O-Rings

Chapter 1: What is an O-Ring?

An O-ring is a circular elastic seal used in both static and dynamic applications. Its primary function is to create a seal between structures such as pipes, tubes, pistons, and cylinders. Made from various materials to suit different applications, O-rings are highly flexible. When positioned between two surfaces, they effectively prevent the leakage of liquids or gases.

As a static seal, an O-ring remains fixed in place to contain pressure or seal a vacuum. In dynamic applications, O-rings can accommodate reciprocating or rotating motion. They are self-energizing seals, applying pressure within a tube or pipe to ensure a tight seal.

Chapter 2: What is the process for making O-rings?

The production of O-rings involves several key processes: extrusion or injection molding, compression molding, and transfer molding. During the extrusion process, elastomers are shaped to prepare them for the subsequent molding stages.

Selecting the Mold

The mold for O-rings consists of two halves between which the material is compressed. The choice of mold depends on the desired diameter of the O-ring. Because the material expands when compressed, the groove width should be 1.5 times the O-ring's diameter. For custom O-rings, molds are computer-designed and produced to accommodate any required size. O-ring blanks are cut from steel using a lathe.

For rapid O-ring production, spliced and vulcanized methods can be used. This approach does not require a specialized mold but utilizes extruded elastomer cord instead.

Material Selection

Selecting the right material for an O-ring is crucial to ensure optimal performance. Factors such as chemical compatibility, temperature resistance, and other specific requirements dictate the choice of material and its suitability for a given application.

O-rings are manufactured from a variety of elastomers, with common types including PTFE, Nitrile (Buna), Neoprene, EPDM Rubber, Fluorocarbon (Viton™), and Silicone. Silicone is particularly suited for high-temperature applications. The chart below provides an overview of several O-ring materials and their properties. The performance and characteristics of elastomers are derived from the specific materials used in their formulation.

Extrusion

In the extrusion process, elastomer is fed into an extruder, where it is heated and forced through a die. This process shapes the material into cords of the desired configuration, which are then used in the molding process. The die is selected based on the diameter of the finished O-ring.

Molding

Three primary molding processes are used in the production of O-rings: compression molding, transfer molding, and injection molding.

Compression – Compression molding is used when there is a need for a high volume small non-standard O-rings. With compression molding, the extruded material is placed in the mold cavity and held at a high temperature under pressure, which forces it to take the shape of the mold.

Transfer Molding – Transfer molding is a process that combines elements of both compression and injection molding. In this method, the material is first placed in a transfer pot and then forced into the mold under uniform pressure as the mold is closed. This process results in higher dimensional tolerances and reduced environmental impact. The material, which can be solid, is heated and transferred into the preheated mold to achieve the desired shape.

Injection Molding – In the injection molding process, the material is preheated and then injected under pressure through an injection nozzle into the mold. The material flows through a series of sprues into the enclosed mold cavity. Once the material fills the mold, it is allowed to cool and harden, taking on the shape of the mold cavity.

Post Mold Curing – Post mold curing is a process used to enhance the physical properties and performance of molded O-rings. During post curing, the O-ring is exposed to elevated temperatures, which improves its characteristics. This process aids in cross-linking, thereby increasing tensile strength, flexibility, and heat distortion temperature beyond what is achieved with room temperature curing.

Spliced and Vulcanized Extrusions

Another method for manufacturing extruded cord is spliced vulcanization, which does not involve using a die to create O-rings. Spliced vulcanized O-rings are made from extruded cord that is cut and bonded. This method is suitable for static sealing applications, quick production runs, or when only a few O-rings are needed. They can be made from a variety of elastomers and can be produced in any size.

To create a spliced and vulcanized O-ring, the extruded cord is cut to the required length, and the ends are joined using a bonding agent. The bonded ends are then placed in a high-temperature mold to form a molecular bond at the joint.

Spliced and vulcanized O-rings are designed for static use only and should not be used in applications involving moving parts. They are not recommended for dynamic applications. This method is ideal for producing small quantities and short production runs.

Finishing

After molding, O-rings often have excess material around the edges where the molds meet. This excess material, known as flash, needs to be removed to achieve the correct shape and size of the O-ring. Flash can be removed using three different processes to ensure the O-ring is perfectly round.

• Drumming – The O-rings are placed in a rapidly rotating drum that contains stones. As the drum turns, the excess material is removed by rubbing against the stones.
• Buffing – For larger O-rings that cannot be placed in a drum, the flash is removed by the abrasive action of a buffer.

• Cryogenic – Cryogenic deflashing is a computer controlled process that uses nitrogen gas to freeze the O-rings causing the flash to freeze and later be removed with grit. It is a safe clean process that removes outer diameter (OD) and inner diameter (ID) flash.

  

  
  

Curing

Once the O-rings are deflashed, they need to be cured. How long the O-rings are in the curing oven depends on the type of elastomer and can vary from a few hours to a day. The purpose of this step is to stabilize the finished O-rings and drive off any by contaminants from the production process.

Chapter 3:What are the design considerations and materials used for O-rings?

Although rubber was originally the primary material used to produce O-rings, the range of materials available has significantly expanded in recent years. The selection of a specific material depends on the O-ring's final application, which is to act as a seal between two surfaces to prevent the leakage of gases or liquids.

The choice of material is crucial in designing an O-ring. Other important factors include the intended application, the design and size of the groove or gland, surrounding conditions, and the O-ring's cross-sectional diameter and roundness.

O-Ring Design

Although an O-ring may seem simple—essentially a circle made of elastomer—the term "design" is quite relevant. Several factors must be considered when producing an O-ring, including its inner diameter (ID), cross-sectional diameter (CS), material hardness, durability, and overall shape. Each of these aspects is critical in selecting the appropriate O-ring for a specific application.

