Understanding Mould cooling channel and Cooling system in factory

Understanding Mould cooling channel and Cooling system in factory Introduction Injection moulding process is cyclic in characteristic. Cooling time is about 50 to 75% of the total cycle time. Therefore, optimising cooling time for best performance is very important from quality and productivity point of view. Cooling time is proportional to square of wall thickness. Therefore part design should ensure more or less uniform wall thickness through out the part. Part design should also ensure that the melt flow is uniform in all direction from the gate and melt should reach the boundary of the part more or less at the same time. Cooling channel design - location and size and type - should ensure that melt freezes uniformly inside the mould. Cooling channel design can be perfected with the help of MOLDFLOW analysis. It is necessary to understand Heat Exchange and Cooling Channel design in the mould. Heat Exchange in mould During every injection moulding cycle following heat transfers take place: • from the hot melt to mould steel (heat input to the mould) and • from mould steel to coolant flowing through cooling channel of the mould. (heat removal from the mould) If heat input is more than heat removal, then the mould temperature would keep on increasing from cycle to cycle. Therefore moulding quality would not be constant from cycle to cycle. The moulding quality would be erratic- i.e. varying from cycle to cycle. Therefore, there is a need to balance between the heat input and heat removal in the mould after the desired mould surface temperature is reached. In other words, removal of heat by circulating coolant through the mould cooling channel would arrest the rise of mould temperature above the desired value. In practice, it may not be possible maintain constant mould temperature with respect to time. However, the mould temperature would fluctuate between two values around the desired value. During injection moulding cycle heat flow takes place from polymer melt to mould steel by • effective thermal difusivity of polymer melt and • conduction. This heat is to be removed by circulating cooling fluid through the cooling channels in core as well as cavity during cooling period in order to maintain the desired temperature. Uneven temperature of the mould surface results (uneven shrinkage) in parts with moulded-in stresses, warped sections, sink marks, poor surface appearance and varying part dimensions from cycle to cycle and even cavity to cavity. cont...