Polyethylene Injection Molding

Inox Cast Polyethylene Injection Molding

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Polyethylene Injection Molding: The Ultimate Guide

In this guide, you will find all information you’re looking for about polyethylene injection.

Whether you want to learn about injection molding techniques, condition requirements, or mold design – you will find all information right here.

1. What Is Polyethylene Injection Molding?

The industry world has a lot of materials that are in use, but thermoplastics are one of the most noted and essential materials.

When it comes to injection molding, thermoplastics are the most preferred because of their formability.

The injection molding process is versatile, and that is why it goes well with polyethylene since it is very versatile.

Polyethylene injection molding is a procedure used to manufacture polyethylene parts by injecting molten material into a mold.

polyethylene injection molding

2. Properties For Polyethylene For Injection Molding

Polyethylene is one of the most significant and widely used thermoplastics.

Polyethylene has different ranges based on its hardness, and its properties majorly depend on the type of grade.

Some of the grades are hard and rigid, while some are soft and flexible.

The properties of include;

• Polyethylene is a lightweight material
• Has high toughness
• Polyethylene has a perfect chemical resistance property and cannot be attacked by strong acids and bases.
• It is impermeable, meaning no water or steam to passes through it.
• Also, it has low coefficient of friction and good impact on resistance

3. Polyethylene Injection Molding Temperature

Injection molding temperature of polyethylene mostly depends on the grade being used.

The molding temperature of low-density polyethylene is 160-220 degrees Celsius, while that of high-density polyethylene is about 180-240 degrees Celsius.

Besides, the melting temperature is between 120-180 degrees Celsius for high density and 105-115 degrees Celsius for low density.

4. Benefits Of Injection Molding Polyethylene

Polyethylene is one of the most common and essential thermoplastics.

Injection molding of polyethylene is quite popular and one of the most efficient injection molding processes.

Polyethylene injection molding has certain advantages that one can benefit from, and they include;

• One can achieve part designs that are different using polyethylene injection molding.

This means you can get several part designs that are identical or even different.

Parts with high quality and any design specifications can be achieved using polyethylene injection molding.

• Polyethylene injection molding allows for easy modification.

One can get a variety of parts with the required material and color. You can also make the needed parts and can cause several parts.

• The labor costs are meager when using polyethylene injection molding.

It can produce many quality parts at very high speeds, reducing labor costs.

The process itself does not require much supervision.

• Even though most of the time, the speed depends on the size and how complex the part is, polyethylene has proved to be quite fast and efficient.

One can create many parts rapidly, thus reducing labor costs.

• Polyethylene injection molding is the best option if you want to have substantial and long-lasting parts.

Since most of the parts made from polyethylene injection molding are for general use, they are preferred strong and durable.

• Polyethylene injection molding is a high-volume production process that works best to minimize waste production.

A lot of plastic goes to waste during the injection molding process, but with polyethylene injection molding, a lot of plastic is not wasted.

5. Conditions For PE Injection Molding

Some of the main conditions you should consider include:

Injection Pressure

During the injection molding process of polyethylene, the injection pressure mostly depends on the configuration of the part and the size.

Always choose pressure carefully since it may result in defects.

At the same time, the injection pressure should be high enough to fill up most parts to avoid defects.

The pressure should not be too high since that too can cause defects.

injection pressure

High injection pressure should be too small mold plastic, while lower injection pressure should be too large mold plastic.

Melt Temperature

Polyethylene injection molding requirements that have to be followed to ensure a quality end product.

The melt temperature is one of them, and it depends on the grade of polyethylene one is using.

The melt temperature should not be too low or too high.

Defects such as short shots, flow marks, weld lines, and many others may be brought about by a shallow melt temperature.

melting temperature

Too high melt temperature can also result in defects such as void formation, flashing, sink marks, etc.

Mold Temperature

The mold temperature depends on the grade.

The mold temperature of low-density polyethylene should range between 30-45 degrees Celsius.

