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Polyphenylene Sulfide
34 Polyphenylene Sulfide 34.1 Heated Tool Welding
still permit good welding results. With higher additions, however, weldability deteriorates.
Ticona: Fortron
Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
This method is preferably employed for joints exposed to mechanical stress in service, large joint surfaces or part geometries that preclude the use of other welding methods. It is important to ensure that the heated tools used are designed for the high temperatures required. Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.2 Ultrasonic Welding Chevron Phillips Chemical: Ryton
Ryton PPS compounds are relatively easy to weld together. Joint design is, however, critical to the finished part strength. A shear joint is the best overall, although the step joint has been used successfully with Ryton PPS R-4. The shear joint will generally be six times stronger than the step joint. When welding shear joints, use high power with a high amplitude booster, low pressure, and slow horn speed. When welding the parts, caution should be used since too high an amplitude and/or too long an application time could destroy the part. Shear joints are usually not recommended for parts with a maximum dimension of 3.5 inches (89 mm) or greater, sharp 90° turns, or irregular shapes, due to the difficulty of holding the required molding tolerances. Ryton PPS may extend these limits, however, since it can hold tight molding tolerances. Reference: Ryton Design Guide, Supplier design guide, Chevron Phillips Chemical Company LP, 2004.
Ticona: Fortron
Fortron moldings can be joined by the usual ultrasonic assembly methods. Joints produced have high strength. Fortron is suitable for both near- and far-field ultrasonic welding. However, because of the relatively brittle-hard behavior of the material, it should be borne in mind that the alternating strains that have to be absorbed by the parts being joined can lead to localized damage. Additions of up to 40% reinforcing materials
LNP Engineering Plastics: OF1006 (material composiition: 30% glass fiber)
Polyphenylene sulfide, being a semi-crystalline thermoplastic, is not ideally suited to ultrasonic welding. In a semi-crystalline plastic the amorphous portions soften at a low temperature with a corresponding increase in mechanical loss factor, which results in more energy being needed to melt the crystalline portions. This phenomenon is reflected in the results of the weldability trials. The results of the weldability study suggest that joints can be formed so long as sufficient power is applied to the joint, that is, it is necessary to employ a high vibration amplitude and to contact the welding horn as close as possible to the joint. A projection joint has proved to be the most successful joint design. Far field welding is not feasible for this material. The ultrasonic welding of 30% short glass fiber filled PPS was studied using a 1500 W commercial ultrasonic welding machine. Projection and shear joints were used for weldability trials. The effect of the base fixturing material was investigated by comparing aluminum, Devcon and PTFE. • 30% short glass fiber PPS (grade LNP OF-1006) can be welded by ultrasonics in the near field. A high vibration amplitude, 80 μm (0.003 inches) and low weld force, 275 N (61.8 lbf), is required to ensure that sufficient heat is generated at the joint. Poor tolerance to variations in welding parameters means that critical optimization of welding procedures is required. • If ultrasonic welding is required, the quality of the injection molded component is of great importance. Defects in the molding, such as internal weld lines, affect ultrasonic energy transmission and can act as energy absorbers within the component. This results in damage to the specimen, either cracking or overheating, and poor joint quality as a result of insufficient energy availability at the weld line. 389
390
MATERIALS
• The fixturing material affects the weld quality. In the present trials, a PTFE fixture gave a wider tolerance to welding parameters and less scatter than aluminum, but did not improve the maximum joint strength achieved. Reference: Taylor N: The ultrasonic welding of short glass fibre reinforced thermoplastics. ANTEC 1991, Conference proceedings, Society of Plastics Engineers, Montreal, May 1991.
strength. At the same time, the range of melt layer thicknesses resulting in optimal strengths is comparable to that in heated tool butt welding. The obtained strengths of PPS welded seams exceeded 45 MPa (6530 psi). This corresponds to a welding factor of approximately 0.6 for a base material strength of 80 MPa (11,600 psi). Reference: Potente H, Michel P, Heil M: Infrared radiation welding: a method for welding high temperature resistant thermoplastics. ANTEC 1991, Conference proceedings, Society of Plastics Engineers, Montreal, May 1991.
