Technical Information

Considerations for Moulding

Recommendations for successful plastics moulding for electroplating

Drying times for plastic powder/s;
ABS – The recommended minimum drying time for ABS plastic is 4 hours at 190° to 200°F, 90° to 95°C.

PC/ABS – The recommended minimum drying time for PC/ABS plastic is 4 hours at 200° to 220°F, 95° to 105°C

Flow / Knit lines; to reduce or eliminate flow/knit lines, the process temperature generally needs to be in the region of 60° - 90°C

Stress; The tool design is as critical as the process temperature; the ‘A’ face of the part needs to be as stress free as possible. Use as large a ‘gate’ as possible, which combined with the higher tool temperature, allows the plastic to flow more freely. Avoid high holding pressure and long holding times; it should be enough to fill but not to over pack the tool creating a hard skin.

Mica / micre / splash / silvering / fish eyes; The most common cause of this is moisture (see drying times above) but other characteristics that can create this are; lack of back pressure, too long a ‘residence’ time in the barrel, ‘cold spots’ in the barrel and runner design [not too many changes of direction (bends/corners) or too small an orifice], ‘suck back’ can introduce air into the moulding, this too can cause mica/silvering.

Material Changeover; Ensure that all residues of other materials are fully purged from the barrel, screw, hopper etc., as this can also cause mica or stress.

Hard spots; can be caused by ‘gate debris’, residue materials, ‘gas trappage’ (especially on polished faces where no venting is adjacent to the area). A tool-cleaning programme may relieve some of these problems; which may necessitate disposing of the first few shots after cleaning.

Flash; Though sometimes acceptable on mouldings not intended for plating, flash is to be avoided as the plating process will turn the flash into a razor sharp shard or edge and can propagate nickel burn. For the same reasons, sharp corners should also be avoided.

Sink Marks; However slight they may appear in the virgin moulding, they are magnified manifold by the shine of the Chromed surface finish. To reduce the problem further, avoid sudden changes in material thickness or the use of thick walled bosses on the ‘back face’ or long ribs.

Recommended materials;

ABS materials;- Polylac 727, Cycolac S705, Novador P2MC in plating grade ABS

PC/ABS where the Polycarbonate is not greater than 45% i.e., Bayblend T45 [NOT T65 or T85]