AGMA 920-B15-2015 Materials for Plastic Gears.pdf

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1、AGMA920-B15AGMA 920-B15 (Revision of AGMA 920-A01) AGMA Information Sheet Materials for Plastic Gears AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved ii Materials for Plastic Gears AGMA 920-B15 CAUTION NOTICE: AGMA technical publications are subject to constant imp

2、rovement, revision or withdrawal as dictated by experience. Any person who refers to any AGMA Technical Publication should be sure that the publication is the latest available from the Association on the subject matter. Tables or other self-supporting sections may be referenced. Citations should rea

3、d: See AGMA 920-B15, Materials for Plastic Gears, published by the American Gear Manufacturers Association, 1001 N. Fairfax Street, Suite 500, Alexandria, Virginia 22314, http:/www.agma.org. ABSTRACT The purpose of this document is to aid the gear designer in understanding the unique physical, mecha

4、nical and thermal behavior of plastic materials. The use of plastic materials for gear applications has grown considerably due to cost and performance issues. Growing markets include the automotive, business machine, and consumer-related industries. Topics covered include general plastic material be

5、havior, gear operating conditions, plastic gear manufacturing, tests for gear related material properties, and typical plastic gear materials. There are no quantitative details on material properties or any comparative evaluations of plastic types. Such specific information is left to be provided by

6、 material suppliers and gear manufacturers. Published by American Gear Manufacturers Association 1001 N. Fairfax Street, Suite 500, Alexandria, Virginia 22314 Copyright 2015 All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise

7、, without prior written permission of the publisher. Printed in the United States of America ISBN: 1-55589-048-3 American Gear Manufacturers Association AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved iii Contents Foreword . v 1 Scope 1 2 General nature of plastic

8、materials . 1 2.1 Elastic and viscoelastic behavior 1 2.2 Response to load 1 2.3 Effect of rate of load application . 2 2.4 Effect of temperature 2 2.5 Effect of moisture 3 3 Gear operating conditions and related material properties 3 3.1 General operating conditions 3 3.2 Special operating conditio

9、ns . 5 3.3 Vibration and noise . 8 4 Gear manufacturing and related material properties 9 4.1 Manufacture by machining 9 4.2 Injection molding process . 11 5 Tests for gear related material properties 13 5.1 Strength properties . 13 5.2 Wear and frictional characteristics 21 5.3 Thermal properties 2

10、3 5.4 Environmental properties 25 5.5 Miscellaneous properties 26 6 General description of plastic materials . 28 6.1 Classification . 28 6.2 Additives . 31 6.3 Available forms . 32 7 Plastic materials widely used for gears 33 7.1 Engineering thermoplastics 33 7.2 Thermosets . 34 8 Material selectio

11、n procedure 34 8.1 Environmental considerations . 35 8.2 Mechanical considerations . 37 8.3 Regulatory requirements 38 8.4 Manufacturing considerations . 38 8.5 Cost considerations 38 8.6 Quality . 40 Annexes Annex A Bibliography 42 Tables Table 1 Additives in plastics for molded gears 32 Table 2 Pl

12、astic materials for molded gears 34 Table 3 Plastic materials for machined gears 34 AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved iv Figures Figure 1 Representative creep behavior of ductile plastic . 2 Figure 2 Representative creep behavior of non-ductile plasti

13、c 2 Figure 3 Effect of strain rate and temperature on stress-strain curves 2 Figure 4 Typical fatigue curve (NOTE: Linear scale used for stress axis.) 3 Figure 5 Effect of temperature on stress vs. strain for acetal (POM) 5 Figure 6 Effect of moisture on stress vs. strain for nylon 6-6 (PA 6,6) at 2

14、3C . 6 Figure 7 Polymer impact strength as a function of temperature 8 Figure 8 Simple gear with three gates . 12 Figure 9 ASTM D638 Type 1 tensile specimen . 13 Figure 10 Typical DMA curves normalized at 23C . 15 Figure 11 Tensile DMA 16 Figure 12 DMA, amorphous polymers . 17 Figure 13 DMA, semi-cr

