B.3.3 Plastic Parts With Integrally Molded Threads, Farbig

CA LC U L AT I O N S · D ES I G N · A PPL I CAT I O N S B . 3 .3 Plastic parts with integrally molded threads COPYRIGHT: All rights reserved, in particular for reproduction and copying, and for distribution as well as for translation. No part of this publication may be reproduced or processed by means of electronic systems, reproduced or distributed (by photocopying, microfilm or any other process), without written permission by Ticona. © 2004 Ticona GmbH, Kelsterbach NOTICE TO USERS: To the best of our knowledge, the information contained in this publication is accurate, however we do not assume any liability whatsoever for the accuracy and completeness of such information. The information contained in this publication should not be construed as a promise or guarantee of specific properties of our products. Further, the analysis techniques included in this publication are often simplifications and, therefore, approximate in nature. 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The products mentioned herein are not intended for use in medical or dental implants.ticona. 3 Deformation of the threaded section 4.2 Types of thread and key dimensions Fixed joints 3.1 notes 13 13 Self-locking Stress concentration in the 2.2 integrally molded External thread Internal thread threads 17 17 17 Movable joints 5.1 examples 10 8.4 Vehicle jack with threaded hopper Fastening nut for Grain mill spare wheel made from POM 12 9.1 Movable joints 2. Explanation of symbols 21 10. Requirements for joints with integrally molded threads Fixed joints 2. Reversible-flow filter made from Hostaform C 2521 5. 4 4 thread engaged with (zone II.2.1 Notch factors K 14 in disengaged 14 thread zone I 6.2 Stress distribution within the internal 3.1.2 Design calculations for threaded joints Fixed joints 4.1 Stress in the vulnerable cross-section 4.3 Stress concentration in the thread 6. Calculation 5. Literature 22 Hostaform Acetal copolymer (POM) Hostacom polypropylene (PP) Reinforced Hostalen PP Polypropylene (PP) Celanex Polybutylene terephthalate (PBT) = registered trademark . 10) Static the external thread 14 runout 6 6.2.2 10 Examples of applications Water filter housing 8.3 15 4.1 8.3 8. 6 with sealing of plastic components integrally molded threads 15 6 6 7 8 9 7.1.1.1 7.2 Drainage plug for water on 19 19 separator 19 20 20 Hose connector made from 11 nut diesel vehicles for corn Hostalen PPN 1060 5.2.1 4.2 3 3 3 threaded section 6.2 Flank pressure p 4.Contents 1.2 6. Injection molding of components with 7. Introduction 3 6.3 8. fig.1 Movable joints 3. Design 6. the joint must be fixed and leaktight and should be suitably designed to prevent it loosening by itself. for example. Requirements for joints with integrally molded threads The unique freedom of design afforded by injection mold ing al enables this process to be used for the production of components with integrally molded threads. valves and submersible and circulating pumps. for the fluff filter on washing machines. also known as helical gears. These threads are designed as single.g. generally to keep different materials Integrally molded threads are also used for movable joints 2. Leaktightness is achieved by integral sealing elements or additional sealing elements such as O-rings. threads are 2. Movable threaded should joints. permit smooth.1 Fixed joints The function of the above-mentioned Integrally molded used for detachable fixed joints in many different components. Examples include housing parts for washing machines and dishwashers.and multi-start. filters. fittings and screwed pipe joints. locking rings. reversing spindles in vending machines etc. In filter housings. and Once-only lubrication of the thread improves the slip properties of the mating thread and should always be carried out if possible. . C 9021 G C 9021 M. housing parts is safely apart from each other. spindle nuts on car jacks.1. Examples include valve stems. Introduction 2. C 9021 K. Single-start threads are generally self-locking with low efficiency. bottles and drums. from the modified Hostaform grades C 9021 TF. e. The addition mold complexity and cost involved in terms of the injection (for demolding the thread) is relatively small. the joint should be quick and easy to undo in order to clean or change filters. e. For this purpose. closures for packaging such as tubes. Movable joints telescopic spindles for ventilation windows. on water meters and mincers. The product of flank pressure p and speed v may not exceed certain limit values to ensure that unac ceptable heating up of the thread flanks does not occur.g.2 to convert rotary motion into linear motion or torque into linear forces and vice versa. electric rear view mirror and seat adjusting systems and central locking in motor vehicles. jolt-free transmission of motion. Good low-friction and threads wear properties are exhibited by produced. 