A Practical Approach to Scientific Molding E-Book

Gary F. Schiller

• Herausgeber: Carl Hanser Verlag GmbH & Co. KG
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 186

Veröffentlichungsjahr: 2018

Beschreibung

This easy-to-understand guide provides the necessary information to implement a scientific molding program. It is a hands-on reference for people on the molding floor, including those previously lacking theoretical background or formal education.

The book covers how the injection molding machine prepares the plastic and understanding of plastic flow. The functions of the main machine components are explained and understanding of correct procedures and testing is developed. Each step of the process is clearly explained in a step-by-step manner, and simple examples of important calculations are provided. The practical approach is augmented by useful guides for troubleshooting and machine set-up.

An Excel spreadsheet with a process test and a machine performance test is available as bonus material.

Contents

1. Injection Unit: Screw
2. Injection Unit: Barrel
3. Clamping Unit
4. Ejectors/Controllers, Human Machine Interface (HMI)
5. Machine Performance Testing
6. Process Development Test
7. Plastic Temperature
8. Plastic Flow
9. Plastic Pressure (Pack/Hold)
10. Cooling
11. Benchmarking the Injection Molding Process
12. Process Troubleshooting
13. What is Important on a Set-Up Sheet?
14. Commonly Used Conversion Factors and Formulas
15. Machine Set-Up
16. Things That Hurt the Bottom Line of a Company
17. Terms and Definitions

Leseprobe

Gary F. Schiller

A Practical Approach to Scientific Molding

The author:

Gary F. Schiller, Erie, PA

Distributed in North and South America by: Hanser Publications 6915 Valley Avenue, Cincinnati, Ohio 45244-3029, USA Fax: [phone] Phone: [phone]www.hanserpublications.com

Distributed in all other countries by Carl Hanser Verlag Postfach 86 04 20, 81631 München, Germany Fax: [phone]www.hanser-fachbuch.de

The use of general descriptive names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the author nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.

The final determination of the suitability of any information for the use contemplated for a given application remains the sole responsibility of the user.

Cataloging-in-Publication Data is on file with the Library of Congress

Bibliografische Information Der Deutschen Bibliothek Die Deutsche Bibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über http://dnb.d-nb.de abrufbar.

All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or by any information storage and retrieval system, without permission in writing from the publisher.

© 2018 Carl Hanser Verlag, Munich

Editor:Dr. Mark Smith Production Management: Jörg Strohbach Coverconcept: Marc Müller-Bremer, www.rebranding.de, München Coverdesign: Stephan Rönigk

