Flow Mark in Injection Molding: Causes and Solutions

A flow mark is commonly referred to as a flow line. It can occur during the manufacturing process of injection molding. Flow marks in injection molding are defects that manifest as a line or series of lines forming a pattern different in color from the other parts of the molded material.
Flow marks in injection molding can be avoided if adequate measures are taken. The plastic injection molding industry ensures that safe plastic products are produced for different sectors. And effectively creates identical products on a large scale.
This process involves injecting molten materials into a mold. Several materials are used in the plastic molding process, including plastic, metals, glasses, confections, and elastomers.
If you have been thinking about how to start a plastic injection molding business or require plastics to be made for your business in large quantities, it’s essential to understand the system and process. The plastic industry is a lucrative one, and plastic production is predicted to double by 2050.
Making injected molded plastics is an art as well as science. Good knowledge and technical expertise is required to prevent errors. These errors can lead to huge losses for companies, especially in large-scale production.
Consequently, it is essential to know some common injection molding defects and how to fix them. The focus of this post is on flow marks. But below is a list of some other common errors in plastic injection molding production.

Sink marks

Small depressions can occur in thicker injection mold areas when shrinkage occurs inside the finished products. Sink marks occur as a result of an insufficient cooling time of the plastic in the mold.

Vacuum voids

These are uneven voids of air trapped close to the surface or within the product. Vacuum voids can develop from a portion of the cast from a mold when two parts are not correctly aligned. It can also occur from uneven solidification.

Weld lines

The process where molten plastics flow from different molds can create lines shaped like a plane. It is caused by inadequate bonding of two or more flow fronts.

Short shots

This happens when molten plastic does not get to some mold cavity. This can occur due to the wrong calibration of the shot capacities leading to a shortfall of plastic materials to fill the cavities.

Causes of flow marks in injection molding

These usually appear as lines, streaks, or patterns in a different color from the product color. Several factors can be responsible for the appearance of flow marks in injection molding.

A slow rate of injection speed

Flow marks in injection molding can occur when the injection speed is slow. When this happens, it is challenging to form a jet flow, thus allowing unevenness in the surface layer that results in flow marks. Furthermore, if the product is too thick and the gate is small, it could delay the filling speed leading to flow marks.

Low mold temperature

With low mold temperature, the surface layer solidifies quickly, making it difficult to establish a jet flow, resulting in a flow mark. It could also occur when the surface layer hardens faster than the resin filling.

Solutions to flow marks in injection molding

Typically, manufacturers will monitor the efficiency of the equipment used in the molding process to ensure the injections work at the right speed. Inspectors will examine samples of the plastic goods for flow mark patterns.
If they notice any flow mark in the injection molding process, they will make the necessary adjustments before the next lot is poured using the same equipment.
Plastic products with flow marks are often sold at a lower price even when there is no decrease in functionality. Many businesses try to produce plastic goods without any flow marks when the production requires smooth surfaces. Here are some solutions to the flow mark in injection moulding.

Raise the injection speed

This method is effective in eliminating the flow marks. Raising the injection speed can decrease or altogether remove any incidence of flow marks occurring. However, if the molded product is thick and the gate is small, this can affect the filing speed.

Slow down surface solidification

Another way to reduce the occurrence of flow marks is to increase the mold temperature. This makes it easier to form a get flow and reduces flow marks. It is imperative to skillfully implement these measures to prevent other problems from occurring
Sometimes, flow marks in injection molding are intentionally created by adjusting the speed of the injection. The plastic has the chance to cool and form a pattern. You can create an interesting design on the plastic products by regulating the various speed throughout the process.

The need to limit defects during injection molding

It is essential to maintain the standard procedures when handling injection molding tasks. A slight variation in the process can alter the outcome. In many cases, that means you will not get the best results and possibly experience loss of your resources. To avoid these pitfalls, it is essential to master a process that can be consistently followed at all times.
Some of the external variables that could influence the injection molding process include; the consistency of the plastic materials that are worked on and the injection mold’s thermodynamic features. However, we know that it is not possible to entirely eliminate the external variables. Still, the operator can make efforts to lower the impact.
We have identified some of the best ways to avoid flow marks in injection molding. However, certain ecological elements can have a significant impact on the molding outcome as well. These elements can alter the processes by influencing the conditions in which they are done.
Such elements include the humidity level in the factory, environmental temperature, and the elevation level of the product that is worked on. In particular, the humidity level can cause hydrolysis in the mold, which significantly affects the process. In other words, if these elements can be maintained at the proper level, common errors like flow marks in injection molding can be avoided.
Finally, injection molding is a complex process that may encounter challenges. The impact of defects can affect the quality and aesthetics of the product. The physical conditions of the molding process should be checked to prevent defects. Please visit our website for more information.

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