`
` PDLHANDBOOKSERIES TT
`
`A Practical Guide
`
`2nd Edition
`
`Meetot
`
`q-’)
`
`i|
`
`ClearCorrect Exhibit 1043, Page 1 of 563
`
`

`

`Copyright © 2008 by William Andrew Inc.
`No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying,
`recording, or by any information storage and retrieval system, without permission in writing from the Publisher.
`
`ISBN: 978-0-8155-1581-4
`
`Library of Congress Cataloging-in-Publication Data
`
`Troughton, M. J.
` Handbook of plastics joining : a practical guide / M.J. Troughton. -- 2nd ed.
` p. cm.
` Includes bibliographical references.
` ISBN 978-0-8155-1581-4
` 1. Plastics--Welding--Handbooks, manuals, etc. I. Title.
` TP1160.T76 2008
` 668.4--dc22
` 2008007369
`Printed in the United States of America
`
`This book is printed on acid-free paper.
`
`10 9 8 7 6 5 4 3 2 1
`
`Published by:
`William Andrew Inc.
`13 Eaton Avenue
`Norwich, NY 13815
`1-800-932-7045
`www.williamandrew.com
`
`ENVIRONMENTALLY FRIENDLY
`This book has been printed digitally because this process does not use any plates, ink, chemicals, or press solutions that
`are harmful to the environment. The paper used in this book has a 30% recycled content.
`
`NOTICE
`To the best of our knowledge the information in this publication is accurate; however the Publisher does not assume any responsibility
`or liability for the accuracy or completeness of, or consequences arising from, such information. This book is intended for informational
`purposes only. Mention of trade names or commercial products does not constitute endorsement or recommendation for their use by the
`Publisher. Final determination of the suitability of any information or product for any use, and the manner of that use, is the sole respon-
`sibility of the user. Anyone intending to rely upon any recommendation of materials or procedures mentioned in this publication should
`be independently satis(cid:191)ed as to such suitability, and must meet all applicable safety and health standards.
`
`ClearCorrect Exhibit 1043, Page 2 of 563
`
`

`

` The Handbook of Plastics Joining is a unique ref-
`erence publication that provides detailed descriptions
`of joining processes and an extensive compilation
`of data on the joining of particular plastic materials.
`Although the basic characteristics of joining processes
`are generally well defi ned by manufacturers, data on
`joining particular plastics is not well compiled or eas-
`ily accessed. This volume serves to turn the vast amount
`of disparate information from wide ranging sources
`(i.e., conference proceedings, materials suppliers, test
`laboratories, monographs, and trade and technical jour-
`nals) into useful engineering knowledge.
` Joining a molded plastic part to another part com-
`posed of the same or a different plastic material or to
`a metal is often necessary, when the fi nished assembly
`is too large or complex to mold in one piece, when
`disassembly and reassembly is necessary, for cost
`reduction, or when different materials must be used
`within the fi nished assembly. Thermoplastics are fre-
`quently joined by welding processes, in which the part
`surfaces are melted, allowing polymer chains to inter-
`diffuse. Other methods used in joining plastics are
`adhesive bonding, in which a separate material applied
`at the bond line is used to bond the two parts, and
`mechanical fastening, which uses fasteners such as
`screws or molded-in interlocking structures for part
`attachment.
` The information provided in this book ranges from
`a general overview of plastic joining processes to detailed
`discussions and test results. For users to whom the
`joining of plastics is a relatively new fi eld, the detailed
`glossary of terms will prove useful. For those who wish
`to delve beyond the data presented, source documenta-
`tion is presented in detail.
` As in the fi rst edition, an effort has been made to
`provide information for as many joining process and
`material combinations as possible. Therefore, even if
`detailed results are not available (i.e., the only informa-
`tion available is that a joining process is incompatible
`for a particular material), information is still provided.
`The belief is that some limited information serves as a
`reference point and is better than no information.
` Although this publication contains data and infor-
`mation from many disparate sources, in order to make
`the book most useful to users, the information has been
`arranged to be easily accessible in a consistent format.
`Flexibility and ease of use were carefully considered in
`
` Introduction
`
`designing the layout of this book. Although substantial
`effort has been exerted throughout the editorial process
`to maintain accuracy and consistency in unit conver-
`sion and presentation of information, the possibility of
`error exists. Often these errors occur due to insuffi cient
`or inaccurate information in the source document.
` How a material performs in its end-use environ-
`ment is a critical consideration and the information
`in this book gives useful guidelines. However, this
`publication or any other information resource should
`not serve as a substitute for actual testing in determin-
`ing the applicability of a particular part or material in a
`given end-use environment.
` This second edition of the Handbook of Plastics
`Joining has retained all the information from the fi rst
`edition, but it has been revised extensively and updated
`to include new information generated over the last ten
`years.
` I am indebted to the following polymer joining
`experts at TWI who were involved in the preparation of
`this handbook: Chris Brown, Ewen Kellar, Natalie
`Jordan, Scott Andrews, Ian Jones, Richard Shepherd,
`Amir Bahrami, Ajay Kapadia, Marcus Warwick, Andy
`Knight, and Farshad Salamat-Zadeh. Finally, I would
`like to thank my wife, Sue, and children, Hayley and
`Bradley, for their patience and understanding through-
`out the preparation of this book.
`
` How to Use This Book
`
` This book is divided into two major sections. Part 1,
`comprising Chapters 1–18, provides a detailed descrip-
`tion of all the processes available for joining plastics,
`including some that are still at the development stage.
`Welding processes that generate heat through friction
`(spin, vibration, ultrasonic, and friction stir welding),
`by use of an external heat source (heated tool, infrared,
`laser, hot gas, extrusion, radio frequency, and fl ash free
`welding, and heat sealing) and by heating an implant
`placed at the joint line (induction, resistive implant,
`and microwave welding) are described, in addition to
`solvent welding, adhesive bonding, and mechanical
`fastening methods.
` Part 2 of the book, comprising Chapters 19–43,
`covers material-specifi c information. It is an extensive
`compilation of data on the joining of particular plastics
`
`xxi
`
`ClearCorrect Exhibit 1043, Page 3 of 563
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`

