Kayış Kasnak Mekanizmaları

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1 Kayış Kasnak Mekanizmaları
Hareket İletim Mekanizmaları Makine Elemanları II İ.T.Ü. Makine Fakültesi (Belt and Pulley mechanism)

2 Kayış tipleri

3 Kayış tipleri Comparison of flat belt and V belt

4 Kayış Kasnak Mekanizmaları
Düz kayış V- kayışları Dişli kayışlar Zincir mekanizmaları Sürtünmeli çarklar

5 Dişli Çarklar ve Kayış Kasnak

6 Teorik Esaslar Çevrim oranı sarım açısı ile sınırlıdır. Bu şekildeki sarım açısı 100o kadardır.

7 Kayış Kuvvetleri Normal Doğrultu: sin(dβ/2)≈dβ/2

8 Kayış Kuvvetleri Normal Doğrultu: sin(dβ/2) ≈ dβ/2

9 Kayış Kuvvetleri Teğetsel Doğrultu: Cos(dβ/2≈1

10 Kayış Kuvvetleri dN reaksiyon, gelen kuvvetler FT1 ve FT2 , Eytelwein - Grashof

11 Çevre Kuvveti Çevre Kuvveti Yatak Kuvveti (Aks Kuvveti) β = 180o ise β ≠ 180o ise

12 Aks Kuvveti Çevre Kuvveti Yatak Kuvveti (Aks Kuvveti) β = 180o ise

13 Kayış Gerilmeleri A : Kayış kesiti ; Faydalı gerilme

14 (Santrifüj) Merkezkaç Kuvvet Tesiri
Çevre hızı sebebi ile σf santrifrüj gerilmesi ve FTf kayış kuvveti meydana gelir.

15 Merkezkaç Kuvvet Tesiri
Merkezkaç kuvvetler sebebi ile σf gerilmelerinin tayini için kayış elemanı üzerindeki kuvvetler

16 Merkezkaç Kuvvet Tesiri
FTf kayış kuvvetleri ile bileşke Ff merkezkaç kuvveti arasındaki denge

17 Merkezkaç Kuvvet Tesiri
Ff gelen, FTf reaksiyon kuvvetleri

18 Merkezkaç Kuvvet Tesiri
Merkezkaç kuvveti tesiri dikkate alınırsa ifadesi kullanılmalıdır. Bileşke kuvvet Ff , ΔFf kısmi kuvvetlerinin toplamıdır.

19 Eğilme Gerilmesi σb eğilme gerilmesinin tayini için kayış elemanındaki geometrik oranlar s, dk'ya göre küçük olduğundan;

20 Eğilme Frekansı z kasnak sayısı, v kayış hızı ve L kayış uzunluğunun fonksiyonudur.

21 Kayış üzerindeki gerilmeler

22 Toplam Gerilme ; birim alana gelen güç

23 Optimum Kayış Hızı Nispeten küçük bir gerilme olan σb hesaba katılmaz ise faydalı güç; A=b.s kesidine orantılı P/A=σnv gücünün v çevre hızına bağlı olarak değişimi

24 Optimum Kayış Hızı Nispeten küçük bir gerilme olan σb hesaba katılmaz ise faydalı güç; olduğu yerde optimum hız elde edilir. vopt = 38 m/sn (kösele kayış)

25 v hızına bağlı kayış gerilmeleri
v çevre hızına bağlı olmak üzere kösele kayıştaki gerilmeler

26 Kayış Mekanizmaları Kayış uzunluğu geometrik eğrilerin toplamıdır.

27 Düz kayışların boyutlandırılması
Kayış uzunluğu

28 Boyutlar a: eksenler arası mesafe β: sarım açısı

29 Boyutlar x a α a

30 Kayış iç uzunluğu ve alınarak

31 Çok tabakalı düz kayışlar
Kayış Genişliği P1 = 1 cm genişliğe gelen güç c1 = yük faktörü c2 = açı faktörü Extremultus Kayışlar Uzama : ; 80 tipi için

32 Mil Kuvveti FA1 ; birim genişlikteki çekme kuvveti
Poliamid kayışlar yüksek elastikdir. Sonradan bir kontrol lüzumlu değildir.

