Inox Cast LDPE Injection Molding

Inox Cast is a popular supplier of LDPE injection molding to different industries around the world. Here in Inox Cast, we are committed to making your business and project more successful. For the best LDPE injection molding, choose Inox Cast.

For more than 20 years, Inox Cast is an expert in developing, designing, production, and services of LDPE injection molding. We are passionate about providing customers exceptional LDPE injection molding services that will suit your application.

As a professional manufacturer, we have a rich experience on LDPE injection molding. Due to its extreme flexibility and lightweight, LDPE or low density polyethylene is suitable for injection-molded and is very useful for various applications.

LDPE injection molding offers highly recyclable materials on every parts and component. It can also maintain the pliability and toughness of the product even in an extreme temperature range. Inox Cast LDPE injection molding quality and services can cater any size of products.

Physical Properties of LDPE:

• Lightweight
• Excellent impact resistance
• Translucence
• Compliance to FDA standards

Applications of Inox Cast LDPE Injection Molding

Inox Cast LDPE injection molding is a very famous method for industrial and consumer manufacturing plant because of its versatility.

• Food containers
• Medical products
• Toys
• Industrial parts
• Food service and storage
• Consumer goods

Because of our vast understanding and knowledge, Inox Cast can surely cater your needs. We can also offer OEM services to meet your demands. All our products and services are offered at a competitive price.

If you have questions or inquiries, don’t hesitate to contact us today!

LDPE Injection Molding: The Ultimate Guide

If you want to learn more about LDPE injection molding then read this guide.

It has all information you need about injection molding LDPE plastic.

Let’s dive right in.

1. What Is LDPE Injection Molding?

Low density polyethylene is a popular method in industrial products that offers pliability hence it is a flexible thermoplastic that has toughness through a wide range of temperature.

LDPE injection molding

It is made up of multiple units of ethylene with a highly branched chain structure hence it has a tensile strength of 4550 pounds per inch.

Under mechanical and thermal stress, LDPE injection molding high thermal expansion inclined to fail.

2. Benefits Of Injection Molding LDPE

• Low-cost polymer that is easy to manufacture and form hence it has efficient production plan to exact specifications.
• Delivery is on time and there is also a free sample hence before and after every sale services.
• It has professional customizing Low Density Polyethylene molding service hence through both shipping and production.
• Help customer decrease overall cost and increase manufacturing efficiency hence it has a high-quality Low Density Polyethylene material that has strict production and quality control.
• Chemical resistance with high impact strength thus superior moisture resistance and good thermal resistance.
• It is commonly used in products like plastic bags and films thus its branching characteristic leads to imperfect intermolecular bonds and temporary packed molecules.
• Due to its high ductility, Low Density Polyethylene is widely used in applications of plastic bags.

Hence it has many different uses in different companies since it is the most versatile plastic.

• LDPE is produced during the linking of monomers into polymer chains hence monomer ethylene gas is compressed in an autoclave to facilitate polymerization.
• The polymer has a few compresses molecular structures since LDPE has high level of both long and short chain branching.

3. Properties Of LDPE For Injection Molding

Lower Density.

It has a high point of branching since it is a grade of polyethylene that carries with it a lower density and the polymer has few constrict molecular structures.

Semi-crystalline Polymer.

It has a tightly packed molecular chains thus they can vary in shape and size with amorphous areas existing between the crystalline areas.

LDPE has a density of 0.91 to 0.94g/cm3 hence it is softer and more flexible product compared to High Density Polyethylene.

Soft And Flexible.

It is commonly used in products like plastic bags and films thus its branching characteristic leads to irregularly packed molecules and weaker intermolecular bonds.

This results in softer, flexible and low tensile strength hence greater ductility and can be stretched without breaking.

Versatile.

Due to its high ductility, Low Density Polyethylene is widely used in applications of plastic bags.

Hence is the most versatile plastics and has many different uses in various industries.

