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Welding and Bonding of Plastics

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1 Welding and Bonding of Plastics
Chapter 31

2 Objectives Describe uses of plastics. Identify types of plastics.
Describe plastic welding processes. Identify common plastic weld faults. Make various plastic groove, fillet, and edge welds on sheet, plate, and pipe.

3 Plastics Synthetic polymers (thermoplastics) been used in world economy for over 100 years Welding and fabrication part of manufacturing industry since mid-1930s Birth of hot-gas welding technique No public documentation regarding requirements for use, design criteria, and application AWS covers plastics welding in Volume 3 of its Welding Handbook Technical committee, GI, focused on plastic welding

4 Usefulness of Plastics
Corrosion resistant, lightweight, and fatigue resistant, and when composite structures used, great strength-to-weight ratios achievable Manufacturing simplified Parts made in one step Abundant and recyclable

5 Key Points for Welding Welding produces very strong joints
Some plastics can only be joined by welding Fusion line usually same as for bulk polymer, so easily recyclable Relative insensitivity to surface preparation as pressure used to make weld forces surface layers from fusion line Process time very fast

6 Thermoplastic Polymers
Consist of many strands intertwined but still capable of moving past each other Soften and/or melt when heated and can be welded Can put heated polymers in cooled mold of shape required to form useful parts Thermosetting plastics usually formed by polymerization of polymers in a heated mold of the shape required for a part Joined by mechanical fasteners or adhesives

7 Requirements Before Starting Any Plastic Welding
Know application Factors such as temperature usage, strength, corrosion resistance, and UV resistance Know material Critical in selecting filler metal and which joining process to use Know welding process Manually or automatically

8 Know Your Plastics Color should never be used for identification
Look for identification number Can be referenced back through producer of part to determine plastic used Symbol used for identification Used in recycling of plastics Look at Table 31-1 for rest of symbols

9 Plastics That May Not Have Symbols
Polyurethane Flexible, foamy-type plastic Polycarbonates Very tough transparent plastic Acrylic Hard rigid plastic Can be polished, cut and shaped by heating to 310ºF ABS Good finish, heat and impact resistant

10 Plastics That May Not Have Symbols
Nylon Very tough plastic with high abrasion resistance Can be turned and shaped well on lathe PTFE Very low friction value and expensive MF Thermoset (considered unweldable) Heatproof and chemical resistant, but brittle

11 Plastics That May Not Have Symbols
Urea formaldehyde Thermoset, heatproof, and chemical resistant Polyester resin Epoxy resin Similar to polyester resin but more dimensionally stable and more expensive Rubber Very flexible and stretchy

12 Scratching Test Not very accurate test
Gives some idea of type of plastic you are working with Scratch with fingernail Scratches: One of softer-type plastics: PE, PP, PTFE Does not scratch: Not ABS, PVC, or any other of harder plastics

13 Sound Test Have different specific weights and surface hardnesses that cause them to sound different from one another Take solid piece and drop it on hard and even surface from height of approximately 5–10 in. Hear specific tones Train ear to different tones Generally reliable enough to determine plastic’s family

14 Floating Test Only help identify plastic's family
All plastics have specific weight higher or lower than specific weight of water Take glass of clean water at room temperature Insert small piece of plastic to determine if it will float or not Only two plastics will float: PE and PP

15 Burning Test Every plastic reacts differently when burned
Most accurate test Have good ventilation Remove thin sample and put it on surface resistant to heat Light torch or some other flame source and attempt to ignite sample Observe reaction

16 Identification of Plastics by Burning
Plastic material observation PE: Produces blue/yellow flame, smokes, and smells like paraffin PP: Produces blue/yellow flame, drips, and smells like diesel ABS: Smells sweet, lacks sooty flame, does not extinguish Polyamide: Smells like burnt horn, stringy, does not extinguish Polycarbonate: Black sooty smoke, may extinguish PVC: Acrid smell, black smoke, does not extinguish

