Table of Contents
Ⅲ. Countermeasures Increase the nozzle diameter. Increase the nozzle temperature. Increase injection speed. Increase injection pressure. Raise the cylinder temperature. Reduce the cushion. (Reduce the charging amount.).
What causes flow marks?
Flow marks are most commonly caused by resin cooling too quickly or improper gate location. They are supposed to be made by a sudden change of the flow front speed. The sudden change of the flow speed causes the difference in the cooling condition of the surface.
What is Flow Mark defect?
Flow marks, also known as flow lines, are molding defects that can occur in the manufacturing process of injection molding. They commonly occur when there is a large variation between cooling speeds of sections of the material as it flows through the mold.
What is sink mark in injection molding?
Description: Sink marks are small craters or depressions that develop in thicker areas of the injection molded prototype when shrinkage occurs in the inner portions of the finished product. The effect is somewhat similar to sinkholes in topography, but caused by shrinkage rather than erosion.
What causes flow lines in injection molding?
What Causes Flow Lines? Flow lines are often the result of variations in the cooling speed of the plastic as it flows in different directions through the mold. They also can occur when you’re creating pieces of differing thicknesses, as the thinner areas cool before thicker areas are fully filled, causing flow lines.
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 high gates in injection molding?
Injection fill speed is too high. The speed at which resin enters the mold has a big impact on finished parts. If the mold is filled too quickly, the molten plastic will react to the flow restriction at the gate.
How do you get rid of knitting lines?
How to eliminate Knit Lines Select resins that are less susceptible to knit line formation. Change the boss or gate locations. Thicken part walls to slow down the resin cooling process however be careful not to make them too thick that it causes sink marks.
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.
What is a sink mark?
Sink Marks are areas in a molded part where the surface is deformed into a depression. The depressions typically occur in areas of thick geometry and are caused by uneven cooling of the injection material. Sink marks are areas in a molded part where the surface is deformed into a depression.
What is nozzle drooling?
When nozzles are moved away from the mold after injection molding has been carried out, trickles of plastic from the sprue gate occur. This trickle of plastic is generally called the drooling (trickling), which is said to be caused by residual pressure stored in the sprue and runner.
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.
What is a 2 plate mold?
Two plate mold is the easiest injection mold structure and has many advantages. It’s consist with A side and B side 2 main parts, when it is load in ejection machine to do molding, A side is fixed and held still, B side is movable.
What does 3 plates weigh?
Two plates most often means two 45-pound plates per side of the bar, which including the weight of the Olympic barbell gives you a total weight of 225 pounds. Three plates, again, usually means three plates per side. Plus 45-pounds (which is how heavy the barbell weighs) gives you a total of 315 pounds.
What is the difference between two plate and three plate mould?
To sum up, two plate molds are the most commonly used injection moulds. It consists of one parting plane and mold splits into two halves, whereas three plate injection mold consists of two parting planes and mold splits into three sections.
How can I improve my sink mark?
A) Sometimes sink marks can be reduced by increasing the packing pressure along with the holding time and slowing the injection speed. This will depend on the location of the gates relative to the thicker wall sections and whether there is sufficient time to fill all areas of the cavity before the gate freezes off.
How do you stop a sink mark?
How to Prevent Sink Marks in Injection Molding Check Your Melt Temperature. In processing, one of the first things we want to verify to correct sinks is melt temperature. Make Sure You Have Enough Pack and Hold Pressure. Adjust Pack and Hold Time. Avoid Excess Mold Temperature. Ensure Proper Part and Mold Design.
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.
What is 3 plate mold?
A three-plate mold is used when part of the runner system is on a different plane to the injection location. This second parting plane enables the runners and sprue to be ejected when the mold is opened. In the following diagram of a three-plate mold, the runners will be ejected separately to the cavities.
