Optimization of Operating Hardening Parameters and Hence Hardness Profile of Traction Gears

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 2, Issue 12, December 2012)

430

Optimization of Operating Hardening Parameters and Hence

Hardness Profile of Traction Gears

Mr. Pramod Singh

1

, Mr. Rohit Rajvaidya

2

, Pankaj Kumar

3

1

Deputy Manager, Bharat Heavy Electricals Limited, Bhopal

2_{Asst. Professor, Department of Mechanical Engineering, UIT, Barkatullah University, Bhopal} 3_{Student, Master of Technology, Department of Mechanical Engineering, UIT, Barkatullah University, Bhopal}

Abstract – Bharat Heavy Electricals Limited (BHEL), Bhopal manufactures a wide variety of traction equipment for railway , viz action motors, alternators and generators. The heavy duty gear wheels and pinions, used in various types of traction motors ( viz165 , 253 BX/AZ , TM4939 etc ), are manufacture by BHEL . The manufacturing procedure of gear wheels include hardening to 415 HV minimum. The gear wheels were being hardened by conventional hardening process know as water Quenching process. This include heating of gear wheels quenching and tempering to achieve the required hardness. BHEL Bhopal at present is manufacturing 1500 to 1800 traction heavy duty gears per annum. Heavy duty gears usually work under most severe conditions as such the gears should possess high strength and good wear resistance. But in actual practices some difficulties arise while hardening process such as non-uniform hardness and hence cracking of gears, non-uniform temperature profile, distortion of teeth, etc. Optimization here refers to the experimental analysis according to which it was found economical and productive to switch over to induction hardening of gears instead of conventional hardening. The various pros and cons were analyses and finally induction machine has been imported and commissioned .The induction hardening resulted in hardening of gear flanks in the range of 44 to 52 Rc and a case depth of 1.5 to 3 mm. The operating parameters under consideration for hardening were Operation frequency, A.C power, Heating time and Temperature.

Keywords- Optimization, Hardness profile, Traction Gears, Wear Resistance, Strength, Hardness Pattern.

I. INTRODUCTION -TRACTION GEARS

As evident by its name the term traction gear is concerned with relative load carrying capacity or traction for a given size of the gear. The load capacity is the permissible horse-power or torque of the pinion or of the gear wheel . The load capacity is limited either by consideration of surface stress ( conventionally referred to as wear or the bending strength ). Heavy duty gears usually work under most severe conditions of service and hence it is mandatory that they should posses following properties –

1. High strength

2. High wear resistance

Heavy traction gears manufactured by BHEL for type 165 motors and 253 BX/AZ motors along with their specifications are shown in table 1.1.

Specification BX 253 AZ TYPE 253

No. of Teeth 65 91 92

Form Special Special Special

Module 11.25 7.094 7.094

Pressure Angle 20 25 25

Tooth Thickness 14.68 8.71 8.71

Depth (mm) 7.455 4.67 4.67

Chord Diameter (mm)

224.03 263.805 268.00

Base Circle Dia. (mm)

689.526 585.053 591.05

Table 1.1 – Specifications of gears manufactured by BHEL.

material for traction heavy duty gear

BHEL mainly use plain carbon steels for manufacturing traction heavy duty gears . The properties of steels vary rather widely depending on composition and heat treatment . Some interesting general principle can be noted which are :-

1. The steel used for gears contain carbon varying from 0.2 to 0.6 % .

2. All the steel could be heat treated to obtain desired hardness.

3. All the steel except AISI 1020 could be heated to 350 BHN.

4. The hardness of a steel is generally a function not of its composition but of its heat treatment.

5. It is true that the max. obtainable hardness for a given steel is determined by its composition. 6. The UTS of steel is a very direct function

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7. The yield strength of steels tends to range

from above 60 % of TS in a low hardness steels to 90 % of the TS for a high hardness steel .

II. SPECIFICATION OF GEAR MATERIAL

BHEL uses plain carbon steel to manufacture traction gear of 165 motors , 253 BX/AZ motors. The specification of material is as per BHEL specification number AA19335 which is nearly equivalent to IS:2004 CL-4 & JIS-G-4051 grade S 45- C . The mechanical properties of material and their values are being shown in table 2.1.

Mechanical Property Value Ultimate Tensile Strength 63 kgf/sq.mm

Yield Point 32.63 kgf/sq.mm

[image:2.612.66.269.394.470.2]

Hardness 170 – 210 BHN

Table 2.1 – Mechanical properties of material of gears

The constituent percentage in the material used for gears has been shown in table 2.2.

S.No. Element MIN % MAX %

1 Carbon 0.42 0.48

2 Silicon 0.10 0.30

3 Magnesium 0.45 0.75

4 Sulphur 0.04 0.04

5 Phosphorous 0.04 0.04

Table 2.2 – Constituent percentage in material

III. MANUFACTURING PROCEDURE FOR TRACTION

HEAVY DUTY GEARS

Forged blanks are received in normalize condition from various indigenous / foreign suppliers . After acceptance of blanks the manufacturing procedure of traction gear is as follows :

1. Rough turning 2. Finished turning 3. Teeth cutting

4. Trimming and stamping 5. Heat treatment

6. Shot blasting 7. Turning

8. Bore grinding 9. Teeth grinding 10. Testing

IV. OBJECTIVE

The objective of this thesis is

1. To study and optimize the operating parameters of induction hardening , so as achieve the required hardness profile in gear wheels .