17 Two Basic Types of Plastics
Thermosetting plastics Harden under heat Through chemical reaction formed into permanent shapes that cannot be changed or welded Thermoplastics Soften when heated Solidify when cooled with no chemical change Can be machines, formed, and welded

18 Thermoplastics: Polyvinyl Chloride (PVC)
One of most popular materials of construction Excellent physical properties Ease of fabrication Relatively low cost Ability to be formed into wide range of products Wide forming-temperature ranges and self-extinguishing properties Primary limitation is recommended working temperature range of 140º to 150ºF

19 Thermoplastics: Rigid Polyvinyl Chloride (PVC)
Two broad classifications Type I has normal resistance to impact and high resistance to corrosion Type II modified with rubber to increase impact resistance Best materials for general corrosion protection because of physical properties, chemical resistance, and low cost Can be hot-air welded, cemented, or assembled by mechanical processes

20 Thermoplastics: Modified High Impact Rigid Polyvinyl Chloride
Developed for intermediate corrosion service Readily formed in press and vacuum operations Can be worked and welded at same temperature as regular polyvinyl chloride Oxides but does not burn Can be welded to type I or type II PVC Used in exhaust systems

21 Thermoplastics: Polyethylene (PE)
Available in three classes of material Low density Medium density High density All same chemically Main differences in going from low to high density in corrosion resistance, working temperature, and tensile strength Increase from low density to high density

22 Thermoplastics: Low Density (Branched) Polyethylene
Lighter than metal and floats in water Burns Offers reasonably good corrosion resistance Cannot be joined by cement, can be welded using same class of rod Dry nitrogen recommended as source for hot gas welding units

23 Thermoplastics: Medium Density Polyethylene
Produced as film, sheet, rod, tubing, and block Not cementable Will burn Used for both pressure and conduit tubing and pipe Impact strength good Can be both vacuum and press formed Hot gas welding done with dry nitrogen

24 Thermoplastics: High Density Polyethylene
Also referred to as low pressure polyethylene Much lighter than metal Combustible Can be welded, but not cemented Highest working stress factor and best corrosion resistance of all three classes Reasonably high working temperature under low load conditions

25 Thermoplastics: Polypropylene (PP)
Compared to polyethylene Has lower impact strength, but tensile strength higher and working temperatures superior Offers more resistance to organic solvents and degreasing agents Can be joined by welding, but not cemented Welding rod available in 1/8-, 5/31-, and 3/16-inch coil and flat stock Dry nitrogen recommended for welding

26 Thermoplastics: Acrylonitrile Buadiene Styrene (ABS)
Two classifications of rigid ABS plastics Type I designed for normal temperatures Type II for use in higher temperatures Cementing main joining method Can also be hot gas welded with nitrogen Good corrosion resistance Supports combustion Used in heat-formed structural parts

27 Acrylics Transparent and widely used as substitute for glass
Preshrunk before shipment Necessary to specify corrosion resistance, crazing characteristics, and other specifications desired Can be cemented and welded

28 Welding as a Method of Joining Plastics
Welding of plastic pipe increasing in oil refineries and chemical plants Welding seals leaks instantly in new or old installations Similar to gas welding of metals All basic joint designs used All welding positions possible

29 Basic Joints That May Be Formed and Welded
Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30 Basic Joints That May Be Formed and Welded
Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

31 Preparation of Plastics
Layout Done directly on plastic sheet in pencil, soapstone, or china marker Shrinkage Preshrink for approximately 20 minutes at 250ºF, depending on gauge of material Control cooling so does not buckle and deform Forming Can be heated with heat gun and formed around metal forms to make curved shapes

32 Preparation of Plastics
Cutting Same hand or power tools used to cut wool or metal Sawing Heat buildup in saw blade due to poor heat conductivity of plastic 8–22 teeth blades with negative rake Use special blades

33 Preparation of Plastics
Shearing Done at room temperature Used for cutting of light gauge sheets Routing Used for rimming edges of sheets or for shaping and recessing Feed must be slow and continuous and swarf must be removed by compressed air