541 P 0. Types of thread and Table 1: Comparison of important Half thread dimensions key dimensions Thread type Fixed joints Metric 13 angle Thread of thread DIN depth ß [] 3. This joints in housings to ISO thread = diameters in relation the Metric 513 3 h3 H! = buttress thread Metric ISO 103 15 = 0.5P + a H. 1: Force the sensitivity of the joint H4=0.1 30 h3 H! = 0. - Table 1 compares the half angle of thread depth H! of different thread types. = trapezoidal Whitworth thread 228 27. pipe thread H! = 0.3. 2 a: Metric ISO thread (DIN 13) F. ß and thread Q Q Q %%2 thread ///Y//////////t P .5 P risk is reduced the lower the radial force Fr and the greater the thread depth HI of the thread profile.640 P Threads The radial force Fr is proportional half angle of thread ß.613 P 0. There is a risk that the thread flights will slide over each other and the joint will therefore fail. Radial force Linear force Perpendicular force Half angle of thread HI Thread depth TÏ 1. 2: Thread types.3. The metric ISO large large half thread angles /?. 1.50P (P = thread pitch) pipe to relationships on the thread flank Metric ISO threads and Whitworth threads have comparatively trapezoidal thread and the buttress and trapezoidal threads developed for plastic containers are more favorable. This results in low inherent housing rigidity.5 0. fig. Fig. 2.75 P h3 =0. which lead Fig. fig. to the tangent of the used for preferably plastic 6063 containers buttress thread Fr A = FI tan ß (1) to trapezoidal Round thread part 1 thread part 2 405 10 10 15 c c = 0. illustration and explanation of terms Fig. FI F .5P = large thread depth reduces production tolerances. so that the inner part can be compressed under radial force Fr and the outer part expanded.868 P Threaded can have very large thread comparatively low housing wall thickness typical of injection molded parts.5P 0. radial force Fr. Q Q O o -a -o . c = DI. d DI.b: Metric buttress thread (DIN 513) Fig. d Outside diameter Root diameter c z Thread depth. 2c: Metric ISO trapezoidal thread (DIN 103) Fig. % Male thread ///////s////////////////. d| Root diameter c z Profile depth. c = Profile width P Pitch Fig. 2e: Thread preferably to be used for 6063 part plastic con tainers. dj Profile width P Pitch Fig. 2d: Whitworth pipe thread (DIN/ISO 228) Fig. 2g: Round thread (DIN 405) - -5 W//Ï. preferably to be used for plastics containers. buttress thread (DIN 1) Outside diameter D. trapezoidal thread (DIN 6063 part 2) Thread 2 f: U-P- D. the metric ISO trapezoidal (DIN 103) proved successful.2 3: Vulnerable cross-section AI and A2 Movable joints thread a non= For movable joints. fig. - = It (d32 - d. 1). 0) is From the linear force F] stress (fig. with a half angle of thread a 4. This thread also has thread pitch). however.2) ist.0524). is therefore un 4. In rare cases. 2 g has a angle of thread ß 15 and the thread = 4. 3. . ß = 3 (tan 3 = large thread depth HI = 0.The lowest. 2 where [N/mm2] (2) A.5 P is also in the range of other thread In designing threaded joints.1 Stress in the vulnerable cross-section Fig. part 21. the following account: stress para meters must be taken into stress oz in the vulnerable cross-section A^ 2 High radial forces with the risk of impermissible stresses and deformation may be expected with Whitworth pipe threads with cylindrical internal and conical external threads suitable for surface pressure loading p on the thread flanks change in flank diameters Zld2 and 4D2. (3) A2 = | (Da2-D2) (4) d3 d.. fig. practically negligible radial force Fr occurred with the metric buttress thread. which takes into the thread tooth cut over half the circumference loadbearing surface. the flank overlap H5 is only 0.1 depth H4 profiles. As a result of the special profile design.75 P (P = Design calculations for threaded joints Fixed joints The round thread favorable half = specified in DIN 405. 0. standardized flat profile (half angle of thread ß has used. 2b.0835 P so that locally high surface pressure loadings are the result. 0. This thread type plastic components. (DIN 2999). the cross-section AS n AS=" ( d2 + d3 Y ~ 4\ account as a is calculated. the following tensile results: "1 QZ = A.1 . Da D root diameter [mm] inside diameter [mm] outside diameter [mm] nominal diameter [mm] (more exact) stress According to DIN 13. this is assumed for the purpose of calculating the flank pressure p.1.2. plastic threads.1 -0. are If the calculated stress.1 0.3 F. partially crystalline plastics amorphous plastics force FB from the internal F} linear force section 4. The linear force FI is composed of and operating force FB. Thus: (same) 0. function of temperature The moment prestressing force Fv results from M according to the equation 2M the tightening Material 20 Temperature [C] 60 6 80 100 120 FV = P n +d2-fc cos [N] + (6) Hostaform C 9021 Hostaform C 9021 GV 1/30 Hostalen PPN 1060 10 40 6 3 15 2 _ _ ß dA fA 20 3 10 - _ M P tightening thread pitch [mm] moment [N mm] Hostacom M2 N02 Hostacom M4 N01 Hostacom G2 N02 8 10 12 4 5 9 10 2 3 6 7 2 14 - - - - fe fA thread friction coefficient friction coefficient of the contact 4 5 - surface Hostacom G3 N01 15 8 - d2 dA flank diameter [mm] mean diameter of the half contact surface [mm] (fig.15-0.04-0. prestressing force Fy Table 3 Oz > perm. (8) values for gives guide FI The on = FV + FB (5) tensile S has stresses as a already function of temperature been taken into account).2).. the following