Polypropylene Injection Molding

InoxCast Polypropylene Injection Molding

One of the best materials for injection molding is high-quality polypropylene plastic. Inox Polypropylene injection molding also named PP injection molding is used in a wide range of applications. If you’re looking for a reliable PP injection molding manufacturer and supplier, Inoxcast is the best solution!

Inoxcast PP injection molding is designed to produce more complex forms of polypropylene which cannot be made if it was in its original form.

Inoxcast manufactures all kinds of PP injection molding such as storage containers, plastic boxes, and bottles. Our PP injection molding is useful for different types of water bottles, kitchenware, plastic storage containers, and even piping systems and insulation.

You can put trust in Inox Cast’s vast experience in the industry and capability in supplying durable and cost-effective polypropylene injection molding solutions.  As a leading manufacturer in China, we provide a wide option of polypropylene injection molding products available in different shapes, styles, designs, capacities, and sizes to suit your required applications.

The following are the PP injection molding advantages:

• easy to access and not expensive
• not expensive
• possesses a high flexural strength by virtue of its semi-crystalline property
• rather resistant to moisture absorption
• characterized by a relatively slippery surface
• chemically resistant to an extensive range of acids and bases
• fatigue resistance
• great resistance to impact
• act as a great electrical insulator

Inox is your reliable PP injection molding provider in China, offering almost all types of plastic components and parts. Our company has hardworking employees and skillful engineering personnel.

We aim to customer’s happiness when it comes to polypropylene injection molding needs. Inoxcast can provide a one-stop-shop PP injection molding solution to all our valued clients.

Skyrocket your business with Inoxcast and earn customer satisfaction. For more information, please don’t hesitate to contact us for queries.

Polypropylene Injection Molding: The Ultimate Guide

This guide covers all information you need about polypropylene injection molding process.

From injection molding requirements, molding techniques, applications to molding process – you will find all information right here.

Take a look:

1.  What Is Polypropylene Injection Molding?

A thermoplastic addition polymer that combines many propylene monomers is known as Polypropylene injection moulding material.

Polypropylene injection moulding is the process of transforming solid polymer to molten phase then directing it into a premade cavity to form a product.

polypropylene injection molding

In processing isotactic polypropylene (iPP), polypropylene injection moulding is the method widely used.

A mould formed by reciprocating the screw injects due to a screw in a heated barrel rotating to transport, melt and pressurize the polymer in the barrel.

2.  Polypropylene Injection Molding Parameters And Conditions

The following are the polypropylene injection moulding conditions:

• Plastic injection moulding pressure
• Mold temperature
• Melting point
• Dry

3.  Advantages Of PP Injection Molding

The following are some of the advantages of PP injection molding:

• PP has a corresponding slippery surface.
• Minimal costs are incurred, and access is more accessible.
• PP is an excellent electric insulator.
• Its semi-crystalline property makes it have a high spiral strength.
• PP is resistant to exhaustion.
• PP is excellently resistant to impact.
• PP is chemically resistant to a vast range of acids and bases.

4.  Limitations Of Injection Molding Polypropylene

The following are the disadvantages of injection molding polypropylene:

• Highly flammable
• Its poor bonding properties make it challenging to paint on it.
• PP is very sensitive to Ultraviolet(UV)
• Its high temperature is limited because it has a high thermal expansion coefficient.
• PP is highly resistant to chlorinated aromatics and solvents

5.  Properties Of Polypropylene Making Suitable For Plastic Injection Molding

Polypropylene material has the following properties that make it suitable for plastic injection molding:

Resistance To Exhaustion

After undergoing bending, flexing, or torsion, polypropylene maintains its shape and is thus considered suitable for making living hinges.

Toughness And Elasticity

Polypropylene acts differently in materials during the deformation process.

To a fixed range of deflection, polypropylene acts with elasticity also during the early stage of the deformation process, and it can also experience plastic deformation hence toughness.

Electrical Insulation

Polypropylene is suitable for electronic component uses because it is highly resistant to electricity.

Transmissivity

Polypropylene is naturally manufactured with a natural opaque colour even though it can be made transparent.

Polypropylene is suitable for applications that require the transfer of light.