34 Preparation of Plastics
Other working processes Drilling, punching, machining, milling, threading, knurling, riveting, and bolting Safety Same rules that apply in metalworking

35 Plastic Welding Processes
Hot-plate welding Infrared welding Hot-gas welding Injection welding Resistive implant High frequency welding Induction welding Dielectric welding Microwave heating Spin welding Vibration welding Ultrasonic welding Solvent welding

36 Ultrasonic Welding High frequency vibration directed through plastic join Vibration causes friction, then heat, often causing solid fusion in less than a second Generally frequencies above 20 kilohertz used Well suited for rigid thermoplastic parts Advantages Fast Clean Filler materials not needed Disadvantages Many tool designs required Design rules not always available nor easily applied

37 Other Processes Linear vibration welding Spin/friction welding
Similar to ultrasonic welding, but frequencies are in hundreds of hertz and amplitudes in fractions of an inch Spin/friction welding Two parts spun and contact area builds up heat through friction and pressure Forces fusion between parts and forces out discontinuities Advantages: Produces good weld, air does not enter during welding, inexpensive machines may be used Disadvantages: Circular weld joints required

38 Hot-plate Welding Plastic brought into contact with heated plate to soften or melt plastic Parts removed and pressed together Advantages Simple, easy to perform Disadvantages Slow speed, typically butt joints, requires variety of platens

39 Injection Welding Unit
Used in manual mode Injects molten welding rod below surface of plastic to create weld Injection tip forms weld zone of molten welding rod Physical mixing of plastic substrate and welding rod makes strong, high quality weld Automatic feed system lets welder work gun with one hand

40 Weld being made on inside of a corner joint
Injection Welding Drader Manufacturing Weld being made on inside of a corner joint Drader Manufacturing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

41 Hot Gas Welding One of principle methods of welding plastics
Two basic requirements Heat source Welding rod that aids in fusion of weld to base material Joints identical to those in metal welding and same material preparation Flux not required in welding

42 Hot Gas Welding Plastics poor heat conductors, so difficult to heat uniformly Work in temperature ranges narrower than those in metal welding Only lower surface of welding rod fusible Must apply pressure on welding rod to force fusible portion into joint and make permanent bond

43 Plastic Filler Rod Both hot-gas and injection welding require filler rod Rod need to math properties of plastic to be welded Available in variety of colors, sizes, types, and profiles If don’t know base material and/or filler, perform rod fusion test Scrape area clean Melt rod and fuse it into base material; cool with water Pull rod away to determine strength at fusion point Repeat with various rods until best match found

44 Hot Gas Welding Basic welding procedure for welding plastics. Use of torch and filler rod is similar to gas welding. Joint is outside corner joint, and weld is fillet weld. Seelye Plastics Various types, sizes, and colors of plastic filler rod for hot gas and injection welding. Drader Manufacturing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

45 Stretching and Distortion
Some stretching of welding rod will always occur Should not exceed 15% Thermoplastic rod becomes soft when heated enough to form weld In speed welding, stretching caused by too much pressure on rod or by plastic residue on shoe and in preheating tube

46 Stretching and Distortion
Amount of stretch in completed weld determined by measuring length of rod before and after welding Stretching in multilayer welds must be held to minimum Checks and cracks show up as voids in finished weld and cannot be detected by visual inspection Shrinkage of weld upon cooling greater near crown than at root Distortion can be reduced by using speed welding and triangular welding rod

47 Welding PVC Material must be kept clean at all times
Wipe with methylethyl-ketone or similar solvent Welding edges beveled or offset to provide areas for welding rod and permit better adhesion Cut bevels with jointer, sander, router, or plane Allow root gap in most procedures except when tack welding Thickness, shape, size, and strength dictates type of weld to use

48 Welding Polyethylene and Polypropylene Precautions
Base material should be freshly cut or scraped and clean Welding rod and material must be of same density Subject to stress cracking (use only 1 foot of rod for 1 foot of weld) If welded joint will be under stress in service, weld will be subject to chemical attack that would not occur under normal circumstances (“environmental stress cracking”) Rods tend to loop in direction of the weld (do not force rod and add undue strain on weld)