applies: FB pi = For the number of loadbearing thread L z P.3 -0. P = [N/mm2] H! see (9) 0. stresses long-term permissible (safety factor operating force may be an external force acting the joint or be produced by.25 z jt d2 [N]. in the diameter FI = FV + FB must be equal to or less than the permissible stress..While this is justified with metal of screws with the high material The tensile stress <7z calculated with linear force root case utilization.6) Celanex 2500 Celanex 2300 GV 1/20 Celanex 2300 GV 1/30 5 16 20 _ _ angle of thread 20 25 12 15 10 12 18 The friction coefficients fG and fA depend on a number of influencing factors such as the particular combination of mating materials.25 PCR/metal PCR/AP PCR AP 0. internal Table 3 : Permissible tensile a 0perm. in N/mm2 as pressure p.. ds is used to determine the loadbearing cross-section.4 (different) 0. J dp2 [N] (7) L dp internal pressure [N/mm2] diameter of the pressure-stressed surface [mm] P thread reach [mm] thread pitch [mm] .1 d2 HI z flank diameter thread depth [mm] flights (10) resulting operating pressure p. sliding speed and the presence or absence of lubricant. for example. fA dry PCR/PCR PCR/PCR lubricated Although the linear force FI is not uniformly distributed over the intermeshing thread flights (see section 6.2 Flank pressure p Friction Material combination coe ficient fG. the stress GZ is greater than the permissible shown loadbearing enlarged by increasing reducing the inside diameter d. cross-section AI or A must be the outside diameter Da and/or Table 2: Guide values for the friction coefficients fc and fA of unlubricated and lubricated surfaces 4 . surface roughness.15-0. Guide values in table 2.1. the thread reach L must be increased. the stress a and the deformation formula: check radial deformation of the e can be calculated by the following threaded section if - the thread has ISO a large half angle of thread ß (metric ffi = y_ J jLXg [N/mm2] for the outer part (15) thread.1.5 4. which is Hostacom M4 N01 Hostacom G2 N02 Hostacom G3 N01 5 7 3 6 8 3 10 24 32 2 5 - internal pressure 3. Table 4: Guide values for in N/mm2 as a resulting from the half angle of thread ß (see fig. equation 1) leads to expansion of the outer part and compression of the inner part.Guide values for quoted in table 4 permissible flank pressure pperm. on see Expansion diameter the outer JDm = 8l - Dm = /^r^r [mm] (L>a L>) LI - (19) .5 100 da L z Hostaform C 9021 Hostaform C 9021 GV 1/30 flank diameter [mm]. L - - 32 38 15 20 With wall thicknesses si and s2 of the tubular segments Da-D 1 = [mm] d3-dj [mm] small in with the (13) If the calculated flank pressure p is greater than the per missible. 4: Explanatory diagram part is " PD-Pm Et(Da-D) (17) and on the inner part pD-dm E2 (d3 di) - (18) table 5 part is 1. This causes the flank overlap to be reduced. are (safety factor S is already taken into account). be transmitted at elevated Hence compression of the mean diameter on the outer Fig. The radial force Fr 1 and permissible flank pressure pperm. S2 = (14) 4.5 2.3 Deformation of the to threaded section which are generally comparison mean diameters Dm and It is necessary dm.2 flexural creep modulus of the mean [N/mm2]. To calculate this deformation. 2 20-25 45 6 10 12 15 _ _ 20 1 1 - P thread loadbearing thread flights pitch [mm] comparable with the Hostalen PPN 1060 Hostacom M2 N02 _ - This gives pressure pD.5 18 20 30 40 45 9 7 16 6 2 8 20 25 PD = [N/mm2] TC (12) Celanex 2500 Celanex 2300 GV 3/30 Celanex 2300 GV 1/20 Celanex 2300 GV 1/30 d. Whithworth pipe thread) JL* - a fine pitch is chosen which results in a low thread a2 = PD' m depth HI - d3 to - dj [N/mm2] for the inner part (16) continuous loads have temperatures. thread reach number of fig. it is assumed that the radial force Fr is distributed uni function of temperature formly over the thread overlap area C: Temperature [C] Material 20 60 15 35 4 4 C 120 = JT-d2-L = ^-d2-z-P [mm2] see (11) 80 12 30 2. see table 2 linear force [N].) - (20) JHi S (0.23C. table 5. it is The decrease in the flank 20 to overlap /iHi should not exceed 30 % of the initial value. Adm = e2 dra = Pp-dn [mm] E2 (d3 d. see section 4. 60 n [m/s] (26) so change overlap is calculated as arli ~ ^Dra +Zldm (similar to that for plain design criterion for the helical gear Guide values for permissible p v values for a Hostaform/steel combination are given in table 6. Strictly speaking. Flexural creep modulus Material 5: Helical thread (schematic) [N/mm2]. component under compressive be calculated with sufficient accuracy using may mining factor in transmittable power. the friction PR and resultant tem perature increase on the thread flanks is a crucial deter versa negligible so that. separate characteristic 4. However for deformation ^ 2%. ob = 10 N/mm2 1-min value 6-day value Hostaform C 9021 Hostaform C 9021 GV 1/30 Hostalen PPN 1060 Hostacom M2 N02 Hostacom M4 N01 Hostacom G2 N02 Hostacom G3 N01 2800 9000 1500 7000 1300 1} T _ 16002) 3300 4000 500 2) 1600 2400 3800 5500 2800 Celanex 2500 2000 2900 5900 Celanex 2300 GV 3/30 Celanex 2300 GV 1/20 Celanex 2300 GV 1/30 :> <Tb = 4100 7100 9500 = 8600 5 N/mm2 2> ob 6 N/mm2 The changes in