O-RINGS
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32O-RINGS O-RINGS
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1. INTRODUCTIONBasic characteristics 4Materials used, their properties 4 5Fabrication tolerance, standards 5 6Function and use 6Sealing joint, material hardness 7Installation instructions 8
2. DETERMINING THE RIGHT O-RING SIZEDeterming the thickness (d2) and the inner diameter (d1) 9Detailed groove construction basic notions 10
3. STATIC SEALING RADIAL DIMENSIONDeterming the dimensions rectangular groove 10Tolerance, roughness, max. sealing joint 11
4. STATIC SEALING AXIAL DIMENSIONDeterming the dimensions rectangular groove 12Determing the dimensions trapezoidal groove 12Determing the dimensions triangular groove 13
5. DYNAMIC SEALINGDeterming the dimensions rectangular groove 14Roughness tolerance 15PTFE O-rings 16O-rings for vacuum sealing 16Cords 17Assembly boxes for bonding of O-rings 17Dimension series of NBR O-rings 18 50Dimension series of FPM O-rings 51 81X-rings 82
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1. INTRODUCTION
O-rings are highly precise circular sealing elements, which are efficient and economical at the same time and can be used for a wide range of both static and dynamic applications. O-rings are vulcanized in moulds and, due to their symmetric shape, they can be used as single as well as double seals. The size of an O-ring is defined by its inner diameter d1 x ring thickness d2 (figure 1). Sizes, materials, hardness and installing dimensions are defined by the DIN 3770 or ISO 3601 standard. All dimensions are given in millimetres.
d1 = inner diameter (mm)d2 = O-ring thickness (mm)
Material groups
The following table gives an overview of material groups of elastomeric substances with the option of choosing the material hardness (table 1). The following factors influence the decision on material and hardness: size of sealing joint, temperature, pressure, chemical exposure.
For most applications, the standard quality NBR 70 Sh is sufficient. For higher temperatures and chemical exposures, standard quality Viton FPM 80 Sh can be used.
Material hardness is given on the Shore or IRHD scales.
Please inquire for non-standard materials such as polyurethane, KALREZ, fluorosilicone, NEOPRENE -they can be delivered after the manufacturing plant is consulted.
OK NBR 70 35 x 3
d1 d2type material hardness
dimensions
Properties of selected materials
1 - excellent2 - very good3 - good4 - applicable5 - less applicable6 - not applicableX - not measured for this material type
Production tolerance of O-rings
The following values show tolerances for Nitrile-butadiene-rubber compound with 70 Shore or 73 IRHD hardness. Even with identical moulds, other compounds have different cross-sections and higher tolerances. It is always possible to manufacture special moulds according to your specifications.
O-RINGS MATERIAL (table 1)
Code Trade name Hardness Shore ANB, NBR Nitrile-butadiene-rubber 55, 60, 70, 75, 80, 90FP, FPM Fluorine rubber (Viton) 60, 70, 75, 80, 90SI Silicone rubber 50, 60, 70, 80EP, EPDM Ethylene-propylene rubber 75, 80, 85CR Chloroprene rubber 50, 60, 70, 90NR Natural rubber 45, 65, 80BU Butyl rubber 45, 65, 80CSM Chlorsulphonated polyethylene rubber (Hypalon) 65, 75PTFE Polytetrafluoroethylene (Teflon) -
HARDNESS OF O-RINGS (table 2)
Shore A hardness 60 70 80 90IRHD hardness 63 79 83 92Tolerance 5Tested according to DIN 53505 or 53519
PROPERTIES OF SELECTED MATERIALS (table 3)
Material type NBR FP SI EPDM CR NR BU CSM PTFETensile strength without support 5 5 6 5 3 1 4 5 1Tensile strength with support 2 3 4 3 2 1 3 3 1Elongation at break 2 3 4 3 2 1 2 3 3Reverse elasticity 3 5 3 3 3 2 6 4 xConstant resistance 2 4 5 3 2 2 3 3 3Tensile resistance 3 3 6 3 2 2 3 4 2Resistance to electrical flow 4 4 1 2 3 1 2 4 1Resistance to strain ageing 3 1 1 1 2 3 2 2 1Resistance to ozone 3 1 1 1 2 4 2 2 1Resistance to fuel 1 1 5 5 2 6 6 2 1Resistance to oil 1 1 1 4 2 6 6 2 1Resistance to acid 4 1 5 1 2 3 2 2 1Resistance to alkalis 3 1 5 2 2 3 2 2 1Resistance to hot water 3 2 5 2 3 3 1 3 1Max. temperature (C) 130 220 200 150 120 90 140 130 260Min. temperature (C) -40 -25 -80 -40 -30 -50 -40 -40 -190
TOLERANCE OF O-RINGS (table 4)
diameter d1 tolerance () diameter d1 tolerance ()Up to 3 0,14 Up to 1,8 0,08
3 6 0,15 1,8 2,6 0,096 10 0,17 2,6 3,5 0,1
10 18 0,2 3,5 5,3 0,1318 30 0,3 5,3 7 0,1530 50 0,4 7 8 0,1750 80 0,65 8 10 0,13
80 100 0,85 10 15 0,25100 120 1120 150 1,2150 180 1,4180 250 1,8250 300 2,1300 350 2,5350 400 2,8400 500 3,4500 650 4,3650 800 6,5
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O-rings standards
Function and use
O-rings are sealing elements which, upon being subjected to pressure, function in both radial and axial directions. After pressure is applied to a system, the O-ring generates sealing power. As the operating pressure increases, so does the overall sealing pressure. In comparision to other sealing elements,O-rings have a number of advantages:
- easy installation- availability on stock - cost effective- wide range of use in both static and dynamic applications.
