HDPE Blow Molding

HDPE blow molding technology has high efficiency and quality advantages, and manufacturers apply it to various industries, including household goods, industrial containers, etc. Blow molding molds and blow molding machines are professional tools for producing plastic blow molding containers. The main principle is to inject melted plastic particles into the mold cavity and blow them with compressed air to cool and solidify, forming blow molded parts. The design and manufacturing of blow molding molds by manufacturers determine the production efficiency, quality, and cost control of products. This technology includes converting HDPE resin into hollow seamless plastic products with extraordinary durability and strength.

HDPE blow molding mainly includes three basic steps, namely: billet forming, blow bulging forming, and product cooling. Firstly, plastic is processed into billets through injection molding or extrusion, and then the high-temperature billets are placed in blow molding molds. The manufacturer injects compressed air into the blank, allowing the blank to be tightly blown towards and against the mold cavity wall, and maintains a blowing pressure for some time until the plastic part is completely cooled and shaped.

Blow Molded HDPE

High-density polyethylene (HDPE) ranks among the top in terms of usage among various hollow blow molded plastics and is widely used in food, chemical, and liquid processing and packaging. High molecular weight polyethylene (HDPE) is suitable for blow molding manufacturing of various large fuel tanks and barrels. Due to its excellent transparency and airtightness, polyvinyl chloride (PE) materials are widely used by manufacturers in the packaging of cosmetics, detergents, logistics and transportation products, automotive parts, medical devices, children’s toys, and other fields. With the development and popularization of non-toxic polyvinyl chloride resin and various additives, as well as the development of stretch blow molding technology, the use of polyvinyl chloride containers in the food packaging industry has rapidly increased, and they are gradually being used in the packaging of products containing carbon dioxide.

The linear polyester material is an emerging material that has a relatively short entry time into hollow blow molding. However, due to its smooth and transparent appearance, high mechanical strength, good storage of items in containers, and no environmental pollution during garbage incineration, its development trend has been greatly accelerated. Its products include packaging barrels (especially in pressure-resistant plastic food containers), etc.

The continuous research by manufacturers on the modification and processing technology of polypropylene resin has led to an increasing usage of polypropylene year by year.

Basic Characteristics

High-density polyethylene is an opaque white waxy material with a specific gravity lighter than water, ranging from 0.941 to 0.960. It is soft and tough, but slightly harder than LDPE and can also elongate slightly. It is non-toxic and odorless.

[Burning characteristics] Flammable, can continue to burn after leaving the flame. The upper end of the flame is yellow and the lower end is blue. It will melt during combustion, with liquid droplets and no black smoke emitted. At the same time, it emits the odor of paraffin burning.

Main Advantages

Acid and alkali resistance, organic solvent resistance, excellent electrical insulation, and the ability to maintain a certain degree of toughness at low temperatures. The mechanical strength such as surface hardness, tensile strength, and rigidity is higher than LDPE, close to PP, and tougher than PP, but the surface smoothness is not as good as PP.

Main Disadvantages

Poor mechanical performance, poor breathability, easy deformation, aging, brittleness, lower brittleness than PP, easy stress cracking, low surface hardness, and easy scratching. Difficult to print, surface discharge treatment is required during printing, electroplating is not allowed, and the surface is dull.

Common Problems and Solutions

Uneven Longitudinal Wall Thickness of Blow Molded Products

Cause of Occurrence:

① The phenomenon of severe self-weight sag of the billet;

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

Solution:

① Reduce the melt temperature of the billet, increase the extrusion speed of the billet, replace the resin with a lower melt flow rate, and adjust the billet control device;

② Properly change the product design and use bottom blowing method for molding.

Uneven Lateral Wall Thickness of HDPE Blow Molded Products

Cause of Occurrence:

① Skew extrusion of preforms;

② The temperature difference between the inner and outer parts of the mold sleeve and the mold core is relatively large;

③ Asymmetric product appearance;

④ The expansion ratio of the billet is too large.

