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T E C H N I C A L I N F O R M A T I O N

H I G H - F R E Q U E N C Y I N D U C T I O N H A R D E N I N G O F T H EI N N E R S U R F A C E O F T H i N - W A L L E D H O L L O W C Y L I N D E R S

A . G . R o z h k o v , Y u . S . I v a n o v ,a n d L . I . Z a g a i n o v

UDC 621.78.5:62-434.1

Hardening in a cont inuous sequence with a one- turn inductor is the most widely used method ofhigh-f r equenc y induct ion hardeni ng of the inner surface of s lee ves and other th in-w alled hol low cyl inder s .The high power of the high-f r equenc y current is appl ied to the rela t iv ely small surfa ce of the par t , heat -ing i t to quenching tempe rat ure in 1-2 sec and permi t t in g through hardening.

With ver y ra pid high-f re quenc y heat ing and no holding i t i s poss ible to obtain aus teni te heteroge neousin i ts concentrat i on of carbon and other e lement s . Sect ions of cementi t e , fer r i t e , and carb ides may alsobe retained, resul t ing in spots of low har dne ss af ter quenching. Sel f - t emp er i ng in cont inuous sequencehardenin g of such par ts is imposs i ble , thus requir i ng an addi t ional operat ion ( temper ing) [1] . In th is casethe d isto rti on amounts to 0.6% of the di ame te r in steel s l eev es 153 mm in diame ter [2, 3].

We inves t i gated high-f r equenc y induction hardeni ngwith sel f - t empe r in g of the inner s urface of th in-walled hol low cyl inders by means of s lower one - t ime heat ing in a j ig that res ul t ed in minima l d is tor t ion.The inves t igat ions in the labo rat ory and under ma ss product ion condi t ions were made on s lee ves of s teel45 with a length of 70 mm and inside d ia met er s of 50, 75, and 85 ram, with walls 5 mm th ick. The depthof the hardened layer was 2-3 .5 ram.

The outs ide dia mete r of the s leev es had an al lowance of 0 .06 ram, and there fore the main prob lemwas to des ign an inductor with the pro per coupl ing clearan ce as wel l as the c lear ance between the s leeveand the jig.

. z ,

Fig. 1. Diagra m of apparatus forh igh- f r equency induc t ion harden -ing of hol low cyl in ders .

The s lee ves were hea ted by means of a tube generat or and amult i tu rn inductor both on the inner surface and the face of the shoulde r .The inductor 1 (see Fig. l) , 5 mm in size , was made of shaped cop-per tubing with a di ame te r of 8 1 ram. The coppe r tubing was fittedin a channel of a textol i te mandr el 2 , which also contained the spr aye rfor quenching the part. The face of the shoulde r was heate d by the topcoi l of the inductor with an outs ide diame ter 2-3 mm l arg er than thatof the shoulde r . The dis tance between the upper turn of the inductorand the fol lowing s ix turns used for heat ing the inner surface was se-lecte d so as to prevent overhe at ing the shar p edge of the s leeve , andwas 11-12 mm. The dis tance between the other turns of the inductorand between the inductor and the piece was 2-3 ram. The s le eve ispos i t ione d f ree ly in the sp ecia l j ig 4 and is drawn onto the inductor .

To obtain even hardenin g the maxim um clea rance Areax mustensure contact between the outs ide of the s leeve and the inner surfaceof the jig on heati ng of the slee ve to a tem pe ra tu re below Ac 1. Thus,the s leeve and the j ig can be reg ard ed as a th ick- wall ed cyl ind er inwhich heat flow f rom the inner su rface is ens ured by the rmal conduc-t iv i ty .The opt imal c lea ranc e A ensur ing min imal d is tor t io n of the s leeveaf ter hard ening can be dete rmin ed only by solving the ela s t ic - - p las t ic

Pav lodar Tra c to r P lan t . Trans la te d f rom Meta l loveden ie i Term i ches k aya Obrabo tka Meta l lov ,No. 10, pp.6 9-7 1, Octo ber, 1970.

9 1971 Consultants Bureau, a division of Plenum Publ ishing Corporat ion , 227 West 17th Stree t , New York,N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever withoutpermission of the publisher. A copy of this article is available from the publisher for $15.00.

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T A B L E I

E>

i

50,4

75,6 0,290

o.d. of sleeve after hardening, "ram

[ 0,1560,4 0,16

0,14

w a hmiddle end

0,3487,8 0,35

0,33

87,6 0,240,280,23

Note: The numerators andmeter of the sleeve,

-w ~outmiddle end

60,120. . . . I I - -6 0 , 0 7 0 6 0 , 0 8 5 6 0 , 1 0 0 6 0 , 1 5 6 0 , 2 0

0,24 60,120 60,120 60,125 - -60,100 60,075 60,095 60,I7 59,951

60,075 60,20 60,160,075 60,06560,120 60,09087,115 87,12587,080 87,10587,140 87,14087,115 87,10097,040 87,04087, i40 87,095

denominators are

60,10087,50

8 T A

Depth of hardening,mm~ithout with

2,0f i lm87,130

87,11087~ -- - -87,145 87,25 87,6587,10587 ~ - - - -87,050 87,16 87,3377,105

the lowest and highest values of the outside dia-

problem, taking into account the therm al and struc tural s tre sses occu rring in heating and cooling. Theoptimal cle ara nce for the sle eve with an inside diam ete r of 50 and 75 mm, calcu lated fro m data in [2, 4, 5],amounts to 0.195 and 0.290 mm. The variat ion of the distort ion after harde ning is less than the deviationfrom the optimal clear ance between the sleeve and the jig. More precise calculation of the distortion ofthe sleeve and the jig [4] indicates that this phen omenon is due to harde ning of the slee ve during el as ti c-plastic deformation and also to variation of the deformation of the jig with changes in the cle arance .

