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Welding of Thermoplastics

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Thermoplastic welding is generally considered irreversible. A small number of processes such as induction welding can produce reversible assembly. The choice of which method should be made early in the parts do not count, because the welding of parts design requirements may be important, and significant differences between the different welding methods with Achillea. Hot air welding technique is usually used to weld plastic pipe, sheets or semi-finished products instead of plastic injection molding products. However, many thermoplastic molded parts, particularly automobile plate is hot thermoplastic welding repair, welding heat is sometimes used by the other kind of mold plastic parts. Ultrasonic welding Welding thermoplastic parts of the most common method is ultrasonic welding. This method is the use of low-amplitude, high frequency (ultrasonic) vibration energy to the friction surface and the molecules attached to the welding of plastic parts required for the heat pad. (Sinusoidal ultrasonic vibration) 20-50kHz ultrasonic welding in the frequency range occur, the general amplitude range of 15-60um. As low as 15kHz (high amplitude) the audio is sometimes used for larger parts or soft materials. Welding process usually occurred in the 0.5-1.5s. Luan amount of welding, including welding time, welding head position and welding pressure. Ultrasonic welding equipment normally used in welding, small size of the thermoplastic plastic parts, and much more parts can be welded. Ultrasonic welding or seam welding time according to location (collapse distance) or welding energy control. Welding pressure, and also provide additional cooling time control. Ultrasonic welding equipment is generally not in the 20kHz 40kHz frequency operation. 20kHz device more commonly used. Joint Design: The first category is the most common connector types, the surface being connected using ultrasonic vibration on the vertical direction. Docking and Z-shaped junction fall into this category, for most polymers. The second category includes ultrasonic welding joints and joint vibration parallel to the surface to form a shear state. Various types of cut-and-scarf included in the second category. Energy control din contacts with the use of amorphous materials with the best, the larger energy control clamor Results that are not confined in the semi-crystalline materials applications. The following style pieces with a rough or textured surface improvements. Will improve the quality of welding, weld strength and ease of welding completed. Joints in many other textured appearance are also feasible. Overflow problem can be contaminated by the overflow tank into the lower bearing on the design for safety, the general design of overflow trough over at least 10% of the volume capacity. Pressed joints: In order to minimize the possibility of the formation of excess material, pressed block connector is designed to melt or melt in the melting zone to maintain. Pressed the plastic connector on the semi-crystalline materials such as nylon is useful. Take off because the structure is more complex, then pressed with the relevant parts required relatively strict tolerances. Xiao welding with triangular energy direction compared to the larger amplitude of the joint structure and welding also requires additional energy. Simple leveling parts without any measures to solve the docking leveling with each other or in parts. Leveling is more suitable for molding parts with pins or double spiral to complete. The z-shaped access to automatic leveling, and in use, and improved resistance to tensile shear load of practice. And to eliminate the external overflow. Trough of tongue not only provides a shear strength of joints and provides the tensile strength. This is a self-pair bonding, bonding region must be relatively large to accommodate the thickness of the tongue groove joints design. In addition, the workpiece is relatively strict tolerances. Intervals to improve the joint leveling ribs. Joint number, the use of shear connection is recommended. Require high strength, high-quality circular and rectangular access Bei parts are used shear connectors. No. joints with lap shear wall part of the workpiece, when the joints are welded and embedded in each turn, the lap part of the production tolerances and local shear. To facilitate leveling parts, fittings included some adjustment. In order to focus fusion energy, obstructions on the side of the angle in the initial contact with the surface decreased. Because the melting temperature of the material consistent throughout the contact surface, the workpiece being welded, the two surface melt evenly. 1.0-2.0mm depth of the use of 0.13-0.5mm range of tolerance values. In order to prevent the welding process resulting from the tolerance of the external wall of warping, the vertical parts should be as shallow, but improved in the side of the slot with a cut tongue connector parts can be used with deep stretching parts provided in the wall joints, which allows the tolerance of the minimum warpage arising from sidewalls. Bonding with the slope angle 30 ° -60 ° ± 1 ° and should be within the assembly. Melting area for additional increase in material thickness tolerance 0.10-0.25mm and the excess material produced welds. When a functional or aesthetic can not accept the overflow when to use the collector. Welding with embedded seal ring with an embedded elastic or ductile and reliable sealing gasket is also available. Connector parts as shown in Figure 7 with an elastic ring to improve the bonding can be achieved by ultrasonic welding sealing security, or in a continuous peripheral weld impossible circumstances. Ultrasonic welding Variation of ultrasonic welding is ultrasonic welding. Parts of a thermoplastic that is fixed in a different way on the workpiece material. In the bottom of the rivet or boss should have a very large radius or rounded to prevent cracking or melting. In order to focus ultrasonic energy, the top boss should be designed as the initial contact with the welding head minimum. Boss at the top can be flat or conical, semi-crystalline polymers or filled conical better. Depends on the integrity of ultrasonic welding and the welding head rivet capacity between the exact relationship. Standard welding 1.6-4.0mm in diameter, this flat head rivets. Non-rigid and flexible thermoplastics wear the standard form is recommended. Hemispherical riveting rivet diameter less than 1.6mm is recommended on the hemispherical riveting. Plastic is appropriate for wear. Riveting riveting overflow overflow requirements used in the flat surface uplift and chain letters or the thickness of the workpiece is allowed to use the application. Hollow riveting diameter greater than 4mm, or rivets to the core boss after boss of Health blind hole. When the engagement holes are not allowed in parts, the ultrasonic welding equipment can also be a mechanical interlock. Molded plastic rivets (used for welding and similar) and in parts of the blind mating chamfer can be formed by tolerance-based (assuming that the parts do not melt with chamfer) of the real mechanical bonding. Material factors of ultrasonic welding ultrasonic welding operation is suitable for most thermoplastic materials. An amorphous polymer, particularly outside the glass room temperature, amorphous materials, welding process is usually a good candidate material. Glassy amorphous polymers with good transmission properties, allows to see near and far field welding welding technology successfully. When the material is relatively soft, the open amorphous materials ultrasonic welding to a problem. Such as: welded high impact than the welded universal ps ps need more energy and additional general amplitude. 