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LLDPE Powder
 
 

PROBLEM

POSSIBLE CAUSES

SUGGESTED SOLUTIONS

EXCESSIVE OVEN CYCLE 1. LOW OVEN TEMPERATURE 1. INCREASE OVEN TEMPERATURE CHECK OVEN DAMPER AND TIMER

2. EXCESSIVELY THICK MOLDS

2. REDUCE MOLD WALL THICKNESS
3. OVEN HEAT CAPACITY INSUFFICIENT 3. CLEAN AND READJUST BURNERS CHECK AIR VELOCITY AND CORRECT
4. MOLDS SHIELDED

4.

A) ELIMINATE SHIELDING OF MOLD

B) USE LOWER DENSITY RESIN

C) USE HIGHER MI RESIN

RESIN BRIDGED IN MOLD

1. POOR MOLD DESIGN 1. DESIGN RECESSES WITH MORE GENEROUS RADII. AVOID RIBS WITH WIDTH OF LESS THAN 4X WALL THICKNESS.
2. IMPROPER MOLD ROTATION 2. CORRECT RATIO AND SPEED OF ROTATION
3. POOR POURABILITY OF POWDER

3.

A) MAKE SURE POWDER HAS ACCEPTABLE POURABILITY. CHECK AIR VELOCITY AND CORRECT.

B) USE LOWER DENSITY RESIN

C) USE HIGHER MI RESIN

WARPED PARTS

1. UNEVEN COOLING CAUSED BY RESIN PULLING AWAY FROM MOLD WALL 1. EXCESSIVE OR TOO EFFECTIVE OLD RELEASE ROTATE DURING COOLING CYCLE. MAKE SURE MOLD IS VENTING TO PREVENT VACUUM INSIDE PART. ADD AIR PRESSURE THROUGH DRILLED SPINDLE DURING COOLING. REDUCE COOLING RATE DURING INITIAL PART OF COOLING CYCLE. REDUCE OVEN TEMPERATURE. AVOID LARGE FLAT PANELS.
2. UNEVEN COOLING CAUSED BY SHIELDING PANELS 2. REMOVE SHIELDING PANELS AND REPLACE WITH SCREEN
3. UNEVEN COOLING CAUSED BY CLOGGED WATER NOZZLES 3. CHECK AND CLEAN NOZZLES ON A PERIODIC SCHEDULE
4. COLLAPSE DUE TO VACUUM INSIDE 4. VENT MOLD
5. EXCESSIVE RELEASE AGENT

5.

A) REDUCE AMOUNT OF MOLD RELEASE AGENT

B) USE LOWER MI RESIN

POOR PART RELEASE

1. LACK OF RELEASE AGENT 1. REAPPLY OR USE MORE RELEASE AGENT. IN SOME CASES, OLD RELEASE AND FILM MUST BE REMOVED, AND NEW MOLD RELEASE APPLIED FOR GOOD RESULTS.
2. IMPROPER RELEASE AGENT 2. USE MOLD RELEASE THAT IS EFFECTIVE FOR RESIN AND TEMPERATURES USED
3. UNDERCUTS IN MOLD 3. DESIGN MOLD WITH TAPER OR PARTING LINE AT UNDERCUT SO THAT MOLD HAS DRAFT ANGLE FOR PART REMOVAL.
4. SHRINKING ONTO LARGE, DEEP INSERTED AREAS 4. PROVIDE ADEQUATE TAPER. USE VERY EFFECTIVE MOLD RELEASE ON INSERT AREA. REMOVE PART WARM. PROVIDE ADEQUATE PROVISION FOR APPLYING FORCE TO SEPARATE MOLD HALVES.
5. MOLDING TOO HOT 5. INCREASE COOLING CYCLE
6. DEGRADATION OF PLASTIC

6.

