feature fle xi xib b le co u p lin g s
New pum p coupling coupling reduc reduces es efff ec ef ectt s of t orque, m is isalignm alignm ent and unba u nbalan lanc ce At last year ’s Int erna t ional Pump Users Sym posium, Balt Balt im ore-bas ore-based ed Kop-Flex Kop-Flex ® , a divi sion of Eme rs rson on Pow Pow er Transmiss Transmission, ion, int roduced a new design of elastom eric coupling coupling f eat uring dual flex eleme nts. In this article, M att M cGi Ginnity nnity and Jon M ancus ancuso o disc discuss uss t he design’s charac haracteristic teristics s, and present experim ental data comparing its perform anc ance e t o existing elastom eric coupling coupling s.
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n 2004, Kop-Flex introduced a unique elastomeric coupling. Tra Trade-na -named ‘Ody Odyssey’, this this patented new development features dual-flex elements in the form of urethane urethane diaphrag diaphragms bonded to each end of a composite spacer (Figure 1). The dual-fle l-flex x ela elas stom tomeric diap iaphra hragm eleme element was designed using using the latest latest engineering technology: finite element analysis (FEA ) and 3D 3D CA C A D. The cha characteristics tics req required of this this new pump coupli coupling were defined defined based on an industr industry y survey urvey of pump manufacturers manufacturers and pump users, which whi ch yielded 16 desirable qualitative coupling coupling characteristics racteristics:
a)
b)
c)
d)
1. Good torque torquecapacity city compared to OD
Figure 2. Various types of pump couplings: (a) gea r coupling, (b) disc disc coupling, (c) grid coupling, coupling, and (d) dual-flex dual-flex diaphrag m elastom eric coupling. coupling.
2. No lubrication
5. Easeof field fi eld replacement
3. Ease of field field installation
6. H igh reli relia ability bili ty
4. Easeof maintenance
7. Lowweight ight 8. Good balancequality ality (meet A PI 610A GMA Class9 requirements) 9. Low reaction cti on forces forceson bearings rings 10. A t lea least five fi ve years of life li fe without replacem replacement 11. Reserve operating rati ngangular misalignm misalignment capacity city and also parallel rall el offsetmis misalig alignment capabilities without producing excessive loads loadson equipment
Figure Figure 1. The The Odyssey dua l-flex l-flex elastom eric diaphra gm cou pling.
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02 62 17 62 /05 © 20 05 Elsevier Ltd. A llrigh ts reserved
12. Rea Reasonable ble axial capacity capacity to accommodate reasonable onable errors rrors in shaft-to-shaft errors for applications pli cations using interference interference hubs
13. Operatein ambient bient temperature of at lea l east 65.5°C (150°F) 14. Pred P redictable modeof failure fail ure that that does not cause causeexcessive excessive damage to equipment 15. Low L ow axial stiffnes stiffness 16. Some Sometorsional torsional damping. ping. The dual-flex elas lastom tomeric elem lement provides not only high angular misalignment capacity, but also high offset misalignment capacity, with low reaction moments and forces transferred to the connected equipment. T he spacer i s made from lightweight composite material, which makes the dual-flex concept feasible for an elastomeric type coupling, and, because of its low weight, it reduces the unbalance
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feature fle xib le co u p lin g s a)
a
b
a
c
b
F
c 0
Bearing
Bearing
SHAFT PARALLEL OFFSET
b)
0'
M0
a
M3
M2
M1
b
F
a
b F1 Offset
SHAFT ANGULAR
c)
Bearing
Bearing M2 M0 F a
b
a
SHAFT COMBINATION
d)
b F1 Offset
Bearing
Bearing M2 M0 F COUPLING ALIGNMENT
Figure 3. Types of misalignm ent (see t ext for full discussion).
effect from eccentricity of the centre section. Reducing the force and moments at the bearings should increase seal and bearing life, and ultimately increase the equipment life cycle and decrease operating costs.
Types of coupling s Therearefour basic types of couplings used on pumps: gear, disc, grid and elastomeric (Figure 2). Today, the most common coupling used on pump applications is the elastomeric type. These typically transmit torque and accommodate misalignment by deflection and/or sliding of a rubber or urethane flexible element. Looking more closely at the various types of elastomeric couplings used on pump systems shows they can have widely different characteristics. These
Figure 4. Comparison of reaction loads for Odyssey dual-flex elements (top), tyre-type with th e flex element in the centre (middle), and a w rap-jaw type with t he flex element o n one end (bottom).
characteristics can greatly affect how a pump will perform and ultimately the overall operating cost of the equipment – which includes installation cost, maintenance cost, downtime, etc.
