An Informational Brief on Polymer Machining

 

Hemodialysis bloodline tubes connected to hemodialysis machine. Health care blood purification kidney failure transplantation medical equipment concept.Polychlorotrifluoroethylene (PCTFE) is a thermoplastic chlorofluoropolymer; some of its fluoropolymer cousins include: FEP, Kynar® PVDF, Teflon® PTFE and Halar® ECTFE. Fluoropolymers are known for their excellent chemical and hydro-resistance. This makes them candidates for critical applications, such as medical devices and industrial piping, where fluid exposure and hazardous materials can wear on a machined plastic part.

 

AIP has over 37 years of experience machining complex components from thermoplastics like Polychlorotrifluoroethylene PCTFE. In this insightful technical brief, we will discuss what goes into machining PCTFE and how it differs from other manufacturing options such as metal machining, injection molding, and 3D printing.

 

Properties of PCTFE

 

It is helpful to keep information on the properties of a thermoplastic before machining. This helps in selecting the right material for your project. Also, it helps determine if the material is a candidate for the end-use requirement. Below are some of the key characteristics of PCTFE:

 

Key Properties

  • High Chemical Resistance
  • Extremely Low Moisture Absorption
  • High Compressive Strength
  • Low Deformation
  • Low Gas Permeability
  • Nonflammable

 

PCTFE offers high compressive strength, low deformation, low gas permeability and extremely low moisture absorption. Nonflammable and resistant to most corrosive chemicals, PCTFE additionally has a much lower cold flow characteristic than other fluoropolymers.

 

Able to maintain excellent chemical resistance and ultraviolet stability in a temperature range from -400°F (-230°C) to 393°F (201°C), PCTFE has many applications in food processing, industrial and aerospace applications.

 

The table below displays the material properties for KEL-F®, a trade name for PCTFE.

 

Material PropertyUnitsValue
Tensile Elongation at Break @73 F%140
Flexural Modulus of Elasticity @ 73 Fpsi190000
Tensile Modulus of Elasticity @ 73 Fpsi220000
Flexural Strength @ 73 Fpsi8500
Densityg/cm3
lb/in3
2.13
0.077
Tensile Strength @73 F, (ult)/(yld)psi5700/(ult)
Notched Izod Impact @73 Fft-lb/in of notch1.5
Heat Deflection Temperature @ 264 psiF167
Flammability RatingUL94V-0
Coefficient of Linear Thermal Expansion @73 Fin/in/F3.5E-05
Dielectric Strength, Short TermVolts/mil500
Water Absorption 24 hours% by weight0.00

 

Applications of PCTFE

 

There are two main qualities that direct PCTFE’s application usage: water resistance and chemical stability. PCTFE films are used as a protective layer against moisture. Some applications include: moisture barriers in pharmaceutical blister packaging, protection of LCD panels, cryogenic seals and components.

When it comes to chemical resistance, PCTFE acts as a protective barrier for coatings and prefabricated liners. It is used for laminating other polymers like PVC, Polypropylene, PETG, APET and more. It can be found in transparent eyeglasses, tubes, valves, chemical tank liners, O-rings, seals and gaskets.

 

Common Applications

  • Aerospace Applications
  • Food Coating Films
  • Instrumentation
  • Seats
  • Valves
  • Films
  • Fluid Handling Systems

 

AIP Machining Capabilities: Unrivaled Expertise

 

We machine various grades and brand name PCTFE, including the following:

  • NEOFLON® / KEL-F®

 

Our close ties with the industry’s leading plastics manufacturers give us even further insight and access to technical help in material selection, sizing and manufacturing procedures. Whatever your application, our machinists can help you in material selection, sizing and manufacturing techniques from concept to completion.

 

Machining PCTFE

 

Annealing PCTFE

As with any CNC machined part, annealing and stress-relieving is crucial to the machining process. Coolants, lubricants and trained procedures prevent cracking and crazing in a precision machined component. We recommend slow heating and cooling during the annealing process of thermoplastics. This reduces the chances of these stresses occurring from the heat generating during machining polymers like PCTFE. Our AIP machinists use computer controlled annealing ovens for the highest quality precision temperatures and time control.

 

Machining PCTFE

PCTFE and other fluoropolymers are known for their dimensional stability – PCTFE has a melting point temperature of 419oF and a continuous use temperature of 250oF. However, once it reaches elevated temperatures, it will start to decompose. For the best results, use sharp tools, avoid excessive clamping and cutting forces and use coolants to prevent overheating. We recommend non-aromatic, water-soluble coolants because they are most suitable for ideal surface finishes and close tolerances. These include pressurized air and spray mists. Coolants have the additional benefit of extending tool life as well.

 

Some companies machine both metals and plastics, which has detrimental outcomes for machined polymer products. Many past experiences have shown parts going to customer without cracks, only to develop surface cracks and warping over time due to exposure to metal machine shop fluids. Be sure to use a facility like AIP that only machines polymers.

 

Preventing Contamination

Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace and medical sciences. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics with any sub-manufactured metalwork processed outside our facility. This allows us to de-risk the process from metallic cross contamination.

 

 

PCTFE Machining Guide: Supportive Information

 

Quality Assurance Certifications
Chemical Resistant Materials

 

Looking for innovative, high-performance thermoplastics designed to perform in hostile, critical environments? Here’s 7 Thermoplastics We Recommend.