flank diameter AD2 and Ad2 also approximately correspond to the diameter changes ZlDm and ^dm. a p v value can be determined as a bearings) and used . applies for the frictional energy: PR = The following the flexural creep modulus.On the inner part.1 sliding speed [m/s] Table 5: Flexural creep modulus values based DIN EN 20 899-2 on (DIN 54 852) Fig.3) Hi (24) The deformation of and a plastic component is not only timetemperature-dependent but is also a function of stress level. for example.1. the flexural value. For E fG-Fi-v[W] (25) characteristic therefore.2 to 0. creep modulus is used as the fc FI v thread friction coefficient. the variation between the characteristic values is the deformation of stress a with helical gears. With flank pressure p from equation (9) B P = [N/mm2] z n d2 H <4D24Dm Jd2~Zldm that the (21) (22) in flank and n v = d.2 Movable joints In the conversion of rotary into linear motion and vice values should be determined for each type of stress. 1 Calculation examples C 2521 Sliding speed [m/s] ^0. The Fig.Table 6: Permissible p v values Hostaform/steel combination (guide values) for a 5. e.15 0. Hostaform/ Celanex. 6: Reversible-flow filter (schematic diagram) plastic/plastic combinations. If once-only lubrication is carried out before assembly.g. the vulnerable cross- section is in the inner part. quoted values apply to unlubricated sliding partners. Fig. 6 screwed together N/mm2) with a cap nut with S 128 x 6 metric buttress thread.5 1. 5. 7: Vulnerable cross-section in the inner part 10 . up to 50 % higher p v values can be permitted. fig.06 housing are halves of the reversible-flow filter shown in fig. With Stress in the vulnerable cross-section Because of the lower wall thickness.5 v Permissible p v value Reversible-flow filter made from Hostaform two [W/mm2] The 0. 7.10 0. the permissible p v values should be halved because of the poorer thermal conductivity.0 1. The filter is designed for nominal pressure PN 10 (= 1 at room temperature. 75 9498.75.28 N/mm2 Flank diameter Pitch Thread D2 P = = 1.45 N/mm2 at PN = 10 bar be FB = 3 3 PN A [N] 9498.5 is thus = 6 3. H. calculated from equation (9) = Thus the flank pressure p is FB A.7mm2 Mean diameter of contact 0.5 mm Fi =FB DIN 19632 must z number of L 2 loadbearing thread flights specifies that mechanically operating = . can a flank pressure of p = 1.75 A = | d. 5 N Dimensions of the RVs thread: Outside diameter of thread D 16.35 N/mm2 Thus In the long term. filters be tested with three times the nominal pressure rating. which is sealed with = 0. =0.5 = 1994. = j (d32 - d.5 = 0. the operating force and is thus smaller than aperm.337 0.2 [mm2] Thus the maximum flank pressure is ^ = HO2 mm2 Pmax.75 mm 6 = 123.5 mm2 = 4.2 accepted.P = 4. FB FI.The tion loadbearing (3) area A] is calculated according to equa Flank pressure As n A. 5 mm2 angle of thread ß = 27. [N/mm2] = 1994.5 mm 3.856 The long-term-acting PN Oz = tensile stress is depth nut Hi = Outside diameter of A Da L = 19. The aim in this case is to omax. = - [N/mm2] is when tightened check how great the expansion of the nut 1000 N mm. 27.8 1994.7mm2 = mm mm mm mm = 14. = 10 N/mm2.2) [mm2] HO2) explained above.x The cap nut made from polypropylene shown in fig.5 (cos tan 27. 5 internal pressure H. is ignored: FI = Fv.5 10 mm Thread reach Half = mm ^r~ 1 N/mm2 -9 498.7 mm2 d2 flank diameter [mm] d2 = d-0. = f (1212 P - = it d.5 N Hose connector made from Hostalen PPN 1060 The maximum tensile stress ffm.5 N 123. 11 . the linear force is essentially determined by the In this a filter. see table 3. = IN/mm2 = 28 495.7 15. in this case with 30 bar 3 N/mm2 The pressurestressed area =P 22. with a torque of M = 28 495. 8 is part of a hose connector for irrigation systems.75P 128 - radially deformed and thus requires a negligible prestressing force O-ring FV. JT 28 495.5 mm 4.76 N/mm2 For the present calculation example.887.5206) surface dA = 15 mm = 4.5mm2 5. 49 (19. Dm= -19.8 mm = --18.2. speed speed of v = 150 mm/min is maintained motor.5206 = 286.8 mm 10 mm = 0. a threaded feed nut injection Fi = [N] D2-fG + + cos molded from POM engages with a steel spindle.. The serviceability of the jack is tested in a long-term trial on * ß dA fA special rig in which the jack is lowered position by a specified distance and then a from its raised highest 50 times under the nominal load F = 4500 N.1- This expansion is not critical depth H! 0.2 N The linear force FI leads to a radial force (equation 1) Fr = FI tan ß 0.887 Fig. = in relation to the thread The to a tightening torque M leads linear force 2M according to equation (6) 5.2 - permissible p value is exceeded in the trial.E Fig. 15. A The friction coefficients fA and fG 2 1000 N are assumed to be 0.3 N/mm2 -RÏ/8-14.5- - - = 18.856 mm.7 = - .023 15.49 0.2 it 0.3 N/mm2 This pressure leads to an expansion (equation 17) S.337mm + whether the 0.. = 9: Jack with threaded feed nut (arrow) 286. 8: Cap (from ^ table nut 5) Da 1300 N/mm2 + D - 19. S The flank diameter D2 expands by ZlD2 = ! D2 [mm] 10-3 mm = 1.95= 2 18.8 mm + 15 mm 0.2 N 149 N = This force corresponds = to a pressure (equation 12) PD W^-L [N/mm2] 149 N Jt 15.3 Vehicle jack with threaded nut made from POM On the jack shown in fig.5 + 16. 