PVDF Plastics Material for Nozzle

Is improper nozzle material costing your time and money?PVDF nozzle material for food, chemical etching and electronic industries

Key IssuesNozzles are mechanical devices that are used to control the fluid flow characteristics when they enter or leave an enclosed pipe or chamber, through an orifice. The various fluid flow characteristics that need to be controlled are mass and rate of fluid flow, direction, shape, pressure and the speed of the fluid. Nozzle are also used for dispensing various media such as powder, steam, abrasives, adhesive, water chemical, coolants, coating, ink, lubricants. They may look simple enough, but spray nozzles are highly engineered precision components that can wear over time or suffer damage during normal operations or even cleaning. There are several factors to influence or shorten the nozzle operating life, sometimes more than one at the same time : 1) Erosion/ Wear : Nozzle wear is indicated by an increase in nozzle capacity and by a change in the spray pattern, in which the distribution (uniformity of spray pattern) deteriorates and increases drop size. Choice of a wear resistant material of construction increases nozzle life. Because many single fluid nozzles are used to meter flows, worn nozzles result in excessive liquid usage. 2) Corrosion : spray nozzle material can break down due to the chemical properties of the sprayed material or the environtment. The effect is similar to that caused by erosion and wear, with possible additional damage to the outside surfaces of the spray nozzle. Corrosion is material related and caused by chemical attack. There is a very wide range of materials from which nozzle can be made and the proper selection of the nozzle material will minimise problems. 3) Exposure to high temperature : Melting or softening of nozzle material establishes maximum temperature limits. However, these limits must be reduced when corrosion, erosion, oxidation or chemical attack are also present in the given application 4) Caking/ bearding : build-up of material on the inside, on the outer edges or near the orifice is caused by liquid evaporation. A layer of dried solids remains and obstructs the orifice or internal flow passages. 5) Clogging : unwanted solid particles can block the inside of the orifice. Flow is restricted and spray pattern uniformity disturbed. 6) Accidental damage : damage to a nozzle orifice can occur if a spray nozzle is dropped or scratched during installation, operation or cleaning 7) Improper re-assembly : some spray nozzles require careful re-assembly after cleaning to ensure that internal components, such as gasket, o-rings and valves, are properly aligned. Improper re-assembly causes leaking and inefficient spray performance.

Selecting MaterialImproved reliability, proper performance and maximum wear life of a spray nozzle often begin with the correct material selection. Corrosion and erosion caused by abrasive wear are the most common factors that could lead to degradation of a nozzles performance. It is important to select the right nozzle material depending on the environmental conditions of the given process. Spray nozzles are generally made of such materials as bronze, stainless steel, or plastic. Brass (Bronze) is the easiest material for nozzle manufacturers to work with and is a common material, but bronze nozzles have insufficient resistance to abrasion at middle/high pressure, and limited resistance to corrosion by corrosive chemicals. Due to its relatively high abrasion and corrosion resistance, stainless steel is widely employed in nozzle manufacture. When the liquid to be sprayed or the surrounding atmosphere is corrosive however, spray nozzles made of SUS316 or SUS31L stainless steel, both of which have more resistance to corrosion, are more suitable. Relatively few types of spray nozzles are manufactured from plastic. Plastic nozzles are useful for spraying chemicals that corrode metal nozzles too quickly. Unlike metal, plastic materials do not display corrosion rates. That is the corrosion of plastic materials is dependent totally on the materials chemical resistance rather than an oxide layer, so the material is either completely resistant to a chemical or it deteriorates. Thermoplastics deteriorates is indicated by material softening, discoloration, charring, embrittlement, stress cracking, swelling, dissolving and other effects.

stainless steel and bronze nozzle

PVDF plastic nozzle

LEFT: Stainless steel full cone nozzle. RIGHT: same nozzle after spraying with limestone slurry. The erosion and corrosion occurred in less than 2 weeks, demonstrating the need for choosing the correct nozzle material to suit the conditions.

