코오롱플라스틱(주)

Pre-Drying

KOPA^®-PA66 resin is kept at max. 0.2% moisture content in packages. However, it is apt to absorb moisture during processing work. Therefore, processing should be completed in less than two hours after the package is opened. Once moisture is absorbed, the resin must be dried by means of a hot-air dryer or dehumidifying dryer. Normally, the latter is better. Drying normally requires 5 hours at 70~80℃ .

Injection Molding

Selection of Injection Molding Machine
In is preferable to adopt in-line screw and screw-plunger type, as these are advantageous for melting power, temperature adjustment, prevention of material loss, and speedy internal pressure formation.

Pressure
If injection pressure is too low, part structure will be defective, and if too high, the resin layer floats during cooling, or causes deviation in structure or density, and/or easy breakage or damage from stress.

Temperature of Cylinder
Temperature is adjusted in accordance with the structure of parts and specification of injection molding machines. The resin melts at 255℃, and standard grade is maintained at 265~280℃, whereas a 10~20℃ increase in temperature is applied for glass fiber reinforced grade. Resin properties may be degraded if the temperature is too high and/or injection time is too long.

Temperature of Mold
Mold temperature is adjusted between 40℃ and 80℃ depending on the required property of molded parts. Cosmetic and mechanical properties of parts can be improved by increasing mold temperature.

Examples of Injection Molding Condition for Each Grades

GRADE별 성형조건 예

Item		Unit	KN311 KN333H R	KN333 HI	KN3322 VO	KN333 G30	KN3321 G15V0	KN333 MS
Cylinder	Rear	℃	260	260	260	265	260	255
Temp	Middle Front Nozzle		270	270	270	285	280	270
			280	275	275	290	290	280
			270	265	270	280	280	270
Mould Temperature		℃	80	70	80	80	80	80
Injection Pressure	1st 2nd	㎏/㎠	900	1000	950	1100	1200	850
		㎏/㎠	450	520	450	420	600	500
Back Pressure		Sec	10	10	10	15	15	10
Injection Time		Sec	5	5	5	4	4	4
Cooling Time		Sec	10	20	14	10	10	8
Delay Time		Sec	2	3	2	2	2	3
Screw RPM		Sec	100	100	100	110	110	100
Injection Speed		1st step	Low	Low	Low	Middle	Middle	Middle
		2nd step	Middle	Middle	Middle	high	high	Middle
		3rd step	Low	Low	Middle	Middle	Middle	Low

Trouble shooting Guide for KOPA^®-PA66 Resin Molding Problems

To achieve optimum part quality and minimum cycle time, the molder must know how to overcome molding problems.
The follow figure is a guide for troubleshooting and offers solutions for most problems encountered with KOPA^®-PA66 resin.

GRADE별 성형조건 예

Item	Britt leness	Short Shot	Poor Surface	Stain	Flash	Void	Flow Mark	Poor Mold Release	Warpage	Burning
Cylinder Temp
Mold Temp
Nozzle Temp
Injection Speed
Injection Pressure
Holding Pressure
Back Pressure
Cooling Time
Screw rpm
Nozzle Diameter
Gas Vent
Gate Size
Gate Position
Drying

Note. : Need to Increase    : Need to Decrese    : Study for Effecting Factors

Products and Mold Design

Parts Design
In designing an injection molded part using KOPA^®-PA66, thicknesses of 0.75~3mm for glass fiber reinforced grade and 0.5~5mm for non-reinforced grade are standard. If they are too thick, distortion or shrinkage is likely to occur. Therefore, changes should be done on a gradual basis. A rib 0.5 or 0.6 times thicker can prevent shrinkage, though for painting work, a thickness of 0.3 times is advised. The tolerance of injection molding under normal conditions is + 2%, though this figure can be adjusted down to + 0.5~0.1% when mold temperature is well controlled, processing cycles are normal, and no undue impact occurs to the injection molding machine.

Mold Design
Steel is the ideal material for making molds, as KOPA^®-PA66 does not corrode metal. But for the flameproof grade, it is desirable to use a base metal with higher chrome content, as the grade can corrode metal. A 0.5~1% of taper is good. For the shrinkage factor, parallel to flow direction, 2.5~3% is the standard for the general grade, 0.5~1% for the glass fiber reinforced grade. The shrinkage factor of molds for any resin vary in accordance with the additive used, process condition, thickness and shape of the part, the position of mold gate, cooling circuit, etc., making it very hard to determine. When processed parts are loosening from stress and finally stabilized, an additional 15~30% shrinkage occurs.