3D Blow Molding
3D blow molding is a method of extruding molten thermoplastic raw materials from an extruder, sandwiching them in a mold, and then blowing air into the raw materials. The molten raw materials expand under the action of air pressure, adhere to the wall of the mold cavity, and finally cool and solidify into the desired product shape.
Solutions to Defects in Blow Molding Mold
During the operation of blow molding mold, it is necessary to prepare some solutions to deal with problems that may arise during the processing at any time. For example, in the ABS blow molding process, the drying of raw materials needs to be considered, in the HDPE blow molding process, the flowability of raw materials needs to be considered, and in the 3D blow molding process, the wall thickness needs to be considered.
Types of Blow Molding Molds
Solutions for blow molding mold should be proposed based on the type of blow molding, mainly including stretch blow molding, extrusion blow molding, injection blow molding, and other processes.
- Stretch Blow Molding
Advantages
-Stretch blow molding is very suitable for processing with low demand and short-time
-The products produced by stretch blow molding molds have certain tensile and airtight properties, suitable for filling carbonated beverages
-Very suitable for blow molding manufacturing of cylindrical, rectangular, or elliptical bottles
-Blow molded products have uniform wall thickness and good aesthetics
Limitations
-The molds and equipment for stretch blow molding have a large footprint
- Injection Blow Molding
Advantages
-The bottleneck is made by injection molding and has high-precision
Limitations
-The molding efficiency of injection blow molding is relatively low
-Suitable for blow molding small capacity and small volume containers
-The physical properties will not change, and the tensile and tensile strength cannot be increased
-The grip on the container design cannot be directly produced using injection blow molding molds and requires further processing, which is a cumbersome process
- Extrusion Blow Molding
Advantages
-In the process of extrusion blow molding, the billet is formed by the machine head and inflated under lower pressure, which brings less residual stress and improves the strain resistance of the product, such as tensile, bending, and impact resistance, and has a good service life.
-The raw material (PE) used for extrusion blow molding molds has excellent low-temperature resistance and chemical stability, as well as good crack resistance and durability.
-Forming is simple and easy to operate, and more raw materials can be selected for processing.
-After plasticizing and melting, the embryo flows out through the extruder head and directly enters the blow molding mold for molding, eliminating the step of secondary heating and achieving high production efficiency.
Limitations
-Before entering the blow molding mold for molding, it is important to pay attention to and prevent any sagging or wrinkling defects in the billet. If the vertical depth is too long, the amount of waste will increase, and if the vertical depth is too short, it cannot be fully formed.
Defects and Solutions of Blow Molding Molds
The main problems and solutions that are prone to occur in blow molding mold processing are:
Products Formed by Blow Molding Molds Have Many Burrs and Thick Edges
-Reason:
- The blade of the blow molding mold is worn, resulting in a certain deviation of the guide column
- The escape groove at the cutting edge of the billet is too shallow, and the corresponding depth of the cutting edge is too shallow
- When expanding the mold, the set locking pressure is too low
- The time for inflating the billet starts too early
- Misalignment during inflation and deviation of the billet
-Solutions:
- Adjust the inflation time and direction of the billet
- Repair or replace the mold blade, calibrate or replace the mold guide column
- Increase the locking pressure of blow molds and reduce the inflation pressure according to processing needs
- Correct the center position of the billet and the blowing rod to align the subsequent inflation
- Adjust the mold and deepen the depth of the escape groove or knife according to actual needs
The Appearance of The Product Presents Orange Peel-Like Patterns or Pockmarks
-Reason:
- The inflation speed adjustment is too slow
- Poor exhaust of the mold resulted in trapped gas
- The inflation ratio is set too small
- Incomplete melting and plasticization of the billet, resulting in the billet being too hard and cracking during blowing
- The inflation pressure is set too low
- Mold leakage or condensation phenomenon in the mold cavity
-Solutions:
- Clearing and clearing the air passage, checking whether the blowing rod can leak or exhaust normally
- Replace the mold sleeve and core, and further adjust the blowing ratio of the billet
- Steps for stopping sandblasting of mold blanks, adding multiple exhaust holes to ensure smooth exhaust
- Reduce the screw speed appropriately and adjust the heating temperature of the extruder according to the actual situation
- Repair the mold and adjust the mold cooling temperature to above the “dew point”
- Appropriately increase the inflation pressure according to the actual processing situation
Blow-molded Products Have Unclear Contours or Patterns
-Reason:
- The melt temperature of the billet is low, and the degree of plasticization is incomplete
- The temperature of the mold cooling is too low, and the mold has a “condensation” phenomenon
- Poor exhaust from the cavity exhaust hole
- Set the inflation pressure to a lower level
-Solutions:
- Adjust the inflation pressure
- Repair the mold, pause the sandblasting step of the mold cavity, or add an exhaust groove
- Raise the mold temperature until it is above the dew point temperature
- Adjust the heating temperature of the extruder and head, and add an appropriate amount of filling masterbatch if necessary
The Weight of Blow-Molded Products Varies Greatly
-Reason:
- Sudden change in billet wall thickness
- There was a blockage in the feeding section, and the feeding part malfunctioned
- Unbalanced heating temperature
- The recycled materials added for secondary use are not mixed evenly
-Solutions:
- After fully mixing the recycled materials, use the fully mixed materials for processing and extend the mixing time within the allowed processing time; In the case of sufficient surplus materials, the amount of corner return materials can be minimized as much as possible
- Repair the billet
- Switch to electric heating and adjust the heating temperature
- Remove foreign objects from the feed inlet and perform timely repair and cleaning
