What the R6000 can do for your products.
R6000 is a material testing system.
It is a capillary rheometer. The rheometer melts the material in the bore and give shear rate to the material to push it through the small diameter capillary and measures the shear stress. By changing the piston speed, you can get the variety of shear rates. With the special construction, which is unique to R6000, it can measure rubber, plastic, ceramics and medicines.
In the plastic industry, a Melt Indexer or MRI is very popular.
Melt Indexer has a bore, also, just like R6000. However, the measurement is different. You put a weight on the material (shear stress) and measure the amount of material that runs through a small diameter capillary.
The plastic processing machine like injection molding machines, extrusion machines, blow molding machines has a certain shear rate rage to process the material. The typical numbers are from 100/s to ,1000/s for extrusion, and 100/s to 10,000/s for injection molding machine.
R6000 can measure the shear rate range from 10/s to 98,000/s.
Melt Indexer can measure around 1/s shear rate range. Since what you give to the MI is shear stress, and shear rate is the results, you cannot control the shear rate range to measure.
So, MI gives you some basic data, but little information on processing data.
The another way of measuring the material processability is rotational viscometer. The rotational rheometer has both control stress and control shear rate system. The limit of the rotational rheometer is the molten material has to be in the certain shape of the cone and plate, or whatever the measurement cup design is. It is a pretty accurate system, but the shear rate range is from 0.001/s to 10/s. It gives a very good idea about the materials construction, how the internal construction changes according to the given stress or shear rate. However, it gives little information about the processibility.
Most of the material in the plastic processing, like rubber and plastic, has a visco-elasiticity. This means the materials are non-newtonian. So, you cannot predict the behavior of the material by measuring the different shear rate range. In order to understand the flow behavior of the molten plastic or rubber, you need to measure the shear rate range of the processing machine.
What do you do with the measured data?
R6000 measures both shear viscosity and elongational viscosity.
(Click here for more information about elongational viscosity.)
Shear viscosity gives the information how the material behaves under certain shear rate or shear stress. By using the computer aided engineering (CAE) program, you can predict the shear heating of the material in the processing channel, and/or if the channel creates gels for that material and so on. Shear viscosity gives the insight of the material where the shear is present.
Elongational viscosity is how material stretches in the conical geometry.
Most of the processing machine needs both shear and elongational viscosity data. By having those data ready for the material, you can control the stability of the processing. The R6000 can be used by the material supplier to customize the material to the processing conditions. Or production company can use R6000 for the acceptance test of the material.
When combined with the right CAE program, the application is very wide and it is impossible to cover all of them here.
Please ask for more details with IMATEK ASIA!
In general, Shear viscosity is the material’s resistance against the shear.
In capillary viscometry, the shear rate is given by the piston speed, and shear stress is measured. The shear stress is measured as a pressure drop in the small capillary. When you measure the pressure drop in the piston like the following configuration, what you measure is 1. Pb the pressure drop to run the bore, 1. Pe the entering pressure drop and 3. Pd the pressure drop in the die (small capillary). What you need for the “accurate” shear viscosity is to measure the Pd. So, what you do is to change the length of the capillary to get different pressure drop. The changed pressure is the Pd. They recommend to measure with 2 or 3 different length of the die. This is called Bagley correction.
Also, capillary viscometry assumes the flow of the material to be in the ideal diagonal shape. However, the real material flows as a plug flow most of the time. So, you need to adapt the flow shape factor in the calculation. This is called Rabinowith correction.
The shear viscosity measured directly from the capillary rheometer is called apparent viscosity. And Bagley and Rabinowith corrected viscosity is the accurate shear viscosity. As you see, it is time consuming to measure the same material by chaging the capillary die several times. That’s why R6000 offers twin bore capillary. One side of the die has normal length like 16:1 (long die), and the other has a die which has almost 0 length (short die). 0 length die gives the pressure drop very close to that of 0. So, deducting the pressure drop measured from the long die by short die, gives almost pure Pd.
This will save a lot of time to have the accurate shear viscosity data.
There are more for the R6000
As you can see from the schematic, measuring the pressure at the top of the piston is rather difficult job. Since the piston has to push material with as small leakage as possible. But the piston needs to slide smooth, otherwise, it measures the friction as a pressure drop. So, we measure the pressure in the bore by the pressure sensor. Also, we made it interchangeable so that the pressure sensor can be adjusted to very low pressure or high pressures.
This eventually gave the piston free from damaging the pressure measurement system. So, we can design high pressure force applied to the material. Thus R6000 can test wider variety of materials with wider variety of temperatures.
Accurate shear viscosity will help you identify the material behavior and the data can be used in the CAE program for further analysis.