What are Filter Plates Made From? A Look at Different Types of Filter Plate Materials

What Are Filter Plates? 

Filter plates are one of the most critical components of a filter press system, responsible for supporting the filter media and creating the pressure-resistant chambers where liquid-solid separation takes place. These plates form the structure of the press, working together to capture solids while allowing liquid to pass through. This process is commonly used in industrial dewatering and slurry filtration.

In operation, slurry is pumped into the press and pressure forces the liquid through the filter cloths mounted on the plates, trapping solids inside each chamber. The result is a collection of filter cakes (compacted solids) and a clear filtrate that can be reused or further processed.

The material composition of filter plates plays a direct role in the performance, efficiency and lifespan of the filter press system. Different plate materials offer varying levels of chemical resistance, mechanical strength and thermal stability. 

Common Materials Used to Make Filter Plates

Filter plates come in a range of materials to suit different compatibilities, pressures and temperatures. The selection of the filter plate material is heavily dependent on the application and process parameters. It is important to understand the benefits of each filter plate material because choosing the right one ensures optimal performance, longevity and cost-effectiveness of the filtration system. Here is an overview of four popular filter plate materials, including what they’re made of, their key benefits and ideal applications.

 
1.    Polypropylene (PP)

Polypropylene is a lightweight thermoplastic polymer known for its chemical resistance, especially against acids, alkalis and solvents. Polypropylene plates are typically produced via injection molding or compression molding, yielding a smooth, inert surface. It is considered the standard plate material and is used in many applications. 

Advantages: 
•    Optimal corrosion resistance in pH 2-12 environments
•    Low density (≈900 kg/m³), reducing handling weight
•    Cost-effective for moderate-duty filtration
•    Good electrical insulator 

2.    Polyvinylidene Fluoride (PVDF)

PVDF is a robust, high-performance fluoropolymer offering superior chemical and thermal stability compared to polypropylene. PVDF plates are semi-crystalline, with a slightly higher density (~1780 kg/m³) and can withstand elevated temperatures. It is ideal for applications involving high acidity, elevated temperatures and low pH levels.

Advantages:
•    Broad chemical resistance, including chlorinated solvents and oxidizers
•    Service temperatures up to 150 °C (302 °F)
•    Optimal mechanical strength and dimensional stability
•    Low permeability to gases and liquids

3.    Stainless Steel

Stainless steel is an alloyed steel (typically grades 304 or 316) that combines iron, chromium and nickel. Stainless steel plates are usually cast, welded or machined, providing robust structural integrity and high pressure ratings. It is commonly used in applications that have elevated temperatures, high chemical aggression and are required to withstand pressure higher than 15 bar. 

Advantages:
•    Optimal strength and pressure resistance 
•    Excellent wear, abrasion and corrosion resistance
•    Fully recyclable and easy to clean

4.    Cast Iron

Cast iron is an iron-carbon alloy (usually 2-4% carbon) known for its rigidity and vibration-damping properties. Cast iron plates are manufactured via sand-casting or shell-molding, and they are typically coated with a rust-inhibitive coating. This material is commonly used in applications that have elevated temperatures and need to withstand high pressure and corrosion. 

Advantages: 
•    Excellent compressive strength and durability
•    Vibration resistance, reducing plate fatigue
•    Heavy mass helps stabilize large filter stacks
 

How to Choose the Right Filter Plate Material

Selecting the appropriate filter plate material is crucial for ensuring efficient filtration performance, equipment longevity and compliance with industry standards. The choice depends on a variety of factors including the type of slurry, chemical compatibility, operating conditions and applicable regulations.

The characteristics of the slurry, such as particle size, abrasiveness and solids concentration, play a central role in determining the right filter plate material. For example, highly abrasive slurries may rapidly wear down softer materials like polypropylene, making more robust options like stainless steel or cast iron a better choice. However, slurries that contain fine or sticky particles often require smooth, non-stick surfaces such as those found in PVDF plates. These plates can resist clogging and aid in easy cake release. 

The chemical makeup of the slurry is another critical consideration when choosing a filter plate material. Slurries that contain corrosive or reactive chemicals demand materials that can resist degradation. For example, polypropylene is a popular choice for general chemical resistance but may degrade under prolonged exposure to strong oxidizers and certain solvents. If the application requires a material that offers superior chemical resistance and is suitable for aggressive acids and solvents, PVDF would be the ideal option. Stainless steel can handle many chemicals but does not fare well in the presence of chlorides or low pH environments. While cast iron plates provide lasting durability, they are generally not recommended for corrosive applications due to their susceptibility to chemical corrosion. 

Filtration processes often operate under high pressure and elevated temperatures, which can exceed the capabilities of some materials. Polypropylene has moderate temperature tolerance (up to approximately 90 °C/194 °F) and performs well in environments with low or medium pressure. PVDF can handle higher temperatures (up to approximately 150 °C/302 °F) and maintains structural integrity in more demanding conditions. Stainless steel and cast iron, both known for their strength and thermal stability, are well-suited to applications with high pressure and temperature. They are commonly used in heavy-duty industrial settings. 

It is also important to consider industry regulations and requirements regarding contamination control and material certifications. In the food and beverage industry, materials must comply with your region’s regulatory governing body, such as the FDA or EMA. In some regions, polypropylene or stainless steel are often required to ensure product safety and prevent contamination. The pharmaceutical and biotech sectors usually require high-purity materials, making PVDF a preferred option due to its compatibility with stringent chemical standards. Industries that prioritize mechanical strength and abrasion resistance, such as mining and heavy manufacturing, typically favor steel or cast iron plates. Additional protective coatings may be applied to filter plates for increased longevity. 

Overall

Filter plates are an essential component in many industrial filtration systems and play a key role in liquid-solid separation. Choosing the right filter plate material is crucial for ensuring efficient, reliable and compliant filtration. Whether it’s the chemical resistance of PVDF, the durability of stainless steel and cast iron or the versatility of polypropylene, each material offers distinct advantages depending on the demands of your application. It is important to carefully consider factors such as the characteristics and chemical makeup of the slurry, operating pressure and temperature and industry-specific regulations so you can make an informed decision that supports both performance and longevity in your filtration system.