The purpose of the Manifold Balance step is to evaluate the thermal and melt flow balance of the head tooling manifold distribution system and to establish uniform melt flow to each die on multi-head blow molding systems. The melt flow control (normally a choker valve) must adjust freely at normal operating temperature. The valve design must be capable of adjusting material flow to each die head so that the melt flow is stable over a range of extrusion rates.
Both the parison weight and length differences are an indicator of the degree of melt balance control and the quality of the manifold system design. A typical, well-balanced manifold will be balanced to within 5%. It is critical to have the flows balanced to each die or the part-to-part variation may be large and process capability may not be achievable.
Initial manifold control valve balance adjustments should be made during the Parison Centering step to optimize the manifold system flow balance. The Manifold Balance step may have to be repeated at higher extrusion rates, i.e. production rate, as melt flow pressure gradients change with melt flow rate and can affect the manifold melt flow balance.
Proceed to the Verify Mold Operation step if the blow-molding machine is a single die head system.
All the steps during the procedure that involve intimate contact with the bow-molding machine are to be done by a qualified blow molding machine operator.
Shuttle Process Procedure:
Task Description:
1. Verify that the zone temperature controller displays indicate a relatively uniform temperature distribution for the manifold system and head tooling.
2. With the extruder operating at a low rate, cut the parison close to the die face (using the cut device where applicable), extrude a parison and note a reference length for the parison. Typically the reference parison length will be the required parison length for the mold. Shorter parison reference lengths should be used for larger containers to avoid parison sag effects. Use a stopwatch and record a reference parison extrusion time from when the parison was cut until the end of the parison reaches the reference length position. Cut the parison again and record the parison weight for that die head.
Both the parison weight and length differences are an indicator of the degree of melt balance control and the quality of the manifold system design. A typical, well-balanced manifold will be balanced to within 5%. It is critical to have the flows balanced to each die or the part-to-part variation may be large and process capability may not be achievable.
Initial manifold control valve balance adjustments should be made during the Parison Centering step to optimize the manifold system flow balance. The Manifold Balance step may have to be repeated at higher extrusion rates, i.e. production rate, as melt flow pressure gradients change with melt flow rate and can affect the manifold melt flow balance.
Proceed to the Verify Mold Operation step if the blow-molding machine is a single die head system.
All the steps during the procedure that involve intimate contact with the bow-molding machine are to be done by a qualified blow molding machine operator.
Shuttle Process Procedure:
Task Description:
1. Verify that the zone temperature controller displays indicate a relatively uniform temperature distribution for the manifold system and head tooling.
2. With the extruder operating at a low rate, cut the parison close to the die face (using the cut device where applicable), extrude a parison and note a reference length for the parison. Typically the reference parison length will be the required parison length for the mold. Shorter parison reference lengths should be used for larger containers to avoid parison sag effects. Use a stopwatch and record a reference parison extrusion time from when the parison was cut until the end of the parison reaches the reference length position. Cut the parison again and record the parison weight for that die head.
3. Adjust the flow control valve(s) as required to achieve relatively uniform melt flow rates to each die head.
4. Repeat steps 2 through 5 until a satisfactory flow balance is achieved.
5. Calculate the percent imbalance.
4. Repeat steps 2 through 5 until a satisfactory flow balance is achieved.
5. Calculate the percent imbalance.