`

`xxii
`
`INTRODUCTION
`
`and is organized by materials; trade names, grades, and
`product forms are also included. Each chapter repre-
`sents a single generic family (e.g., polyamides) and is
`then subdivided into individual resin types (e.g., poly-
`amide 6, 66, 11, 12).
` The data in Part 2 appear in textual, tabular, image,
`and graphical forms. Textual information is useful as it is
`often the only information available, or the only way to
`provide an expansive discussion of test results. Tables
`and graphs provide detailed test results in a clear, concise
`
`manner. Each table, graph, or fi gure is designed to stand
`alone, be easy to interpret, and provide all relevant and
`available details of test conditions and results.
` The book is organized such that the joining pro-
`cesses and the information specifi c to a material of inter-
`est can be found in Part 2; general information about
`those joining processes can then be found in Part 1.
`Information of interest can be found quickly using
`the general index, the detailed table of contents, and
`through the subheadings within each chapter.
`
`ClearCorrect Exhibit 1043, Page 4 of 563
`
`

`

` 1 Heated Tool Welding
`
`temperature increase over time. When the melting tem-
`perature of the plastic is reached, molten material begins
`to fl ow. This melting removes surface imperfections,
`warps, and sinks at the joint interface and produces a
`smooth edge. Some of the molten material is squeezed
`out from the joint surface due to the applied pressure.
`In Phase II, the melt pressure is reduced, allowing fur-
`ther heat to soak into the material and the molten layer
`to thicken; the rate at which the thickness increases is
`determined by the heat conduction through the molten
`layer. Thickness increases with heating time—the time
`that the part is in contact with the hot tool.
` When a suffi cient melt thickness has been achieved,
`the part and hot tool are separated. This is Phase III, the
`changeover phase, in which the pressure and surface
`temperature drop as the tool is removed. The duration
`of this phase should be as short as possible (ideally,
`less than 3 seconds) to prevent premature cooling of
`the molten material. A thin, solid “skin” may form on
`the joint interface if the changeover time is too long,
`affecting the weld quality.
` In Phase IV, the parts are joined under pressure,
`causing the molten material to fl ow outward laterally
`while cooling and solidifying. Intermolecular diffusion
`during this phase creates polymeric chain entangle-
`ments that determine joint strength. Because the fi nal
`molecular structure and any residual stresses are formed
`during cooling, it is important to maintain pressure
`throughout the cooling phase in order to prevent warp-
`ing. Joint microstructure, which affects the chemical
`resistance and mechanical properties of the joint, devel-
`ops during this phase [ 1, 2 ].
` Welding by pressure requires equipment in which
`the applied pressure can be accurately controlled. A
`drawback of this technique is that the fi nal part dimen-
`sions cannot be controlled directly; variations in the
`melt thickness and sensitivity of the melt viscosities of
`thermoplastics to small temperature changes can result
`in unacceptable variations in part dimensions.
` In welding by distance, also called displacement
`controlled welding, the process described earlier is
`modifi ed by using rigid mechanical stops to control the
`welding process and the part dimensions. Figure 1 .2
`shows the process steps.
` In Step 1, the parts are aligned in holding fi xtures;
`tooling and melt stops are set at specifi ed distances on the
`holding fi xture and hot tool (heating platen), respectively.
`
`3
`
` 1.1 Process Description
`
` Heated tool welding, also known as hot plate, mir-
`ror, platen, butt or butt fusion welding, is a widely used
`technique for joining injection molded components or
`extruded profi les.
` The process uses a heated metal plate, known as
`the hot tool, hot plate, or heating platen, to heat and
`melt the interface surfaces of the thermoplastic parts.
`Once the interfaces are suffi ciently melted or softened,
`the hot plate is removed and the components are
`brought together under pressure to form the weld. An
`axial load is applied to the components during both the
`heating and the joining/cooling phases of the welding
`process.
