Elastomers: A Beginner’s Guide

选择弹性体似乎是一个小决定，但它可以产生重大影响。不适合应用的密封材料可能会导致许多问题，从膨胀到剥落或开裂。

To help avoid these issues, analyze the elastomer already being used in the same or a similar application. Variables such as chemical compatibility, temperature, pressure, and mechanical wear can make it challenging to predict with certainty what the best material will be. In most cases, several materials will work, but some elastomers will have a longer life than others. If agasket性能好，成本低，通常不需要更换材料。

When an elastomer must be selected for a brand new application, there are several important guidelines to consider.

STANDARDS

考虑必须达到的标准。很容易认为三元乙丙橡胶就是三元乙丙橡胶，但故事还有很多。三元乙丙橡胶o型环可以完全安全地进行卫生处理，或者，根据o型环的制造方式，它可能含有任何数量的潜在有害成分。这些成分有可能渗入成品中。

Understand which specific standards are important for an individual application. Are the components consideredfood grade? Do they meet食品药品监督管理局(FDA) standards? Biopharmaceutical processors often require that seals meetUSP Class VI standards.

有时，提供固化剂的选择。例如，一些硅酮是用过氧化氢固化的。然而，大多数food,beverage, orpharmaceutical公司不能让过氧化物污染他们的产品，所以用铂固化的硅酮通常是卫生应用的首选。

密封件类型

弹性体将执行的工作决定了所需密封的类型。看不到任何移动的静态密封可能与动态密封有不同的需求。研磨性产品在动态密封（如阀座或移动部件上的o形圈）上比被动密封（如三夹垫圈）上更硬。

Sugar syrups can be tricky with dynamic seals. In general, they are very benign and work well with any elastomer. However, sugar crystals can build up on seals, sometimes called “plating.” On a valve seat, the crystals can behave like sandpaper when the seat closes, quickly wearing away the seat. When abrasion is a concern, PTFE, also known as Teflon, is often the best choice.

Another consideration for the type of seal is the resilience of the elastomer. Buna and EPDM have good resilience and “bounce back” more like natural rubber when compressed. They’re great for a good seal, especially after repeated compression (such as in a butterfly valve seat or a gasket for a fitting that is often removed). Viton can be somewhat flexible and resilient but becomes less flexible at lower temperatures.

聚四氟乙烯，俗称特氟隆，没有记忆，可以“冷流”，导致它改变形状时压缩。通常，它在第一次使用时提供足够的密封，但如果拆下三夹钳接头并用相同的垫圈更换，则可能会有一些泄漏。因此，创建了包络式垫圈。这些是聚四氟乙烯垫圈与一个更具弹性的材料，如三元乙丙橡胶的核心，结合了聚四氟乙烯的机械和化学韧性与橡胶的弹性。

化学相容性

Chemicalcompatibility is another important factor. Here are some general guidelines to follow:

油或高脂肪产品

Buna, while usually the least expensive option, is often the top performer when it comes to oil-based products. EPDM might be more expensive than Buna, but when it comes to fats and oils, it is a poor choice and inferior to Buna. Viton works well with most oils, as does PTFE. Either can come in handy when your oils are at a high temperature. Silicone is not always a good choice with oils – if you don’t have prior experience with it in your application, check a compatibility chart first.

Acids and Caustics

As far as acids and caustics go, it’s usually best to consult a chemical compatibility chart. Because an elastomer might react differently depending on the type of chemical and concentration, it’s difficult to predict compatibility.

In general terms, Buna is usually acceptable up to about 2% caustic or 0.5% acid. EPDM does fairly well with both. Viton works better with caustics than acids but can be acceptable for either. Silicone can be finicky – it’s best to consult a compatibility chart. Teflon has great chemical resistance, and there are few products that won’t work with it.

Since there is an endless list of chemicals out there, it can be helpful to consult a chemical compatibility chart to inform your decision.

温度

A final consideration is the temperature that your elastomer will experience. As with the other success factors for an elastomer, we can only speak in general terms until we try an elastomer in the specific application. Time at temperature, variations in temperature, and the combination of temperature with other chemical and mechanical stresses can all affect elastomer life.

As a guideline, here are rough high-temperature limits for some common elastomers:

EXOTIC MATERIALS

你有时可能会碰到一个普通嫌疑犯之外的弹性体。市场上有许多品牌和专用材料，可作为某些类型卫生设备的选择。你可能会不时在宣传册上看到像Kalrez、PEEK或Delrin这样的名字。每一种都有优点和缺点，在卫生处理领域有一些情况需要专门的材料。

For example, steam-in-place operations can cause headaches with traditional elastomers. Although they can resist the heat, silicone tears and deforms easily, while PTFE can lead to leaks when it cold flows. Even envelope gaskets can wear quickly in this tough environment. Several gasket manufacturers now offer a material made of PTFE and fine particles of stainless steel. The gasket is inflexible, but has the same temperature resistance as PTFE and resists cold flow.

Other specialty elastomers include special colors, which can aid in visibility, and metal-detectable elastomers, allowing your in-line metal detectors to catch a broken gasket as well as a lost nut or bolt.

PRICE

The cost of a gasket often influences a decision. A gasket that costs less than 50 cents in Buna could run $1.50 as an envelope gasket with Viton and PTFE, or $5.00 in a PTFE /stainless compound like “Silverback” or “Tuf-Steel.” The goal is to find the lowest-cost material that will meet your needs.

要确定哪种弹性体效果最好，唯一的方法就是试验，从满足应用要求的最低成本选项开始。可能会有一些取舍；氟橡胶的使用寿命可能比三元乙丙橡胶长，但它可能不值得增加成本。根据应用情况，成本较高的弹性体并不总是更好的选择。

在许多情况下，丁纳橡胶是一个低成本的选择，而三元乙丙橡胶可以是一个更高的价格。聚四氟乙烯、铂固化硅酮和氟橡胶价格较高，氟橡胶通常是这三种材料中价格最高的。包封垫圈和特殊化合物可以更高。价格可以改变，这取决于弹性体的可用性。

如果你对如何选择最好的弹性体感到困惑，请查看main page for gasketsalong with the accompanyingelastomer guide，或致电417.831.1411向CSI代表寻求决策过程方面的帮助。