Sealants, Seals, Gaskets, and O-rings are essential components for hydraulic systems and equipment. Without these components, high-pressure Hydraulic Cylinder Repair Near Me hydraulic systems would be impractical or impossible to operate. Therefore, the selection of the appropriate sealing material is a nuanced process, as it often involves trade-offs between various factors, such as resilience versus stiffness, softness versus hardness, low-temperature versus high-temperature performance, and cost-effectiveness.
Nitrile Rubber Seals
Nitrile rubber seals, also known as Buna N seals, enjoy widespread use in the hydraulic industry due to their outstanding resistance to oil, a practical working temperature range spanning from -40 degrees C to as high as 135 degrees C, and cost-effectiveness. The presence of oil on the surface of nitrile rubber even helps prevent oxidation and aging, addressing common issues when nitrile materials are exposed to air and sunlight.
These seals exhibit excellent performance in Hydraulic Cylinder Repair Near Me fluid power systems. For instance, Parker Seal Company conducted rigorous tests to determine the fluid pressure capacity of a typical nitrile O-ring without extruding into the gap. To make the tests more meaningful, they maintained a constant temperature of 71 degrees C and cycled the pressure 100,000 times at various levels.
The hardness of elastomeric materials is typically measured using the shore durometer scale. Nitrile rubber seals most commonly have hardness ratings of 70, 80, and 90 shore.
Urethane Resists Abrasion
Polyurethane elastomers, commonly referred to as urethanes, bridge the gap between synthetic rubbers and plastics. They possess a unique combination of hardness, resilience, load-bearing capacity, and exceptional resistance to abrasion. Their temperature rating is moderate, reaching up to 93 degrees C. Urethane formulations are proprietary and result in a wide range of available properties. This material can be adapted for extrusion, molding, casting, or machining, with hardness ranging from as soft as a pencil eraser to as hard as a bowling ball. Urethane exhibits superior wear resistance compared to most rubbers, plastics, and even some metals. Additionally, its coefficient of friction tends to be relatively low, which decreases further as hardness increases. Urethane seals find extensive use as rod scrapers and other dynamic seals in high-pressure hydraulic hoses, highlighting their strength and ability to withstand harsh conditions.
Dupont supplies Viton fluoroelastomer, a somewhat costly material, to seal manufacturers. However, it is renowned for specific performance advantages that justify its use in numerous applications. Viton can even replace lower-cost seals when reliability outweighs initial expenses.
The Hydraulic Cylinder Repair Near Me normal maximum operating temperature for Viton ranges from 200 degrees C to 315 degrees C for intermittent service, retaining some hardness and resilience at these elevated levels. Even if the high operating temperature is not required, the hot tear strength of Viton allows for easy removal from molds without damage, facilitating the creation of intricate shapes. The material also exhibits good dynamic properties and low-temperature performance.
Teflon, produced by Dupont, and similar fluoroplastics like Halon from other companies possess two key properties that make them intriguing choices for sealing applications. They can operate efficiently across a broad temperature range, from cryogenic to 315 degrees C, and they possess self-lubricating properties. However, these materials have some drawbacks, including creep (cold flow) and limited methods for forming parts. Addressing creep involves designing the seal to either contain the plastic flow within the seal area or incorporating a metal or elastomer spring to maintain sealing force despite the creep. The blending and manufacturing of Teflon seals are akin to the art of powder metallurgy.
Hydraulic Cylinder Repair Near Me Universal Seals offers a solution to conflicting requirements of resilience and hardness through their uni-ring, a one-piece sealing ring with dual-durometer properties. The sealing surface of the seal is made from hard (97 durometer) urethane, while the backup consists of softer (45 durometer) urethane. Various other combinations are possible, such as incorporating a nitrile rubber O-ring within a urethane U-cup to achieve a spring-loaded rod and piston seal. In this configuration, the O-ring ensures effective sealing at low fluid pressure, and the sealing force increases with rising pressure.
O-rings are unassuming yet highly versatile components. They are one-piece molded elastomeric seals with a circular cross-section that achieves sealing by distorting their resilient, elastic material. O-ring dimensions adhere to the ANSI/SAE AS568A standard, which includes both imperial (inches) and metric (mm) sizes. While standard ring sizes are well-defined by identifying dash numbers, the compounds used to make O-rings may vary among manufacturers, each using distinct designations. For example, 230-8307 represents a standard O-ring size 230 (2.484” ID x 0.139” width) made from compound 8307, a general-purpose nitrile material.
Numerous O-ring compounds have been formulated for specific applications, with their hardness measured using the shore A durometer. Softer O-rings with 50 and 60 shore A ratings stretch more easily, exhibit lower breakout friction, seal better on rough surfaces, and require less clamping pressure than their harder counterparts. With harder rings, higher durometer hardness results in increased friction due to the greater compressive force exerted by these rings.
Properly installed in a groove, an O-ring is typically slightly deformed, causing its naturally round cross-section to be squeezed diametrically out of round before pressure is applied. This compression ensures that, under static conditions, the Hydraulic Cylinder Repair Near Me O-ring is in contact with the inner and outer walls enclosing it, creating a zero-pressure seal thanks to the resiliency of the rubber material.
When pressure is introduced, it pushes the Hydraulic Cylinder Repair Near Me O-ring across the groove, further deforming it and causing it to flow into the fluid passage, effectively sealing it against leakage. With increasing pressure, the O-ring deforms into a ‘D’ shape. However, if the clearance gap between the sealing surface and the groove corners is too large or if the pressure exceeds the deformation limits of the O-ring material (compound), the O-ring may extrude into the clearance gap, reducing the seal’s effective lifespan.
For low-pressure static applications, improving seal effectiveness can involve using a softer durometer compound or applying additional squeeze. However, this may decrease the ring’s dynamic sealing ability, increase friction, and shorten its lifespan.