October 2009

October Meeting

Skylights, Reaction Injection Molding and Hurricanes:
145 MPH Uplift Winds! 150 fps Ice Balls!
Tour of VTECH Industries

Speaker: Art Valentz
Art Valentz, the President of VTECH will be our tour guide as we are shown the processes of Reaction Injection Molding of Skylight surrounds. VTECH Industries utilizes Reaction Injection Molding (RIM) technology combined with a patented aliphatic polyurethane material to encapsulate glass and acrylic creating products that represent the latest in skylight technology.

2009 Breakfast Bunch Invitational Golf Outing

Windrose Golf Club
Friday October 23rd, 2009
Tee-Off at 8:00am
Lunch and prizes to follow golf
$60 to play / $10 for non-players lunch only
Register online:  www.spe-stx.org

Sponsors:  Ciba, part of the BASF group, Bamberger Polymers, Ametek Westchester Plastics, Ingenia Polymers, Kenny Speight Agency, Community Insurance Associates

President’s Message

Greetings! I hope that you had a chance to join us at another successful opener with the Houston Astros at Minute Maid Park on September 8th. We had approximately 130 people attend this year’s kick off event where the Houston Astros narrowly lost to the Atlanta Braves 2 to 1. Many thanks to our sponsors who make this event possible: Gold Sponsors – Ticona, Centerpoint Energy, Silver Sponsors – Vertec Polymers, Ashland, Osco and ThomasNet

I hope that you will be able to join us on October 12 to see skylights manufactured at V-Tech Industries and learn about Reaction Injection Molding. Art Valentz, President of V-Tech Industries will be leading the tour and discussing the how V-Tech industries meets the demanding requirements of this industry. Art and his program team have many exciting programs lined up to meet the diverse interests of our section.

One of the benefits of active involvement in SPE is having the opportunity to connect to the pulse of the industry. Our industry has experienced a tremendous amount of change in the past year. However, if you have participated in some of the recent breakfast and lunch bunch meetings you may be encouraged to hear that activity appears to be picking up. We have heard that material suppliers are receiving orders to replenish depleted inventories, funds for developmental projects are beginning to be released and quoting activity remains high. We don’t expect a rapid growth but are encouraged to see business gain confidence and positive signs of growth. Come and get connected as the breakfast bunch will be hosting their fall golf tournament at Windrose Golf Club on Friday, October 23.

The mission of the SPE is to promote scientific and engineering knowledge relating to plastics. In addition to our professional technical programs, we continue our commitment to support local SPE student chapters, scholarships and grants at 10 colleges and Universities in our region.

On behalf of all of the directors and chairpersons, we look forward to serving you in a way that will grow our businesses, expand our technical knowledge and our relationships.

Best wishes!

Jeff Applegate
SPE South Texas President 2009-2010

Extrusion of Engineering Plastics Seminar

November 9, 2009 9:00am–November 11, 2009 4:30pm
Instructor: Dr. Pravin Shah
Houston, Texas USA
Expertise Level: II

Purpose & Overview
This seminar, developed for plant managers, production engineers and process engineers as well as extrusion supervisors and technicians, provides a simplified and thorough treatment of the extrusion of engineering plastics and exotic polymers, with major emphasis on:

(1) How to select the right grade of each material to extrude strip, tubing, profile, and rod.

(2) How to develop critical process parameters such as barrel temperature profile and screw design requirements for extruding exotic materials of today, using melt rheology as a practical tool.

Utilizing a workshop approach this seminar teaches how to correlate materials, process, and equipment parameters for extruding engineering plastics into various shapes. Attendees learn how to improve extrusion of current and new engineering plastics, reduce scrap and downtime, and improve yield and output rates.

The laboratory session will take place at Killion Laboratories and will focus on extrusion runs with engineering or novel polymers; attendees receive hands-on training.

