POM Injection Molding

Polyoxymethylene, abbreviated for POM,  is a semi-crystalline thermoplastic. It’s also referred to as acetal, polyacetal, and polyformaldehyde. POM demonstrates high tensile strength, an incredible creep resistance, a low coefficient of friction and excellent dimensional stability which makes it an ideal injection molding material for gears and bearings. It is also a popular choice for plumbing equipment such as valve and pump housings, and lawn equipment due to its high-temperature resistance. 

In this article, we have conducted an in-depth analysis of POM injection molding material and its techniques to help you understand whether it’s best suited material for your project. 

Table of Contents

What is Polyoxymethylene?

POM resins are produced through the polymerization of CH2O, which is purified formaldehyde.
POM how it is made

The following diagram illustrates the chemical structure of polyoxymethylene:  

pom chemical structure

Types of polypropylene

Homopolymer

Homopolymer is produced from anhydrous, monomeric formaldehyde which is polymerized by anionic catalysis in an organic liquid reaction medium which is further stabilized by reacting to acetic anhydride.

  • Greater degree of regularity in their structure
  • Stiffer, Stronger and Higher tensile strength 
  • Moderate toughness under repeated impact
  • Shorter molding cycles and potential for cost reductions
  • Provides better mechanical properties
  • Allows for thinner and lighter part design to be manufactured

Copolymer

Copolymer requires the conversion of formaldehyde into trioxane using acid catalysis and cationic polymerization. This reaction is then followed by purification of the trioxane through distillation or extraction. This removes water and other active impurities containing hydrogen.

  • It’s easier to process 
  • Superior long-term performance (creep resistance, fatigue, endurance, strength retention)
  • Less gassing and odor
  • Heavy metal free colors, i.e. cadmium and lead (safer for workers / environment)
  • Better maintenance of color
  • Under ultraviolet light exposure
  • Faster molding cycles and less mold deposits
  • Stable in alkaline environments

What other names does Polyoxymethylene have?

Polyoxymethylene has several different names and they are often referred to by their technical or industrial names.

POM Technical Names:

Polyoxymethylene or POM is also known by the following chemical names:  

  • Acetal 
  • Polyformaldehyde
  • Polyacetal
  • Polyoxymethylene glycol
  • Polymethylene glycol

POM Brand Names:

Brand names are basically trade names that refer to the product that has been developed by the company. The following enlist some of the famous POM brand names:  

  • Delrin® is POM Homopolymer plastic made by DuPont. 
  • Celcon® is the POM Copolymer plastic made by Ticona 
  • Duracon® is the POM Copolymer plastic made by Polyplastics. 
  • Kepital®-POM is the POM Copolymer plastic made by KEP. 
  • Hostaform® is the POM Copolymer plastic made by Celanese Corporation.
  • Tecaform® is the POM Copolymer plastic made by Ensinger Company. 
  • Ultraform® is the POM Copolymer plastic made by BASF.

POM Plastic Properties

pom plastic properties

POM Plastic Characteristics

POM characteristics
  1. Polyoxymethylene has a very low coefficient of friction. 
  2. It also has excellent geometrical and dimensional stability. 
  3. It is impact resistant and also has a very high-temperature resistance. 
  4. POM is a tough and elastic material. 
  5. It has a good creep resistance even at low temperatures. 
  6. If the crystallization degree is higher, it can lead to higher shrinkage. POM plastic has different shrinkage rates for a variety of different reinforced materials but it typically can reach 2% to 3.5%.

Is POM toxic or harmless?

POM is not toxic in its solid form however, it can be harmful if it’s absorbed into the skin or eyes in its vapor or liquid form during the manufacturing process. That is why you will mostly find PP (Polypropylene) for consumer goods.

Advantages and Disadvantages of POM Plastic

Advantages of POM:

  • It has excellent rigidity and impact toughness. 
  • Its resistance to abrasion, creep resistance and solvent. 
  • It has a good appearance. 
  • It has a low coefficient of friction. 
  • It demonstrates hydrolytic stability and fatigue endurance. 

Disadvantages of POM:

  • It has a high mold shrinkage (approximately 2%). 
  • Post molding, the shrinkage is about 0.1% which is normally complete within 48 hrs. 
  • It is very rapidly attacked by nitric acid. 
  • It has a very poor resistance to UV radiation. 
  • It demonstrates an explosive decomposition if processed with halogens.

POM Injection Molding

1. POM Plastic Processing: 

Polyoxymethylene resins have a low water absorption rate which is generally between 0.2% to 0.5%. Usually, POM resins can be processed without drying. 