Steps to Designing an O-Ring

1. Choose a material that has the properties and characteristics for the application.
2. A key factor in selecting an O-ring is its ability to withstand the conditions it will have to endure. The main concern is the temperature of the application, which can damage the elasticity of the O-ring by increasing its cross link density.
3. Different O-ring materials are capable of being used with certain liquids and gases since some can withstand the effects of chemicals and oil, while others are not designed for such conditions. During the design phase, it is important to consider, and closely examine, the types of gases or liquids the O-ring may be subjected to.
4. The hardness of the O-ring has to fit the needs of the application. O-rings vary in hardness from rubber band softness to the hardened wheels of a shopping cart or conveyor.

5. A major factor in the design of an O-ring is the size of the groove or gland where it will be placed. The determining factor when choosing the proper O-ring is the cross sectional (CS) dimensions of the O-ring, which can be seen in the chart below.

   

   
   

O-Ring Materials

As new applications for O-rings have emerged, a variety of materials have been developed to meet these increasing demands. These materials include various types of rubber, silicone, and polymers. Regardless of the material used, all O-ring materials share fundamental qualities, such as elasticity and strength, which are essential for performing well under critical and demanding conditions.

Polytetrafluoroethylene (PTFE) O-Rings

Polytetrafluoroethylene (PTFE) O-rings are white and highly valued for their resistance to a wide range of substances, including acids, bases, solvents, oils, alkalis, and oxidants. They can operate effectively within a temperature range of -100°F to 500° F (-73°C to 260°C. While PTFE O-rings are durable and resistant to abrasion, they are not easily compressible, which may result in a less secure seal.

Unlike many other elastomers, PTFE O-rings do not degrade over time and have an extended shelf life. They are also resistant to ultraviolet light and generate minimal friction. PTFE O-rings are self-lubricating and, due to their low friction properties, are well-suited for use in hoses and pipes.

Silicone

Silicone is derived from silicon, an element extracted from quartz, and is produced by combining it with organic groups such as methyl, phenyl, or vinyl. The specific properties of silicone are determined by these additional elements. Silicone is resistant to oils, chemicals, heat, ozone, corona, and solvents, and it retains its flexibility even at low temperatures. Typical silicone can operate within a temperature range of -60° to 225°C, while specially formulated versions can withstand temperatures from -100° to 300°C.

Viton™

Viton™ is a synthetic fluoropolymer elastomer used for O-rings in demanding and harsh conditions. It is the preferred choice for applications requiring an O-ring that can withstand extreme heat and severe environmental conditions, including exposure to oxygen, mineral oils, various fuels, hydraulic fluids, chemicals, and solvents. Viton™ O-rings are known for their exceptional performance in extreme temperature conditions.

Nitrile butadiene rubber (NBR)

NBR, also known as acrylonitrile butadiene or Buna-N, is a synthetic rubber copolymer made from butadiene and acrylonitrile. It offers excellent mechanical properties and wear resistance, which vary depending on the proportion of the components used in its production. Higher nitrile content enhances its resistance to oils and fuels. NBR is used in applications involving dilute acids, alkalis, and salt solutions and is available in a wide range of colors.

Ethylene Propylene (EPDM or EPM)

EPDM (ethylene propylene diene monomer) is a terpolymer consisting of ethylene and propylene with a monomer like diolefin to facilitate vulcanization. It is highly resistant to ozone, sunlight, and weathering, and maintains good flexibility at low temperatures. EPDM is used for O-rings due to its resistance to dilute acids, alkalis, and certain solvents, as well as its electrical insulation properties. Available in various colors, EPDM is suitable for applications involving phosphate ester-based hydraulic fluids, glycol-based brake fluids, and conditions with hot water or steam up to 150°C.

Polyurethane

Polyurethane rubber is a thermoplastic elastomer created by reacting a polyol with a diisocyanate or polymeric isocyanate, often with the aid of a catalyst. It boasts high strength and excellent resistance to tears, abrasions, and leakage. Polyurethane O-rings are known for their resistance to hydraulic oil, gasoline, hydrocarbons like propane, grease, water, oxygen, and aging. These properties make them ideal for use in hydraulic systems, cylinder and valve fittings, pneumatic tools, and firearms.

Chlorosulfonated polyethylene (CSM)

CSM O-rings are produced by treating polyethylene with a blend of chlorine and sulfur dioxide under UV radiation. The chlorine content typically ranges from 20% to 40%, with a minor amount of chlorosulfonyl. This treatment aids in the vulcanization process, which enhances the strength of the O-rings. CSM O-rings are resistant to dilute acids, alcohols, ozone, oxidation, and weathering. Due to their low compression resistance, they are primarily suited for static applications.

Neoprene (CR)

Neoprene, a homopolymer made from chloroprene, is one of the earliest synthetic rubbers used for sealing. The production process begins with polychloroprene in powder form, to which other materials are added to adjust cell size, adhesion, bulk, and color. After mixing, the material is formed into sheets in a heat press and then processed through extrusion. Neoprene is valued for its resistance to oxidation and weather conditions, and its low cost is a significant advantage. Additionally, sulfur curing enhances its resistance to flammability.

Fluorosilicone (FLS)

Fluorosilicone shares many properties with silicone but incorporates trifluoropropyl groups, enhancing its resistance to solvents, oil, fuel, acids, and alkalis. This makes it ideal for static sealing applications in aerospace, automotive, and aviation industries. Fluorosilicone benefits from properties typical of fluorocarbons, such as exceptional flexibility, excellent aging characteristics, and resistance to UV rays. The addition of fluorine in its production process also provides superior chemical resistance and lower surface energy.

