Rib is a frequently used feature in plastic injection molded parts design for the purpose to enhance the strength of the plastic parts, typical rib design see below figure.
The thickness and location is essential of the rib design. Usually, ribs should be designed with a thickness of 1/2 of the wall thickness to avoid a thick section at the base of the wall, which would cause sink marks on the part surface. Ribs are usually spaced at a distance at least twice the wall thickness to allow enough steel between the ribs for adequate cooling.
There are thousands reason to use hot runner system in injection molding but seems lacking of info not prefer the hot runner. As I know the hot runner can be considered as the extension of the barrel. In some cases it combines with the injection gate that it can inject to the part directly.
A appearance issue on a rear lamp part for automotive due to first use of a PMMA material. This is a blue opaque colored plastic including metallic particles in order to get a shiny aspect. There is important visual defect such as flow mark due to poor aggregation of particles with material.
This sounds more like the melt front losing injection pressure allowing the metallic particles to separate out or a knit line, which will be very difficult to solve. The melt fronts collide and then the particles fail to align in the same direction, creating a different look. Melt and mold temperatures will help, and valve gate changes as well, if used in the injection mold.
Try to schedule machines so that they will be running the same resin types: i.e.- leave a press to run clear and white resins or one that runs all of the nylon jobs. That will reduce the amount of purging required to get rid of the ABS when switching to PC and so on. Run a press empty before starting a changeover. Make sure everyone is prepared for the change over before it happens. If you must do a color change between molds, run a bit of natural through the last mold, providing it has a hot runner. Cold runners will be more about cleaning the hopper, barrel and screw out. Make sure the material handlers know how to properly clean a resin line or hose/hoppers. Use Nerf balls with WD-40 on them is one of the best ideas I've used over the years.
If you want to eliminate or reduce the parting line on you plastic products, there are too many ways to solve it.
- The mold design must be very robust and the sliding cores that form the parting line are located in such a way that the slides come together in exactly the same position every time.
- There is enough pre stress on the heel blocks so that no movement occurs during injection.
- Most important the faces that butt together must be a very good finish using a surface grinder and a fine polishing wheel. Be allowed to spark out thus taking a longer time than normal.
- The mold design must allow the parting line to part assembled accurately and be clamped together during machining edm and of course must be polished together.
It is very common to use PP to test the function of a mould re slide movements venting flash etc. before using the more expensive and more demanding resins. PP is also used at the end of the run to purge along with a suitable purging compound and ensure there are no deposits of the high temperature resin left in the system as can play havoc with a hot runner mold being hung later. There are also wax injection systems available for testing moulds on the bench. I haven't used one for a long time now. Or the old trick of burning a candle under the sprue. The resulting soot deposits inside the mold can tell you a lot. i.e. mismatch and flash.
Ribs that are deep should be quite narrow with as much draft as you can get. Use you tolerances and DRAW POLISH the mold. The more and deeper the ribs, you have to have that much more ejection area just to get the plastic part out without marks or distortion of the part, just based on friction of the shrinking part and the steel; and the likely result of not filling the rib at all (even more shrinkage). As a rule of thumb, the rib should be no thicker than the wall that it is attached to (sink marks), in fact only 50% of the wall and 2-3X wall for the depth would be a lot better.
The best way for you to learn mold design would be to work for a company that designs and makes a lot of molds. Do some research and try to get a job with a mold company that has a very good reputation. Try to find someone to learn from that has a lot of experience, good working skills and knowledge of mold design, and then learn everything from him or her that you can.
While having an education is good it will not give you everything you need to be a successful mold designer. You can learn to use CAD software and get a general idea of how molds are made in school but there is nothing like real life hands on experiences in the factory to learn from.
Let's face it, those of us in the plastics molding industry typically have to deal with sink marks with most parts. We all understand that the Geometry, Variations in Wall stock and Interior features sometimes go beyond design guidelines and result in sink marks. For reducing sink marks there are some process adjustments that may resolve the problem. If you have Quality Tooling and an accurate water temperature controller, you might be able to "Freeze Off" the Cavity side of the part while keeping a good hold pressure on the resin. This technique would usually add time to the total cycle but perhaps worth it. I have also used the RHRC (Rapid Heat Rapid Cool) process which is not used at many molders since it requires a Steam System that is piped to the Molding Presses
Soft start is designed to make sure any moisture that may get into the heaters will be baked out at low slow temperature rise before higher temperatures are applied. This will prevent your heaters burning out prematurely. Many times when I have to trouble shoot a hot runner in the field, a customer has issues starting up a system that has been running a filled resin. The suggestion of cleaning out the filed resin at shut down would not void a warranty. In fact, if the hot runner supplier heard that they would support it.
Using the mold to make plastic parts or Nylon part, depending on the application, one long core pin from one end of part. Cores mounted on top of mold.
The plastics are molded in the vertical position in the mold. The ID of these parts or Zero draft, to allow for the mixing elements to be inserted without regard to position - they fit either way and must be a snug fit to the ID of the nozzle. Water bubblers run the entire length of each core with a threaded tip on the end- water tight with a little super glue.
By applying all the above it is arrived per cavity about 3.4 KN force will be required to pull out the core, then for 4 cavities and multiplying by 1.5 as w.o spring load concept consideration, total force needed to pull out the 4 core pins for this 4 cavity mold will be around 21 KN or 2140 Kgf.
Draft will be, for the ID:15mm, the core pin dia will be at the end it is Dia 15mm and in the bottom 14.1, even the core pins are provided as two halfs (155mm Length each) to match the overall length 310 from top and bottom. Both side the core pulling will be done.