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What’s the cold slug? It’s the small nub of plastic that cools and solidifies inside the nozzle tip during the cooling phase of the injection cycle. This occurs because—while the nozzle is heated—the tip of the nozzle is pressed against the cold, water-cooled mold steel.
What causes cold slug in injection molding?
Cold slugs – A small non-uniform area on the part caused by an improperly heated piece of plastic becoming attached to the part. Flow marks – A wavy pattern or discoloration caused by a slow injection speed which allows the material to cool too quickly.
What is the purpose of the Cold slug well?
A trap placed opposite the sprue in an injection molding machine. Designed to capture a cold slug so that it does not interfere with the subsequent production cycle.
What is back pressure in injection molding?
Back Pressure in an injection molding process is often defined as “the resistance of the screw to recover as the metering section pumps molten plastic through the non-return valve to the front of the screw.” When this position is reached, the screw will stop rotating.
What causes porosity in injection molding?
Once the material is injected into the mold cavity, it begins to cool and shrink. This shrinkage can cause voids or porosity to form in the middle of the wall thickness, as the material shrinks towards the mold wall that is causing the cooling. Porosity is generally found in thicker sections of parts.
How do you prevent jetting in injection molding?
To avoid jetting, mould geometry and process conditions have to be altered to induce laminar flow within the cavity, filling from the gate end as an unfolding melt front rather than an uncontrolled jet of melt. Reducing overall injection speed will help.
How do you fix short shot injection molding?
A short shot is the incomplete filling of a mold cavity which results in the production of an incomplete part.Remedies Avoid hesitation. Eliminate air traps. Increase mold and melt temperature. Increase ram speed. Change the part geometry. Use a different material. Increase the maximum injection pressure for this part.
What is Mould temperature control?
The mold temperature controller circulates cooling fluid through the mold’s cooling circuits to provide equilibrium to the heat flux experienced by the mold for every cycle. It is common to run separate mold temperature controllers for each mold half. This set-up allows for greater process control and processability.
What are the types of runner according to cross section?
There are two primary types of runner systems – cold runners and hot runners. Cold runners are cut along the parting line of a mold, are cooled by the mold, solidify and are ejected from the mold during each molding cycle.
How do you prevent warp in injection molding?
Solution: Increase residence time by adding time to the cooling process of the cycle. This will ensure the material receives the proper amount of residence time and eliminate mold warping. If the barrel temperature is too low, the resin is not able to heat up to the proper flow temperature.
How do you get rid of flow lines in injection molding?
How to Prevent Flow Lines Increase the injection speed, pressure, or material temperature: Slow-moving molten plastic is more likely to cool quickly and cause flow lines. Round the corners of the mold where wall thickness increases: This helps keep flow rate consistent to the thicker sections and prevents flow lines.
What is a sprue puller?
A sprue puller is one of many design requirements for most two-plate, cold-runner molds in order for it to run fully automatic. It is typically located directly opposite the shank end of the sprue bushing and its purpose is, as the name implies, to pull the molded sprue out of its bushing.
How do you know if you have injection mold?
A clear indication as to whether an object has been injection moulded is its complexity, signs of feed points (see Fig. 1) or ejector pin marks (see Fig. 2). Nearly all, complex three-dimensional plastic components are injection moulded.
Why are injection molds water cooled?
Chilled water is channeled through the molds and tooling to remove heat as quickly as possible from the injected plastic. Cooling is most often the longest part of the production cycle, so any reduction in wait time is beneficial.
Why sprue bush is in the shape of taper?
During casting or molding, the material in the sprue will solidify and need to be removed from the finished part. It is usually tapered downwards to minimize turbulence and formation of air bubbles.
What is meant by cold slug?
What’s the cold slug? It’s the small nub of plastic that cools and solidifies inside the nozzle tip during the cooling phase of the injection cycle. This occurs because—while the nozzle is heated—the tip of the nozzle is pressed against the cold, water-cooled mold steel.
How are injection molds cooled?
Injection Mold Cooling Methods There are two standard methods for cooling systems: air cooled or fluid cooled. Air cooled molds are not frequently used as they take a long time to reduce the heat in the injection mold via heat transfer dissipation to the surrounding air.
How do you fix injection molding problems?
Redesign the mold with wider channels or gates for better flow. Increase injection speed or pressure or choose a thinner base material to improve flow. Increase mold temperature to prevent material from cooling too rapidly. Add additional air vents or enlarge existing vents in the mold to allow trapped air to escape.
How do you reduce injection pressure?
Select a different material with a lower viscosity, which requires less injection pressure to fill the mold. Increase the melt temperature to reduce the viscosity. This reduces the injection pressure required to fill the mold.
How the jetting problem can be solved?
Remedies. Optimize gate design and position. Direct the melt against a metal surface by repositioning the gate or use an overlap or a submarine gate. Use a tab or fan gate to slow down the melt with a gradually divergent flow area.
What do you mean by cooling system in injection molding?
The aim of the cooling system of a plastic injection mold is to provide thermal regulation in the injection molding process. When the hot plastic melt enters the mold cavity, it cools down and solidifies by dissipating heat through the cooling system.
What is the difference between runner and gate?
From the molding nozzle the sprue leads into the runner, which then directs the melt into the mold cavity through the gate. At the end of the runner is the gate leading into the mold cavity. The gate leaves a surface blemish on the part. It is small and designed to freeze before the part, runner, or sprue freeze.