3a); and angular – the axes of the shafts intersect at the centre (Figure 3b). Typically, the actual misalignment is a combination of parallel offset and angular misalignment (Figure 3c).
M isalignment
Coupling misalignment
Therearetwo types of misalignment – shaft misalignment and coupling misalignment.
Shaft misalignment Shaft misalignment is the physical relationship between the driving and driven shafts. This can be broken down into two components: parallel offset – the axes of the connected shafts are parallel, but not in the same straight line (Figure
Coupling misalignment comes into play when you look at how the coupling accommodates for shaft misalignment. There are two general approaches. One is when using a double-flex coupling, such as a gear, disc or diaphragm, which has flex elements that can only accommodate angular misalignment at each flexing plane. This means there must be two flex elements per coupling in order to accept shaft misalignment (Figure 3d). The second is to use a single flexible element that is capable of
Table 1: Forces and m om ent s sum ma ry fo r Odyssey versus th e uret hane t yre coupling (a) Od yssey Tyre co upling
(b) Od yssey Tyre co upling
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Force (lbs) 5-inch spacer@ 5-inch spacer@ 0.060 inch 0.090 inch
M oment (lb-in) 5-inch spacer@ 5-inch spacer@ 0.060 inch 0.090 inch
30 70
42 NA
260 575
400 NA
7-inch spacer@ 0.060 inch
7-inch spacer@ 0.130 inch
7-inch spacer@ 0.060 inch
7-inch spacer@ 0.130 inch
30 70
30 NA
100 650
275 NA
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feature fle xib le co u p lin g s Table 2: Summ ary o f Balance Force at Variou s Speeds & Obta ined AGM A Class Type-Size
Bore Size Inches [mm]
Uncla m ped Do nut -112 Uret ha ne Tyre-112 Od ysse y-112 Wra p-Ja w -138 Od ysse y-138 Od ysse y-162 Wra p-Ja w -175 Uncla m ped Do nut -188 Uret ha ne Tyre-188 Od ysse y-188 Od ysse y-212 Od ysse y-238 Uret ha ne Tyre-288 Od ysse y-288
1.12 1.12 1.12 1.38 1.38 1.62 1.75 1.88 1.88 1.88 2.12 2.38 2.88 2.88
[28.4] [28.4] [28.4] [35.1] [35.1] [41.1] [44.5] [47.8] [47.8] [47.8] [53.8] [60.5] [73.2] [73.2]
Unbalance Force @ 1800 rpm Lbs [New t ons] 11 7 4 26 6 8 59 47 28 13 22 30 97 43
Unbalance Force @ 3600 rpm Lbs [New t ons]
[48.9] [31.1] [17.8] [115.6] [26.7] [35.6] [262.2] [209.1] [124.5] [57.8] [97.9] [133.4] [431.5] [191.3]
45 [200.2] 28 [124.5] 16 [71.3] 105 [467.0] 24 [106.8] 33 [146.8] 235 [1045.3] 189 [840.7] 112 [498.2] 64 [284.7] 90 [400.3] 120 [533.8] 387 [1721.4] 171 [760.6]
various coupling components. This should not to be confused, however, with the allowable limits set for successful operation of the equipment. In some cases, the coupling capacity can be ten times the limit that the equipment can accept.
M oments and forces
Figure 5. Miscellan eous type s and sizes o f c o u p l in g s t e s t e d , i n c l u d i n g d u a l -f l e x elastomeric diaphrag m, urethane tyre, u n c l a m p e d d o n u t , ja w i n sh e a r a n d wrap-jaw.
accommodating offset misalignment as well as angular misalignment by deflection or deformation in the radial direction.
Difference betw een equipment alignment and coupling tolerances When selecting a coupling, it is important not to be confused by the term ‘allowable misalignment’. Coupling cataloguesspecify thisasthe capacity of the coupling. The misalignment capacities given by the coupling manufacturer are usually based on the life or fatiguelimits of the
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AGM A Class 9 9 9 7 9 9 7 8 8 10 9 9 8 9
with the increase in the spacer length, whereas offset capacity of the tyre-type coupling remains constant. The tyre coupling at 5-inch shaft–shaft separation (s-s) is limited to 0.060 inches offset, whereas the Odyssey can handle 0.090 inches. When the separation increases to 7 inches, the tyre coupling has no increase in offset capacity but the Odyssey can now handle 0.130
Most elastomeric couplings accommodate both parallel offset and angular shaft misalignment through one elastomeric flex element. But, because the Odyssey coupling is a dual-flex diaphragm-style elastomeric coupling, its elements flex from OD (outside diameter) to ID (internal diameter) rather than compressing the element radially. Figure 4 shows the difference between a dual-flex coupling arrangement and two single-flex style coupling arrangements. The dual-flex allows for greater parallel offset misalignment with lowermomentsandforcesback at the equipment. To verify this, Kop-Flex measured the forces and moments for several different types (Figure 5) of elastomeric couplings. Table 1 shows the comparison of Odyssey to one of the urethane tyre-type couplings tested. A s illustrated by Table 1, the offset capacity of this dual-flex elastomeric coupling increases
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feature fle xib le co u p lin g s
inches, more than twice capability of the tyre coupling.
