1) Explanation of Terms Used :
Closing Speed ::..
The speed at which mould gets closed, controlled flow by electroproportional valve/pressure relief valve.
Opening Speed ::..
The speed at which the mould gets opens is controlled flow by
Electropro-portional valve/pressure relief valve.
Slow-Fast-Slow ::..
The Slow movement of mould during opening and closing at beginning
and end of stroke is known as slow. This action controlled by electropropotional valve/pressure relief valve setting through PLC.
Locking Force ::..
The force at which the two mould plates are held together during
injection. Locking force depends on the injection pressure and projected area of the article.
Melt Temperature ::..
It is measured by thermocouples situated in the wall of the
injection chamber and barrel. This controlled by PID type temperature controllers. It should be borne in mind that the temperature indicated is not that of the material but of the barrel and hence it is only a comparative value. Temperature controller is incorporated in PLC.
Injection Pressure ::..
This is the pressure required to inject the plasticised material Into the mould. It can be varied from material to material, mould to mould and the temperatures being processed. The maximum pressure available will depend on the capacity of the barrel head being used.(standard, medium and low pressure).
Injection Speed ::..
It is the rate at which the plasticised material can be injected into the mould, and can be varied by the proportional Valve to inject the material at low pressure at the end of stroke. It can be controlled through PLC system.
Reduced Injection Pressure ::..
It is required to hold the molded material at a lower pressure after injection has been completed. It is regulated by proportional valve/pressure relief valve and PLC setting.
Injection Period ::..
It is the period during which plasticised material is being injected in the mold.
Screw Refill ::..
For refilling, the pre-plasticising screw is rotated by the hydraulic motor. This conveys the plasticised material in barrel head and screw. The unit will travel back due to accumulated material it presses in the barrel head. This unit will travel back until the proxy/limit switch PS3A/LS3A is activated, which determines the refilling stroke. The screw speed during refill can be infinitely varied to the maximum RPM by electroproportional valve/pressure relief valve and PLC control.
Cooling Period ::..
It can be set by cooling timer according to the requirement of the molded article. During this period, the screw refilling starts and the molded article solidifies in the mold.
Suck Back ::..
To prevent nozzle drooling during cooling time, this system is Provided. As soon as cooling time is over suck back action will start and screw will be pulled back till proxy/limit switch PS3B/LS3B is activated.
Delay Cycle ::..
It is the time between two consecutive cycles when machine is running in fully automatic mode. This time can be set by adjusting delay cycle timer. Usually during this period molded article gets ejected from mould automatically.
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2) Causes for Moulding Defects : |
Que: Short Shots ? |
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Material |
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Improper Lubrication. |
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Material flow is not smooth and proper. |
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Que: Mold ? |
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Faulty gate balance. |
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Insufficient gate runner, sprue. |
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Mould temperature is low. |
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Cavity is not thick enough. |
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Que: Machine ? |
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Insufficient Injection capacity. |
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Insufficient supply of material. |
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Low Injection capacity. |
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Low temperature. |
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Resistance at nozzle unit is high. |
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Screw feed in is poor. |
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Nozzle is cooled. |
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Damaged back flow prevention ring. |
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Flash ::.. |
| Material |
Mold |
Machine |
| Viscosity of resin in molding is too low. |
Mold face is not parallel. |
Injection Pressure is high. |
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Parting line is not designed properly. |
Weak dies clamping force. |
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Foreign materials caught between the matching surfaces. |
Injection amount is
too high. |
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Projected area is high. |
Resin temperature
is high. |
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Die temperature,
too high. |
Injection pressure dwelling time is long. |
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Surface uneven on the parting line. |
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Sink Marks ::.. |
| Material |
Mold |
Machine |
| Resin flow is too slow. |
Die temperature is high. |
Low Injection pressure. |
| Contraction rate of the material is high. |
Die temperature is uneven. |
High resin temperature. |
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Runner gate is small. |
Die opens to soon. |
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Runner and sprue is small. |
Resistance at nozzle part is high. |
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Thickness of cavity is not uniform. |
Damaged back flow prevention ring. |
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Shape of ejector pin is improper. |
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Silver Streaks ::.. |
| Material |
Mold |
Machine |
| Moisture or volatile in mixed in the material. |
Die temperature is low. |
Insufficient injection capacity and plasticizing efficiency. |
| Air mixed in the material. |
Poor degassing. |
Overheat resolution of resin. |
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Improper gate position. |
Insufficient meeting due to low resin temperature. |
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Improper design of cavity (resin flowing across the ribs or sudden change in thickness) |
Insufficient back pressure. |
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Gate, runner, sprue are small |
Dirty cylinder. |
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Moisture and lubricants on mould surface. |
