Silicone Mixing Quality

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]

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

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

Coefficient of Variation (%) Quality of Mixing Corrective Actions
<10 Excellent
10-15 Good Increase number of roller mill passes
15-20 Fair Increase number of roller mill passes

Inspect roller mills for wear

Alter sequencing of additives

>20 Poor Consult raw material supplier or mill manufacturer for professional advice

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