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“Innovations in Cure Meter and Mooney Viscometer Technology” : Page 2
The Three-In-One Concept
Since the Shearing Disk Viscometer (Mooney) and the Oscillating Disk type curemeter (ODR) have similar operating principals, the Mooney rotates while the curemeter oscillates a rotor embedded in the test sample, and many common mechanical and electrical components, it is somewhat surprising that an instrument that performs both tests has not been developed.
The XDR® accomplishes this goal using a series of interchangeable modules as shown in Figure 1 and Figure 2.
Curometer Configuration
Figure 1 illustrates the curemeter mechanical configuration and the three interchangeable ODR modules. These include the conventional ODR, ODR with heated rotor, and the novel “virtual” moving die rheometer (virtual MDR). The XDR® / ODR can be readily converted to any of these three configurations by a simple change of the rotor / die assembly.
It should be noted that a strain transducer is a key component in the design of this curemeter. It provides a continuous measurement of the strain imposed on the test sample. This measurement allows the determination of the mechanical properties of the test sample as well as correcting for any unavoidable deflections in the system.
The application of this feature and the “heated rotor” ODR and “virtual” MDR are key to overcoming some of the performance limitations of existing curemeters. These facets are discussed in detail in the sections to follow.
Mooney Configuration
The XDR® with the Shearing Disk Viscometer module in place is illustrated in Figure 2. This transformation is readily accomplished by replacing the central shaft assembly of the curemeter with that of the Mooney. The Mooney module consists of a central shaft with attached motor drive assembly, auto—sample ejector, torque transducer, and auto dead—weight calibrator.
The XDR®
Image 1: XDR® Commercial Version
The Mooney die / rotor is directly interchangeable with any of the three curemeter die / rotor modules.
A photograph of the commercial version of the XDR® is shown in the previous column. In addition to the basic machine, there is a computer with an integrated signal processor, interfacing electronics, a monitor and a printer.
The C++ language in a graphical programming environment is used, providing detailed manipulation, display and printout of test curves, numerical values, and statistical analysis of all data operating beneath a graphical user interface (GUI) in the Microsoft® Windows operating system.
The computer generated report options will be covered in a later section.
Design Limitations & Solutions
A well known problem exists in both the ODR and Mooney instruments. The temperature of the test sample is not homogeneous due to heat leakage from the unheated rotor to the lower temperature areas of the machine. This results in the temperature of the rotor being substantially below that of the dies which enclose the sample [12,13,14].
For example, ODR experiments show that at typical die temperatures, the rotor is roughly 10 to 15 C° lower than the die set temperature. Heat is lost continuously by conduction from the rotor down the drive shaft causing the rotor to be colder than the dies [11]. Even worse, the average effective cure temperature can never be accurately measured or reproduced because of this unpredictable temperature gradient.
Therefore, to translate cure parameters from an existing ODR to practical isothermal applications is difficult and at best an approximation. This condition not only negatively impacts reproducibility, but also substantially increases the time for the sample to cure while giving erroneous and misleading — presumed to be isothermal — cure parameters. Therefore, it has been shown that ODR generated cure curves consistently lag those made on an MDR [13,14].
Temperature Uniformity & Control
The MDR rheometer, e.g., Monsanto's MDR 2000®, was developed to overcome this problem. It provides uniform temperature control by directly heating the two dies that engage and heat the test sample.
Thus, a meaningful comparison between test results from the ODR and MDR is clearly impossible since the ODR sample is always below the test temperature. The appropriate solution to this problem is to maintain the rotor at the set—point temperature of the dies by directly heating the head of the rotor.
This is difficult due to the location of the rotor with respect to the clamping system and the contiguous mechanical parts, which makes the rotor virtually inaccessible.
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Copyright © 2006 CCSi, Inc. • All Rights Reserved • Published February, 2006
Corporate Consulting, Service & Instruments, Incorporated
221 Beaver Street • Akron, Ohio 44304 USA
Telephone: 800.742.8535 / 330.376.3600 • Facsimile: 800.229.9329 / 330.376.8500