Solution:

① Adjust the gap width deviation of the mold to ensure even wall thickness of the billet; Before closing the mold, the straightening type is damaged;

② Increase or decrease the heating temperature of the mold sleeve, and improve the temperature deviation inside and outside the mouth mold;

③ Before closing the mold, pre-clamp and pre-expand the billet to appropriately offset it towards the thin-walled direction;

④ Reduce the expansion ratio of the billet.

Orange Peel-like Patterns or Pitting Appears on the Surface of Blow Molded Products

Cause of Occurrence:

① Poor mold exhaust;

② Mold leakage or condensation in the mold cavity;

③ Poor plasticization of the billet, resulting in melt fracture of the billet;

④ Insufficient inflation pressure;

⑤ Slow inflation speed;

⑥ The inflation ratio is too small.

Solution:

① Sand blasting treatment is carried out on the mold blank, and exhaust holes are added;

② Repair the mold and adjust the cooling temperature of the mold to above the dew point;

③ Reduce the screw speed and increase the heating temperature of the extruder;

④ Raise the inflation pressure;

⑤ Clean the compressed air channel and check if the blowing rod is leaking air;

⑥ Replace the mold sleeve and core, and improve the blowing expansion ratio of the blank.

Reduced volume of HDPE blow molded products

Cause of Occurrence:

① The increase in wall thickness of the billet leads to the thickening of the product wall;

② The increase in product shrinkage leads to a reduction in product size;

③ The inflation pressure is low, and the product has not inflated to the designed size of the mold cavity.

Solution:

① Adjust the program control device to reduce the wall thickness of the billet; Increase the melt temperature of the billet and reduce the expansion ratio of the billet after leaving the mold;

② Replace resin with low shrinkage rate, extend blowing time, and reduce mold cooling temperature;

③ Appropriately increase the pressure of compressed air.

Unclear Contour or Graphics of HDPE Blow Molded Products

Cause of Occurrence:

① Poor exhaust of the cavity;

② Low inflation pressure;

③ The temperature of the billet melt is too low, resulting in poor plasticization of the material;

④ The cooling temperature of the mold is too low, and there is a phenomenon of condensation in the mold.

Solution:

① Repair the mold, sandblast the cavity, or add an exhaust groove;

② Increase the inflation pressure;

③ Appropriately increase the heating temperature of the extruder and the head, and if necessary, add an appropriate amount of filling masterbatch;

④ Raise the mold temperature above the dew point temperature.

HDPE Blow Molded Products have too Many Thick Flying Edges

Cause of Occurrence:

① Insufficient mold expansion and locking pressure;

② Wear of the mold blade and deviation of the guide pillar;

③ When blowing, the billet deviates;

④ The material escape groove at the edge of the blank cutting edge is too shallow or the depth of the cutting edge is too shallow;

⑤ The inflation of the blank is started too early.

Solution:

① Increase the mold locking pressure and appropriately reduce the inflation pressure;

② Repair the mold blade, correct or replace the mold guide pillar;

③ Correct the center position of the blank and the blowing rod;

③ Repair the mold and deepen the depth of the material chute or knife;

④ Adjust the inflation time of the blank.

Excessive Vertical Stripes Appear

Cause of Occurrence:

① The mold mouth is dirty;

② Mold sleeve, with burrs or notches on the edge of the core;

③ The decomposition of color masterbatch or resin produces dark stripes;

④ The filter screen is perforated, and impurities are mixed in and deposited at the mold mouth.

Solution:

① Clean the mold mouth with a copper knife;

② Trim the mouth mold;

③ Reduce the temperature appropriately and replace the color masterbatch with one with good dispersibility;

④ Replace the filter screen and use the leftover material that has been soaked.

When the Embryo is Formed, it is Blown Open

Cause of Occurrence:

① The mold blade is too sharp;

② Impurities or bubbles in the blank;

③ Excessive inflation ratio;

④ The melt strength of the billet is low;

⑤ Insufficient length of the billet;

⑤ The parison wall is too thin or the parison wall thickness is uneven;

⑥ The container expands and cracks during mold opening (insufficient venting time);

⑦ Insufficient mold locking force.

