GB1565691A

GB1565691A - Apparatus and method for measuring plasticity and viscosity

Info

Publication number: GB1565691A
Application number: GB618376A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1976-02-17
Filing date: 1976-02-17
Publication date: 1980-04-23

Description

(54) APPARA'lJS ANI) Mll'l'll()l) l:()R MLASURlNG PLASTICITY AND VISCOSITY (71) We, IMPERIAl (CHEMICAL INDUSTRIES LIMITED, Imperial Chemi- cal House, Millbank, London SWIP 3JF a British Company, do hereby declare the invention, for which we pray that a patcnt may he granted to us, and the method by which it is to he performed, to be particularly described in and by the following statement: The present invention relates to an apparatus and to its use in measuring the plasticity and viscosity of materials.

The apparatus comprises: (a) two cylindrical bodies disposed in spaced apirt non-circumjacent rclationship with their arcs parillel ind located so that they can be placed into contact with opposite sides of material under test said cylindrical bodies being rotatable relative to one another while remaining in contact with said material, and means for adjusting the dis trance between said cylindrical bodies so that test material of various thicknesses can be accommodated in the space between them in contact with both under constant cylindrical bodies under constant and predetermined pressures, (b) means for rotating at least one of said cylindrical bodies and, a torque measuring device connected to one of said cylindrical bodies for measuring the torque imparted to the latter upon rotation of the cylindrical body(ies) when test material is located between and in contact with said cylindrical bodies, It is usually convenient for one of the cylindrical bodies to be stationary, the other being movable ie. a roller. The cylindrical bodies surfaces should be uniform so as to give a constant frictional resistance and to this end they may be polished, e.g. polished steel, or uniformly roughened.The cylindrical bodies are adjustable with respect to one another to vary their distance apart so as to accommodate material of varying thicknesses under a constant and predetermined pressure. This may be achieved most conve niently by maintaining one of the cylindrical bodies in a fixed position the other cylindrical body being adjustable in rclation thereto.

the means for moving one or both of the cylindrical bodies relative to the other is pre fcrahly an electric motor although obvious equivalents such as mechanical or pneumatic motors may also be used.

The apparatus measures the torque imparted to one cylindrical body by the rela tivc movement of the cylindrical bodies the torquc being transmitted through the material under test which is thereby subjected to a shearing stress,the magnitude of the stress being reflected in the magnitude of the measured torque. As may be seen from Figure 3 the torque and hence the stress increases until eventually the material shears when the torque remains constant. The shearing stress at this point is a measure of the flowability or viscosity of the material.

The torque of the shaft driving the rotating cylindrical body may be measured or alternatively the rotating cylindrical body may be driven at a constant speed and the torque imparted to the other cylindrical body may be measured. In both instances the torque measurement may be made by known means, suitably electronically, the values obtained being intermittently registered or continuously recorded.

It is advantageous for one at least of the two cylindrical bodies to be capable of being maintained at a constant temperature which can be varied as desired. This may be achieved by electrical means or by use of a liquid heat transfer medium. For example, one of the cylindrical bodies may be in the form of a drum which may be filled with a fluid such as a mineral oil held at a constant desired temperature, e.g. 0 to 200 C.

The apparatus according to the invention may be used in a wide range of applications where the material under investigation has a high viscosity. It finds use therefore in the food industry, in the testing of doughy and rubber or plastic materials and also in the plastics industry particularly in the field of sheet moulding compounds. In most uses the apparatus may be used to compare the rheological properties of a sample under test with the same properties of a sample known to be satisfactory in service.In this manner the apparatus is in fact calibrated against the known sample The use of the apparatus provides a method of measurement which comprises placing the sample under test between and in contact with adjacent cylindrical bodies moving said cylindrical bodies while remaining in contact with the sample, at different speeds relative to one another, measuring the effect of the sample on the torque imparted to one of the cylindrical bodies and comparing the measurement with a measurement of a comparable sample known to be satisfactory in practice.

An important use of the apparatus and method is in the field of unsaturated polyester resins which are well known commercial materials which consist of the product of copolymerising an ethylenically unsaturated polyester with an ethylenically unsaturated comonomer so that the polyester is crosslinked to produce a solid resin. For many applications the polyester and comonomer are used in conjunction with a reinforcing material such as chopped glass fibres so that the final polymerised article or structure has greater strength. One form in which such a reinforced composition is used is as a sheet moulding compound" in which the polyester, comonomer and reinforcing material are in the form of a sheet which can be formed into the desired shape and then polymerised or cured, e.g. by the application of heat.