Recyclable.

It is easily recyclable hence known by the resin ID code ‘4’ and is gathered by various recycling programs across the world.

Some Low Density Polyethylene materials such as plastic overwrap, retail bags and zip-top food storage bags are flexible hence they can be dropped off at retails stores.

However, the rigid LDPE products like containers, caps and bottles are accepted through curbside recycling program.

Excellent Chemical Resistance

Chemical resistance with high impact strength thus superior moisture resistance and good thermal resistance.

Good resistance to alcohols, dilute alkaline and acids hence limited resistance to aliphatic and aromatic hydrocarbons, mineral oils and halogenated hydrocarbons.

Transparent in thin film form and very low water absorption.

4. Uses Of LDPE Injection Moulded Parts.

Low density polyethylene is commonly used in;

• Toys.
• Pharmaceutical industry.
• Wiring and cables.
• Cable jacketing.
• Water pipes
• Housewares.
• Food containers.
• Consumer goods.
• Medical products.
• Food service and storage.
• Films for baked goods
• Cartons.
• Bottles.
• Laminations.
• Tamper evident.
• Trash bags.
• Liners.

5. Recommended LDPE Molding Temperature

Maximum temperature 176 F – 80c

Minimum temperature -58F – 50c

Melt temperature is 180-280c

Mold temperature is 20-70c

However, the distance from the surface of the mold to the edge of the cooling channel should not be more than 1.5times the diameter of the cooling channel.

The recommended cooling channel diameter should be at least 8mm.

6. LDPE Injection Molding Vs HDPE Injection Molding

Low density polyethylene and High-density polyethylene share a lot of characteristics.

Also, the polymer chains that make up both materials are branched in Low Density Polyethlene.

Moreover, the polymers have more crystalline structure in High Density Polyethylene.

High Density Polyethylene  is found in pellet form thus is a resin used in injection molding applications designed .

LDPE injection molding

Hence to withstand high possess crack resistance and provides good processability for moulders.

It has good stiffness, durable, high sustainability, recyclable and high impact resistance hence is typically lower in cost and has a great chemical resistance.

HDPE can withstand environment stresses due to its liner structure and optimal strength thus it can be moulded into many types of different shapes and sizes.

Here are the differences between High density polyethylene and Low-density polyethylene;

• HDPE is manufactured at a very high temperature thus the process of heating petroleum releases the ethylene gas monomers.

Hence it is then combined to form polymer chains.

LDPE is produced during the linking of monomers into polymer chains hence monomer ethylene gas is compressed in an autoclave to facilitate polymerization.

• HDPE provides the best chemical resistance thus it can withstand higher temperatures due to its higher melting point than LDPE which has a low melting point.
• LDPE has a density of 0.91 to 0.94g/cm3 hence it is softer and more flexible product compared to HDPE which 0.94 to 0.97g/cm3 making it rigid.
• HDPE is rigid and durable hence its more crystalline structure results in opaqueness of the material while LDPE is softer and more likely to crack under pressure.
• Both LDPE and HDPE are recyclable but LDPE is more difficult to recycle since it softer while HDPE is rigid and easier to transport and run through recycling equipment.
• In general application LDPE is used in shrink wraps, films, extrusion mouldings and laminates while HDPE is used to make film products such as hollow plastic products and pipes.
• LDPE has high level of short chain branching and long chain branching while HDPE has low level of short chain branching.

HDPE injection molding

7. Conditions For Injection Molding LDPE

The following are the conditions for LDPE injection molding;

Melting temperature is – 180-280 c

Molding temperature is– 20-70 c

Material injection pressure is up to 150MPa.

LDPE has a density of 0.91 to 0.94g/cm3 hence it is softer and more flexible product compared to HDPE.

Injection speed-profiled speeds can limit warpage problems of large surface area parts hence fast speeds are recommended.

Chemical and physical properties –at a high pressure and temperature, low density polyethylene is produced by the polymerization.

