White Mountain Process is a supplier of mixing tanks and mixing vessels to support the industrial mixers and agitators we specialize. With focus on the biopharm and sanitary mixer users, we offer all stainless sanitary polished tanks, sanitary high viscosity blending equipment, and biotech ready tanks and vessels. We also offer FDA and USP VI plastic tanks and plastic tank mixer packages including stainless tank stands.

 

Typical sanitary mixing tanks include mechanical polish and electropolishing with cGMP documentation packages.

 

White Mountain Process specializes in custom fabricated sanitary mixing impellers in many configurations. Mixer and tank polishing, passivation, and electropolishing are services offered, as well as agitator impeller repairs and retrofits.

 
TYPES OF POLY TANKS AND METAL VESSELS FOR AGITATION

There are many choices when it comes to selecting a mixing tank or vessel material. This article will review the parameters typically used in selecting an appropriate tank and a summary of some producer’s recommendations for various materials of construction.

There are two main types of mixing tanks, plastic and metal. Plastic mixing tanks include High Density Polyethylene (HDPE), Polypropylene (PP), Polyvinylidene (PVDF) and Teflon (PTFE). Metal tanks are usually 304 Stainless Steel, 316L Stainless Steel, Hastelloy C and other exotic metals. We will be focusing on selecting tanks for sanitary or food grade applications which require approval from the FDA.

The main parameters considered in mixing tank or vessel selection are contents, corrosion resistance, volume, temperature, location, and other conditions. Plastic mixing vessles offer advantages over steel mixing tanks including cost, weight, rapid fabrication time compared to stainless steel, and the ability to see liquid level. Metal tanks are more resistant to cracking and temperature effects but they require polishing of the base metal and welds and so the cost to manufacture is typically much higher than plastic tanks. If you need pressure or vacuum rating then it’s an easy choice for a stainless steel mixing tank. Certain critical heating and cooling applications also would point to a jacketed stainless process vessel. Poly tanks in PP and PVDF are USP VI rated, so they are very common for use in DI and RO ultrapure water systems and biopharma mixing applications such as buffer prep, media prep, chrome slurry agitation, etc.

White Mountain Process www.wmprocess.com offers mixing and blending packages (mixer and tank system) in stainless steel or poly materials.

POLYETHYLENE – PE TANK
FDA Resin White Translucent
FDA 21 CFR177.1520
Linear PE tanks offer very good chemical resistance and stress-crack resistance. The operating temperature is from 140 F (60 C) down to -94 F (70 C). HDPE has good impact resistance and can be used for sanitary conditions. These tanks are typically used for caustics, metal finishing, plating, and brine. Strong oxidizing agents, aromatic hydrocarbons, and solvents should be avoided. PE we offer is an FDA approved resin.

Fluorinated PE tanks are often used for ultra pure water storage where ozone is used for sterilization. Cross linked PE is not typical for sanitary use so we generally do not offer that.

POLYPROPYLENE – PP MIXTANK
USP VI Resin White
Autoclaveable
Non Cytotoxic, USP VI and FDA 21 CFR177.1520
PP tanks offer very good chemical resistance and excellent stress-crack resistance. It’s operating temperature is from 220 F(104 C) down to 32 F (0 C). It only has a fair impact resistance and can be used for sanitary applications. PP tanks are good for many organic chemicals and etching chemicals. Strong oxidizing agents and aromatic or chlorinated hydrocarbons should be avoided.

KYNAR – PVDF PROCESS VESSEL
Polyvinylidene Tank
USP VI Resin
Great corrosion resistance and high temp, very high purity
Non Cytotoxic, USP VI and FDA 21 CFR177.1520
PVDF tanks offer superior resistance to inorganic acids, strong oxidizing agents and halogenated compounds. PVDF tanks also offer excellent resistance to stress-crack but only fair resistance to impacts. It has a temperature operating range of 230 F (110 C) down to -40 F (-40 C)

TEFLON – PTFE BLENDING VESSEL

PTFE tanks offer superior chemical and corrosion resistance. PTFE also has a wide range of temperatures from 260 C down to -270 C. PTFE is a excellent material for sanitary applications as it is inert but also is more costly. PTFE is not as strong as other plastics but can be obtained with fillers to increase its physical strength.

Mixer shaft/impeller are available with USP VI Teflon and ETFE coating.

304SS – STAINLESS STEEL TANK AND MIXER

304 Stainless Steel is used for pharmaceutical and chemical industries due to its high corrosion resistance. 304 SS tanks can be used at wide temperature ranges and have high physical strength but are more costly than most plastic tanks due to the higher material costs and the labor required to grind smooth the surface and especially welds.

316LSS – STAINLESS STEEL VESSEL AND AGITATOR

316L SS alloy has a higher corrosion resistance than 304 SS and has a higher operating temperature range. This material is resistant to strong acids so is used for more aggressive applications such as digesters, tanks, and evaporators.