34.3 Spin Welding Ticona: Fortron
For Fortron moldings with rotationally symmetrical joint faces, spin welding is a suitable assembly method to obtain gas-tight, high strength joints. The most suitable welding conditions, such as surface speed, contact pressures and rotational speeds, will depend on the Fortron grade and part geometry and must be determined by optimizing trials. Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.4 Laser Welding Ticona: Fortron
In the laser welding process the laser beam has to be transmitted through the first welding part and absorbed by the second one. Trials with Fortron grades showed that reinforced ones have a good absorption behavior. The wall thickness for the first (laserpermeable) part made of unfilled Fortron should be less than 2 mm (0.079 inches). Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.5 Infrared Welding Bayer: Tedur 9611 (reinforcement: 45% glass fiber)
Due to the orientation of the glass fibers, the bulk material specimen (3 mm; 0.118 inch thick plates) showed a strength of 120 MPa (17,400 psi) parallel to the welded line and 80 MPa (11,600 psi) normal to it. In tests showing the actual weld strength of IR welded polyphenylene sulfide (PPS) plates as a function of weld layer thickness, PPS does not show a minimum in
34.6 Resistive Implant Welding PPS (reinforcement: continuous carbon fiber and glass fiber)
An experimental study on resistance welding of glass fiber and carbon fiber PPS based composites with a metal mesh heating element was performed. The welding pressure showed a relatively limited effect on the weld strength for both materials investigated. The results showed that, for an intermediate power level (110 kW/m2), a pressure between 0.6 and 1.0 MPa (87–145 psi) is needed. Welding pressures below this range lead to deconsolidation and very high void content, resulting in weak bonding. Welding pressures above the optimal range lead to excessive squeeze flow and dry bonds with low mechanical properties. It was noted that, due to a much higher heat transfer coefficient of the carbon fibers in the longitudinal direction, carbon fiber reinforced specimens needed substantially more energy than glass fiber ones to reach the optimal weld range. For lower power levels, the difference mounted up to three times the energy input for glass fiber specimens. Reference: Stavrov D, Bersee HEN, Beukers A: Resistance welding of continuous fibre reinforced PPS composites with metal mesh heating element. Innovation and Integration in Aerospace Sciences, Conference proceedings, Belfast, UK, August 2005.
34.7 Induction Welding PPS (reinforcement: carbon fiber fabric)
In order to prove the efficiency of the continuous induction welding process for fabric-reinforced thermoplastics, the characteristics of single-lap welded specimens were determined in tensile shear tests and by means of microscopy. The laminates to be joined
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391
were moved on a slide in relation to the inductor and were heated up to the processing temperature by an electromagnetic field. After the heating operation, a press-on roller applied the welding force and, at the same time, absorbed the heat from the welded component so that the matrix polymer resolidified. Results showed that the greatest weld strength was achieved at a welding force of 200–300 N (45–67 lbf). With regard to the advance, there was an almost linear decrease in the weld strength as the advance speed increased. Photomicrographs of the welded joints showed that complete welding occurred at low advance speeds, up to 3.6 mm/s (0.14 inches/s), so that the weld could no longer be distinguished from the rest of the laminate. The number and scope of the delaminations (disbonding of one laminate layer from another) and of the air inclusions in the laminate increased along with the advance speed. The time of action of the welding force was obviously no longer sufficient to eliminate the delaminations arising during the molten phase and to consolidate the laminate once again. Reference: Rudolf R, Mitschang P, Neitzel M: Induction welding of fabric-reinforced fibre-plastic composites. Schweissen und Schneiden, 53(10), p. 690, October 2001.