Instructor:
Dr. Pravin Shah - Biography

Seminar Content
• Introduction to Engineering Plastics
• Basic Understanding of the Extrusion Process
• A Simple Guide to Selecting Critical Materials and Extrusion Parameters From Melt Rheology Data
• Introduction to Die Design (for Tubing, Blown Film, Flat Film, and Sheet)
• A Processor’s Guide to Extrusion of Engineering Plastics
• A Workshop Session to Solve Extrusion Problems

Hotel Information:
Sheraton Houston Brookhollow Hotel
3000 North Loop West Freeway
Houston, Texas 77092
+1 888-627-8196
Rate: $129.00 plus tax
Attendees are responsible for making their own hotel reservations.

Transportation:
The Sheraton Houston Brookhollow Hotel is located approximately 30 minutes from George Bush International Airport and approximately 45 minutes from Hobby Airport in Houston. Transportation to the hotel from these airports should be arranged through your travel agent.

Seminar Hours:
Monday, November 9: 9:00 a.m. to 4:30 p.m. with lunch from 12:00 p.m. to 1:00 p.m
Tuesday, November 10: 9:00 a.m. to 4:30 p.m. with lunch from 12:00 p.m. to 1:00 p.m.
Wednesday, November 11: 9:00 a.m. to 3:00 p.m.
Please schedule your departures after this 3:00 p.m. ending time.

Suggested Attire:
Casual Business attire is appropriate. Please be prepared for moderate temperature variations in the seminar room.

Seminar Cancellation Policy:
Refunds will not be granted five (5) days prior to seminar. Substitutes may be sent in place of the registrant with prior notification to SPE. Cancellations are subject to a $100 processing fee. Written cancellations must be received at SPE headquarters prior to the seminar.

SPE reserves the right to cancel a seminar or substitute instructors. If SPE should cancel, the attendee will be contacted as soon as possible prior to the seminar. It is recommended that a refundable airline ticket be purchased. SPE is not responsible for penalty fees or any costs incurred by the attendee due to cancellation of the seminar.

Registration Fees:
Your registration fee covers classroom instruction, educational materials, transportation to and from the laboratory session at Davis-Standard, refreshment breaks, and lunch on Monday and Tuesday. It does not include hotel accommodations.

Registration Information:
You may register for this seminar online or by phone +1 203-740-5403.

Registration is limited and on a first-come, first-served basis. Early registration is strongly recommended.

Polyolefins Conference and FlexPackCon – Mark your calendars!

The 2010 International Polyolefins Conference and FlexPackCon will be held at the Hilton Houston North (formerly known as the Wyndham), Feb 22-24, 2010. 

This year’s program will again include both the traditional Polyolefins focus as well as the Flexible Packaging program. One of the themes for FlexPackCon will be sustainability and will include talks by Chet Rutledge, Director of Packaging Procurement,WalMart; Larry Dull, Partner, Packing Knowledge Group (PKG) LLC; and Victor A. Bell, President, Environmental Packaging International. They will discuss the WalMart scorecard and it’s extensions, how to used the scorecard to evaluate new opportunities, and packaging Life Cycle Analysis. FlexPackCon will also provide updates on food law (e.g. FDA) and potential regulatory expansions.

If you know of particular developments which should be presented at the conference, please contact Robert Portnoy for Polyolefins rportnoy@portnoytechnicalservices.com) or Andy Christie (andy@optexprocesssolutions.com) for FlexPackCon.  If you’d like to sponsor a coffee break or exhibit, please contact Emery Jorgenson (emery@jorgensonmachinery.com).

We look forward to seeing you at the conference!

http://www.facebook.com/group.php?gid=35280334773&ref=ts

Join the South Texas Section of the Society of Plastics Engineers on Facebook. Click on the above link and you will be directed to our group page. We hope that this will serve as another communication tool for our Professional Section and be a familiar platform to welcome and inform the Student Sections. It is easy and free, so join in. (TOM = Tomorrow)

Bulletin Board

Plastics Information: Check it Out

The Houston Public Library on McKinney has resources on plastics and polymers. Check out their catalog at www.hpl.lib.tx.us. If you are not near the McKinney location, you can arrange to pick up your books at your local branch.