In case the raw material is moist or wet, the drying temperature should be set above 80℃ for 2 to 4 hours. 

2. Mold and Gate Design: 

The mold and the gate should be optimally designed according to the plastic. In the case of POM plastic, the following parameters can should be paid attention to: 

  • Common mold temperature should be controlled between 80-90℃
  • Flow channel diameter should be between 3-6mm 
  • The length of the gate should be 0.5mm
  • The circular gate diameter needs to be at least 0.5 times of the product thickness.

3. Melting Temperature:

The melting temperature is as follows: 

  • POM Homopolymer should be set between 190 – 230℃. 
  • POM Copolymer Kit should be set between 190 – 210℃. 

4. Injection Molding Speed

The Injection Molding Speed should be medium-fast. If it’s too slow, then ripples can occur. If it’s too fast, ripples and shear overheating can occur.

5. Back pressure

The backpressure should be as low as possible and it should not exceed more than 200bar.

POM for Prototype Development on CNC Machines, 3D Printers, & Injection Molding Machines

  • 3D Printing POM: Printing POM can be extremely difficult due to high temperature technicalities which is why it must be avoided. 

  • CNC Machining POM: In the case of CNC machining, POM is widely used and there aren’t a lot of limitations.

  • Injection Molding POM: POM is available in the form of resins or pellets for injection molding. It’s easy to mold and it flows well within the mold if all the injection molding factors are adhered to. 

It’s important to note that POM plastic shrinks at a rate of about 2%. This factor may be pronounced by a number of other factors such as holding pressure, melt temperature, mold wall thickness, mold temperature, and the type of additives.

Applications of POM molded plastic parts

Automotive Industry - Modern Fuel Systems

There are very few polymers that can withstand permanent contact with aggressive automotive fuels and the increasing temperatures encountered in engine compartments. Due to its high temperature resistant property, POM copolymer (POM) is the preferred injection molding material for modern fuel systems.

gas tank lid pom
Picture from https://unsplash.com/

POM can be applied to various applications in the fuel systems such as fuel caps, fuel filler necks, lifetime filter, valves, fuel pumps, and fuel rails.

Automotive Industry - Interior Appearance

Polyoxymethylene plastic is often used  in automotive interiors for soft, warm finishes as it can offer a molded-in low-gloss effect. In addition, it also provides design flexibility, excellent dimensional stability and is resistant to cleaning solutions. Take a look how molded parts for the automotive industry look in detail.

Picture from https://unsplash.com/

Medical and Healthcare Industry

POM copolymers are highly-crystalline and easily processed. POM plastic is often a popular choice for medical and healthcare equipment as it delivers high strength, stiffness, toughness and lubricity over a broad range of temperatures and chemical environments. POM offers high purity and are FDA Compliant and pharma-friendly properties.

syringe pom
Picture from https://unsplash.com/

Industrial Uses - Fluid Handling Applications

POM copolymer offers good flow and moldability. In addition, their very low moisture absorption permits dimensional stability when in contact with water thus, they are a popular choice for fluid handling applications such as plumbing, irrigation, water softeners, water filters, shower heads, and sprinklers.

shower head POM
Picture from https://unsplash.com/

Where can you purchase POM Plastic?

POM Plastic is available in various forms that can range from resins, rods, films and sheets. We have listed some of the leading suppliers for POM Plastic:

  1. Ticona: Ticona is a subsidiary of Celanese located in Florence, Kentucky, US and they are known to manufacture Celcon®, the POM Copolymer. 
  2. DuPont:  DuPont, located in Wilmington, Delaware, US are global supplier of Delrin®, the POM Homopolymer plastic. 
  3. Polyplastics: Polyplastics is a chemical company located in Taiwan, China and they are known for manufacturing POM Copolymers Duracon® and Tepcon®. 
  4. Korea Engineering Plastics Company: Korea Engineering Plastics Company, also abbreviated as KEP is located in Seoul, Korea and they are known for manufacturing Kepital®-POM. 
  5. Ensigner: Ensinger is located in Washington, Pennsylvania, US and they are known for manufacturing Tecaform®, a POM Copolymer plastic. 
Contact Us for POM Injection Molding

VEM Tooling has the expertise for your POM injection molding project. At VEM Tooling, we offer a dependable service and ensure that you have a great experience  with a seamless manufacturing process. 

To better understand how VEM tooling can serve you for your POM injection molding project, contact us or request a quote today.