CONTROLLING LOSS IN UPVC EXTRUSION PROCESS:

UPVC profile manufacturing industries are prone for reasonable amount of waste during production, with major contribution of scrap generated are pertaining due to defects in manufacturing process. Profile extrusion process has different defects such as surging, melt fracture, degradation, voids, gels and specks etc.

Some of the many problems that can occur during extrusion are traceable to the processed raw material; that is, the raw material is not up to specification. Regardless of any quality assurances by manufacturers of raw materials and countless programs such as ISO 9000, reengineering, and Just in Time (JIT) manufacturing, plastic batches and even bags or boxes within batches have their idiosyncrasies. With all extrusion parameters the same, the profile or sheet will have a different look, bend, color, or texture. While this may sound unscientific or preposterous, these problems do occur on the floor. Despite all the computer programs and hardware designed to keep the quality constant, there are variations.

Extrusion being a high volume manufacturing process any occurrence of defects in the process can lead to large amounts of scrap and necessitate time-consuming teardowns.

OVECOMING MAJOR DEFECTS AND REJECTIONS USING MECHANICAL PURGING COMPOUND:

SURGING: Surging is a cyclical product thickness variation in the direction of extrusion. The surge cycle time is typically between 30 seconds and 3 minutes, and the cause can be inside or outside the extruder. Outside causes are easier to see and correct. For example, the take-off pull may be irregular; in this case the screw rpm and ammeter readings remain steady. Sometimes screw motor speed varies because its regulation is not working properly. This is rare and will show up as unsteady rpm. Sometimes the feed is uneven because of particle size, light weight, or bridging in the hopper and throat. With very small extruders, the feed channel depth is not much bigger. Than the feed particles, and they may feed erratically for this reason alone. If none of these outside causes are observed, it is probable that the surging originates inside, typically at the beginning of the compression zone, where the solid bed-the mass of pellets—may be locking and breaking up irregularly. Screw rpm might be steady but the ammeter shows variations of ± 5% or more. Sometimes this can be cured by increasing the temperature of the feed to promote earlier melting. sometimes raising the barrel Temperature cause sticking of the pellets to the wall there and causing degradation which could result in severe rejection rates. UNICLEANPLUS purging grades has the capability of pulling out the break down UPVC material fractions and provide a clean friction less surface to the steel surface.

MELT FRACTURE: This refers to fine ridges or rough surface seen when the melt comes too fast out of a narrow die. It is most common with profile extrusion where the material gets excessive shear or friction in the die lip. Using Mechanical grades from UNICLEALPLUS purging compounds will pull out the hard layer caused due to raw material shear and molecular degradation.

DISCOLORATION DUE TO OVER HEATING: Overheating may limit the rate if the take-off cooling is limited, or it may produce degradation, make dimensional control and sizing difficult. In such a case using a mechanical grade purging compound from UNICLEANPLUS that can be operated at the lowest processing temperature gives a great relief in removing burnt material without requiring further temperature rise that might result in exaggerating the problem and causing costly rejections.

UNICLEANPLUS purging grades provide significant advantages by

• Eliminate carbon accumulation and color streaking occurrence.
• Decontaminate the die quickly.
• Thoroughly clean the screw and barrel.
• Can be effortlessly removed by backing up your processing resins after the purge.
• Significantly lower rates of scrap and defects.
• Reduce time needed for material and color changes.
• Keep your machine sealed and prevent oxidation during longer shut downs.
• Promote quicker and effortless screw pushes.
• Facilitate simpler starts after shut downs.
• Formulated to enable no or little residue after purging.

CONCLUSION: -?Various studies and analysis on defect in UPVC profile extrusions has been carried out. It has been proved that UNICLEANPLUS low temperature mechanical purging solutions shows a very good value preposition in purging extrusion process, thereby resulting in the best extrusion product. UNICLEANPLUS purging compounds of has shown significant reduction in percentage of loss, gives better predictability in production output and product quality.

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