What are the possible causes and remedies of black spots problem? Material is ABS Transparent .

Dear Kamaljeet, you need to set recommended temperature profile of the injection barrel,lower back pressure and moderate injection speed.Also use short nozzle if possible with little larger orifice than current nozzle. Avoid any material leakage from nozzle / head.If the black spot appears at particular location,check for proper air vents.

Kamal, There are numerous possibilities that will result in Black Spots/Specs in Clear molded parts. I would first suggest that for Clear parts, the Molding Press (Barrel, Screw and Material delivery system) be strictly dedicated to Clear resin. If your molder changes to colored resins in the same Press, you will typically see spots/specs of residual resin migrating into the resin flow from previous colored runs. This may also be a problem if your Mold is used for multiple colors since it is extremely difficult to purge and clean the inner surfaces of a mold-----and this of course is a function of the intricacy of the material delivery system ( Hot Runner Manifold, Multiple Gates, etc.). Another basic screening should be made on your raw material. Based on the grade of material you purchase, you may find that if you are getting material which contains spots/specs as typical in most standard resin grades. Optical grade resin may suite your application and has a higher quality for transparency and minimum contaminents. There are many other causes for spots/specs but I don't want to write a book here. Hope that this helps.

Sometimes thare is burnt on material on the screw and barrel. I recommend to pull the screw and clean the barrel and screw to remove any burnt on material.

@ kamal jeet

May be the constaint are

> temperature
> air blockage
> pre-heating
> you can also make a cross-check on material (ABS) quality or grade.

Another lesson learned. In the injection molding of Clear parts where Clarity and/or Contaminents result in cause for rejects, a Cleaning Process for the raw pellets should be considered. When pellets are packaged in bags or in a gaylord, normal shipping will cause the pellets to abraid----thus resulting is very fine powder in the bags or gaylords. This fine powder, when introduced into the materila delivery system---typically by vacuum tubes which suck up the pellets, will burn in the barrel and cause spots/specs in the material flow prior to entering the mold. Although an additional process, there are a number of manufacturers that make cleaning units (both dry and wet) that clean the raw pellets before use in the molding process. I was involved with studies that captured the "Root Causes" of the main contributors for molded Lens rejects and this Pre-Cleaning Process had a very positive effect.

A simple QC check. To verify that the Spots/Specs ARE NOT contained in the raw material (pellets), Take a few pellets (perhaps 10) and melt them on an electric Hotplate being careful with the temperature as to not burn them. Once you have the clear pellets melted you can easily inspect them under a microscope to see if any Spots/Specs are evident in the base material. This will at least confirm if you have a material issue and that your problem may not be molding related.