While that of high-density polyethylene should range between 12-20 degrees Celsius.

The mold temperature should be high enough to make quality parts but should not be too high to cause defects.

mold temperature

Charging Barrel

Temperature of the charging barrel should be higher than its melting point.

It should be at least 10 degrees Celsius higher than its melting point.

The melt flow rate and the degree density have a close link to the temperature of the charging barrel.

charging barrel

Injection Time

If the injection time is not correct during the injection molding process there will be defects.

injection time

6. Applications Of Polyethylene Injection Molded Parts

Polyethylene injection molded parts are used in many parts of the world.

The parts are used as follows;

• Milk crates
• Sporting goods
• Toys
• Appliances
• Storage containers
• Construction products
• Pipe thread protectors
• Hardware
• Food processing parts
• Packaging applications
• Conveyor guides
• Chemical holding tanks
• Liquid dispensing equipment
• Medical equipment

7. Polyethylene Injection Molding Process

Plastic pellets are used to start the injection molding process.

The pellets are fed through the hopper into a barrel with a reciprocating screw.

As the plastic pellets melt as they pass through the gap between the screw and the heated barrel.

The resulting equal melt is injected into the injection chamber.

As it rotates, the screw goes backward.

polythylene injection molding process

 Once the appropriate shot size is reached, the screw’s backward motion is stopped by a limit switch.

This activates a hydraulic cylinder, which moves the screw forward.

Now, the screw’s forward motion drives the molten plastic into the mold chamber.

Also, the melt cannot flow backward because of the check valve.

The molds close, and the product cools by pumping cooling fluid through the cooling lines.

As the product cools, the screw reverses, and another cycle begins.

After the specified cooling time, the mold is opened, and the cooled product is removed. Ejector pins assist in removing the product from the mold.

8. Polyethylene Injection Molding Technology

Overmolding Polyethylene

Overmolding is an injection molding process in which two or more materials are molded into a one product.

Overmolding is a process that one can use to produce plastic items with a rubber handle, or a one-part is created using a combination of two or more plastics.

Manufacturers who wish to add a soft-touch surface to their products that improve grip or feel and gives a sleek, appealing appearance are ideal candidates for overmolding.

Insert Molding Polyethylene

Insert molding is a single-step procedure that involves molding or joining plastic parts around non-plastic parts or inserts to produce a finished part.

Typically the inserted object is a simple component, such as a surgical tube, rod, or knife blade, but inserts can be battery or motor in some cases.

Insert molded plastics are used for improved wear resistance, tensile strength, and weight reduction, while metallic materials are used for strength and conductivity.

Micro Molding Polyethylene

Micro molding is a procedure used to manufacture tiny parts and components that require high precision.

The mold with a cavity in the shape of the required object is created in the tooling department.

Rapid injection of thermoplastic into the cavity is done at a high speed creating the component.

Micro molding is by far one of the most complicated injection molding procedures.

Since it deals with minimal parts, it becomes pretty complex compared to working with more significant parts.

In the medical industry it is used in surgical devices.

Medical Molding Polyethylene

Polyethylene’s medical molding is an economical procedure and is best suited to produce high volume production.

Medical injected molded parts are reliable, last longer, and meet FDA regulations.

One of the properties of injection molded parts that make them very useful in the medical industry is their increased versatility.

The medical molded parts can be made with metal to make medical products with enhanced properties

Medical polyethylene injection is cost effective.

2-shot Injection Molding Polyethylene

This is a procedure that requires filling a mold with a thermoplastic resin, then adding another resin, making an end product.

This method can make a bond that stops the two resins from detaching.

It is a procedure one can use to make parts that enhance the look of an end product or add tactile features.

2 shot injection molding

Two-shot injection molding allows for better control over the quality and more design flexibility, and it is faster than holding two parts separately.

Ultrasonic Bonding

Ultrasonic bonding is industrial welding that uses ultrasonic vibrations to fuse polymers, metals, or other materials.