The Fondren Library at Rice University has the most complete collection of books on plastics and polymers. This is also a prime resource for patent and trademark information, as well as other US Government documents. You cannot check out books there unless you join Fondren Library [$50], but you can arrange for books to be sent to your library by inter-library loan. Use their catalog at http://library.rice.edu/.

The next best place to browse is at the MD Anderson Library at the University of Houston central campus. South Texas Section has donated many plastics books to this library. If you plan ahead, you can get a TexShare library card from a library where you are a member, which will allow you to check out books from any U of H library. Their catalog is at www.library.uh.edu/.

Book Bag

	Plastic Conversion Processes: A Concise and Applied Guide Eric Cybulski, 2009; 165 pages $70.00 Many books describe a single plastic-conversion process, like injection molding, but until now, none has described and compared several processes. This book provides a basic overview of seven conversion processes used in the industry. These processes account for more than 97% of all plastic products. Each chapter begins with a process attribute table to serve as a quick guide. The particular conversion process is then briefly described, along with a short history. To better explain each process, sections detailing equipment, tooling, and materials have been added. Also included are sections on design guidelines and on how to identify which process was used to manufacture a plastic part. Contents: Injection Molding Plastic Extrusion Blow Molding Thermoforming Reaction Injection Molding Rotational Molding Compression Molding
	Mixing and Compounding of Polymers: Theory and Practice, 2nd Edition Ica Manas-Zloczower, 2009; 850 pages ISBN: 978-1-56990-424-4 $249.00 Finally available in its second edition, this classic monograph covers everything from the basic principles to the various practical applications of state-of-the-art mixing and compounding. It discusses the basic mixing mechanisms encountered in polymer processing; the latest results in modeling, flow simulation and visualization, and scale-up rules for the most important batch and continuous mixers; the properties of various additives used in the plastics and rubber industry and their effects on the properties of the compound; working principles and practices for reactive polymer compounding; compatibilization mechanisms applicable to blends and composites; mixing practices in the current commercial mixing devices; key aspects of mixing at nanoscale; and scale-down of mixing equipment and fundamentals of microfluidics. Contents: Part I: Mechanisms and Theory Basic Concepts - Mixing of Miscible Fluids - Mixing of Immiscible Fluids - Dispersive Mixing of Solid Additives - Distributive Mixing - Distribution Functions and Measures of Mixing Part II: Mixing Equipment - Modeling, Simulation, Visualization Batch Equipment Simulation - Batch Equipment Visualization - Continuous Equipment Simulation - Dispersive Mixing Devices in Single Screw - Twin Rotor Mixers - Co-Kneader - Visualization - Scale-up of Mixing Equipment - Scale-down of Mixing Equipment Part III: Material Consideration, Properties and Characterization Solid additives (inorganic) - Solid additives (organic) - Compatibilizers (mechanisms, theory) - Material Consideration for Mixing at Nanoscale - Effect of Mixing on Properties of Compounds - Effect of Mixing on Rubber Properties Part IV: Mixing Practices Internal Mixers - Single Screw Extruders - Twin Screw Extruders - Intermeshing Twin Screw Extruders - Reciprocating Screws - Reactive Compounding - Farrel Continuous Mixer