Leading Manufacturers and Suppliers

Chapter 4: What are the sizes of O-Rings?

The size of an O-ring is defined by its inner diameter (ID) and cross-sectional diameter (CS). The dimensions of O-rings are commonly specified by the AS568D sizing standard, though a Japanese sizing system is also used.

AS568D, established by the Society of Automotive Engineers (SAE), is the aerospace size standard for O-rings. This standard specifies the inner diameters, cross-sectional diameters, and tolerances, and includes a numbering code for O-rings used in sealing applications. The AS568D sizing chart provides configurations in both inches and millimeters, and is widely used by manufacturers to determine O-ring dimensions.

Each O-ring size is identified by a code in the format AS568-XXX. For general reference, the AS568 prefix is often omitted, leaving the last three digits. In this code, the first digit represents the cross-sectional diameter, while the second digit denotes the inner diameter. For accurate sizing information, consulting the AS568D chart is essential.

Measuring an O-Ring

Inner Diameter

To measure the inner diameter (ID) of an O-ring, position the beginning of a tape measure at the inner edge of one side of the O-ring and read the measurement at the inner edge on the opposite side. Accurate measurement of the O-ring ID is crucial to ensure that, when under pressure, the O-ring does not extrude into the gap between the surfaces. The ID should precisely match the diameter of the groove where the O-ring will be installed.

Cross Section

The cross section (CS) of an O-ring refers to the width of the material that makes up the ring, measured as the thickness of the O-ring's material. To measure the CS, place the O-ring on a flat surface and measure the width of the material directly. Common CS sizes for O-rings include 0.040", 0.070", 0.103", and 0.139". Standard metric sizes range from 1 mm to 5 mm. Of these measurements, the CS is the most critical, as it determines how well the O-ring fits into its groove and is crucial for preventing O-ring failure and leaks.