2 semi-crystalline polymers generally more difficult to weld using ultrasonic energy. Increase the energy emitted by the welding system of values (an increase of amplitude); reduce welding head / workpiece contact surface and the distance between the interface connector; using near-field ultrasonic welding technology; with amplitude up to 0.05-0.15mm of the welding head. These high-amplitude required welding of titanium welding head. When you need high strength, sealing assembly, the shear bonding joints and slope are suitable for semi-crystalline polymers. 3 hygroscopic polymer welding: welding parts immediately after molding (when they are still drying); drying parts before welding; welding parts before storing in the dryer. Vibration Welding Vibration welding is friction welding process in which the parts are welded together under pressure until the friction generated heat from friction and shearing the first side to reach the full molten Kuwana. Once the molten film is formed deep enough into Da access area, the relative motion stops, the weld cool under pressure and cured. Vibration welding thermoplastic trunk for almost all of plastic, the direction of reciprocating motion of the unconstrained movement has allowed the weld parts, medium or large parts. Vibration welding and ultrasonic welding material factors like: the amorphous material is more suitable than the use of semi-crystalline polymer similar vibration welding. Ring vibration welding weld zone size can be connected to the rotation axis and the welding area approximately equal distance from the workpiece. Linear vibration welding is allowed on the linear vibration of one direction on the sets of parts. When connected to the entire joint surface is flat or slightly curved plane when the vibration of the parts for welding process is ideal. Spin welding Spin welding joints used to connect the surface with a rotationally symmetric parts, it is a friction welding process. Is connected to the cylindrical thermoplastic parts vary in the most effective technology. Welding with a rotating assembly parts often have a vertical interconnect with neighboring and other features. It's raw processing variables are relative to shear rate, the welding pressure and welding time. Rotating welded joint strength depends on the material, joint design and processing conditions used; most thermoplastics can be achieved strong gas seal weld. Spin welding material on the transmission performance is not good especially suitable. Electromagnetic welding Electromagnetic welding materials are generally magnetic rotation of the filled polymer, it is the same polymer material and the parts or compatible polymer manufacturing. The strong magnetic filled polymers, including fine dispersed, micron-size iron particles, iron oxide particles, magnetic stainless steel particles or other substances, they become the target of electromagnetic energy. By volume of strong magnetic powder loading amount is usually less than 15% when the applied force on the workpiece in the shear produced at the welded joints, weld the strong. The most common practice is the slot connector joints and Z-shaped junction tongue. Induction welding with additional costs need to use embedded welding materials, and very suited to sensitive parts of the workpiece with electromagnetic. Contact (resistance) welding Contact with electrical wires or bands of resistance welding is directly into the joint interface, the wires connected to the circuit and the loss of direct electrical resistance heating. Thermal conductivity of heat passing through the adjacent plastic material, so the solid plastic softening or melting in the local area. Power, the welding zone or cooling, pressure to engage parts to one another. Minimum equipment requirements, the welding process is simple and fast, especially suitable for welding large parts. But the loss of heat needed wires, welding wires remain in situ after the increase of processing costs, and the existence of wire weld strength of the finished product have an adverse effect. Hot plate welding Hot plate welding (on the flat-type parts), it is electric heating of metal molds to make plastic parts to be connected to soften the thermoplastic surface of the welding process. Suitable for almost all thermoplastic, large or small parts. Particularly suitable for semi-crystalline soft welding thermoplastics such as PE or PP. As the surface temperature of the mold can be different names for two different thermoplastic materials, this process is most suitable for welding different materials. Hot plate welding can achieve high weld strength. However, this process may be relatively long period, small parts to be 15s, while the large parts to be a few minutes. Hot air welding Hot gas welding is widely used for connecting thermoplastic profiles and sheets produced in large parts of the welding method. Need for local assembly of small parts injection molding, thermoplastic-like parts of the repair and manufacture of molded parts. Welding parts to be used with the same brand of polymer electrodes is an important production Extrusion Welding Extrusion welding is evolved by the welding heat welding method. The main structure of the larger pieces of automatic welding. Bonding The same adhesive used to connect the plastic parts of polymer materials, generally used, taking the parts manufactured by different materials. Thermosetting plastic parts to each other or to make plastic parts and metal connection. Adhesive benefits include: Aesthetics, design flexibility; Uniform stress distribution; Able to connect different materials; Able to provide air water air tight seal; Soft adhesives to dampen vibration; Substrate with thin and soft with use; Provide electrical insulation and thermal insulation. A variety of adhesives limitations: Joint performance uncertainty; Permanent assembly; Integrated chemical processes; Need a clean surface; No joint detection; Time to reach maximum strength. Adhesive selection Application-specific choice of adhesive depends on factors such as: use of the environment, stress, substrate surface chemistry, substrate rigidity characteristics, the substrate coefficient of thermal expansion, sealing requirements and application methods. Solvent Bonding Solvent bonding of thermoplastic parts can be assembled in some ways, the most commonly used parts on amorphous thermoplastics. Solvent bonding is the formation of solid amorphous thermoplastic seal assembly of simple parts, relatively inexpensive method. Low viscosity solvents require the bend of the adhesive and the parts should be relatively tight tolerances with molding.
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