9. again lifting through the to of the drive The aim here is v determine mm F.7 mm) ID'3 /. = PD E (Da Dm - D) 12 .= 1.5 16.1 mm 2 0.1 mm mm - 61 = 1300 N/mm2 1. 0428 m/s FB. torque M at the turned as far as they Before this position is reached.225 W/mm2 d2 is -n = generally between 0. the minus sign denotes tightening under load withdrawal (reversal of direc a tion).5 m/s. JT 75 min"1 Thus the sliding speed n tan y D2 60 n v = [mm/s] 2 fr \d2-n ' cos/? (28) n 10. following equation applies 21 4500 N n 10. No In table 6. an additional frictional force becomes effec tive in the contact area.0826 6.1.04 to 0. bricated operation. the P = Jt D2 H. for permissible 0. With lubricated operation as is pos sible in the present case this value can be increased by a sliding speed = of v = 0. fr cos occurs when the - - up to 50%.9 mm mm depth Number of loadbearing thread flights For the flank pressure.78 N/mm2 tan (a y') = tan tan y The lifting speed spindle speed of n = of 150 mm/min corresponds to a P tan d. F = 1. the quotient p-v. 0. a self-locking takes place. With lubricated surfaces (fG surfaces self-locking to occurs permissible. In some situa tions. it is table 2). ß of d2 n In the case Thus a permissible = p v value of P single-start threads.1).0428 m/s > d.15 W/mm2 is quoted for unluv value of p p vperm.Dimensions of the M 12 nut: x 2 thread in the threaded feed 6.060 (metric (Whitworth pipe thread) and thread) so that with unlubricated = The calculated p v value is about 10 /o higher than the (see friction coefficients IG in 0. pauses are pro cycles to allow the threaded temperature again.9 mm 1. nut to Hence in the vided between the individual cool to room long-term trial. necessary check in each individual case whether self- place.1 describes the relationship between linear force FI and tightening equation (9) applies [N/mm2] z when the threaded parts are will go. a special thread with a smaller pitch P should be still takes used. i. i. i.e.5 0.9 mm 75 60s The = plus sign In this in brackets denotes 42.78 N/mm2 0. 13 .e. = -JT cos .25 W/mm2 0. Self-locking expression in brackets is negative.016 buttress is obtained.1 =21 Equation (6) point in section 4. especially since external vibrations locking can further limit the range of self-locking.perm.e.0826 mm M = FB --y** tan(y') ' (27) = 5. p-v = 5.15-1.8 mm/s ^ 0. 0. Design Self-locking notes Flank diameter Thread D2 H! z = 10. The p v case value is calculated as torque M if the expression the linear force FB is converted into in brackets is positive. 2. - compared with a smooth molding. in the presence of certain media. the nominal stress of the notch cross-section K = 2. eN 6.3. linear force FI is absorbed by the first loadbearing thread flight when the inner and outer parts consist of the same material. section 4. the notch factor is ON K = 2 to 3 Since linear-elastic material behavior is assumed.6. the tensile stress resulting 6. show that about 30 to 40% of the total and outside diameter Da - type of stress (tensile. in to 14 .2-di2) (Da2 - radiusing on R associated with pitch P has an important influence see the notch factor. 10: Characteristic values related notch factor KO = ON time result of creep processes at the stress. part in force transmission. 10) - - and dimensions of the molded part notch geometry: radiusing R at the transition between design In sections 4.2 Stress concentration in the threaded section For the components discussed here. These notches lead to increased stress as In tensile [12]. the notch factor increases with greater thread size. the Fig. can lead to failure of the component. it was assumed that the indi thread zone vidual thread flights in the engaged play an the thread flank and thread root. root = The ratio of the root geometrically to similar thread model - as maximum stress in the notch 0N thread <Tmax.1.2 Stress distribution within the internal thread This notch factor depends on engaged with the external thread (zone II.1.. inside diameter d. These strains zones can produce flow and microcracks which. Studies on model threads however. The grooves of a thread correspond in their effect to a series of notches. with diminishes.4 A.2 and 4. This method is material behavior applied of plastics. fig. flexural. the notch factor for metric thread M 8 under stress was determined using an enlarged. torsional). an ana logous factor for strain concentration can be defined (high notch factors for large nominal thread diameters and vice Ke = versa). flight depends on the level of linear increasing linear force.2. The proportion of force absorbed by the first In [10] an extended method of calculation is stress presented. while the strain-related notch as a decreases over point factor of highest Kf : N increases with time.3 to 2. Since the ratio P/D becomes smaller with A2 = D2). stress- Notch factors aK in disengaged thread zone I In components under tensile stress.:-f and The (d. Notch factors for the metric ISO is described as the notch factor or stress concentration trapezoidal thread are factor On given K0 = in [13].1 from linear force FI has the greatest a constant importance. the proportion well. thread depth HI. loadbearing thread which enables account as concentration to be taken into for non-linear-elastic and plastic [11] material behavior viscoelastic force FI. increasing nominal thread diameter D. equal [12]. Depending on the nominal thread diameter.1.1. a (load-dependent) notch factor a* is defined. deformable plastics (e.2. this region yielding and hence the load is evenly over the thread flights. Because a runout generally machined. Thread runouts such as described DIN 76 part 1 and part 3 must be avoided with integrally molded threads. evenly over the individual thread possible design to achieve this is shown in Fig.