The locations of the air leakage areas in the moulds are located in the areas that are filled at the end of the injection cycle or phase. A common cause of the trapped air defect is an insufficient size of the mould vents. Another common cause is when racetracking occurs (tendency of the polymer melt to flow preferentially in thicker sections leaving thinner areas with trapped air). Translated with www.DeepL.com/Translator (free version)

Now, let’s step into a hospital. Those medical devices and components? A lot of them trust PP. Why? Because it can be sterilized and stands strong against chemicals. It’s like having a reliable soldier in the medical battlefield. And don’t get me started on automotive parts. With its endurance, PP is often the go-to for parts that face daily wear and tear.

Sinkage marks are depressions in the surface of the plastic injection moulded part caused in the last phase or stage of the plastic injection moulding process, during the cooling process. The thicker sections of the plastic cool at a slower rate than the others, resulting in a higher percentage of shrinkage in that local area. After the material on the outside has cooled and solidified, the material on the inside begins to cool and its shrinkage pulls the surface inwards, causing a surface depression.

Remember those advantages of PP we talked about? Here’s where they shine. In the food industry, PP is like the unsung hero. Those storage containers in your kitchen? Probably made of PP. It’s not just about being cost-effective. Its chemical and moisture resistance means your food stays fresh and safe. Imagine a container that can handle your hot soup and cold ice cream without a fuss. That’s PP for you.

Lastly, the gate. This is the last stop before our PP fills the mold cavity. It’s like the doorway to a room. The gate’s depth and type play a pivotal role. For instance, a depth of the gate that’s about half of the wall thickness ensures optimal flow.

Some of the practices we develop in the Moldblade Engineering Department to correct the problem of incomplete filling are:

If welding or joining lines cannot be avoided, a good practice is to ensure that they are generated in low visibility or mechanically non-critical areas. This is often done by modifying the plastic injection gate, modifying the flow fronts and the areas where the weld/joint lines occur. Another practice is to try to achieve a good joint between the two fluxes so that the mechanical weakness that occurs is not excessive. To do this, the aim is for the junction of the two flux fronts to take place at the highest possible temperature and pressure, so that they are not far from the inlet port. Translated with www.DeepL.com/Translator (free version)

High pressure is the name of the game here. We’re talking about pressures up to 1500 bars. But, here’s a fun fact: PP hates moisture. So, we need to keep it super dry, ideally below 0.2% moisture content. It’s like keeping your phone away from water; it just works better.

In the world of PP injection molding, understanding the gating system is key. This is the pathway that guides the melted polypropylene into the mold, and it’s crucial for a successful molding process.

The jetting defect occurs when molten polymer is pushed at speed through a small area, such as the injection nozzle or gate, to access a much larger area. The jetting defect results in mechanical weakness in the part, surface imperfections and multiple internal defects.

Occasionally, the use of high compaction pressures causes acceptable sink marks by reducing volumetric shrinkage although these cannot be completely eliminated. This is because the volumetric change of plastic from melt to solid is about 25% and the compressibility of plastics at typical injection moulding pressure is only 15%, which means that it is impossible to compact the molten plastic sufficiently to compensate for cooling shrinkage.

The following recommendations can be used to reduce the impact of weld lines and parting lines on injection moulded parts.

Incomplete filling occurs when a one injection moulded part is missing material to correctly generate its geometry. This occurs when the molten polymer cannot fill the entire cavity (or cavities) in the Injection mould, usually the thinner sections where the polymer melt cools before completely filling the mould. Any factor that increases the flow front resistance of the polymer melt can result in incomplete filling. Some of these factors are:

Okay, think of PP plastic as the everyday hero in the world of plastics. It’s like your daily coffee—it’s everywhere, and it won’t empty your wallet. In fact, using PP can make things cost up to 20% less. And the best part? No waiting around! It’s always there when you need it. Making products with it? It’s a total win.

Do you recall playing with those modeling clays as a child? Imagine a slightly more sophisticated version of that. Plastic injection molding is where plastic materials (in this case, polypropylene) are melted and then injected under high pressure into molds. Once they solidify, we have our desired plastic parts. A process I’ve come to respect and admire for its precision and efficiency.

The warping or twisting of an injection-moulded plastic part is therefore due to the existence of a series of residual internal stresses in the part which are in turn generated by the differential shrinkage of the material during cooling. If the shrinkage throughout the part is uniform, the resulting part does not warp or twist, it simply shrinks uniformly and becomes smaller. Thecrystalline polymers, e.g. acetal, nylon, high density polyethylene, polyethylene terephthalate and polypropylenecause the most serious problems with shrinkage from 1 to 4%. Amorphous polymers, e.g. polystyrene, acrylic and polycarbonate are more treatable, with shrinkages of only 0.3 to 0.7%.

