PVC Injection Molding

Inox Cast PVC Injection Molding

Looking for perfect injection molding for your PVC production? Inox Cast has perfect customizations for you.

Inox Cast PVC injection molding has plenty of applications and production support in different production industries. We designed perfect and durable PVC injection molding to prevent leaking and produce perfect surface finishing and product textures.

Our PVC injection moldings are customizable according to product types. We can custom your ideal PVC injection molding from sizes, designs, shapes, colors, and more. PVC is widely used in different production industries like making pipes and fittings, enclosures, parts, and more.

Inox cast PVC injection molding is used in many production industries like electrical, plumbing, household, construction, kitchenware, engineering, and so on. It is widely used for many types of fabrications for industrial and commercial purposes.

We can offer our perfect quality PVC injection molding made of certified materials designed with perfect features, specifications, dimensions, applications, conditions, and more. You need to consider a lot of options in choosing the right PVC injection molding for your production needs.

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PVC Injection Moulding: The Ultimate Guide

In this guide, you are going to learn everything about PVC injection moulding.

Whether you want to learn about properties of PVC, actual injection molding process or moulding requirements – all information is right here.

Let’s dive right in.

1.  What Is PVC Injection Moulding?

Polyvinyl chloride injection moulding is a manufacturing process that utilizes PVC granules to produce plastic parts.

It begins by heating PVC granules in the machine barrel, thereafter feeding the mould with molten PVC for cooling and hardening.

PVC Injection molding machine

 The process then starts again repeating similar steps and can produce hundreds to millions of similar parts.

When using PVC thermoplastic certain moulding condition must be met for the process to be successful.

2.  Properties Of PVC Making It Suitable For Plastic Injection Moulding

Polyvinyl chloride is a unique thermoplastic material and it bears the following properties.

• Technical name: (Polyvinyl chloride)
• Chemical formula: (C2H3Cl) n
• Melting temperature: 212-500F or (100-260⁰C)
• Tensile strength: Flexible PVC (6.9-25MPa/1000-3625PSI), Rigid PVC (34-62MPa/4930-9000PSI)
• Heat Deflection Temperature (HDT): 92⁰C or 198F
• Excellent insulating or dielectric feature
• Chemical and abrasion resistance
• Good flame
• Durable

All these properties are what constitute PVC material and are as a result of multiple material composition of the PVC.

3.  Plastic Alternatives To Polyvinyl Chloride Injection Moulding

There are other plastic alternatives that can be used in injection moulding besides PVC plastics. These plastic alternatives exhibit similar or better properties to PVC and are not corrosive.

Some of the plastics that can be used are; thermoplastic elastomers (TPE) or thermoplastic polyurethane (TPU).

Thermoplastic elastomers and thermoplastic polyurethane are all classified under thermoplastic elastomers (TPE).

TPE materials are further classified into six commercially available classes as follows:

• Thermoplastic olefins (TPE-o)
• Thermoplastic polyurethane (TPU)
• Elastomeric alloy (TPE-v or TPV)
• Styrenic block copolymer (TPE-s)
• Thermoplastic polyamides
• Thermoplastic copolyester

Advantages Of TPE And TPU Thermoplastics

TPEs and TPUs possess desirable properties that make them also ideal for injection moulding process.

• They are thermally stable and do not need the addition of stabilizers.
• Are energy efficient
• Have improved consistency
• They have better colourability
• Require little to no compound
• No cure system or reinforcing agents needed.

Like PVC materials, TPEs and TPUs can be applied in different industries such as construction, automotive, medical, etc.

4.  PVC Injection Moulding Process

Polyvinyl chloride injection moulding process is a step by step process that begins with PVC pellets or powder form.

Due to the presence of chlorine ions, PVC tends to absorb moisture prompting drying before moulding begins.

PVC injection molding process

Drying can be done between temperature of 167Farenheight (F) to 194Farenheight for 1 to 3 hours.

Melting

The pellets or powder is then introduced into an injection moulding machine barrel and heated to temperatures between 212Fto 500F.

