Choosing a Steel Coating for Wire Baskets: Halar® vs Teflon™ vs Plastisol

Specialized polymer coatings can do a lot to add to the utility and durability of a custom wire basket. With the right basket coatings, you can prevent damage to delicate parts during intense parts cleaning processes, minimize the risk of corrosion by keeping the chemicals from coming into contact with the bare steel, and prolong the useful life of an expensive precision-engineered custom wire basket.

However, it’s important to choose the right basket coating for the job. Picking the wrong coating can be a waste of time and money—and even make the basket actively worse at accomplishing the task it was built for.

So, a lot of Marlin’s customers ask us: “Is coating X better than coating Y?” The short answer is: “It depends on what the application is.” In this blog, we’ll take a look at when you should consider a specialized polymer coating for your stainless steel baskets and racks, when a coating is unnecessary, the different types of coatings and their advantages, and more.

QUICK LINKS

• Why Use a Coating on Your Stainless Steel Basket or Rack?
• Halar Coatings
• Plastisol Coatings
• Teflon Coatings
• When Not To Use a Coating
• Making Your Coating Choice + Comparison Chart

Why Use a Coating on Your Stainless Steel Basket or Rack?

“To coat, or not to coat?” That is the question for many manufacturers when they’re considering parts stainless steel part washing basket designs. In some cases, coatings can be unnecessary; in others, they’re vital to the design of the basket. With this in mind, let’s take a look at using coatings vs using a “naked” basket design.

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.

For example, if you have ultra-delicate parts or if avoiding metal-on-metal contact is a must, then a coating would be necessary for your parts washing basket—even when stainless steel would meet all other tolerance requirements.

The process of making a coated stainless steel adds time and material expenses but can be well worth it for certain applications. Generally speaking, it’s best to use a coating when the chemicals in the process would damage the base basket material, or when you need to prevent the metal of the basket from making direct contact with your parts for other reasons. Otherwise, using uncoated stainless steel is a perfectly viable option for most parts washing baskets.

What Are the Types of Coatings?

There are many different kinds of coatings and many different kinds of basket materials in need of coating protection. The three major types of coatings you may want to consider are Halar^®, Plastisol, and Teflon^™.

What Is Halar^®?

Halar^® is the brand name for a copolymer of ethylene and chlorotrifluoroethylene (ECTFE) that is sold by Solvay, 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, the material 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 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 it 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^®. It can, at most, withstand up to 300° F of heat before failing. As such, it is not recommended for high-temperature sanitation processes.

Read about how Marlin Steel built Halar®-Coated Steel Baskets for a Lens Manufacturer

What is Plastisol?

Plastisol is a unique material because of how variable its properties are depending on the specific mixture used and how it is applied to a basket. Using additives, it is possible to customize Plastisol in a variety of ways, changing its:

• Texture
• Color
• Hardness
• Rigidity
• Flexibility
• Temperature Resistance

For example, the hardness of Plastisol can vary between a rating of 35A to 95A on the durometer scale (basically, from the hardness of a pencil eraser to the hardness of plastic skateboard wheels). Even at its hardest, Plastisol coatings aren’t especially tough. This makes Plastisol a popular coating for ultrasonic cleaning processes, where a semi-soft surface can be useful for minimizing the risk of scratching parts.

Likewise, the maximum use temperature of Plastisol can vary. Some formulations of this basket coating have a maximum use temperature of ~200 ˚F (93 ˚C), while others can take up to ~300 ˚F (148 ˚C). If oven-like temperatures are an issue for your manufacturing process, you may want to specify which formulation of Plastisol you need, or even go with a more temperature-tolerant basket coating.

There are two general methods of applying a Plastisol coating to a custom wire basket:

1. Dipping Baskets in Liquid Plastisol. Here, a basket (or other metal form) is dipped in a bath of liquid Plastisol. The Plastisol coating sticks to the item being dipped, forming a thick and soft coating. This is often used for tool handles in home applications. These coatings only cover the parts of the basket that were submerged in the Plastisol, creating a clear “dip line.” This method is not preferred for fine wire mesh, since it can cause webbing and messy drip marks.
2. Fluid Bed with Powdered Plastisol. Instead of dipping a basket in liquid Plastisol, the fluid bed process takes a heated basket and dips it into powdered Plastisol (or a cloud of ionized Plastisol power, which is called the electrostatic fluidized bed coating process). This method tends to create a much thinner coating than the dipping process (being 15-20 mils, or 0.015” – 0.020”), which minimizes the risk of webbing. Also unlike dipping processes, fluid bed processes tend to coat the entire custom wire form—which is ideal for applications where the basket will be completely immersed in water or other chemicals.