49 Plastic Welding Equipment
Hot-gas torches divided into two basic types: Electrically heated Used in manufacturing plants Compact and easy to handle Gas heated Used primarily in field operations Welding gas (compressed air or nitrogen) passes over heat source raising temperature to 450º–800ºF

50 Simple Outfit for Plastic Welding
Double-jacketed and insulated stainless-steel heating tube enclosing 110 volt, a.c.-d.c. heating element Lightweight nylon handle for ease and comfort Twenty feet of neoprene-insulated, three-wire grounded electric cord inside neoprene air hose Self-relieving air regulator and easy-to-read gauge Welding tip

51 Miscellaneous Tools Wire brush Sharp knife Rotary sander Rasp
Bending spring Files Saws C-clamps Heat gun

52 High Speed Electric Welding Torches
Laramy Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

53 Internal Construction of Typical Electric Welding Torch
REPLACE WITH: boh73710_31-13.jpg Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

54 Setting Up the Equipment
Make sure you have proper type of torch for work at hand. Select proper heating element. Relieve regulator-adjusting screw to prevent damage to regulator due to sudden excessive air pressure. Connect welding unit to air or nitrogen supply and adjust regulator for 3 pounds pressure.

55 Setting Up the Equipment
Connect torch with 115-volt electric outlet. Let torch warm up for 3 or 4 minutes; make sure compressed air or nitrogen flowing continuously through barrel of the torch. Select proper tip or high speed welding tool for type of work. Select proper air pressure for size of heating element (in watts) and for temperature desired at tip end.

56 Rules for Welding with Electric Welding Torches
Be sure welding gas supply is clean Never leave electricity on when welding gas turned off Volume of welding gas passing over heating element determines welding temperature To increase temperature, reduce gas volume To decrease temperature, increase gas volume To determine temperature of heated air, hold thermometer 1/4 inch from end of welding tip

57 Rules for Welding with Electric Welding Torches
Always ground torch to prevent short circuit, electric shock, and damage to heating element Never touch end of torch barrel or welding tip when torch turned on To obtain maximum life from heating element, use recommended welding temperature Read manufacturer’s operating instructions before using torch for first time

58 Rules for Welding with Gas Welding Torches
Be sure torch equipped with proper jet for heating gas being used Be sure welding gas supply is clean When regulating welding temperatures, reduce volume of welding gas or increase pressure of heating gas to raise the temperature To lower temperature, increase volume of welding gas or reduce pressure of heating gas

59 Rules for Welding with Gas Welding Torches
Never touch end of torch barrel or welding tip when torch turned on Always turn welding gas on before lighting torch Never leave torch lighted when welding gas is off (turn off flame before shutting off welding gas) Always read manufacturer’s instructions before using torch for first time

60 Inspection and Testing
Strength of plastic weld dependent on combination of six interrelated factors: Strength of the base material Temperature and type of welding gas Pressure on the welding rod during welding Proper weld and joint selection Proper material preparation before welding Skill of the welder Dressing plastic welds decreases strength of completed welds by approximately 25%

61 Good Welds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kamweld Products Co.

62 Faulty Welds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kamweld Products Co.

63 Discolored – Too Much Heat
Basic Bead Structure No Flowlines – Cold Weld Good Flowlines – Good Weld Discolored – Too Much Heat Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kamweld Products Co.

64 Reasons for Faulty Welds
Overheating base material or plastic filler rod Underheating base material or plastic filler rod Improper penetration through entire root of weld Porosity caused by air inclusions or dirt Stretching filler rod Incorrect handling of welding torch

65 Reasons for Faulty Welds
Wrong torch or tip work and travel angle Too slow or too fast travel Lack of or faulty fanning motion of torch Heat at torch tip too close or too far away from work Heat at torch tip not centered on weld bead

66 Good Plastic Weld Requires
Thorough root penetration Proper balance between the heat used on the weld and the pressure exerted on welding rod Correct handling of welding torch Correct preparation of joint to be welded Table 31-4 presents causes of common plastic welding troubles and how to correct them