\ %\ &-> 0% "5 %a The 10 Proportion of load taken by the forcetransmitting thread flights large notch factor K which results can lead to fail of the component at this point when under internal ure in pressure stress. A similar Fig. of hard.7 high A notch factors can be reduced if force trans mission is distributed flights.g. i. 12: V-notch runout on the internal thread produced by thread cation and deflection on the thread flank. rigid plastics. sealing tape) should be used in the thread. 11. which additionally takes into account load appli Fig.3 Static sealing of plastics components with integrally molded threads 40 30 20 10 0% Proportion of load taken by the forcetransmitting thread flights basically take place outside the thread. 13: Screw closure with integral seal be achieved if the internal and external parts made from nut made from materials with different fitting with internal part forced polypropylene and cap screw rigidity. fig. the thread flight on the mold end with the complete thread profile. Sealing should By introducing is a recess at more designed can to be distributed effect are more the end of the nut.To describe the stress concentration in the engaged thread zone. 15 . therefore. elastomer-modified plastics). curvature on is produced In the case the external thread which forms small radius of a V-notch with very the internal thread (fig. 11: Design mission in the improved force trans individual thread flights measure for Thread runout V-notch !:i Î5G3 i"T3 OS u< _x * > X 40 30 20 f / ^5 v/. 12). polyethyl ene.e. 6. the components can be sealed with molded-on sealing lips or other readily deform able zones (fig. The measured root are notch factors in the thread * These =5 to 8. additional seals must be used. no seals (hemp. Example: glass-fiber-rein from unreinforced PP. 13).3 Stress concentration in the thread runout The internal thread of a plastics molding is formed in an injection mold by the on cores are a core with external thread. core must 6. In the case of flexible. leak. fig. As result. radial deformation O-ring prestressing force. because of the relatively large contact require high prestressing forces Fy to achieve a satis factorily high contact pressure. specified by the manufacturer In the 16. 16 . pressure-loaded Squeezing process result of initial compression as a po _ and sealing gaskets (fig. the joint can 16: Triangular and rectangular grooves. 17: of the Rectangular groove. Fig. be installed in rectangular and triangular fig. Flat pressure p PB = p + pv processes in the thread and stress relaxation in the tensileare not stressed thread constant start to zones. advantage that the contact pressure necessary for sealing is increased by the pressure of the medium being sealed. 17 is more favorable. Owing to bedding down area. The force and thus case required to deform rings to create contact than is the the gaskets. examples shown in fig. in which defor mation of the O-ring is achieved by suitable dimensioning of the internal and external parts and is not dependent on in the a Fig. O-rings have O-rings grooves. The groove dimensions and tolerances should be observed.A joint is sealed when the contact pressure in the seal is two greater than the pressure difference between the sides of the seal. in O-rings placed which the cause a more appropriately dimensioned to grooves them be deformed in the closed joint are suitable solution. 15: Automatic sealing effect with elastic seals Fig. can with flat In pressure is much less addition. axial deformation of O-rings Fig. 15. The arrangement in fig. 14: Flat gasket Seal located in sealing groove Seal compressed but not pressure-loaded Squeezing process result of initial compression as a Pv Seal. these prestressing forces a but decrease with time. 14). 16. the O-rings are deformed longitudinal direction by prestressing force Fv. 19: Slides with flattened thread which collapse thread. 21. For longer runs. 7. flash can be formed as a particular molding conditions or wear. Any flash of the way of the 19. Fig. various length of the production run demolding options may The external thread forms external undercuts in slides. Injection molding of components with molded threads If even parting marks from the slides are not allowed to integrally be visible.7. fig. Fig. fig. the threaded cores are unscrewed inside the mold. The is necessary rotary produced either with the aid of a coarsely threaded spindle via the mold opening movement or via a hydraulically operated rack and pinion system or drive motor. so-called lost released by 18. the action of at movement of the slides angle pins right angles to the cores are inserted into the opening direction. Outside the mold. This flash makes it difficult or even impossible to screw the threaded parts. For short runs. the thread must sleeve which is unscrewed after be formed in a single threaded injection molding. opposing thread and Another way to demold internal threads is to use a collap sible core. the core is then unscrewed manually or with a special device. This type of core is divided into segments be an obstruction.2 Internal thread the intended 7. 