R-TR-76-044 /1/0* HEAT SETTING PROCEDURES FOR HELICAL Q COiLED SPRINGS HENRY P. SWIESKOWSKI DECEMBER 1976 FINAL REPORT RESEARCH DIRECTORATE ! ~ Approved fo~r public release; distribution unl.mdecd. "" GfRAL THOMAS J. RODMAN LAIORATORY ROCK ISLAND ARSENAL ROCK ISLAD, ILLINOS 61201 xw7777n 777m
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HEAT SETTING PROCEDURES FOR HELICAL Q … as weri the music wire springs. Test data for the chrome vat.-adjure springs are given iii tables 13 to 17. The criteria used in measuring
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R-TR-76-044
/1/0*
HEAT SETTING PROCEDURES FOR HELICAL
Q COiLED SPRINGS
HENRY P. SWIESKOWSKI
DECEMBER 1976
FINAL REPORT
RESEARCH DIRECTORATE
! ~ Approved fo~r public release; distribution unl.mdecd.
"" GfRAL THOMAS J. RODMAN LAIORATORYROCK ISLAND ARSENAL
ROCK ISLAD, ILLINOS 61201
xw7777n 777m
DISPOSITION INSTRUCTIONS:
Destroy this report when it is no longer needed. Do notreturn it to the originator.
DISCLAIMER:
The findings of this report are not to be construed asan official Department of the Army position unless sodesignated by other authorized documents.
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GZ- THOMAS J. RODMAN LABOPATORY AJ.1cM 3297.o6.7431RO-CK ISUA1D AFGENA3A, ROC ISuuND, i. 1o ___________
$1 CONJTROLLING OFFICE NAME AND ADDRESS
OCDR, ROCK ISLAND ARSENAL |/7GEN THOMAS J. RODMAN LABORATORY, SARRI-RLR ti"
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1S SUPPLEMeNTARY NOTES
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--- Various heat setting procedures for the manufacture of helical compressionsprings were in:estigated to determine optimus heat setting methods that willminimize operational spring set and load losses. Production springs werefabricated from misic wire, stainless steel and chromie vanadiun materials. Thesprings were given heat set.ing treatments under Ii>:•- ... o -t~~~~ ..... tel-t ncL1-conditions of ten-p-eratures, time durations and stress levels, Effects of the various heat setti
procedures on spring set and ý.oad reductions were evaluated by laboratory
FORMDD I jAN 73 1473 EDITION OF NOVr65 IS ODsW'F.TF R. \SSIFI
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ABSTACT - cont.
endurance tests. lecomended heat setting procedures based on study nrisultsare given for the spring materials and test conditions investigated in thisproject.
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UNCIASSIFIESECURITy CLASSIFICATION OF THI:; P.GEM(h, Dat .te Entered)
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Contents
DD Form 1473 i
Contents iii
Objectives 1
Introduction 1
Discussion 1
A. Material and Heat Setting Treatments 1
B. Test Procedures and Results 3
Conclusions 4
Recommendations 4
Appendix 6
Distribution Si
•i- iii
OBJECTIVES
The objectives of tnis program were to evaluate varioc:s heat set-ting procedures and to determine the most beneficia& procedi•es to min-imize operational set and load losses of helical cor')'ession springs.
INTRODUCTION
The ad-rantages of presetting (also called cold setting or scragging)of springs have been recognized for some time. This operation inducesbeneficial residual stresses viithin the spring material vhiLh increasesits elastic limit and load capacity. This prmcedure consists of coilingthe spring to a length somevbat greater than the f.vee length desired andthen compressing the spring beyoad the elastic limit. Figure 1 in theAppendix shows a typical load deflecticn d.'•.ram thus obtained.' PointP, represents the iritial elastic limit and P2 the maximum load durirgthe operation. On unloadine the spring, th;., load drops along the dasbedcurve which is essentially a straight li., wnd same set occurs. Onreloading, the resultant elastic limit is zraised to point ; which i.sconsiderably higher than the original %alu- R , Presetting is a strainhardening operation that allows the use of .higher design stresses, butit also adds another step to the manufact\Jfi-ýg process.
Similar to presetting of springs, heaL ,,etting also induces favor-able residual stresses within the wire :r,%eri-l] however, the stresspattern produced is deeper and more permaeent, and thus dill providesprings that are more resistant to setting. Heat setting differs frompresetting in that the springs are compressed on fixtures to a speci-fied stress level and then subjected to a pescribed tcmperature whilecompressed for the required time. A spring so treated will take somepermanent set depending on the severity of the stress level and tez oera-ture used in the heat set"ting operatioý,. lifwcver, if the spring aeaignand the heat setting procedure are correct, the completed spring willmeet the desired specifications and will not take appreciable set insubsequent service. In this study, relatively low heat setting temp-atures were applied because the subseqient evaluation endurance testswere conducted at ambient temperatures.