67 Faulty Welds Porous Weld Poor Penetration Scorching Distortion
Laramy Products Co. Laramy Products Co. Porous Weld Poor Penetration Laramy Products Co. Laramy Products Co. Scorching Distortion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

68 Faulty Welds Warping Poor Appearance Stress Cracking Poor Fusion
Laramy Products Co. Laramy Products Co. Warping Poor Appearance Laramy Products Co. Stress Cracking Laramy Products Co. Poor Fusion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

69 Visual Inspection Permits only partial evaluation of weld bead
Internal defects as incomplete fusion and penetration, air inclusions, and cracks cannot be determined by visual inspection Visual evidence of a good weld is flowlines that present, continuous, and uniform Will reveal faults such as voids, scorching, and notching

70 Testing of Welds Welded joints sites of potential weakness in plastic structure Show welded joint fit for intended purpose Achieved by appropriate destructive, nondestructive, and chemical testing techniques Organizations such as American Society of Testing Materials and American Welding Society have established procedures for testing plastics and plastic welds

71 Destructive Testing Tensile test Creep rupture test
Used to evaluate butt joint-groove welds on rigid sheet Value of 80–100% considered acceptable Creep rupture test Compares long term performance of plastic welds Test under constant load and elevated temperature and time to failure measured; carried out in water

72 Destructive Testing Bending test Burst test Impact test
While weld still hot, bend it double along axis of weld; another bend test conducted after 24 hours Burst test Most effective way of testing pipe butt joint-groove welds and fillet welds on fabricated fittings and couplings Impact test Weld subjected to sudden impact by hitting it with hammer

73 Destructive Testing Fracture mechanics tests More rigorous testing
Can be used to quantitatively qualify characteristics of plastic welds Test conducted using either three-point bend loading or single edge notch bend specimen If plastic brittle, use linear elastic fracture mechanics test If plastics show great deal of crack tip plasticity, may require elastic-plastic fracture mechanics test

74 Nondestructive Testing
Spark coil test High frequency, high voltage spark-coil tester detects pores and cracks in plastic weld Sparks have voltages up to 55 kilovolts and frequencies around 200 kilohertz Electro-Technic Products, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

75 Nondestructive Testing
Radiography Most efficient method of plastic weld inspection Gives complete detailed picture of internal characteristics of weld joint and permanent record High cost Chemical tests Test specimen immersed in acetone for 2 to 4 hours Dye penetrant painted or sprayed on weld

76 Instructions for Completing Practice Jobs with the Hot-gas Process
Important “musts” concerned with plastic welding: Small beads should form along each side of weld where rod meets base material Rod should hold its basic round shape Neither rod nor base material should char or discolor Length of rod used should be no more nor less than length of the weld Do not use oxygen or other flammable gases

77 Instructions for Completing Practice Jobs with the Hot-gas Process
Plastics must be clean and dry prior to welding and during welding operation Clean by scraping off first layer of material surface Best tool scraping blade Pick up moisture and must be dried Plastic filler rod must be same composition as type of plastic being welded Considerations: Type of plastic, joint design, thickness of material, position of welding, and type of equipment

78 Instructions for Completing Practice Jobs with the Hot-gas Process
Heat supplied by heated gas Compressed air, nitrogen, or inert gas Gas passes through torch where heated by heating element and then directed through torch tip to surface of joint Filler rod can be fed by hand or automatically with use of high speed welding tip Tip increases speed of welding Temperature of welding gas regulated by increasing or decreasing volume of gas to torch

79 Using High Speed Welding Tip
Seelye Plastics Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

80 Procedure for Tack Welding
Attach tack welding tip to torch. Wait for 1 or 2 minutes so tip can reach proper temperature. Hold tip at work and travel angle of approximately 90º and place directly on joint to be tacked. Draw tacker tip along the joint for the desired length (about 1/2 to 1 inch long). Unit now ready for continuous welding. Practice.

