81912
Description
Flashcards by Alec Stevens, updated more than 1 year ago
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Created by Alec Stevens
over 11 years ago
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| Question | Answer |
| Washers | Washers can be used as spacers, anti-vibration devices, locking devices and to prevent friction between components. Also can be used for gas or liquid sealing. Distribute load when tightening bolt/nut. |
| Rivets | Rivets permanently join metal. Solid rivets are manufactured from soft iron. They can be countersunk or flat and simply have one end hammered into shape once it has passed through the hole. Pop and snap rivets are pushed through the hole with one end in the rivet gun. The rivet is then compressed and is now too large on the other side to fit back through the hole - the metal is joined. The piece of metal in the gun snaps off and the rivet is left. Solid rivets are extremely out-dated and any rivets at all are now being replaced by spot-welding. |
| Oxy-acetylene Welding | Two gases (Oxygen and Acetylene) mixed and ignited. Very hot, and a filler rod of the same material as the one being welded used to complete the joint. Steel is commonly welded - aluminium is not because it has a low melting point and oxidises fast when heated. |
| MIG Welding | Metal Inert Gas An electric arc is struck between the work and the electrode - this is the source of heat and the filler is a thin wire gradually being fed into the joint. An inert gas, usually argon, flows around the joint to keep oxygen away. |
| TIG Welding | Tungsten Inert Gas Non-consumable tungsten electrode makes an arc with the work. Argon/helium insulates the work from oxygen and a filler metal is usually used. Grants operator greater control over the weld, which can mean greater strength and quality, but also makes the process slower. Is a complex process and takes time to master. |
| Brazing | Joining mild steel to mild steel using heat and spelter - an alloy of 65% copper and 35% zinc. The joint must be prepped by cleaning and applying flux. Flux keeps the joint clean, stops it from oxidising, and breaks down surface tension so that the spelter can flow into the join. |
| Hard Soldering | Like brazing, sometimes called silver-soldering. Used often to join materials like copper, or silver in jewellery making. Requires flux and a clean joint like brazing. Hard solder has a range of melting points from 625° - 800° which is useful when joining multiple things to one piece of work. |
| Tensol Cement | Used to join thermoplastics. A solvent which literally melts the plastic, the joint must be pushed together and ideally clamped for 24 hours. A permanent joint which gives off fumes and should be used with caution (COSHH). |
| Polystyrene Cement | Similar to Tensol cement - a chemical weld which melts the surface and lets the component parts to fuse. As the solvent evaporates the strength returns to the plastic. Must be clamped and held like Tensol cement. Thermosetting plastics cannot be joined with Tensol or Polystyrene cement because they do not melt! |
| PVA | Polyvinyl acetate. Wood glue which is water soluble and dries clear. Joints must be clean and match without gaps. Takes 24 hours to set/harden fully. |
| Epoxy Resin | A thermosetting plastic which cures when mixed with a catalyst (hardener). Very useful as they can be used on almost any material in almost any situation. Most common type is Araldite. Should be clamped whilst glueing, don't get on hands! |
| Contact Adhesive | Made from natural rubber and neoprene. Useful when materials like laminates need to be glued to flat surfaces. Must make sure surfaces are free from dirt or grease and clean. Adhesive must be applied to each surface thinly and left to dry till they are dry or just sticky to the touch. Two surfaces should be pushed together carefully, as bonding occurs almost immediately and the joint cannot be adjusted. Gives of fumes, use in a well ventilated area. |
| Hot Melt Glue | The glue used in glue guns. A thermoplastic adhesive. Good for small model making application. Can cause blistering from heat if it comes into contact with skin. |
| Nuts and Bolts | Usually manufactured from low or medium carbon steel. The advantage is that they can easily be undone and re-done up, meaning that components joined by them can be replaced or repaired. The diameter is always given in millimetres. BS Whitworth thread has a root angle of 55°. ISO metric thread has a root angle of 60°. Nuts have different types of threads depending on what is required, e.g. locking nuts can be used if vibration could be a problem. |
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