The main feature of PVC profiles for blanking collapse, cold blunt rupture. The industry believes that the factors causing the poor performance of material products are the following:
一, mixing process and formula unreasonable
1, filling too much, because the current market prices of profiles are low and raw material prices are rising, many profiles manufacturers are on the reduction of costs. And formal profiles manufacturers are in the premise of not reducing quality, through the formulation of the combination of optimization to reduce costs; some manufacturers are in reducing costs, but also reduce the quality of products.
2, the amount of shock modifier and the kind of additive, under stress, impact modifier can improve the total energy of PVC rupture. At present, CPE, ACR, MBS, ABS and EVA is the main anti impact modifier of hard PVC, therein CPE, EVA, ACR does not contain a double bond in the molecular structure, good weather resistance, suitable for outdoor building materials, they blend with PVC can effectively improve the hard polyvinyl chloride ethylene impact resistance, processability, weatherability and in a certain range to improve the strength of fillet weld.
3, stabilizers too much or too little, the role of stabilizers is to inhibit degradation, or with the release of hydrogen chloride reaction, and prevent PVC processing discoloration. The amount of stabilizer will affect the impact strength of the section, too much or too little will result in the reduction of the profile strength and the embrittlement of the profile.
4, excessive amount of lubricant, lubricant and resin intermiscibility is low, can promote the sliding between resin particles, thereby reducing the friction heat and delayed the melting process, the effect of lubricant in the process of early (before the friction heat is generated in the external heating effect and internal characteristics of resin resin completely lose the recognition the melting and melt) is the largest.
5, hot mix feeding sequence, t, temperature setting values, and curing time on the performance of the material also has a decisive factor
PVC -U formula of many components, the selected sequence should be conducive to play the role of each of these additives, and is helpful to improve the dispersion speed, and avoid its negative synergies, additives of sequence should help to improve the effect of fertilizer supplement each other, overcome phase grams of destructive effects, should be dispersed in PVC resin additives, fully into the inside of PVC resin.
二. the extrusion process is not reasonable
1, plasticizing excessive or insufficient, which is related with the temperature and feed ratio, the temperature too high will cause the material over plasticizing, the component part of lower molecular weight components will decompose, volatilization; not completely different molecular components in the fusion temperature is too low, the molecular structure is not strong. The feed ratio is too large, resulting in increased heating area and shear, pressure increases easily lead to excessive plasticizing; the proportion of feed is too small, causing the heating area of materials and shear less, it will cause less plasticizing. Whether it is over plasticizing or less plasticizing, it will cause the cutting of the profile.
2 ,The machine head pressure not enough, on the one hand is related to the mold design (which separately described below) on the other hand is related to feeding ratio and temperature setting, lack of pressure, density of material is poor, it will become loose tissue appeared brittle phenomenon, then should adjust the feeding speed and the rotation speed of the screw extrusion die the pressure control at 25Mpa-35Mpa.
3. The low molecular components in the product are not excreted. The low molecular components in the product are generally produced in two ways. One is produced during hot mixing, which can be expelled by wetting and venting systems during hot mixing. The two part is the residual water and the hydrogen and hydrogen chloride gas produced by the extrusion. This generally through the forced exhaust system host exhaust section to force discharge, the vacuum degree is generally between -0.05Mpa-0.08Mpa, do not open or too low, will remain low molecular components in the products, resulting in a decline in mechanical properties of profiles.
4,screw torque is too low, the values in the stress state under the mechanical response, process temperature set value, the ratio of feeding are directly reflected in the screw torque value, screw torque is too low to some extent reflects the low temperature or feeding proportion is small, so that the material in the extrusion degree the same is not fully plasticizing, will also reduce the mechanical properties of the profiles. According to different extrusion equipment and mold, the screw torque is generally between 60%-85%, can meet the requirements.
5, traction speed does not match with the extrusion speed, traction speed too fast will cause a decline in mechanical properties of thin wall sections, and the traction speed is too slow, the resistance profile, products in high tension, will affect the mechanical properties of materials.
三、 mold design is unreasonable
1, the die section design is unreasonable, especially the distribution of internal reinforcement and the angle of interface. This will lead to stress concentration and improve the design and elimination of the right angles and sharp angles at the interface.
2, the die head pressure is insufficient, the die head pressure size is directly affected by the compression ratio of the die, especially the length of the flat section of the die. The compression ratio of the die is too small or flat, and the segment is too short, which will cause the product to be not dense and influence the physical performance. Die pressure change on the one hand can be adjusted by changing the flow resistance of the die head straight section length; on the other hand can choose different compression ratio change of extrusion pressure in the mold design stage, but must pay attention to and head compression ratio of extruder screw compression ratio to adapt; also by changing the formulation, adjustment of the extrusion process the porous plate to change the parameters, increase the size of the melt pressure.
3, for the poor performance caused by the poor convergence of the reinforcement, the length of the tendon and the external surface, the joint of the tendon and the tendon should be increased properly, or the compression ratio should be increased.
4, the mouth mold uneven discharge, resulting in non-uniform wall thickness, or the consistency of density. This also caused the difference between the mechanical properties of the two profiles, we sometimes cold in the experiment, one side qualified, one side failed, but also precisely proved this point. As for wall, thin and other non-standard profiles, here will no longer say.
5. The cooling rate and cooling water temperature of the setting die are not paid enough attention. The function of cooling water is to cool and shape the large molecular chain which is stretched in time, so as to achieve the purpose of use. Slow cooling allows molecules to have enough time to stretch and shape. The rapid cooling, water temperature and extrusion parison temperature difference is too large, the product is quenched, is not conducive to the low temperature performance of products.
四, incision rupture phenomenon
We should discuss is a situation in profile sampling test, whether it is punching, or corner strength after heating the size change rate of all the standard, (GB/T8814-2004), but the incision in the feeding or slightly less obvious rupture phenomenon, especially in the bar.
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