	Injection Molding: Fundamentals and Applications Musa R. Kamal, Avram I. Isayev, S. Liu, 2009; 800 pages ISBN: 978-1-56990-434-3   $249.00 This book surveys the state of the science and technology of the injection molding process. It represents a comprehensive, balanced mix of practical and theoretical aspects for a wide range of injection molding applications. The authors of the 21 chapters are experts and leaders in their respective areas of specialization in the injection molding field. While it is not possible to cover all aspects of such a dynamic growing field, readers should find sufficient information and background to become acquainted, at various levels of depth, with key components of the science and technology of injection molding. Contents: Injection Molding: Introduction and General Background Injection Molding Machines, Tools, and Processes The Plasticating System for Injection Molding Machines Non-Conventional Injection Molds Gas Assisted Injection Molding Water Injection Techniques (WIT) Flow Induced Fiber Micro-Structure in Injection Molding of Fiber Reinforced Materials Injection Foam Molding Powder Metal Injection Molding Micro Injection Molding Internal Visualization of Mold Cavity and Heating Cylinder Injection Molding Control Optimal Design for Injection Molding Development of Injection Molding Simulation Three-Dimensional Injection Molding Simulation Viscoelastic Instabilities in Injection Molding Evolution of Structural Hierarchy in Injection Molded Semicrystalline Polymers Modeling Aspects of Post-Filling Steps in Injection Molding Volumetric and Anisotropic Shrinkage in Injection Moldings of Thermoplastics Three-Dimensional Simulation of Gas-Assisted and Co-Injection Molding Processes Co-Injection Molding of Polymers
	ANTEC™@NPE 2009 Conference Proceedings - Thumb Drive SPE, Chicago, Illinois USA, June 2009, Thumb Drive $250.00 In Chicago in 2009, ANTEC® (Annual Technical Conference), sponsored by the Society of Plastics Engineers, celebrated its 67th year of excellence. The largest peer-reviewed technical conference serving the plastics industry, ANTEC® is perfectly positioned to help the plastics specialist achieve new levels of professional development. Order the ANTEC® 2009 proceedings on thumb drive or CD-ROM. Includes 700+ papers detailing the latest developments in: Alloys and Blends, Applied Rheology, Automotive, Biopolymers, Blow Molding, Color and Appearance, Composites, Decorating and Assembly, Electrical and Electronic, Engineering Properties and Structure, Extrusion, Failure Analysis and Prevention, Flexible Packaging, Injection Molding, Joining of Plastics and Composites, Marketing and Management, Medical Plastics, Mold Making and Mold Design, Nano/Micro Molding, Plastic Pipe & Fittings, Plastics in Building and Construction, Plastics Environmental, Polymer Analysis, Polymer Modifiers and Additives, Process Monitoring and Control, Product Design and Development, Radiation Processing of Polymers, Rotational Molding, Thermoforming, Thermoplastic Elastomers, Thermoplastic Materials and Foams, Thermoset, and Vinyl Plastics.