LDPE at room temperature is resistant to many solvents hence swelling is usually caused by chlorinated hydrocarbons.

The exact shrinkage values are dependent on the molding conditions thus when density is between 0.91-0.925g/cm3, the shrinkage is of the order of 1.5-4%.

Under very high temperatures, low density polyethylene is prepared from gaseous ethylene and high pressures in the presence of oxide initiators.

Polymer structure with both short and long branches are produced during these processes.

8. Low Density Polyethylene [LDPE] Injection Molding Process.

The injection molding process involves heating and injecting plastic material under pressure into a closed mold tool.

This allows thousands of identical parts to be made quickly and cheaply.

The molten plastic cools and hardens into the shape inside the mould tool hence it opens to allow the mouldings to be ejected or removed for inspection.

Injection Moulding LDPE Process Step By Step Process

Stage 1:

Material granules from the hooper feed into the heated barrel and rotating screw thus the melted material is then forced through a check valve to the front by the rotating screw.

Stage 2:

Having been moved backwards by the shot of the material at the front, the screw is forced forward by hydraulic ram.

This action injects material into the mould cavity in the closed mould tool hence the displaced air escapes through vents in the injection pins and along the parting line.

Runner, vent design and gates are important since they ensure the mold is properly filled.

Stage 3:

The tool is held closed under pressure until the plastic material cools and sets hard in the mould cavity.

This depends on the type of resin used and the thickness of the part since it is the longest part of the injection moulding.

Water is cycled through the mold to maintain a constant temperature thus each mold is designed with internal cooling or heating lines.

Stage 4:

The screw starts to move back for the next moulding.

The tool then opens and new plastic resin id drawn into the barrel from the material hoper hence the heater bands maintain the needed barrel temperature for the type of resin being used.

Stage 5:

The mold opens and the ejector pins are moved forward by the ejector rod hence the parts fall and is captured in a bin that is below the mold.

The runner is then recycled to reduce cost of maintenance and repair hence the useable parts are then weighed, counted and packaged for assembly.

low density polyethylene injection molding process

9. Defects In LDPE Injection Molding

The following are some defects in Low density polyethylene injection molding and how to control them;

Vacuum Voids.

These are enclosed space close to the surface of an injection moulded prototype thus the inner sections of the prototype do not solidify uniformly causing the defect.

To avoid voids, you must hold pressure and time during moulding process since it can also occur from a part that is cast from a mold with two halves.

Ensure less gas is captured as air is able to escape more rapidly by switching to a less viscous plastic.

At the thickest part of the molding, locate the gate to ensure that mold parts are correctly aligned.

Warping.

Warping is caused by uneven cooling rates in various parts of the mold which cause the plastic to cool differently and produce interior stresses.

It occurs where it is not expected thus it is like a bent shape hence when molding you should consider plastic materials that do not shrink and deform.

Flow Marks.

It can be regarded as minor or serious depending on the parts since they usually occur close to the gate area and the joint area.

Hence, its common in narrow sections of the components.

The defect can be avoided by increasing the moulding temperature, the molten material temperature and the injection speed.

Jetting.

The viscosity of the plastic becomes too high when the temperature is too low and the speed is very high.

Hence jetting occurs when molten plastic fails to stick to the mold surface.

Ensure adequate contact between the molten plastic and the mold by modifying gate design thus the viscosity increases when the plastic comes in Contact with the mold walls.

Flash.

Molten plastic escapes from the mold cavity when the mold is not clinched together with enough force thus causing flash defect.

The mold parts should remain shut during shots since excessive injection pressure may force the plastic out through the route of least resistance.

This therefore, increase the clamp pressure to avoid defect.

Burn Marks.

They look like a light yellow or black discoloration due to excessive melting temperature, overheating in the presence of trapped air on the molding parts.

Reduce temperature, injection speed and cycle time hence it is caused by delay in removing the air in the cavity and improper runner system design.

