The Mix-Molder System: FAQ's

This question is not simply answered because for every “type” of plastic such as polyethylene (PE), polystyrene (PS), polypropylene (PP), etc., there are often numerous “grades” to choose from that can vary widely in their processing requirements. Some grades of a particular type of plastic may be designed by the resin manufacturer to melt at a lower temperature, and others at a higher temperature. Some grades may be formulated to flow very easily, and others not so easily. Some grades may have chemical additives or fillers mixed in with them to modify their properties, and others won’t. To make it even more complicated, sometimes two different types of plastics are blended together to create a COPOLYMER that has the combined properties of both plastics. In addition, thermoplastic resin manufacturers are constantly coming out with new grades and copolymer combinations, and discontinuing the ones that don’t sell well. It should also be noted, our machines are designed for use with thermoplastics, but not thermosets. The difference is, thermoplastics will remelt when they’re heated, thermosets won’t.

When choosing a particular thermoplastic, it’s important to make sure the temperature required to process it is within the capability of our machine (i.e. 600 F max.). Another important consideration is its melt flow rating (MFR), which is a measurement of how easily the plastic flows when it’s molten. In general, the higher the MFR, the easier it flows. Plastic grades formulated with a higher MFR usually work best in our hand-operated machines because less injection force (and torque, when mixing) is required to make them flow. Determining what MFR is required to successfully make your part depends on its size and shape. In other words, one particular plastic grade may flow well enough to inject a small part with simple geometry, but not flow well enough to completely fill the mold cavity of a larger part with thin walls or many intricate pathways. Choosing a grade that flows extremely easily usually comes at the expense of strength or other physical properties. So, determining the best plastic grade & MFR for a particular application is often a matter of selecting one that flows the easiest, but still exhibits the physical properties you require in the finished part.

The positive thing about having so many choices, is if one particular resin grade doesn’t work well, you can often find an alternative grade that produces better results. It’s not uncommon for thermoplastic resin manufacturers to offer several grades that are substantially similar to each other, except for a having different MFR. A good website to find and compare the properties (processing temp, MFR, etc.) of nearly every thermoplastic resin grade on the market is

Because there is such a wide variety of colorants, fillers and additives on the market, available in various forms (e.g. powders, liquids, pellets, etc.) we cannot make any sort of generic statement of what is suitable. Successfully mixing a colorant, filler or additive in with a molten polymer also partly depends on the polymer itself. If you try mixing together materials that are inherently incompatible with each other, our mixing device will do nothing to change that incompatibility. It’s also important to keep in mind that whatever you mix must also be capable of being injected. For example, although you might be able to successfully mix a thermoplastic polymer with a filler material comprising long fibers, that resulting mixture could still clog the nozzle orifice of the Model-S injection molder when trying to inject it. So, the process limitations of both the Model-M mixing device and the Model-S Injection Molder must be taken into consideration when deciding what materials to mix together.

Notwithstanding the above caveats, we have mixed polymers with various types of colorants, fillers and chemical additives, in different forms (powdered, liquid and pellet), all with excellent results. And, we have mixed different types of polymers together to create hybrid blends, also with excellent results. We have also conducted some limited experiments mixing nanomaterials in with various polymers, and at least visually, they appear to mix in well, however we do not have a SEM to properly analyze the distribution and dispersion of the particles on a nano scale.

We believe our Mix-Molder ® System would be an invaluable tool for any lab that wants to mix and inject molten polymers on a small scale for testing and experimentation, because of its simplicity, compact size, ease of use, and low price point as compared to conventional plastics processing equipment. In addition, the innovative helical blade mixing element of our Model M-100 creates exceptional laminar and chaotic flow within the melt chamber, offering the potential to make new discoveries and observations not typically possible with conventional screw type mixers and augers.

A hand mixing tool comes included with the Model M-100 device.

The hand mixing tool is ideal for stirring a molten polymer before injecting it, even if nothing is added to it. Stirring it briefly by hand ensures the entire melt is at a uniform temperature, and also reduces the time it takes for the polymer to completely melt, which decreases the chance of degradation for heat sensitive polymers. A uniformly melted polymer is also easier to inject.