O-Ring Size Chart

Cross Section (MM)	Inside Diameter (MM)	Outside Diameter (MM)
1.02	0.74	2.78
1.27	1.07	3.61
1.52	1.42	4.46
1.78	1.78	5.34
1.78	2.57	6.13
1.78	2.90	6.46
1.78	3.68	7.24
1.78	4.47	8.03
1.78	5.28	8.84
1.78	6.07	9.63
1.78	7.65	11.21
1.78	9.25	12.81
1.78	10.82	14.38
1.78	12.42	15.98
1.78	14.00	17.56
1.78	15.60	19.16
1.78	17.17	20.73
1.78	18.77	22.33
1.78	20.35	23.91
1.78	21.95	25.51
1.78	23.52	27.08
1.78	25.12	28.68
1.78	26.70	30.26
1.78	28.30	31.86
1.78	29.87	33.43
1.78	31.47	35.03
1.78	33.05	36.61
1.78	34.65	38.21
1.78	37.82	41.38
1.78	41.00	44.56
1.78	44.17	47.73
1.78	47.35	50.91
1.78	50.52	54.08
1.78	53.70	57.26
1.78	56.87	60.43
1.78	60.05	63.61
1.78	63.22	66.78
1.78	66.40	69.96
1.78	69.57	73.13
1.78	72.75	76.31
1.78	75.92	79.48
1.78	82.27	85.83
1.78	88.62	92.18
1.78	94.97	98.53
1.78	101.32	104.88
1.78	107.67	111.23
1.78	114.02	117.58
1.78	120.37	123.93
1.78	126.72	130.28
1.78	133.07	136.63
2.62	1.24	6.48
2.62	2.06	7.30
2.62	2.84	8.08
2.62	3.63	8.87
2.62	4.42	9.66
2.62	5.23	10.47
2.62	6.02	11.26
2.62	7.59	12.83
2.62	9.19	14.43
2.62	10.77	16.01
2.62	12.37	17.61
2.62	13.94	19.18
2.62	15.54	20.78
2.62	17.12	22.36
2.62	18.72	23.96
2.62	20.29	25.54
2.62	21.89	27.13
2.62	23.47	28.71
2.62	25.07	30.31
2.62	26.64	31.88
2.62	28.24	33.48
2.62	29.82	35.06
2.62	31.42	36.66
2.62	32.99	38.23
2.62	34.59	39.83
2.62	36.17	41.41
2.62	37.77	43.01
2.62	39.34	44.58
2.62	40.94	46.18
2.62	42.52	47.76
2.62	44.12	49.36
2.62	45.69	50.93
2.62	47.29	52.54
2.62	48.90	54.14
2.62	50.47	55.71
2.62	52.07	57.31
2.62	53.64	58.88
2.62	55.25	60.49
2.62	56.82	62.06
2.62	58.42	63.66
2.62	59.99	65.23
2.62	61.60	66.84
2.62	63.17	68.41
2.62	64.77	70.01
2.62	66.34	71.58
2.62	67.95	73.19
2.62	69.52	74.76
2.62	71.12	76.36
2.62	72.69	77.93
2.62	75.87	81.11
2.62	82.22	87.46
2.62	88.57	93.81
2.62	94.92	100.16
2.62	101.27	106.51
2.62	107.62	112.86
2.62	113.97	119.21
2.62	120.32	125.56
2.62	126.67	131.91
2.62	133.02	138.26
2.62	139.37	144.61
2.62	145.72	150.96
2.62	152.07	157.31
2.62	158.42	163.66
2.62	164.77	170.01
2.62	171.12	176.36
2.62	177.47	182.71
2.62	183.82	189.06
2.62	190.17	195.41
2.62	196.52	201.76
2.62	202.87	208.11
2.62	209.22	214.46
2.62	215.57	220.81
2.62	221.92	227.16
2.62	228.27	233.51
2.62	234.62	239.86
2.62	240.97	246.21
2.62	247.32	252.56
3.53	4.34	11.40
3.53	5.94	13.00
3.53	7.52	14.58
3.53	9.12	16.18
3.53	10.69	17.75
3.53	12.29	19.35
3.53	13.87	20.93
3.53	15.47	22.53
3.53	17.04	24.10
3.53	18.64	25.70
3.53	20.22	27.28
3.53	21.82	28.88
3.53	23.39	30.45
3.53	24.99	32.06
3.53	26.57	33.63
3.53	28.17	35.23
3.53	29.74	36.80
3.53	31.34	38.40
3.53	32.92	39.98
3.53	34.52	41.58
3.53	36.09	43.15
3.53	37.69	44.75
3.53	40.87	47.93
3.53	44.04	51.10
3.53	47.22	54.28
3.53	50.39	57.45
3.53	53.57	60.63
3.53	56.74	63.80
3.53	59.92	66.98
3.53	63.09	70.15
3.53	66.27	73.33
3.53	69.44	76.50
3.53	72.62	79.68
3.53	75.79	82.85
3.53	78.97	86.03
3.53	82.14	89.20
3.53	85.32	92.38
3.53	88.49	95.55
3.53	91.67	98.73
3.53	94.84	101.90
3.53	98.02	105.08
3.53	101.19	108.25
3.53	104.37	111.43
3.53	107.54	114.60
3.53	110.72	117.78
3.53	113.89	120.95
3.53	117.07	124.13
3.53	120.24	127.30
3.53	123.42	130.48
3.53	126.59	133.65
3.53	129.77	136.83
3.53	132.94	140.00
3.53	136.12	143.18
3.53	139.29	146.35
3.53	142.47	149.53
3.53	145.64	152.71
3.53	148.82	155.88
3.53	151.99	159.05
3.53	158.34	165.40
3.53	164.69	171.75
3.53	171.04	178.10
3.53	177.39	184.45
3.53	183.74	190.80
3.53	190.09	197.15
3.53	196.44	203.50
3.53	202.79	209.85
3.53	209.14	216.20
3.53	215.49	222.55
3.53	221.84	228.90
3.53	228.19	235.25
3.53	234.54	241.60
3.53	240.89	247.95
3.53	247.24	254.30
3.53	253.59	260.65
3.53	266.29	273.35
3.53	278.99	286.05
3.53	291.69	298.75
3.53	304.39	311.45
3.53	329.79	336.85
3.53	355.19	362.25
3.53	380.59	387.65
3.53	405.26	412.32
3.53	430.66	437.72
3.53	456.06	463.12
5.33	10.46	21.12
5.33	12.07	22.73
5.33	13.64	24.30
5.33	15.24	25.90
5.33	16.81	27.47
5.33	18.42	29.08
5.33	19.99	30.65
5.33	21.59	32.25
5.33	23.16	33.82
5.33	24.77	35.43
5.33	26.34	37.00
5.33	27.94	38.60
5.33	29.51	40.17
5.33	31.12	41.78
5.33	32.69	43.35
5.33	34.29	44.95
5.33	37.47	48.13
5.33	40.64	51.30
5.33	43.82	54.48
5.33	46.99	57.65
5.33	50.17	60.83
5.33	53.34	64.00
5.33	56.52	67.18
5.33	59.69	70.35
5.33	62.87	73.53
5.33	66.04	76.70
5.33	69.22	79.88
5.33	72.39	83.05
5.33	75.57	86.23
5.33	78.74	89.40
5.33	81.92	102.58
5.33	85.09	95.75
5.33	88.27	98.93
5.33	91.44	102.10
5.33	94.62	105.28
5.33	97.79	108.45
5.33	100.97	111.63
5.33	104.14	114.80
5.33	107.32	117.98
5.33	110.49	121.15
5.33	113.67	124.33
5.33	116.84	127.50
5.33	120.02	130.68
5.33	123.19	133.85
5.33	126.37	137.03
5.33	129.54	140.20
5.33	132.72	143.38
5.33	135.89	146.55
5.33	139.07	149.73
5.33	142.24	152.90
5.33	145.42	156.08
5.33	148.59	159.25
5.33	151.77	162.43
5.33	158.12	168.78
5.33	164.47	175.13
5.33	170.82	181.48
5.33	177.17	187.83
5.33	183.52	194.18
5.33	189.87	200.53
5.33	196.22	206.88
5.33	202.57	213.23
5.33	208.92	219.58
5.33	215.27	225.93
5.33	221.62	232.28
5.33	227.97	238.63
5.33	234.32	244.98
5.33	240.67	251.33
5.33	247.02	257.68
5.33	253.37	264.03
5.33	266.07	276.73
5.33	278.77	289.43
5.33	291.47	302.13
5.33	304.17	314.83
5.33	329.57	340.23
5.33	354.97	365.63
5.33	380.37	391.03
5.33	405.26	415.92
5.33	430.66	441.32
5.33	456.06	466.72
5.33	481.46	492.07
5.33	506.86	517.47
5.33	532.26	542.87
5.33	557.66	568.27
5.33	582.68	593.34
5.33	608.08	618.74
5.33	633.48	644.14
5.33	658.88	669.54
6.99	34.29	48.26
6.99	37.47	51.44
6.99	40.64	54.61
6.99	43.82	57.79
6.99	46.99	60.96
6.99	50.17	64.14
6.99	53.34	67.31
6.99	56.52	70.49
6.99	59.69	73.66
6.99	62.87	76.84
6.99	66.04	80.01
6.99	69.22	83.19
6.99	72.39	86.36
6.99	75.57	89.54
6.99	78.74	92.71
6.99	81.92	95.89
6.99	85.09	99.06
6.99	88.27	102.24
6.99	91.44	105.41
6.99	94.62	108.59
6.99	97.79	111.76
6.99	100.97	114.94
6.99	104.14	118.11
6.99	107.32	121.29
6.99	110.49	124.46
6.99	113.67	127.65
6.99	116.84	130.82
6.99	120.02	134.00
6.99	123.19	137.17
6.99	126.37	140.35
6.99	129.54	143.52
6.99	132.72	146.70
6.99	135.89	149.87
6.99	139.07	153.05
6.99	142.24	156.22
6.99	145.42	159.40
6.99	148.59	162.57
6.99	151.77	165.75
6.99	158.12	172.10
6.99	164.47	178.45
6.99	170.82	184.80
6.99	177.17	191.15
6.99	183.52	197.50
6.99	189.87	203.85
6.99	196.22	210.20
6.99	202.57	216.55
6.99	215.27	229.25
6.99	227.97	241.95
6.99	240.67	254.65
6.99	253.37	267.35
6.99	266.07	280.05
6.99	278.77	292.75
6.99	291.47	305.45
6.99	304.17	318.15
6.99	316.87	330.85
6.99	329.57	343.55
6.99	342.27	356.25
6.99	354.97	368.95
6.99	367.67	381.65
6.99	380.37	394.35
6.99	393.07	407.05
6.99	405.26	419.24
6.99	417.96	431.94
6.99	430.66	444.64
6.99	443.36	457.34
6.99	456.06	470.04
6.99	468.76	482.74
6.99	481.46	495.44
6.99	494.16	508.14
6.99	506.86	520.84
6.99	532.26	546.24
6.99	557.66	571.64
6.99	582.68	596.66
6.99	608.08	622.06
6.99	633.48	647.46
6.99	658.88	672.86
1.42	4.70	7.54
1.63	6.07	9.33
1.63	7.65	10.91
1.83	8.92	12.58
1.83	10.52	14.18
1.98	11.89	15.85
2.08	13.46	17.62
2.21	16.36	20.78
2.46	17.93	22.85
2.46	19.18	24.10
2.95	21.92	27.82
2.95	23.47	29.37
2.95	25.04	30.94
2.95	26.59	32.49
2.95	29.74	35.64
2.95	34.42	40.32
3.00	37.47	43.47
3.00	43.69	49.69
3.00	53.09	59.09
3.00	59.36	65.36