34.8 Adhesive Bonding GE Plastics: Supec
A study was conducted to determine the bond strength of a representative matrix of plastics and the adhesives best suited to them. The block-shear (ASTM D 4501) test was used because it places the load on a thicker section of the test specimen; the specimen can therefore withstand higher loads before experiencing substrate failure. In addition, due to the geometry of the test specimens and the block shear fixture, peel and cleavage forces in the joint are minimized. The substrates were cut into 1"× 1"× 0.125" (25.4 × 25.4 × 3.175 mm) block shear test specimens. All bonding surfaces were cleaned with isopropyl alcohol. The test specimens were manually abraded using a 3 M heavy-duty stripping pad. The surface roughness was determined using a Surfanalyzer 4000 with a traverse distance of 0.03 inches (0.76 mm) and a traverse speed of 0.01 inches per second (0.25 mm/s). While the bond strengths in Table 34.1 give a good indication of the typical bond strengths that can be achieved, as well as the effect of many fillers and additives, they also face several limitations. For example,
Table 34.1. Shear Strengths of Supec PPS to PPS Adhesive Bonds Made Using Adhesives Available from Loctite Corporation* Loctite Adhesive
Material Composition
Black Max 380 (Instant Adhesive, Rubber Toughened)
Prism 401 (Instant Adhesive, Surface Insensitive)
Prism 401/ Prism Primer 770
Super Bonder 414 (Instant Adhesive, General Purpose)
Loctite Depend 3105 330 (Light (Two-Part, Cure No-Mix Adhesive) Acrylic)
Supec grade W331
30% glass reinforced PTFE filled 9 rms
100 (0.7)
150 (1.0)
400 (2.8)
250 (1.7)
150 (1.0)
550 (3.8)
Grade W331 roughened
24 rms
150 (1.0)
500 (3.5)
400 (2.8)
400 (2.8)
350 (2.4)
550 (3.8)
Grade G301T
30% glass reinforced
200 (1.4)
400 (2.8)
150 (1.0)
350 (2.4)
250 (1.7)
1200 (8.3)
Grade G401
40% glass reinforced
200 (1.4)
300 (2.1)
300 (2.1)
300 (2.1)
450 (3.1)
1100 (7.6)
Grade G323
65% glass/mineral filled
250 (1.7)
400 (2.8)
900 (6.2)
600 (4.1)
300 (2.1)
2050 (14.1)
Grade CTX530
30% glass reinforced PPS/PEI blend
150 (1.0)
250 (1.7)
400 (2.8)
400 (2.8)
200 (1.4)
900 (6.2)
*All testing was done according to the block shear method (ASTM D4501). Values are given in psi and MPa (within parentheses).
392
while the additives and fillers were selected because they were believed to be representative of the most commonly used additives and fillers, there are many types of each additive and filler produced by many different companies, and different types of the same additive or filler may not have the same effect on the bondability of a material. In addition, the additives and fillers were tested individually in Table 34.1, so the effect of interactions between these different fillers and additives on the bondability of materials could not be gauged. Another consideration that must be kept in mind when using this data to select an adhesive/plastic combination is how well the block shear test method will reflect the stresses that an adhesively bonded joint will see in “real world” applications. Adhesively bonded joints are designed to maximize tensile and compressive stresses, and to minimize peel and cleavage stresses, so the magnitude of the former two are generally much larger than the latter two. Thus, the shear strength of an adhesive is generally most critical to adhesive joint performance, but since all joints experience some peel and cleavage stresses, their effects should not be disregarded. Finally, selecting the best adhesive for a given application involves more than selecting the adhesive that provides the highest bond strength. Other factors such as speed of cure, environmental resistance, thermal resistance, suitability for automation, and price will play a large role in determining the optimum adhesive system for a given application. Adhesive Performance: Flashcure 4305 light cure adhesive and Hysol E-30CL and E-214HP epoxy adhesives achieved the highest bond strengths on the standard grade of PPS evaluated. In general, all the adhesives tested exhibited good adhesion to PPS. The exceptions are Black Max 380 instant adhesive, Loctite 3340 light cure adhesive, hot melt adhesives and Loctite 5900 flange sealant. Surface Treatments: Surface roughening caused a statistically significant increase in the bond strengths achieved by all the adhesives evaluated, with the exception of Loctite 3105 light cure adhesive and Prism 401 instant adhesive, both of which experienced no statistically significant change. The use of Prism Primer 770, in conjunction with Prism 401 instant adhesive, or Prism 4011 medical device instant adhesive with Prism Primer 7701, did not produce any statistically significant change in the bondability of PPS. Other Information: PPS is compatible with all Loctite adhesives, sealants, primers, activators, and accelerators. Recommended surface cleaners are isopropyl alcohol and Loctite ODC Free Cleaner & Degreaser.
MATERIALS
Reference: The Loctite Design Guide for Bonding Plastics, Vol. 4, Supplier design guide, Loctite Corporation, 2006.
Chevron Phillips Chemical: Ryton
There are many adhesives that will bond Ryton PPS compounds, provided the surface is properly prepared to allow the adhesive to wet the surface. Reference: Ryton Design Guide, Supplier design guide, Chevron Phillips Chemical Company LP, 2004.