	Injection Molding - Thumb Drive SPE, Chicago, Illinois USA, June 2009, Thumb Drive $50.00 Injection Molding Titles Include: Optimizing the Molding Process — Chapter from Plastics Technician’s TOOLBOX, by Jerry Golmanavich, Golmanavich Enterprises Shear Induced Imbalances and MeltFlipper® Technology, by John P. Beaumont, Penn State Erie & Beaumont Technologies, Inc. The Warpage Simulation with In-mold Constraint Effect in Injection Molding, by Dr. Venny Yang, CoreTech System Co., Ltd. The Investigation of Flow Behavior of Polymeric Melts in Water Assisted Injection Molding, by Dr. Chao-Tsai Huang, CoreTech System Co., Ltd. Injection Molding of Woodfiber Plastics Composites, by Michael Burgoyne State of the Art of Electric injection Molding, by M. Barr Klaus, Electric Injection Services, Inc. Mold Ejector Pin Melt Flow Volume Sensor, by Fred Buja, FjB PlasTechnology Water up to 400°F – The Best Way To Heat up Your Mold, by Anna Birkhofer, consultant Asia Tooling and Molding: How To Be Successful, D.B. "Dusty" Rhodes, Waypoint Bellwether, Inc. It Is as Easy To Be an Injection Molding Compounder as It Is To Be an Injection Molder, by Peter Lipp, Krauss-Maffei Corporation Effect of Injection Molding Process Parameters on the Morphology and Quality of Microcellular Foams, by Jingyi Xu Microcellular Injection Molding of Polylactide-Montmorillonite Nanocomposites, by Sarah Gong, Assistant Professor, University of Wisconsin-Milwaukee
	Extrusion - Thumb Drive SPE, Chicago, Illinois USA, June 2009, Thumb Drive $50.00 Extrusion Titles Include: Understanding Blown Film Process Variables and Bubble Geometry, by Kirk Cantor, Pennsylvania College of Technology A Perturbation Method To Characterize Melting During The Extrusion of Polymers and Blends, by Mark D. Wetzel, E. I. du Pont de Nemours and Co., Inc., & Chi-Kai Shih, Chi-Kai Shih, LLC Woodfiber/Plastics Composites - Introduction and Overview, by Frank Maine, PSA Composites Kinematics Model of Solids Conveying for Extrusion, by Stephen J. Derezinski, Ph.D., Extruder Tech, Inc. Extruded Open Cell Foams Using Two Semicrystalline Polymers, by Patrick Lee, University of Toronto Extrusion Screws for Thermoplastic Materials, by Tim Womer, Xaloy Formation of Barrier Plastic Materials by Chaotic Blending, Dave Zumbrunnen, Clemson University The Vented Barrier Screw, by Stephen Derezinski, Extruder Tech, Inc. Understanding Why Adhesion In Extrusion Coating Decreases With Diminishing Coating Thickness, Part I: Penetration of Porous Substrates, by Barry A. Morris, DuPont Development and Utilization of Metallized and Clear High Barrier Packaging Films, by Eldridge M. Mount, III, EMMOUNT Technologies The Impact of Screw Threads on Cost Cutting and Performance: High Performance Compound Angle Design, by Russell D. Hendee, Semblex Corporation Metering Channel Flows and Troubleshooting Single-Screw Extruders, by Mark A. Spalding, Dow Chemical Company Extrusion Troubleshooting, by Frank Van Haste, NOVACHEM Recent Trends and Developments in Twin-Screw Processing, by Stuart Kapp, American Leistritz Extruder Corporation Flow Surging in Single Screw, Plasticating Extruders, by Mark Spalding, The Dow Chemical Company Myths and Realities of Purging for Extruders and Blow Molders, by Frank Van Haste, NOVACHEM Can I Run PLA on My Existing Extruders? A Practical Application Guide, by Edward L. Steward, American Kuhne Corporation Twin-Screw Extrusion Design Enhancements for Processing Heat-Sensitive and Shear-Sensitive Biopolymers, by Charlie Martin, Leistritz