The unsaturated polyester and comonomer are, usually, liquid and in order to prevent them draining out of the reinforcing material it is customary to add a thickening agent, commonly magnesium oxide, which by chemical reaction causes the polyes terxcomonomer solution to thicken so that it does not flow from the reinforcing material but does allow it to flow in the mould. The thickening process generally takes a period of time to complete so that the sheet moulding compound is not immediately ready for moulding. The present invention provides a method of testing a sheet moulding compound to decide whether it is suitable for use.

The method may also be used to test the suitability of other plastic moulding compounds either thermoplastics e.g. PVC, or uncured thermosettable compositions.

It is one of the advantages of the present method that it can be used to test sheet moulding compounds which are being manufactured continuously. Thus the sheet may pass continuously between the cylindrical bodies and by means of a suitable recorder the condition of the sheet along its length may be determined by intermittently moving the cylindrical bodies into contact with the sheet and taking a measurement. It is also an advantage of the method that the polyethylene sheet which usually covers the surfaces of an unsaturated polyester sheet moulding compound need not be removed for the test to be carried out. In this case it is preferred that the surfaces of the cylindrical bodies be roughened.

Figure 1 shows one form of the apparatus which comprises a mild steel cylindrical body 1 and a mild steel roller 2 both with knurled surfaces of diamond pattern. Cylindrical body 1 mounted on shaft 8 is stationary and does not rotate but is movable up and down by means of screws 3 and 4 controlled by a knurled nut 5 so that a known pressure as indicated by gauge 6 can be exerted on sheet moulding compound between the rollers.

The roller 2 is fixed in position but is rotatable at constant speed by means of motor 7 the time for which it rotates being preset and the rotation automatically stopped when this time is reached. The torque exerted on the shaft 8 is measured electrically and recorded by recorder 9, the instrument being precalibrated so that the torque is converted to kilopascals.

Figure 2 shows a preferred modification of roller 2 which now consists of a hollow cylinder 10 containing oil 11 and a heating element 12. The cylinder is rotatable and the presence of the element and the oil enables the cylinder surface to be maintained at a constant temperature.

In operation a sample e.g. of sheet moulding composition, comprising an unsaturated polyester resin and glass fibre, is placed between the cylindrical body and roller and held in position by tightening nut 5. Roller 2 as shown in Figure 2 containing oil at a temperature of 20"C is caused to rotate for a period of 2 minutes when a recorded trace as shown in Figure 3 is obtained the trace being a plot of shear stress in kilopascals against time, point A being the time at which the roller 2 was stopped. The trace is indicative of the flowability of the sample under test the height of the curve being a measure of its stiffness. Different samples give different curve shapes and heights but for a given composition its suitability for use in moulding can be decided by comparison of its trace with the trace of a sample made from the same materials and which has proved suitable in practice.

WHAT WE CLAIM IS: 1. An apparatus which comprises: (a) two cylindrical bodies disposed in spaced apart non-circumjacent relationship with their axes parallel and located so