Curves and angles are key in PP projects. For radii, aim for at least 0.5 times the wall thickness. It helps in reducing stress points. And for draft angles? A 1° to 2° angle is a good rule of thumb. It ensures the molded parts pop out smoothly without any hitches.

Next up, the runner. Think of this as the hallways in our house, branching out from the main entrance. The runner’s job? Distributing the molten PP to various parts of the mold. Now, here’s where things get interesting. Cold runner molds are commonly used in the plastic industry, especially for PP products. Their size? Often ranging between 3mm to 5mm in diameter. This size ensures a balance between material flow and cooling time, essential for product manufacturing with excellent resistance to defects.

Here’s something neat: PP plastic doesn’t let water or chemicals bully it. It has top-notch chemical resistance. So, when you’re thinking of food containers that don’t get all mushy with your lunch, or medical devices that stay strong, you’re thinking of polypropylene. It’s like the superhero cape for your spicy curry storage containers.

This one’s an old friend. It’s the most common material, a polymer derived from propylene monomers. With its high flexural strength and fatigue resistance, it finds its place in numerous consumer products.

Now, There are various types of gates available, choosing the right gate is like picking the perfect outfit. It needs to be just right. For PP, we often use pin gates. Why? Because they offer a good balance between flow control and minimizing stress on the material. The diameter of a pin gate is usually about half of the wall thickness of the part being molded. This ensures a fast injection molding speed while also preventing defects.

Polypropylene, or PP, is a star when it comes to living hinges. Why? Its natural flexibility. But, to get it right, you need to focus on design. Aim for a wall thickness of about 0.5mm to 1mm. This ensures the hinge is flexible yet durable. And a tip? Make sure to reduce internal stresses; it helps in the long run.

– Reduce the injection speed. High plastic injection speeds can cause jetting, which causes trapped air to appear right at the inlet gate. Reducing the injection speed will give the displaced air at the gate enough time to escape through the aeration zones.

You know, polypropylene (or PP for short) is pretty cool in the world of plastics. It’s a type of plastic polymer that can melt and be remolded without getting ruined. Imagine something that melts between 160°C to 220°C, and that’s PP for you! That’s why many industries love it for high-heat work.

Imagine the sprue as the front door of a house. It’s the primary channel where our molten polypropylene, a popular thermoplastic polymer, makes its grand entrance. Typically, the sprue’s diameter is designed to ensure a smooth flow, but it’s essential to remember that its size can influence the plastic injection molding speed. A larger sprue might speed things up, but it could also lead to wastage.

The burr is a defect that occurs when part of the molten polymer flows through the existing gaps in the injection mould such as parting plane, aeration zones, ejectors, etc. Burring occurs for the following reasons:

However, achieving uniform shrinkage is complicated by the presence and interaction of many factors such as the orientations of the polymer molecules, temperature variations in the mould walls, compaction variations in the plastic parts (over-compacted areas and under-compacted areas, due to unbalanced flow paths), etc. Note that areas of higher compaction, such as injection gates, have a lower shrinkage since part of the compaction of the molten polymer compensates for it. In contrast, areas further away from the gate are subject to less compaction and therefore tend to have a higher shrinkage.

Ever had toys that just won’t quit? Bet they had some PP components. This plastic’s got moves—it’s smooth, meaning things don’t wear out fast. Talking about its strength? Well, imagine a tireless runner. That’s PP for you, especially in the automotive industry. It’s perfect for automotive parts that face the hustle and bustle every day.

A complex dance of propylene with other monomers results in block copolymers and random copolymers. They are generally more flexible and have better resistance to external conditions, making them ideal for certain applications where the homopolymer might falter.

So, you’ve heard of polypropylene, right? Most folks just say PP. It’s light, weighing in at around 0.895 to 0.92 g/cm^3. But here’s the cool part: even though it’s light, it’s super strong. We’re talking about handling big-time pressure, like around 30 MPa kind of strong.

Trapped air will result in voids and bubbles within the moulded plastic part, incomplete filling or surface defects such as stains or burn marks.

Let’s break down the steps of molding polypropylene, or PP. First, we melt those tiny PP pellets. Then, we inject this melted goodness into molds. Next, we apply some serious pressure. And finally, we let it cool down. Sounds simple, right? But there’s more to it.

And you know what else? PP is super stretchy. Imagine a really, really stretchy rubber band, and that’s PP for you! It can stretch a whole bunch, sometimes even more than double. But it’s not just about stretching. If you bend it, it’s tough there too, with a strength of about 1.5 GPa.