What is Teflon^™?

Teflon^™ is basically a household name at this point, famous for being used in home cookware as a nonstick coating. The thing is, the term Teflon^™ covers several different coatings:

• Polytetrafluoroethylene (PTFE)
• Fluorinated Ethylene Propylene (FEP)
• Perfluoroalkoxy (PFA)
• Ethylene-tetrafluoroethylene (ETFE, or Tefzel®)

Each of these polymers under the Teflon^™ brand name has different characteristics, so generalizing can be a bit difficult. However, some common characteristics of these Teflon basket coatings are that they tend to be very porous, have nonstick properties, and are typically applied in very thin layers—around 0.5 – 5 mils (0.005” – 0.050”) thick.

The most common types of Teflon^™ coatings applied to custom wire baskets tend to be PTFE and FEP. What is PTFE and FEP? These are Teflon basket coatings with exceptionally high-temperature tolerances compared to most other polymers—FEP can take temperatures up to 400 ˚F (204 ˚C) and PTFE can withstand temperatures up to 500 ˚F (260 ˚C); in fact, the melting point of Teflon PTFE is actually 620˚F! This makes both of these coatings more suitable for high-temp applications than Plastisol.

These coatings also tend to be and fairly hard—for example, FEP coatings rank 56 Shore D on the durometer scale (about as hard as a cart’s caster wheels). It should be noted that other formulations of Teflon^™ (like PFA and ETFE) are harder than this on the durometer scale. So, if your manufacturing process involves high temperatures and some rough treatment of the basket, then Teflon^™ basket coatings may be your best option. The temperature tolerance and durability of these coatings help to ensure a long useful life in oven-like conditions.

Because Teflon^™ coatings are so porous, they aren’t generally preferred for total immersion applications, like ultrasonic cleaning, since chemicals can seep into the cracks to attack the basket being coated directly. However, ETFE, or Tefzel®, is sometimes used for immersion purposes because of its thicker coating layer.

It’s important to note that Teflon^™ 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.

Read more about the specific characteristics of PTFE, FEP, PFA, and ETFE Teflon basket coatings.

When Not To Use a Coating on Stainless Steel

Stainless steel alloys such as grade 304 and grade 316 stainless steel possess a number of positive qualities when it comes to temperature/chemical resistance, tensile strength, and surface hardness. These qualities tend to make stainless steel an excellent choice for parts washing baskets in numerous applications.

The right stainless steel alloy can outperform certain coating materials in specific performance categories such as temperature or abrasion resistance, making them useful with or without a specialized coating.

That being said, some of the more specialized alloys of stainless steel can be prohibitively expensive compared to using a specialized coating with a less rare alloy.

So, stainless steel vs Teflon and other coatings: when is using uncoated stainless best? Generally speaking, uncoated stainless steel is best when the alloy of steel being used for your basket meets or exceeds all of the tolerances needed for your parts washing processes. No-coating is a cost-effective option that many of Marlin’s clients have used in the past to fulfill their parts finishing needs.

Making the Choice Between Coatings + Comparison Chart

Picking out a specific fluoropolymer coating for your wire forms is difficult to do based on broad general information. The specific plastic that you will want to use will vary depending on a number of factors, such as the temperatures that your wire frame will be exposed to, your abrasion resistance needs, the specific chemicals that the coating will be exposed to, and whether or not total immersion will occur, among other variables. 

The coating comparison chart provides a very basic overview of each type of steel coating.

Remember, there are different formulations of these coatings that can change these generalized properties so you’ll want to speak with one of our experts about your specific industry and needs to determine which coating is right for your metal baskets and racks (and if you even need a coating).  

In addition to coating formulations, there are a number of other variables that could exist in your washing process, so it is important to look at each application individually. At Marlin Steel, we work with various coating manufacturers to get our clients exactly what they need for their specific applications. We recently worked with a medical client who wanted PT-801, a very specific type of specialized Teflon^™ coating. We were able to accommodate the request through our manufacturing partnerships and deliver the final products quickly. We can do the same for you! Contact Marlin Steel today to learn more.