20: Unscrewing mold for internal thread In the contact area of the slides. fig. The problem can be avoided by flattening result of the the thread in the will then lie not out area of the contact surfaces. These undercuts that allow mold are be considered. 18: Slide mold for external thread injection mold and ejected with the part after injection molding. movement Fig. inwards so permitting release of the 17 .1 External thread Depending and thread on requirements. 22. Germany demoldabie undercut Internal threads via can be demolded much continuous thread is are more angle slides. 58579 Schalksmühle. right: demolding position Manufacturer/sales : Fig. e.g.Fig. take creasing cooling time the shrinkage forces also increase. in the event of interruptions to production. this can lead to demolding difficulties if the prescribed cooling time is exceeded. 22: Segmented internal thread DME-Zentrale. 74196 Neuenstadt. Germany Rudolf Riedel GmbH.e. if a simply. not required but sufficient to In general it should be noted that onto a molding with internal thread shrinks the threaded core and that with in- instead individual threaded segments the linear force FI. 18 . fig. left: injection molding position. i. With unscrewing cores in particular. 21: Collapsible core. The wall thickness of the internal part pans s2 = si = 6. 23 left. Fig. the screw bolt is centrally bored and laterally recessed.4 mm. the number of loadbearing thread flights z 2. The two housing made from Hostahousing halves are screwed = filter The drain thread.1 mm.8 mm). fig. This thread and region owing to the sharp-edged thread problem was remedied by shortening the ending it with a complete profile.5 together with an S 80 x 4 buttress thread. O-ring. stress flange cracking occurred in this runout. The plug is held captive housing by two snapfit hooks. the core the internal thread is unscrewed in the mold. forming Although the transition from the screw bolt to the is well rounded (R = 0.1 housing 8. This housing. which is constantly under mains water pressure.2 Drain plug for water separator on diesel vehicles Photo 1 shows a water form C 9021. is sealed with an axially deformed O-ring. The plug shown in water photo 2 and fig. fig.8. an plug is sealed with in the separator The external thread is formed in splits. To achieve the required deformability for snapfitting. 23: Drain plug 19 . 23 right. the wall thickness of external 4. Examples of applications Water filter 8. 23 is an screwed x into the base of the separator with M 10 1. 3 Grain hopper for corn mill 8. chemically coupled) is used a 80 20 P 4 = five-start. The internal the thread reach.25 thread 20 . The thread is areas are offset demolded via core. The external thread is formed in two slides. each cover ing an angle at the circumference of 120. depth HI fasten the spare wheel of a car onto The M 8 x 1. The threaded to fig. thread is divided into two threaded segments. rectangular internal thread. not complete but only over half the circumference in each half of 24.4 Fastening nut for spare wheel This an hopper (photo 3) x made from Hostalen PPT 1070 has a The nut shown in M 90 x 2 metric external thread and non-standard (PP to + 30% w/w photo 4 made from Hostacom G3 N01 glass fibres.25 nut thread is however formed threaded bolt. Only through contact with the spare wheel is the axis of the nut aligned with the axis of the threaded bolt so that the thread flights of the nut and bolt can become engaged and the nut tightened up. thread 1 mm. 24: Interrupted M 8 x 1.8. nut quickly This makes it easy over the threaded bolt. two slides running on the tapered inner push the slightly tilted by 180. Fig. KS Kö. - notch factors fc FB _ thread friction coefficient N N N operating force a* - load-dependent half notch factor Fi F Fr Fv linear force ß force o angle of thread perpendicular radial force r e o angle strain of friction N N prestressing force Oz N/mm2 N/mm2 tensile stress "perm. N/mm2 W/mm2 permissible flank pressure mm thread mean core diameter p v value material-dependent design dimension for helical gears and slide bearings mm diameter of the surface a contact di mm inside diamter of diameter of the Ç11 t"T3 L/C dU. permissible tensile stress H. notch cross-section Symbol M n Unit Explanation tightening mm2 N-m torque min"1 spindle speed flank pressure pressure B.9. c H5 mm thread flank depth mm overlap 21 .1 let PP joint p mm thread pitch dp mm pressure-stressed PR PN W frictional energy bar mm nominal pressure dm. nominal thread diameter p. 2 Explanation vulnerable cross-section. Explanation of symbols Unit Symbol A.h3. internal pressure d2. area thread reach P N/mm2 N/mm2 N/mm2 mm2 D mm overlap PD d.D2 d3 dA mm thread flank diameter Pperm.. H4. Dm mm mean ^\ Da + D R s radiusing wall thickness diameter outside diameter of 2 mm Da E mm a joint v m/s - sliding speed number of N/mm2 flexural creep modulus friction coefficient z f thread a o loadbearing flights helix fA _ friction coefficient of the contact angle surface K. L C mm engaged thread thread zone.. p. Literature [1] DIN 2244 [9] DIN 19632 Gewinde.W. Bl. Bl. Übersicht [3] DIN 13. Neuber: Gewindedurchmesser. 