HASTELLOY – GRADE B AND C AGITATED TANK

Hastelloy C is a nickel-chromium-molybdenum-tungsten alloy with superior corrosion resistance and is highly resistant to pitting and cracking. Hastelloy C can be used in a wide variety of applications including corrosive chemicals at elevated temperatures, flue gas scrubbers, and nuclear fuel reprocessing. This alloy has a high cost for construction and polishing.

The information above is an overview of different manufacturer’s specifications and guidelines. Specific manufacturer’s will have detailed information on their particular materials of construction and should be consulted to make your final determination for material selection. Please contact wmprocess.com 800-737-9619 for any questions.

GENERAL TYPES OF MIXING TANKS
1. Open top mixtank
2. Dust tight tank with lid, mixer will have sealed transition to vessel
3. Portable mixing tank on castors, can be poly or stainless
4. Closed tank with sealed agitator, typically a mixer lip seal or mechanical seal – any pressure or vacuum application would be stainless steel or metal tank
5. Multishaft / Multimotion agitation
6. Sanitary and/or Biopharma ready
7. More sophisticated automated blending system

Plastic Mixer Impellers
PTFE and POLY Plastic mixers and stirrers

Although stainless steel is the standard for mixer and agitator shaft and impellers, more users are specifying plastics such as Teflon and Polypropylene for their mixer impeller. Excellect corrosion resistance, sanitary in nature, and easy to clean are some of the reasons. A solid plastic shaft/impeller assembly is much more robust than a spray coating, so you can eliminate chipping and pinholes and equipment downtime. Teflon impellers are the most common, but also available are Kynar, Polypropylene, Polyethylene, and these can be supplied with USP VI and FDA grades of plastics. Biotechnology and Pharma users are finding the lightweight medical grade mixers are very accommodating to buffer prep, solution hold, and multiple use blend tanks.
It is very common to utilize all plastic on a mix tank system:
PROCESS VESSEL – plastic (PE or PP)
MIXER AGITATOR – plastic shaft/impeller (PE, PP, PVDF, PTFE)
MIXER STAND – can be plastic, or all stainless steel or painted steel

What is a Fluoroplastic or Fluoropolymer?
A group of plastic where the molecules contain carbon and fluorine which change the properties to include: high working temperatures, easy to clean, no stick characteristic, very high corrosion resistance to chemicals, acids, and solvents, and light weight which is good for portable mix vessels.

PE (Polyethylene)
Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene (IUPAC name ethene). The recommended scientific name polyethene is systematically derived from the scientific name of the monomer. The name is abbreviated to PE in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognized scientifically. Polyethylene contains the chemical elements carbon and hydrogen. PE is available in FDA resin and is commonly used on tanks, vessels, and mixing tanks.

PP (Polypropylene)
polypropylene PP is a lightweight plastic that offers relatively high purity characteristics at a price well below PVDF or PTFE. PP is similar to polyethylene but is lighter and offers even better heat resistance, tensile strength, abrasion resistance, and lower dielectric constant. Polypropylene is a thermoplastic polymer, used in a wide variety of applications. PP is unusually resistant to many chemical solvents, bases and acids. There are many manufacturers of extruded and blown polypropylene.

PVDF ( Polyvinylidene Fluoride )

PVDF polyvinylidene-fluoride PVDF is a high molecular weight thermoplastic polymer. PVDF is a very hard plastic roughly comparable to ECTFE, but relatively inexpensive in comparison to other fluoroplastics. Good chemical resistance, but not as good as ECTFE or ETFE. The most common base resins are Kynar® manufactured by Elf Atochem North America or Solef® manufactured by Solvay

PTFE (called Teflon) polytetrafluoroethylene Basic PTFE is a linear polymer of TFE and is a true homopolymer. Virgin (pure) PTFE is the most unusual and exhibits the best performance in terms of temperature resistance, chemical resistance, and non-stick properties. Its major disadvantage is that it does not actually melt when heated and therefore is difficult to process, and very unconventional techniques are needed to mold, extrude and weld it.

Modified PTFE polytetrafluoroethylene Modified PTFE is skived from a modified homopolymer PTFE resin containing some percentage of a fully fluorinated comonomer (usually PPVE). This chemically modified version of PTFE yields a material with improved electrical and physical properties over virgin PTFE. The result is a material that exhibits equivalent chemical resistance, increased tensile strength and greater elongation. Unlike virgin PTFE, conventional plastic techniques can be used to process this material (ie thermally bonding or fusing Modified PTFE to itself). Because of these properties Modified PTFE is often a lower cost alternative to other melt processable films (ie PFA and FEP). There are a variety of different resin manufacturers and different processor recipes available, but only three resin types have been found to be suitable for Thermal Impulse Heat Sealing. We recommend Modified PTFE skived from Dyneon TFM 1700 resin, DuPont NXT 70 resin or Daiken M-111 resin. Manufacturers of Skived Modified PTFE from these resins include DeWal Industries: DW 200 from Dyneon TFM 1700 resin, DW 220 from Dyneon TFM 1700 resin, and DW 201 from DuPont NXT 70 Resin.

Contact White Mountain Process www.wmprocess.com 800-737-9619 for details on tanks, mixers, or mixing impellers.