` Welding can be performed in either of two ways:
`welding by pressure or welding by distance. Both pro-
`cesses consist of four phases, shown in the pressure
`versus time diagram in Fig. 1.1 .
` In welding by pressure, the parts are brought into
`contact with the hot tool in Phase I, and a relatively
`high pressure is used to ensure complete matching of
`the part and tool surfaces. Heat is transferred from the
`hot tool to the parts by conduction, resulting in a local
`
`Heated tool
`
`I
`
`II
`
`III
`
`IV
`
`Pressure
`
`Time
`
` Figure 1.1. Pressure vs. time curve showing the four phases
`of heated tool welding (Source: TWI Ltd).
`
`ClearCorrect Exhibit 1043, Page 5 of 563
`
`

`

`4
`
`1
`
`Holding fixture
`Tooling stop
`
`2
`
`Melt stop
`Part
`Parts are held and aligned by
`holding fixtures.
`3
`
`Heating Platen is inserted.
`
`4
`
`Parts are pressed against
`platen to melt edges.
`5
`
`Heating platen is withdrawn.
`
`6
`
`Parts are compressed so
`edges fuse as plastic cools.
`
`Holding fixtures open, leaving
`bonded part in lower fixture.
`
` Figure 1.2. The heated tool (welding by distance) process
`(Source: Forward Technology).
`
`The hot tool is inserted between the parts in Step 2, and
`the parts are pressed against it in Step 3. Phase I, as
`described for welding by pressure, then takes place.
`The material melts and fl ows out of the joint interface,
`decreasing part length until, in this case, the melt stops
`meet the tooling stops. Melt thickness then increases
`(Phase II) until the hot plate is removed in Step 4, the
`changeover phase (Phase III). The parts are then pressed
`together in Step 5 (Phase IV), forming a weld as the
`plastic cools; tooling stops inhibit melt fl ow. The
`welded part is then removed in Step 6.
`
` 1.2 Advantages and Disadvantages
`
` Heated tool welding is a simple economical tech-
`nique in which high strength, hermetic welds can be
`achieved with both large and small parts. Joints with
`fl at, curved, or complex geometries can be welded, and
`surface irregularities can be smoothed out during the
`heating phases. Dissimilar materials that are compatible
`but have different melting temperatures can be welded
`using hot tools at different temperatures. The welding
`process can be easily automated with full monitoring
`of the processing parameters. Since the process does
`not introduce any foreign materials into the joint,
`defective welded parts can be easily recycled [ 1, 3 ].
` The major disadvantage of the process is the long
`cycle time compared with other common techniques
`such as vibration or ultrasonic welding. Welding times
`
`JOINING PROCESSES
`
`range from 10–20 seconds for small parts, and up to
`30 minutes for large pipes. For the welding of smaller
`parts, production effi ciency can be improved by the use
`of multiple-cavity tools, allowing simultaneous weld-
`ing of two or more components.
` A second disadvantage is the high temperatures
`required for melting. Heat is not as localized as in
`vibration welding, and in some cases can cause plastic
`degradation or sticking to the hot plate. When the mol-
`ten surfaces are pressed against each other, weld fl ash
`is produced. For certain applications, this must be hid-
`den or removed for cosmetic reasons. In welding by
`pressure, part dimensions cannot always be controlled
`reliably due to variations in the molten fi lm thickness
`and sensitivity of the melt viscosities of thermoplastics
`to small temperature changes [ 4 ].
`
` 1.3 Applications
`
` Hot tool welding can be used to join parts as small as
`a few centimeters to parts as large as 1600 mm (63 inches)
`in diameter, such plastics pipes (Section 1.9.2). It can
`also be used for the continuous welding of lining mem-
`branes (Section 1.9.3).
` The heated tool welding method is widely used in
`the automotive sector, where one of the most common
`applications is the welding of vehicle tail lights and
`indicators ( Fig. 1.3 ). The housing, usually made of
`acrylonitrile-butadiene-styrene (ABS) is welded to the
`colored lens which is made from either polymethyl-
`methacrylate (PMMA) or polycarbonate (PC). These
`represent one of the few material combinations that are
`compatible for heated tool welding. ABS to PMMA
`
` Figure 1.3. Hot plate welded vehicle indicator lamps
`(Source: Branson Ultrasonics Corp.).
`
`ClearCorrect Exhibit 1043, Page 6 of 563
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`

