Articles posted by Jehbco Silicones

It is often a challenging task identifying an unknown rubber compound, as they can look and feel very similar to one another. At Jehbco Silicones, we regularly provide 100% silicone alternatives to original equipment manufacturer (OEM) parts, and as such need to know what material the original part was supplied in.

There are multiple methods of determining what type of rubber is used in a product, but methods such as elemental analysis are costly, require specialised equipment, and is not practical in the field. One tried and tested method that we use regularly at Jehbco is a burn test, in which a small sample of the rubber material is combusted. The characteristic burning pattern, smell, smoke colour, and mode of extinguishing are all indicators that can be used to identify what the composition of the burned sample is.

The table below is a basic guide that outlines the main components of the burn test:

There have been numerous cases where customers have thought they were purchasing one type of material, but in actuality they have been supplying an inferior grade of material or a different material altogether. We recently had a case where one of our customers wanted to replace what they thought was a nitrile O-Ring, but when we conducted a burn test on the material it melted and had a distinct burning rubber smell, which was indicative of a natural rubber material. Luckily for the customer, they were not using the O-Ring for a sensitive application, but this uncertainty in material could have had catastrophic consequences in a more critical or sensitive application.

Even within the niche area of silicone materials, some manufactures opt to add fillers to reduce costs, at the expense of inferior mechanical and chemical properties. We have conducted burn tests on many silicone parts made overseas, and an alarming amount of these parts did not behave as expected during the burn test (no white ash produced, black smoke) which suggests that fillers have been added.

At Jehbco, we only produce 100% pure silicone products for your guaranteed peace of mind. If you have any doubt about the quality of your existing rubber products, or want to manufacture a custom solution that you can be confident with, feel free to consult our applications page and contact us with any questions.

Silicone sponge is one of Jehbco’s most unique materials, finding applications in a variety of industrial applications from lighting gaskets to dry seals and oven manufacturing. The most important feature of a closed-cell silicone sponge is its extreme compressibility, which allows it to form airtight seals with very low sealing loads. This feature combined with silicone’s naturally ability to withstand high and low temperatures (-60°C to 200°C) and the increased insulating properties of sponge rubber makes silicone sponge an exceptionally versatile elastomer suitable for many different applications.

Jehbco’s closed cell silicone sponge in a variety of profiles.

Silicone sponge is what is known as an expanded elastomer. Many elastomers can be formulated into a kind of sponge by incorporating air into the bulk of the elastomer during the manufacturing process. Typically, this air is visible on the final product as well-dispersed bubbles, which can vary in size depending on the cell structure. This incorporation of air increases the softness and compressibility of the elastomer while simultaneously lowering its density. The amount of air and overall consistency of the air inclusions determines the cell structure of the sponge, which has significant impact on the mechanical properties of the final sponge.

Two different kinds of sponge rubber can be made depending on the cell structure of the sponge itself. The first is called an open-cell sponge, which is the same kind of cell structure as the sponges used for dishwashing. In an open-cell sponge, all the inclusions of air are connected by channels, which allows fluids to flow through the sponge. This is crucial when the absorption or passage of fluids through the sponge is required for the desired application. Open-cell sponges can be very heavily compressed upon the application of pressure and will expand back readily as air can easily flow back into the air pockets of the material. However, open-cell sponge is not suitable for the formation of air-tight seals.

In a closed-cell silicone sponge, all the inclusions of air are completely enclosed by rubber. This means that the air inclusions are completely inaccessible to any fluids or microorganisms. These air pockets can still be deformed by the application of pressure, in the same fashion as a rubber ball can be compressed, providing significantly improved compressibility over solid silicone. This allows air-tight seals to be easily formed. To maximise compressibility and also improve the appearance of the sponge, smaller, more consistently shaped and dispersed air inclusions will form a higher quality sponge rubber. In accordance with ASTM D1056, a closed cell sponge must not absorb more than 5% of its weight in water, while a sponge that absorbs more than this value is classified as open-cell.

Typically, closed-cell sponge rubber is made using a chemical blowing agent, which decomposes during the curing process to produce gas, which mechanically expands to form small inclusions in the bulk rubber. Over time, air slowly through the bulk of the silicone, replacing these gasses with air. However, due to the unique chemistry and processing temperatures of silicone rubber, many traditional blowing agents are chemically incompatible with silicones. Typically, silicone sponge employs a peroxide curing system together with a carefully formulated mix of additives and blowing agents to produce a high quality closed-cell silicone sponge with a low density and a consistent cell structure. As can be expected, the blowing process causes severe expansion of the silicone profile, so it is extremely difficult to manufacture specific profiles. Jehbco is one of few silicone manufacturers that have dedicated extensive amounts of research and resources to perfecting the sponge making process so that even the most intricate custom profiles can be made. Jehbco’s sponge can be made into a wide range of profiles, or custom-made to suit your requirements, and is available in three softness grades (soft, medium and firm) depending on your preferences.