Chapter 5: What are the different types of O-rings?

O-rings come in a vast array of types and applications. Despite their small, circular shape and diverse materials, O-rings play a crucial role in various mechanisms and equipment. Their classification depends on the material they are made from and the specific application they are designed for. During the design process, engineers select the appropriate O-ring based on these factors to ensure optimal performance and reliability.

Nitrile O-Rings

Nitrile O-rings, also known as Buna-N or NBR O-rings, operate effectively within a temperature range of -50° C to 120° C (-58° F up to 248°. They are favored for their resistance to tearing and abrasion. Nitrile O-rings are particularly valued for their durability against water, oils, and hydraulic fluids. However, they can be adversely affected by certain hydrocarbons, brake fluids, ketones, and phosphate esters.

Viton™ O-Rings

Commonly known as FKM O-rings due to their fluorocarbon base, Viton^TM O-rings boast exceptional mechanical properties, low gas permeability, and low compression set, with a temperature range of -40°C to 250°C (-40°F to 482°F). They are resistant to acids, halogenated hydrocarbons, petroleum, and silicone fluids and gases. However, they should not be used with heated hydrofluoric acids, amines, esters, Skydrol, or ethers such as dimethyl, methyl ethyl, or diethyl. The versatility of Viton^TM O-rings makes them suitable for a wide range of conditions.

Silicone O-Rings

Capable of withstanding temperatures of-100°C up to 300°C (-148°F up to 572°F, silicone O-rings have the widest temperature tolerance range of any of the O-ring materials, with an extreme range of -115°C to 315° C (-175°F to 600°F) for short periods of time. Regardless of their many positive properties, such as their resistance to the effects of water, steam, and petroleum, silicone O-rings are susceptible to ripping and damage from abrasions, which makes them ideal for static applications.

Teflon (PTFE) O-Rings

Teflon O-rings are highly effective in environments exposed to extreme temperatures, chemicals, solvents, and anti-adhesives. Thanks to their PTFE composition, these O-rings offer remarkable tensile and compressive strength, along with dielectric properties, a low friction coefficient, and non-toxicity. They can withstand continuous use at temperatures up to 250°C (482°F) and retain nearly zero compressive plasticity at lower temperatures. The operational temperature range for Teflon O-rings extends from -200°C up to 250°C (-328°F up to 482°F).

Clear O-Rings

Clear O-rings, referred to as medical O-rings, are a specialty O-ring used in applications that require a seal that can be visually checked and monitored. They are made of silicone or fluorocarbon that allows for easy detection of contamination, damage, or deformation. The necessity of visual inspection is important in applications involving high precision machines or laboratory equipment. They are an essential part of food production and medical equipment as a means of hygiene.