Resistant To Chemical

Polypropylene is suitable for containers such as first-aid products and cleaning agents because it does not voluntarily react with dilute acids and bases.

6.  Polypropylene Injection Molding Process

The following are the steps to be followed for the polypropylene injection molding process:

Screw

The design of the screw has a significant impact on the injection molding process of PP because the process depends on it to drive the fluidity.

Output is affected by the diameter of the screw.

The compression ratio effects of the screw influence the pressure value and the volume and finished product effect.

To accelerate the fluidity, friction heat energy will be produced by the friction of raw materials even though the flow of raw materials majorly depends on the heater.

Therefore, the flow is small, the screw compression ratio is small, and the rotational speed should be maximized, leading to more friction heat than the screw with a large compression ratio.

Melting

The heater makes raw material particles melt into liquid flow gradually.

If the temperatures increase, it will fasten the flow of raw materials, leading to an efficiency increase, but that does not warranty positive results.

Therefore temperature balance needs to be arrived at.

Mold or Mold Head

Mold or mold head is a significant factor in plastic retyping.

The shrinkage rate should be considered, the mold is more complex, and the injection molding product is three-dimensional.

Other products are strip, flat and needle-like continuous product heads.

The production efficiency can be improved by the considerable pressure caused by the extrusion force directed by the screw at the small outlet.

Cooling

The injection mold has a cooling chamber where the material design is cooled.

Except for the air knife, which cools water directly on the blowing bag, hollow air blowing, and other cooling methods, for extrusion molding to attain a cooling effect.

It depends majorly on the cooling channel in the roller.

Extension

Extruded products have various elongations. To enhance the extension of finished products is through processing.

In high-speed production, the molecular weight distribution can affect the elongation effect.

Another form of extrusion is vacuum and air compression molding.

Contraction

The internal stress caused by cold contraction, crystallization, and expansion leads to shrinkage problems of raw materials.

Maintaining pressure continuously and prolonging cooling time helps curb cold contraction and thermal expansion.

Compared to non-crystalline materials, crystalline raw materials are likely to have a considerable shrinkage difference.

This part is fixed in the mold by adding additives to reduce shrinkage.

Polypropylene injection molding process

7.  How To Reduce Polypropylene Injection Molding Cost

There are different ways to reduce the mold cost because the injection molding process is quite expensive.

The following are ways in which mold costs are reduced:

• Considering the part size
• Exclusion of undercuts
• Eliminating irrelevant features
• Initiating the use of family type or multi-cavity mold
• Using a core cavity technique
• Minimizing cosmetic finishes
• Redesigning and re-using the existing molds
• For parts that self-mate, it is crucial to design them
• Monitoring the DFM (Design for Manufacturability) analysis

8.  Recommended Polypropylene Injection Molding Temperature

Polypropylene is recommended to be molded at a cylinder temperature ranging between 400 and 500⁰ F to yield positive results.

The cylinder temperature should range between 52 and 50⁰ F higher than the minimum temperature needed to fill the part.

Molding temperatures mostly range between 400 and 525⁰ F.

If temperatures lower than 400⁰ F is used, it can lead to poor quality surfaces and flow marks.

If temperatures higher than 500⁰ F are used, it can result in shrinkage, warpage, burning, and flashing.

9.  Choosing Mold For Injection Molding PP

When choosing the mold for injection molding of polypropylene, the following are the properties to consider;

Cost Of Material

The material cost is an essential element to consider when choosing fabric for the injection molding process as it will help get a clear budget of the costs to be incurred.

Weight Of Material

The weight of the end product will be determined by the density of the polypropylene used in the injection molding process.

The density will help determine how light or heavy the result will be after being manufactured.

Flexibility Of Material

The material’s elasticity is a significant factor when choosing an injection molding material.

Material Hardness

Resistance to indentation or material hardness is measured using a device to measure the shore hardness.

Then are separated into two types measuring the more complicated and softer polypropylene materials.

The scale for both types ranges from 0 to 100

It is essential to choose the right polypropylene for the correct part production as each different material is used for various applications.

The following are the factors to be considered when choosing the material:

• Environmental conditions
• The material uses
• Abrasion type
• Experiences incurred by the user on using the material.