 

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The last step in finishing a part is to apply an appropriate finish. Finishing a machined part can be as simple as smoothing off the burrs and other sharp edges or painting and coating the material to improve aesthetics and functionality. In the initial design phase of your project, talk to your machinist about the finishing processes to get a highly precise and extremely resilient piece.

 

AIP has over 37 years of experience machining complex components from thermoplastics. In this technical blog, we discuss putting the finishing touches on your CNC machined part, including: finishing, deburring, painting and polishing.

 

Common Finishing Techniques for CNC Machining

 

As Machined

The “as machined” part is the standard finish for the material. Many times, it has visible tools marks, but it has no additional cost to the machining process. Also, this finish has the tightest dimensional tolerances. Our standard AIP machined finish has almost no tool marks – we go the extra mile for our customers to produce unparalleled results. Taking pride in our craftsmanship and attention to detail is what makes us stand out from other CNC machine shops in the industry.

 

Deburring

Deburring involves the removal of burrs and sharp edges. A variety of tools may be used including die grinders, deburring scrapers, files and various stones.

 

Painting

Painting a finished part fulfills two requirements: 1) improves appearance (aesthetics) and 2) enhances the function of the piece.

 

Various coatings and treatments provide protection and add color to the surface of machined parts:

 

  • Plating: Chrome plating, nickel plating and other kinds of metal can be applied via plating processes.
  • Painting: Resins generally come in many different colors and can be painted to fit the exact specifications of a project.
  • Powder Coating: Powder coating adds a wear and corrosion finish to the surface of a part. It has a higher impact resistance compared to anodizing and a large range of colors are available.
  • Silk Screening: This is an inexpensive way to print text or logos on the surface of a CNC machined part. The print can be applied only to external surfaces on a part.

 

Polishing

There are several different types of polishing to finish off a machined plastic part. Here are a few of the most common methods:

 

  • Vibratory Polishing: This method uses rotating or vibrating tumblers along with a variety of media to deburr, remove tooling marks and polish parts. It is convenient for large bulk items that need polishing. Put them in a tumbler and go do something else.
  • Bead Blasting: This process uses compressed air to blast an abrasive media at the material. This method is done inside of a blast cabinet. It adds a uniform matte or satin surface finish on a machined part and removes all tool marks.
  • Filing: Filing down the edges or burrs on a small machined part is a craft, however, a good file offers efficiency. This technique is often taught to apprentice machinists.
  • Stoning: Machinists use stones and oil to deburr and knock off sharp edges that tear and snag.

 

Case Study: Making a Splash with Machined PPS

 

The finishing plays a major role in the quality, durability and utility of a machined plastic part. For our client in the theme park business, it meant reducing a water ride’s overhauls by 25 times.

 

When a popular ride experiences downtime, the negative impact on guest satisfaction is immediate. Lost interest and value in a park experience can mean loss of customers and in effect revenue. For our Florida theme park client, this was the case with their log flume coaster ride. While this ride was thrilling for its daily customers, the ride required nightly repair and part replacement. They specifically needed new wheel bushings from a more innovative material.

 

Since we had worked with this client previously, we were able to assess the project. The log flume’s passenger carts originally used bronze bushings due to their nice, soft wear, however, the speed and load of the carts generated a great deal of heat when the ride would plunge into its steep vertical drop. The moment each cart hit the cool water below, the wheel bushings would suddenly experience “shock cooling” damage.

 

Between this and the constant exposure to chemicals in the water (chlorine), the bronze bushings had a very short life cycle.

 

Our team selected Quadrant’s BG1326, a bearing-grade high-performance thermoplastic PPS.

 

PPS CNC Machining ExamplePPS has a low moisture absorption rate and can be machined to the exact tolerances necessary for clearing and shaft. With low-wear, high temperature stability and a low coefficient of friction, the chosen PPS grade proved to be an excellent fit for the log flume’s wheel bushings.

 

Our machinists at AIP worked diligently with the ride engineers to ensure the PPS bushings were built to exact specifications. The chosen method for machining the parts was precision machining. This way the components could meet the precise tolerances and finishes demanded by the speed and load of the log flume.

 

The Benefits

 

The main benefit of the machined PPS bushings was the reduction in ride downtime. The previous bronze bushings required around 25 times the overhauls of the new PPS bushings. The change in materials not only saved on maintenance and inventory costs, but improved guest satisfaction with the increase in uptime.

 

The PPS bushings also removed the potential for grease to affect seals or chemicals in the water. As a self-lubricating plastic, PPS removed the need for nightly greasing the wheel bushings. The lower energy cost of the PPS material also made for a more environmentally friendly and efficient design.

 

Preventing Contamination

 

Some companies machine both metals and plastics, which can open the door to contamination of a product. Although some sources state that most CNC machining tools can be used for both metal machining and plastic machining, this is not recommended. Past experiences have shown parts going to customer without cracks, only to develop surface warpage and cracks over time due to exposure to metal machine shop fluids.

 

Mitigate contamination by working with a facility like AIP that works solely with polymers. We ensure the highest level of sanitation down to the sub-molecular level by designing, heat-treating and machining only plastics. This allows us to eliminate the risk of metallic cross contamination.

 

Supporting Materials

 

Certifications and Regulatory Resources

 

We promise unmatched precision and unrivaled expertise at AIP.

 

Learn more about our capabilities and reach out to our machinists for a consultation on your precision machined project.

 

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