Screw revolution is high. |
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Flow Makers ::.. |
| Material |
Mold |
Machine |
| Resin flow is not smooth. |
Die temperature is low. |
Insufficient fluidity due to low resin temperature. |
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Die cooling is not proper. |
Insufficient injection holding pressure. |
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Slug well is too small. |
Holding time is short. |
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Enlarge the gate. |
Cushion amount of material is insufficient. |
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Cold slug, produces cold flow mark. |
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Surface Clouding ::.. |
| Material |
Mold |
Machine |
| Moisture or volatile matter mixed in the material. |
Mould temperature is high or too low. |
Uneven resin melts causing partial overheating. |
| Due to volatile matter mixed in the lubricant. |
Gate, runner and sprue are too small. |
Cooled off nozzle. |
| Mixing of other materials. |
Slug well is too small. |
Nozzle aperture is small. |
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Moisture and lubricant on die. |
Overheat decomposition of resin. |
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Poor degassing. |
Insufficient cushion amount. |
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Weld Marks ::.. |
| Material |
Mold |
Machine |
| Moisture and volatile matter present. |
The welding unit is a long distance from the gate |
Fluidity is poor due to low resin temperature. |
| Material flow is not smooth. |
Die temperature is low. |
Injection pressure is low. |
| Soot assimilation. |
Improper position and number of gates. |
Nozzle is cold. |
| Lubricant is not proper. |
Gate and runner are too small. |
The back pressure high. |
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Exhausting is not proper. |
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Excessive usage of parting agent. |
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Air Bubbles ::.. |
| Material |
Mold |
Machine |
| Contraction rate is high. |
Degassing is not proper. |
Injection pressure is low. |
| Moisture and volatile matter. |
Cavity (not proper thickness or sudden change in thickness). |
Poor fluidity due to low resin temperature. |
| Air mixed in the material. |
Gate position improper. |
Gas generated due to high resin temperature. |
| Lubricant is not proper. |
Small gate, runner and sprue. |
Air drawn in. |
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Cooling temperature is low. |
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Mould temperature is low. |
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Excessive air drawn in. |
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Black Streas ::.. |
| Material |
Mold |
Machine |
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Adherence of grease oil. |
Overheating of material. |
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Decomposition due to friction heat from gate units. |
Over accumulated resin in a portion of the cylinder. |
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Improper degassing. |
Over heating of material due to friction or adiabatic compression by air in the cylinder. |
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Existence of volatile matter. |
The hopper installing parts & cooling not proper or
insufficient. |
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High cylinder temperature. |
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Injection pressure is high. |
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Cooling time too long. |
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Detention time in the cylinder is too long. |
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Screw speed is high. |
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Article surface not good ::.. |
| Material |
Mold |
Machine |
| Improper annealing. |
Gate is too wide. |
Injection pressure high. |
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Low die temperatures. |
Low resin temperature due too poor fluidity. |
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Poor mould release. |
Melting of resin insufficient. |
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Core becomes vacuum in mould release. |
Extension of cooling time. |
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Improper cavity design. |
Use a cooling fixture after mould release. |
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Avoid generation of inner stress and concentration. |
Slow injection speed. |
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Improper projection. |
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Cooling insufficient or uneven |
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Poor Mould Release ::.. |
| Material |
Mold |
Machine |
| Improper lubrication. |
Insufficient cooling due to adheres to the die. |
Injection pressure high. |
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Mould temperature is high. |
High resin temperature so fluidity is too smooth. |
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Gate is too wide. |
Time is too long of injection holding time. |
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Poor degassing. |
Excessive measuring. |
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Improper gate balance. |
Extend cooling time. |
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Nozzle larger than sprue hot. |
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Stationary side temperature is too high. |
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Not proper sprue diameter (taper). |
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Not proper projection amount. |
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Insufficient agent. |
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Sticking in the sprue ::.. |
| Sprue Condition |
Mold |
Machine |
| Match sprue radius to nozzle redius. |
Pull out force increase. |
Use sprue break. |
| Correct sprue nozzle seating. |
Mould temperature reduced. |
Feed reduces. |
| Nozzle orifice not large than the sprue orifice. |
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Injection pressure reduces. |
| Polish the sprue. |
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Injection forwarded time reduces. |
| Taper of the sprue increase. |
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Material temperature reduces. |
| Diameter of the sprue it is too larger for cooling. |
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Reduce cylinder temperature. |
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Nozzle temperature reduces. |
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