How to Join Plastic Parts
After plastic mold is ready,Splicing is arguably the most mature and simplest ways of fabricating or fastening two injection molding pieces together. Infact, splicing methods have been known even before other methods like welding, bolting or soldering.
The concept of splicing involves the connection of pieces by using the surface adhesion between the plastic molding parts and the adhesives’ firmness or cohesiveness. One of the best features in splicing is an even distribution of stress. In addition, other benefits are that totally different materials can be brought together, large splicing areas can be made quickly, and the adhesive itself fills uneven surfaces. Nevertheless, splicing also involves certain pitfalls. In certain cases, the strength is limited and not all materials are suitable for splicing (Polyolefins), and proper storage of the chemicals is vital. Changes in temperatures will render problems for moist adhesives. Also, a different expansion between the plastic and the adhesive will cause stress and loss of strength in the splicing. Polyolefins show a very low surface energy, which can be increased with a primer or an electrical or flame treatment. This will help to produce a decent joint, albeit only temporary. Welding may prove to be better than splicing as far as polyolefins are concerned.
Adhesive materials have been extensively used in splicing of thermoplastics. Whenever hot-air or extrusion welding is not an alternative for the joining of thermoplastic materials, the answer can be provided by adhesive materials which are basically demarcated into six adhesive groups. The variations in their chemical structures render certain technological properties.
Melting Glue: Consists of a single-component, thermoplastic adhesives that essentially needs heating-up to the melting stage. These adhesives provide fast curing time, convenient storage and handling. The adhesives in this group are solvent free and efficient. However, this group exhibits shortcomings including inability to handle sufficiently big splicing areas and low temperature resistance. Hot Glue is an avid example of an adhesive in this group.
Polycondensate: Have adhesives like Phelolics which are typically two-component, thermoset adhesive. The components react to each other when combined. The adhesives in this group provide extremely good thermal resistance, sturdy splicing and makes the splicing of wide areas convenient. But the proportion of components in the mixture has to be accurate and emphasis has to be given to adequate storage.
Solvent Adhesive: Consists of a single-component, thermoplastic adhesives, which is dissolved in a solvent. The adhesive hardens following the disappearance of the solvent. The adhesives in this group like Cement are good for uneven large surfaces but they are reported to emit harmful gases and storage is critical issue.
Polymerisate: Is another group of single-component, thermoplastic adhesives; however, the adhesives require a catalyst to initiate the reaction. In this case the moisture from the surrounding environment will do. These enable a fast curing time and strong bond. The pitfall is that splicing is brittle as well as the parts need to have good cohesive surfaces.
Polyaddition: Has a two-plastic molding-component, thermoset adhesive. The two components react with each other. The benefits are very sturdy splicing, a wide range of use and high thermal resistance. The disadvantage is the mixture - that has to be exact. Proper storage is critical and can be quite expensive. Epoxies belong to this group of adhesives.
The design of the connection depends, like always, on the application. If an overlap, a T-connection or any other kind of connection is chosen the following will apply with all splicing. It is essential to ensure that the adhesive is able to handle the medium the glue will come in contact with later.
The preparation of the splicing surface is a crucial step in assuring a successful bond. Firstly, heavy dirt, dust or grease should be removed. Then, splicing area should be roughened employing a sanding or grinding paper (grit 100-150). Following, remove the grinding dust by using oil-free compressed air.
Alternatively, degrease-able solvent can be used to remove any residue. Consider that some plastics are not resistant to some solvents. In that case, try the cleaner first on a sample. Alcohol, gasoline etc. are not recommended, because they leave residue. After these steps are done, avoid touching the prepared surface with bare hands. Every fingerprint and any soil left on the surface weakens the strength of the bond. In any case, the splicing should be done immediately after the areas have been prepared. Before starting the process, area should be cleaned where the bonding will occur with enough room for the pieces, tools and personal protection.
Lastly, prepare the equipment including the parts to be spliced, clamps, trowels, a scale, rubber gloves, mixing containers, solvents, rags and most importantly, the adhesive. It is also a good practice to have enough adhesive prepared so that you can use the leftover to monitor the curing time of the mixture. This ensures that it really is hardened and the mixture was correct. Leave it overnight in a safe place and check on it the next day. However, some adhesives will cure in response to using UV-light rays or heat. Basically for storage of adhesives a dark, dry space with good ventilation is ideal.
