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 PlasticsSynthetic polymers (thermoplastics) been used in world economy for over 100 yearsWelding and fabrication part of manufacturing industry since mid-1930sBirth of hot-gas welding techniqueNo public documentation regarding requirements for use, design criteria, and applicationAWS covers plastics welding in Volume 3 of its Welding HandbookTechnical 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 achievableManufacturing simplifiedParts made in one stepAbundant and recyclable
5 Key Points for Welding Welding produces very strong joints Some plastics can only be joined by weldingFusion line usually same as for bulk polymer, so easily recyclableRelative insensitivity to surface preparation as pressure used to make weld forces surface layers from fusion lineProcess time very fast
6 Thermoplastic Polymers Consist of many strands intertwined but still capable of moving past each otherSoften and/or melt when heated and can be weldedCan put heated polymers in cooled mold of shape required to form useful partsThermosetting plastics usually formed by polymerization of polymers in a heated mold of the shape required for a partJoined by mechanical fasteners or adhesives
7 Requirements Before Starting Any Plastic Welding Know applicationFactors such as temperature usage, strength, corrosion resistance, and UV resistanceKnow materialCritical in selecting filler metal and which joining process to useKnow welding processManually or automatically
8 Know Your Plastics Color should never be used for identification Look for identification numberCan be referenced back through producer of part to determine plastic usedSymbol used for identificationUsed in recycling of plasticsLook at Table 31-1 for rest of symbols
9 Plastics That May Not Have Symbols PolyurethaneFlexible, foamy-type plasticPolycarbonatesVery tough transparent plasticAcrylicHard rigid plasticCan be polished, cut and shaped by heating to 310ºFABSGood finish, heat and impact resistant
10 Plastics That May Not Have Symbols NylonVery tough plastic with high abrasion resistanceCan be turned and shaped well on lathePTFEVery low friction value and expensiveMFThermoset (considered unweldable)Heatproof and chemical resistant, but brittle
11 Plastics That May Not Have Symbols Urea formaldehydeThermoset, heatproof, and chemical resistantPolyester resinEpoxy resinSimilar to polyester resin but more dimensionally stable and more expensiveRubberVery flexible and stretchy
12 Scratching Test Not very accurate test Gives some idea of type of plastic you are working withScratch with fingernailScratches: One of softer-type plastics: PE, PP, PTFEDoes not scratch: Not ABS, PVC, or any other of harder plastics
13 Sound TestHave different specific weights and surface hardnesses that cause them to sound different from one anotherTake solid piece and drop it on hard and even surface from height of approximately 5–10 in.Hear specific tonesTrain ear to different tonesGenerally 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 waterTake glass of clean water at room temperatureInsert small piece of plastic to determine if it will float or notOnly two plastics will float: PE and PP
15 Burning Test Every plastic reacts differently when burned Most accurate testHave good ventilationRemove thin sample and put it on surface resistant to heatLight torch or some other flame source and attempt to ignite sampleObserve reaction
16 Identification of Plastics by Burning Plastic material observationPE: Produces blue/yellow flame, smokes, and smells like paraffinPP: Produces blue/yellow flame, drips, and smells like dieselABS: Smells sweet, lacks sooty flame, does not extinguishPolyamide: Smells like burnt horn, stringy, does not extinguishPolycarbonate: Black sooty smoke, may extinguishPVC: Acrid smell, black smoke, does not extinguish
17 Two Basic Types of Plastics Thermosetting plasticsHarden under heatThrough chemical reaction formed into permanent shapes that cannot be changed or weldedThermoplasticsSoften when heatedSolidify when cooled with no chemical changeCan be machines, formed, and welded
18 Thermoplastics: Polyvinyl Chloride (PVC) One of most popular materials of constructionExcellent physical propertiesEase of fabricationRelatively low costAbility to be formed into wide range of productsWide forming-temperature ranges and self-extinguishing propertiesPrimary limitation is recommended working temperature range of 140º to 150ºF
19 Thermoplastics: Rigid Polyvinyl Chloride (PVC) Two broad classificationsType I has normal resistance to impact and high resistance to corrosionType II modified with rubber to increase impact resistanceBest materials for general corrosion protection because of physical properties, chemical resistance, and low costCan be hot-air welded, cemented, or assembled by mechanical processes
20 Thermoplastics: Modified High Impact Rigid Polyvinyl Chloride Developed for intermediate corrosion serviceReadily formed in press and vacuum operationsCan be worked and welded at same temperature as regular polyvinyl chlorideOxides but does not burnCan be welded to type I or type II PVCUsed in exhaust systems
21 Thermoplastics: Polyethylene (PE) Available in three classes of materialLow densityMedium densityHigh densityAll same chemicallyMain differences in going from low to high density in corrosion resistance, working temperature, and tensile strengthIncrease from low density to high density
