Rishikesh Electromatic Pvt. Ltd.

Borivali East, Mumbai, Maharashtra

The oscillating Disc type Rheometer is an efficient, simple and reliable testing equipment. It is quite easy to operate. The Rheometer describes precisely and quickly curing and processing characteristics of vulcanizable rubber compounds. It works on a very simple principle. A test piece of rubber compound is contained in a sealed test cavity under positive pressure and maintained at a specified elevated temperature. A Rotor ( biconical disc )is embedded in the test piece and is oscillated through a small specified rotary amplitude. This action exerts a shear strain on the test piece and the torque (force) required to oscillate the disc depends upon Stiffness (shear modulus) of the rubber compound.

The stiffness of the specimen compound increases when cross links are formed during cure. The direct Proportionately posited between the shear modulus and the cross linking density is based on the statistical theory of rubber elasticity .At a constant temperature of the test, a cross linking isotherm is the function of time of that property which serves to measure the course of the cross linking reaction. In the context of Rheometer, the cross linking isotherm is thus the function of time, of the oscillating shear force F, or of the Rheometer indication proportional to it, occurring at a given temperature as a result of vulcanization. A plot of this torque (force) value against time gives a typical graph called "Cure Curve or Rheograph". A trained eye can monitor the initial trough i.e. processing behavior of the compound, the slope of rise during cure phase i.e. curing characteristics and final shape of the curve. Internationally designated parameters like MI, MH, TS2, TS5, TC50, TC90 etc. are markers which can be used to describe a graph. The Cure Curve obtained with Rheometer is a finger print of compound's vulcanization & processing character.

Application
In order to produce consistent quality of rubber product, it is of vital importance that compounded rubber is of consistent quality. The process of mixing is subject to variations due to

• Ingredients variations
• Machinery variation
• Man variation
• Batch to batch variation

as the compound is mixed in batches. To minimize the effect of above four variables one has to design technique to overcome it. If randomly selected batches are subjected to Rheometeric analysis, one could in a large sample size, workout upper and lower control limits, range, mean and standard deviation, with reference to Rheological parameters. Each batch on testing can be classified in Pass/Fail criteria depending upon the quality control limits. Based on this, the internationally acceptable control called "Statistical Quality Control" (SQC) can be designed. One can also design quality control gates which can be marked on the screen so that a quick decision can be made regarding acceptability or rejection . Rheometer is a versatile instrument and of numerous applications . A compounder can use it to his advantage in areas like development of new compound, rationalization of existing compound both in terms of quality and economics, optimization of curing process in the manufacturing process to get a better yield. It is up to the user to design his own techniques with the help of this excellent tool to suit his process.

Moving Die Rheometer(MDR) is a testing equipment which analysis the cure characteristics of Rubber Compound & monitors the processing characteristics as well as physical properties of the material. It is based upon international technology. It is the only instrument in the rubber industry which helps to choose right ingredients and its appropriate dose to meet the end products "Rishikesh make" Moving Die Rheometer is a Rotor less Instrument in which Die oscillate and measures the change in stiffness of rubber compound compressed between two heated dies. The MDR generates 3 curves S', S" and Tan Delta.The MDR produces a cure curve labeled S' which is similar to the ODR curve.

Definition of S' and S"
S' is called the storage modules , elastic modulus or in phase modulus. S" is called the loss modulus, viscous modulus, or out-of-phase modulus. All of these terms have been used to mean the same thing. The unit of S' and S" in the product family instruments are in lbs. These are units of torque. They can also be in dnm. Which are also torque units.

Tan Delta
The Tan(Delta) is computed from the ratio S"/S' or loss of modulus divided by storage modulus. The smaller the Tan delta, then the more viscous the material.

Application of S"
There have been many research articles which discuss the benefits of using S"(Loss modulus) or Tan (Delta). A relationship may exists between dynamic properties and processability (e.g. die swell) of uncured compound. After cure, the loss modulus can indicate whether a compound will meet some special application. For example, the rubber used in an automotive engine mount should have high Tan(Delta). S" in order to dampen vibration. On the other hand, the compound used in a rubber band needs a low Tan Delta .

Mooney Viscometer is a shearing disk viscometer, designed for accurate measurement of viscocity, scorch time and cure rates of the elastomers.

The instrument consists of flat, cylindrical disk, driven by a motor to rotate slowly and continuously in one direction. This disk is embedded into elastomer specimen which is confiend in a heated die cavity maintained at specified temprature and kept closed by a specified force. As the disk rotates its experiences a shear strain. This resistance to rotates offered by the elastomer is shearing viscosity which is proportional to mean absolute viscosity of the specimen.

Normally a preheat period is given to the elastomer following which the disk starts to rotate. A initial high viscosity is recorded and then as the viscosity also decreases, to a minimum value Viscosity obtained with large rotor are approximately twice those of small rotor.

The viscosity is reported as under

• Method of sample preparation
• Mooney viscosity number
• Rotor size
• Preheat time
• Time interval to viscosity reading
• Tamperature of test

Typical test results are started as under
= 50ML(I+4) 100C

Where

• 50M = Viscocity in mooney units.
• L = Large rotor (for small replace it with 'S')
• I = Preheat time in minutes
• 4 = Time in minute after starting the motor at which the reading is taken
• 100 C = Test temprature