`

`1: HEATED TOOL WELDING
`
`5
`
`lights can be welded using a single hot plate, because
`their melting points are similar. Dual hot plates are nec-
`essary for ABS to PC. Vacuum fi xtures with suction cups
`are employed to limit any scuffi ng to the lens.
` Custom-built heated tool welding machines are
`used in the manufacture of blow-molded high density
`polyethylene (HDPE) fuel tanks. These can require as
`many as 34 parts to be welded onto the tank, such as
`clips, fi ller necks, vent lines, and brackets.
` Other automotive components welded by heated
`tool include battery casings, carburetor fl oats, coolant
`and screen wash reservoirs, and ventilation ducts.
` Domestic appliance components welded by heated
`tool include dish washer spray-arms, soap powder
`boxes ( Fig. 1.4 ), and steam iron reservoirs.
` Miscellaneous items welded by the process include
`lids on HDPE barrels, sharps boxes for medical needle
`disposal, polypropylene (PP) transport pallets, and the
`corners of polyvinyl chloride (PVC) window frames.
`
` 1.4 Materials
`
` Heated tool welding is suitable for almost any ther-
`moplastic, but is most often used for softer, semicrys-
`talline thermoplastics such as PP and PE. It is usually
`not suitable for nylon or high molecular weight materi-
`als. The temperature of the molten fi lm can be con-
`trolled by regulating the hot tool temperature so that
`plastics that undergo degradation at temperatures only
`slightly above the melting temperature can be welded.
` The properties of the plastics to be welded affect
`the strength of the weld, including melt viscosity and
`density. Lower melt index polymers produce higher
`melt viscosities and can tolerate higher heating tem-
`peratures without melt sticking to the hot tool. As a
`
`result, the size of the heat affected zone (HAZ)—the
`area of the part affected by heat—can be larger, result-
`ing in a higher strength joint. For a constant melt index,
`increasing polymer density results in joints with lower
`tensile strength. Higher density polymers have a greater
`proportion of crystalline regions, which melt in a nar-
`rower temperature range than polymers of lower crys-
`tallinity. As a result, a thinner HAZ and more brittle
`welds are obtained [ 5 ].
` In hygroscopic materials such as PC and nylon,
`absorbed water may boil during welding, trapping steam
`and lowering the weld strength. High weld strengths
`can be obtained by pre-drying materials; alternatively,
`processing parameters can be adjusted to compensate
`for absorbed water [ 6 ].
` Dissimilar materials having different melting
`temperatures can be welded by heated tool welding,
`provided they are chemically compatible; instead of a
`single plate with two exposed surfaces, two plates are
`used, each heated to the melting temperature of the part
`to be welded. Different melt and tooling displacements
`and different heating times for each part may be neces-
`sary, and due to different melt temperatures and vis-
`cosities, the displacement of each part will be different.
`High strength welds equal to the strength of the weaker
`material can be achieved [ 4 ].
`
` 1.5 Weld Microstructure
`
` Weld quality is determined by the microstructure of
`the HAZ of the weld. The HAZ consists of three zones
`in addition to the weld fl ash. The stressless recrystalli-
`zation zone consists of crystals with a spherulitic shape,
`indicating that crystallization occurred under no signifi -
`cant stress. This zone results primarily from reheating
`and recrystallization of the skin layer and the molten
`layer near the joint interface. The columnar zone con-
`sists of elongated crystals oriented in the fl ow direc-
`tion; lower temperatures in this zone lead to an increase
`in melt viscosity, and crystals formed during melt fl ow
`aligned with the fl ow direction. In the slightly deformed
`zone, deformed spherulites are present, resulting from
`recrystallization under the joining pressure. Higher
`heating temperatures result in larger HAZs and greater
`bond strength; however, too high a temperature or pres-
`sure results in void formation at the joint interface [ 1 ].
`
` 1.6 Equipment
`
` Figure 1.4. Hot plate welded soap powder housing
`(Source: Branson Ultrasonics Corp.).
`
` Depending on the components to be welded, heated
`tool welding machines can be standard models or
`
`ClearCorrect Exhibit 1043, Page 7 of 563
`
`

