Education_ Handouts HEAT-GUN-PVC-bending_ Fundamentals of Electrical and Electronics Technology-Lecture 1 PDF

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Summary

PVC pipe is commonly used as electrical conduit as well as irrigation piping. It's rigid and strong, which doesn't allow it to bend at all. Elbows and couplings make it possible to manipulate the path of PVC, but a better way is to bend the PVC without breaking or kinking it....

Description

PVC is a thermoplastic - which means that it becomes soft when heat is applied. PVC electrical conduit is rigid yet lightweight; durable yet readily cut; and PVC electrical conduit is less cost than its metallic counterparts. In short, PVC electrical conduit is an excellent choice for most designs where cost is a factor in the protection of electrical cables, and the additional properties of the alternatives are not needed. When working with PVC conduit electricians do one of two things when bends are involved. Either: 1) we will buy “manufactured bends” like pre-bent “90’s, 45’s, and 30’s” 2) we will use a heat gun to manually bend the conduit to fit the application. Manufactured bends are often sold in the same aisle as the PVC conduit itself, and come in several angles. However, sometimes the job requires a slightly trickier bend to be made so we need to do it by hand. Often pre-manufactured bends are too large or create too small of an offset so it’s time to break out the heat gun. The best tool for heating the pipe is a heat gun.

HEAT GUN  Heat guns are electric hand tools which look and work in a similar way to hair dryers operating a fan that pulls air into the body of the tool and drives it across an electric heating element and out through a nozzle. Heat guns are sometimes referred to as hot air guns.  Heat guns are lightweight, easy-to-use tools which are less likely than blow torches to scorch wood or crack glass when being used. This means they’ve predominantly replaced the old-fashion paraffin and bottled gas blow torch for stripping paint on timber.  The hot air flow of a heat gun is less dangerous than a naked flame, but it can still cause flammable items to catch fire, crack glass and cause injury if directed on to the skin. One advantage of this tool is the heat is almost instantaneous, so it can be switched off during pauses while working – whereas flame blow torches need to be relit if the flame is extinguished, which is less convenient.  While flames can damage the surface being heated and potentially cause a fire, the hot air from a heat gun is a safer source of heat. For most jobs, 399°C (750°F) is hot enough, and many heat guns allow you to adjust the temperature.

FEATURES OF HEAT GUNS As a simple hand tool, there aren’t many differences between the various models of a heat gun, but here are some important features to consider:

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Wattage – this refers to the power of the heat gun. They commonly range from 1,000W to 2,000W. If there are heat and/or airflow controls, the higher the wattage, the more effective it is.

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Power switch – it’s normally a dead man switch so that power is turned off when finger pressure is removed, which is a good safety feature as the heat gun stops if it’s accidentally dropped.

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Variable temperature setting – a choice of temperature controls makes the tool more useful.

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Airflow setting – having variable or more than one setting makes the heat gun more versatile.

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Thermal cut out – this switches off the tool if it overheats.

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Hanging hook – useful for storage.

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Surface stand – this enables the heat gun to be safely rested during pauses. It also allows the gun to be used hands-free when two hands are required on the task, for example when bending a plastic pipe.

SAFETY PRECAUTIONS WHEN USING HEAT GUNS 1. Wear PPE - safety goggles and heat-resistant gloves, as well as a respirator mask if working in a restricted area. 2. Before you start work, ensure that the cord is long enough to easily reach the area you’re working in – if it isn’t, plug the heat gun into an extension lead to extend your reach. (Check the wattage capacity of the extension wire) 3. It’s always prudent to keep a fire extinguisher on hand in case of any problems. 4. Tie back long hair and don’t wear any loose clothing. 5. Be sure to have good ventilation in the area. 6. Make sure any surfaces are free from debris like shavings and sawdust as they could catch on fire. 7. Always use the heat setting recommended by the manufacturer. 8. Don’t block the air inlet grills on the heat gun when it’s being used. 9. When the job is finished, always unplug it and place the heat gun on a heatproof surface and leave it to cool completely before putting it away.

IDENTIFYING DIFFERENT TYPES OF BEND  The PVC or polyvinyl chloride rigid conduit is one of the most commonly used conduits in electrical wiring installation today. Its preparation for installation is much easier than the metallic rigid conduit.

 In preparing a non-metallic rigid conduit for installation, an electrician needs to do cutting, heating and bending. Like in metallic rigid conduit offset bends, 90o angle bends and other bends are also made on PVC rigid conduit.  In making bends on PVC rigid conduit, the electrician should see to it that the internal diameter of the conduit is not reduced and damaged so that the capacity of the conduit to accommodate maximum number of conductors will not be lessen and to facilitate easy pulling of conductors.

TYPES OF BEND 1. Stub up bend. 90 - A stub up bend is a 90° bend used to bring a raceway from under the floor up to a receptacle box or into a panel or wireway. The stub bend is made by bending a piece of conduit into an L shape or 90° bend by placing the free end (short end) of the tube to a predetermined length as indicated in the diagram below. This is the most common bend and is a building block for other bends. Common uses for this bend are: Running conduit into electrical boxes, running conduit up or down walls, running conduit into walls through floors and ceilings and making inner and outer corner turns. It is usually between 12” and 36” high. Because the stub up bend is so close to the end of the raceway; the bender must be placed on the back side of the mark which is placed on the raceway. The electrician will need to deduct 5” or 6” from the height of the stub up to compensate for bending in the "wrong" direction. Deduct 5” for ½” EMT tubing. Deduct 6” for ¾” EMT tubing, etc. 2. Offset bend - This bend is made up of two equal degree bends that are bent in opposite directions. This bend can be used when the run of raceway is changing elevations. Both marks are placed on the raceway before any bending takes place. A box offset is a small offset bend (usually two 10° bends) which is used to lift a raceway from the surface up to the height of the knockout of the box it is entering. This bend is usually made without marking the conduit. It allows the connector to enter the box on a straight angle less than 90° bend, it is used when the conduit crosses an obstacle or when the conduit is entering an electrical box. 3. 3 Point Saddle - Three-point saddle bend (round saddle bend) is used when the conduit run across circular objects like pipes. The 3-point saddle is used to jump over small obstructions 6” or less, such as an installed raceway which is running perpendicular to the raceway you are installing. This bend is made by bending the middle bend twice the degree of the two-side bends. All three marks are placed on the raceway before any bending takes place.

4. 4 Point Saddle - The 4-point saddle (square saddle bend) is made up of two equal size offset bends, bent in opposite directions. This bend is used to jump over larger blockages

than a 3-point saddle can handle. All four marks are placed on the raceway before any bending takes place. Square saddle is just a combination of two offset bends. 5. Back-to-back bend - A back-to-back bend is any bend that needs a 90bend located a predetermined distance away. This is probably the most common type of bend. A mark is made on the raceway at the exact distance that is needed for the 90bend.

BEND DEFECTS 1. Burned 2. Kinks or Groove 3. The diameter of the conduit is greatly reduced due to improper bending procedure...