Temperature Range Durometer Chart
The temperature range for any compound is determined by the base elastomer used. This chart depicts the maximum temperature range for each elastomer. The temperature range for a specific compound may not reach these maximum limits. Higher temperatures may be considered if exposure is short term or intermittent.
The hardness of rubber compounds is measured by Shore A durometer; the higher the durometer number, the harder the compound. Wherever possible 70 durometer hardness should be used as it offers the best combination of properties for most O-ring applications. Softer compounds stretch easier and seal better on rough surfaces. Harder compounds offer greater abrasion resistance and resistance to extrusion. Extrusion must always be considered when high pressures are used. The proper hardness may be selected from this chart by matching the fluid pressure with the maximum extrusion gap.
Temperature Range Chart
The temperature range of any compound is largely influenced by the base elastomer it is made from. Different elastomers have distinct properties that determine how well they can withstand high or low temperatures without degrading. The chart provided outlines the maximum temperature ranges for each type of elastomer, giving a general guideline for their performance under various thermal conditions. However, it is important to note that the specific temperature range for a given compound may not always reach these maximum limits.
In cases where the compound is exposed to high temperatures, it may be acceptable if the exposure is short-term or intermittent. Prolonged exposure to extreme heat or cold can cause the elastomer to lose its flexibility, strength, or overall integrity, so careful consideration should be given to the duration and frequency of temperature variations when selecting an elastomer for a particular application.
Durometer Chart
The hardness of rubber compounds is typically measured using the Shore A durometer scale, which quantifies the resistance of the material to indentation. The higher the Shore A durometer number, the harder the rubber compound. For most O-ring applications, a Shore A hardness of 70 is often recommended, as it provides an optimal balance of flexibility, durability, and sealing performance. This hardness is generally the most versatile and well-suited for a wide range of sealing applications.
Softer compounds, with lower durometer values, offer better stretchability, which allows them to conform to irregular or rough surfaces, ensuring a more effective seal. These softer compounds are ideal for applications where the sealing surface is not perfectly smooth or where a tight, leak-free seal is critical. However, softer materials may not offer the same level of resistance to wear and abrasion.
On the other hand, harder rubber compounds, with higher durometer values, offer increased abrasion resistance and are more resistant to extrusion, especially under high-pressure conditions. When selecting a compound for high-pressure applications, extrusion resistance becomes a critical factor. Extrusion occurs when the rubber material is forced out of the sealing area due to excessive pressure, leading to seal failure. To prevent this, it’s essential to select a compound with adequate hardness to withstand the forces exerted during operation.
To determine the appropriate hardness for a specific application, you can refer to the chart provided, which correlates fluid pressure with the maximum extrusion gap. By matching the operating conditions with the recommended hardness, you can ensure the rubber compound selected will provide optimal performance, durability, and resistance to extrusion. Properly considering both the sealing needs and pressure conditions will lead to more reliable and long-lasting O-ring performance.
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