15、ystalline polymer 17 Figure 14 Flexural fatigue specimen 19 Figure 15 Representations of creep strain vs. time 21 Figure 16 Representations of creep creep modulus vs. time . 21 Figure 17 Representations of creep isochronous stress vs. strain . 21 Figure 18 ASTM D-3702 thrust washer wear and friction

16、 test . 22 Figure 19 Two-dimensional representation of crystalline and amorphous thermoplastics 29 Figure 20 Modulus behavior vs. temperature of crystalline and amorphous resins, neat and glass fiber reinforced 30 AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved v F

17、oreword The foreword, footnotes and annexes, if any, in this document are provided for informational purposes only and are not to be construed as a part of AGMA 920-B15, Materials for Plastic Gears. Plastic materials differ considerably from metals in performance and processing. Many of the importan

18、t differences, especially those that are critical to gear applications, are not widely recognized. This is partly because many plastic materials specialists are not familiar with gear requirements. Similarly, many gear specialists are not familiar with plastic material characteristics. Hence the nee

19、d for reference material which will help bridge these gaps. The AGMA Plastics Gearing Committee has brought together technical representatives from plastic material suppliers, gear manufacturers and designers. This document represents their efforts to further this exchange of information. It will no

20、t supply answers to many of the questions that arise in the application of plastic materials to gears, but it should encourage inquiry and information exchange. One issue that requires special attention is the availability of plastic material properties in the form most suitable for plastic gear des

21、ign. This includes properties that are counterparts of those used in the design of metal gears, and those that are special to plastic materials in these applications. To a very large extent, plastic gear designers have access only to property data taken from ASTM tests as reported by material suppli

22、ers even though such tests were created to meet other objectives. It was therefore judged essential to include brief descriptions of these tests supplemented by comments on any limitations of such test data when applied to gears. Various industry initiatives are now underway to develop gear specific

23、 property data, which will in time supplement the information provided here. The first draft of AGMA 920-A01 was made in 1993. It was approved by the AGMA membership in October 2000 and approved for publication by the Technical Division Executive Committee on October 22, 2000. This edition of the in

24、formation sheet, AGMA 920-B15, was created to: - revise definition of i found in Clause 5.1.3.3; - renumber figures to meet current style guidelines; - revise title of Figure 12, which previously appeared as Figure 11 in 920-A01. The first draft of AGMA 920-B15 was made in January 2015. It was appro

25、ved by the AGMA Plastics Gearing Committee in October 2015. Suggestions for improvement of this standard will be welcome. They may be submitted to techagma.org. AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved vi PERSONNEL of the AGMA Plastics Gearing Committee Chai

26、rman: Richard R. Kuhr Richard Kuhr Gear Consulting and Training Vice Chairman: Ernie Reiter. Web Gear Services Ltd. ACTIVE MEMBERS T. Barry . Phillips-Moldex Company F. Eberle . Hi-Lex Controls Inc. G. Ellis ABA-PGT, Inc. R.G. Layland Precision Gage Company T. Padden . DSM Engineering Plastics D. Sh

27、eridan Celanese Engineered Materials (Michigan) Z.P. Smith. Retired B. Stringer Gleason Plastic Gears E.H. Williams, III . SABIC Innovative Plastics J.H. Winzeler Winzeler Gear AGMA 2015 All rights reserved 1 AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 American Gear Manufacturers Associatio

28、n Materials for Plastic Gears 1 Scope This information sheet provides descriptions of plastic materials commonly used in gearing. It relates the general properties of these materials to typical operating conditions of gears. Properties that relate to the manufacturing processes of machining and mold

29、ing are discussed, including the property of shrink rate in molding. It also describes the types of tests that are customarily used to obtain published values of these properties. It is intended that this information sheet serve only as an introductory guide to the designer of plastic gears when it

30、comes to selecting candidate materials. The designer is advised to look to material suppliers and plastic gear manufacturers for their expert guidance on selecting materials for specific applications. It is also important to recognize that thorough application testing is often needed to confirm the

31、suitability of a material choice. Only a limited number of plastic materials are mentioned here as commonly used for gears. Gears have been made from other plastics as well, but generally because some special material property or commercial consideration was judged essential to a particular applicat