Flat O-Rings

The traditional and common profile of an O-ring is round. However, flat O-rings have a rectangular or square profile, known as torus shapes. They are used in spaces where traditional O-rings do not fit but provide the same tight seal. Flat O-rings are recommended for rotary sealing and hydraulic and pneumatic equipment. They require less pressure to create a seal and can be easily replaced. Additionally, flat O-rings tend to last longer, cost less, and experience less wear and tear, which reduces the need for lubrication.

Large O-Rings

Manufacturing large O-rings requires specialized processes, as typical O-ring production methods are inadequate for these sizes. A common method for producing large O-rings is thermobonding, also known as spliced and vulcanized. In this process, the joints of the O-ring are sealed with an adhesive and then cured, providing the O-ring with exceptional flexibility. Large O-rings find applications in various industries, including chemical processing, food processing, electronics, and pharmaceuticals, where they are used in applications ranging from panel displays to threaded tube fittings.

Metal O-Rings

Metal O-rings are designed for high-temperature and high-pressure applications, such as those involving fluids in exhaust systems, melt stream plastics, combustion processes, hydraulics, and valves. They are well-suited for extreme conditions, including high heat, cold, pressure, and vacuums, making them ideal for situations where polymer O-rings may fall short.

Known for their durability, metal O-rings can last for many years and are the only type of O-ring capable of creating a four-point seal. They offer resistance to corrosion, pressure, and temperature and can be manufactured with a plastic coating when full contact is necessary.

Stainless steel is commonly used to make metal O-rings due to its exceptional properties. These O-rings have a temperature range of -267° C up to 704° C (-450° F up to 1300° F). They are made from coiled metal tubing, which is cut and welded to the required size. Wall thickness, outer diameter (OD), inner diameter (ID), and cross-sectional profiles can vary to meet the specific needs of an application.

Metric O-Rings

Metric O-rings perform the same functions as O-rings measured using the imperial system but are produced using metric measurements for the outer diameter (OD), inner diameter (ID), and cross-sectional profile. They are designed for use in countries that utilize the metric system for the manufacture of machines and equipment. Most manufacturers offer O-rings in both imperial and metric measurements, and they are available in the same materials as those produced using the imperial system.

O-Ring Seals

O-ring seals are dynamic seals employed in rotating or reciprocating machinery, including pistons, cylinders, and rotating shafts. They are placed in a gland or groove, where they are positioned between machinery connections to form an air- and water-tight seal. O-ring seals are designed to endure high pressure, varying temperatures, and extreme stress.

When pressure is applied, the O-ring seal is compressed and deformed to fill the gap between connected machinery. The temperature range for O-ring seals varies depending on the material used, with some capable of withstanding temperatures as low as -55° C (-67° F) to as high as 205° C (401° F).

Rubber O-Rings

The first O-rings, introduced during the Industrial Revolution, were made of rubber by J. O. Lundberg of Sweden. Niels Christensen introduced these O-rings to the United States in 1891 and patented his design in 1937. Since their inception, rubber O-rings have evolved with the incorporation of elastic polymers, enhancing their sealing capabilities and stability.

A significant advancement in O-ring technology occurred in 1986 following the Challenger disaster. The investigation revealed that the explosion was caused by an O-ring failure due to excessively low temperatures. This revelation led engineers to develop more resilient and reliable O-rings.

The term "rubber O-ring" encompasses a variety of synthetic rubbers designed for different applications, conditions, and environments. Each type of synthetic rubber O-ring offers distinct temperature ranges, chemical resistances, and pressure tolerances. Among the most common synthetic rubbers used for O-rings are Nitrile and Viton™.

High Temperature O-Rings

One of the key advantages of O-rings is their ability to maintain a seal across a wide range of temperatures, from extreme lows to extreme highs. High-temperature O-rings are categorized based on the maximum temperature they can withstand for over 1000 hours, determined by analyzing the specific application in which they will be used. The temperature range for high-temperature O-rings typically spans from 204°C (400°F) and 316°C (600°F).

Types of materials used for high-temperature O-rings and their maximum temperatures:

• Perfluorinated (FFKM) up to 600°F (316°C)
• Tetrafluoroethylene-Propylene (TFE, AFLAS®) up to 450°F (232°C)
• Fluorocarbon (FKM, VITON®) up to 400°F (204°C)
• Fluorosilicone (FMQ, FVMQ) up to 400°F (204°C)
• Silicone (VMQ) up to 400°F (204°C)

Exposure to temperatures beyond an O-ring's design limits can cause it to harden and become brittle. This results in cracking, leakage, and a loss of elasticity known as compression set.

To assist with OEM part identification and prevent assembly errors, high-temperature O-rings are often produced in various colors. They are highly valued for their reliability and stability, making them essential for demanding applications.

Chapter 6: How are O-rings used?

Since their inception in the late 19th century, O-rings have been a crucial component in a range of machinery. Their ability to effectively seal and contain gases and liquids has made them indispensable in equipment design. As technology has progressed, the O-ring has evolved from a simple rubber component to a versatile part made from a wide array of materials, catering to diverse applications.

O-Ring Applications: Static vs Dynamic

The applications of O-rings are classified based on the type of motion between the two surfaces they seal. Static applications involve surfaces that do not move relative to each other, while dynamic applications involve surfaces that move in relation to one another. Dynamic applications can include reciprocating, rotating, oscillating, or vertical and horizontal movements. Although the distinction between static and dynamic applications is straightforward, the materials used to manufacture O-rings must be specifically designed to withstand the pressure, tolerance, and conditions of the intended use.

Static O-Ring

A static O-ring is designed for applications where it seals between two or more stationary surfaces, with the sealing action being parallel to the centerline of the O-ring. The O-ring compresses between a groove cut into one flat surface and a second flat surface, which presses the O-ring into the groove. In this setup, the O-ring remains stationary and does not move. The diagram below illustrates the cross-sectional (CS) view of the O-ring in red.

