In the process of extrusion blow molding products, there are always many technical problems. Let's share with you the causes of these problems and the corresponding solutions, hoping to provide you with relevant suggestions to solve the problems.

一、Uneven longitudinal wall thickness of blow molding products:

The causes are as follows:
①The self weight sag of the blank is serious

②The diameter difference between the two longitudinal cross sections of blow molded products is too large

Solutions measures:
①Reduce the melt temperature of the billet, improve the extrusion speed of the billet, replace the resin with low melt flow rate, adjust the control device 
②The product design should be changed properly and the bottom blowing method should be used for forming

二、Uneven transverse wall thickness of blow molding products:
The causes are as follows:
①Billet extrusion skewness

②The temperature difference between the inside and outside of the mold core is large

③Product shape asymmetry

④The blow up ratio of parison is too large

Solutions measures:
①Adjust the gap width deviation of the die to make the thickness of the blank uniform; before closing the die, the straightening type is broken 

②Increase or decrease the heating temperature of the die sleeve, and improve the temperature deviation inside and outside the die 
③Before closing the die, the blank is pre clamped and pre expanded to make the blank offset to the thin wall properly 
④Reducing blow up ratio of parison

三、Orange peel pattern or pockmarks appear on the surface of blow molded products:
The causes are as follows:
①Poor exhaust of mould

②Mold leakage or mold cavity condensation phenomenon

③The melt fracture occurs in the blank due to poor plasticization 

④Insufficient inflation pressure

⑤The blowing speed is slow

⑥The blowing ratio is too small

Solutions measures:
①The mold blank was sandblasted and the vent was added 
②Repair the mold, adjust the mold cooling temperature to "dew point" above 
③Reducing screw speed and increasing extruder heating temperature 
④Increase the inflation pressure

⑤Clean the compressed air channel and check whether the air blowing rod leaks 
⑥Change the mold sleeve and core to improve the blow up ratio of the blank

四、Volume reduction of blow molding products:
The causes are as follows:
①The increase of parison wall thickness leads to the increase of product wall thickness

②The increase of product shrinkage leads to the shrinkage of product size

③The design dimension of the product is not blown to the cavity due to the small inflation pressure

Solutions measures:
①Adjust the program control device to reduce the wall thickness of the blank, increase the melt temperature of the blank and reduce the expansion ratio of the blank 
②Change the resin with small shrinkage, prolong the blowing time and reduce the cooling temperature of the mold 
③Properly raise the pressure of compressed air

五、Unclear outline or graphics of blow molding products:
The causes are as follows:
①Poor cavity exhaust

②Low inflation pressure

③The melt temperature of the blank is low and the plasticization of the material is poor 
④The cooling temperature of the mold is low, and the mold has "Condensation" phenomenon

Solutions measures:
①Repair the mold, sandblast the cavity or add the vent

②Increase the inflation pressure

③Properly raise the heating temperature of extruder and die, and add appropriate filling masterbatch if necessary 
④Adjust the mold temperature above the dew point

六、Too much and too thick flash of blow molding products：
Reason：
①Die expansion, insufficient clamping pressure

②The tool edge of the die is worn and the guide pillar is offset

③When blowing, the blank deflects

④The chute at the edge of the blank holder is too shallow or the depth of the edge is too shallow 
⑤Premature start of parison inflation

Solutions measures:
①Increase the die locking pressure, suitable for reducing the inflation pressure

②Repair the die edge, correct or replace the die guide post 
③Correct the center position of parison and blow bar 
③Trim the mold to deepen the depth of the chute or knife 
④Adjust the charging time of the billet

七、There are too deep longitudinal stripes：
Causes：
①The die is dirty 
②Die sleeve, burr or notch at core edge 
③The color masterbatch or resin decomposes to produce dark stripes

④The filter screen is perforated, and the material is mixed with impurities and deposited at the die opening

Solutions measures：
①Clean the die with a copper knife

②Trimming die 
③Properly reduce the temperature and replace the masterbatch with good dispersion 
④Replace the filter plate and use the leftover materials

八、Blow of the shaped embryo during molding：
Causes：
①The edge of the die is too sharp

②There are impurities or bubbles in the blank 
③The blowing ratio is too large

④Low melt strength of billet

⑤Blank wall is too thin or uneven 
⑥Expansion crack of container during mold opening (insufficient venting time)

⑦Insufficient clamping force of die

Solutions measures：
①Increase the width and angle of knife edge appropriately 
②Use dry raw materials, use wet raw materials after drying, use clean raw materials; clean die mouth 
③Replace the mold sleeve and core to reduce the blow up ratio of the damaged mold 
④Change suitable raw materials and reduce melt temperature properly

⑤Check the control device of extruder or storage cylinder head, reduce the change of process parameters and increase the length of parison

 ⑥Change the die sleeve or core, thicken the blank wall, check the blank control device, and adjust the die gap 

⑦Adjust the time of bleeding or delay the start time of mold start

⑧Increase the clamping pressure or decrease the inflation pressure

九、It is difficult to demould blow molding products：
Causes：
①The cooling time is too long and the cooling temperature is low 
②Poor design of the mold, burr on the surface of the cavity 
③When the mold is started, the moving speed of front and rear templates is unbalanced 
④Mold installation error

Solutions measures：
①Shorten the time of parison blowing and increase the temperature of die 
②Trimming the mold; reducing the groove depth, rib slope of 1:50 or 1:100; using mold release agent 
③Repair the mold locking device to make the front and rear templates move at the same speed

④Re install the mould and correct the installation position of the two half moulds

十、The quality of blow molded products fluctuates greatly：
Causes：
①Sudden change of the thickness of the billet

②The mixing of mixed materials is not uniform

③The feeding section is blocked, resulting in the fluctuation of extruder discharge

④Uneven heating temperature

Solutions measures：
①Repair blank control device

②Adopt good mixing device to prolong mixing time and reduce the amount of corner return material when necessary

③Remove the caking at the feed opening

④Reduce the temperature at the material inlet

⑤Replace electric heating cabinet