General Design Principles for DuPont Engineering Polymers - Module

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Test results on gears of Delrin ® acetal resin and Zytel ® nylon resin are shown in Figures 9.02 and 9.03. Figure 9.02 is based on injection molded, continuously lubricated gears of Zytel ® 101 running against each other. Figure 9.03 is based on injection molded, continuously lubricated gears of Delrin ® 500 running against each other. The lines have been reduced 25 percent below the lines which represent actual failure of the gears on test. The tests were run at room temperature conditions. Cycle life is simply the total revolutions of the gear. Caution should be exercised in using this data for gear teeth larger than 16 pitch or smaller than 48 pitch. Since this data was based on injection molded gears running in a room temperature environment with continuous lubrication, a design factor “K,” Tables 9.01 and 9.02 should be applied to compensate for cut gears vs. molded gears, initial lubrication vs. continuous, pitch line velocity and tooth size (diametral pitch) Figure 9.02 Maximum bending stresses for gear teeth of Zytel ® nylon Bending Stress, × 1,000 psi Cycle Life, Millions Figure 9.03 Maximum bending stresses for gear teeth of Delrin ® 50 Table 9.01 Values of Design Factor K, Zytel ® P.L. Velocity, Teeth Lubrication* fpm Pitch K Factor Molded Yes below 4000 16–48 1.00 Molded Yes above 4000 16–48 0.85 Molded No below 1600 16–32 0.70 Molded No above 1600 16–32 0.50 Molded No below 1000 32–48 0.80 Cut Yes below 4000 16–48 0.85 Cut Yes above 4000 16–48 0.72 Cut No below 1600 16–32 0.60 Cut No above 1600 16–32 0.42 Cut No below 4000 32–48 0.70 * Yes—refers to continuous lubrication No—refers to initial lubrication Table 9.02 Values of Design Factor K, Delrin ® * MTL Mating Gear Teeth Material Material Lubrication** Pitch K Factor Molded 500 500 Yes 20–32 1.00 Molded 500 500 No 20 0.45 Molded 500 500 No 32 0.80 Molded 100 100 Yes 20–32 1.40 Molded 100 100 No 20 0.50 Molded 100 Hob Cut Steel Yes 20 1.20 Molded 100 Hob Cut Steel No 20 0.80 * Values based on maximum pitch line velocity of 1600 fpm. ** Yes—refers to continuous lubrication No—refers to initial lubrication variations. Thus, multiply the allowable tooth bending stress obtained from Figures 9.02 and 9.03 by “K.” In addition, the allowable tooth bending stress should be modified by the ratio of the yield strength at operating temperature to the yield strength at room temperature. Again, the effect of environment on fatigue and thermal aging must also be considered. The “K” factors in Table 9.01 are based on molded gears of Zytel ® nylon resin running against each other and cut gears of Zytel ® nylon resin running against cut gears of Zytel ® nylon resin. Zytel ® nylon resin running against steel should provide higher “K” factors because steel is a good conductor of heat and the heat buildup due to friction is less. There is no test data. However, many years experience in a multitude of steel to Zytel ® nylon resin applications would support this contention. As can be seen from Table 9.02, a higher “K” factor does exist when Delrin ® acetal resin is run against steel rather than itself with initial lubrication. It should be noted that Delrin ® acetal resin does not run against itself as well as Zytel ® nylon resin does against itself when there is little or no lubricant present. Also note that Delrin ® 100 performs about 40 percent better in gear applications than
Delrin ® 500. See the section on Delrin ® acetal resin vs. Zytel ® nylon resin for more on material selection. Pitch line velocity is determined from the following equation: P.L.V. = π Dpn 12 where: P.L.V. = pitch line velocity, fpm Dp = Pitch diameter, in n = speed, rpm Diametral Pitch—Tooth Size Once the admissible tooth bending stress has been determined, the designer can proceed with the selection of the other variables necessary to continue with the gear design; namely, face width and diametral pitch (or metric module). Nomographs have been prepared (see Figures 9.04 and 9.05) to facilitate the design procedure. Normally, the next step is to calculate the tangential force, either in Newtons or pounds, on the teeth at the pitch circle. Knowing the torque to be transmitted by the gear, the tangential force is calculated by use of the following equation: Figure 9.04 Gear nomograph (S.I. units) M (mm) F (N) f (mm) S (N/mm 2 ) 3 2.5 2 1.75 1.5 1.25 1 0.8 0.7 0.6 0.5 0.4 0.3 0.25 M M S (N/mm 2 ) = 1.7 F (N) M f (mm 2 ) f M – Module F – Load on pitch circle f – Face width S – Allowable stress Reference line f F 51 F = 2T T = 63,000 HP Dp n F = Tangential force on tooth at pitch circle T = Gear torque, in pounds HP = Horsepower transmitted Dp = Pitch diameter, in n = Gear speed, rpm The nomographs are based on a tooth form factor of 0.6, and provide completely suitable accuracy at this stage in the development of the gear. There is little point in using equations with factors having three decimal places when this is only a first and rough approach to the final gear design. Only after adequate testing of molded prototypes will the final design be achieved. Using the allowable stress and the tangential force, a line can be drawn intersecting the Reference line. At this point either the face width or the module (diametral pitch) must be known. Unless space is very critical, it is wise to choose first the diametral pitch, as this determines the size of the teeth, regardless of the pitch diameter. 2000 1000 800 600 400 200 100 80 60 40 20 10 8 6 4 2 1 0.8 0.6 2500 24 1500 22 20 900 18 700 500 16 300 90 70 50 30 9 7 5 3 14 12 10 8 6 4 2 25 50 19 17 15 13 11 9 7 5 3 40 30 20 10 9 8 7 6 5 4 3 2
Page 1 and 2:
dDuPont Engineering Polymers Genera
Page 3 and 4: 8—Gears . . . . . . . . . . . . .