When pressure is applied, it forces the O-ring outward to match the groove's outer diameter (OD), minimizing any shifting or movement of the O-ring within the groove. Other types of static O-rings include crush seals, dovetail glands, and radial seals.

Dynamic O-Ring

A dynamic seal is required when there is motion between two components, necessitating a seal that can withstand movement. Dynamic O-rings must meet more complex requirements, including enhanced toughness, strength, and resistance to abrasion and friction.

Unlike static seals, dynamic O-rings are subject to wear and tear from continuous motion, which can lead to abrasion and damage. Regular lubrication is essential for maintaining the performance of dynamic O-rings. The effectiveness of these seals is influenced by several factors, including fluid swell, the surface finish of metal parts, lubrication quality, system pressure, thermal cycling, O-ring squeeze, stretch, and friction. Since these factors interact, it's crucial to consider all possible dynamic sealing conditions.

Dynamic O-rings are commonly used in reciprocating and rotary applications. In some cases, such as valve stem sealing, a combination of these types may be employed.

• Reciprocating Seal: A reciprocating seal refers to the use of a moving piston or rod, which is the most common form of dynamic O-ring usage. The factors that have to be considered for this type of application are pressure shock, squeeze, stretch, and thermal cycling where there is a wide variation in the temperature. For the best results with a reciprocating seal, surfaces should not be highly finished since they will not be able to retain lubrication.
• Rotary Seal: A rotary seal involves a turning shaft that protrudes from the ID. For this application temperature, friction, seal stretch, squeeze, and type of shaft have to be examined. For rotary operations, shafts should be made of hard metal with a 0.0005” TIR and with surfaces having a finish of 16 RMS as well as being non-abrasive.

How O-Rings are Used

High Temperature

High temperature applications demand O-rings that can endure elevated temperatures while still providing an effective seal. The chart below offers an overview of popular O-ring materials and their respective temperature ranges. Industries that commonly require high-temperature O-rings include refineries, chemical processing plants, turbo engines, and aerospace.

High Pressure

O-rings are commonly used in high-pressure applications, where the pressure applied causes deformation of the O-ring within the groove. This results in uniform mechanical stress on the O-ring's surface. The key is to ensure that the pressure gradient remains within the O-ring's stress rating, preventing seepage or leaks.

However, mechanical failure can lead to extrusion and damage of the O-ring. To avoid such issues, selecting the appropriate O-ring material for the specific application is crucial.

For engine seals, O-rings must be compatible with temperature, pressure, and chemical conditions. Standard rubbers and polymers often lack the necessary strength and resistance for engine applications, necessitating the use of hybrid materials specifically designed for these demanding environments.

Carbon Dioxide (CO2)

Carbon dioxide poses particular challenges for O-rings because softer materials can absorb the gas and swell, compromising the seal's reliability. If the gas absorption is not controlled, the O-ring may crack and deteriorate over time.

Vacuum

Vacuum O-rings are used in compressors and ultra-high vacuum (UHV) pumps. They are manufactured from materials that are impermeable, deformable into the sealing surface, and outgassing. For effective sealing, the surface where the O-ring sits must be rough, flat, and finished to allow proper deformation of the O-ring into the groove.

Different O-rings have varying permeation rates depending on the type of gas they are exposed to. For instance, silicone exhibits high permeability to air, while FKM and Viton™ are less permeable. Vacuum O-rings are designed to adapt to surface irregularities of the vacuum chamber and are often lubricated to smooth out both the surface and the O-ring. These O-rings are typically used in static applications.

Chapter 7: What is the proper care for O-rings?

While O-rings are designed to be durable and robust, they still require regular monitoring and potential replacement depending on their application. To maximize their lifespan and maintain optimal performance, various maintenance actions are essential. Proper care can help extend the life of an O-ring and ensure it operates effectively.

For O-rings to function correctly, they must be kept free of dirt and debris. Any foreign contaminants can interfere with the O-ring's ability to properly seal within its groove or gland. To ensure reliable sealing, it's important to regularly inspect, clean, and lubricate the O-ring.

Installation

Proper installation is key to O-ring maintenance. Ensure that the groove or gland is free from any metallic debris that could cut or damage the O-ring. Place the O-ring carefully, avoiding any twisting or torquing to ensure a uniform seal. Applying a suitable lubricant and using a tape cover can provide additional protection and extend the O-ring’s service life.

Lubrication

To extend the lifespan of O-rings, they should be coated with a thin layer of lubricant. Dryness is a major cause of damage, as it prevents the O-ring from maintaining an effective seal.

Cleaning

Regular cleaning of O-rings with soap and water is essential. Avoid using harsh solvents like trichloroethylene and carbon tetrachloride, which can harm the O-ring. Soap and water or methylated spirits are safer options. Sharp tools and brushes should be avoided to prevent damage to the O-ring.

Chemical Damage

Inspect O-rings for signs of blistering, cracking, or discoloration, which can indicate chemical damage. Choosing the right lubricant and O-ring material for the specific application can help prevent such issues.

Replacements

Always keep replacement O-rings on hand. Store them in a cool, dark place, away from ultraviolet light and sunlight, which can degrade the O-ring’s outer layer.

Swelling

Swelling is indicated by a loss of the O-ring’s circular shape and a flattening effect. This permanent deformation occurs when the O-ring is over-compressed, reducing its compressive ability. Avoid over-compression to prevent this issue.