`

`6
`
`JOINING PROCESSES
`
`specialized, custom units. Standard machines have the
`capability of welding different components by means of
`interchangeable hot plates and tooling fi xtures. These
`tend to be more labor-intensive, requiring manual load-
`ing and unloading of the components. Custom machines
`are usually dedicated to one particular component
`and may form part of a high volume, integrated pro-
`duction line. These will often feature a high degree of
`automation including conveyor feeding and component
`removal devices, typically with robotic assistance.
` The key components of a heated tool welding
`machine are the hot plate assembly with two exposed
`surfaces, fi xtures for holding the parts to be welded,
`and the actuation system for bringing the parts in con-
`tact with the hot plate and forming the weld. Dual
`platen hot tool welding machines are used for welding
`dissimilar materials.
` Hot plates are usually made from aluminum alloys,
`which are good conductors of heat and are corrosion
`resistant. For complex joints, contoured plates are used
`that match the profi le of the joining surfaces. A number
`of electrical heating cartridges are positioned within
`the structure of the plate, to ensure even temperature
`distribution across both faces. A thermocouple, posi-
`tioned close to the plate surface, regulates the tempera-
`ture, typically within 10°C (18°F) of the set point. A
`coating of polytetrafl uoroethylene (PTFE), bonded to
`the plate surfaces, prevents sticking of the molten poly-
`mer during the changeover phase. Since PTFE starts to
`degrade at 270°C (518°F), the temperature of the hot
`plate should not exceed this value. For high tempera-
`ture welding (Section 1.9.1), an aluminum-bronze hot
`plate without PTFE coating is used.
` For accurate mating and alignment, holding fi xtures
`(collets, gripping fi ngers, mechanical devices, and vac-
`uum cups) must support the parts to be joined, to avoid
`deformation under welding pressures. Pneumatic or
`hydraulically activated mechanical fi xtures are pre-
`ferred. Complex shapes or those with delicate surfaces
`may employ vacuum suction cups. To increase produc-
`tivity, two or more tool cavities are used for holding
`the parts.
` The actuation system is powered by either pneu-
`matics or hydraulics to give accurate alignment and
`pressure control. The response must be rapid to ensure
`that the molten faces break away cleanly from the hot
`plate surface at the end of heating, and to ensure that
`the changeover phase is as short as possible.
` Statistical control of weld cycles can be achieved
`through operator control panels that display all machine
`parameters and diagnostic functions, and pressure
`or displacement can be programmed throughout the
`
` Figure 1.5. A typical semiautomatic heated tool welding
`machine (Source: Branson Ultrasonics Corp.).
`
`welding cycle. Part conveyors or drawer-load features
`are optional equipment. A typical heated tool welding
`machine is shown in Fig. 1.5 .
`
` 1.7 Joint Design
`
` The choice of joint design depends on the applica-
`tion for the welded part. The squeeze fl ow in heated tool
`welding always produces weld fl ash, which for some
`applications can be objectionable. Flash traps can be
`incorporated into the design to hide the fl ash ( Fig. 1.6 ).
` Load transfer through the weld can be increased by
`enlarging the joint surfaces, as shown in Fig. 1.6 b. This
`is desirable when welding plastics with a high fi ller
`
`(a)
`
`(b)
`
`(c)
`
`(d)
`
` Figure 1.6. Joint designs for heated tool welding: (a) simple
`butt joint; (b) increased joint area; (c) double fl ash trap;
`(d) skirt joint (Source: TWI Ltd).
`
`ClearCorrect Exhibit 1043, Page 8 of 563
`
`