A) REDUCE OVEN TEMPERATURE

B) INCREASE CYCLE TIME

MOLDING BUBBLED, PINHOLED ON EXTERIOR OR HAVING ROUGH INTERIOR SURFACE

1. WATER IN MOLDD 1. ELIMINATE WATER IN MOLD BY RUNNING WITH WARM MOLDS AND DRY MOLD BEFORE CHARGING WITH POWDER
2. INSUFFICIENT CYCLE TIME OR MOLDING TEMPERATURE 2. INCREASE OVEN CYCLE. INCREASE OVEN TEMPERATURE. REDUCE WALL THICKNESS OF PART. USE HIGHER MI RESIN. USE LOWER DENSITY RESIN.
3. MOLD SURFACE DIRTY 3. CLEAN MOLD SURFACE

SURFACE PITTING

1. CONTAMINATED MOLD SURFACE 1. CLEAN MOLD
2. RELEASE AGENT NOT APPLIED SMOOTHLY 2. USE LESS MOLD RELEASE SPREAD RELEASE AGENT BY WIPING PRIOR TO DRYING

POOR TOUGHNESS

1. INCOMPLETE FUSION OF RESIN 1. INCREASE OVEN CYCLE. INCREASE OVEN TEMPERATURE. USE RESIN WITH LOWER DENSITY. USE RESIN WITH LOWER MI.
2. NOTCH SENSITIVITY OF RESIN 2. ELIMINATE NOTCH IN MOLDING
3. TOO SLOW COOLING 3. AVOID EXCESSIVE AIR COOLING. COOL AS RAPIDLY AS POSSIBLE.
4. PART TOO HOT ON EJECTION 4. REMOVE PARTS AFTER SUFFICIENTLY COOLING.
5. IMPROPER COLORING 5. SELECT PIGMENT AND PIGMENT LOADING THAT DO NOT MATERIALLY AFFECT IMPACT STRENGTH. USE COLOR COMPOUNDS.

BUBBLE ON PARTING LINE

1. VACUUM INSIDE PART DUE TO PLUGGED VENT OR LACK OF VENT 1. OPEN VENTS. INSTALL VENTS. RELOCATE VENT TO END IN MIDDLE OF MOLD. USE SMALL AMOUNT OF GLASS WOOL IN VENT. USE LOW CONDUCTIVITY MATERIAL SUCH AS TEFLON OR VERY THIN STAINLESS STEEL TUBE FOR VENT TUBE.
2. DIRTY MOLD PARTING LINE

2.

A) CLEAN PARTING LINE. CORRECT MOLD MOUNTING.

B) DECREASE OVEN TEMPERATURE. DECREASE OVEN TIME.

UNEVEN WALL THICKNESS

1. IMPROPER MOLD ROTATION 1. CORRECT MOLD ROTATION TO GET ADEQUATE NUMBER OF POWDER OVERLAYS AND EVEN COVERAGE
2. UNEVEN MOLD THICKNESS 2. USE CARE IN DESIGNING MOLDS TO ELIMINATE EXCESSIVE VARIATIONS IN MOLD WALL THICKNESS (ESPECIALLY IMPORTANT WITH STEEL MOLDS)
3. SHIELDING OF MOLD 3. MOUNT MOLD ON SPIDER TO MINIMIZE SHIELDING
4. BUFFETING OF AIR FLOW IN DEEP- DISHED AREAS 4. AVOID DEEP-DISHED AREAS. REDUCE THICKNESS OF MOLD IN DISHED AREAS. OPEN HOLE THROUGH HANDLE AREA TO ALLOW AIR FLOW THROUGH KISS-OFF IN MOLD.

EXCESSIVE FLASH ON PARTS

1. POOR PARTING LINE

1.

A) CLEAN PARTING LINE AND APPLY NEW MOLD ELEASE ON PARTING LINE

B) REMATE PARTING LINE

C) CHECK VENT FOR PLUGGINGG

D) REDUCE AIR PRESSURE IN PART, IF USED

E) USE LOWER MI RESIN

DISCOLORED PART

1. POLYMER DEGRADED 1. DECREASE OVEN TEMPERATURE. DECREASE OVEN TIME. FLUSH MOLD WITH INERT GAS.
2. IMPROPER/POORLY STABILIZED COLORANT. 2. USE APPROPRIATE COLORANT.

SPECKED COLOR AND LUMPS OF COLOR IN DRY BLENDED COLORS

1. INSUFFICIENT BLENDING 1. BREAK UP AGGLOMERATES OF PIGMENT BEFORE BLENDING. USE HIGH INTENSITY MIXER. USE A COLOR COMPOUND.