22 Thermoplastics: Low Density (Branched) Polyethylene Lighter than metal and floats in waterBurnsOffers reasonably good corrosion resistanceCannot be joined by cement, can be welded using same class of rodDry nitrogen recommended as source for hot gas welding units
23 Thermoplastics: Medium Density Polyethylene Produced as film, sheet, rod, tubing, and blockNot cementableWill burnUsed for both pressure and conduit tubing and pipeImpact strength goodCan be both vacuum and press formedHot gas welding done with dry nitrogen
24 Thermoplastics: High Density Polyethylene Also referred to as low pressure polyethyleneMuch lighter than metalCombustibleCan be welded, but not cementedHighest working stress factor and best corrosion resistance of all three classesReasonably high working temperature under low load conditions
25 Thermoplastics: Polypropylene (PP) Compared to polyethyleneHas lower impact strength, but tensile strength higher and working temperatures superiorOffers more resistance to organic solvents and degreasing agentsCan be joined by welding, but not cementedWelding rod available in 1/8-, 5/31-, and 3/16-inch coil and flat stockDry nitrogen recommended for welding
26 Thermoplastics: Acrylonitrile Buadiene Styrene (ABS) Two classifications of rigid ABS plasticsType I designed for normal temperaturesType II for use in higher temperaturesCementing main joining methodCan also be hot gas welded with nitrogenGood corrosion resistanceSupports combustionUsed in heat-formed structural parts
27 Acrylics Transparent and widely used as substitute for glass Preshrunk before shipmentNecessary to specify corrosion resistance, crazing characteristics, and other specifications desiredCan be cemented and welded
28 Welding as a Method of Joining Plastics Welding of plastic pipe increasing in oil refineries and chemical plantsWelding seals leaks instantly in new or old installationsSimilar to gas welding of metalsAll basic joint designs usedAll welding positions possible
31 Preparation of Plastics LayoutDone directly on plastic sheet in pencil, soapstone, or china markerShrinkagePreshrink for approximately 20 minutes at 250ºF, depending on gauge of materialControl cooling so does not buckle and deformFormingCan be heated with heat gun and formed around metal forms to make curved shapes
32 Preparation of Plastics CuttingSame hand or power tools used to cut wool or metalSawingHeat buildup in saw blade due to poor heat conductivity of plastic8–22 teeth blades with negative rakeUse special blades
33 Preparation of Plastics ShearingDone at room temperatureUsed for cutting of light gauge sheetsRoutingUsed for rimming edges of sheets or for shaping and recessingFeed must be slow and continuous and swarf must be removed by compressed air
34 Preparation of Plastics Other working processesDrilling, punching, machining, milling, threading, knurling, riveting, and boltingSafetySame rules that apply in metalworking
36 Ultrasonic WeldingHigh frequency vibration directed through plastic joinVibration causes friction, then heat, often causing solid fusion in less than a secondGenerally frequencies above 20 kilohertz usedWell suited for rigid thermoplastic partsAdvantagesFastCleanFiller materials not neededDisadvantagesMany tool designs requiredDesign 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 inchSpin/friction weldingTwo parts spun and contact area builds up heat through friction and pressureForces fusion between parts and forces out discontinuitiesAdvantages: Produces good weld, air does not enter during welding, inexpensive machines may be usedDisadvantages: Circular weld joints required
38 Hot-plate WeldingPlastic brought into contact with heated plate to soften or melt plasticParts removed and pressed togetherAdvantagesSimple, easy to performDisadvantagesSlow speed, typically butt joints, requires variety of platens
39 Injection Welding Unit Used in manual modeInjects molten welding rod below surface of plastic to create weldInjection tip forms weld zone of molten welding rodPhysical mixing of plastic substrate and welding rod makes strong, high quality weldAutomatic feed system lets welder work gun with one hand
41 Hot Gas Welding One of principle methods of welding plastics Two basic requirementsHeat sourceWelding rod that aids in fusion of weld to base materialJoints identical to those in metal welding and same material preparationFlux not required in welding
42 Hot Gas WeldingPlastics poor heat conductors, so difficult to heat uniformlyWork in temperature ranges narrower than those in metal weldingOnly lower surface of welding rod fusibleMust apply pressure on welding rod to force fusible portion into joint and make permanent bond
43 Plastic Filler RodBoth hot-gas and injection welding require filler rodRod need to math properties of plastic to be weldedAvailable in variety of colors, sizes, types, and profilesIf don’t know base material and/or filler, perform rod fusion testScrape area cleanMelt rod and fuse it into base material; cool with waterPull rod away to determine strength at fusion pointRepeat with various rods until best match found