This temperature range is ideal for PVC thermoplastic to reach its melting point.

When the temperature range is exceeded, PVC material decomposes and releases a harmful gas; hydrogen chloride (HCL).

Additive such as stabilizer is added to aid in thermal stability.

Heating time is also a parameter to be monitored and controlled.

Injection And Cooling

Next, the liquefied PVC is injected under pressure into the two-part custom mould with mould temperature of between 80F to 113F.

Since the temperature is lower here, cooling of the mould begins and the product takes the shape of the mould cavity.

Calibrator and shrinkage controller maybe used to correct and control product deformation.

Molten PVC uses gates and runner to fill in the mould, therefore, they should be large, short and thick walled.

This is to avoid losing pressure during the flow and also fill the cavity quickly.

Due to poor fluidity of molten PVC, plasticizer can be added to boost fluidity of the liquefied PVC.

Ejection

Finally, the solid moulded product is then ejected into collection bin. The gates and mould then close and the process repeats.

This finished PVC injection moulded product proceeds to the next stage for secondary processing and finishing.

5.  Advantages Of Injection Moulding PVC

There are many advantages associated with using PVC injection moulding.

• Budget friendly

The cost of buying PVC thermoplastic is less compared to other alternatives.

• Environment friendly

Using PVC injection moulding allows for recycling because PVC does not degrade when heated. Therefore, the PVC pellets can be reheated and injection mould again and again.

This reduces environmental impact from PVC waste and is also cost effective in the long run.

• Easy availability

PVC material is easy to come by anywhere around the world and in different durometer form, from flexible to rigid and hard.

• Long lasting

Polyvinyl Chloride material is naturally strong and durable and can withstand both chemical and environmental degradation for some time.

• Strength

PVC material has excellent material stability as well as tensile strength making it a strong material. It can bend to a certain level without breaking.

Other advantages include:

• Lightweight
• Good colour retention
• Minimal finishing, etc.

6.  Requirements For PVC Injection Moulding

PVC like any other thermoplastic material, has specific requirements under which injection moulding can successfully occur.

Drying Temperature

This is the temperature within which PVC material loses absorbed moisture content due to the presence of chlorine ions.

Drying occurs in oven at a temperature range of 167 to 194F for 1 to 3 hours before injection moulding process.

Melting Temperature Range

This is temperature range of between 325 to 425F within which PVC material turn into a molten state.

The temperature is a range because PVC is amorphous and does not have a specific melting temperature point.

If the melting temperature is exceeded, PVC emits harmful hydrogen chloride fumes decomposing the material.

Mould Temperature

The mould temperature is normally lower than melting temperature and ranges between 65 to 158F.

moulding temperature allows molten PVC to start cooling down as it hardens into the mould shape.

Injection Speed

It is the rate with which the plunger moves to inject molten PVC during the process. This injection speed influences the outcome of the final product.

PVC injection moulding requires slow injection speed to prevent material degradation.

Other factors such as dimension of the mould and thickness of the PVC. Thin parts are injected at higher speed than thick PVC parts.

Tensile strength

PVC material exhibits excellent tensile strength about 6500psi in its base form, thus known as rigid (RPVC).

This feature makes it stronger and harder than other thermoplastics as well as durable hence popular in various industries.

Low shrinkage

The shrinkage rate for PVC material for both rigid and flexible form is between 0.002 to 0.006mm. Shrinkage is affected by the components in PVC, moulding process conditions and mould design.

Short flow area and larger gate decreases shrinkage gate whereas, long flow area and small gate increase shrinkage.

Packing Pressure

Also known as holding pressure, is the pressure with which the final 5% of the cavity gets filled. This pressure is usually lower than injection pressure (100MPa) and held for some time.

Packing pressure help achieve three things;

1. Trapped air is allowed to escape through the vent.
2. Molecules in the materials get time to align to enable them achieve high density.
3. It relieves stress from the moulded part.