Solution:

① Increase the width and angle of the blade appropriately;

② Use dry raw materials, dry wet raw materials before use, use clean raw materials, and clean the mold mouth;

③ Replace the mold sleeve and core to reduce the blowing expansion ratio of mold damage;

④ Replace appropriate raw materials and reduce the melt temperature appropriately;

⑤ Check the control device of the extruder or storage cylinder head to reduce process parameter changes and increase the length of the billet;

⑥ Replace the mold sleeve or core, and thicken the blank wall; Check the blank control device and adjust the mold gap;

⑦ Adjust the release time or delay the mold start time;

⑧ Increase the locking pressure or decrease the inflation pressure.

Difficulty in Demolding Blow Molded Products

Cause of Occurrence:

① The cooling time for product expansion is too long, and the cooling temperature of the mold is low;

② Poor mold design with burrs on the surface of the mold cavity;

③ When starting the mold, the movement speed of the front and rear templates is uneven;

④ Mold installation error.

Solution:

① Properly shorten the blowing and swelling time of the billet, and raise the mold temperature;

② Repair the mold; Reduce the depth of the groove, with a slope of 1:50 or 1:100 for the convex ribs; Use release agents;

③ Repair the locking device to ensure consistent movement speed of the front and rear templates;

④ Reinstall the mold and correct the installation position of the two halves of the mold.

The Quality of Blow Molded Products Fluctuates Greatly

Cause of Occurrence:

① Sudden change in the wall thickness of the billet;

② Uneven mixing of edge and corner materials added;

③ Blockage in the feed section, causing fluctuations in the extruder discharge;

④ Uneven heating temperature.

Solution:

① Repair the blank control device;

② Using a good mixing device to extend the mixing time; If necessary, reduce the amount of corner material used for recycling;

③ Remove lumps at the material outlet;

④ Reduce the temperature at the material inlet.

Applications of HDPE Blow Molding

Packaging Industry

The packaging industry is one of the primary beneficiaries of HDPE blow molding. This process is extensively used to produce a wide range of containers, bottles, and jars for various products, including:

Household and Personal Care Products

HDPE blow-molded containers are widely used for packaging household cleaners, detergents, shampoos, and other personal care items. These containers are durable, lightweight, and resistant to chemicals, ensuring the safe storage and transportation of these products.

Food and Beverage Containers

HDPE blow-molded bottles and jars are commonly used for packaging milk, juices, and other beverages, as well as food products like cooking oils and condiments. The material’s inert nature and resistance to moisture make it an ideal choice for preserving the quality and freshness of these items.

Industrial Packaging

HDPE blow-molded containers are widely used in the industrial sector for packaging chemicals, lubricants, and other industrial fluids. The material’s chemical resistance and durability ensure the safe storage and transportation of these products.

Automotive Industry

The application of HDPE in the automotive field has become increasingly widespread, and some noteworthy applications include:

Fuel Tanks: HDPE blow-molded fuel tanks are widely used in automobiles due to their lightweight, impact resistance, and compatibility with gasoline and diesel fuels. These tanks are designed to meet stringent safety and environmental regulations.
Automotive Fluid Containers: HDPE blow-molded containers are used for storing and transporting various automotive fluids, such as windshield washer fluid, coolants, and brake fluids. The material’s chemical resistance and durability make it an ideal choice for these applications.
Air Intake Systems: HDPE blow-molded components are used in air intake systems, such as air ducts and resonators, due to their ability to withstand high temperatures and resist moisture.