The joined materials are usually kept together by a fixture and a vibrating metal tool during welding.

ultrasonic bonding

This is especially essential in metal bonding applications where high temperatures might result in undesirable characteristics.

Pad Printing

Pad printing is utilized when a part requires more than one color. This method is used to improve a product’s appearance.

pad printing

Pad printing, a reliable and widely used alternative to hot stamping and screen printing, you can use to apply color graphics and typography to various items.

9. Mold Design For Polyethylene Injection Molding

First part of an injection mold is the runner.

Then the runner has channels through which molten plastic flows into the mold cavity.

Also, the mold design for injection molding must have an opening or a gate.

Again, opening is essential as it is used to inject molten plastic into the mold cavity.

The location of the gate, the type of the gate, and the design can significantly affect the part component.

For example, it might affect how the part looks or even cause warping.

Here, the gate and the runner’s system should be designed keenly to ensure even distribution of plastic and cooling.

10. Secondary Operations For Injection Molded Polyethylene Parts

Secondary operations are manufacturing stages that are added after the part has been molded.

They add features or elements to the item that were impossible during the molding procedure.

To save money on tooling, secondary operations are sometimes arranged for at the start of a project.

Polyethylene can be decorated using pad printing, hot stamping, silk screening, and UV coating.

11. Types Of Polyethylene For Polymer Injection Molding

Polyethylene is composed of various grades that can be told apart based on their density, which is best for a particular application.

A grade with the highest density equally has the greatest strength, chemical resistance, and hardness.

Though its lifespan is shorter and has increased low-temperature brittleness.

The following are the types of polyethylene for polymer injection molding;

• Low-Density Polyethylene (LDPE) – it is very stretchy because of its poor tensile strength and high elasticity characteristics.

It’s also flexible and has unique flow qualities.

• Linear Low-Density Polyethylene (LLDPE) – the only difference between this and LDPE is, it has greater tensile strength and impact resistance and also has a lower thickness than LDPE.

This allows it to be utilized for stretch wrap and flexible tubing.

• High-Density Polyethylene (HDPE) – It’s commonly used for stiffer but relatively flexible items like chopping boards, trash cans, and milk cartons since it is stiff and tough.
• Ultra High Molecular Weight Polyethylene (UHMW) – this is a very dense material.

Compared to HDPE, it has a molecular weight that is a lot more than that of HDPE.

When spun into threads, it has a tensile strength greater than steel and is commonly used in bulletproof vests and other high-impact items.

12. Polyethylene Injection Molding Defects

Any injection molding process can have defects.

Defects generally occur during the injection molding process.

They may cause unfinished parts or parts that may not work as they should.

Polyethylene injection molding can have defects such as;

Warping – Warping, also known as warpage, is where some regions of the molded component are altered by shrinkage that is not equal.

Cooling of the mold material unevenly is the cause.

The dark color and transparent edges – low mold temperature during the injection molding process is the leading cause.

The temperatures should always be correct to avoid such.

Jetting – the melt temperature is too low, and the viscosity of the molten plastic becomes too high.

Hence, increasing the resistance of the molten plastic’s flow through the mold, causing jetting.

Burn marks – Burn marks form on the surface of injection molded prototypes and are brownish.

Burn markings are made from either a significant number of injection speeds or overheating, resulting in the breakdown of the plastic material.

Voids – sometimes, air pockets become trapped within the surface of the injection-molded prototypes causing vacuum voids.

Vacuum spaces arise because of uneven solidification between the prototype’s character and inner portions.

Short moldings – when molten plastic does not fill the mold cavity or cavities, it causes short moldings.

The end product will then have a section that has no plastic.

Excessive shrinkage is caused by the gates being too small and may also be caused by the processing conditions.

Flashing – Flash is a molding flaw caused by molten plastic escaping from the mold cavity.

A flash can occur when the mold is not held together enough force to withstand the opposing party, allowing the plastic to seep through.

For all your polyethylene injection molding needs, contact us today.