Therefore, choosing the material that can withstand temperatures, erosion, and pressure is crucial.

Surface Of Mold

The mold surface should have a thick, wear-resistant, and hard layer.

Size And Precision Requirement Of The Injection Molding Process

There can be high-precision and low-volume injection molding; therefore, choosing the material based on production size is essential.

10.  Allowable Polypropylene Injection Molding Tolerances

Allowable polypropylene injection molding tolerances are +/-0.005 inches.

Parts with tight tolerances are more expensive to produce than parts with normal tolerances.

Hence, it is essential to find the optimum tolerance for parts that manufacture high-quality results at a minimal cost.

The following are some of how engineers and designers need to optimize part tolerances:

• Administering repeatable process controls
• Know injection molding tooling
• Knowing properties of materials you want to injection mold

11.  Polypropylene Injection Molding Defects

The following are the polypropylene injection molding defects.

• Shrinkage deformation
• Vacuum hole
• Bending deformation
• Bubbles
• Weld line
• Cracking and whitening
• Surface porosity
• Under injection
• Overflow flash
• Flow mark
• Silver streaking

12.  Types Of Polypropylene Injection Molding Techniques

Some of the polypropylene injection molding techniques include:

Reaction Injection Molding

The reaction injection molding process is used to mold polypropylene.

It is a low-temperature and low-pressure injection process.

The process is majorly used in industrial, automotive, and medical industries.

Parts that are lightweight and strong and can be painted easily are often molded using reaction injection molding.

Reaction injection molding involves a two-component system made of isocyanate liquids and polyol mixed at high pressure, and then at low pressure, they are metered into the closed tool.

After expanding, the material is ejected in 5 minutes to fill the tool.

The first step in the reaction injection molding process involves dispensing the isocyanate and polyol (polypropylene) liquids in storage tanks under high-pressure pumps.

reaction injection molding

The polypropylene is redistributed from the storage tank to a multi-stream mix-head and back in a vicious circle.

This injection molding process uses low-viscosity liquid polypropylene. They then thicken and stretch through various chemical reactions.

The polypropylene finally hardens after being injected into the heat mold.

Some of the advantages of reaction injection molding include:

• Minimal tooling cost

The reaction injection molding process enables tools to be produced faster and lower costs.

• Large parts

Polypropylene properties allow it to fill molds for substantial parts.

• Flexibility

Reaction injection molding is flexible as both thin and thick walls can be designed.

• Lightweight, solid and flexible parts are produced and can be painted
• Fast cycle times

Limitations of reaction injection molding include:

• Raw materials are costly
• Compared to injection molding, it has slow cycle times

Gas-assisted Injection Molding

Gas-assisted injection molding process involves a polypropylene melt pushed into the mold at the end of the polymer stage by an inert gas at pressure.

Advantages

• Low clamp force
• Thick parts can be molded
• There are no sink marks
• Products are lightweight
• Part deformation is reduced

Disadvantages

• Plastic materials are an exception to this method
• The method is challenging for the production of multi-cavity mold.

Gas assisted injection molding

Thin-wall Injection Molding

Type of injection molding process that involves large-scale production of plastic parts that are light and thin.

It saves on material costs and ensures short cycle times; higher productivity.

Thin-wall injection molding process focuses on the size of the part rather than its wall thickness.

Advantages of a thin-wall injection molding process

• Fast cycle times
• Produces safe, lean, and cheap parts
• Parts can be manufactured from recyclable plastic
• The molding process reduces fuel usage and cuts weight and other resource consumption.

Limitations of a thin-wall injection molding process

• Injection molders can be pretty expensive; hence high capital investment cost
• Highly skilled experts are required for the thin-wall injection molding process, which is hard to find and maintain
• Leads to environmental litter

Applications of a thin-wall injection molding process

• Mobile telecommunications
• Automotive industries
• Computing equipment
• Medical and packing of food

thin wall injection molding

die casting

Injection Molding Of Liquid Silicone Rubber

Injection molding of liquid silicone rubber is an injection molding process that involves polypropylene parts being produced.

The high-volume parts are durable and flexible.

