GB2164160A

GB2164160A - Apparatus for measuring the dependence of specific volume of a plastics on pressure and temperature

Info

Publication number: GB2164160A
Application number: GB08520735A
Authority: GB
Inventors: Lubomir Zeman
Original assignee: Statni Vyzkumny Ustav Materialu
Current assignee: Statni Vyzkumny Ustav Materialu
Priority date: 1984-08-17
Filing date: 1985-08-19
Publication date: 1986-03-12
Also published as: GB8520735D0; CS246238B1; DE3528581A1; CH670314A5; CS622884A1; GB2164160B

Abstract

Apparatus for measuring the dependence of a specific volume of a plastics material on pressure and temperature comprises a heat-insulated pressure cell (2) and a program controlled straight line hydromotor 12 with an electrohydraulic servo valve (13) for application of a load, means (3,4,5,6) for adjustably heating or cooling said heat insulated pressure cell (2), and feed back means comprising a pick-up device (14) for measuring force and a pick-up device (15) for tracking the movement of the pressure piston. The electrohydraulic valve (13) is connected to a summary recorder (22), and the pick-up devices for tracking movement and for measuring force (14,15) are connectable in turn to an input of the summary recorder (22) via a change-over switch (23). A programmer (19) is also connected to the summary recorder (22) via a change-over switch (24), and an output of said summary recorder (22) is connected to the servo valve (13). The arrangement enables the measurement of specific volume change when test piece 1 is subjected to isothermal hydrostatic compression or isobaric heating and cooling. <IMAGE>

Description

SPECIFICATION Apparatus for measuring the dependence specific volume of a plastics on pressure and temperature This invention relates to an apparatus for measuring the dependence of the specific volume of a plastics on pressure and temperature. The results of such measurements provide information about the reaction of material to isothermic hydrostatic compression or to isobaric cooling or heating respectively. The knowledge of these measured values of different plastics is utilized in practice for the design of machines for the working of plastics, for determination of adiabatic heating of plastics and in recent times particularly as values of a set of input parameters for automatic regulation and control of the technological process of pressure die-casting of plastics.

Apparatus for measuring of these dependences of plastics are of different design, mostly three fundamental types are used, namely: -the first group form arrangements, the main part of which is a pressure cell having the shape of a pressing tool clamped to the table of a hydraulic press; -the second group includes arrangements where the pressure cell is situated in a thermostat and the pressure on the test piece is generated hydraulically; a modification of this system is an arrangement where the hydraulic liquid acts directly on the test piece; -the third group represent arrangements where a test piece of any shape is situated within a yieldable vessel filled with mercury, which is submerged in a tempered pressure vessel filled with liquid.

None of these aforementioned arrangements enables measuring of both dependences, said arrangements enable all merely a measuring to be made on the principle of isothermic hydrostatic compression and are complicated, do not enable automation of measurements, and their accuracy is not high.

It is an object of this invention to eliminate or at least to reduce said drawbacks of arrangements for measuring said dependences of plastics comprising a pressure cell and an arrangement for application of a load.

The apparatus for measuring of these dependences of plastics according to this invention comprises in a first aspect a controllable heated or cooled heat-insulated pressure cell and a program-controlled arrangement for application of a load including a straight line hydromotor and an electrohydraulic servo valve and pick-up devices for measuring applied force and movement.

The electrohydraulic servo valve is connected via a program change-over switch with a programmer.

This arrangement for measuring of the dependence of specific volume of a plastics on pressure and temperature enables a quick, accurate and highly automated measuring and evaluation of the required dependence. For instance in case of an automatic computerized arrangement of the injection process, the measured values are utilized for adjustment of changes of volumes of extrusions of plastics in the forming cavity of the injection mould, leading to a substantial improvement of the quality of products thus manufactured.

A circuit arrangement of an arrangement for measuring of the dependence of specific volumes of plastics on pressure and temperature according to this invention is shown, by way of example only in the single figure of the attached drawing, comprising a heat-insulated pressure cell with temperature control equipment, an arrangement for application of a load and a control unit with the respective circuits.

A test piece 1 is situated in the working space of a heat-insulated pressure cell 2. The pressure cell is heated by an electrical heater 3 adjusted by control means 4 by way of a pickup device 5 for the temperature or is cooled by a liquid or gaseous medium in a cooling coil 6, the temperature of which medium is controlled by a control apparatus 7 including a temperature pick-up 8 for the tempering medium and a through-flow meter 9. The test piece 1 is compressed by a pressure piston 10 having a temperature pick-up 11 for the test piece 1 situated in a bore in the front wall of the piston 10. The drive of this piston 10 is derived from a straight line hydromotor 12 controlled by an electrohydraulic servo valve 13 and by feed-back pick-up devices 14 for measuring the generated force or by a pick-up 15 of deformations or of the movement of the piston rod.The extrusion of the test piece from the working space and cleaning of the working space is accomplished by a lower mobile piston 16 with a pressure pick-up 17 situated at its front part. The measuring of the temperature of the pressure cell is accomplished by a temperature pick-up 18, and the program adjustment of the force of deformation by a programmer 19. All measured values are recorded by a recording device 20 and are evaluated in a unit 21.

The arrangement operates either at isothermic hydrostatic compression, i.e. at T=const.

where the test piece 1 is stressed at constant deformation y=const. realized by constant speed of the movement of the pressure piston 10. In that case the pick-up of the track of the movement of the piston 10 generates a signal y, related to the actual value of the movement for the programmer 19 and the summary recorder 22 where this signal is compared with the value y=const. and instructions are released for a change of y and thus for equalizing the required and the actual values of the track of the pressure piston 10. In order to ascertain the real course of the test, the value y, is continuously recorded. The test at isobaric cooling or heating, i.e. at constant pressure p-const. proceeds similarly, whereby the test piece is stressed by a constant force F=const.The force F is adjusted on the programmer 19 and is compared at the summary recorder 22 with the actual force Fx determined by the pick-up device 14 of. the force F. This test is based on the principle that in case of a change of the length of the test piece 1 due to its controlled cooling or heating, the value of the force F=const. changes to Fx and after comparison in the summary recorder 22 a signal is released for a change of the adjustment of the piston of the straight line motor 12. The course of the force Fx is recorded throughout the course of the test. Both described processes are repeated for given levels F=const. and y=const.

In order to secure a constant temperature of the test piece 1 in case of a prolonged heating, electric heater 3 controlled by control means 4 is provided. The data about the adjustment of the temperature TE const. are transmitted from the programmer 19 to the control means 4 where the heater 3 is controlled by the supplied heating power Pw. The temperature pick-up device 5 picks up the actual temperature TEX which is compared by the control means 4 with TE const. resulting in a change of the supplied power Pw. Simultaneously the temperature pick-up device picks-up the temperature Tx of the pressure cell 2.

A liquid or gaseous medium tempered in the tempering arrangement 7 to the required temperature TK const. is used for direct cooling or heating of the test piece 1. This tempering is alternately made for the required temperature gradient. The tempering medium (having a temperature TE const. and a through-flow amount of Q const.) passes through the tempering system of the pressure cell 2, whereby its temperature TKX at the outlet from the cell is determined by a pick-up 8 monitoring the temperature of the tempering medium. The real temperature of the cell 2 is Tx which is recorded and represents an input value for comparison with TKX.

In the course of the whole measuring both at isothermic and also at isobaric conditions, the readings from pick-up devices 11 and 17 are picked up and recorded in a memory. The temperature T, indicated by the pick-up device 11 represents the closest approximation to the proper temperature of the test piece 1, the same holds true about the value F, of the force or the value p, of pressure measured by the pick-up device 17 which simultaneously serves as control value for the value indicated by the pick-up device 14.

Change over switche 23 is provided to switch the measurements places whilst change over switch 24 is provided to switch programs.

The following designations have been used when describing the operation of the object of this invention: y=const. constant deformation of the test piece real deformation of the test piece y difference between y=const. and y, F=const. constant force acting on the test piece F, real force acting on the test piece F difference between F=const. and F TE,,,,st adjusted temperature value of electrical heating TEX real temperature close to the electrical heating power supplied to the electrical heating TKc,x,t adjusted temperature for heating or cooling temperature gradient TKX temperature of the tempering medium on the outlet from the cell real temperature of the cell of the test piece.

Qc,,,t through flow amount of tempering medium real temperature of the test piece F, real control force acting on the test piece p, real pressure in the test piece Index of reference marks 1 test piece 2 pressure cell 3 electric heating 4 control of electric heating 5 pick-up of temperature 6 liquid or gas cooler/worm/ 7 tempering arrangement 8 pick-up device of temperature of the tempering medium 9 through flow meter 10 pressure piston 11 pick-up device of temperature of the test piece 12 straight line hydromotor 13 electrohydraulic servo valve 14 pick-up device of the force 15 pick-up device of the track 16 lower piston 17 pick-up device of the pressure 18 pick-up device of the temperature 19 programmer 20 recording device 21 evaluation unit 22 summary recorder 23 change-over switch of measuring places 24 change-over switch of programs

Claims

1. Apparatus for measuring the effect upon the volume of a plastics material of changes in temperature and pressure, which apparatus comprises means for applying hydrostatic pressure to a sample of a said plastics material means for measuring the pressure so applied and feed back means for adjusting the applied pressure in accordance with the pressure so measured; means for heating or cooling a said sample, means for measuring the temperature of a said sample and feed back means for adjusting the temperature of a said sample in accordance with the temperature so measured and selection means for selecting between measuring the effect upon the volume of a said plastics material respectively of isothermic hydrostatic compression and of isobaric cooling or heating.

2. Apparatus according to claim 1, wherein said means for applying hydrostatic pressure comprises a straight-line hydromotor.

3. Apparatus according to claim 1 or 2, wherein said feed back means for adjusting the applied pressure includes an electrohydraulic servo valve.

4. Apparatus according to any of claims 1 to 3, wherein said feed back means for adjusting the applied pressure includes a programmable device for controlling said adjustment.

5. An apparatus for measuring the dependence of a specific volume of a plastics material on pressure and temperture comprising a heat-insulated pressure cell and means for application of a load, means for adjustably heating or cooling said heat insulated pressure cell, said means for application of a load being program-controlled and comprising a straight line hydromotor with an electrohydraulic servo valve and feed back means comprising a pick-up device for measuring force and a pick-up device for tracking the movement of the pressure piston, said electrohydraulic valve being connected with a summary recorder, said pick-up devices for tracking movement for measuring force being connectable respectively to input of said summary recorder via a change-over switch, a programmer being also connected to said summary recorder via a changeover switch, and an output of said summary recorder being connected to said servo valve.

6. Apparatus for measuring the dependence of the volume of a plastics material upon temperature and/or pressure, substantially as hereinbefore described with reference to the accompanying drawing.