Ticona: Fortron
The high solvent resistance of Fortron permits only contact adhesion. Depending on the application, twopack adhesives based on epoxy resin, methacrylate or polyurethane, one-pack adhesives based on cyanoacrylate or hot melt adhesive may be used. Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.9 Mechanical Fastening Chevron Phillips Chemical: Ryton
Snap-fit Assemblies: High strength and rigidity of Ryton PPS compounds provide good holding strength with a minimum of flex and interference. Typically, Ryton PPS snap-fit applications involve only one time assembly. Rivets: Ryton PPS can be successfully assembled using semi-tubular style rivets. The definition of a semi-tubular rivet is a rivet whose mean hole depth, measured on the wall, does not exceed 112% of its mean body diameter. This design will put less stress on the molded parts, especially if the distance between the hole and the underside of the head is the same as the combined material thickness. In order to ensure that minimum stress is placed on the molded parts during riveting operations, it is essential that the rivet setter be adjusted to exert the minimum impact required to clinch the rivet. Tapped Threads for Bolts: In most applications where repeated assembly and disassembly is not required, Ryton PPS moldings with tapped threads work very well. Tapped holes in Ryton PPS glass mineral filled compounds have excellent bolt holding power. Bolts screwed into a depth of four bolt diameters equaled or exceeded the tensile strength of brass and mild steel bolts. Bolts screwed in three turns and those at two bolt diameters also had excellent strength.
34: POLYPHENYLENE SULFIDE
Self-tapping Screws: The excellent creep resistance of Ryton PPS makes it well suited for assembly with self-tapping screws. Due to the hardness of Ryton PPS compounds, thread-cutting types, rather than threadforming types, perform best. Ultrasonic Inserts: Ryton PPS can be conveniently assembled using ultrasonic inserts. Inserts of these types are recommended when repeated disassembly is required, and good pull-out strength is desirable. Molded-in Threads: Because of the excellent processability of Ryton PPS, molded-in threads can be designed into most parts. This will eliminate the need for expensive secondary machining operations. Molding in the threads should also provide superior performance, as compared to machined threads, due to the normal skin effect on injection molded parts. Molded-in Inserts: Because of the excellent processability of Ryton PPS, molded-in inserts can be designed into many parts. Molded-in inserts may be used when repeated assembly and disassembly of parts is required. Since Ryton PPS easily molds around inserts, excellent pull-out strengths should be expected. Inserts are recommended when an appreciable amount of preload is desired. The insert should be designed such that the load is carried through the metal insert and not the plastic. Flanged type inserts work well for highly loaded applications. Heat Staking: The optimum process conditions for a typical 1/8 inch (3.2 mm) diameter post might be, for an amorphous part, a tip temperature of 590°F (310°C). For a crystalline part, use a tip temperature of 620°F (327°C). The downward force is typically 150 lbf (68 kgf) applied for 40 seconds. Since the staked area will be amorphous after the melt/deformation, the assembly should be annealed at 400°F (204°C) for 2 hours if the application requires a fully crystalline part. Since all glass reinforced compounds can be abrasive, we rec-
393
ommend the staking tip be made of a hardened steel with a Rockwell C rating of 60 or greater. Reference: Ryton Design Guide, Supplier design guide, Chevron Phillips Chemical Company LP, 2004.
Ticona: Fortron
Snap-fit Assemblies: Fortron is a rigid-hard engineering plastic for which the low-cost, snap-fit assembly technique can be used. For this method to be successful, it is important to ensure that the snap-fit elements are correctly designed. The following guide values for outer-fiber strain should be regarded as an upper limit: • Fortron 1131L4, 1140L4, 1140L6: 1.3% • Fortron 4184L4, 4184L6: 1.1% • Fortron 6165A4, 6165A6: 0.8% The friction factor, which is necessary for the calculation, depends on the sliding partners, surface roughness and surface pressure. Typical with Fortron are: • Fortron/Fortron: 0.3–0.4 • Fortron/steel: 0.4 Assembly with Screws: Due to the low expansibility in comparison with other polymers, Fortron cannot compensate stress peaks in the same way and is very sensitive to notches. For these reasons, part shapes with a very high stress should be designed with more attention. For parts made of Fortron, the following screw methods have been used: molded threads, molded-in inserts, and bolting with through bolts and direct bolts (e.g., self-tapping screws). Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
still permit good welding results. With higher additions, however, weldability deteriorates.