7.  Applications Of PVC Injection Moulding

Besides its two forms; flexibility and rigidity, PVC thermoplastic is easy availability and low cost thus is used in multiple industries.

• Construction
• Healthcare
• Agriculture
• Aerospace
• Automotive
• Consumer products
• Oil and gas

8.  Considerations In PVC Injection Moulding?

Polyvinyl chloride injection moulding process requires an understanding of the PVC material, machine type, moulding conditions like temperature, speed, etc.

We will explore how each of the above affects PVC injection moulding and why they should be considered.

Injection Moulding Machine

The type of injection moulding used for PVC material is critical as it affects the product outcome. PVC materials are mostly injection moulding machine consisting of reciprocating screw system.

This ensure that the molten plastic maintains its temperature through to injection cycle.

While considering the machine to use, factors such as below will guide you accordingly.

• Production capabilities in terms of volume
• Clamp capacity
• Technology applied
• Automation of machine; robotic or manual
• Mould design and number of cavities
• Production speed and cost
• Maintenance cost

PVC Material C

PVC material exists in two forms; soft or hard and each form is responsible for a particular product outcome.

Given that PVC does not have a definite melting temperature, a range of 325F to 445F is ideal for either forms.

PVC Material C

Melting temperature should be strictly controlled for a desired outcome.

Other factors to consider include; shrinkage rate, hardness of the product and injection speed.

Moulding Conditions

These include; temperature, injection speed, pressure, cooling time, holding pressure, moulding time, etc.

Temperature

Melting temperature helps convert solid PVC pellets or powder into hot liquid or molten state.

This temperature ranges from 325F to 445F and is critically controlled to avoid material decomposition.

Once PVC material is degraded by decomposition it cannot be recycled.

Another temperature control point is that of injection nozzle.

This should be kept at optimum to avoid cases of frozen nozzle and leaking molten PVC.

Frozen nozzle interferes with injection speed and pressure during injection.

Injection Pressure

There are four types of pressures involved in PVC injection moulding process. Clamping pressure, injection pressure, holding pressure and back pressure.

injection pressure

Understanding how these pressure work together and balancing them is key to having quality products, determine production time and cost.

• Clamping pressure

Clamping pressure is the force needed to hold together two-halve of the moulds when closed.

It is important to accurately calculated this force to avoid mould opening during injection.

• Injection pressure

Injection pressure is as a result of hydraulic system pushing molten PVC into the mould cavity.

This should be balanced with clamping pressure and controlled to avoid flushing.

This pressure accounts for the 95% filling of mould cavity and not 100%. This is because the mould develops resistance as it gets filled leaving 5% of the cavity unfilled.

• Holding pressure

As the mould cavity gets filled, injection pressure tends to drop and is replaced by holding pressure. Holding or packing pressure ensure the remaining part of the mould is completely filled.

Besides, it helps release trapped air and also align molecules together for maximum density.

Holding pressure should be within a short time to avoid gate freezing and blockage by solidification.

• Back pressure

This force is as a result of resistance of the fluid to flow back to the reservoir due to a valve.

Back pressure is always set to slow or medium and it ensure proper PVC injection into the mould cavity.

Injection Speed

Injection speed is determined by the size of the mould and the desired thickness of the PVC product. Thin PVC parts and products are injected at higher speed compared to thick PVC products.

Injection Time

The time takes for every PVC unit to be moulded varies with size, temperature and moulding dimensions.

Typically, PVC takes between 30 to 60 second for each complete process. Time will determine your production lead time and cost.

9.  Choosing PVC Injection Moulding Machine

When choosing a PVC injection moulding machine consider the following:

• Stainless steel or chrome plating machine prevent corrosion from the acidic chlorine ion component of PVC material.
• Machine durability
• Easy to operate and maintain
• Efficiency
• Meets all your specifications at a low cost

PVC injection molding machine

10.  Common Injection Moulding PVC Problems And How To Solve Them

While PVC material has desirable characteristics that make it popular among other thermoplastics, there are problems associated with its use.