The distortion in the outside dia meter of the sleeve after high-fre quency induction hardening is givenin Table 1. The large "swelling" of the sleeve at the end (with the same depth of hardening) is evidentlydue to the end effect, the magnitude and princ iple of which arc d esc rib ed in [2,4].

As the result of the investigations at the Pavloda r Tra cto r Plant, high-fre quency induction hardeningof the inner surface and face of the shoulder with self -temp erin g of six different sle eves was introduced in1967 in place of the continuous sequen ce hardeni ng pre viou sly used. The new technique has red uce d theheating tim e of the sleev es by a facto r of 1.5-2, redu ced temp erin g and final grinding of the outer s urfa ceof the slee ves after ha rdenin g, and res ult s in a har dne ss of at least HRC 56 in slee ves of steel 45.

The sleeves are heated from a tube generator with a power of 100 kW and quenched in a water spray.The heati ng and cooling time s depend on the dimension s of the piece (inside d iam ete rs of 50, 60, 70, 75,and 85 ram; 70 mm long; wall thickness of 5-6 ram) and are controlled by relays, resulting in no more than0.05% distortion in mass production with the optimal clearance between the sleeve and the jig.

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I n t h e c o u r s e o f m a s s p r o d u c t i o n t h e i n s i d e d i a m e t e r o f t h e j i g i n c r e a s e s t o a s i z e a t w h i c h t h ec l e a r a n c e b e t w e e n t h e j i g a n d t h e s l e e v e n o l o n g e r e n s u r e s d i s t o r t i o n o f t h e s l e e v e w i t h i n t h e a l l o w a b l el i m i t s , w h i c h i s d u e t o t h e r m o c y c l i c d e f o r m a t i o n o f t h e j i g . J i g s w i t h a w a l l t h i c k n e s s o f 2 0 m m a r e r e -p l a c e d e v e r y 3 0 , 0 0 0 h a r d e n i n g c y c l e s w h e n u s e d f o r s l e e v e s o f t h e t y p e i n d i c a t e d . A c l e a r a n c e b e t w e e nt h e s l e e v e a n d j i g o f o v e r 0 . 4 m m f o r s l e e v e s 6 0 m m i n d i a m e t e r a n d o v e r 0 . 6 m m f o r s l e e v e s 7 5 m m i nd i a m e t e r n o l o n g e r e n s u r e s e v e n h a r d e n i n g d u e t o l o c a l i n c r e a s e s i n t h e d e p t h o f h a r d e n i n g , i n c l u d i n gt h r o u g h h a r d e n i n g . I n t h i s c a s e t h e d i s t o r t i o n o f t h e s l e e v e e x c e e d s 0 . 2 % .

O n e - t i m e h a r d e n i n g o f t h e s l e e v e s w i t h o u t t h e u s e o f t h e j i g , e v e n w i t h h e a t i n g f r o m a t u b e g e n e r a t o ro f 2 0 0 k W p o w e r , a l w a y s l e a d s t o t h r o u g h h a r d e n i n g i n t h e m i d d l e o f t h e s l e e v e ( i n s t e a d o f t h e 2 - 3 . 5 m ms p e c i f i e d ) a n d d i s t o r t i o n o v e r t h a t a l l o w a b l e .

C O N C L U S I O N SWe demonstr ated the possibili ty of high-quality hardening with self -tem peri ngof the inner surface

of thin-walled hollow cylinders by means of slower one-ti me heating, resulting in no more than 0.5% dis-tortion of the dia meter and even hardening to a given depth.

1 .

2 .

3 .

4 .5 .

L I T E R A T U R E C I T E DK . Z . S h e p e l y a k o v s k i i , S e l f - T e m p e r i n g i n H i g h - F r e q u e n c y H a r d e n i n g [ i n R u s s i a n ] , M a s h g i z , M o s -c o w ( 1 9 5 5 ) .G . F . G o l o v i n a n d M . M . Z a m y a t i n , H i g h - F r e q u e n c y H e a t T r e a t m e n t [ i n R u s s i a n ] , M a s h i n o s t r o e n i e ,M o s c o w - L e n i n g r a d ( 1 9 6 8 ) .M . F . A l e k s e e n k o a n d A . S . L i v s h i t s , I n d u c t i o n H e a t i n g i n H e a t T r e a t m e n t o f S t e e l [ i n R u s s i a n ] ,O b o r o n g i z , M o s c o w ( 1 9 5 3 ) .V . V . A b r a m o v , R e s i d u a l S t r e s s e s a n d D i s t o r t i o n i n M e t a l s [ i n R u s s i a n ] , M a s h g i z , M o s c o w ( 1 9 6 3 ) .H a n d b o o k o f M a c h i n e C o n s t r u c t i o n M a t e r i a l s , V o l . 1 [ i n R u s s i a n ] , M a s h g i z , M o s c o w ( 1 9 5 9 ) .

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