81 Tack Welding Kamaeld Products Co.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

82 Hand Welding (Beading)
Purpose to joint two or more pieces permanently together with rod or strip as filler Welder applies pressure on filler rod with one hand while applying heat to rod and base material with hot gas from welding torch Fusion result of proper combination of heat and pressure Must be kept constant and in proper balance

83 Procedure for Hand Welding PVC Plastics with Round Tip
Install heating element that produces from 450 to 500ºF. Attach round tip to torch. Set air pressure according to recommendations by manufacturer of the equipment. Obtain flat piece of PVC about 6 inches long, 4 inches wide, and at least 3/31 inch thick; make sure surface clean; clamp piece to workbench. Secure PVC filler rod 1/8 inch in diameter and cut end at a 60ºangle with cutting pliers.

84 Procedure for Hand Welding PVC Plastics with Round Tip
Check for correct temperature. Hold torch 1/4 to 3/4 inch from material to be welded and preheat starting area and rod until appears shiny and becomes tacky; rod held at angle of 90º to each side of base material. Too much heat in rod softens it so pressure bends rod rather than forcing it into base material; too little heat causes it to lay on surface of material without being fused to it. Move torch up and down with fanning or weaving motion in order to heat both filler rod and base material equally.

85 Procedure for Hand Welding PVC Plastics with Round Tip
Good start is essential. Exert only as much pressure on rod as necessary to cause fusion to take place. Too much forward pressure causes stretching which will lead to cracking as you weld. Should notice small bead forming along both edges of welding bead and small roll forming under welding rod. Slight yellowing of rod and base material caused by slight overheat.

86 Procedure for Hand Welding PVC Plastics with Round Tip
To end, stop all forward motion and direct quick heat directly at intersection of rod and base material. Remove heat and maintain downward pressure for several seconds until rod cool. Release downward pressure. Twist rod with fingers until breaks.

87 Hand Welding with Round Tip
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

88 Hand Welding PVC Plastics with Round Tip
Seelye Plastics Seelye Plastics Starting welding operation Torch motion during welding Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

89 Hand Welding PVC Plastics with Round Tip
Seelye Plastics Note bead being formed along both edges of weld Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

90 Hand Welding of Joints Three basic types of butt joints used in plastic construction: Square-groove butt joint Single V-groove butt joint Double V-groove butt joint

91 Square-groove Butt Joints
Generally made in light gauge sheets as thick as 3/31 inch No preparation of edge required Root gap of approximately 1/64 inch necessary to permit full penetration through back side Welding from both side when possible Acceptable when work not of critical nature and when cost consideration

92 Square-groove Butt Joints
Obtain two pieces of plastic sheet 6 inches long, 3 inches wide, and 3/31 inch thick. Set up pieces with root gap of 1/64 inch to allow semimolten plastic to flow through to back side of joint. Use same welding technique described for beading (weld one pass on each side of plate). Inspect the weld carefully for faults. Test weld.

93 Square-groove Butt Joints
Kamweld Products Co. Double square groove weld for butt joints, welded from both sides Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

94 Single V-groove Butt Joints
Used when only one side of plastic sheet accessible Obtain two pieces of plastic sheet 6 inches long, 3 inches wide, and 1/8 inch thick. Prepare pieces with 30º bevel and 1/31-inch flat face at root. Set up pieces with root gap of about 1/64 inch to allow semimolten plastic to flow through to back side of work. Weld first pass along root of weld.

95 Single V-groove Butt Joints
Weld two additional passes along edge of each sheet. (Make sure that the weld is built up evenly; joint completely filled with overlaps on top beveled edges.) Weld bead on back side; reinforced makes it somewhat stronger than double V-groove butt joint. Inspect weld carefully for faults. Test weld. Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

96 Double V-groove Butt Joint
Both sides of joint must be accessible for welding Obtain two pieces of plastic sheet 6 inches long, 3 inches wide, and 1/8 inch thick. Prepare edges of sheets to be welded with 30º bevel (allow root gap of 1/31 to 1/64 inch). Weld first pass along root of weld on one side (penetrate through to back side). Weld two additional passes along edge of each sheet.