PVC material emit harmful hydrogen chloride fumes when the melting temperature is exceeded. This is due to the presence of chlorine ion in PVC material.

Hydrogen chloride fumes can easily lead to environmental pollution. To prevent this, melting temperature condition is strictly controlled.

Secondly, the material is not thermally stable and can easily degrade during heating. This is corrected by addition of stabilizers during injection moulding process.

Finally, PVC materials have a brittle structure in their rigid form, making them delicate for use for certain products.

This can be solved by using alternative thermoplastic such as TPE or TPU elastomers.

Overall, the problems are manageable and preventable thus making PVC still an excellent material for injection moulding process.

11.  Examples Of Parts Made From Injection Moulding PVC

PVC material is widely used in several different industries due to its properties. Some of the products made from PVC injection moulding are:

a) Bottle tops

b) Electric wire insulators

c) Home flooring

d) Plumbing pipes

e) Water pipes

f) Dashboards

g) Construction parts

h) Packaging materials

i) Window handles

j) Vinyl siding

k) Medical devices

12.  How PVC Injection Moulding Temperature Affect Quality Of Final Part

Temperature playas a vital role in PVC injection moulding product quality.

There are two different but related temperatures; melt and mould temperature.

Melt Temperature

This the temperature at which PVC changes from solid to liquid form and flows into mould cavity.

Melt temperature is carefully monitored and controlled for PVC forms because it affects the functionality, feel and appearance of final product.

Effects Of Melt Temperature On Product Quality

a) Viscosity: Higher melt temperature, lowers PVC viscosity leading to poor and thinly filled mould cavity resulting into an incomplete product.

b) Molecular weight: High melt temperature, lowers PVC molecular weight thus drawing more PVC material into the mould cavity.

This forms a stronger and durable end product.

c) Shrinkage and decomposition: Shrinkage is caused when a lot of material is drawn resulting into a thick and weak product.

When melt temperature is exceeded, PVC material decomposes releasing HCl gas and the end product with burnt marks.

Mould Temperature

Mould temperature is the temperature of the mould surface and like melt temperature it equally impacts product quality.

It affects how PVC heats and cools down during injection moulding process.

Effects Of Mould Temperature On Product Quality

a) Durability: If the mould is quickly cooled, it lowers its resistance to force or impact making it brittle and easily breakable.

b) Moulded-in stress: Incorrect mould temperature can add on to materials inherent stress. For instant, shock-cooling may interfere with product resilience and endurance.

c) Wear resistance: Resistance to friction, impact, abrasion, etc. is determined by mould temperature consistency.

e) Molecular weight: The weight determines how much stress can be applied and for how long it can be applied.

13.  Choosing Right PVC Injection Moulding Grade

The selection of the right PVC injection moulding grade is determined by the use of the end product and desired properties.

There are different grades of PVC material and each one has unique properties that make it suitable for certain use.

• PVC-U

Un-plasticised PVC is one that has no plasticised additives and is naturally hard and rigid.

They are safe, economical, highly durable, highly resistant to chemicals, UV exposure and are 100% recyclable.

PVC-U are used for transporting drinking water, soil, waste and sewage.

• C-PVC

Chlorinated PVC has chlorine compounds in it is more ductile than un-plasticised PVC, can withstand high temperatures and is recyclable.

Used for residential pipe system as well as commercial constructions.

• PVC-O

Molecular orient PVC is a PVC-U that has undergone a process to turn its amorphous structure into layered structure.

It has better properties than PVC-U such as resistance to corrosion, impact, fatigue and better balance between strength, stiffness and flexibility.

Commonly used in pressure pipes for drinking water, irrigation and sewer pumping systems.

• Modified PVC

These are PVC with added modifying agents that result in improved properties like, toughness, ductility, impact resistance, etc.

Modified PVC products like pipes with thin wall have excellent toughness with improved hydraulic properties.

Modified PVC pipe can be used to transport natural gases.

For all your PVC injection molding needs, contact INOX now.