Agricultural and Horticultural Applications

The agricultural and horticultural sectors have embraced HDPE blow molding for various applications, including:

Irrigation Systems: HDPE blow-molded pipes and fittings are widely used in irrigation systems due to their resistance to chemicals, UV radiation, and environmental factors. These systems are designed to efficiently distribute water to crops and landscaping.
Greenhouse and Nursery Containers: HDPE blow-molded pots, trays, and containers are commonly used in greenhouses and nurseries for growing and transporting plants. These containers are durable, lightweight, and resistant to moisture and chemicals.
Agricultural Chemical Storage: HDPE blow-molded tanks and containers are used for storing and transporting agricultural chemicals, such as pesticides and fertilizers, due to their chemical resistance and durability.

Recreational and Outdoor Products

HDPE blow molding has found applications in the recreational and outdoor product industries, including:

Kayaks and Canoes: HDPE blow-molded kayaks and canoes are lightweight, durable, and resistant to impact and abrasion, making them ideal for outdoor adventures and water sports.
Playground Equipment: HDPE blow-molded components are used in the construction of playground equipment, such as slides, swings, and climbing structures, due to their durability, weather resistance, and low maintenance requirements.
Outdoor Furniture: HDPE blow-molded furniture, such as chairs, tables, and benches, is becoming increasingly popular due to its weather resistance, durability, and low maintenance requirements.Medical and Pharmaceutical Applications

Medical and Pharmaceutical Applications

The medical and pharmaceutical industries have recognized the benefits of HDPE blow molding for various applications, including:

Medical Containers and Bottles: HDPE blow-molded containers and bottles are used for packaging and storing medical supplies, pharmaceuticals, and other healthcare products due to their chemical resistance, durability, and ease of sterilization.
Medical Equipment Components: HDPE blow-molded components are used in various medical equipment, such as respiratory devices, fluid handling systems, and diagnostic equipment, due to their chemical resistance and ability to withstand sterilization processes.
Pharmaceutical Tanks and Vessels: HDPE blow-molded tanks and vessels are used in the pharmaceutical industry for storing and processing various chemicals and pharmaceutical products due to their chemical resistance and ease of cleaning.

The provided examples of HDPE blow molding applications are not exhaustive. The versatility, durability, and cost-effectiveness of this manufacturing process render it an indispensable technology for producing a wide range of products that meet the stringent demands of various industries.

Tips for HDPE Blow Molding Mold Maintenance

Each set of molds should be equipped with a record card, which should record and record in detail their use, care (lubrication, cleaning, rust prevention), and damage situation. Based on this, it can be found which parts and components have been damaged, and the degree of wear, and provide information and data for discovering and solving problems, as well as the molding process parameters and materials used for the mold, to shorten the trial run time of the mold and improve production efficiency.
Under normal operation of the injection molding machine and mold, test the various performances of the mold, and measure the size of the final formed plastic part. Through this information, the existing status of the mold can be determined, and the damage to the cavity, core, cooling system, and parting surface can be identified. Based on the information provided by the plastic part, the damage status of the mold and maintenance measures can be determined.
Key tracking and inspection of important components of the mold: The function of the ejection and guide components is to ensure the opening and closing movement of the mold and the ejection of the plastic parts. If any part of them gets stuck due to damage, it will lead to production stoppage. Therefore, it is necessary to regularly maintain the lubrication of the mold ejector pin and guide pillar (using the most suitable lubricant), and regularly check whether the ejector pin and guide pillar have deformation and surface damage. Once found, they should be replaced promptly; After completing a production cycle, professional anti-rust oil should be applied to the working surface, movement, and guiding components of the mold. Special attention should be paid to protecting the elastic strength of the bearing parts of the mold with gears and racks, as well as the spring mold, to ensure that they are always in good condition.
As the production time continues, the cooling water channel is prone to deposits of scale, rust, sludge, and algae, resulting in a smaller cross-section of the cooling channel and narrower cooling channel, greatly reducing the heat exchange rate between the coolant and the mold, and increasing the production cost of the enterprise. Therefore, sufficient attention should be paid to the cleaning of the channel.
It is important to pay attention to the surface maintenance of the mold, as it directly affects the surface quality of the product, with a focus on preventing rust. Therefore, it is particularly important to choose a suitable, high-quality, and professional rust-proof oil.

HDPE Blow Molding