Thermal Degradation

To avoid thermal degradation, select the appropriate O-ring material and ensure it is not exposed to temperatures beyond its rating. High temperatures can reduce the O-ring's elasticity and increase hardness, but choosing the right elastomer can resolve this problem.

Extrusion

Extrusion is noticeable when an O-ring gets caught between two surfaces, leading to a portion of the O-ring being pushed out of the groove. This can result in leaks and should be addressed immediately by replacing the O-ring.

Degradation

Exposure to high-energy light can cause O-ring degradation, resulting in discoloration or a blotchy appearance. This occurs due to the interaction between the O-ring material and light wavelengths, leading to cracking and potential leakage. Protecting O-rings from such exposure can prevent this issue.

Abrasions

One of the most common forms of damage to O-ring seal surfaces is abrasion, which can compromise the seal's effectiveness. Abrasions occur due to friction between the O-ring and the housing, generating heat that alters the O-ring's properties. This increased friction accelerates wear and tear, leading to lacerations and surface damage on the O-ring.

To prevent abrasion damage, applying a suitable lubricant can help slow down the deterioration process. Since abrasions typically affect only one side of the O-ring, they are relatively easy to identify and address.

Chapter 8: What are the industrial uses for O-rings?

The history of O-rings is closely linked to the development of rubber vulcanization. Initially, O-rings were used primarily as sealants for pistons and cylinders, a role they still fulfill today. During World War II, new applications for O-rings were discovered, making them a crucial component of the war effort.

The use of O-rings in industry has expanded rapidly as new applications are continually identified. From dental tools to camera lenses, O-rings are now integral to a diverse range of industrial uses.

Transportation

Buses, trucks, and cars rely on O-rings to seal various fluids within their systems. These fluids include fuels, refrigerants, and lubricating oils, each with unique temperature and usage conditions. O-rings are crucial for sealing braking systems and engine and transmission lubricants, preventing leaks and ensuring reliable performance.

Aerospace

In aerospace applications, O-rings are vital for aircraft construction, protecting jet engines from extreme temperatures and harsh conditions. Commercial aircraft use thousands of O-rings, each designed for specific functions, including handling high and low pressures, aggressive lubricants and fluids, and significant temperature variations.

As aircraft designs evolve, new O-ring materials have been developed to meet the increasing demands, with recent advancements enabling O-rings to operate at temperatures exceeding +275°F and with more durable compounds.

Medical

The United States Pharmacopeia (USP) establishes standards for materials utilized in the health and pharmaceutical sectors. Typically, O-rings are used to create seals for fluids and gases that may experience significant temperature and pressure fluctuations. In medical applications, however, O-rings must also meet additional requirements to ensure sanitary conditions and cleanliness.

Silicone elastomers are commonly employed in pumps, valves, piping, couplings, reaction vessels, and biomatter containers due to their ability to handle a broad spectrum of media and pharmaceutical ingredients (APIs), as well as their resistance to aggressive cleaning and sterilization processes. Medical O-rings must adhere to stringent regulations and hygiene standards set by the Food and Drug Administration (FDA), United States Pharmacopeia - Class VI (USP Class VI), 3-A Sanitary Standards, and Good Manufacturing Practice (GMP).

Oil

In the petroleum, oil, and gas industries, O-rings are essential for exploration, refining, and transportation of oil products. These O-rings must perform reliably under harsh conditions often found in mining and extraction environments. They must meet high standards for temperature and pressure, surpassing those required in many other industries.

Electronics

O-rings in the electronics industry are used for electromagnetic interference (EMI) shielding. Made from elastomers that resist a range of ohms from 7 cm to 0.002 cm, these O-rings are employed by telecommunications, military, and consumer electronics sectors. They provide a conductive interface for various applications and are available in sizes to meet diverse conditions.

Food

Silicone O-rings used in the food industry are FDA-approved and must meet the same stringent standards as those used in medical applications. They must comply with the FDA’s “White List” in Code of Federal Regulations – Title 21, Section 177.2600, which outlines requirements for materials in contact with food. Most of these materials are designed for high compression due to curing limitations.

Dentistry

In dentistry, silicone O-rings are used for securing dental implants. The O-ring fits over a ball that holds the implant in place, with precise sizing required for a secure fit. Unlike past methods involving paste or glue, modern implants use a permanently placed ball to retain the implant. Silicone O-rings act as buffers, preventing irritation by ensuring the implant does not rub against the gum.

In this scenario, silicone O-rings function as a cushioning layer to prevent the implant from rubbing against the gum and causing irritation.

Scuba Diving

In scuba diving, O-rings are critical for sealing underwater cameras, regulators, lights, and tank valves. Their primary function is to withstand water pressure and prevent leaks. For deep-water diving, O-rings are crucial for maintaining the diver’s air supply and protecting equipment and suits from water ingress.

Plumbing

Plumbing applications utilize a variety of O-rings in different sizes, gauges, and designs. Typically made from NBR, these O-rings are found in duct work, pipe fixtures, and around taps and fittings. They are essential in push-fit connections, providing a seal to prevent water leakage and allowing for rotation of the fitting. NBR O-rings are integral to piping and water systems.

Conclusion

• An O-ring is a round elastic loop that is used as a seal for static and dynamic applications.
• The production and manufacture of O-rings involves the use of two production processes, which are extrusion and injection, compression, and transfer molding.
• The choice of a specific material used to produce an O-ring is dependent on its final use, which is to serve as a seal between two surfaces to prevent leakage of a gas or liquid.
• As new applications for O-rings arise, different materials have been adapted to fit the increased need.
• O-ring types are divided by their function and the material used to produce them. The two functional designs of O-rings are static and dynamic.

Leading Manufacturers and Suppliers