DISCUSSION
A. Material and Heat Settin• Treatments
The helical compression springs that were used in this programwere fabricated from the following spring tempered materials and giventhe specified stress relieving treatments.
'Wahl, A.M., Mechanical Springs, M -aw-Hill Book Company, Inc.,New York, New York, 1963.
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1i) Music Wire, QQ-9-JM7
•r 'Wire diameter = 0.043 iALChStress relieve: Heat at 450'+ 100 for 30 minutes
2) Stainless Steel, QQ-W-423, Comp. FS302Wire diameter = 0.043 inchStress relieve: Heat at 8000 F + 250 for 30 minutes
3) Chrome Vanadium, QQ-W-412, Comp. 1Wia di.ameter = 0.043 inchStress relieve: RTeat at 7000 F + 200 for 30 minutes
One basic spring design wns used in this pv.,gramm; detail specificationsfor this design are given in the Appendix. One hundred and thirtysprings were fabricated from each materia2 end thress relieved in ac-cordance with the abvcye instructions. Each group of one bhndred andthirty springs were divided into thirteen sets of ten uprings each andgiven the following heat setting procedures.
Springs compressed to a stress level of 100,000 psi
Set No. Temperature(OF) Tine at teMpemature(min.)1 200 302 200 603 300 304 300 6o5 400 306 400 60
SprIngs cn.pr3Lssed to a stress level of 150,000Li
Set No. Temperature(°F) Time at tmuperature(rin.)7 200 308 200 6o9 300 30
10 300 6011 4oo 3012 400 6013 Contro~led set - no heat setting applied
The springs were compressed on suitAble fixtures to the prescribedstress levels and then secured at that compressed height. They werethen subjected to the specified temperature for the required time-period. The above stress values are uncorrected and correspond to thefollowing conpressed spring heights.
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For music wire and chrome vanadium materialsc) 100,000 psi corresponds to 1.580 inchesb) 150,0O0 psi corresponds to 1.020 inches
For stainless steel materiala) 100,000 psi corresponds to 1.470 inehesb) 150,000 psi corresponds to .860 inches
It was required that all wire material used in this program be frAefrom surface irý.egularities. Prior to coiling, the material was ex-amined thoroughly with the txid of a microscope. No cracks or surfacedefects were observed and the material was accepted for winding sprinr3.
B. Test Procedures and Results
Test fixtures *.ere designed end fabricated to endurance test thesprings on the Krouse spring tester. A photograph of a heat set springassembled onto the tester is shown Ln Figure 5 in the Appendix. Someexperimentation in the enturance testing was necessary in order toestablish the proper test conditions for the working stress levelsand cynlic frequency which would produce spring set with the minimunamount of sprirg breakage. It was determined that the music wire springsshould be cycled between the heights of 2.500 and 1.000 inchee whichcorresponds to stress levels of 18,000 psi and 152,000 psi respectively;and at a frequency of 1275 cycles per minute. Springs were cycled fora total of 50,000 compressions with measurements taken of the freeheights and spring loads periodically during the test.
Load at 2.500 iaches and free height measurements taken on theindividual music w- re springs before and after 50,000 compressioncycles are shown in tables 1 to 6 in the Appendix. Test results of onlyfour springs are given for set 1 because six springs from this set wereexpended to establish the stress and frequency test conditions. Fewerthan 10 springs are also listed in some of the other sets, due to springbreakage that occurred before the completion of 50,000 cycles.
The stainless steel springs were endurance tested between thehe-.ghts of 2.200 and 1.000 inches which cormesponds to stress levels of41,000 psi and 139,000 psi respectively; and at a rate of 1000 cycles
per minute. Three springs each from sets 2 and 6 were used to establishthe test conditions. Measured free height and load measurements takenon the springs before and after cycling are shown in tables 7 to 12.Five springs each from sets 9 and 10 were tested since this samplewas considered sufficient to provide adequate data to assess springcharucteristics.
The chrome vanadium springs were endurance tested under the same con-ditiona as weri the music wire springs. Test data for the chrome vat.-adjure springs are given iii tables 13 to 17.
The criteria used in measuring the amount Of spring set are theload at a particular compressed height and the change in free height.The spring load (at 2.500 inches) is considered a more practical andmeaningful method to measure set for this project. Some of the heat
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setting procedures that were used proved to be too severe for the springmaterial and produced an excessive set. In s(ne cases, the resultantfree height after the heat setting operation was less than 2.500 inches;this occurred with the heat setting procedures that were performed ata stress level of 150,000 psi and at the maximum temperature. Ex-cessive set as a result of the heat setting treatment occurred to sets11 and 12 of the music wire and stainless steel springs as well as tosets 9 to 12 of the chrome vanaditin springs. Consequently, these setswere not endurance tested because the free heights were slightly aboveor below the 2.500 value.
