Have you ever stared blankly at an injection molding machine wondering what the heck all those technical parameters mean? Me too! But, like an old pair of jeans, once you get to know them, they fit you like a glove. So, let’s talk about them!
Here’s the thing, when it comes to selecting the perfect injection molding machine for your production line, there’s more to it than meets the eye. The right machine will depend on the product’s weight, shape, material, and how much of a speed demon you’re feeling like.
So, keep your eyes peeled because we’re going on a wild ride through the land of technical parameters, and when we’re done, you’ll be the coolest kid on the block.
So, What’s the Big Deal About the Injection Unit?
The injection unit is the heart and soul of the injection molding machine, and it’s got a few tricks up its sleeve. Let’s unravel them one by one, shall we?
From the following parameter table, it can be seen that there are six main parameters for the injection unit: screw diameter, screw aspect ratio, and theoretical injection volume; Injection pressure; Injection rate; Plasticizing ability.
1.1 Screw diameter (mm)
Think of it as the doughnut hole of the screw. Too big or too small, and you’re in trouble. The diameter needs to be just right for your production requirements.
1.2 Screw L/D ratio
The ratio of the length to diameter of the screw.
This isn’t a fancy cocktail recipe, but the ratio of the screw length to its diameter. Nail this ratio and you’re golden.
L：D
In the formula:
L: Screw length
D: Screw diameter
1.3 Theoretical Injection volume (cm3)
Ever wonder how much material the screw can spit out during injection? That’s your theoretical injection volume! It’s like the capacity of your coffee cup, only way more technical.
The theoretical volume means theoretical maximum volume,that the screw (or plunger) can maximum discharge during injection.
Or the cross-section of the screw multiplied by the stroke of the screw.
Vc =π /4 x D2 x S
In the formula:
Vc – Theoretical injection volume,
D – Screw diameter
S – Screw injection stroke,
1.4 Injection Weight (g)
This one’s a tough cookie. It’s all about the stroke and diameter of the screw, and let’s not forget about the temperature difference in the barrel and the injection pressure.
Injection weight = The maximum weight of a single injection
The injection weight of an injection molding machine is the maximum amount of injection that can be achieved during a single maximum injection stroke of the screw.
Due to the variety of plastics, their densities also vary. Therefore, for the convenience of statistics, the weight of PS (polystyrene) plastic is used as the standard.
During the entire process of injection molding, the density of plastic raw material changes correspondingly with changes in temperature and pressure.
Different plastics have different density changes:
Amorphous plastics: (PC,ABS,PS) density change of about 7%,
Crystalline plastics: The density change of (PE, PP, PA) is even greater, approximately 15% -20%.
Therefore, there is a difference in the measured volume of raw materials under plasticization compared to the volume of products at room temperature and pressure.
In addition, during injection, the molten material flows back into the screw groove, check ring, etc. Therefore, the injection quality of the machine should be:
W=Vc* αβ P= Vc* K * P= Vc* * P’
In the formula:
W – Injection weight (g)
Vc – Theoretical injection volume
α– Density correction coefficient, determined by plastic type and process conditions
β– Leakage correction coefficient of plasticizing device
P-Density of plastic products at room temperature
K-injection coefficient
P ‘– Corrected calculated density
What’s Next on the List?
1.5 Injection Pressure
You know the pressure you feel when you’re trying to squeeze a workout into your lunch break? That’s how your injection molding machine feels when it’s trying to fill the mold cavity with molten material. Only, it’s got plastic properties, geometric shapes, and mold structures to consider. Talk about pressure!
In order for the molten material to fill the mold cavity in a short period of time during injection, it is necessary to overcome the flow resistance at the nozzle, runner, mold cavity, etc. The injection pressure is not only a necessary condition for the molten material to fill the mold, but also directly affects the quality of the product, which has a significant impact on the dimensional accuracy of the product and the stress after molding. Therefore, the requirement for injection pressure is not only sufficient numerical value, but also stable and controllable. There are many factors that affect injection pressure, such as plastic properties, geometric shape and accuracy requirements of molded products, plasticization methods, nozzle and mold structures, as well as resin and mold temperatures.
The injection pressure is mainly determined by the following three aspects:
1) Factors that affect the flow performance of plastics: resin melt index, plasticization and mold temperature, injection speed, etc
2) Factors affecting flow resistance: mold runner and product shape and size
3) Requirements for dimensional accuracy of products.
1.6 Injection Rate:
This is all about speed, baby. A high injection rate is the need for speed that ensures your products have a uniform density and precision. Plus, it can reduce your molding cycle! Who doesn’t want to save time and money?
1.7Plasticizing Capacity
Last but not least, we’ve got plasticization capacity. It’s like the engine capacity of your car, but for your screw and material. This determines how much qualified molten resin they can produce per unit time.
Wrapping It Up: Are You a Master Yet?
Understanding the technical parameters of your injection molding machine is like solving a Rubik’s cube. It can be a bit overwhelming at first, but once you get the hang of it, it’s a walk in the park.
Remember, the right machine can make or break your production line. So, take a deep breath, arm yourself with this knowledge, and go conquer that production line like a boss!
You’ve got this, champ! Now, go out there and show that injection molding machine who’s boss!