32、ion. It is also possible that the suitability of other materials for gears has not yet been recognized. Furthermore, new plastic materials are continually being developed and some, no doubt, will prove themselves as important additions to those discussed in this information sheet. 2 General nature o

33、f plastic materials Although plastic materials are successfully used in place of metals in load carrying applications such as gears, there are important differences between the two types of materials. These differences generally appear in combination and can have a significant effect on plastic gear

34、 performance. 2.1 Elastic and viscoelastic behavior Most structural metals behave as essentially elastic materials. Plastics, on the other hand, behave as a combination of elastic and viscous materials, with the balance varying considerably with the type of plastic, its molecular structure, and the

35、type, quantity, and orientation of any additives. This special nature of plastic materials does not interfere with their use in a very wide range of applications which benefit from their many other special properties. It does, however, require a thorough understanding of reported material properties

36、 data and their relationship to the specific application. 2.2 Response to load When load is applied to elastic materials such as steel, the resulting deformation is essentially immediate, constant over time, independent of a wide range of temperature, and fully recoverable when the load is removed.

37、When the material has a viscous component combined with the elastic, the initial deformation will increase with time under load (creep deformation) and will depend to a considerable degree on temperature. When the load is removed, there will be some delayed recovery and, possibly some permanent defo

38、rmation. The time dependent deformation of ductile polymers under constant load is quantified in creep testing. A family of curves resulting from varying the constant load (stress) and recording the increasing creep strain is shown in Figure 1. As the polymer is held under constant stress (load) ove

39、r time, the creep strain initially increases at a rapid rate (primary creep) and then plateaus to a significantly lower creep strain rate (secondary creep). For nonductile polymers the material will experience creep rupture while deforming under secondary creep (see Figure 2). However, for ductile p

40、olymers, the material will AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved 2 experience another increase in creep strain rate (tertiary creep) and will creep rupture in tertiary creep. For non-ductile polymers the locus of creep rupture points forms the creep ruptu

41、re envelope. However, the creep rupture envelope for ductile polymers is the locus of points resulting from the transition from secondary to tertiary creep. Creep deformation appears not to be a factor in gears under continuous operation because the load is applied to gear teeth only for a short tim

42、e duration. However, for gears run into stalled conditions creep deformation and creep rupture of polymers needs to be considered. 2.3 Effect of rate of load application Because of the time dependent nature of viscoelastic plastic materials, the strength properties and elasticity modulus are typical

43、ly greater when the load is applied and removed more rapidly. See Figure 3. This characteristic is especially important in gear applications. 2.4 Effect of temperature 2.4.1 Strength and deformation Because a higher temperature reduces the resistance to movement of the polymer chains, the material a

44、t high temperatures can be viewed as less viscous (decrease of the viscous component). This decrease in the viscous component of polymers at higher temperatures causes the strength and stiffness properties to decrease with increasing temperatures (see Figure 3). Temperature increases of the polymer

45、at critical locations in gears could result from friction, hysteresis, or both in combination. This temperature rise of the gear material at critical locations could, therefore, reduce the load resisting capability of the gear. This condition is a significant factor to consider in gear performance.

46、Figure 1 Representative creep behavior of ductile plastic Figure 2 Representative creep behavior of non-ductile plastic Figure 3 Effect of strain rate and temperature on stress-strain curves AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 920-B15 AGMA 2015 All rights reserved 3 2.4.2 Expansion Plastics

47、 have higher thermal expansion rates than metals. These high rates can be partially offset by compounding the plastics with various fillers and reinforcements. Thermal expansion should be considered in those applications in which the gears operate over broad ranges of temperature and the structure t

48、hat controls gear center distance is made from a material of a significantly different expansion rate. See 3.1.3.1. 2.4.3 Heat aging If a plastic material is subjected to an elevated temperature for an extended period of time, its properties at the end of the period may be degraded from those before

49、 the high temperature exposure. 2.5 Effect of moisture A change in moisture content can act in a manner similar to a change in temperature in its effect on strength, deformation and expansion. Materials vary considerably in their moisture absorption, making this influence more significant in some materials than in others. 3 Gear operating conditions and related material properties In order to evaluate a material for a specific gear application, the operating conditions should be recognized along with