- Materials or foreign objects. Reduce the temperature at the material inlet
During Molding, the Embryo is Blown Apart
-Reason:
- The billet wall is too thin or the thickness of the billet wall is uneven
- The blade of the mold is too sharp
- The inflation ratio is set too high
- The container swells and cracks during mold opening, lacking exhaust time and insufficient exhaust
- The locking force of the mold is too small
- Impurities or bubbles exist in the billet
- The strength of the billet melt is too high
- Lack of length of the green pituitary gland
-Solutions:
- Increase the width and angle of the blade appropriately
- Use fully dried raw materials, wet raw materials should be used after drying, clean raw materials should be used, and the mold mouth should be cleaned
- Check the control installation of the extruder or storage cylinder head, try to maintain stable process parameters, and increase the length of the billet without excessive waste
- Adjust the exhaust time or delay the start time of the mold
- Change the mold sleeve and core to reduce the blowing ratio of the billet
- Change to more suitable plastic materials and appropriately lower the melt temperature
- Increase the locking pressure and reduce the inflation pressure
Difficult to De-mold
-Reason:
- Mold parameter setting error
- The blowing, cooling, and solidification time of the product is too long, and the cooling temperature of the mold is low
- Poor mold design, rough surface of the mold cavity, and presence of burrs
At the beginning of production, there is an imbalance in the movement speed of the front and rear templates
-Solutions:
- Repair the lock mold installation to ensure that the front and rear templates move at the same speed
- Reinstall the mold and correct the device position of the two halves of the mold
- Shorten the blowing time of the billet appropriately and increase the temperature of the mold
- Repair the mold; Reduce the depth of the groove and set the slope of the convex reinforcement to 1:50 or 1:100; Use a release agent
Blow Molding Product Volume Reduction
-Reason:
- The increase in the thickness of the billet wall leads to the thickening of the product wall
- The inflation pressure is low, and the product has not been inflated to the design size of the mold cavity
- The increase in the shrinkage rate of the product leads to a reduction in its size
-Solutions:
- Control the installation of the conditioning program to reduce the wall thickness of the billet; Improve the melt temperature of the billet and reduce the shrinkage ratio of the billet after demolding
- Replace the resin with a lower shrinkage rate, extend the blowing time, and lower the mold cooling temperature
- Properly increase the pressure of compressed air
Uneven Vertical Wall Thickness of Blow-Molded Products
-Reason:
- Serious sagging phenomenon of the weight of the billet
- The difference in diameter between the two longitudinal cross-sections of blow-molded products is too large
-Solutions:
- Reduce the temperature of the preform melt, increase the extrusion speed of the preform, switch to using resins with lower melt activity speed, and adjust the control and installation of the preform
- Properly modify the product design and adopt bottom blowing method for molding
Uneven horizontal wall thickness of blow-molded products:
-Reason:
- Extrusion inclination of the billet
- There is a large temperature difference between the inside and outside of the mold sleeve and the mold core
- The blowing ratio of the billet is too high
- Asymmetric appearance of the product
-Solutions:
- Adjust the width deviation of the mouth mold gap to make the wall thickness of the billet even; Before closing the mold, the straightened shape is damaged
- Before closing the mold, stop pre-clamping and pre expanding the billet to properly offset it towards the thin-walled direction
- Reduce the blowing ratio of the billet
- Increase or decrease the heating temperature of the mold sleeve to improve the temperature deviation inside and outside the mouth mold
Presenting Excessively Deep Vertical stripes
-Reason:
- The mold mouth is too dirty and there are too many foreign objects
- The molded sleeve has burrs or gaps on the edge of the core
- Color masterbatch or resin synthesis produces dark stripes
- The filter screen is perforated, and impurities mixed in with the material accumulate at the mold mouth
-Solutions:
- Use a copper knife to clear the mold mouth
- Reduce the temperature appropriately and switch to a color masterbatch with good dispersibility
- Replace the filter screen plate
- Trim the mold incision
Maintenance of Extrusion Blow Moulding Equipment
Even the most excellent extrusion blow moulding equipment and molds, if not maintained and serviced, will have a certain impact on the subsequent manufacturing process.
Before the formal blow molding process begins, it is necessary to maintain and upkeep the extrusion equipment, such as adding lubricating oil to each movable and easily worn part. This can make the subsequent production and processing smoother, avoid equipment jamming, and slow and insensitive movements, increase maintenance and processing time, and slow down efficiency. Once there is a problem with the operation of blow molding equipment, it will greatly affect the operation of the entire production process and the quality of the final product. After adding lubricating oil, the equipment cannot be immediately started. It is necessary to preheat the equipment for a certain period to ensure that there are no problems before feeding for processing and production.
After shutting down the blow molding equipment, it is necessary to reset each speed to zero and close the mold. The mold should be coated with rust inhibitor or rust-proof film to extend its service life. Before turning off the main power, the manufacturer needs to lubricate and maintain the equipment again, add lubricating oil, clean the equipment, and prevent rusting.
In addition to turning on and off the equipment, maintenance of the extrusion blow moulding mold is also very necessary, requiring regular cleaning and polishing. This step cannot be omitted, which can better ensure the coordination between the mold and equipment and produce higher quality and high-precision blow molded products.
The attention points for extrusion blow moulding are far less than these, including the setting of some parameters such as temperature, pressure, time, etc. In the forming process, multiple factors need to be considered to shape better products.
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