the
If we consider the radial forcesat the bearings due to offset misalignment, based on an offset of 0.060 inches and a 5 inches s-s, the tyre coupling will react with 70 lbs (311 N), whereas the Odyssey will react only with 30 lbs. As to the bending moment, the tyre coupling will react at 0.060 inches with 575 lb-ins (65 N.m) of moment at 5-inch s-sandwith 650 lb-insat 7-inch s-s (a greater moment ass-s increases), whereas the Odyssey will react with 250 lb-in for the 5-inch s-s and only 100 lb-in for the 7-inch s-s coupling – a lower moment as the s-s increases.
a)
b)
c)
d)
Figure 6. Elastomeric couplings b eing t ested o n b alancing equipment: (a) Odyssey, (b) unclamped do nut type in spacer configura tion, (c) urethane tyre type in spacer configuration, (d) wrap-jaw type in spacer configura tion.
Table 3: AGMA classes and eq uivalen t micro-inch di splacement AGM A class
Reduced forces and moments increase bearing and seal life and reduce operating costs.
6 7 8 9 10 11
Effect of b alance on equipment Most elastomeric couplings fall into the AGM A 7-8 category (8000–4000 micro-inches). When single-flex elastomeric couplings are used in the spacer configuration they tend to be closer to a class 7. T his is because the flex element is in the centre, or at one end, and any force is multiplied by the distance from the flex centre to the bearing centre. Figure 6 shows the configurations of four different couplings on balancing equipment.
tested only met AGM A 7 or 8. Six sizesof the Odyssey met AGMA 9 and one size consistently met AGMA 10 or better. Table 3 shows the equivalent displacement in micro-inches for the various AGM A classes.
Table 2 shows the magnitude of the force that will be seen back at the bearing for the variousA GMA classes met by the different elastomeric coupling designs. The unbalance force was calculated for 1800 rpm and also Kop-Flex measured the amount of 3600 rpm. One can see that the residual unbalance for three different magnitude of the unbalance is types of comparable elastomeric proportional to the square of the couplings. It checked two or three speeds [the multiplication factor = sizes of each, and two different (3600/1800)2] so at 3600 rpm the couplings of each size. T he data in the unbalance force is four times than at following table are for the highest 1800 rpm. Also the data show the readings measured in any plane of difference in unbalance force seen by these coupling samples. The company the Odyssey lightweight composite also checked all seven sizes of the spacer design compared to the other Odyssey current product series. A s can types of elastomeric couplings. For be seen in Table 2, all the small-size example, the Odyssey 188showslower 112 couplings met AGMA 9 (NB: unbalance forces at both 1800 rpm Size 112, 138, etc. couplings have a and 3600 rpm (13 lb and 64 lb, 1.12 inch, 1.38 inch, etc. bore). But respectively) compared to identically the larger sizes of the other couplings sized urethane tyre and unclamped
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M ass eccent ricit y (equivalent displacement) in micro-inches 16 000 8000 4000 2000 1000 500
donut types, as well as the wrap-jaw 175size.
In summ ary A s a result of innovative technology, advanced materials and new computerization techniques, the dualflex design can now be applied to elastomeric couplings – a concept that has been unattainable for the past 75 years. With operating stresses for the elastomeric element lower for a given misalignment and reduced loads due to unbalance, coupling life cycles increase, ensuring high reliability and better-than-ever equipment life. CONTACT Matt McGinnity, Mana ger Product Engineering and Jon Ma ncuso, Director Engineering Kop-Flex, a divsion o f Emerson Pow er Tra nsm ission PO Box 1696 Baltimore, MD 212203, USA. Tel: + 1 410 768 2000 Fax: + 1 800 262 3292 E-ma il: mmcginn
[email protected] m w w w.emerson-ept.com
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