Councilor’s Corner

Did you get to ANTEC this year? It was a very busy event with NPE serving as the “exhibition”! About 750 technical papers were presented in the ANTEC program, a significant increase over recent years. The Sustainability session by the Flexible Packaging Division was “standing room only”, and the regulatory systems session (REACH and the food law systems, including the brand new Chinese system) drew a strong audience as well. While I can’t comment on all 100+ sessions, I can report on “hall talk” about how interesting and different many of the presentations were, such as “solid-state drawn talc-filled PP as an alternative plastic lumber”. There were special activities for student members from “how to build your professional network” to “speed interviewing”.

Next year, ANTEC will be in Orlando (Marriott’s World Center). The call for papers is out, so log onto http://www.4spe.org/antec-2010-technical-program to post your abstract.

ANTEC is the “grandfather of SPE conferences” and also hosts the largest governance meeting. The SPE Council has about 120 representatives, coming from the Divisions, Special Interest Groups, and sections like South Texas. This body is ultimately responsible for the strategic direction of SPE. As your Councilor, I welcome your suggestions, and will be delighted to discuss issues with which Council is or should be addressing.

Frankly, one of the largest issues for SPE currently is decline in membership. As you’ve experienced, the industry has been contracting, especially in North America and Europe where our membership is concentrated. SPE membership has suffered concurrently. The reduction in revenue from dues has challenged finances, driving several changes. The staff has been minimized, particularly with outsourcing of activities such as publications (Plastics Engineering magazine and the SPE Journals.) Fortunately, the headquarters building was sold, allowing staff to move to a smaller more appropriate office space. The net proceeds from the sale of the building will be maintained in a capital fund and not consumed by operations. As SPE looks to distant locations for growth (Asia, etc.), it is increasingly adopting internet-based platforms for delivering products and services. The website has been redesigned to allow better functionality, but the improvements are not all in place yet. The vision is to have all SPE-related information available (and readily searchable!) on the one site. In addition to searching for member contact details and conference proceedings, you’d be able to read newsletters from the various divisions and keep up with the schedules for other local sections. Since it’s still a “work in progress”, I’d appreciate your suggestions. What information would you like incorporated?

The Council will meet again in October, so please contact me with any helpful ideas. Scott Owens, President of Chemtrusion here in Houston, is serving on the SPE Executive Committee this year. I’m sure he’d welcome your suggestions also.

Thanks,

Donna S. Davis
Councilor, South Texas Section

Flow and Cure Modelling of Rim Mouldings – Thermal and Flow Validation

A. J. Mateus, P. G. Martinho, P. J. Bartolo
Mechanical Engineering Department, Polytechnic Institute of Leiria, 2401-951 Leiria, Portugal

Abstract

The RIM process involves simultaneous flow and exothermal curing reactions. The optimisation of these events enables to produce parts with better quality and improved properties. The integration of appropriate mathematical models simulating the thermal and flow aspects is experimentally verified.

Introduction

Polyurethanes (PU) are step-addition polymers formed by the reaction of di-or poly-isocyanetes with diols or polyols. They represent a unique class of polymers widely used as foams, coatings, adhesives and elastomers as their properties can be easily tailored by the variation of their components. They are usually processed through reaction injection moulding (RIM) in which the two low-viscosity and highly reactive components are mixed and injected into a mould [1-3]. This process allows large complex parts to be produced without the need of high clamping pressures. A typical RIM machine is schematically shown in Figure 1.

The curing reaction of PUs involves the formation of a three-dimensional network through the reaction among polyfunctional groups [2,3]. The curing process starts from a formation and linear growth of a chain. This chain rapidly starts to branch and then cross-link. As the curing proceeds, the molecular weight increases rapidly and several chains are linked together into a network of infinite molecular weight. This reaction is characterised by two main events: gelation and vitrification [13,14].

Gelation corresponds to the incipient formation of an infinite molecular network, which is associated to an increase in viscosity and a decrease in processability. After gelation, as the reaction further progresses, the amount of solid material increases and the polymer becomes more cross-linked increasing its stiffness and strength. Vitrification corresponds to the formation of a glassy solid material, due to an increase in both the cross-linking density and the molecular weight of the polymer being cured. The onset of vitrification occurs when the increasing glass transition temperature, T_g, reaches the cure temperature, T_cure. The rate of the reaction will undergo a significant decrease after vitrification and the reaction becomes very slow as it is controlled by the diffusion of the reactive species. The diffusion-controlled effect, that produces a slow down of the solidification process, will also determine the final degree of conversion.

The RIM process involves simultaneous flow and exothermic curing reactions. The optimisation of these events enables to produce parts with better quality and improved properties. Several commercial softwares such as Moldflow, Moldex and SigmaSoft have been developed for injection moulding simulation. However, due to the industrial importance that RIM has gained in recent years, these softwares developed specific routines to sudy the reaction injection moulding process. In this paper, the accuracy of the models used by Moldflow for RIM simulation is evaluated based on both numerical simulation and experimental work.

