(56) Spray pattern Injection Molding Process Defect Handling Manual (65 types)

1. What is a jet print? (Appearance)
Generally, dissolved resin flows in the form of a jet stream. However, when flowing from a narrow area to a wide area, if the flow rate is too fast, it will sometimes fly out in a ribbon and flow without contacting the mold. This is referred to as a spray pattern. According to the way spray patterns appear on the surface of the finished product, some appear as ribbons, while others appear as fog, but the reasons for both are the same.
2. Reasons for formation of spray marks
(2-1) The gate size is too small
The biggest cause of spray marks is the gate size. If you imagine a water gun, it is not difficult to understand the phenomenon of spray marks. The smaller the hole (gate), the more powerful the force to fly out, and the more severe the spray pattern will become. The reason why the hole is small is because it means that the pressure increases and the speed increases there.
(2-2) Injection speed is too fast
With the same gate diameter, the faster the injection speed, the more severe the spray pattern.
(2-3) High viscosity/low fluidity
With the same gate diameter and injection speed, the higher the viscosity of the resin (the lower the fluidity), the more severe the spray pattern.
The conditions that affect the increase in viscosity are as follows:
(1) Low resin temperature
(2) Low mold temperature
(3) Material viscosity
(2-4) Low pressure retaining
Maintaining pressure will make the spray pattern too inconspicuous to a certain extent. On the contrary, if the pressure retaining is not fully applied, the spray pattern will be obvious.
3. Countermeasures for spray marks
(3-1) Try increasing the gate size
First, check whether the gate size can be changed. Although this depends on the shape and size of the product, there is scope to eliminate spray marks by changing the gate size. It is best to use a short and wide gate land; A design style that opens in a fan shape and has an angle is also effective.
(3-2) Attempt to change the gate position
Then check whether the gate position can be changed. The spray pattern is basically caused by the strong force of the resin flying out. And the more open the target space is, the more serious it becomes. However, if the resin flying out of the gate quickly hits the wall, the spray marks can be eliminated.
Even if it is impossible to change the gate position, it is expected to achieve the same effect if something such as pins or walls can be additionally installed on the front of the gate in the product mold cavity.
(3-3) Try to lower the injection temperature
Try lowering the injection speed setting. The countermeasure is to use multi stage injection and only slow down the speed through the gate (not the overall reduction).
◆ Recommended injection conditions for various materials
Resin injection pressure Injection speed V-P switching position
Duracon max 8-19mm/sec is about 90% of the filling amount of the product
Duranex 〃 16～33mm/sec 〃
Fortron 〃 25～42mm/sec 〃
Vectra 〃 30～50mm/sec 〃
(3-4) Reducing resin viscosity
Methods for reducing resin viscosity:
(1) Increase resin temperature
(2) Increase mold temperature
(3) Change the level to high flow type
(3-5) Check and maintain pressure
◆ Recommended pressure retaining conditions for various materials
Resin pressure maintaining time
Duracon 59 ～ 98MPa gate seal+1 ～ 2sec
Duranex 59～98MPa 〃
Fortron 39～69MPa 〃
Vectra 29～49MPa 〃