Ultimately, if you are looking for a soft, low-density material with excellent compressibility and extreme chemical and heat stability, enquire about our closed-cell silicone sponge. Jehbco has spent many years formulating and developing closed-cell silicone sponge and have consistently impressed our customers with our high-quality sponge rubber. For help selecting a material for your application, consult our applications page and contact us with any questions.

Choosing an elastomer for a new design or application can be overwhelming due to the wide range of materials available on the market today. We at Jehbco are often asked to help consult our customers on what elastomer is the right choice for their application.  Are our 100% silicone products the right choice for you? Or would a different material be more appropriate?

In this article, we’ll explore the different properties of silicone and neoprene, and what applications each material would be best suited for. Silicone and neoprene are both commonly used materials for o-rings, gaskets, seals, tubing and membranes. While both elastomers may be used to create similar products, the specific application and environment will ultimately determine whether neoprene or silicone will be the better choice for you. The table below summarises some of the key differences between the two materials.

Both neoprene and silicone can operate at extremely low temperatures, although silicone is the far better option in high temperature environments. Silicone can resist intermittent temperatures of up to 230°C, or up to 280°C if a heat stabiliser is added into the raw material.

Silicone vs Neoprene

Neoprene has high tensile strength and excellent abrasion resistance, whereas silicone has good tensile strength, but poor abrasion resistance. For dynamic applications with friction, neoprene would most likely be a better option.  With this being said, silicone can be formulated to have improved tear strength, making it an ideal choice for applications such as vacuum sheeting and peristaltic pumps. Silicone also has the superior compression set, which makes it a better choice for applications requiring a long lasting, reusable seal, especially in high temperature environments.

While silicone has an excellent resistance to ozone and UV, neoprene can also resist ozone and UV to a degree, making both options viable for most outdoor applications. Neoprene is more suited for any applications that require contact with alkali compounds or dilute acids, while silicone is more suitable for applications that require contact with high temperature oils. Neither material is compatible with hydrocarbon fuel, but silicone is resistant to automotive brake fluids.

It is clear to see that there is merit in using either neoprene and silicone, depending on what physical properties you require and the operational environment.  For help selecting a material for your application, consult our applications page and contact us with any questions.

At Jehbco, we ensure that every product is of the highest quality before being sent to our customers. Raw silicone must be fed through a roller mill to mix in any extra additives or colouring, but insufficient mixing can lead to a poor-quality product. For example, if an additive to improve fire resistance is not properly mixed into the raw silicone, there may be portions of the final product that may not be fire resistant. Hence, it is crucial that the quality of mixing during the milling stage of silicone rubber production is constantly monitored, to ensure a homogenous product.

Figure 1: Raw silicone being passed through a roller mill for mixing [1]

One method of measuring the mixing quality during the milling stage is to calculate the coefficient of variation of additive particles in samples of the mixed silicone material. The coefficient of variation is a percentage that represents how similar each sample is to one another. Samples of the mixed silicone product are taken and analysed under a scanning-electron microscope (SEM). The high magnification of the SEM will allow the user to determine the approximate concentration of additive particles in each sample, which can be used to determine the coefficient of variation, as shown in figure 2 below.

Figure 2: Coefficient of Variation Equation

A low coefficient of variation means that the amount of additive in each sample is similar, which suggests a well-mixed product. Thus, the quality of mixing can be determined using the coefficient of variation. Table 1 below correlates the calculated coefficient of variation of the samples, to the quality of mixing in the mixed silicone product. For example, if the coefficient of variation of the samples is between 10-15%, the quality of mixing in the mixed product is good, but can be improved by increasing the number of passes through the roller mill.

Table 1: Correlation between correlation of variation and quality of mixing

By calculating the coefficient of variation, and hence, the quality of mixing in the mixed product, a high quality of silicone rubber product can be consistently maintained. At Jehbco, we strive to provide only the highest quality of silicone products for your needs.

For further information or advice about which silicone rubber best suits your application, please review the Jehbco website www.jehbco.com.au, and contact us with any questions.

References:

[1] Medical Design. (2013, April 3). [Roller Mill with Raw Silicone]. Retrieved November 14, 2017, from http://medicaldesign.com/silicone/new-silicone-elastomer-offers-wider-processing-flexibility