Print-ISBN 978-1-56990-686-6 E-Book-ISBN 978-1-56990-687-3

Table of Contents

Title page

Copyright page

Table of Contents

Preface

About the Author

1 Injection Unit: Screw

1.1 Prepares the Melt

1.2 Flows the Melt

1.3 Pressurizes the Melt

1.4 Sections of the Screw

1.4.1 Feed Zone

1.4.2 Transition or Compression Zone

1.4.3 Metering Zone

1.5 L/D or Length/Diameter

1.6 Compression Ratio

1.7 Profile

1.8 Injection Pressure

1.9 Injection High Limit Fill Time

1.10 Injection Pack Pressure/Time

1.11 Injection Hold Pressure/Time

1.12 Non-return Valve Function

1.13 Different Styles of Non-return Valves

1.14 Decompression/Pull Back/Suck Back

1.15 Screw Rotate Delay

1.16 Mixing Head on a Reciprocating Screw

1.17 Barrier Screws

2 Injection Unit: Barrel

2.1 Barrel

2.2 Thermocouples

2.3 Heater Bands

2.4 Spacing of Heater Bands

2.5 Wattage

2.6 Worn Barrel

2.7 Feed Throat

2.8 Venting of the Barrel

2.9 Hopper

2.10 Hopper Dryer Diagram

2.11 Filter Packs/Dispersion Disks/Screen Packs

3 Clamping Unit

3.1 Hydraulic

3.2 Toggle

3.3 Weakness

3.4 Tie-Bar-Less

3.5 Single Point

3.6 Platen Wrap

3.7 Mold Coverage Area

3.8 Cleanliness of the Platens

3.9 Care of Bolt Holes

3.10 Proper Bolt Location

3.11 Weight of Mold Calculations

3.12 Mold Height

3.13 Calculating Clamp Tonnage for a Press

4 Ejectors/Controllers, Human Machine Interface (HMI)

4.1 Ejector Pattern and Spacing

4.2 Ejector Spacing

4.3 Controllers

4.3.1 Open Loop

4.3.2 Closed Loop

4.4 Key Pads

5 Machine Performance Testing

5.1 Rear Barrel Zone Optimization

5.2 Load Sensitivity

5.2.1 Purge Disk

5.3 Pressure Response

5.4 Dynamic Non-return Valve Test (FILL)

5.5 Static Non-return Valve Test (PACK/HOLD)

5.6 Injection Speed Linearity

6 Process Development Test

6.1 Tonnage Calculation/Projected Area

6.2 On Machine Rheology Curve (Viscosity Curve) or Fill Time Study

6.3 Construction of Viscosity Curve Graph

6.4 Least Pressure Curve

6.5 Plastic Flow Rate (Qp)

6.6 Shear Rates

6.7 Gate Freeze, Gate Seal, or Gate Stabilization

6.8 Runner Weight Study

6.9 Range Finding for Gate Seal

6.10 Manifold Imbalance and Balance of Fill Analysis

6.11 Cooling Optimization Study

6.12 Pressure Loss Study

7 Plastic Temperature

7.1 Molecular Structure of Common Materials

7.2 Morphology

7.2.1 Amorphous Resin Morphology

7.2.2 Semi-Crystalline Resin Morphology

7.3 Glass Transition Temperature (Tg)

7.4 Melt Transition Temperature (Tm)

7.5 Shrinkage

7.5.1 Isotropic Shrinkage

7.5.2 Anisotropic Shrinkage

7.6 Melt Density versus Solid Density

7.7 Advantages/Disadvantages of Hot Runner versus Cold Runner

7.8 Induced Shear through a Hot or Cold Runner System

8 Plastic Flow

8.1 Fountain Flow

8.2 Flow of Plastic

8.3 How to Calculate Flow Rate (Qp)

8.4 Calculating Volume of Shot Size

8.5 Blocking a Cavity

8.6 Flow through a Mold

8.7 Orientation

8.8 Transfer/Cut-Off Position

8.9 Viscosity Changes

8.10 Intensifying Ratio (Ri)

8.11 Pressure Limited Process

8.12 Safe Start-Up Shot Size

8.13 Runner Sizing

9 Plastic Pressure (Pack/Hold)

9.1 Plastic Pressure

9.2 Dynamic versus Static

9.3 Viscosity Changes

9.4 End of Cavity Pressure Loss

9.5 Part Shrinkage versus Cavity Pressure

9.6 Maximum Average Pressure at Parting Line before Flashing

10 Cooling

10.1 Plastic Cooling

10.2 Turbulent versus Laminar Flow

10.3 Reynolds Number

10.4 Water Lines

10.5 Area of Water Line

10.6 Series/Parallel

10.7 Cooling Rate

10.8 Ineffective Cooling

10.9 Cooling Time

10.10 Depth, Diameter, and Pitch

10.11 Baffles/Bubblers

10.12 How a Thermolator/Mold Heater Works

11 Benchmarking the Injection Molding Process

12 Process Troubleshooting

12.1 Black Specks

12.2 Blush

12.3 Brittleness

12.4 Burns

12.5 Burns in Gates

12.6 Cloudy Parts

12.7 Color Streaks

12.8 Deformation: Ejector Pin Marks

12.9 Degraded Polymer

12.10 Design

12.11 Fish Hooks

12.12 Flash

12.13 Flow Lines

12.14 Hot Tip Drool

12.15 Jetting

12.16 Long Gates

12.17 Nozzle Drool

12.18 Parts Sticking in Mold

12.19 Pulls

12.20 Shorts/Non-Fills

12.21 Sinks

12.22 Splay

12.23 Sprue Sticking

12.24 Surface Imperfections

12.25 Voids

12.26 Warpage

12.27 Weld Lines

