Measuring device which continuously measures the quality of molds produced on molding machinery where different compaction processes are considered.
The sensors SP-P (Fig. 1) and LP-I (Fig. 2) were designed, developed and built.
The SP-P sensors has small dimensions (diameter: 25mm, height: 22mm) to enable the installation in the pattern plate of DISAMATIC molding machinery. It is designed for the following compaction processes: Squeezing and Shot squeezing. The LP-I sensor is a bit bigger and distinguishes itself by compensating the leading air pressure wave in the sensor in case of the air flow squeezing or the pulse process so that the test pin gives a signal only upon molding material movement (compaction). For this reason, slit nozzles (Fig. 2) are arranged on the surface through which the air charges a balance piston. The sensor interior consists of a movable pin whose upper end is rounded and which sits on a spring. If the rounded top is set under pressure, the pins begins to move and transfers the load to the spring. The spring presses on a pressure cell and an electrical signal is triggered which is display on a computer through the relevant converters and measuring software.
Since this signal depends on the molding material compactibility, the sensor has to be calibrated to the relevant molding material. Fig. 3 shows how to install the sensor for performing measurements, whereas depending on the area to be tested the sensor can also be placed on the pattern surface or on lateral patterns.
Fig. 4 illustrates a typical compaction process curve with a two-level molding material compaction (air flow and squeezing compaction).
It is important to emphasize that the sensor, although making a movement, is not based on an inductive measuring system but it measures the actual stress state of the molding material at the measuring point. Thanks to the calibration, density values and green properties of the molding material can be determined through dependencies set up in advance.
The relation between sensor display and density is linear, whereas depending on the molding material compactibility the starting point, the so-called starting density, differs. Fig. 5 illustrates the compactibility effect on the snsor display. A lower compactibility under the dem squeezing pressure results in a higher density.