67 620 mm) [13] K. Kloos. Schwabach Metrisches ISO-Trapezgewinde (Gewindedurchmesser 8 bis 300 mm) für nicht im Gewinde dichtende Firmenschrift der Fa. Munich Vienna 1990 [8] DIN 405 Rundgewinde (Gewindedurchmesser 8 bis 200 mm) 22 .H. 25 Rohrgewinde Verbindungen [7] DIN Tl. l Metrisches ISO-Gewinde. K. Mechanisch wirkende Filter in der Trinkwasser installation. Konstruktion 20 (1968) 7. techn. Bl.Weiß: Zur Berücksichtigung der Kerbwirkung bei viskoelastischem Materialverhalten Plaste und Kautschuk 35 [4] DIN 513 Metrisches Sägengewinde (Gewindedurchmesser 10 bis 103 (1988) 2. Prüfungen. Auswahl für Durchmesser und Steigungen. l + 3 Gewindeausläufe. Gastrow: Der Carl Hanser Spritzgießwerkzeugbau in 100 Beispielen Verlag. von A. Regeln [10] [11] des DVGW DIN EN 200 Regelgewinde DIN 13. 245 [12] E. Pahl. Thomala: im [5] DIN Spannungsverteilung [14] G. Feingewinde 40 bis 300 mit Steigung 4 mm Über die Berücksichtigung der Spannungs konzentration bei mm Gewindedurchmesser. Schraubengewinde Bergner. Tl. 9 von von l bis 68 mm Sanitär armaturen H. 12 300 Regel- und Feingewinde l bis mm Gewindedurchmesser. l Tl. Richard Bordas. von Festigkeitsberechnungen DIN 13. 2 6063 Konstruktion 37 DIN 76. p.10. Gewindefreistiche Gewinde vorzugsweise Sägengewinde Trapezgewinde [16] H. Anforderungen. p. Oedekoven: [6] DIN/ISO 228 Berechnung [15] für Kunststoffbehältnisse Trapezgewinden (1985) l. Begriffe [2] DIN 202 Gewinde. 3. Hoechst aims want to to Engineering plastics Design Calculations Applications Publications so provide exploit the properties Hostaform.3. Hoechst as manufacturers of the starting mate rial will be pleased to give the names of other processors of plastics for engineering applications.1 Spur gears with gearwheels made from Hostaform. Production C. guaranteeing specific properties of the products described or their suitability for a particular application. 1. The quality of our products is guaranteed under our as A.3. state will be A.3.3.2 Hostaform - Characteristic values and Characteristic values and General Conditions of Sale. calculation A. design and on our pleased processing. therefore be - Celanex. Engineering plastics A.2. to useful information for designers who of engineering polymers team such as Our technical service on far in this series: advise you materials.3 examples - Hostacom calculation examples B. thermally conductive torpedo Hot runner system Indirectly heated.2. thermally conductive torpedo Design principles and examples of molds for processing Hostaform Machining Hostaform Design of moldings made from engineering plastics Guidelines for the design of moldings in engineering plastics Outsert molding with Hostaform - © Copyright by August Hoechst Aktiengesellschaft Issued in 1996/1 st edition 23 . Hostacom.In this technical information brochure. 1.3 B.2.3.5 Grades and properties Vandar.2 Grades and properties A.5 of technical mouldings runner system Indirectly heated. This information is based - present of knowl - - Hostaform Hostacom Hostalen GUR edge products strued and is intended and their to provide general It should not notes on our con uses.4 Grades and properties A.3 C.3. Celanex and Hostalen GUR B.5 B.2 Worm gears with worm Applications involving the use of the Hoechst materials Hostaform.7 Design calculations for snapfit joints in plastic parts Fastening with metal screws Plastic parts with integrally moulded threads Design calculations for press-fit joints Integral hinges in engineering plastics Ultrasonic welding and assembly of emgineering plastics C.3.2.4 B. Impet A.2.1 Hot C. wheels made from Hostaform B.1 C.4 C.2 B. Hostalen PP and Celanex are developments or products of the plastics processing industry. Any existing industrial property rights must be observed.2 C.1 Calculation principles .2. 1 1 Grades and properties A.3.3. Design of technical mouldings B.1 B. 1. 1. : +49 (0) 180-5 84 26 62 (Germany) +49 (0) 69-30 51 62 99 (Europe) Fax: +49 (0) 180-2 02 12 02 eMail: [email protected] ® .ticona.com Americas Ticona LLC Product Information Service Tel.com Internet: www. Celcon ® Celanex® Impet ® polyoxymethylene copolymer (POM) thermoplastic polyester (PBT) thermoplastic polyester (PET) Vandar® thermoplastic polyester alloys Riteflex® Vectra ® thermoplastic polyester elastomer (TPE-E) liquid crystal polymer (LCP) Fortron ® polyphenylene sulfide (PPS) Celstran ® .: +1-800-833-4882 Fax: +1-908-598-4306 eMail: prodinfo@ticona. Compel ® GUR ® long fiber reinforced thermoplastics (LFRT) ultra-high molecular weight polyethylene (PE-UHMW) Europe Ticona GmbH Information Service Tel.ticona.de Internet: www.com .