So, let’s wrap this up. We’ve dived deep into this plastic stuff called polypropylene. It’s super cool how it doesn’t let water or chemicals mess with it. This makes it great for things like food boxes and even car parts. Plus, it’s friendly to our wallets. It’s more than just making stuff – it’s thinking ahead and being smart. Here’s to the rockstar of plastics, polypropylene, and its big future!

A rule of thumb to avoid excessive distortions in the part due to temperature differences after injection, is that the average temperature differences in any part of the part after injection should not be greater than 15-20ºC.

The trapped air defect appears when a certain amount of air cannot escape out of the mould during injection, a small area without material appeared in the injected part. In a correct Injection mould design, at each injection, air is exhausted through mould vents, mould inserts or even ejectors, which also act as vents.

A weld line (also called a weld mark) is formed when two melt flow fronts travelling in opposite directions meet. In contrast, a bond line occurs if these two fronts flow parallel to each other creating a bond line.

Let’s paint a picture: Cars need parts that are light but also strong, right? PP is the go-to choice for this. Using the injection molding method, we get parts that are perfect for cars because they help save fuel.

Traditionally, the joint angle between the two faces is used to differentiate weld lines from joint lines. A joint angle of less than 135º produces a weld line, while a joint angle of more than 135º is defined as a joint line. In general, a weld line mark disappears when the joint angle reaches between 120º and 150º. The weld lines are considered more critical than joint lines in terms of both aesthetics and mechanical properties of the joint. Translated with www.DeepL.com/Translator (free version)

Ah, the world of polypropylene injection molding. Brings back memories, doesn’t it? Of course, for some, it may seem like an intricate web of terminologies and processes. But don’t fret, dear reader. As a woman of experience, I’ll take you down the nostalgic alleys of my past where injection molding held my hand through various projects.

If you’re venturing into the world of injection molding, remember, choosing the right partner can make all the difference. ACO Mold makes over 300 mold on various products annually. With its expertise and commitment to quality, we can be the ally you need to bring your visions to life.

Weld lines and joint lines can be caused by holes or insertions in the part, the existence of multiple injection gates, or due to areas of varying wall thickness where hesitation or race-tracking occurs.

Think of PP molding like making pancakes. Too thick, and it won’t cook evenly; too thin, and it might tear apart. For PP, a consistent wall thickness, ideally between 1mm to 4mm, works best. And watch out for those sink marks; they can sneak up if the design isn’t spot on.

Now, temperature is a biggie. PP flows like honey when melted, thanks to its low melt viscosity. But, we need to keep things just right, between 200°C and 275°C. Too hot, and it might degrade. Too cold, and it won’t flow right.

The formation of wrinkles or waves is due to the fact that a part of the flow front cools rapidly on the mould walls producing a fold on the flow front itself. Themain factors influencing the formation of these wrinkles are the flow velocity, the temperature of the mould walls, and the temperature of the molten polymer, among others.

Ever noticed how some plastics shrink a bit after cooling? That’s PP for you. It can shrink by about 1-2.5%. So, when designing, always account for this little quirk. Think of it like buying a cotton shirt a size bigger because you know it’ll shrink after the first wash.

And guess what? Making stuff with PP is super fast. Sometimes it takes just a few seconds for one cycle, depending on what we’re making. So, it’s great for making lots of things quickly, which saves money in the long run.

A poor finish can be caused by the formation of wrinkles or waves at the edges of the part or in the last filling areas during injection moulding.

What makes PP special? Well, it’s lighter than most plastics because it has a low density. So, it’s super useful when you want something that’s not too heavy. Plus, it’s tough against many chemicals and even water. That’s why you often see it used in stuff like food packaging.

Some of the actions to be taken to improve the surface finish are related to actions to increase the flow rate and temperature of the molten polymer and the mould walls. Therefore, the improvement of the surface quality is achieved by measures such as:

The dimensional shrinkage of parts is inherent to the injection moulding process. Shrinkage occurs because the density of the polymer varies from processing temperature to ambient temperature (see, for example, the specific volume of a semi-crystalline polymer in Figure 5.46 – PVT curve). During the stages of the injection moulding process, cooling shrinkage produces a series of internal stresses in the part. These residual stresses act on the part with similar effects as possible externally applied stresses. If the residual stresses induced during moulding are high enough, the part after ejection from the mould may warp / twist or warp, resulting in defective parts.

One little thing to note: after you mold it, PP likes to shrink a tiny bit as it cools. Think of it like that shirt that gets a bit smaller after you wash it the first time. So, if you’re making something with it, just remember this, so everything fits perfectly. Neat, huh?