LDPE is suitable for a wide range of applications because of its balance of toughness, flexibility and low cost. In the injection molding process, LDPE granules are melted and injected into the molding cavity under high pressure. After the plastic cools and solidifies to a sufficient degree (i.e. below the glass transition temperature), the mold is opened and the finished part is ejected.
Rapid cycle times and relatively easy molding properties make LDPE very suitable for fast and high volume production by injection molding.
LDPE injection molding plays a important role in a surprising range of consumer, medical and industrial sectors due to its low cost and spectrum of useful properties. Renowned for flexibility, toughness and chemical resilience, it is ideal for cost-effectively molding into a huge range of shapes and sizes, from tiny insulators to small boat hulls. LDPE injection molding produces lightweight and durable components, best used where close dimensional precision is less important than flexible toughness and chemical resilience.
LDPE injection molding is heavily utilized across the packaging sector to manufacture containers, bottles, caps, lids and general packaging components. These benefit from its flexibility, durability and chemical durability.
The material is utilized in the production of a wide range of toys, household products, kitchenware, and sporting goods, benefitting from impact resistance and excellent conformance to complex shapes and details in molding. LDPE injection molding is employed in the automotive industry to manufacture interior trim, door panels, dashboard parts etc. The material is extensively injection molded for the healthcare sector for medical devices, laboratory equipment and disposable medical supplies, favored for biocompatibility, sterilizability and chemical resistance. LDPE injection molding is utilized to produce electrical enclosures, cable insulation, connectors and small component insulators in the electrical and electronics.
LDPE is typified by a relatively low density and melting point compared to other grades of polyethylene. Density typically ranges from about 0.910 to 0.940 grams per cubic centimeter (g/cm³) at room temperature (20°C or 68°F), a defining characteristic of LDPE. The melting point of LDPE typically lies between 105 to 115°C (221 to 239°F). This relatively broad melting range due to variances in chain atomic structure and irregularity of side branching, delivering a range of molecular weights.
These properties make LDPE suitable for applications requiring flexibility, impact resistance, and low-cost/ease of processing.
The processing conditions of ldpe injection molding are greatly influenced by the specific grade, the design of the part (particularly section thickness), the type of mold tool technology and the molding machines being used.
The temperature of the barrel and nozzle should lie between 160°C to 220°C (320°F to 428°F) to achieve appropriate melt-flow properties. This temperature will require trial setting based on experience.
Injection pressure typically lie between 500 to 1500 bar (7250 to 21750 psi), depending on design complexity and mold configuration. Thinner sections and longer fill paths typically need higher injection pressures. The injection speed should be adjusted to ensure proper filling of the mold cavity without causing excessive shear heating or mold flash. Flow speed is typically a byproduct of pressure, so there is a balance to be struck in this setting. Sufficient cooling time allows the part to solidify adequately before ejection, but this is heavily influenced by part thickness and geometry, so trials will be required for fine tuning.
The mold temperature should be controlled to ensure uniform cooling and minimize warp, within the range 10°C to 60°C (50°F to 140°F). Proper venting of the mold is important to prevent trapped air from causing voids or bubbles. Parameters such as screw speed, back pressure, and shot size must be optimized through experience and tool trials. These are general guidelines but specific processing conditions must be adjusted based on the particular requirements of the application and the equipment being used.
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