Signature Control Systems Inc., a Denver-based developer of chemical processing monitoring equipment and programs, has developed an algorithm-based predictive rubber curing system.
The system uses in-mold ``impedance sensors'' to collect real-time data from the rubber being cured.
The system is designed to help molders achieve optimum cure, according to Richard Magill, director of research and development for Signature Control Systems. He spoke at the inaugural International Rubber Molding Conference in Cleveland.
Optimizing the cure cycle results in shortened cure times without performance property degradation, Magill said. The test case Magill outlined in his presentation, at a North American plant of a major anti-vibration component maker, produced 23-percent shorter cure times.
The sensors-ceramic coated and machined into the mold-can be connected to the company's monitoring and control systems, and have been designed to withstand demanding processing conditions, Magill said.
The sensors are rated for high temperature (up to 500°F) and high-pressure (up to 30,000 psi) operation. The ones used in the test case were subjected consistently to pressures of 18,000 psi in presses operating 24 hours a day, Magill said.
The sensing technology creates an electrical circuit with the sensor acting as one plate of the capacitor, while any adjacent metallic surface acts as the other plate. The product being molded, sandwiched between the sensor and the wall, acts as the dielectric in the capacitor.
Impedance sensing involves applying a low-level AC voltage to the sensor, which results in a complex current flowing through the material to the grounded mold surface.
The system then measures conductance and capacitance of the material to determine changes in the dielectric properties of the material.
These changes have a direct correlation to the material's rheometry, Signal Control Systems development has shown, and can be programmed into the company's software, which automatically adjusts the cure time to the optimum.
The in-mold sensors are offered in two sizes-0.75 inches in diameter and 0.875 inches deep and 1.25 inches in diameter and 0.75 inches deep. The smaller size sensor typically is used on thin cross-section products while the larger size allows it to sense cure state through thicker products, according to company literature.
Thus far, the impedance sensing technology has been used with polar rubbers such as natural or nitrile rubber, Magill said, but the company is working now to modify the system to accommodate EPDM and other rubbers.
The sensors also are useful in applications in which the product has a metal insert. In these cases, the sensor is capable of measuring the material cure between the sensor and the insert.