Ticona: Fortron
Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
This method is preferably employed for joints exposed to mechanical stress in service, large joint surfaces or part geometries that preclude the use of other welding methods. It is important to ensure that the heated tools used are designed for the high temperatures required. Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.2 Ultrasonic Welding Chevron Phillips Chemical: Ryton
Ryton PPS compounds are relatively easy to weld together. Joint design is, however, critical to the finished part strength. A shear joint is the best overall, although the step joint has been used successfully with Ryton PPS R-4. The shear joint will generally be six times stronger than the step joint. When welding shear joints, use high power with a high amplitude booster, low pressure, and slow horn speed. When welding the parts, caution should be used since too high an amplitude and/or too long an application time could destroy the part. Shear joints are usually not recommended for parts with a maximum dimension of 3.5 inches (89 mm) or greater, sharp 90° turns, or irregular shapes, due to the difficulty of holding the required molding tolerances. Ryton PPS may extend these limits, however, since it can hold tight molding tolerances. Reference: Ryton Design Guide, Supplier design guide, Chevron Phillips Chemical Company LP, 2004.
Ticona: Fortron
Fortron moldings can be joined by the usual ultrasonic assembly methods. Joints produced have high strength. Fortron is suitable for both near- and far-field ultrasonic welding. However, because of the relatively brittle-hard behavior of the material, it should be borne in mind that the alternating strains that have to be absorbed by the parts being joined can lead to localized damage. Additions of up to 40% reinforcing materials
LNP Engineering Plastics: OF1006 (material composiition: 30% glass fiber)
Polyphenylene sulfide, being a semi-crystalline thermoplastic, is not ideally suited to ultrasonic welding. In a semi-crystalline plastic the amorphous portions soften at a low temperature with a corresponding increase in mechanical loss factor, which results in more energy being needed to melt the crystalline portions. This phenomenon is reflected in the results of the weldability trials. The results of the weldability study suggest that joints can be formed so long as sufficient power is applied to the joint, that is, it is necessary to employ a high vibration amplitude and to contact the welding horn as close as possible to the joint. A projection joint has proved to be the most successful joint design. Far field welding is not feasible for this material. The ultrasonic welding of 30% short glass fiber filled PPS was studied using a 1500 W commercial ultrasonic welding machine. Projection and shear joints were used for weldability trials. The effect of the base fixturing material was investigated by comparing aluminum, Devcon and PTFE. • 30% short glass fiber PPS (grade LNP OF-1006) can be welded by ultrasonics in the near field. A high vibration amplitude, 80 μm (0.003 inches) and low weld force, 275 N (61.8 lbf), is required to ensure that sufficient heat is generated at the joint. Poor tolerance to variations in welding parameters means that critical optimization of welding procedures is required. • If ultrasonic welding is required, the quality of the injection molded component is of great importance. Defects in the molding, such as internal weld lines, affect ultrasonic energy transmission and can act as energy absorbers within the component. This results in damage to the specimen, either cracking or overheating, and poor joint quality as a result of insufficient energy availability at the weld line. 389
390
MATERIALS
• The fixturing material affects the weld quality. In the present trials, a PTFE fixture gave a wider tolerance to welding parameters and less scatter than aluminum, but did not improve the maximum joint strength achieved. Reference: Taylor N: The ultrasonic welding of short glass fibre reinforced thermoplastics. ANTEC 1991, Conference proceedings, Society of Plastics Engineers, Montreal, May 1991.
strength. At the same time, the range of melt layer thicknesses resulting in optimal strengths is comparable to that in heated tool butt welding. The obtained strengths of PPS welded seams exceeded 45 MPa (6530 psi). This corresponds to a welding factor of approximately 0.6 for a base material strength of 80 MPa (11,600 psi). Reference: Potente H, Michel P, Heil M: Infrared radiation welding: a method for welding high temperature resistant thermoplastics. ANTEC 1991, Conference proceedings, Society of Plastics Engineers, Montreal, May 1991.