Short Shots.

The molding falls short because it does not fully occupy the mold cavity and by being incomplete, result becomes deficient.

Short shots can be caused by the plastic being too viscous then it solidifies before it fully occupies all the cavities hence incorrect standardization.

The gas should not be entrapped within the mold hence increase mold or melt temperature so as to increase flowability to account for gas generation.

Surface Delamination.

Foreign materials from the finished products find their way into the molten plastic hence making the contaminants and the plastic not to bond.

Reduce the dependence release agent by focusing on the ejection mechanism since an over-dependence on mold release agents can also cause delamination.

Sink Marks.

This is caused by unbalanced plastic material shrinking in the mold cavity.

Hence its look like lack of material on that sink area which is not matching to the part geometry.

It commonly happens to the thick wall area or lack of cooling system in the mold thus it occurs due to uneven wall thickness on the part design.

It can be avoided by adding some insert to the thick area to reduce the wall thickness and increasing the cooling time.

Weld Lines.

Weld line usually appears in the part with opening where the two resin flows meet hence at this point, the temperature of the two resin is usually lower.

The weld line appears as dark line when inorganic decorative effect pigments are used thus conspicuous in dark, transparent or brilliant mouldings.

Therefore , having smooth surfaces polished.

You can fix the weld line by increasing the injection speed, pressure and temperature.

Hence avoid weld lines in areas which need strength or the area that needs to appear smooth.

Modify runner system design by increasing the melting temperature at the flow front thus maintaining the same flow rate hence reducing runner attributes.

10. Molds For LDPE Injection Molding.

There are many types of Molds that can be used for LDPE such as;

Hot Runner Molds.

It requires a temperature controller to reduce runner scrap from the cycle hence the controller is being sized to match the manifold in the mold.

This improves the cycle times and saves the runner expensive wasted material hence some mold maintenance costs are higher on hot runner tool.

Plastic Blow Molds.

The gas blows into the piston to push each plastic part out of the mold hence that’s the only difference with the injection mold.

It is cost effective because it is faster compared to other types.

Unscrewing Molds.

They are automated with small drive systems that are tied into process and rotate threaded features hence the threaded features can be internal or external.

They usually utilize multiple manifolds within one tool hence can be used to for colour changes within a product line.

It is the common method of creating threaded holes within a plastic part and the extraction is tied into the press cycle.

Plastic Compression Molds.

This tooling includes custom steel Molds placed inside a hydraulic press to pressurize and shape heated plastic.

Family Mold.

It allows production of two or three different parts hence it has a single mold base with two or more different cavities.

It provides cost savings and versatility hence during molding the size, shape, resin an anticipated volumes are similar leading to good production results.

Plastic Injection Molds.

It is one of the most economic options with the shortest lead times thus it begins with custom steel Molds placed within the injection molding machines.

Each part is removed from the mold by placing it in hot water upon completing the process.

11. Low Density Polyethylene Injection Molding Technologies

Injection molding can be used to make a small quantity of prototypes, full production runs in the millions.

Hence there are many technologies available to produce your products.

Here are some of the injection molding technologies used to produce LDPE;

metal injection molding

Structural Foam Molding.

It is a low-pressure injection molding thus is suited for large plastic parts.

Hence inert gas is introduced into melted polymer for the purpose of reducing density of finished product.

structural injection molding

Multiple parts are produced on a single machine in a single cycle at a lower cost because the lower pressure allows more efficient molding equipment and tooling to be used.

Gas-assisted Injection Molding.

This technology can prevent warping and distortion by injecting pressurized gas into a plastic material-filled injection mold.

Molding parts with thick walls for structure and durability has a risk of warping.

Hence pressure keeps the plastic on the outside smooth and interior of the part porous.

Gas assisted injection molding

This will reduce the cost of the part and deformation on the part hence using less material since the part is hollow.

For all your LDPE injection molding, contact INOX now.