Wear Test

COMPARATIVE WEAR TESTTest Medium : 2.5 % kaolin in water

Ceramic : Highly resistant to abrasive and provides superior wear resistance in abrasive applications and high pressure. Ceramics have excellent corrosion resistance except in very high pH environments. Polyacetal POM (Polyoxymethylen) : Provide good resistance to alkalis, susceptible to high concentrated acids. Can be used in temperature +90 C exhibits a high thermal stability and high resistance to hydrolysis. POM shows good sliding properties and high resistance to wear and tear because of the strength and smooth surface. There is a very low risk of stress cracks. Polyvinyldene fluoride (PVDF) : Excellent resistance to strong acid and alkalis, good resistance to wear, resist many reagents and high temperatures (up to 130C), susceptible to high temperature above water boiling in combination with concentrated sulphuric and nitric acids. Preferred in industrial spraying applications. Stainless steel : Good resistance to chemicals and provide average wear resistance Brass (bronze) : Average resistance to most chemistry and poor wear resistance, susceptible to corrosion especially with fertilisers PEEK : is used to replace metals in harsh environments. This highest performance engineered thermoplastic offers excellent resistance to wear, chemicals, fatigue and high temperatures up to 320F (160C).

ApplicationMost nozzle are constructed of stainless steel, but some are made of plastic material such as POM, PVDF, PEEK.

PVDF NozzlesPVDF (polyvinyldene fluoride), the durable yet economical fluoroplastic that stands up to wear, heat, and corrosion. PVDF Nozzle for Food Industry In general, foods are not corrosive, but consumable foods like sauces and fruits can have pH ranges between 2.0 and 3.5, this can be very aggressive environment over time. PVDF plastics components are often machined and used in the processing of cranberry, hot sauces, alcoholic beverages, lime juices and a few other relatively common foods. The abrasion resistance of PVDF and its ability to be sterilized with various chemicals and steam also adds to the attractiveness of this material for food, dairy and beverage applications. PVDF is an extremely pure polymer, physiologically non toxic, and meets the european directive 90/128/EEC relating plastic material to contact with foodstuffs. It is particular suitable for high purity applications handling hot and cold water in the semiconductor, and pharmaceuticals industries.

PVDF Nozzle for Etching and Electronic Industry PVDF nozzles are especially suited to the spraying of acids during etching operations. And their high thermal stability makes them ideal for high temperature stripping operations. For spraying corrosive fluids or for operation in corrosive environtments. PCB (printed circuoit board) manufacturers are looking for nozzles to increase product yield. Nozzle made from PVDF material offer consistent spray patterns along with superior chemical resistance, capable of effectively spraying a variety of chloride, acid, basses, oxidizing agent and ammonia base etchants, these chemical resistance nozzles can withstand temperatures up to 300 F at 100 psi (149 C at 7 bar).

ConclusionPVDF is an outstanding choice as a nozzle material for many reasons: Chemical resistance PVDF is typically resistant to: most acids salts and weak bases, halogens and halogenated solvents, alcohols, oxidants, De-ionized water, UV and nuclear radiation. Temperature range PVDF can be used at temperatures as high as 285 F (140C) depending on the chemical environment and operating pressures of the system. Like most fluoropolymers PVDF is inherently flame retardant. Abrasion resistance PVDF is one of the most abrasion resistant fluoropolymers. In abrasion tests PVDF ranks with the best plastics and in most nozzle applications it will outlast many metals, PVC and PTFE. Mechanical strength PVDF is one of the most rigid fluoropolymers. PVDF's exceptional tensile strength allows nozzle construction without the thick sections normally associated with plastics, while allowing operating pressures normally available only with metallic materials. FDA acceptance PVDF is accepted by the FDA for use in a broad range of food and pharmaceutical applications where stainless steel was once the only choice.

PVDF PROPERTIES DATA SHEETStructure : Crystalline Specific density : 1.77 Water absorption rate (%): 0.03 Elongation at break (%): 50 Tensile strength (psi): 5800 Compression strength (psi): 10000 Flexural strength (psi): 7800 Flexural modulus (psi): 260000 Impact (Izod ft. lbs/in): 6.6 Hardness: R95 Deflection temperature (deg. F) - @ 66 psi: 300 (150 deg.C) - @ 264 psi: 190 (90 deg. C) Utilization temperature (deg. F) - min: -40 (-30 deg.C) - max: 310 (150 deg. C) Melting point (deg. F): 340 (170 deg. C) Coefficient of expansion: 0.000022 Arc resistance : 60 Dielectrical strength (kV/mm): 22 UV resistance : Good Chemical resistance : Excellent

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