34.3 Spin Welding Ticona: Fortron
For Fortron moldings with rotationally symmetrical joint faces, spin welding is a suitable assembly method to obtain gas-tight, high strength joints. The most suitable welding conditions, such as surface speed, contact pressures and rotational speeds, will depend on the Fortron grade and part geometry and must be determined by optimizing trials. Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.4 Laser Welding Ticona: Fortron
In the laser welding process the laser beam has to be transmitted through the first welding part and absorbed by the second one. Trials with Fortron grades showed that reinforced ones have a good absorption behavior. The wall thickness for the first (laserpermeable) part made of unfilled Fortron should be less than 2 mm (0.079 inches). Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.5 Infrared Welding Bayer: Tedur 9611 (reinforcement: 45% glass fiber)
Due to the orientation of the glass fibers, the bulk material specimen (3 mm; 0.118 inch thick plates) showed a strength of 120 MPa (17,400 psi) parallel to the welded line and 80 MPa (11,600 psi) normal to it. In tests showing the actual weld strength of IR welded polyphenylene sulfide (PPS) plates as a function of weld layer thickness, PPS does not show a minimum in
34.6 Resistive Implant Welding PPS (reinforcement: continuous carbon fiber and glass fiber)
An experimental study on resistance welding of glass fiber and carbon fiber PPS based composites with a metal mesh heating element was performed. The welding pressure showed a relatively limited effect on the weld strength for both materials investigated. The results showed that, for an intermediate power level (110 kW/m2), a pressure between 0.6 and 1.0 MPa (87–145 psi) is needed. Welding pressures below this range lead to deconsolidation and very high void content, resulting in weak bonding. Welding pressures above the optimal range lead to excessive squeeze flow and dry bonds with low mechanical properties. It was noted that, due to a much higher heat transfer coefficient of the carbon fibers in the longitudinal direction, carbon fiber reinforced specimens needed substantially more energy than glass fiber ones to reach the optimal weld range. For lower power levels, the difference mounted up to three times the energy input for glass fiber specimens. Reference: Stavrov D, Bersee HEN, Beukers A: Resistance welding of continuous fibre reinforced PPS composites with metal mesh heating element. Innovation and Integration in Aerospace Sciences, Conference proceedings, Belfast, UK, August 2005.
34.7 Induction Welding PPS (reinforcement: carbon fiber fabric)
In order to prove the efficiency of the continuous induction welding process for fabric-reinforced thermoplastics, the characteristics of single-lap welded specimens were determined in tensile shear tests and by means of microscopy. The laminates to be joined
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391
were moved on a slide in relation to the inductor and were heated up to the processing temperature by an electromagnetic field. After the heating operation, a press-on roller applied the welding force and, at the same time, absorbed the heat from the welded component so that the matrix polymer resolidified. Results showed that the greatest weld strength was achieved at a welding force of 200–300 N (45–67 lbf). With regard to the advance, there was an almost linear decrease in the weld strength as the advance speed increased. Photomicrographs of the welded joints showed that complete welding occurred at low advance speeds, up to 3.6 mm/s (0.14 inches/s), so that the weld could no longer be distinguished from the rest of the laminate. The number and scope of the delaminations (disbonding of one laminate layer from another) and of the air inclusions in the laminate increased along with the advance speed. The time of action of the welding force was obviously no longer sufficient to eliminate the delaminations arising during the molten phase and to consolidate the laminate once again. Reference: Rudolf R, Mitschang P, Neitzel M: Induction welding of fabric-reinforced fibre-plastic composites. Schweissen und Schneiden, 53(10), p. 690, October 2001.