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. high viscosity. It finds use therefore in the food industry, in the testing of doughy and rubber or plastic materials and also in the plastics industry particularly in the field of sheet moulding compounds. In most uses the apparatus may be used to compare the rheological properties of a sample under test with the same properties of a sample known to be satisfactory in service.In this manner the apparatus is in fact calibrated against the known sample The use of the apparatus provides a method of measurement which comprises placing the sample under test between and in contact with adjacent cylindrical bodies moving said cylindrical bodies while remaining in contact with the sample, at different speeds relative to one another, measuring the effect of the sample on the torque imparted to one of the cylindrical bodies and comparing the measurement with a measurement of a comparable sample known to be satisfactory in practice. An important use of the apparatus and method is in the field of unsaturated polyester resins which are well known commercial materials which consist of the product of copolymerising an ethylenically unsaturated polyester with an ethylenically unsaturated comonomer so that the polyester is crosslinked to produce a solid resin. For many applications the polyester and comonomer are used in conjunction with a reinforcing material such as chopped glass fibres so that the final polymerised article or structure has greater strength. One form in which such a reinforced composition is used is as a sheet moulding compound" in which the polyester, comonomer and reinforcing material are in the form of a sheet which can be formed into the desired shape and then polymerised or cured, e.g. by the application of heat. The unsaturated polyester and comonomer are, usually, liquid and in order to prevent them draining out of the reinforcing material it is customary to add a thickening agent, commonly magnesium oxide, which by chemical reaction causes the polyes terxcomonomer solution to thicken so that it does not flow from the reinforcing material but does allow it to flow in the mould. The thickening process generally takes a period of time to complete so that the sheet moulding compound is not immediately ready for moulding. The present invention provides a method of testing a sheet moulding compound to decide whether it is suitable for use. The method may also be used to test the suitability of other plastic moulding compounds either thermoplastics e.g. PVC, or uncured thermosettable compositions. It is one of the advantages of the present method that it can be used to test sheet moulding compounds which are being manufactured continuously. Thus the sheet may pass continuously between the cylindrical bodies and by means of a suitable recorder the condition of the sheet along its length may be determined by intermittently moving the cylindrical bodies into contact with the sheet and taking a measurement. It is also an advantage of the method that the polyethylene sheet which usually covers the surfaces of an unsaturated polyester sheet moulding compound need not be removed for the test to be carried out. In this case it is preferred that the surfaces of the cylindrical bodies be roughened. Figure 1 shows one form of the apparatus which comprises a mild steel cylindrical body 1 and a mild steel roller 2 both with knurled surfaces of diamond pattern. Cylindrical body 1 mounted on shaft 8 is stationary and does not rotate but is movable up and down by means of screws 3 and 4 controlled by a knurled nut 5 so that a known pressure as indicated by gauge 6 can be exerted on sheet moulding compound between the rollers. The roller 2 is fixed in position but is rotatable at constant speed by means of motor 7 the time for which it rotates being preset and the rotation automatically stopped when this time is reached. The torque exerted on the shaft 8 is measured electrically and recorded by recorder 9, the instrument being precalibrated so that the torque is converted to kilopascals. Figure 2 shows a preferred modification of roller 2 which now consists of a hollow cylinder 10 containing oil 11 and a heating element 12. The cylinder is rotatable and the presence of the element and the oil enables the cylinder surface to be maintained at a constant temperature. In operation a sample e.g. of sheet moulding composition, comprising an unsaturated polyester resin and glass fibre, is placed between the cylindrical body and roller and held in position by tightening nut 5. Roller 2 as shown in Figure 2 containing oil at a temperature of 20"C is caused to rotate for a period of 2 minutes when a recorded trace as shown in Figure 3 is obtained the trace being a plot of shear stress in kilopascals against time, point A being the time at which the roller 2 was stopped. The trace is indicative of the flowability of the sample under test the height of the curve being a measure of its stiffness.Different samples give different curve shapes and heights but for a given composition its suitability for use in moulding can be decided by comparison of its trace with the trace of a sample made from the same materials and which has proved suitable in practice. WHAT WE CLAIM IS:

1. An apparatus which comprises: (a) two cylindrical bodies disposed in spaced apart non-circumjacent relationship with their axes parallel and located so

that they can be placed into contact with opposite sides of material under test said cylindrical bodies being rotatable relative to one another while remaining in contact with said material and means for adjusting the distance between said cylindrical bodies so that test material of various thicknesses can be accommodated in the space between them in contact with both cylindrical bodies under constant and predetermined pressure, (b) means for rotating at least one of said cylindrical bodies and, (c) a torque measuring device connected to one of said cylindrical bodies for measuring the torque imparted to the latter upon rotation of the cylindrical body(ies) when test material is located between and in contact with said cylindrical bodies.

2. An apparatus according to Claim 1 in which one cylindrical body is stationary the other being movable.

3. An apparatus according to any one of the preceding claims in which one at least of the cylindrical bodies is capable of being maintained at a constant temperature which can be varied as desired.

4. An apparatus according to Claim 3 in which the cylindrical body is heated electrically or by means of a liquid heat transfer medium.

5. An apparatus according to Claim 4 in which one of the cylindrical bodies is in the form of a drum which is filled with a fluid which can be held at a constant desired temperature.

6. An apparatus according to any one of the preceding claims in which the means for moving one or both cylindrical bodies relative to the other is an electrical, mechanical or pneumatic motor.

7. A method of measuring using an apparatus according to any one of the preceding claims which comprises placing a sample under test between and in contact with the cylindrical bodies moving the cylindrical bodies while remaining in contact with the sample at different speeds relative to one another, measuring the effect of the sample on the torque imparted to one of the cylindrical bodies and comparing the measurement with a measurement of a comparable sample known to be satisfactory in practice.

8. A method according to Claim 7 in which the sample is an unsaturated polyester resin sheet moulding compound

9. A method according to Claim 7 or Claim 8 in which the apparatus is used to test sheet moulding compounds which are being manufactured continuously.

10. An apparatus substantially as described and shown in Figures 1 and 2 of the drawings.

11. A method of testing a high viscosity material substantially as described in the specification with reference to Figure 3.

12. A method according to Claim 11 in which the material is an unsaturated polyester resin sheet moulding composition.