Alpha Technologies' product and service solutions have the ability to evaluate the curing or post-curing properties of a compound to measure the density, dispersion and dynamic properties, evaluate the gel and cure of thermosets, processability and much more.
Cure refers to the crosslinking reaction in rubber compounds. Alpha Technologies produces curemeters to measure the crosslink density of mixed rubber compounds. These measurements ensure that the rubber viscosity, cure times, and final stiffness of the compound are in specification. With these measurements, one can optimize cure cycle times which can lead to improved throughput and energy and cost reductions while maintaining product quality.
A density measurement determines the weight per volume of a material. In the rubber industry, this is often described in grams/cm3. The most common reason to perform a density measurement is to ensure that the amount of filler is correct in a mixed rubber compound. A compound with incorrect filler content will have different properties than the compound formulator intended. This could lead to premature product failure among other deleterious effects.
A dispersion measurement is determined after a compound is mixed to ensure that the fillers are thoroughly mixed into the rubber. The dispersion method from Alpha Technologies uses an optical method to view a freshly cut surface of an uncured or a cured compound. The undispersed filler particles will appear as white particles against a darker background. Computer analysis of the image provides a quantitative measure of the dispersion. It is known that poor filler dispersion will negatively affect the properties of the compound. By measuring the dispersion, one can optimize the mixing process in order to obtain a well mixed compound with less expended time and energy.
Rubber compounds are often developed to provide specific properties for product performance. For example, the tread stock of tires is often compounded for low rolling resistance. Other products are compounded to reduce vibration or noise. Both of these qualities depend on the dynamic properties of the compound. Measuring these properties can be beneficial in both R&D and quality control settings allowing one to assess experimental formulations and ensure consistency of final products, respectively. Alpha Technologies provides several products to measure the dynamic properties of rubber compounds including the world standard RPA 2000.
Gel and Cure of Thermostats
There are many other materials besides rubber that undergo a thermoset reaction. The initial stage of these reactions is often referred to as the formation of gel. Alpha Technologies has created the PremierTM ESR for the thermoset industries to measure the gel point and the reaction times for these materials. Testing these materials with an ESR can provide valuable information from both a process and storage perspective. In particular, material that has been in storage for an extended period of time can be tested and compared to its original state in order to ensure that it has not changed appreciably.
The hardness is an indication of the stiffness of a rubber compound. This was an early method to ensure that the physical properties of the rubber compound after cure would meet the requirements of a product. Still today many products have hardness specifications associated with them. If these specifications are not met, the product may not perform as intended.
These include tensile modulus, tensile modulus at break, elongation at break, and hardness. These tests verify that a rubber product will meet its performance requirements. A product that does not meet these requirements may experience premature failure. For this reason, physical property testing is considered to be crucial to a well-run quality control program.
The properties of an elastomer can predict the ease of mixing. By having a history of the viscoelastic properties of incoming elastomers, one can determine if a new bale of elastomer will have difficulties in the mixing operation. The properties of an uncured rubber compound can predict the ease of extruding, calendaring, or injection molding. Again, by having data on previous batches, one can ascertain if the current batch will have any issues processing. Being able to predict processing issues beforehand saves time, money, and energy and reduces waste. Alpha Technologies offers several products that can predict processability.
Performing quality tests is only useful if the data that is collected can be analyzed and used correctly. Implementing a quality management system can help increase production, ensure consistency, and enable better decision making by making quality data available to the people who need it when they need it.
This property indicates how long a rubber compound can remain warm for processing before it loses its ability to change its shape. Often once a rubber compound is scorched, it can no longer be processed. From an R&D perspective, it is important to measure the scorch time and adjust it based on the processing conditions. In a quality control environment, evaluating the scorch time ensures that no time is wasted processing or molding material that will not create a good product. For example, premature scorch can lead to underfilled mold cavities as the material loses its ability to flow before completely filling the space.
Rubber compounds in the cured and the uncured state respond quickly to strains. Shortly after the strain is applied, the resistance of the rubber compound is reduced as a function of time. This is referred to as stress relaxation. Stress relaxation performed on a polymer can provide information about its molecular characteristics and elasticity. Stress relaxation of an uncured compound can be an indication of the processability of the material. Stress relaxation of a cured compound can indicate physical properties such as compression set.
Viscosity is a fluid property that indicates the resistance of a fluid to either stress or movement. Materials such as rubber before cure show a reduced viscosity with increasing stress or movement. This shear thinning behavior is important to processing operations. As the shear rate is increased, the viscosity decreases so, in the case of extrusion, a doubling in throughput does not require a doubling in motor power requirements. Additionally, monitoring the viscosity of the polymers and/or compounds allows one to assess the potential for processing issues.