34.8 Adhesive Bonding GE Plastics: Supec
A study was conducted to determine the bond strength of a representative matrix of plastics and the adhesives best suited to them. The block-shear (ASTM D 4501) test was used because it places the load on a thicker section of the test specimen; the specimen can therefore withstand higher loads before experiencing substrate failure. In addition, due to the geometry of the test specimens and the block shear fixture, peel and cleavage forces in the joint are minimized. The substrates were cut into 1"× 1"× 0.125" (25.4 × 25.4 × 3.175 mm) block shear test specimens. All bonding surfaces were cleaned with isopropyl alcohol. The test specimens were manually abraded using a 3 M heavy-duty stripping pad. The surface roughness was determined using a Surfanalyzer 4000 with a traverse distance of 0.03 inches (0.76 mm) and a traverse speed of 0.01 inches per second (0.25 mm/s). While the bond strengths in Table 34.1 give a good indication of the typical bond strengths that can be achieved, as well as the effect of many fillers and additives, they also face several limitations. For example,
Table 34.1. Shear Strengths of Supec PPS to PPS Adhesive Bonds Made Using Adhesives Available from Loctite Corporation* Loctite Adhesive
Material Composition
Black Max 380 (Instant Adhesive, Rubber Toughened)
Prism 401 (Instant Adhesive, Surface Insensitive)
Prism 401/ Prism Primer 770
Super Bonder 414 (Instant Adhesive, General Purpose)
Loctite Depend 3105 330 (Light (Two-Part, Cure No-Mix Adhesive) Acrylic)
Supec grade W331
30% glass reinforced PTFE filled 9 rms
100 (0.7)
150 (1.0)
400 (2.8)
250 (1.7)
150 (1.0)
550 (3.8)
Grade W331 roughened
24 rms
150 (1.0)
500 (3.5)
400 (2.8)
400 (2.8)
350 (2.4)
550 (3.8)
Grade G301T
30% glass reinforced
200 (1.4)
400 (2.8)
150 (1.0)
350 (2.4)
250 (1.7)
1200 (8.3)
Grade G401
40% glass reinforced
200 (1.4)
300 (2.1)
300 (2.1)
300 (2.1)
450 (3.1)
1100 (7.6)
Grade G323
65% glass/mineral filled
250 (1.7)
400 (2.8)
900 (6.2)
600 (4.1)
300 (2.1)
2050 (14.1)
Grade CTX530
30% glass reinforced PPS/PEI blend
150 (1.0)
250 (1.7)
400 (2.8)
400 (2.8)
200 (1.4)
900 (6.2)
*All testing was done according to the block shear method (ASTM D4501). Values are given in psi and MPa (within parentheses).
392
while the additives and fillers were selected because they were believed to be representative of the most commonly used additives and fillers, there are many types of each additive and filler produced by many different companies, and different types of the same additive or filler may not have the same effect on the bondability of a material. In addition, the additives and fillers were tested individually in Table 34.1, so the effect of interactions between these different fillers and additives on the bondability of materials could not be gauged. Another consideration that must be kept in mind when using this data to select an adhesive/plastic combination is how well the block shear test method will reflect the stresses that an adhesively bonded joint will see in “real world” applications. Adhesively bonded joints are designed to maximize tensile and compressive stresses, and to minimize peel and cleavage stresses, so the magnitude of the former two are generally much larger than the latter two. Thus, the shear strength of an adhesive is generally most critical to adhesive joint performance, but since all joints experience some peel and cleavage stresses, their effects should not be disregarded. Finally, selecting the best adhesive for a given application involves more than selecting the adhesive that provides the highest bond strength. Other factors such as speed of cure, environmental resistance, thermal resistance, suitability for automation, and price will play a large role in determining the optimum adhesive system for a given application. Adhesive Performance: Flashcure 4305 light cure adhesive and Hysol E-30CL and E-214HP epoxy adhesives achieved the highest bond strengths on the standard grade of PPS evaluated. In general, all the adhesives tested exhibited good adhesion to PPS. The exceptions are Black Max 380 instant adhesive, Loctite 3340 light cure adhesive, hot melt adhesives and Loctite 5900 flange sealant. Surface Treatments: Surface roughening caused a statistically significant increase in the bond strengths achieved by all the adhesives evaluated, with the exception of Loctite 3105 light cure adhesive and Prism 401 instant adhesive, both of which experienced no statistically significant change. The use of Prism Primer 770, in conjunction with Prism 401 instant adhesive, or Prism 4011 medical device instant adhesive with Prism Primer 7701, did not produce any statistically significant change in the bondability of PPS. Other Information: PPS is compatible with all Loctite adhesives, sealants, primers, activators, and accelerators. Recommended surface cleaners are isopropyl alcohol and Loctite ODC Free Cleaner & Degreaser.
MATERIALS
Reference: The Loctite Design Guide for Bonding Plastics, Vol. 4, Supplier design guide, Loctite Corporation, 2006.
Chevron Phillips Chemical: Ryton
There are many adhesives that will bond Ryton PPS compounds, provided the surface is properly prepared to allow the adhesive to wet the surface. Reference: Ryton Design Guide, Supplier design guide, Chevron Phillips Chemical Company LP, 2004.
