Why is a gearbox shift required in WP’s extruders when producing polypropylene of different grades?

This post was last edited by ljtjbx on 2015-9-26 09:15. Products with a low melt index indeed require greater shear force and mixing intensity, which is reflected in the host unit as an increase in torque. Typical extruders are equipped with two speed settings: high speed and low speed. For most products, the high speed setting is sufficient, but there are some products that require operation at low speed. However, modern extruders are often fitted with melt pump systems, which greatly helps in determining the types of products that can be processed by the extruder as well as the load capacity of the extruder. @Tianyi

Thank you. However, I have always had a question: whether using a lower speed will reduce production capacity. My understanding is that since the screw moves more slowly at a lower speed, less resin is transported. But is it necessary for the screw to be fully filled? Because if it’s not fully filled at high speeds, could increasing the feed amount at a lower speed to fill the screw enable the production capacity at that lower speed to be equal to that at high speeds? To give an example, this year the production capacity for a grade with an MFR of 30 is 200,000 tons per year, with the screw rotating at 240 r/min. In the following year, the production requirements change and it becomes necessary to produce a grade with an MFR of 0.5; in this case a lower rotation speed is required to generate more torque, namely 180 r/min. So, can the same production volume of 200,000 tons per year still be achieved for this new grade?

Products with a low melt index are not produced on an annual basis; therefore, an annual production volume of 200,000 tons cannot be achieved with a melt index of 0.5 throughout the whole year. Producing materials with a low melt index does indeed reduce the load on the extruder, but this effect is less noticeable when a melt pump system is used. Currently, the extruders in the 300,000 tons/year PP plant are equipped with melt pump systems, and the production capacity – or load – is the same for materials with low melt index and those with normal melt index. I’m not sure if your extruders are equipped with melt pumps Is the material used for your 0.5 product of the PPR type? The market size also won’t allow you to produce large quantities of this grade.

When the screws are fully filled, the load at low speed is low

Thank you. Is this low-load, low-speed gear used when producing products with a low MFR? Are there any production data sheets available that show the production capacity corresponding to each grade, as well as the values for screw speed and MFR?

In my opinion, the low-speed gear is probably designed to reduce energy consumption; it has nothing to do with the melt index. I think for materials with a low melt index, it’s better to use the high-speed gear. Different processes, material grades, and loads are all related to the design aspects, and there are no specific data tables available. There’s also no inherent relationship between melt index and rotational speed – the high-speed gear usually operates at around 240 revolutions per minute, while the low-speed gear is around 180 revolutions per minute. I haven’t used machines with a low-speed gear, so I’m not entirely sure if what I’m saying is correct

The speed has decreased, the motor power remains unchanged, but the torque of the entire system has increased. If the same material is being produced, and the feeding amount has not reached its maximum level, the output will increase, rather than decrease. If the viscosity of the material increases, the speed is reduced and torque is increased to ensure the quality and output of the material