General Design Principles for DuPont Engineering Polymers - Module

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Unidirectional Ribbing Curves have been developed which compare by means of dimensionless ratios, the geometry of flat plates and unidirectional ribbed structures of equal ridigity. The thickness of the unribbed wall, typically, would be based on the calculations an engineer might make in substituting plastic for metal in a structure that must withstand a specified loading. When the wide, rectangular cross section of that wall is analyzed, its width is divided into smaller equal sections and the moment of inertia for a single section is calculated and compared with that of its ribbed equivalent. The sum of the small section moments of inertia is equal to that of the original section. The nomenclature for the cross-section are shown below: t = T – 2H Tanα A (area) = BW + H (T + t) 2 Wd = Thickness for deflection Ws = Thickness for stress To define one of the smaller sections of the whole structure, the term BEQ is used. BEQ = total width of section = B number of ribs N Based on the moment of inertia equations for these sections, the thickness ratios were determined and plotted. These calculations were based on a rib thickness equal to 60 percent of the wall thickness. The curves on Figures 4.10 and 4.11 are given in terms of the base wall thickness for deflection (WD/W) or thickness for stress (WS/W). The abscissae are expressed in terms of the ratio of rib height to wall thickness (H/W). The following problems and their step by step solutions illustrate how use of the curves can simplify deflection and stress calculations. t a° T B B H W Wd - Ws 28 Problem 1 A copper plate (C), fixed at one end and subject to a uniform loading of 311.36 newtons (70 lb), is to be replaced by a plate molded in Delrin ® acetal resin (D). Determine the equivalent ribbed section for the new plate. Flex modulus (E) for copper (C) = 107600 MPa (15,600,000 psi) Flex modulus for Delrin ® acetal resin (D) = 2830 MPa (410,000 psi) 254 mm (10 in) 311.36 N (70 lb) 3.8 mm (0.15 in) 101.6 mm ( 4 in) The wall thickness for a plate in Delrin ® acetal resin with equivalent stiffness is calculated by equating the product of the modulus and moment of inertia of the two materials. E 3 3 c × Wx = ED × WD WD = 12.8 mm where: Ec = Modulus of Copper ED = Modulus of Delrin ® acetal resin Wx = Thickness of Copper WD = Thickness of Delrin ® acetal resin Since a wall thickness of 12.8 mm (0.50 in) is not ordinarily considered practical for plastic structures, primarily because of processing difficulties, a ribbed section is recommended. Therefore, assume a more reasonable wall of 3.05 mm (0.12 in), and compute for a plate with nine equally spaced ribs. WD = 12.8 = 4.20 W 3.05 BEQ = B = 101.6 = 11.28 BEQ = 11.28 = 3.70 N 9 W 3.05 From the deflection graph (Figure 4.10) we obtain: H = 5.5 H = 5.5 × 0.12 = 0.66 W From the stress graph (Figure 4.11) for H = 5.5 W and BEQ = 3.70 we obtain: W Ws = 2.75 Ws = 2.75 × 3.05 mm = 8.39 mm W
Determine the moment of inertia and section modulus for the ribbed area. I = BW3 D = 101.6 × 12.8 3 = 17,755 mm 4 12 12 Z = BW 2 s = 101.6 × 8.392 3 = 1192 mm 6 6 Maximum deflection at the free end: δ max = FL3 = 311.36 × 2543 = 12.7 mm 8EI 8 × 2824 × 17755 Maximum stress at the fixed end: σ max = FL = 311.36 × 254 = 33.17 MPa 2Z 2 × 1192 Since Delrin ® acetal resin has a tensile strength value of 68.9 MPa (10,000 psi), a safety factor of 2 is obtained. Problem 2 Determine deflection and stress for a structure as shown made of Rynite ® 530 thermoplastic polyester resin. 667.2 N (150 lb) 508 mm (20.0 in) Substitute the known data: BEQ = B = 61.0 = 15.25 N 4 BEQ = 15.25 = 5 W 3.05 H = 18.29 – 3.05 = 15.24 H = 15.24 = 5 W 3.05 61.0 mm (2.4 in) 1.83 mm (0.072 in) 1¡ 3.05 mm (0.12 in) 18.29 mm (0.72 in) 29 From the graphs: WD = 3.6 W Wd = 3.6 × 3.05 = 10.98 mm Ws = 2.28 W Ws = 2.28 × 3.05 = 6.95 mm I = BW d 3 = 61.0 × 10.98 3 = 6729 mm 4 12 12 Z = BW s 2 = 61.0 × 6.95 2 = 491 mm 3 6 6 δ max = 5 × WL3 = 5 × 667.2 × 508 3 = 18.8 mm 384 EI 384 × 8963 × 6729 σ max = WL = 667.2 × 508 = 86.29 MPa 8Z 8 × 491 Since Rynite ® 530 has a tensile strength value of 158 MPa (23,000 psi), there will be a safety factor of approximately 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: Example 1 It there are no restricti
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 and 54: 9—Gear Design Allowable Tooth Ben
Page 55 and 56: Delrin ® 500. See the section on D
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
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The holder a, will have equal and o
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Calculations for Inertia Welding To
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If, for example, the angles of the
Page 97 and 98:
Welding Double Joints The simultane
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Figure 11.37 Commercial bench-type
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Heat is generated throughout the pa
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Figure 11.45 Tapered or stepped hor
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Weld strength is therefore determin
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) General Part Design The influence
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eticule in the eye piece is suitabl
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For this reason, if the strength of
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Figure 11.64A shows a variation whi
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3. Vibrations, generated either by
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If one part is only vibrated at twi
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Another joint design, with flash tr
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Figure 11.82. A linear welded motor
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B) Commercial linear and angular we
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Hot Plate Welding of Zytel ® One o
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Figure 11.94 Applications of riveti
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Tolerances may be difficult to hold
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are used in either hand- or power-o
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ather than scrape, these drills wil
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The polishing operation is performe
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General Design Principles for DuPont Engineering Polymers - Module

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