Additional safety considerations should be observed while splicing of plastic parts. Eating, drinking and especially smoking in the splicing area should be prohibited at all times. There are fumes and dust particles floating in the surrounding air and you may swallow or inhale these particles with your food and cigarettes. Besides, open flames are not allowed in close proximity because of the flammability of most adhesive’s fumes. Avoid skin contact because some solvents will find their way directly into the blood stream, contact could also cause allergic reactions. Good ventilation is important whenever adhesives or solvents are used. Lastly, all adhesives are basically special waste and should be disposed of in the proper way.
by steven www.sino-mould.com.cn www.plasticmoulds.net
The concept of splicing involves the connection of pieces by using the surface adhesion between the plastic molding parts and the adhesives’ firmness or cohesiveness. One of the best features in splicing is an even distribution of stress. In addition, other benefits are that totally different materials can be brought together, large splicing areas can be made quickly, and the adhesive itself fills uneven surfaces. Nevertheless, splicing also involves certain pitfalls. In certain cases, the strength is limited and not all materials are suitable for splicing (Polyolefins), and proper storage of the chemicals is vital. Changes in temperatures will render problems for moist adhesives. Also, a different expansion between the plastic and the adhesive will cause stress and loss of strength in the splicing. Polyolefins show a very low surface energy, which can be increased with a primer or an electrical or flame treatment. This will help to produce a decent joint, albeit only temporary. Welding may prove to be better than splicing as far as polyolefins are concerned.
Adhesive materials have been extensively used in splicing of thermoplastics. Whenever hot-air or extrusion welding is not an alternative for the joining of thermoplastic materials, the answer can be provided by adhesive materials which are basically demarcated into six adhesive groups. The variations in their chemical structures render certain technological properties.
Melting Glue: Consists of a single-component, thermoplastic adhesives that essentially needs heating-up to the melting stage. These adhesives provide fast curing time, convenient storage and handling. The adhesives in this group are solvent free and efficient. However, this group exhibits shortcomings including inability to handle sufficiently big splicing areas and low temperature resistance. Hot Glue is an avid example of an adhesive in this group.
Polycondensate: Have adhesives like Phelolics which are typically two-component, thermoset adhesive. The components react to each other when combined. The adhesives in this group provide extremely good thermal resistance, sturdy splicing and makes the splicing of wide areas convenient. But the proportion of components in the mixture has to be accurate and emphasis has to be given to adequate storage.
Solvent Adhesive: Consists of a single-component, thermoplastic adhesives, which is dissolved in a solvent. The adhesive hardens following the disappearance of the solvent. The adhesives in this group like Cement are good for uneven large surfaces but they are reported to emit harmful gases and storage is critical issue.
Polymerisate: Is another group of single-component, thermoplastic adhesives; however, the adhesives require a catalyst to initiate the reaction. In this case the moisture from the surrounding environment will do. These enable a fast curing time and strong bond. The pitfall is that splicing is brittle as well as the parts need to have good cohesive surfaces.
Polyaddition: Has a two-plastic molding-component, thermoset adhesive. The two components react with each other. The benefits are very sturdy splicing, a wide range of use and high thermal resistance. The disadvantage is the mixture - that has to be exact. Proper storage is critical and can be quite expensive. Epoxies belong to this group of adhesives.
The design of the connection depends, like always, on the application. If an overlap, a T-connection or any other kind of connection is chosen the following will apply with all splicing. It is essential to ensure that the adhesive is able to handle the medium the glue will come in contact with later.
The preparation of the splicing surface is a crucial step in assuring a successful bond. Firstly, heavy dirt, dust or grease should be removed. Then, splicing area should be roughened employing a sanding or grinding paper (grit 100-150). Following, remove the grinding dust by using oil-free compressed air.
Alternatively, degrease-able solvent can be used to remove any residue. Consider that some plastics are not resistant to some solvents. In that case, try the cleaner first on a sample. Alcohol, gasoline etc. are not recommended, because they leave residue. After these steps are done, avoid touching the prepared surface with bare hands. Every fingerprint and any soil left on the surface weakens the strength of the bond. In any case, the splicing should be done immediately after the areas have been prepared. Before starting the process, area should be cleaned where the bonding will occur with enough room for the pieces, tools and personal protection.
Lastly, prepare the equipment including the parts to be spliced, clamps, trowels, a scale, rubber gloves, mixing containers, solvents, rags and most importantly, the adhesive. It is also a good practice to have enough adhesive prepared so that you can use the leftover to monitor the curing time of the mixture. This ensures that it really is hardened and the mixture was correct. Leave it overnight in a safe place and check on it the next day. However, some adhesives will cure in response to using UV-light rays or heat. Basically for storage of adhesives a dark, dry space with good ventilation is ideal.
Additional safety considerations should be observed while splicing of plastic parts. Eating, drinking and especially smoking in the splicing area should be prohibited at all times. There are fumes and dust particles floating in the surrounding air and you may swallow or inhale these particles with your food and cigarettes. Besides, open flames are not allowed in close proximity because of the flammability of most adhesive’s fumes. Avoid skin contact because some solvents will find their way directly into the blood stream, contact could also cause allergic reactions. Good ventilation is important whenever adhesives or solvents are used. Lastly, all adhesives are basically special waste and should be disposed of in the proper way.
by steven www.sino-mould.com.cn www.plasticmoulds.net
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