Ticona: Fortron
The high solvent resistance of Fortron permits only contact adhesion. Depending on the application, twopack adhesives based on epoxy resin, methacrylate or polyurethane, one-pack adhesives based on cyanoacrylate or hot melt adhesive may be used. Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.
34.9 Mechanical Fastening Chevron Phillips Chemical: Ryton
Snap-fit Assemblies: High strength and rigidity of Ryton PPS compounds provide good holding strength with a minimum of flex and interference. Typically, Ryton PPS snap-fit applications involve only one time assembly. Rivets: Ryton PPS can be successfully assembled using semi-tubular style rivets. The definition of a semi-tubular rivet is a rivet whose mean hole depth, measured on the wall, does not exceed 112% of its mean body diameter. This design will put less stress on the molded parts, especially if the distance between the hole and the underside of the head is the same as the combined material thickness. In order to ensure that minimum stress is placed on the molded parts during riveting operations, it is essential that the rivet setter be adjusted to exert the minimum impact required to clinch the rivet. Tapped Threads for Bolts: In most applications where repeated assembly and disassembly is not required, Ryton PPS moldings with tapped threads work very well. Tapped holes in Ryton PPS glass mineral filled compounds have excellent bolt holding power. Bolts screwed into a depth of four bolt diameters equaled or exceeded the tensile strength of brass and mild steel bolts. Bolts screwed in three turns and those at two bolt diameters also had excellent strength.
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Self-tapping Screws: The excellent creep resistance of Ryton PPS makes it well suited for assembly with self-tapping screws. Due to the hardness of Ryton PPS compounds, thread-cutting types, rather than threadforming types, perform best. Ultrasonic Inserts: Ryton PPS can be conveniently assembled using ultrasonic inserts. Inserts of these types are recommended when repeated disassembly is required, and good pull-out strength is desirable. Molded-in Threads: Because of the excellent processability of Ryton PPS, molded-in threads can be designed into most parts. This will eliminate the need for expensive secondary machining operations. Molding in the threads should also provide superior performance, as compared to machined threads, due to the normal skin effect on injection molded parts. Molded-in Inserts: Because of the excellent processability of Ryton PPS, molded-in inserts can be designed into many parts. Molded-in inserts may be used when repeated assembly and disassembly of parts is required. Since Ryton PPS easily molds around inserts, excellent pull-out strengths should be expected. Inserts are recommended when an appreciable amount of preload is desired. The insert should be designed such that the load is carried through the metal insert and not the plastic. Flanged type inserts work well for highly loaded applications. Heat Staking: The optimum process conditions for a typical 1/8 inch (3.2 mm) diameter post might be, for an amorphous part, a tip temperature of 590°F (310°C). For a crystalline part, use a tip temperature of 620°F (327°C). The downward force is typically 150 lbf (68 kgf) applied for 40 seconds. Since the staked area will be amorphous after the melt/deformation, the assembly should be annealed at 400°F (204°C) for 2 hours if the application requires a fully crystalline part. Since all glass reinforced compounds can be abrasive, we rec-
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ommend the staking tip be made of a hardened steel with a Rockwell C rating of 60 or greater. Reference: Ryton Design Guide, Supplier design guide, Chevron Phillips Chemical Company LP, 2004.
Ticona: Fortron
Snap-fit Assemblies: Fortron is a rigid-hard engineering plastic for which the low-cost, snap-fit assembly technique can be used. For this method to be successful, it is important to ensure that the snap-fit elements are correctly designed. The following guide values for outer-fiber strain should be regarded as an upper limit: • Fortron 1131L4, 1140L4, 1140L6: 1.3% • Fortron 4184L4, 4184L6: 1.1% • Fortron 6165A4, 6165A6: 0.8% The friction factor, which is necessary for the calculation, depends on the sliding partners, surface roughness and surface pressure. Typical with Fortron are: • Fortron/Fortron: 0.3–0.4 • Fortron/steel: 0.4 Assembly with Screws: Due to the low expansibility in comparison with other polymers, Fortron cannot compensate stress peaks in the same way and is very sensitive to notches. For these reasons, part shapes with a very high stress should be designed with more attention. For parts made of Fortron, the following screw methods have been used: molded threads, molded-in inserts, and bolting with through bolts and direct bolts (e.g., self-tapping screws). Reference: Fortron Polyphenylene Sulphide, Supplier design guide, Ticona, 2000.