Section 9 Spur Gear Design

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Part 9 Spur Gear Design Pinion Gear

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Lecture Steps: Quick survey, outfit geometry (Chapter 8) Transmitted burdens (overhead) Review bowing anxiety, twisting anxiety number, St, suitable bowing anxiety number, Sat and balanced admissible bowing anxiety number, S'at . Audit contact stretch number, Sc, passable contact push number, Sac and balanced admissible contact push number S'ac . Review outfit outline steps. Example(s) equip plan!! present

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Quick audit: Bending Stress No: Required Allowable Bending Stress No: Contact Stress No: Required Allowable Contact Stress No:

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Steps for Gear Drive Design: From plan necessities, distinguish speed of pinion, n P , wanted yield speed of rigging, n G , and energy to be transmitted, P. Pick kind of material for the apparatuses (steel, cast press, bronze, and so on.) Determine over-burden consider, Ko , utilizing table 9-5 Calculated P des = K o P and compute a trial esteem for the diametral pitch, P d (for steel utilize Figure 9-27). Note diametral pitch must be a standard size (see Table 8-2). Note, as P d diminishes, tooth estimate builds along these lines cutting down St and Sc. In any case, .. As P d increments, # teeth increments and apparatus prepare runs smoother and quiter and the drive gets littler also!

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Steps for Gear Drive Design: Specify N p and N G to meet VR prerequisite. Figure focus separate, D, OD to ensure there aren't any impedance issues. Determine confront width utilizing suggested extend: 8/Pd < F < 16/Pd. Expanded, confront width lessens St and Sc yet consider arrangement calculate. Confront width is regularly under 2X Dp . Figure transmitted load, Wt, pitch line speed, vt , quality number, Qv , and different variables required for computing bowing anxiety and contact stretch. Figure St and required Sat. Does material in 2 meet Sat #? No – then select new material or characterize new geometry (step 4). In the event that yes, keep on 9. Ascertain Sc and required Sac. Does material in 2 meet Sac? No – then select new material to meet Sac and Sat or characterize new geometry (step 4). On the off chance that yes, keep on 10. Compress plan

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Problem # 9.61 An apparatus combine is to be a part of the drive for a processing machine requiring 20 hp with the pinion speed at 550 rpm and the rigging rate to be somewhere around 180 and 190 rpm. Given: Driven = Milling Machine Power = 20 hp Pinion Speed = 550 rpm Output Speed = 180 - 190 rpm ≈ 185 rpm Continuous Use = 30,000 hours Find: Compact Gear Design

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Solution: Design Power: Assume: Light Shock Driver and Moderate Shock Driven Ko = 1.75 ( Table 9-5, page 389 ) P Design = (Ko)(P Input ) = (1.75)(20hp) = 35hp

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Trial Size Pick Sizes Pd = 5 T/in Dp = 4.80 in DG = 14.2 in Np = 24 teeth NG = 71 teeth Check physical size!!

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Center Distance Pitch Line Speed Tangential Load Note: Use Input Power Here as Ko is connected Later! Confront Width

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Assumptions: Design Decisions Quality Number, Q v = 6 (Table 9-2, Page 378) Steel Pinion Steel Gear More exactness, higher quality number! C p = 2300 (Table 9-9, Page 400) Softer material, more relative twisting, in this manner contact zone increments and stretch declines

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Geometry Factors Pinion: J P = .36 Gear: J G = .415 Figure 9-17, Page 387

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Geometry Factors Cont… Page 402 I = .108

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Load Distribution Factor Equation 9-16, Page 390; Equation is understood on next slide Page

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Load Distribution Factor Cont… Size Factor Page 389 k s = 1.0 since P d ≥ 5

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Rim Thickness Factor Page For this issue, indicate a strong apparatus clear K B = 1.00 K B = 1.00 for m B = 1.2 or bigger

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Rim Thickness Factor Cont… We are expecting a strong rigging clear for this issue, however in the event that not then utilize: Min Rim Thickness = (1.2)(.45 in) = .54 in Min go down proportion

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Safety Factor S F = 1.25 (Mid-Range) Hardness Ratio C H =1.00 for early trials until materials have been determined. At that point change C H if noteworthy contrasts exist in the hardness of the pinion and the rigging. Unwavering quality Page 396 K R = 1.5 (for 1 in 10,000 disappointments)

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Dynamic Factor K v Page 393

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Dynamic Factor Cont… K v Q v originates from Figure 9-21 K v can be ascertained like in above conditions or taken from Figure 9-21. Conditions are more precise.

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Design Life N cp = (60)(L)(n)(q) L = 30,000 hours from Table 9-7 n = 550 rpm q = 1 contacts N cp = (60)(30,000 hours)(550 rpm)(1 contact) = 9.9x10 8 cycles N cG = (60)(30,000 hours)( 185.92 rpm)(1 contact) = 3.34656x10 8 cycles

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Stress Cycle Factors Page 395

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Stress Cycle Factors Cont… Page 403

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Bending Stress Numbers Pinion: Gear:

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Required Bending Stress Allowable:

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Contact Stress Number

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Required Contact Stress Allowable: Pinion: Gear:

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Hardness Numbers BENDING (Grade 1) Page 379 Pinion Bending S atp = 34,324.5 psi = HB 270 Gear Bending These anxieties are OK S atG = 28,741.9 psi = HB 215 Go to informative supplement A3 or A4 and spec out material that meets this hardness necessity! Illustration AISI 1040, Temper at 900 F

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Hardness Numbers CONTACT (Grade 1) Page 380 Pinion Contact S acp = 261,178 psi Gear Contact These Stresses are too HIGH! Qualities are off table! S acG = 245,609 psi

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Summary of Problem Contact anxieties are too High. Must repeat until stretch are sufficiently low until a usable material can be found. NOTE: Contact Stress for the most part controls. In the event that material can't be found for bowing, contact push is too high! Emphasize! Diminish P d and increment F Excel is a GREAT apparatus to use for these Iterations. This issue illuminated after third cycle utilizing Excel

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Guidelines for Adjustments in Successive Iterations. Diminishing the numerical estimation of the diametral contribute comes about bigger teeth and by and large lower stresses. Additionally, the lower estimation of the pitch for the most part means a bigger face width, which diminishes stretch and builds surface strength. Increment the measurement of the pinion diminishes the transmitted load, by and large brings down the burdens and enhances surface sturdiness. Increment the face width brings down the stretch and enhances surface toughness however less effect than either the pitch or pitch distance across. Gears with increasingly and littler teeth tend to run more easily and unobtrusively than riggings with less and bigger teeth. Standard estimations of diametral pitch ought to be utilized for simplicity of make and lower cost (See table 8-2). Utilize high compound steels with high surface hardness – brings about the most reduced framework yet the cost is higher. Utilize gears with great number, Qv – includes cost however brings down load dispersion figure, Km. The quantity of teeth in the pinion ought to be as little as could be expected under the circumstances to make the framework minimal. Be that as it may, the likelihood of obstruction is more noteworthy with less teeth. Check Table 8-6 to guarantee no obstruction will happen.