare wire electrode fed continuously into the weld pool through torch by spool. An inert gas, e.g. argon, has a fluxing action and creates a protective shield around the weld pool. The feed and flow rate are set by the operator. Does not produce slag…. Continue Reading →

Polymers – Differences between Thermoplastics and Thermosetting plastics

Thermosetting Plastics Bonding Bonding by Covalent bonds. Primary bonds held together by strong cross links. Process: Condensation Polymerisation Forms strong primary bonds between chains. Two monomers react to form a new molecule with water or alcohol emitted as a bi-product. The polymer cannot be resoftened. E.g. Phenol Formaldehyde Properties High melting… Continue Reading →

Polymers – General definitions

Co-Polymer: Two unlike monomers joined together in a polymer chain. E.g. Poly Vinyl Acetate Elastomer: A group of polymers consisting of linear chains that are coiled, entangled and are subject to cross linking. This allows these materials to be very elastic at room temperature. Lubricants: Make the polymer easier to mould. Various types of waxes… Continue Reading →

Polymers – Condensation & Addition Polymerization

Monomer: A monomer is a molecule of a compound which reacts with other monomers to form a polymer. Mer: A mer is a repetitive unit in a polymer.  Addition Polymerisation of Ethylene (Thermoplastics) Ethylene consists of 4 hydrogen atoms and 2 carbon atoms joined together by a double bond. (Primary and secondary… Continue Reading →

Heat Treatment – Engineering Notes

Hardening Process The piece is heated to a cherry red colour and then cooled rapidly in water oils and brine. At the cherry red colour the steel will have undergone structural changes (FCC to BCC, martensite) and the rapid cooling does not allow it to revert to its original condition. Result Very hard and Brittle…. Continue Reading →

Iron Carbon Equilibrium Diagrams – Engineering Notes

Lower Critical Point Occurs at 723°c. Temperature change occurs. The metal contracts dimensionally, glows less brightly and loses its magnetism. Known as Decalescence. Upper Critical Point Varies depending on amount of carbon in the steel. Above this point, the metal exists as FCC austenite. Eutectic Point Liquid to solid Occurs… Continue Reading →