97 Double V-groove Butt Joint
Inspect welds carefully for good fusion and appearance. Turn plate over and repeat on other side. Inspect welds carefully for faults. Test weld. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kamweld Products Co.

98 Butt Joint Test Tested by fracturing it
Place joint in jaws of vise with weld bead facing away from you and 3/16 inch above and parallel to top of vise jaws Cover with cloth Strike with hammer on weld side If break occurs through weld bead with some portion of weld on each piece – weld good

99 Fillet Welds Used to attach two sheets of plastic at 90º to each other in T-joints and corner joints Vertical plate should be beveled Welding from both sides stronger 45º 45º Kamweld Products Co. Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

100 Lap Welds Used to join two sheets or welding plastic angle to sheet
Welds made by fusing overlapping areas with flat tip, or round tip with filler rod Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

101 Edge Welds Used to weld heads and bottoms into tanks or boxes and to weld angle to edge of sheet Two flat surfaces set up side by side, and two edges welded together If material heavy, edge of each plate chamfered and weld is a groove Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

102 Repairs Two most common types of repairs are fixing cracks and replacing broken or missing parts Causes of cracks Internal stress Improper storage or handling Incorrect use of piece

103 Repairing Cracks Stop crack from traveling further
Drill hole approximately 3/31 inch in diameter at each end of crack If runs whole length, prepare crack by opening it up like V-groove Use stick scraper to get 60º to 79º groove angle Most critical part of making quality weld is maintaining proper temperature Weld both sides if possible Finish weld and smooth down weld bead

104 Replacing Missing Pieces
Cut out entire damaged area in shape that is round, square, or rectangular Radius corners of square or rectangular shape so no stress risers Take time to get good fit of replacement piece Match material (cut from other damaged parts) Match material thickness

105 High Speed Welding High speed welding tip increases average welding speed to over 4 feet per minute on flat Feeds welding rod automatically in right position and produces uniform weld head One hand left free to steady or turn work and insert new rods Cutting blade attached to tip 500-watt heating element recommended

106 Operation of High Speed Welding Tip
Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

107 Procedure for High Speed Welding with Round Rod
Secure two pieces of PVC about 18 inches long, 3 inches wide, and 3/31 inch thick. Select high speed tool designed for diameter of filler rod to be used (cutting one end of rod at a 60º angle). Set up equipment and allow unit to warm up. Hold welding unit straight down at a 90º work and travel angle in relationship to work. Hold shoe of high speed tool about 1/2 to 3/4 inch above surface of workpiece, and hold at starting point.

108 Procedure for High Speed Welding with Round Rod
Insert beveled filler rod into preheated tube and push into softened base material until rod bends slightly backwards. Change travel angle of tip to about 60º in direction of welding (apply pressure on top surface of rod until it starts to fuse to surface). Continue to exert pressure with shoe and start pulling torch in the direction of welding. Continue to press on top surface of the rod with shoe as you proceed with weld.

109 Procedure for High Speed Welding with Round Rod
Once weld started, there can be no hesitation. Speed of weld can be increased by lowering travel angle of welding unit to about 45º Note flowlines which are similar to those visible in hand welding Observe emerging rod constantly so any corrective action can be taken immediately If stretching occurs, withdraw tip, cut off rod, and make new start before point where rod started to stretch. Rate at which weld proceeds governed by temperature, consistency of rod, and travel angle of welding unit.

110 Procedure for High Speed Welding with Round Rod
Make sure preheater hole and shoe always in line with direction of weld so only material in front of shoe preheated. To stop welding process, (a) withdraw tip quickly until rod is out of tube, and (b) bring tip quickly to 90º travel angle and cut off rod with end of shoe. Good speed weld in V-joint has slightly higher crown than normal hand weld, and more uniform.

