Welding PVDF

Pol5winylidene fluoride can be welded by all standard welding techniques. Detailed instructions on welding conditions can be obtained by referring to Ref. 41. 

Welding is carried out in successive passes in order to completely fill the bevel. In order to equalize as much as possible the stress which will occur 

With extrusion welding, the support is prepared (beveled or preferably double beveled) and preheated using a hot air gun to reach a surface temperature of 250°C-260°C. The molten extrusion (maximum length— 20 cm) is pressed into the bevel using stainless steel or PTFE coated tools. 

The weld factor, which is generally defined as the relation between the strength of the weld and the strength outside the welded zones, determined by tensile stress tests, will give values between 0.7 and 

In the extrusion welding technique, the mating parts are heated by pressing onto a metal heater which is held at 250°C-270°C and which has been surface-treated (usually with PTFE) to minimize adhesion. For butt welding, the heater is a flat plate for spigot and socket welding, there are male and female surfaces. The ideal pressure on the hot surface is 50-60 kPa, and the time should be sufficient for the fusion of the material to a depth of 4-5 mm at the contact surface. The heating unit is removed and contact is made under a pressure of ideally 0.06 to 

---

Other configurations are commercially available. PVDF has a use range from -40 to 302°F (150°C). PVDF has a high tensile strength, flex modulus, and heat deflection temperature. It is easily welded, resists permeation, and offers a high-purity smooth polymer surface. This is the polymer of choice for high-purity applications such as semiconductor, bioprocessing, and pharmaceutical industries. 

Parts from PVDF can be machined, sawed, coined, metallized, and fusion bonded more easily than most other thermoplastics. Fusion bonding usually yields a weld line that is as strong as the part. Adhesive bonding of PVDF parts can be done epoxy resins produce good bonds.24 Because of a high dielectric constant and loss... 

PP, PVDF, and PE are not jointed using solvent cements, but the weld regions contain relatively high levels of intrinsic stress caused by the thermal fusion process. Chemical stress cracking could occur at these welds if exposed to certain chemicals. When performing material compatibility tests for any... 

PVDF, however, has been used primarily in water systems that operate at ambient temperatures. There is some skepticism in the use of PVDF in hot (176°F) WFI distribution loops, mainly because it has been observed that exposure to heat will discolor the material. The discoloration is the result of alterations to the chemical structure of PVDF on the atomic scale. Testing of piping samples revealed that leaching was insignificant and welds remained strong after 1 to 16 week exposures to hot ultrapure water. 

Temperatures required to adequately produce a molten layer of the surfaces vary from 210°C-290°C. Welds may be particularly susceptible to stress cracking in strongly alkali solutions where discoloration develops as a result of dehydrofluorination. VF2/ HFP fluoropolymers exhibit improved resistance to a high pH environment, where PVDF homopolymers have been known to become brittle over time. 

Adhesive- bonded Synthetic and glass backed PVDF(60, 90, 118 mils) ECTFE (60, 90) Glass backed ETFE (60, 90 mils) PTFE (80, 120 mils) FEP ( 60, 90 mils) PFA (90, 110 mils) MFA (60, 90 mils) Contact or thermosetting adhesive Weld rod and Cap strip welds Shop or field Pressure OK Full vacuum up to 120°F (49°C) Max Temp 275°F (135°C) None Visual Spark Possible Testing recommended... 

PVDF parts are easily welded using spin welding. Welding data for 25 mm diameter, 1.9 mm thick pipes are as follows ... 

Ultrasonic welding can be used to weld parts made from all grades of PVDF including copolymers or alloys, reinforced or not. The standard pro-... 

Based on the principle of dielectric loss, induction welding is particularly suitable for high-loss thermoplastics such as PVC. However, by adapting certain measures, PVDF films from 10 to 50 pm can be welded. 

The mechanical testing conducted on high-quality infrared welds has shown that the welding factors achieved for PVDF when tested at -40°C were greater than 0.9. 

PVDF parts can be welded using a PVDF powder base bonding agent, dissolved in a polar solvent such as dimethylformamide. This technique, which at first sight appears easy to apply, nevertheless has certain disadvantages. 

PVDF pipe liners and tubes can be butt-welded in a similar procedure to the one used for PFA (Sec. 

Top finishes are formulated using clear acrylic, acrylic/vinyl or acrylic/ polyurethane resins and are applied at a thickness ranging from 0.1 mm to 0.4 mm. Other top finishes on a base of fluorocarbonpolymers, e.g. PVDF, PVF or FEP, are applied within a range of 1.0-1.5 mm. If the top layer is applied as a foil, e.g. 0.03 mm PVF foil, it will give better protection than would a top coat applied in liquid form, because the surface will be more effectively sealed against environmental impact. If weldable textiles or foils are welded together, the non-weldable top coats have to be removed from the welding area. If not done properly, this already critical zone is left partly unprotected. 

Resistance to weather and chemicals thermoformable stain resistance cleanability. Ability to solvent cast very thin, pigmented formulations onto carrier films, creating extremely smooth surfaces. Extruded films also Chemical resistant and ease of forming relatively thick coatings from liquid systems. Extruded PVDF tubing and sheet easily thermoformed. Bead welding with PVDF rod to form seamless joints in liners... 

In computer-controlled machines, sensors continuously monitor the three parameters— rotational speed, axial pressure, and weld time—in addition to the weld penetration, weld or penetration veloeity, and interfacial torque. For reprodueible results and eonsistent weld strength, proeess monitoring is reeommended. Figure 14.24 is a sensor output traee obtained during welding ofpolyvinylidene fluoride (PVDF). Axialpressure and rotational speed were set at 4.3 MPa and 3500 rpm, respectively. 

Figure 14.24 Sensor output data from computer-controlled monitoring of the spin welding of PVDF. When rotational speed reaches its set value, axial pressure is engaged, and weld penetration begins. Interfacial torque, penetration velocity, and weld penetration are monitored throughout the spin welding cycle.

Ultrasonic welding can be used to weld parts made from all grades of PVDF including copolymers or alloys, reinforced or not. The standard procedure for crystalline polymer welding by ultrasonic techniques (geometry of weld joint, type of booster, and horn) can be applied for all elements made from PVDF.I" ]... 

---