33 V- Kayış Mekanizmaları
Kayışın yuvaya şekil ve kuvvet bağlı olması halinde sürtünme katsayısı μ’nün tayini için kuvvetler

34 V- Kayış Mekanızmaları
ΔF: öngerilme kuvveti ΔN: normal kuvvet μ ΔN: sürtünme kuvveti

35 Çevre Kuvveti Sürtünme katsayısı

36 Dar V-Kayışları Sarım Açısı: a

37 Çalışma Uzunluğu mm arasında Lw : öngerilme verildikten sonra ölçülür bw : tarafsız eksendeki kayış genişliği Ld = Lw + 2πhw : dış uzunluk 

38 Takribi çalışma uzunluğu

39 V Kayış özellikleri Dar V-kayışlarında h/b~1/1,123'dir, (Normal~1/1,6). Eğilmeye karşı daha elastiktir. Daha küçük kasnak çaplarında kullanılabilirler, yer ve ağırlık tasarrufu sağlanır.

40

41 Kayış Mekanizmaları Dişli kayış

42

43 Belt tensions

44 Belt tensions

45 Selection procedure Belt type: initial Selection
Estimates of belt speed and speed ratio can be used as shown below to make an initial Selection of the type of belt required. If a constant speed ratio is important, use a Toothed belt if belt speed < 30 m/s, use a Vee belt

46 Belt type: initial Selection
if belt speed < 40 m/s and, - speed ratio < 7:1, use a Vee belt - speed ratio < 8:1, use a Wedge belt otherwise, if speed ratio > 8:1 or belt speed > 40 m/s, use a Flat belt

47 Duty/Service factor Types of duty are categorised as follows: Light duty Medium duty Heavy duty Extra heavy duty The type of duty determines the service factor involved (S).

48 Duty/Service factor Service factors for typical driving and driven machines and for a variety of duties are shown in the table below. Further allowacne may be required if the consequences of failure are particularly serious. Some manufacturers' catalogues may give further advice on suitable values.

49 Duty/Service factor

50 Nominal speed ratio The speed ratio is a function of the pulley sizes. The minimum recommended pulley size for a given section depends on the flexibility of the belt and the mass/unit length. Pulleys are normally manufactured in standard sizes so the choice of the driving pulley should be the smallest standard size which is recommended for the chosen belt section such that the ratio obtained is near to the required value when matched with a larger standard size pulley.

51 Nominal speed ratio Pulley sizes are normally based on a pitch diameter, which may be less than the outside diameter. Minimum pulley diameters recommended for a range of belt types are as follows: Vee 67 mm Wedge 60 Flat 40 Polyvee 18 Timing 16

52 Belt length Belt Length (L) is a function of shaft center distance and pulley diameters. Most belts are made in standard lengths which are cheaper and easier to obtain than non- standard ones. Some (particularly plain flat belting) can be supplied in straight lengths which can be joined round the pulleys.

53 Belt length

54 Belt length However, these are recommended only if the assembly of a continuous belt is difficult. The nominal length calculated above should be modified to the nearest standard length, and the shaft centre distance amended to suit. Manufacturers’ catalogues should be consulted to determine the standard lengths available for specific belt types.

55 Power factors Allowable Power per Belt (Pb) is a function of the dimensions of the belt section and is obtainable from the manufacturer's catalogue. Plain flat belting is often rated as power per width dimension (kW/mm).

56 Power factors Power Correction Factors may be required to compensate for: Speed ratio Length of belt/pulley contact Total length of belt Appropriate manufacturers' catalogues will provide values and method of application.

57 Number of belts Number of Belts (X) refers to the total number of separate belts or the total width of (flat) belt required. This is given by: X = P'/Pb In the case of Vee type belts the value of X should be rounded up to the nearest whole number. For flat belt types the value of X should be rounded up to the nearest standard belt width available from the manufacturer.

58 Other factors Further refinement of the belt choice will result from consideration of commercial and reliability factors such as cost, availability etc, and belt life, pulley wear etc.

59 Select the type of belt required
Optimising the choice of a suitable element is now a process of finding the best compromise (in the opinion of the designer) between the priorities of the system and the availability of the hardware. Select a suitable belt type, using 'best match" criteria.

60 Select the type of belt required
As far as the factors involving numerical data are concerned, some yield a 'go/no-go‘ situation which will eliminate those which are too costly, too heavy, too big etc. The table below indicates the maximum performance to be expected from different belt types

61 Typical belt performance

62 Installation During the design of the installation for a belt drive, particular attention should be paid to the following: Maintenance of initial tension (where required), Adjustability of tension, Pulley alignment, Ease of removing and fitting belt, Protection from pollutants (lubricants, acids, grits etc) , Guarding from interference with operators' clothing, person etc

63 Belt types and features
Five main types of belt are currently available. Details of their construction and performance are shown in the table below. An initial Selection of belt type should be made at an early stage of the design, based on estimates of speed and speed ratio.