Thermo-rheo-kinetic model

The simulation of the RIM process through Moldflow comprises both fluid flow and heat transfer. The fluid flow is modelled by both the mass conservation and momentum equations.

where p is the density, g is the acceleration of gravity and is the dynamic viscosity. Viscosity changes associated with the cure process are modelled by Moldflow through the following equation:

In the previous equations r is the shear stress at the transition between Newtonian and power law behaviour and ₀ is the viscosity at zero shear rate.

The heat transfer is described through the energy conservation equation, which includes an exothermic heat generation term given by an appropriate kinetic model.

where h is the specific enthalpy of the resin, k is the thermal conductivity, H is the exothermic heat released during the curing reaction per unit of mass, a is the fractional conversion (amount of solid material formed), and is the rate of gel formation described by the kinetic model.

Many phenomenological models have been developed for the curing simulation of thermosetting materials. These models, assuming that only one reaction can represent the whole cure process, are expressed by the following equation [4]:

where f(a) is a function of conversion (a) and K(T), the rate constant, a function of the temperature

In the case of PUs, the curing reaction is described in Moldflow by the Kamal and Souror model [5,6]:

where K₁(T) and K₂(T) are rate constants, m and n are constants, representing the sum of m and n, the overall reaction order. The order of the reaction, according to its definition, indicates the number of atoms, molecules or reactive groups whose concentration determines the reaction rate.

Rate constants are supposed to observe an Arrhenius law [4, 7], so can be expressed by the following equations:

where A is the pre-exponential factor of the rate constant, E is the activation energy, R is the gas constant, +T is the absolute temperature.

Experimental work and computer simulation

Part and mould design
The geometry of the part, used in this research study, is shown in Figure 2. One acrylic mould was produced to visualise the flow of the polymeric mixture.

Material and mixing system
The polyurethane chosen for this study consists of a polyether polyol (RIM 876, Axson) and a diphenyl-methane diisocyanate (RIM 900, Axson).

An Econo-Mix low-pressure injection moulding system was used for the mouldings. This machine (Figure 3) allows an injection pressure ranging from 1 bar to 10 bar discharging at a maximum rate of 3.5 Kg/min. The pump pressure at the polyol and isocyanate containers is approximately 2 bar. The mixing process is set at room temperature.

Experimental analysis
Moulds were manually closed using fast-
tightening clamps (Figure 4), due to the low pressure values used in the filling phase. The polymeric material is set at room temperature for the curing phase after mould filling. Once cured, parts are extracted from the mould and then submitted to a post cure operation.

The injection process was performed with the mould placed at both horizontal and vertical positions to assess the importance of gravity effects. Different injection positions were also considered (Figure 5). The injection pressure values used were: 3, 4.5 and 6 bar.

Figures 6 shows the flow front advancement at different instants of time. The injection pressure value used was 6 bar.

The influence of the injection position on the location of air holes is illustrated on Figure 7. The experimental results are indicated in Table 1.

Computer simulation
The software Moldflow, version 4.1, and three-dimensional solid elements were used for simulation purposes.

Filing phase:
Figure 8 shows the sequence of images of the filling process for different injection positions predicted by Moldflow. The parameters used in these simulations are indicated in Table 2. The filling times are presented in Table 3.

Curing phase:
In order to access the accuracy of Moldflow both thermographic and DSC experimental work was performed.

The Flir ThermaCAM PM575 camera was used for the thermographic studies and the mixing and reaction calorimeter C80, from Setaram, was used for the DSC studies.

Figures 9 and 10 show, respectively the maximum temperature value and the final conversion of the PU material. The maximum temperature value at the surface of the part obtained by thermography is approximately 100ºC. This value is higher than the value predicted by Moldflow. Effectively, several other computer simulations have shown that Moldflow is almost non-sensitive heat released regarding RIM. The DSC studies (Figure 10) show that the curing reaction of non-stoichiometric mixtures is strongly influenced by diffusion-controlled mechanisms. In these cases, the final amount of solid material obtained through the cure, at room temperature, is lower than 100% as predicted by Moldflow. These differences are due to the kinetic model used, which does not include the effects of vitrification and unimolecular termination mechanisms.

