What is the impact of melt flow index MFR on the selection of extruders?

This post was last edited by ljtjbx on 2015-9-14 at 14:40. The selection of an extruder depends primarily on its capacity, and it is also necessary to take into account the MFR range of the product. Since the MFR range is a very important parameter – ranging from as low as 0.2 g/10 min to as high as 100 or even higher – the design of the extruder must meet the requirements of the customer’s product. Degradation of the product is another factor that needs to be considered as well. The screw design of the extruder (the combination of screw grooves and land designs), the die, the melt pump system, the extruder’s exhaust system, as well as the load (torque) on the extruder – all of these factors need to be taken into account based on the product’s MFR range and quality requirements.

Thank you very much. One more question: what impact does a low MFR have on the machine? I know that MFR affects the selection of machinery; what I want to know is what kind of impact it has. For example, when extruding impact-resistant PP with a low MFR, does the screw design require a longer mixing section or more mixing time? Do the die plates need more holes? Does the melt pump need to operate at higher pressure? And does the torque required by the extruder need to increase?

This post was last edited by ljtjbx on 2015-9-15 08:39. For products with low MFR, in order to achieve proper extrusion and mixing in the extruder, it is necessary to use a higher temperature setting for the barrel (250–270 degrees Celsius). Additionally, greater shear force is required from the extrusion screw, which means that the torque of the extruder will be higher than normal. Since low MFR products are certainly not produced on a long-term basis, when designing the extruder, the production load for such products is often lower than that for regular products; however, this is not absolute. Increasing the mixing length and time can be achieved through the control of the throttle valve ； For the pressure adjustment of the melt pump, it is sufficient to ensure that the inlet pressure is not too low; therefore, the load cannot be too low. Welcome to exchange and learn from each other*. You can also share your ideas or experiences so that we can discuss them together and improve together! Feel free to post and discuss any questions you have.

Thank you very much. I have another question regarding the throttle valve: 1. How is the mixing length defined? Does it refer to the length of the mixing section on the screw? Some sources indicate that the cross-section of the threads in this mixing section is elliptical. It seems that this length is related to the design of the screw; once the screw structure is determined, does this length remain unchanged? 2. Is the mixing time the time it takes for the resin to travel through the mixing length? If the mixing length is fixed, can the time be changed only by altering the speed at which the resin moves? 3. So, which factor of the resin does the opening degree of the throttle valve actually change (pressure, temperature, flow rate, or something else), and is it this change that in turn affects the degree of mixing? I personally think it’s complicated in order to change the pressure of the resin ahead of the throttle valve; I asked a few more questions. I really don’t understand some of the basic concepts related to pelletizers, especially what the function of this throttle valve is

The extruder is equipped with a throttle valve on the cylinder section following the screw section. Due to the different requirements regarding the melt index of the resin, in order to achieve an appropriate mixing effect, the discharge volume of the extruder is controlled by adjusting the throttle valve, thereby changing the extrusion pressure and residence time of the resin, and thus altering the degree of melting of the material flow. At the same time, I’ll @Tianyi, an expert, to help you get an answer.

Regarding MFR and the selection of extruders, when purchasing an extruder, it is generally necessary to provide the manufacturer with information about the basic characteristics of the products to be produced. The extruder supplied by the manufacturer must be capable of producing these various grades of material, and this requirement will be specified in the technical specifications. If you currently do not produce products with low MFR, but plan to develop such products in the future, it is advisable to inform the extruder manufacturer of this situation. The design of extruders takes into account the influence of MFR. When producing products with low MFR, higher levels of mixing of the resin are required, and adjustments to the process parameters are relatively easy to make, mainly at the hardware level. For materials like tubing, due to their low MFR, higher power is required for the main motor and gear pump. If these factors are not taken into account during selection, they can easily become bottlenecks when producing materials with low MFR, limiting an increase in production capacity. Additionally, when the MFR is low, the pressure in the area downstream of the extruder is also higher; as a result, higher requirements are placed on the thrust bearings of the screw. As for the design of the screw threads, I’m not entirely sure whether any special adjustments are necessary. 1. How is the mixing length defined? Does it refer to the length of the mixing section on the screw? Some sources indicate that the cross-section of the threads in this mixing section is elliptical. It seems that this length is related to the design of the screw; once the screw structure is determined, does this length remain unchanged? I too have only started to work with extruders more recently, and I’m not familiar with these terms. I guess the term \"mixing length\" refers to the length of the mixing section; the cross-section is oval in shape. You can look up some general information on this topic. For users of extruders, the structure of the screw in a given model remains fixed – unless it is modified, no adjustments are usually made. 2. Is the mixing time the time it takes for the resin to travel through the mixing length? If the mixing length is fixed, can the time be changed only by altering the speed at which the resin moves? It should be like this. 3. Then, which factor of the resin does the opening degree of the throttle valve actually change (pressure, temperature, flow rate, or something else), and is it this change that in turn affects the degree of mixing? Personally, I think it’s to change the pressure of the resin in front of the throttle valve; the throttle valve mainly alters the residence time of the resin, thereby enhancing mixing.

Regarding MFR and the selection of extruders, when purchasing an extruder, it is generally necessary to provide the manufacturer with information about the basic characteristics of the products to be produced. The extruder supplied by the manufacturer must be capable of producing these various grades of material, and this requirement will be specified in the technical specifications. If you currently do not produce products with low MFR, but plan to develop such products in the future, it is advisable to inform the extruder manufacturer of this situation.

I have a question for everyone: For the ZSK350 model, under the same load, when the throttle valve is closed to enhance resin mixing, the pressure of the resin in front of the throttle valve also increases accordingly. What I would like to ask is that the pressure difference before and after the throttle valve should increase as well; so how does the pressure in front of the die change in this case? 2. Regarding mixing in the production of products with high lipid solubility, I have two ideas. The first is to lower the temperature of the mixing cylinder in order to improve the degree of mixing. The second option is: keep the cylinder temperature constant and adjust the mixing by closing the throttle valve. Both of these can meet the requirements for mixing; however, the resin pressure generated in the latter case will be somewhat higher. 3. The adjustment methods used by everyone when explaining the production process (lipolysis mode 40, without gear pump)