64 Belt types and features

65 Belt types and features

66 Power rating ranges for belt types
The power rating charts for the following belt types are supplied with this guide (courtesy of J.H. Fenner Ltd):

67 Power rating ranges for Vee belt

68 Power rating ranges for belt types Wedge

69 Power rating ranges for Timing Belts (courtesy of J H Fenner & Co Ltd)

70 For each belt type, the range of powers covered by a given belt section is denoted by a thick line and designated by a code. The elements of the code for Vee and Wedge belts are as follows: a number (eg: 200) shows the pulley pitch diameter limit a number (eg: 2) shows the number of belts a letter (eg: C) shows the belt section size

71 For Timing belts, the code simply denotes the section size
For Timing belts, the code simply denotes the section size. Other manufacturers may show similar information in a slightly different format. The rating chart for Timing belts shows similar information from the same manufacturer. This time, the chart is confined to a particular width of belt (25mm) and wider belts should be uprated pro-rata.

72 A rating chart for Flat belts is also supplied, courtesy of Stephens Miraclo Belting Co. Belt codes here denote section size, and power ratings are given per unit belt width.

73 A rating chart for Flat belts

74 Basic Timing Belt Parameters Classical Timing belts

75 HTD- Curvilinear

76 GT - Curvilinear

77 Power method Designing a Synchronous Belt System Belt design procedures can be based on torque calculations or they can be based on power calculations.

78 1) The driven speed and the maximum driven torque required (including inertia load, shock loads, friction, etc) are used to calculate the required driven power 2) From information on the driver, driven equipment and operating period a service factor is obtained - see below

79 3) A design power is obtained based on the product of the Driven Power required and the service factor . 4) A belt section is initially selected using a graph as typically shown below 5) A drive geometry is derived selecting suitable pulleys, and belt Centre Distance – Some Pulley sizes are provided below

80 6) A Basic Power for the belt is calculated and a mesh factor is calculated - see below 7) A suitable belt width is selected -Using a table as provided below- Some iteration may be required

81 Torque Method The classical MXL belt and the Curvilinear more advanced belt options are designed based on torque levels. The outline method for the MXL drive is provided below. The method used for the HTD and other modern belt options will be provided at some future date...

82 The MXL belts operate generally at relatively low belt speeds so the torque levels are similar for the normal range of pulley rotational speed. Torque ratings can be calculated of each of the MXL belt widths as follows: I have converted an imperial formula to a metric formula and minor differences with the original formulae results.. Torque ratings of belts Tr (Nm) at P2 PCDs (mm

83

84 Zincir Dişli Mekanizmaları

85 Zincir Dişli Mekanizmaları
Chordal speed variation %

86 Zincir Dişli Mekanizmaları
Chordal speed variation %

87

88

89 Sürtünmeli Çark Mekanizmaları
Sürtünmeli çark mekanizmaları birbiri ile temasta bulunan ve kuvvet bağı ile güç ve hareket ileten çark mekanizmalarıdır

90 Sürtünmeli Çark Mekanizmaları
Kaymadan yuvarlanma halinde çevrim oranı: tek kademede: i  6 (14) Kayma hesaba alınırsa: kayma: =

91 Sürtünmeli Çark Mekanizmaları
Kaymadan yuvarlanma olması için normal kuvvet:  : sürtünme katsayısı Sürtünmeli Çark Tipleri: Evans Friction Cone Toroidal CVT

92

93 Ders Kitabı (Notu) Ders Notları mevcut
Diğer Kaynaklar Joseph Edward Shigley, Mechanical Engineering Design, McGraw-Hill International Editions, First Metric Edition, 1986. Tochtermann/Bodenstein, Konstruktionselemente des Machinenbaues 1,2, Springer-Verlag Juvinall, R.J. and Marshek, K.M., Fundamentals of Machine Component Design, 3rd Edition, John Wiley & Sons, 2000. Deutschman, A.D., Wilson,C.E and Michels, W.J., Machine Design, Prentice Hall, 1996. Erdman, A.G. and Sandor, G.N., Mechanism Design Analysis and Synthesis, Vol. 1, 3rd Edition, Prentice Hall, 1997. Shigley, J.E., Uicker, J.J., Theory of Machines and Mechanisms, Second Edition, McGraw-Hill, 1995.