Over many years' experience with melt flow index (MFI) testing with many operators we have concluded that for our purposes as a custom injection molder, we do not sweat getting exact numbers compared to the numbers published by the resin supplier. We have built up our own database of acceptable ranges of melt flow index based upon our testing alone.

If there comes a time where a dispute occurs, i.e. we have a reading unacceptable outside of the range of our database of readings and we have revivified by repeated tests. We will use an A2LA registered outside lab service to perform a more sophisticated characterization of the resin. This may be via FTIR, GPC, TGA looking for the presence of contaminants or hybrid molecules of the same resin, and assuming we detect something abnormal, take this to resin maker. This generally ends the dispute. Fortunately this doesn't happen very often with the major resin makers and is more likely to occur with compounders or even bulk distributors who have been known to make packaging/labelling errors when they repackage the material in bags or barrels out of a bulk train car load or similar shipment that they have received.
The labels that we produce here at Aco Mold are also quite durable, and although they are typically meant for indoor applications, we were perhaps the first company in the nation to provide laminate product protection for in-mold labeling on thin unsupported films. This lamination provides wonderful resistance to scratching/scuffing/fading, and allows the color to pop in ways that traditional liquid coatings don't allow for. It turns "throwaway" packaging into something much more long-lasting. I do see in-mold labeling becoming a bigger player in the automotive industry, as the need for decoration will always be great, but it is also making impressive headway in consumer packaging and should continue to grow over the next few years. In-mold labeling saves labor, it saves time, it is very sustainable (product and packaging becomes one), and the decorating quality is vastly improved and can be greatly personalized (especially in short run, digital applications). It can be difficult to convince manufacturers to switch, but it seems the main hurdle is getting the automation set up (and the investments that must be made, Glyn). From there, customers slowly begin to realize the benefits, and there is no turning back.
If you wish to insulate the heated injection mold from the platen. It is best insulate the injection mold from the mounting plate and then use tower temperature water through the mounting plate to dissipate the radiant heat still transfers through.

It is also a good practice to insulate the heated cavity and core from the injection mold base. This will first help maintain the heat (energy) in the needed area. Second it will reduce the time the cavity and core reach the desired process temperature. Third it will reduce the mass of steel the needs to be cooled prior to the injection mold being treated with the proper rust and corrosion preventative. Fourth the cavity and core can be preheated with injection mold from remaining cool enough to handle an safely install.
For starters, my belief is that it's always best to be cautious and practice lock-out/tag-out in the situations, especially if there is any doubt about risk to an employee. Remember that any injection molding machine can easily crush body parts if safeties fail. Certainly, if the part removal or maintenance activity requires climbing on to or in to the injection molding machine, it must be locked out. However, there are instances where I do think that shutting an injection molding machine down to perform some routine maintenance is too extreme.

When you do determine exactly what your lock-out/tag-out policy is make sure you formalize it in a written procedure, or update your current procedure. Then train all personnel who perform these activities to the new practices. Be specific to equipment types, also, as different types of equipment will require different methods. Don't write something so generic that it is of no practical value.
Weld lines is something you tend to get in an injection molded product with multiple flows. Question is 1) Is the weld line strong 2) Is the appearance acceptable. If there is only one/ two weld lines which can not be accepted, in addition to what is already covered, I would add sequential valve gating. Open the valve gate just as it is about to form a weld. I have done many projects simulating on Moldflow by changing thickness (flow leaders/ deflectors) and converting to a meld line which is less severe. The results can not be guaranteed as the flow pattern can change with the viscosity of material and if product design has thickness variations. We have observed that in Moldflow, the weld lines are seen but in product, they are not noticed. This happens if the inner layer material shear heating is high which heats the surface material.

The higher the melt skin temperature and injection mold surface temperature at time of contact with melt and higher the pressure, the better the appearance and strength retention. Weld-lines are an inevitable consequence of any tool feature that splits flow before it rejoins, just as night follows day. Their visibility and physical properties versus the rest of the molding will vary depending on the many variables mentioned. Avoid mold release spray like the plague, unless you want dreadful loss of strength. High aspect ratio metallic and pearlescent pigments are bound to accentuate appearance. Post-machining a real option, but adds cost, creates material swarf or cut blanks that can (with good control) be re-fed into the material feedstock (at a slight energy penalty, of course). No magic solution, just common-sense application of one or other of the approaches mentioned.
The concept of injection molding is to fill plastic materials to the cavity with the least pressure. Because of the compressible nature of a polymer melt there will be a pressure difference between the last point to fill and the gate with a matching difference in density and therefore shrinkage. If you can fill the cavity with a low pressure then the pressure difference from lptf and gate is smallest. To fill the cavity with the least pressure means that the apparent viscosity of the melt must be as low as possible and this is a function of temperature and shear rate (which for any single injection mold can be related to speed of filling). Ultimate filling speed is frequently compromised by poor venting resulting in gas burns or 'Dieseling'. Often the filling speed is reduced (wrongly) in preference to pulling the injection mold and improving the venting - but it is easier to do!
Shot Wt. 34 lbs.
Cycle Time 65 sec.
Resin Polypro
spec heat .87 Btu / (lb. F) See Chart
spec heat H2O 1.003 Btu / (lb/ F) @ 55 F
Ejected Part Temp. 120 F
Melt Temperature 440 F
Delta T 320 F
Temp. Rise in H2O 5 F (This is max allowable temp rise 2-3 F is suggested)
One Gallon H2O 8.33 lbs.
One Ton Chiller 12,000 Btu

Heat Load (Resin Thru put x Spec Heat (Resin) x Delta T = lbs. / Hr. of coolant required
(Spec. Heat (Coolant) x temp rise of coolant)
Thermal management approach does require time, effort and a good understanding of thermodynamics that is well beyond most tooling engineers. As with mold flow analysis, the new thermal approaches will take time to learn. The injection mold is basically a heat exchanger. However, it is a unique and specialized heat machine that requires attention if optimum performance is to be reached. I have seen a lot of injection molds done over the past three decades, from small medical to automotive body components. The approach is the same but different, that is applying engineering over design. I am always surprised at the low level of engineering done in regards to injection molds, even down to basics like structural strength (gee my tool is flashing). Transient heat flow, a CFD method, is becoming reliable. There are learnings from this technique and others that will go a long way to accomplishing solid thermal management.
The injection mold designing stage is the best time to place water in an injection mold but many of us have a shop full of molds that were designed by others and usually for slower cycles than expected today. Another part of the water flow equation as in the whole injection molding process is to find the water flow, injection mold temperature or BTU removal that works for your part. When part quality changes that should be one of the points to check before making adjustments to the process. The dynamics of water flow always wanting to follow the path of least resistance causes different water flow in the plant as injection molds are shut down, started up or changed. If the capacity of your cooling system changes so does the ability to remove heat or in some cases remove too much heat from the injection mold.

One of the things I find most frustrating is that when building multi cavity molds with independent circuits to each core/cavity, I find that the injection mold techs have jumped all the circuits together with a single in and out. When questioned they'll say... but I only have 2 in and 2 out circuits on the machine.
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