It is an instrument consisting of a motor driven disk within a die cavity formed by two dies maintained at specified conditions of temperature and die closure force. It measures the effect of temperature and time on viscosity of rubber or compound.
MOONEY VISCOSITY
It is a measure of the viscosity of a rubber or compound determined in a Mooney shearing disk viscometer. It is indicated by the torque required to rotate the disk embedded in a rubber/compound specimen and enclosed in the die cavity under specified conditions.
Viscosity of rubber or compound plays vital role in deciding its processing behaviour. In Rubber Industry rubber or compound have to undergo
MOONEY VISCOMETER
various processing before it can be vulcanized into its final form. Deviation in viscosity of the compound will critically alter its processibility specially in terms of calendering, extruding or injection moulding. It is necessary that viscosity parameter be maintained within specified limits.
To do this Mooney Viscometer is of vital importance. In fact viscometer has manifold advantages.
Principle
MV’s Mooney Viscometer’s process includes rotation of a flat, cylindrical disk, embedded in an elastomeric specimen which is confined in a heated die cavity and exerts a shear strain on the specimen. The resistance to rotation offered by the elastomer is shearing viscosity which is proportional to mean absolute viscosity of the Generally, a pre-heat period is given to the elastomers, followed by which the disk starts to rotate. An initial high viscosity is recorded and the viscosity decreases to a minimum value. Viscosity that is obtained with large rotors is approximately twice those of small rotors. The complete calibration can be performed directly by Micro Vision’s software.
Sample Preparation
The Mooney Viscosity is affected by the manner in which the rubber is prepared and the condition of storage prior to test. Accordingly, the prescribed procedure should be followed rigorously as given below in the chart.
The test piece consists of two disks of elastomer of 50mm diameter and approximately 6mm thickness sufficient to fill completely the cavity of the viscometer. The specimen should be free from air and from pockets that may trap air against the rotor and die surfaces. A hole is pierced through the centre of one disk for insertion of rotor stem. The specimen be allowed to rest atleast 30 minutes at standard laboratory temperature before the test and tested not later than 24 hours after homogenisation.
Advantages
- A) Processing Behaviour: The invention of new polymers and rubber chemicals compounder is faced within problem of choosing the right ingredient and its dose, specially with respect to its processing behaviour during calendering, extruding or injection moulding. As the processing behaviour of the compound changes with respect to its temperature, one has to predict how it is going to behave during processing. With the help of Mooney Viscometer one can predict its behaviour with respect to temperature and time during processing.
- B) Research & Development: The most tedious part in compounding is to develop a new compound to meet the desired results. It involves:
- a) Defining required quality targets
- b) Designing preliminary compounds, selecting specific ingredients and determination of dosage of each ingredient. Checking the cost factor
- d) Testing each compound
- e) Re-designing the formulation till quality target is achieved. The process involves enormous work which is time consuming, expensive and requires skill. With the help of Mooney Viscometer, one can do all this exercise quickly with minimum wastage of materials.
- C) Quality Control
In order to produce consistent quality of Rubber products, it is of vital importance that compounded rubber is of consistent quality. As the compound is mixed in batches, batch to batch variation, if any, needs attention incontrolling quality of each batch. If randomly selected batches are subjected to Viscosity analysis, one could in a large sample size, workout upper and lower control limits, range, mean and standard deviation, with reference to Viscosity parameters, Each batch on testing can be classified on Pass/Fail criteria depending upon the quality control limits. Based on this, the internationally acceptable control called “Statistical Quality Control” ($QC) can be designed. Computerized data analysis system of Mooney Viscometer viz. “Viscosoft” is ideal in this
- D) Grading of Rubbers
Mooney Viscosity of the rubber is one of the important parameter in grading the quality of rubber. And it is also important parameter in choosing the rubber quality for application.
- E) Choosing the Correct Polymer
While developing new compound one has to choose the right polymer for the end use. Each polymer again is sub divided into various types depending upon their physical and chemical properties. Viscosity is of paramount importance before selecting its acceptability in the formulation. A high viscosity polymer can be selected where high filler loading is desired and a lower viscosity polymer is selected if other properties are important.
- F) Economics
Everything said, but one may still be hesitant in investing in such instruments mainly because of its cost.
Experience has shown that if Mooney Viscometer’s full potential is exploited with regards to few of various advantages mentioned above, the return is quite handsome. Improved quality, minimized wastage, optimized dosage of each ingredient, choice of right ingredients, controlled process certainly makes this instrument singularly ideal for any Rubber Industry.
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