Page 5 and 6: 1—General Introduction This secti
Page 7 and 8: Prototyping the Design In order to
Page 9 and 10: 2—Injection Molding The Process a
Page 11 and 12: As a general rule, use the minimum
Page 13 and 14: Figure 3.11 Cored holes Figure 3.12
Page 15 and 16: Figure 3.19 Mold-ejection of rounde
Page 17 and 18: • Zytel ® nylon resin—Parts of
Page 19 and 20: 4—Structural Design Short Term Lo
Page 21 and 22: Form of section Area A d d R R 1 1
Page 23 and 24: Table 4.03. Formulas for Stresses a
Page 25 and 26: Form of bar; manner of loading and
Page 27 and 28: Figure 4.01 Creep Stress (S), MPa (
Page 29 and 30: Figure 4.05 Creep in flexure of Zyt
Page 31 and 32: Example 1 It there are no restricti
Page 33 and 34: Determine the moment of inertia and
Page 35 and 36: Figure 4.11 Stress curves The compu
Page 37 and 38: Rim Design Rim design requirements
Page 39 and 40: Figure 5.08 Chair Seat Zytel ® 71
Page 41 and 42: Cantilever Springs Tests were condu
Page 43 and 44: 7—Bearings Bearings and bushings
Page 45 and 46: debris is moved around continuously
Page 47 and 48: Table 7.01 Coefficient of Friction*
Page 49 and 50: Figure 7.15: Connecting rod spheric
Page 51 and 52: 8—Gears Introduction Delrin ® ac
Page 53: 9—Gear Design Allowable Tooth Ben
Page 57 and 58: Figure 9.06 Sizes of gear teeth of
Page 59 and 60: The following additional examples i
Page 61 and 62: In practice, the most commonly used
Page 63 and 64: Driving Gear Meshing Gear Table 9.0
Page 65 and 66: A full-throated worm gear is shown
Page 67 and 68: Worm Material Gear Material Possibl
Page 69 and 70: 10—Assembly Techniques Introducti
Page 71 and 72: For these materials, the finer thre
Page 73 and 74: Table 10.01 Self-Threading Screw Pe
Page 75 and 76: Figures 10.07 and 10.08 show calcul
Page 77 and 78: Undercut Snap-Fits In order to obta
Page 79 and 80: Cantilever Lug Snap-Fits The second
Page 81 and 82: 11—Assembly Techniques, Category
Page 83 and 84: Figure 11.03 Drill spindle position
Page 85 and 86: Inertia Welding By far the simplest
Page 87 and 88: Machines for Inertia Welding The pr
Page 89 and 90: This is not always easy, because ap
Page 91 and 92: The holder a, will have equal and o
Page 93 and 94: Calculations for Inertia Welding To
Page 95 and 96: If, for example, the angles of the
Page 97 and 98: Welding Double Joints The simultane
Page 99 and 100: Figure 11.37 Commercial bench-type
Page 101 and 102: Heat is generated throughout the pa
Page 103 and 104: Figure 11.45 Tapered or stepped hor
Page 105 and 106:
Weld strength is therefore determin
Page 107 and 108:
) General Part Design The influence
Page 109 and 110:
eticule in the eye piece is suitabl
Page 111 and 112:
For this reason, if the strength of
Page 113 and 114:
Figure 11.64A shows a variation whi
Page 115 and 116:
3. Vibrations, generated either by
Page 117 and 118:
If one part is only vibrated at twi
Page 119 and 120:
Another joint design, with flash tr
Page 121 and 122:
Figure 11.82. A linear welded motor
Page 123 and 124:
B) Commercial linear and angular we
Page 125 and 126:
Hot Plate Welding of Zytel ® One o
Page 127 and 128:
Figure 11.94 Applications of riveti
Page 129 and 130:
Tolerances may be difficult to hold
Page 131 and 132:
are used in either hand- or power-o
Page 133 and 134:
ather than scrape, these drills wil
Page 135 and 136:
The polishing operation is performe
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General Design Principles for DuPont Engineering Polymers - Module

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