Parts washing is a critical part of many manufacturing processes. Failure to clean parts can result in manufacturing waste such as oil or metal shavings being left on parts, compromising the surface condition of the part and leading to a shortened useful life.
However, many parts washing processes can be harsh on delicate parts, which is why so many industrial parts washing baskets incorporate a coating of soft plastic to better protect said parts. In addition to protecting delicate parts, a plastic coating can also protect the basket itself from the chemicals used in a parts cleaning process, enhancing the useful life of the basket.
There are many different plastic compounds used to coat parts washing baskets. Two of the ones that Marlin Steel’s clients most frequently ask about are Teflon® and Halar.
So, which of these two brand-name fluoropolymers is the best for your parts cleaning application?
Both are durable polymers used for a variety of applications such as nonstick cookware or as aviation materials. Here’s what Marlin’s engineers and experts in the plastic coatings industry have to say about these two materials:
Teflon® and its Benefits
Teflon® is a Chemours brand name that covers four different types of fluoropolymers:
- Polytetrafuoroethylene (PTFE)
- Fluorinated Ethylene Propylene (FEP)
- Perfluoroalkoxy (PFA)
- Ethylene-tetrafluorethylene (ETFE), also known as Tefzel®.
Teflon® polymer compounds have several strengths.
First, Teflon® has a strong resistance to chemical corrosion. This allows Teflon®, and any baskets coated in it, to better survive exposure to harsh chemicals for longer without corroding.
Additionally, PTFE and FEP-type Teflon® coatings have excellent nonstick properties. This is useful in preventing chemical buildup from sticking to the basket, reducing chemical wear and tear.
Beyond their nonstick properties, PTFE and FEP fluoropolymers also have a very high resistance to heat exposure compared to other plastics. For example, FEP can withstand temperatures up to 400° F, while PTFE coatings can take temperatures up to 500° F.
Drawbacks to Using Teflon®
Teflon®, as a coating for parts washing baskets, has a few limitations.
First, the application methods used for Teflon® tend to leave a very thin layer of material on the basket. How thin? A typical coating of Teflon® is only 0.5 to 5 mils thick, or 0.0005” to .005”.
Furthermore, Teflon® coatings are porous, leaving many microscopic holes in the coating. Because of this, Teflon® is not generally recommended for use in parts washing processes that involve complete immersion of the basket in liquid. However, ETFE, or Tefzel®, is sometimes used for immersion purposes because of its thicker coating layer.
Finally, Teflon® coatings can be an expensive solution for coating a basket compared to similar coating materials. However, the cost is well worth it for the temperature tolerance and corrosion resistance of PTFE and FEP Teflon coatings.
Halar and its Strengths
Halar is the brand name for a copolymer of ethylene and chlorotrifluoroethylene (ECTFE) that is sold by Solvay Solexis, a Belgian chemical company. This polymer has several key strengths:
- Halar possesses excellent chemical resistance. In fact, against oxygen, carbon dioxide, chlorine gas, and hydrochloric acid, Halar is 10 to 100 times more effective as a barrier material than FEP or PTFE. Additionally, Halar is water-phobic, absorbing less than 0.1% of its weight in water when submerged.
- Halar can be applied in a much thicker coating than Teflon. Typical Halar coatings range from 5 to 60 mils (0.005” to 0.06”) in thickness, making them several times thicker than a Teflon coating. However, the thickness of a Halar coating is limited by the thermal mass of the object being coated.
- Halar has a low dielectric constant in a variety of temperature environments. This dielectric strength is about 80 kV/mm in 0.025mm-thick coatings.
- Unlike FEP and PTFE, Halar has an exceptionally smooth, non-porous surface. This helps to reduce the proliferation of bacterial colonies on Halar surfaces, making it ideal for the medical and food industries.
- The tensile strength of Halar at yield is about 32 megapascals (4,700 psi) at room temperature. To break Halar in room temperature conditions takes 45 MPa (6,600 psi) of force. However, extreme temperatures will reduce these values.
Because of the thickness of a Halar coating, there are much fewer pores that would allow a chemical to reach the surface of the object being coated, meaning that it is safer for parts cleaning applications that involve totally immersing the basket.
The major limitation of Halar compared to PTFE and FEP Teflon polymers is the comparatively low temperature resistance of Halar. Halar can, at most, withstand up to 300° F of heat before failing. As such, it is not recommended for high-temperature sanitation processes.
Overall Uses of Teflon® and Halar
As a general rule, PTFE and FEP Teflon polymers are applied as a thin film (0.0005” to 0.0030” thick) for use in nonstick applications. PFA can be applied as either a thick or a thin film for both nonstick and corrosion resistance applications. ETFE is applied most often as a thick film (0.010” thick or thicker) for corrosion protection when the basket will be immersed in liquid for a long period of time.
Halar, like ETFE, is applied as thick film for corrosion protection in immersive parts washing applications. Halar coatings are often recommended for high-purity applications because static soak tests in both ultra-pure water and high purity chemicals have shown extremely low levels of metallic and organic extractables coming from Halar coatings.
Most plastics experts caution that many variables might affect the performance of a given plastic coating: temperature, concentration of chemical agents, length of time exposed to certain chemicals, etc.
Because coatings vary in hardness, chemical resistance, and abrasion resistance, it is important to examine your application for the parts washing basket in detail before selecting a specific coating.
Find out how to choose the right materials and coatings for your parts washing basket by reading the free guide at the link below: