▌ Problems and Solutions
Problems and Solutions
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▌ Problems and Solutions
Problems Factors Solutions
Injection Molding Machine Injection Molds Plastic Material
Short shot or short material Shortage of material in mold; injection molding incomplete:
(1)Low performance of injection molding machine(low injection molding and plasticization)
(2)Bad material flow
(3)Small profile of gate; small mold wall thickness
(4)Bad air expelling
(1)Injection rate is required to be increased. If the maximum rate is used and not changed, the injection machine is required to be upgraded.
(2)If co-axial screw is applied, it needs an Shot-off nozzle screw.
(3)Increasing of injection pressure
(4)Solidification temp. for both barrel and nozzle are to be up.
(5)Fuse breaking
(6)Injection nozzle easy to stuck, mold temp. is to increase and the cycle time is required to be higher.
(7)Increasing of injection speed.
(1)Increasing mold temp.
(2)Bring up the air expelling capacity.
(3)Enlarge profile of gate
(4)Increase thickness of product wall.
(5)Add runners to improve material flow.
(1)Choosing of low viscosity material
(2)Add surface lubrication
Overflow Material expelled out from molding line:
(1)Too high temp. of material
(2)Too high of injection pressure
(3) Insufficient clamping force
(1)Keep lower injection pressure.
(2)Shorten injection time.
(3)Keep lower temp. of solidification temp. of barrel.
(4)Decrease injection speed.
(5)Change of higher clamping force machine.
(1)Modify mold and make molding surface more fit tightly.
(2)Clear off foreign material from molding surface.
(1)Choosing of low viscosity material
Shrink mark Dent and shrinkage of product surface is found often on those thick wall products. Its factors are same as "Holes"(see below). While, the major reason is from cooling timing mostly. (1)Increase injection speed.
(2)Increase mold inner pressure (the second pressure)
(3)Lower solidification temp. in barrel.
(4)Increase injection flow.
(5)Increase injection rate
(6)Prolong injection time.
(1)Make mold temperature to be even.
(2)Change position of injection gate.
(3)Enlarge gate.
(4)Shorten runners.
Holes A hole obviously seen:
(1)Density of melting material changing during solidifying.
(2)When surface of polymer contacts lower temp. mold wall, the solidification quickly formed; the shrinkage gathered on the thick part; therefore the holes formed.
(3) Air brought into mold; thus, holes were formed.
(1)Increase injection pressure (and 2nd pressure).
(2)Prolong injection time.
(3)Lower material solidifying time of barrel.

(1)Reduce thickness of part to 6mm below.Add ribs. Remove un-necessary wall thickness evenly.
(2)Enlarge gate.
(3)Shorten runners.
(4)Mold temp. control evenly
(5)Modify position of gate.

Flow mark Going through the gate or other narrow passage, surface of plastics becomes stripes as shape as tree rings. They are formed when melted polymer moves forward during solidifying and polymerization. (1)Enlarge nozzle diameter.
(2)Increase nozzle temp.
(3)Increase injection speed.
(4)Increase injection volume.
(5)Increase barrel Temp.
(6)Reduce injection rate.
(1)Increase mold temp.
(2)Add cooling pond.
(3)Change mold cooling water position of inlet.
(4)Enlarge gate.
Silver streak Material becomes silver streak in its flow direction.
(1)Moisture in material
(2)Material mixing insufficient
(3)Air in while injection
(4)Over additives
(5)Over mold release agent
(1)If it is co-axial screw injection machine, the back pressure can be increased in order to obtain good effect of kneading.
(2)Reduce injection speed.
(3)Barrel cleansing.
(1)Increase mold temp.
(2)Change position of gate.
(3)Enlarge runners and gate.

(1)Material pre-dry completely
(2)Extra red ray device added in hopper dryer
(3)Check material mixing and find out foreign material.

Bad joint line Two streams of material join together and form fine lines. It make molded part become weak and spots, streaks or bubbles are formed.
(1)Material streams separately flowing and re-joining
(2)Material temp. is too low and not high enough for melting.
(3)Bad gas or air dispelling effect
(1)Increase material temp.
(2)Increase injection temp.
(3)Increase injection speed.
(1)Add cooling pond at the joining line.
(2)Add air release
(3)Change position of gate or add gate.
(4)If melting strength is reduced and unavoidable, change position of gate to the place where affect less to the strength of molded piece.
(5)No mold release agent.
(1)Choose good MI material of lower viscosity.
Warpage Warpage happens while object ejected from mold or later after objected was molded. It was due to injection stress left. (1)Reduce injection pressure
(2)Reduce solidifying temp. of barrel.
(3)Prolong cooling time.
(1)Make possible even thickness of object walls.
(2)Reduce dent.
(3)Ejectors movement to be evenly adjusted.
(4)Add ejectors.
(5)Change position of gate.
(6)Mold temp. to be even.
Sticking on mold When plastics sticking on mold of fixed part or movable part, mold ejector may be damaged during movement. The problems are from:
(1)Molds taper angle
(2)Too high injection pressure
(3)Bad molding design

(1)Reduce injection pressure.
(2)Reduce solidifying temp. of barrel.

(1)Increase taper angle.
(2)Improve molding design and remove dents.
(3)Adjust mold temp.
(4)If the molded piece is case like, it is easier to be stuck on fixed part of mold which is under lower temp.
Choose better ejected plastics of micro crystallized material.