O-rings can be used in a number of industrial applications. Due to a wide range of compounds with different properties, O-rings can be employed to seal virtually all fluids and gases.
Fig. 2
Sealing joint
When subjected to pressure, the O-ring is pressed into the opposite side of the groove. To prevent the O-ring from being pressed into the sealing joint, which would result in the ring being damaged, it is advisable to choose O-rings with the largest cross-section possible for a particular application.
Under identical operating conditions and equal sealing joint width, an O-ring with a smaller cross-section is pressed into the (identical) sealing joint relatively more than an O-ring with a larger cross-section. To prevent the O-ring from being pressed into the sealing joint, a harder O-ring may be chosen or the O-ring can be combined with a back-up ring (upon inquiry, we can recommend the right size).
Material hardness
The suitable material hardness of O-rings depends on the width of the sealing joint and sealed pressure. The fol-lowing diagrams (figure 4) show the dependence:
The most important factors for determining the right O-ring hardness are the value of operating pressure and the width of sealing joint. For high pressures and wide sealing joints, it is advisable to choose harder materials to prevent the O-ring from being pressed into the sealing joint. If structurally possible, using a O-ring with medium hardness together with a back-up ring is a technically better solution as the compressive deformation is lower at 70 Sh than at 90 Sh.
type material dimensions
P.S.: Upon enquiry, we can recommend suitable materials and dimensions.
O-ring ordering example
seal
join
t wid
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m)
seal
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t wid
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O-RINGS STANDARDS (Table 5)
StandardRecommended dimensions of O-rings (mm)
Inner diameter d1 Thickness d2
DIN 3770
2 3,75 1,604 10 2,00
10,6 30 2,5018 50 3,1530 80 4,00
50 118 5,0080 315 6,30
118 500 8,00190 800 10,00
ISO 3601
1,8 17 1,8014 38,7 2,6518 200 3,5540 400 5,30
109 670 7,00
US Standard(AS 568A)
(MS 295 13)
1,78 133,07 1,781,24 247,32 2,624,34 456,06 3,53
10,46 658,88 5,33113,67 658,88 6,99
Swedish Standard (SMS 1588)
3,1 37,1 1,603,3 17,3 2,40
19,2 144,3 3,0044,2 499,3 5,70
144,1 249,1 8,40
French Standard
2,4 8,9 1,908,9 18,4 2,70
18,4 37,3 3,6037,43 113,67 5,33
113,67 393,07 6,99
Fig. 3
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pres
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Installation instructions
Given the functionality and quality of O-rings, they are most suitable for static application. For dynamic applications, there are certain restrictions which must be observed. It is important to comply with pressure and temperature limits, medium type, surface roughness, size of sealing joint and other parameters.
The following graphs show values for compression of O-rings for various applications. If these values are observed, sufficient contact surface necessary for good sealing peformance is ensured. In dynamic applications, these values must be lower due to higher friction.
defo
rmat
ion
(%)
2. DETERMINING THE RIGHT O-RING SIZE
It is always advisable to choose O-rings with the largest thickness (d2) possible as they have several advantages compared to O-rings with lower d2 values:
- lower abrasion which means higher service life- lower deformation- larger contact surface
To determine the dimensions of the groove and the inner diameter of the O-ring, proceed as follows:
- choose the highest possible thickness (d2) for your construction - dimensions of L1 and S grooves can be found in the tables for insta