Using the hand mixing tool is often sufficient for mixing in powdered and liquid colorants when the objective is primarily for aesthetics. For example, if the color of the injected part appears uneven or has streaking due to insufficient mixing, simply adding in a larger amount of colorant will typically improve results. Conversely, when using an overhead mixer, the amount of added colorant can be minimized, and it’s easier to maintain repeatable results between batches because the mixing operation is more controlled.

An overhead mixer is generally recommended when mixing two different polymers together, or colorants that are in pellet form (i.e. masterbatch), or other types of fillers or difficult to mix materials, such as carbon nanotubes. To get the best results when mixing these types of materials, a higher rotational speed of the mixing blade is often necessary and sometimes for an extended period of time, which might not be possible with the hand mixing tool.

Our evaluation of different off-the-shelf overhead mixers is ongoing, and we will provide updated information as it becomes available. However, at this time we recommend the following characteristics for whatever overhead mixer you choose:


For example, below are two off-the-shelf overhead mixer models we have successfully used in cooperation with our Model-M Mixing Device.

1. Caframo Model BDC-1850
2. Heidolph Model RZR 2102

Between the above 2 mixers, our choice would probably be the BDC-1850, because it is substantially less expensive, and in our experience seems to perform just as well if not better than the RZR 2102. That said, one advantage of the RZR-2102 is its simultaneous display of the torque and RPM, whereas the BDC-1850 requires you to toggle between the two readouts.

NOTE: If you plan to use an overhead mixer with the Model M-100 device, you will need a machine mixing tool (Item MMT-001-1), which is available for purchase separately. The removable mixing blade included with hand mixing tool will also fit the machine mixing tool.

Both the Model-M and Model-S include a 16 cm3 capacity injection tube (a/k/a melt chamber or barrel). However, two other capacity change-over kits are also available for purchase separately, allowing you to either increase or decrease that capacity.

Our CCK-003-1 change-over kit includes a larger capacity injection tube of 23 cm3.
Our CCK-001-1 change-over kit includes a smaller capacity injection tube of 10 cm3.

Not surprisingly, the advantage of using a larger capacity injection tube is its ability to hold more plastic so you can make larger parts. However, one reason to use a smaller capacity tube is for increased injection force, because the downward pressure applied by the user is concentrated to a smaller surface area, which results in an increased force per square inch. This would be particularly useful if the material you want to inject has a low melt flow rating (MFR) or is otherwise difficult to inject. A smaller capacity tube may also be desirable when there is only a small amount of material available to inject, or if the material or the additive mixed into it is very expensive.

It only takes a few minutes to “change over” the Model-M and Model-S to a different capacity injection tube.

No. To minimize polymer residue from sticking, the injection tube, funnel tray and injection nozzle are all polished and plated. The injection ram is Teflon coated. The helical mixing blade and components of the material stripping assembly are all Teflon coated.

A cleaning tool kit (Item CTK-001-2) is also available for purchase separately. If there is any degraded polymer residue sticking to the inside walls of the injection tube, the cleaning tool can be inserted into the tube to easily remove it, which is much faster than having to purge out the residue by adding in and injecting new material.  

Also, since the injection tube is removable, it can simply be detached from the Model-M or Model-S, allowing you to easily look inside the tube to confirm all is clean.

If you should happen to get any sort of charred polymer residue stuck to the injection tube walls that cannot be cleaned out with the cleaning tool, the nozzle can then be easily detached from the tube, allowing you to insert a tubular brass wire brush to more aggressively clean out the tube.

There is a video posted on our VIDEOS page that demonstrates how to clean the injection tube using the CTK-001-2 cleaning tool kit.

The maximum mold dimensions according to our specifications are: 2.63″ H x 4.00″ W x 2.50″ D (67mm H X 102mm W X 64 mm D).

The mold height is limited to 2.63” (~67 mm) because the nozzle is positioned directly above it. But there is some flexibility to accommodate a larger mold width and depth. In particular:

The depth of 2.50″ (~64mm) could be increased a little if you remove the 3/8″ (~9.5 mm) thick adjustable backing plate and then place the mold directly against the backwall of the machine frame. However, your mold would then need to be radiused (i.e. rounded) at the bottom edge to match the .75” (~19 mm) radius of the inside corner of the frame, where the vertical backwall meets the horizontal base.

The width of the mold could also extend past the 4.00″ (~102 mm) width of the machine if desired, however if it extends too far, you may need to attach c-clamps to the extended mold ends to help hold them tightly closed.

United States