Discussion

The results shown in this paper indicate that:

• the quality of the parts produced by RIM is strongly dependent on the injection position
• The injection position determines the mould design, i.e., the position of air vents, gates, etc…
• The curing reaction is an exothermic process. The heat released increase the curing reaction but also produces thermal stresses contributing to warpage. This is particularly important for parts having a variation of thickness.
• Post curing is usually required to complete the curing process due to vitrification phenomenon. Additional shrinkage and warpage must be considered.
• Moldflow is an important tool for injection moulding simulation, though for RIM, it does not properly describe gravity effects, which are particularly important for both low viscosity materials and low pressure processes.
• The curing model used by Moldflow properly describes the curing reaction of stoichiometric mixtures, while for non stoichiometric mixtures the model is not able to predict vitrification and diffusion-controlled reactions. Thus, Moldflow cannot predict the need of post-curing operations.

Conclusions

RIM computer simulations represent an important tool to study and optimize both mould and part design, though requiring accurate models for both filling and curing phases. Models used in Moldflow give reasonable results for simple and standard cases. However, for more complex cases, like non stoichiometric mixtures, complex parts with significant thickness variation and high injection volumes, important differences between experimental results and simulated values can be observed, so better models are still required.

References

1. C. D. Rudd, A. C. Long, K. N. Kendall, C. G. E. Mangin, Liquid Moulding Technologies, Woodhead Publishing, Lda, 1997

2. C. W. Macosko, RIM Fundamentals of reaction injection molding, Hanser, Munich, 1989.

3. F. M. Sweeney, Reaction Injection Molding Machinery and Process, Marcel Dekker, 1987.

4. G. Woods, The ICI Polyurethanes Book, John Wiley & Sons, LTD, United Kingdom, 1990.

5. M. R. Kamal and M. E. Ryan, in, Fundamentals of computer modeling for polymer processing, Edited by C. L. Tucker, Hanser, Munich, 1989.

6. M.S. Koo, K. Chung, J.R. Youn, “Reaction injection molding of polyurethane foam for improved thermal insulation”, Polymer Engineering and Science, 2001, Vol. 41, 1177-1183

7. P.K. Mallick, S. Newman, Composite Materials Technology – processes and properties, Hanser publishers, New York, 1990.

8. Steve L., The polyurethanes book, John Wiley & Sons, LTD, United Kingdom, 2002.

9. Popescu, C. and Segal, E., Int. J. Chem. Kinet., 30, 313(1998).

10. Prime, R.B. (1997), in Thermal characterization of polymeric materials, Vol. 2, Edited by E.A. Turi, Academic Press, London.

11. Salla, J.M. and Ramis, X., Effect of the inhibitoron the curing of an unsaturated polyester resin, Macromol. Rapid Commun., Polym. Eng. Sci., 36, pp. 35113521 (1995).

12. Li, S., Vatanparast, R. and Lemmetyinen, H. Polymer, 41, 5571 (2000).

13. Mateus, A., Bartolo, P.J. and Costa, V. , Physical and numerical modelling of the flow and curing process during reaction injection moulding, Proceedings of the RPD2002-Advanced Solutions and Development (2002).

14. Mateus, A. e Bártolo, P.J. B – “Kinetic modelling of reaction polymerisation processes through RIM”, Proceedings of the PPS-19, Polymer Processing Society, Melburn, Australia, 2003.

15. Sourour, S. and Kamal, M.R., SPE ANTEC Tech. Pap., 18, 93 (1972).

16. Bartolo, P.J., Optical approaches to macroscopic and microscopic engineering, Unpublished PhD Thesis, University of Reading, UK (2001).

17. Vyazovkin, S. and Sbirrazzuoli, N., Macromol. Rapid Commun., 21, pp.85-90 (2000).