BS EN ISO 294-4 pdf free download
BS EN ISO 294-4 pdf free download.Plastics – Injection moulding of test specimens of thermoplastic materials.
4.2 Injection-moulding machine, in accordance with ISO 294-3:2002. 4.2, but adding the following tolerance limits to the list of operating conditions given in ISO 294-1:2017.4.2.2:
Cavity pressure, pc ± 5 %
4.3 Measuring equipment, capable of measuring the length and width of each test specimen and of the mould cavity to within 0,02 mm, the measurements being made between the centres of opposite sides or between the opposite edges or between pairs of reference marks (see Annex A). When measuring the length of a test specimen, take care to include the 0,5-mm-high step at the gate end of the specimen. If a mechanical instrument is used, ensure that the jaws of the instrument do not produce a significant indentation.
It is recommended that a calibration plate be used to periodically check the measuring equipment.
4.4 Oven, necessary only if post-moulding shrinkage is to be measured, by agreement between the
interested parties.
5 Procedure
5.1 Conditioning of material
As specified in ISO 294-1:2017. 5.1.
5.2 Injection moulding
5.2.1 For the basic injection-moulding conditions, see ISO 294-3:2002, 5.2.
5.2.2 The moulding shrinkage is preferably determined for one or more values of the cavity pressure at hold pcj (see 3) selected from 20 MPa, 40 MPa, 60 MPa, 80 MPa and 100 MPa. Intermediate values may also be used, however.
For values higher than 80 MPa, a correspondingly high locking force will be necessary, and this may not be possible with normal commercial equipment.
5.2.3 Determine the hold pressure PH which corresponds to each selected value of PCH and mould test specimens at each of these pressures, taking into account of the following additional instructions.
a) Select the change-over point, between the injection and hold periods carefully to avoid a depression in the time against pressure curve (see Figure 1, Curve c) and to avoid a peak that, during the 1 s following the change-over point, exceeds the cavity pressure at hold by more than 10 % (see Figure 1. Curve b).
Due to the inertia of the injection-moulding machine, the effective change-over time is longer than its nominal value. The correct change-over point shall therefore be adjusted individually for each value of the injection speed and for each material under test.
NOTE Peaks in the cavity pressure lead to transient overloading of the cavity, followed by partial backflow of the melt. Thus, the mass of material injected into the cavity is not clearly defined and the orientation of the material near the gate will be perturbed.
b) Keep the hold pressure constant during the hold period.
c) For the hold time, see ISO 294-1:2017. 5.2.4. The decrease in the cavity pressure at hold to zero indicates that the material in the gate has solidified sufficiently to stop flow into the cavity.
d) Select the cooling time to be the minimum value at which the mouldings can be removed from the mould without distortion. As the cooling rate of the material is proportional to the square of the reciprocal of the thickness, the minimum cooling time (for the cavity) can be expected to be close to 1,8 times the hold time (cooling time for the gate) for the gate height to plate thickness ratio of 3:4 in ISO 294-3. e) For the maintenance of steady-state conditions, see ISO 294-1:201Z 5.2.5. The change in curvature near point A in Figure 1 indicates the transition from the melt-flow period to the bulk-compression period. At point R, the value of the cavity pressure at hold is recorded. The minimum hold time can be read from the decrease of the cavity pressure to zero. BS EN ISO 294-4 pdf download.
