Investment Cast Stainless Steel Pump Impeller

The most common method is investment casting (also known as lost-wax casting); 90% of industrial stainless steel impellers are manufactured using this process.

Investment casting falls into two categories:

1. Silica sol investment casting (the preferred choice for pump impellers)

Applications: Chemical pumps, sanitary pumps (food/hygiene grade), magnetic drive pumps, corrosion-resistant impellers (316/duplex steel), and closed impellers with complex, twisted vanes.

Impellers produced via this process offer superior surface finish and dimensional accuracy; flow channels can be mirror-polished, and complex twisted vanes or narrow channels can be formed in a single step. Impellers made using this process result in higher pump efficiency.

2. Water glass investment casting (for mid-to-low-end pump impellers)

Applications: Standard inline pumps, self-priming pumps, and 304 stainless steel impellers.

While the precision and surface finish of water glass investment-cast stainless steel impellers are slightly lower than those produced via silica sol casting, the cost is lower, making this method ideal for mass-producing economical impellers.

(Our company offers both of the aforementioned processes)

3. Others

There are other niche casting processes: for example, lost foam casting is suitable for very large-diameter impellers with simple structures produced in smaller batches.

Centrifugal casting is suitable for thick-walled, hub-style impellers.

There are many materials available, but the three mainstream options are CF8 (304), CF8M (316), and 2205 duplex stainless steel. The primary differences among these three lie in their molybdenum (Mo) content and nitrogen (N) content. Mo provides resistance to chloride-induced pitting and crevice corrosion, while N significantly enhances strength as well as resistance to pitting and stress corrosion cracking.

1. 304

304 stainless steel contains no Mo and lacks resistance to media such as saltwater, dilute sulfuric acid, and phosphoric acid.

Applications: Fresh water, purified water, drinking water, food and beverage processing, and neutral, salt-free media at ambient temperatures.

Grades: 1.4301, CF8, 06Cr19Ni10

2. 316

316 contains Mo, offering resistance to chloride ions and suitability for mildly acidic or alkaline media. Pitting Resistance Equivalent Number (PREN) ≈ 25.

Applications: Printing and dyeing wastewater, electroplating wastewater, intermittent seawater exposure, mildly saline sewage, boiler feed water, chemical pumps, and pharmaceutical pumps.

Grades: 1.4401, CF8M, 06Cr17Ni12Mo2

3. 2205 Duplex Stainless Steel

2205 features higher levels of both Mo and N, providing exceptional resistance to chloride-induced stress corrosion cracking. With a PREN ≈ 36, it offers superior resistance to crevice corrosion, erosion-corrosion, and cavitation.

Applications: Seawater, coastal sewage, high-pressure pumps for corrosive chemicals, pulp bleaching, and high-temperature saline circulating water; impeller service life is more than three times that of 316.

Grades: 1.4462, CD3MN, 022Cr22Ni5Mo3N