45 Stretching and Distortion Some stretching of welding rod will always occurShould not exceed 15%Thermoplastic rod becomes soft when heated enough to form weldIn 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 weldingStretching in multilayer welds must be held to minimumChecks and cracks show up as voids in finished weld and cannot be detected by visual inspectionShrinkage of weld upon cooling greater near crown than at rootDistortion 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 solventWelding edges beveled or offset to provide areas for welding rod and permit better adhesionCut bevels with jointer, sander, router, or planeAllow root gap in most procedures except when tack weldingThickness, 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 cleanWelding rod and material must be of same densitySubject 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 heatedUsed in manufacturing plantsCompact and easy to handleGas heatedUsed primarily in field operationsWelding 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 elementLightweight nylon handle for ease and comfortTwenty feet of neoprene-insulated, three-wire grounded electric cord inside neoprene air hoseSelf-relieving air regulator and easy-to-read gaugeWelding tip
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 cleanNever leave electricity on when welding gas turned offVolume of welding gas passing over heating element determines welding temperatureTo increase temperature, reduce gas volumeTo decrease temperature, increase gas volumeTo 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 elementNever touch end of torch barrel or welding tip when torch turned onTo obtain maximum life from heating element, use recommended welding temperatureRead 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 usedBe sure welding gas supply is cleanWhen regulating welding temperatures, reduce volume of welding gas or increase pressure of heating gas to raise the temperatureTo 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 onAlways turn welding gas on before lighting torchNever 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 materialTemperature and type of welding gasPressure on the welding rod during weldingProper weld and joint selectionProper material preparation before weldingSkill of the welderDressing plastic welds decreases strength of completed welds by approximately 25%
64 Reasons for Faulty Welds Overheating base material or plastic filler rodUnderheating base material or plastic filler rodImproper penetration through entire root of weldPorosity caused by air inclusions or dirtStretching filler rodIncorrect handling of welding torch
65 Reasons for Faulty Welds Wrong torch or tip work and travel angleToo slow or too fast travelLack of or faulty fanning motion of torchHeat at torch tip too close or too far away from workHeat at torch tip not centered on weld bead
66 Good Plastic Weld Requires Thorough root penetrationProper balance between the heat used on the weld and the pressure exerted on welding rodCorrect handling of welding torchCorrect preparation of joint to be weldedTable 31-4 presents causes of common plastic welding troubles and how to correct them
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 inspectionVisual evidence of a good weld is flowlines that present, continuous, and uniformWill reveal faults such as voids, scorching, and notching
70 Testing of WeldsWelded joints sites of potential weakness in plastic structureShow welded joint fit for intended purposeAchieved by appropriate destructive, nondestructive, and chemical testing techniquesOrganizations 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 sheetValue of 80–100% considered acceptableCreep rupture testCompares long term performance of plastic weldsTest 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 hoursBurst testMost effective way of testing pipe butt joint-groove welds and fillet welds on fabricated fittings and couplingsImpact testWeld 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 weldsTest conducted using either three-point bend loading or single edge notch bend specimenIf plastic brittle, use linear elastic fracture mechanics testIf plastics show great deal of crack tip plasticity, may require elastic-plastic fracture mechanics test
75 Nondestructive Testing RadiographyMost efficient method of plastic weld inspectionGives complete detailed picture of internal characteristics of weld joint and permanent recordHigh costChemical testsTest specimen immersed in acetone for 2 to 4 hoursDye 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 materialRod should hold its basic round shapeNeither rod nor base material should char or discolorLength of rod used should be no more nor less than length of the weldDo 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 operationClean by scraping off first layer of material surfaceBest tool scraping bladePick up moisture and must be driedPlastic filler rod must be same composition as type of plastic being weldedConsiderations: 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 gasCompressed air, nitrogen, or inert gasGas passes through torch where heated by heating element and then directed through torch tip to surface of jointFiller rod can be fed by hand or automatically with use of high speed welding tipTip increases speed of weldingTemperature of welding gas regulated by increasing or decreasing volume of gas to torch
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.
82 Hand Welding (Beading) Purpose to joint two or more pieces permanently together with rod or strip as fillerWelder applies pressure on filler rod with one hand while applying heat to rod and base material with hot gas from welding torchFusion result of proper combination of heat and pressureMust 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.