13 What is Important on a Set-Up Sheet?

14 Commonly Used Conversion Factors and Formulas

14.1 Conversion Factors

14.2 Common Formulas for Injection Molding

15 Machine Set-Up

16 Things That Hurt the Bottom Line of a Company

17 Terms and Definitions

18 Reference List for Further Courses and Reading

18.1 Courses

18.2 Reading

Preface

This book is designed to help today's plastic molding technician deal with processing issues found day to day in the injection molding environment. It not only describes the functions of the molding machine, but also the auxiliary equipment associated with the process to produce quality parts. The chapters in this book will help the user to have a more thorough and hands-on understanding of the molding machine and the material.

It explains the process from the plastics point of view, and how the material is heated, flowed, packed, and cooled to produce the desired quality parts.

This processing guide not only shows users how to find a solution to the problem but also lets them understand why they are making the change, and what effect it has on the plastic. It details solutions from a hot runner/cold runner standpoint.

Each material has a different characteristic and will present problems in different ways, but through learning to read the part and analyzing the machine, the necessary insight will be provided to remedy most issues seen in everyday molding.

The most important thing to remember when processing or making adjustments to any machine is to make just one adjustment, review the effects on the part, and if that change has no effect, return to the previous set point, before implementing another change. By making a lot of changes in the hope of solving the molding issue, it becomes unclear which change had the effect on the part. Look at the parts, watch the molding machine, and observe what each change is doing to the process and machine.

Never neglect the details:

Walk around the machine and make sure the water is on to all lines going to the mold, or have any water lines been left off? Is the machine functioning properly (pressures, times, heating, with no unusual noises)?

Make sure the mold is functioning as intended and able to produce the quality parts desired.

Observe the material: make sure it is free of contaminants (dirt, foreign resin, or water) and is dried properly.

Then review the process and make sure there are no shortcomings (process is not pressure limited, transfer position is being achieved, not timing out and cycle time achieved).

There are no magic solutions for eliminating all molding issues, but a solid understanding of these scientific molding principles will help eliminate the unnecessary waste and scrap generated from not knowing.

There are three major components to the injection molding process: the injection unit, the clamping unit, and the mold.

In the next chapters, we will discuss the different functions of each major component and how they affect the process and conditions of the material.

I would like to acknowledge and thank the following companies and people:

RJG Inc. Traverse City, MI, especially Gary Chastain, Pat Mosley, and Shane Vandekerkhof.

AIM Institute, Erie, PA, especially John Beaumont and Dave Hoffman.

Technimark LLC, Asheboro, NC, especially Brad Wellington and Bruce Winslow.

Milacron LLC, Batavia, OH, especially Kent Royer.

I would also like to thank Gary Mitchell.

Gary Schiller

About the Author

37 years in the plastics industry

Certified Master Molder I, II, & Train the Trainer; past RJG instructor with over 27 years of scientific molding experience

AIM Institute graduate and alumnus – Plastics Technology and Engineering

AIM Institute Advisory Board

Practical Rheology in Injection Molding – Penn State, Erie, PA

Design of Experiments & Quality Engineering Methods – University of Colorado

TQM – Front Range Community College, Denver, Colorado

Certified Mechanical Inspector ASQ

Certified Quality Technician ASQ

Processing expert with a wide array of plastics

Core Competencies

Stack molding

Cube technology molding

Two shot molding

Insert molding

High cavitation molding

Engineering and commodity resins

1 Injection Unit: Screw