“Inflation also erodes the real value of workers wages, and reduces their living standards. Inflation is expected to peak at around six per cent by the end of the year, impacting businesses and workers, and this also influenced the decision, Ross said. There has also been a sharp rise in the cost of living since last year’s review.” “The improvement in the labour market is forecast to continue in the period ahead. “At the aggregate level, labour market performance has been particularly strong The unemployment rate has fallen to 3.9 per cent compared to 5.5 per cent in April 2021 at the time of the last review. “The most significant changes since last year’s review decision have been a sharp increase in the cost of living and the strengthening of the labour market,” he said while handing down the decision. Supported by the Government of South Australia.This variation is likely caused by an improperly designed or worn screw.Local businesses achieving a new measure of success ![]() Non-uniform melt temperature: Non-uniform melt temperature will result in variable bubble cooling rates and die throughputs. The air ring should also be checked to confirm it is properly centered on the die. To avoid this issue, the air channels in the air ring should be inspected and cleaned periodically to remove any impurities that may cause air-flow disturbances. This can result in portions of film being stretched more than others, which may lead to gauge variation. Non-uniform air-ring cooling: Poor or non-uniform air flow coming from the air ring will result in non-uniform film cooling, which will impact the drawdown ratio of the film. If misaligned, the die can be recentered using the die-adjustment bolts. A misaligned die will result in a non-uniform flow distribution of material leaving the die. To correct this, the die gap should be checked for uniformity along the circumference. Misaligned die: A common source of gauge variation is a misaligned die gap. This can be caused by factors ranging from poor melt quality and surging to die and air ring mis-alignment. Gauge variationĬhanges in film thickness or gauge around the bubble circumference is another problem in the blown film process. To avoid this situation, resin selection can be optimized to reduce the overall melt viscosity of the extrudate and decrease the overall melt temperature.Ĭommon causes and corrective actions for bubble instability 2. However, reducing air flow will subsequently decrease the cooling efficiency of the air ring, which may then cause the frost line to drift away from the die, leading to new problems. This fluttering is caused by high air velocity coming from the air ring.ĭecreasing blower speeds or adjusting air-ring components to reduce the air flow along the bubble surface will prevent bubble fluttering. To avoid this, the die should be inspected for material buildup periodically and cleaned if necessary.īubble fluttering: Bubble fluttering initiates below the frost line and appears as linear marks on the bubble surface in the transverse direction (TD). A non-uniform die throughput may be due to a buildup of degraded material in the die. Another common cause of an unstable frost line is a blockage in the die. One cause of this instability is a non-uniform temperature profile in the extrudate. When a process becomes unstable, the position of the frost line will become unstable as well. Unstable frost line: In a stable process, the frost line will remain at a constant height above the die and is controlled by the cooling rate, die throughput, and film-thickness uniformity. Another solution is to modify the resin selection to decrease the overall elongational viscosity of the film, allowing the film to stretch more in the MD without experiencing any strain hardening. This issue can be prevented by reducing the drawdown ratio. This causes fluctuations in internal bubble pressure and bubble width. ![]() Strain hardening : Strain hardening occurs when molten polymer is rapidly stretched in the machine direction (MD) and stiffens as a result. An example of this is incorporating low-density polyethylene (LDPE) into a linear low-density polyethylene (LLDPE) film to increase its overall melt strength. To avoid it, resin selection can be modified to incorporate a higher-melt-strength material into the film structure to improve the overall melt strength. This problem takes place when the melt strength of the extruded material is insufficient for the selected blow-up ratio (BUR). The main issues include bubble breaks, strain hardening, unstable frost line, and bubble fluttering.īubble breaks : A bubble break occurs when molten material exiting the die is overstretched, resulting in a break in the bubble structure. The term bubble instability encompasses many different types of issues related to the stability of the extruded bubble. This may be one of the most common problems in blown film.
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