`

`1: HEATED TOOL WELDING
`
`7
`
`content, as there is less weldable material available at
`the joint line. Figure 1 .6c shows a double fl ash trap
`joint, which entirely conceals the weld fl ash. It should
`be noted that the load carrying capacity is signifi cantly
`reduced, as the welded area accounts for less than 50%
`of the wall section. Figure 1 .6d shows a skirt joint, which
`would be used when welding lids onto containers.
`Automotive batteries are a typical example.
`
` 1.8 Welding Parameters
`
` Important processing parameters for heated tool
`welding are the hot plate temperature, the pressure dur-
`ing Phase I (matching or heating pressure), heating
`time, displacement allowed during heating (heating dis-
`placement), melt pressure during Phase II, changeover
`(dwell) time, pressure during Phase IV (weld, joining,
`or consolidation pressure), duration of Phase IV (con-
`solidation time or welding time), and displacement
`allowed during Phase IV (welding displacement).
` The hot plate temperature is set in accordance with
`the melting point of the material to be welded. It is usu-
`ally in the range 30°C–100°C (54°F–180°F) above the
`melting point of the thermoplastic. An exception is
`high temperature welding (Section 1.9.1), which uses a
`plate temperature between 300°C (572°F) and 400°C
`(752°F).
` The Phase I (matching) pressure is typically in
`the range 0.2–0.5 MPa (29–72.5 psi) and ensures
`that the parts conform to the geometry of the hot plate.
`Moldings often display some degree of warpage, so
`this pressure ensures that the whole joining interface
`contacts the hot plate surface for good heat transfer.
`The pressure must not, however, cause the parts them-
`selves to deform.
` The heating pressure (Phase II) is lower than the
`Phase I pressure and maintains the parts in contact with
`the hot plate. If this pressure is too large, an excessive
`amount of molten material will be squeezed out of the
`joint line.
` The joining pressure (Phase IV) brings the two
`molten faces together and is controlled so that the right
`amount of material remains at the joint line. If too
`much material is squeezed out, there is the risk of a
`“cold weld” forming (i.e., all the hot material is forced
`out from the HAZ), leaving only cooler material to
`form the weld. On the other hand, if the pressure is too
`low, there is the possibility of entrapped air at the joint
`line or the surfaces not making intimate contact. This
`will limit molecular diffusion across the joint line and
`result in a weak weld.
`
` In welding by distance, the parameters should be set
`so that the displacement (also called the penetration)—
`the decrease in part length caused by the outfl ow
`of molten material—is large enough to control part
`dimensions. Initially in the welding process, there is
`very little molten fl ow, and the molten fi lm thickens.
`The fl ow rate increases with heating time, eventually
`reaching a steady state at which the rate of outfl ow
`equals the rate at which the material is melting; at
`this point in welding by pressure, the penetration
`increases linearly with time. When displacement stops
`are used, however, the penetration ceases when the
`melt displacement stops come into contact with the
`hot tool displacement stops. Until the stops come
`into contact, the melt will fl ow out laterally; afterward,
`the thickness of the molten material increases with
`time.
` Molten layer thickness is an important determinant
`of weld strength. If the thickness of the molten layer is
`less than the melt stop displacement, melt stops cannot
`contact holding stops, part dimensions cannot be con-
`trolled, and joint quality is poor due to limited inter-
`molecular diffusion. In addition to contributing to weld
`strength, adequate displacement in Phases I and II com-
`pensates for part surface irregularities and ensures that
`contaminated surface layers fl ow out before the joining
`phase [ 7 ].
` Melt thickness increases with heating time. For
`optimal molten layer thickness, the heating time should
`be long enough to ensure that the melt thickness is as
`large as the melt stop displacement. High heating pres-
`sures result in larger amounts of squeeze fl ow; dis-
`placement stops may not be reached if too much
`material is lost by being squeezed out of the joint, and
`the decreased molten layer thickness produces a brittle
`weld. If the molten layer thickness is greater than the
`melt stop displacement, molten material will be