111 Welding Positions for High Speed Tip
Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

112 Adhesion of Flexible Strip to Base Material During High Speed Welding
Kamweld Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

113 High Speed Weld Tests Cut through joint and inspect for complete bonding Strips should also be cut from work and subjected to tensile and bending stress tests If pressure test desired, make up small box and subject it to water pressure test Box can be similar to that used for metal arc welding

114 High Speed Welding with a Plastic Strip
Strips come in different shapes and supplied in roll form Only one pass necessary with strip Technique similar to welding with round rod Strip precut in length (1–2 inch for trimming) Start weld by tamping with broad shoe of high speed tool on top of first inch of strip (80º travel angle) Guide strip by hand and continue at sufficient speed To stop, remove tip and allow remaining strip to pull through

115 Welding Plastic Pipe Fusion pipe welding machine
Preparation and welding of pipe similar to that used for flat material One difference: torch and filler rod must follow direction of round shape Laramy Products Co., Inc. Fusion pipe welding machine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

116 Solvent Weld Process (Bonding)
Pipe and fittings solvent welded with MEK Solvent chemically etches surface of both pipe and fittings so when joined, two surfaces fused into each other Like brazed copper or welded steel Original line of division no longer exists Joint stronger than either pipe or fitting

117 Procedure for Bonding Pipe
Use Schedule 40 ABS-DWV pipe and MEK solvent; cut pipe and remove all burrs; clean both pipe and fitting. In applying solvent, use brush large enough to pass around pipe end or fitting socket quickly (fitting socket first and then pipe end). Insert pipe into fitting and position it with quick rotating motion of quarter turn or so.

118 Procedure for Bonding Pipe
After full set, water tests may by applied immediately; pressure systems require longer drying period because of higher pressure tests. Not all plastics nor solvents react the same. Test bonded joints by cutting through joint and inspect for thorough bonding (cut strips from work and subject to tensile and bending stress tests).

119 Gluing of Plastics Approximately 250,000 different adhesives
Selection criteria Must understand how plastic will react to adhesive How joint will be applied What kind of environment it will be located Differences in chemical structure of adhesives All have certain technological properties Preparation of splicing surface crucial step

120 Adhesives or Glue Groupings
Melting glue (hot glue) Thermoplastic adhesive heated to melting stage Fast curing time, easy storage and handling Solvent-free and efficient Not capable of handling large splicing areas Adhesive dispersion (wood glue) Not used in plastic joining Used for woodworking

121 Adhesives or Glue Groupings
Polycondensate (phenolics) Two-component, thermoset adhesive Components react to each other when combines Strong splicing, wide range of use Storage critical and can be expensive Polymerisate (cyanacrylates) One component, thermoplastic adhesive Needs catalyst to start reaction Fast curing time and strong bond

122 Adhesives or Glue Groupings
Polyaddition adhesive (epoxies) Two-component, thermoset adhesive Two components react to each other Very strong splicing Wide range of use Provides enough time to work with it Good heat resistance Storage critical Can be expensive

123 Procedures Prior to Gluing
Clean area where joining will occur Make sure enough room for pieces, tools, and personal protection available Prepare equipment Clean surfaces Roughen splicing area by sanding or grinding paper Remove grinding dust

124 Safety Considerations When Gluing Plastics
Eating, drinking, and especially smoking in splicing area should be prohibited at all times Open flames not allowed in close proximity because of flammability of fumes from most adhesives Avoid skin contact because some solvents will find their way directly into bloodstream; contact could also cause allergic reactions Good ventilation important Read and strictly follow MSDS of adhesive used All adhesives basically special waste and should be disposed of in proper way

125 Care of Plastic Pipe Be careful in storing pipe and fittings (never store in sun) Care must be taken in cutting pipe Pipe must be laid out and cut with high degree of accuracy because errors cannot be rectified with stress, heat, or hammer Plastic pipe must be supported properly

126 Care of Plastic Pipe Never attempt to heat and bend plastic pipe
Plastic pipe may be placed underground with safety since it is impervious to soil acids in this country Plastic piping lends itself to prefabrication Plastic pipe can be joined to pipe made of other materials only with the appropriate adapter fittings


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