2. To compare the convention hardening ( i.e. water quenching ) process to induction hardening process with regards to durability and serviceability of gear . Since heavy duty gear wheels are subjected to various severe stresses , the servicibility of gear wheels can be determined only after these have been out in actual operation . However since the actual service results of water quenching gear are entirely satisfactory , the comparison of hardness profile of the two type of gear i.e. water quenching gear and induction gears serve the purpose of determine the durability and servicibility .

In order to optimize the operating parameters for induction hardening , various trials were conducted by varying the operating frequency , the heating time , temperature , the % of power input etc . Finally by hit and trial runs ,when the results seemed to be satisfactory the gear wheels were subjected to hardness and crack detection tests . Further more gears wheels were induction hardened at the optimized parameters , so as to observe the repeatability and capability of induction hardening process .

V. EXPERIMENTAL SETUP

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Courtesy: BHEL, Bhopal

VI. RESULTS

1. Hardness pattern on tooth of water quenched gears

Sample No. 1 (A8261)

S.no. Crest (mm) Flank (mm)

1 0.5 530

2 1.5 511

3 2.5 479

4 3.5 475

5 4.5 420

6 6.0 380

7 7.0 350

8 8.0 300

9 0.5 516

10 1.5 492

11 2.5 466

12 4.0 400

13 5.0 360

[image:3.612.62.277.129.336.2]

14 6.0 320

Table 6.1 - Hardness Pattern of A8261 (Sample no. 1)

Sample No. 2 (A79000)

S.no. Crest (mm) Flank (mm)

1 3.4 509

2 5.0 499

3 6.7 436

4 8.3 387

5 9.8 326

6 11.7 321

7 13.7 308

8 0.7 527

9 1.9 514

10 3.4 459

11 4.7 325

12 7.5 293

13 1.6 511

[image:3.612.353.537.154.347.2]

14 2.8 511

Table 6.2 - Hardness Pattern of A79000 (Sample no. 2)

Optimization

The parameters which govern the hardness profile of induction hardening are as follows -

1. Induction coil 2. Operating frequency 3. Heating time & temperature 4. A.C power input

The machine has been designed to suit requirements of various traction gear. Further the inductor coil have also been supplied by the supplier of the machine so as to meet the specific requirements . Inductor coil for 165 traction gear is a four turn coil . Inductor coil is specific and cannot be varied trial tests for optimization have been conducted by varying .

1. Frequency 2. Power input 3. Heating time

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2. Hardness pattern on tooth of induction hardened gears

Sample no. 3

S.no. Crest (mm) Hardness (HV)

1 1.22 608

2 2.0 600

3 4.6 570

4 6.5 510

5 9.3 444

[image:4.612.340.549.127.396.2]

6 12.3 315

Table 6.3 – Hardness pattern of sample no.3 w.r.t. crest

S.no. Flank (mm) Hardness (HV)

1 1.40 571

2 2.6 566

3 5.0 475

[image:4.612.71.264.167.380.2]

4 6.7 300

Table 6.4 – Hardness pattern of sample no.3 w.r.t flank

3. Optimization of tempering cycle

Tests were conducted at various temperatures keeping time constant at 4 hrs. So temperature where subjected to side hardness tests at 4 points ( 2 point where taken on the motor side and 2 on the non motor side ) has been obtained. The test data has been shown in table 6.5 .

S.no. Temp. (oC) Time (Hrs.) Rockwell Hardness

1 220 4 55,56,56,55

2 300 4 53,52,53,53

3 320 4 49,50,51,51

Table 6.5 – Trial test data for tempering of gear wheels

Courtesy: BHEL (Bhopal, Induction Coil)

VII. CONCLUSION

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The envisaged tangible benefits are as follows - 1. Saving of over 87 lacks per annum on account

of elimination of heat treatment rejections . 2. Saving of over 4800 man-hours per annum on

account of rejection in heat treatment cycle by almost 6 - 7 hr per gear .

The envisaged intangible benefits are as follows - 1. Better , quality of gears on account of higher

and uniform hardness.

2. Increase in productivity hence increase in production rate .

REFERENCES

[1 ] Johnson, F., “Metal Working and HT Manual” PAUL ELEK [2 ] Michale, G.W., “Precision Gearing” JOHN WILEY AND SONS [3 ] Chironis, “Gear Design” McGRAW HILL BOOK CO. [4 ] ASTM, “Metal Hand Book” ASTM

[5 ] Dr. Khanna, O.P., “Material Science and Metallurgy” DHANPAT RAI PUB.

[6 ] Fitzgerald, C., “Case Hardening in a Home Garage” HEMMINGS [7 ] Dudley, D.W., “Gear Hand Book” McGRAW HILL BOOK CO. [8 ] Higgins, Raymond A. (1983). Part I: Applied Physical

Metallurgy (5th ed.). Hodder & Stoughton. pp. [9 ] Roy F. Dunlap (1963). Gunsmithing. Stackpole Books.

[10 ]Davies, John; Simpson, Peter (1979), Induction Heating Handbook, McGraw-Hill

[11 ] Rapoport, Edgar; Pleshivtseva, Yulia (2006), Optimal Control of Induction Heating Processes, CRC Press

[12 ]Rudnev, Valery; Loveless, Don; Cook, Raymond; Black, Micah (2002), Handbook of Induction Heating, CRC Press

[13 ] Material science ,r.s khurmi ,Dhanpatrai pub.

[14 ]Giacovazzo, C; Monaco HL, Viterbo D, Scordari F, Gilli G, Zanotti G, and Catti M (1992).Fundamentals of Crystallography