The processes use the liquid silicone rubber to produce high-quality parts because it has excellent stability, a low compression set, and can withstand cold and hot temperatures.

liquid silicone rubber injection molding

Advantages of injection molding of liquid silicone rubber

• Cycle times are short
• Repeatability of the process
• It is an automated process
• Injection is direct
• Demolding systems are automated

2k Injection Molding

2K injection molding involves molding using two different colors or polypropylene materials. The process is economical and efficient.

Two materials with different colors, properties, and hardness levels are manufactured into one end product using the 2K injection molding process, thus saving costs.

2K injection molding

Some of the benefits of 2K injection molding include;

• The appearance of the end product is more attractive

The end product is more appealing because it can be made from two colours in one production process, and the two components can fit together perfectly.

• Saves on production costs

The cost price of products is low because 2K injection molding gathers steps together into one injection molding process.

• Is compliant with the user and tailor-made products

Some of the disadvantages of the 2K injection molding process include:

• Combining some plastics might not be possible as some do not bond adequately.
• It can be expensive as the one-time investment cost for a 2K injection molding process can be higher than a single injection molding process.

13.  Injection Molding Polypropylene Resin Tips

Polypropylene has a low density and is resistant to chemicals; hence considered a suitable material for producing items such as automotive parts and medical devices.

Therefore, polypropylene has acquired popularity in the injection molding field.

Temperature thresholds need to be monitored during the melting and molding process. Thus, polypropylene resins are used because of their benefits.

The following are the tips for injection molding polypropylene resins:

Using A Melt Temperature Ranging Between 400⁰ F And 500⁰ F

When setting a temperature melt, ranging between 25 and 50⁰ higher than the minimum fill temperature should be considered.

If temperatures lower than 400⁰ F is used, it can lead to poor quality surfaces and flow marks.

If temperatures higher than 500⁰ F are used, it can result in shrinkage, warpage, burning, and flashing.

Ensuring That Proper Molding Equipment Is Available

Even though polypropylene can be molded accurately using standard and unaltered single-stage screw molding equipment,

It is always essential to ensure proper molding before starting the injection molding process.

Don’t Rush The Injection Process

In order to consume a high volume of each overall cycle, it is good to be prepared before the injection process.

The injection process needs patience because accurate injection helps control shrinkage as injection time does not remarkably influence warpage.

If Using Fixed Polypropylene Resins, Consider Pre-dying Only

Polypropylene is a non-polar substance, and the pre-dying process can be skipped, thus saving time during the injection molding process.

Few filled polypropylene resins are the only resins that may require pre-dying.

Go For An Injection Pressure Ranging Between 800 And 1,500 PSI

Injection molding problems with polypropylene resins can be controlled by injection pressure as an element.

The injection pressure chosen should match the size and construction of the item.

To avoid problems with sticking and flashing, the injection pressure selected should be capable of roughly filling 99% of the item’s part.

Hold Time Should Not Be Rushed.

Hold time is an essential factor in preventing shrinkage and warpage. Giving enough time for the mold to cool is necessary.

It is recommended to allow the part to cool to approximately 130⁰ F to yield positive results.

Choosing A Mold Temperature Ranging Between 50⁰ And 150⁰F

To reduce surface imperfections and stress, mold temperatures should be accurately determined.

Mold temperatures ranging between 50⁰ and 150⁰F help minimize stress and surface imperfections.

To facilitate the component’s ejection from the mold, it is essential to ensure that the mold is cooled uniformly.

Always Ask For Help From Qualified Industry Professional

This is the best technique to ensure positive results are yielded.

Always ask for instructions and guidance from well-trained industry professionals during the PP resin injection molding process.

To Improve The Cycle Time, Use Minimal Back Pressure

The best backpressure for polypropylene injection molding is recommended to improve cycle time to range between 50 and 100 psi.

Though there are cases that require pigment mixing, this rule is an exception.

If Sticking Occurs, Adjust The Polypropylene Grade

Polypropylene has release properties that prevent it from sticking.

If sticking occurs, it is easily corrected by using a polypropylene grade internally lubricated or slight changes to the mold.

For all your polypropylene injection molding needs, contact us.