Possible Causes of Molding Defects of Plastic Food Containers
In the last 2 articles, we've shown you top 10 plastic injection molding defects such as shot shot, flash, knit lines, voids, sink marks and more.
10 Plastic Injection Molding Defects Part 1
10 Plastic Injection Molding Defects Part 2
In this article, I will give you a brief introduction of the possible causes of molding defects of plastic products.
The injection molding defects contributions are 4M: Machines, molds, materials and men (operators). According to the study about "Root causes of the most common injection-molding defects" by Texas Plastic Technologies, we can found that about 60% of the plastic injection defects are caused by molding machines and some by plastic material, molds and operators.
Caused by Injection Molding Machine
1.Excessive Injection Pressure - Trap Air.
If the injection pressure is too high, the air will be trapped inside and compressed. This will lead to the increase of temperature. That's the main cause of the burn marks defects.
2.Excessive Injection Pressure - Force the mold to open.
Excessive injection pressure will overcome clamp pressure of the molding machine and force the mold to open slightly. Therefore some molten plastic might flow out of the mold and become flash.
3.Excessive Temperature - Trap Air.
High temperature will speed up the plastic to melt faster. Thus the molten plastic will be more fluid and trap air inside. That's how voids (bubbles) occur.
4.Insufficient Injection Pressure - Molten plastic crawl over cooling layer.
If the injection pressure is too low, the material will not form smooth layers against molding surface. Instead, the molten plastic covers the cooling layer and causes flow lines.
Caused by Molds
1.Section Thickness Too Great - Pressure Loss
Plastic material nears thicker walls will be cool down lastly. If the section thickness is too great, plastic will be pull away toward solid section and cause a void.
Venting systems are key to exhaust gases and airs out of the mold. If vents are not deep or wide enough and vents are insufficient, then airs will be compressed and form burn marks on plastic products.
Caused by Material
1.Foreign Materials Or Additives
If mixing two incompatible plastic types, the two types can't bond together. When products produced, you will see delamination occurs.
2.Excessive moisture - Steam Escape from Material
All types of plastic need a small amount of moisture in order to be processed properly. However, too much moisture will change into steam when encounter high temperature. Steam will escape from the material and form a gas pocket as a void.
3.Improper flow rate - Pressure Increase When Material Flow Fast
Different plastic have different flow rates. The stiffer materials are usually stronger. If the easy-flow materials are adopts, it will increase the pressure inside and blow the mold open, which causes flash.
Caused by Men (Operator)
1.Inconsistent cycles - Cause Cold Spots in Heating Cylinder
Inconsistent cycles will cause cold spots in the heating cylinder, the material inside will flow slower and solidify sooner and cause a non-fill condition - Short shot.
2. Early gate opening - Material Not Solidified Enough
If the gate is opened too soon, the injection circle is shortened and the material doesn't have sufficient time to cool down which causes sink marks.
Though multiple factors can lead to plastic injection defects, it is not inevitable. For sourcing manager, how to avoid purchasing defective plastic food containers? A skilled plastic food storage containers manufacturer will be reliable. Take us for example, we check the machine and mold in regular basis to prevent any potential risk. When it comes to the material, all we use is type 5 PP plastic and no re-grind resin is used. Our injection molding operators have years of experience and we have our QC team to do inspection during each step of the production. As a premium plastic food storage containers, we are confident to say that not only the appearance, but also the quality are cutting-edge.
- 2018-01-04 09:26:43
In the last 2 articles, we've shown you top 10 plastic injection molding defects such as shot shot, flash, knit lines, voids, sink marks and more.
10 Plastic Injection Molding Defects Part 1
10 Plastic Injection Molding Defects Part 2
In this article, I will give you a brief introduction of the possible causes of molding defects of plastic products.
The injection molding defects contributions are 4M: Machines, molds, materials and men (operators). According to the study about "Root causes of the most common injection-molding defects" by Texas Plastic Technologies, we can found that about 60% of the plastic injection defects are caused by molding machines and some by plastic material, molds and operators.
Caused by Injection Molding Machine
1.Excessive Injection Pressure - Trap Air.
If the injection pressure is too high, the air will be trapped inside and compressed. This will lead to the increase of temperature. That's the main cause of the burn marks defects.
2.Excessive Injection Pressure - Force the mold to open.
Excessive injection pressure will overcome clamp pressure of the molding machine and force the mold to open slightly. Therefore some molten plastic might flow out of the mold and become flash.
3.Excessive Temperature - Trap Air.
High temperature will speed up the plastic to melt faster. Thus the molten plastic will be more fluid and trap air inside. That's how voids (bubbles) occur.
4.Insufficient Injection Pressure - Molten plastic crawl over cooling layer.
If the injection pressure is too low, the material will not form smooth layers against molding surface. Instead, the molten plastic covers the cooling layer and causes flow lines.
Caused by Molds
1.Section Thickness Too Great - Pressure Loss
Plastic material nears thicker walls will be cool down lastly. If the section thickness is too great, plastic will be pull away toward solid section and cause a void.
Venting systems are key to exhaust gases and airs out of the mold. If vents are not deep or wide enough and vents are insufficient, then airs will be compressed and form burn marks on plastic products.
Caused by Material
1.Foreign Materials Or Additives
If mixing two incompatible plastic types, the two types can't bond together. When products produced, you will see delamination occurs.
2.Excessive moisture - Steam Escape from Material
All types of plastic need a small amount of moisture in order to be processed properly. However, too much moisture will change into steam when encounter high temperature. Steam will escape from the material and form a gas pocket as a void.
3.Improper flow rate - Pressure Increase When Material Flow Fast
Different plastic have different flow rates. The stiffer materials are usually stronger. If the easy-flow materials are adopts, it will increase the pressure inside and blow the mold open, which causes flash.
Caused by Men (Operator)
1.Inconsistent cycles - Cause Cold Spots in Heating Cylinder
Inconsistent cycles will cause cold spots in the heating cylinder, the material inside will flow slower and solidify sooner and cause a non-fill condition - Short shot.
2. Early gate opening - Material Not Solidified Enough
If the gate is opened too soon, the injection circle is shortened and the material doesn't have sufficient time to cool down which causes sink marks.
Though multiple factors can lead to plastic injection defects, it is not inevitable. For sourcing manager, how to avoid purchasing defective plastic food containers? A skilled plastic food storage containers manufacturer will be reliable. Take us for example, we check the machine and mold in regular basis to prevent any potential risk. When it comes to the material, all we use is type 5 PP plastic and no re-grind resin is used. Our injection molding operators have years of experience and we have our QC team to do inspection during each step of the production. As a premium plastic food storage containers, we are confident to say that not only the appearance, but also the quality are cutting-edge.
Tom
NO.12, Guanghua North Fourth Road, Jinping Area, Shantou, China
