MECHANICAL FASTENERS 2 PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 27. MECHANICAL FASTENERS 2

 

A Screws Screws have threaded shafts with heads. They may be screwed into a predrilled hole – drilled for the screw to enter. Self-tapping screws do not require predrilled holes. They cut their own hole as they are screwed in. Unlike bolts, screws are not used with nuts and – generally – are not screwed into threaded holes. Most screws heads are designed to be screwed in using a screwdriver. The most common types are shot head screws and crosshead screws. B Screw anchors Fasteners designed to fix objects to walls are called screw anchors. These fit into predrilled holes. A simple screw anchor is a plastic tube called a wall plug (or plug). It is inserted in a hole, and a screw or bolt is then screwed into it. As it enters the plug, the plug expands (its diameter increases). This increases friction, allowing the plug to resist pullout forces – the forces which would cause it to be pulled out of the hole if it were not firmly anchored. An expansion anchor is another type of anchor. It consists of a bolt fitted inside a metal sleeve. The sleeve expands as the bolt is tightened in the hole. C Rivets Rivets are permanent fasteners – they cannot be unscrewed. A solid rivet consists of a short, solid shaft of metal with a head at one end, called the factory head. The river is inserted through a pre-drilled hole, then a special tool is used to deform (change the shape of) the other end of the river, flattening and widening it to form a second head, called the shop head. Solid rivets are widely used in aircraft. EXERCISES 27.1 Make word combinations with screw using words from A and B opposite. Then match the combinations with the descriptions (1-5) below. One description can be used twice. 1. A ____________ screw is thin bolt. 2. A ____________ screw does not require a predrilled hole. 3. A ____________ screw has a straight groove cut into the top. 27.2 Complete the article from a home improvements magazine using the words in the box. Look at A and B opposite to help you. crosshead expand head plug pullout screw screwdriver set in HOW NOT TO USE WALL PLUGS ….. You check the diameter of hole required, then choose a drill bit one millimetre narrower. You’ve tried drilling the specified hole size many times in the past, only for it to be too big, leaving the (1)___________ spinning the hole when you tighten the (2)___________. You decide it’s better to ensure a tight fit. So you drill a smaller hole than suggested, then attempt to hammer in the plug. It bends sideways, useless. You try again. And again. 27.3 Match the descriptions (1-5) to the terms (a-e). look at C opposite to help you. 1 a type of fastener that is hollow a rivet gun 2 a type of fastener that is not hollow b shop head 3 a tool used for installing a type of fastener c factory head

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