`squeezed out, producing weld fl ash and an unfavorable
`molecular orientation at the interface; this also reduces
`the quality of the joint [ 7–9 ].
` Quality control in production can be implemented
`by monitoring parameters during the welding process;
`if one parameter is not within a specifi ed tolerance
`range, the welding machine either produces a signal or
`stops the welding process. More sophisticated tech-
`niques include statistical process control (SPC), in
`which parameters and melt characteristics are moni-
`tored and compared throughout the welding cycle, and
`continuous process control (CPC), in which optimum
`parameters are continuously calculated, with the weld-
`ing machine adjusting conditions as necessary through-
`out the welding process [ 10 ].
`
`ClearCorrect Exhibit 1043, Page 9 of 563
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`8
`
`JOINING PROCESSES
`
` 1.9 Variants of Heated Tool Welding
`
` 1.9.1 High Temperature Welding
`
` During heated tool welding of some thermoplastics,
`especially those whose melt strength and viscosity are
`low, sticking to the hot plate and stringing of the melt
`can be a problem. The melt that remains on the hot plate
`can then degrade and transfer to subsequent welds,
`resulting in welds of poor mechanical and visual qual-
`ity. To avoid this, high temperature heated tool welding
`can be used, where the hot plate surface temperature
`ranges between 300°C (572°F) and 400°C (752°F),
`depending on the type of plastic welded. Since the
`PTFE nonstick coating starts to degrade at temperatures
`above 270°C (518°F), the heated plates are not coated.
` The process sequence is identical to conventional
`heated tool welding, except that the times for Phases I
`and II are extremely short—typically 2–5 seconds. At
`such high temperatures, the viscosity of the melt is
`much lower and the melt tends to peel off the hot plate
`in a cleaner manner when the parts are removed. Any
`residual material that remains on the hot plate surface
`then evaporates or oxidizes, resulting in a clean hot
`plate for the next welding cycle. For this reason, fume
`extraction devices should be installed above the weld-
`ing machine to remove the vaporized material.
` Due to the high temperatures, thermal degradation
`of the surfaces to be welded can also be expected.
`However, any degraded material will tend to be forced
`out into the weld beads during Phase IV and the weld
`quality will be affected only slightly, although reduced
`weld strengths have to be expected with this process.
` High temperature heated tool welding has been
`shown to produce good results for PP and PP copoly-
`mers (e.g., for welding automotive batteries) and for
`ABS and acrylic (e.g., for welding automotive rear
`light clusters). For reinforced or fi lled plastics, residues
`on the hot plate do not evaporate or oxidize completely,
`so devices are required that automatically clean the hot
`plate between welds.
`
` 1.9.2 Heated Tool Welding of Plastics Pipes
`
` The joining of plastic pipes is one of the most com-
`mon applications of heated tool welding. The processes
`of butt fusion, socket fusion, and saddle/sidewall fusion
`are described below.
`
` 1.9.2.1 Butt Fusion
`
` Hot plate welding is a widely used technique for
`welding pipes made from PE, PP, and polyvinylidene
`fl uoride (PVDF), where it is commonly called butt
`
`fusion welding, and the process principles are identical
`to conventional heated tool welding.
` Butt fusion welding machines can be either manual,
`semiautomatic, or automatic in their operation. With a
`manual machine, all the welding times and pressures are
`set and controlled by the operator. In a semiautomatic
`welding machine, the times and pressures are set and
`controlled by an electronic user interface, while the
`trimmer and heater plate are manually controlled. With
`a fully automatic machine all the welding parameters
`are set and controlled by a microprocessor, with hydrau-
`lic actuation of the trimmer and heater plate. Typical butt
`fusion welding machines are shown in Figs. 1.7–1.10.
` All types of butt fusion machines consist of the fol-
`lowing essential components: heater plate, planing
`device, pipe clamp support carriage, various-sized pipe
`clamps, and a control unit (manual or microprocessor).
` The electrically powered heater plate, typically
`made from aluminum, is used to uniformly heat the
`pipe ends. It should have a suitable controller to regu-
`late the temperatur