The average load values before and after 50,000 cycles of each setof music wire springs are shown in figure 2 in the Appendix. For eachset, the left bar column represents the average load before the endur-ance test and the right bar coltmn indicates the average value after the50,000 compressions. Similarly, the average load values for the stain-less steel and chrome vanadiim spring sets are depicted in figures 3and 4 respectively.
CONCLLUIONS
A review of figure 2 shows that the heat setting procediute that ismost effective for music wire springs to minLaize load loss due tooperational set is the procedure that was applied to set 1 (i.e. stresslevel = 100,000 psi, temperature = 200OF and time = 30 minutes.) Thefinal load after testing for set 1 is twice as large as the final loadfor the untreated set 13. The heat setting procedures that were givento sets 2 and 7 were almost equally beneficial since these springssustained a high load level.
Figure 3 shows that all the heat setting treatments that were per-formed at a stress level of 100,000 psi aided to increase the durabilityof the stainless steel springs. However, the treatments that were appliedto sets 1. and 4 provided the best results.
The benefit derived from heat setting by the chrome vanadiumsprings is rather minimal as naa be observed from figure 4. The heatsetting procedure that is related to set 1 induced the most favorablestrength properties.
Load retention property of music wire springs is benefitted moreby heat setting than those of stainless steel or chrome vanadium springs.
Generally, the difference in heating times of 30 minutes and 60minutes had little effect on spring :oad dxrability.
Test results shorw that of the three temperature values that wereused in this study, the t -mperature of 2000F produced the most favorableresults. However, it is possible that a somewhat ltwer temperature mayproduce an even higher re,-istance to sprin• set. Li;qitations on fundsand material precluded the evaluation of other temperature variables.
should be applied to the following materials and operating conditions:
Music wire and chrome vanadium materialsWire size approximately .043 inchStress range of 18,0OC psi to 152,000 psiLoading frequency 1275 cycles per minute
Stainless steel materialWire size approximatelz .043Stress range 41,000 psi to 13",000 psiLoadirg frequency 100C cycles per minute
2. Temperatures in the ra ige of 100OF to 200OF should be investigatedif a further study on ieat setting procedure is conducted.
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Appendix
Figure 1 - Load Deflection Diagram of Spring During PresettingSpecifications - Heat Set SpringTable 1 - Test Results, Music Wire Springs, Set 1 and Set 2Table 2 - Test Results, Music Wire Springs, Set 3 and Set 4Table 3 - Test Results, Music Wire Springs, Set 5 and Set 6Table 4 - Test Results, Music Wire Springs, Set 7 and Set 8Table 5 - Test Results, Music Wire Springs, Set 9 and Set 10Table 6 - Test Results, Music Wire Springs, Set 13Table 7 - Test Results, Stainless Steel Springs, Set 1 and Set 2Table 8 - Test Results, Stainless Steel Springs, Set 3 and Set 4Table 9 - Test Results, Stainless Steel Springs, Set 5 and Set 6Table 10 - Test Results, Stainless Steel Springs, Set 7 and Set 8Table U1 - Test Results, Stainless Steel Springs, Set 9 and Set 10Table 12 - Test Results, Stainless Steel Springs, Set 13Table 13 - Test Results, Chrome Vanadium Springs, Set 1 and Set 2Table 14 - Test Results, Chrome Vanadimu Springs, Set 3 and Set 4Table 15 - Test Results, Chrome Vanadium Springs, Set 5 and Set 6Table 16 - Test Results, Chrome Vanadium Springs, Set 7 and Set 8Table 17 - Test Results, Chrome Vanadium Springs, Set 13Figure 2 - Music Wire Springs, Average Load ValuesFigure 3 - Stainless Steel Springs, Average Load ValuesFigure 4 - Chrome Vanadium Springs, Average Load ValuesFigure 5 - Heat Set Spring Installed on Endurance Tester
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SPECIFICATIONS
HEAT SET SPRING
WIRE SIZE (IN.) .043
OUTSIDE DIAMETER (IN.) .370±. 005
TO0TAL COILS 18.5
TYPE OF END6 CLOSED AND GROUND
FREE HEIGHT, APPROX. (IN.) 2.70MEAN ASSEBLEM D HEIGHT (IN.) 2.500
LOAD AT MEAN ASS&IBLED HEIGHT (LB.) 2.0 REF.
MINIMUM OPERATION HEIGHT (IN.) 1. 000
LOAD-DEFLECTION RATE (LB./IN.) 8.5
MAX.. 'UM SOLID HEIGHT (IN.) .830
SPRING HELIX L.H.
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¶Tble 1
Music Wire Springa
Se. I -Heat Set; Stress = .00,000 psi;TTemerature = 200oF; Time = .30 m.
Load at 2.500 inches (pounds) i'ree height (inches)Before test After 50,000) 3cifore test After 50,000
Set 4 - Heat Set; Stress =1I00 000 sj ;Temperature = 30 0F; ime = 60 min.Load at 2.500 inches (pounds) Free height (inches)Before test After 50,000 Before test After 50,000