90 Hand Welding of JointsThree basic types of butt joints used in plastic construction:Square-groove butt jointSingle V-groove butt jointDouble V-groove butt joint
91 Square-groove Butt Joints Generally made in light gauge sheets as thick as 3/31 inchNo preparation of edge requiredRoot gap of approximately 1/64 inch necessary to permit full penetration through back sideWelding from both side when possibleAcceptable 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.
94 Single V-groove Butt Joints Used when only one side of plastic sheet accessibleObtain 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.
96 Double V-groove Butt Joint Both sides of joint must be accessible for weldingObtain 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.
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 jawsCover with clothStrike with hammer on weld sideIf break occurs through weld bead with some portion of weld on each piece – weld good
102 RepairsTwo most common types of repairs are fixing cracks and replacing broken or missing partsCauses of cracksInternal stressImproper storage or handlingIncorrect use of piece
103 Repairing Cracks Stop crack from traveling further Drill hole approximately 3/31 inch in diameter at each end of crackIf runs whole length, prepare crack by opening it up like V-grooveUse stick scraper to get 60º to 79º groove angleMost critical part of making quality weld is maintaining proper temperatureWeld both sides if possibleFinish weld and smooth down weld bead
104 Replacing Missing Pieces Cut out entire damaged area in shape that is round, square, or rectangularRadius corners of square or rectangular shape so no stress risersTake time to get good fit of replacement pieceMatch material (cut from other damaged parts)Match material thickness
105 High Speed WeldingHigh speed welding tip increases average welding speed to over 4 feet per minute on flatFeeds welding rod automatically in right position and produces uniform weld headOne hand left free to steady or turn work and insert new rodsCutting blade attached to tip500-watt heating element recommended
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 45ºNote flowlines which are similar to those visible in hand weldingObserve emerging rod constantly so any corrective action can be taken immediatelyIf 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.
113 High Speed Weld TestsCut through joint and inspect for complete bondingStrips should also be cut from work and subjected to tensile and bending stress testsIf pressure test desired, make up small box and subject it to water pressure testBox 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 formOnly one pass necessary with stripTechnique similar to welding with round rodStrip 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 speedTo stop, remove tip and allow remaining strip to pull through
116 Solvent Weld Process (Bonding) Pipe and fittings solvent welded with MEKSolvent chemically etches surface of both pipe and fittings so when joined, two surfaces fused into each otherLike brazed copper or welded steelOriginal line of division no longer existsJoint 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 criteriaMust understand how plastic will react to adhesiveHow joint will be appliedWhat kind of environment it will be locatedDifferences in chemical structure of adhesivesAll have certain technological propertiesPreparation of splicing surface crucial step
120 Adhesives or Glue Groupings Melting glue (hot glue)Thermoplastic adhesive heated to melting stageFast curing time, easy storage and handlingSolvent-free and efficientNot capable of handling large splicing areasAdhesive dispersion (wood glue)Not used in plastic joiningUsed for woodworking
121 Adhesives or Glue Groupings Polycondensate (phenolics)Two-component, thermoset adhesiveComponents react to each other when combinesStrong splicing, wide range of useStorage critical and can be expensivePolymerisate (cyanacrylates)One component, thermoplastic adhesiveNeeds catalyst to start reactionFast curing time and strong bond
122 Adhesives or Glue Groupings Polyaddition adhesive (epoxies)Two-component, thermoset adhesiveTwo components react to each otherVery strong splicingWide range of useProvides enough time to work with itGood heat resistanceStorage criticalCan be expensive
123 Procedures Prior to Gluing Clean area where joining will occurMake sure enough room for pieces, tools, and personal protection availablePrepare equipmentClean surfacesRoughen splicing area by sanding or grinding paperRemove grinding dust
124 Safety Considerations When Gluing Plastics Eating, drinking, and especially smoking in splicing area should be prohibited at all timesOpen flames not allowed in close proximity because of flammability of fumes from most adhesivesAvoid skin contact because some solvents will find their way directly into bloodstream; contact could also cause allergic reactionsGood ventilation importantRead and strictly follow MSDS of adhesive usedAll adhesives basically special waste and should be disposed of in proper way
125 Care of Plastic PipeBe careful in storing pipe and fittings (never store in sun)Care must be taken in cutting pipePipe must be laid out and cut with high degree of accuracy because errors cannot be rectified with stress, heat, or hammerPlastic 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 countryPlastic piping lends itself to prefabricationPlastic pipe can be joined to pipe made of other materials only with the appropriate adapter fittings