Four Ways To Clean Twin Screw Extruder Screws

As the workhorse in the field of compounding, the twin-screw extruder's superior performance and customizability are its advantageous features in this position. It can combine different additives and fillers to achieve different particle shapes and properties with different properties.

While a variety of additives and fillers can be processed for extrusion, some methods of obtaining these products can also lead to contamination problems and low flow or low pressure in many areas throughout the barrel.

In a continuous process like extrusion, contamination can have an adverse effect. Compared with other processes, purging in extrusion is often more challenging, and twin-screw extruders face greater challenges because the system is more complex than single-screw extruders.

First, let's take a look at the cleaning methods of twin-screw extruders.

Resin cleaning method

Polyester resin or epoxy resin is used for cleaning the machine. It is generally used for cleaning the machine of new equipment or after the extruder has been used for a period of time, because some materials remain on the screw or barrel and gel, the material extrusion speed slows down, and the color difference of the color change variety is large. This method can be used. Today, with the highly developed commodity economy, there is no shortage of various screw cleaners (screw cleaning materials) on the market, most of which are expensive and have different effects.

Whether to use commercial cleaners depends on different manufacturers and production conditions; plastic processing companies can also use different resins to make screw cleaning materials according to their own production conditions, which can save a lot of expenses for the unit.

The first step to clean the screw is to turn off the feeding plug, that is, to close the feed port at the bottom of the hopper; then reduce the screw speed to 15-25r/min, and keep this speed until the melt flow at the front end of the die stops flowing. The temperature of all heating zones of the barrel should be set at 200°C. Once the barrel reaches this temperature, start cleaning immediately.

Depending on the extrusion process (it may be necessary to remove the die to reduce the risk of excessive pressure at the front end of the extruder), cleaning must be done by one person: the operator observes the screw speed and torque from the control panel, and observes the extrusion pressure to ensure that the system pressure is not too high. Throughout the process, the screw speed should be kept within 20r/min. In the application of low-pressure die heads, do not remove the die head for cleaning first. When the extrudate is completely converted from processing resin to cleaning resin, stop the machine immediately and remove the die head, then restart the screw (speed within 10r/min) to allow the residual cleaning resin to flow out.

Disassembly strategy

1. Manually add washing material from the feed port until the color of the extruded material strip is the same as that of the washing material pellets, stop feeding, empty the material, and stop the twin-screw extruder screw rotation;

2. Open the screw extruder die head and start cleaning;

3. Turn the twin-screw extruder screw and remove the orifice plate to discharge the residual washing material in the barrel and clean the orifice plate;

4. Stop and pull out the screw to observe whether it is cleaned, and manually remove the residual material on the screw. Reinstall the screw; add new material to flush the residual washing material in the barrel, and stop the screw rotation;

5. Install the twin-screw extruder orifice plate and die head to complete the cleaning operation of the twin-screw extruder.

Fire-baking cleaning method

The most common and effective method for plastic processing units is to use fire or fire to remove the plastic fixed on the screw. The blowtorch is used to clean the screw immediately after use. Since the screw carries the heat from the processing experience, the heat distribution of the screw is still uniform. However, acetylene flame must not be used to clean the screw. The temperature of acetylene flame can reach 3000°C. Using acetylene flame to clean the screw will not only destroy the metal properties of the screw, but also significantly affect the mechanical tolerance of the screw.

If the acetylene flame turns into a persistent blue when baking a certain part of the screw, it means that the metal structure of this part of the screw has changed, which will lead to a decrease in the wear resistance of this part, and even the peeling of the anti-wear layer and the base metal. In addition, local heating with acetylene flame will also cause one side of the screw to overheat, resulting in the bending of the screw. Most screws are made of 4140.H.T. steel, and the tolerance is very tight, generally within 0.03mm.

The straightness of the screw is mostly within 0.01mm. After the screw is baked and cooled by acetylene flame, it is usually difficult to return to the original straightness. The correct and effective method: Use a blowtorch to clean the screw immediately after use. Because the screw carries the heat from the processing process, the heat distribution of the screw is still uniform.

Water washing method

Screw water washing; the fully automatic screw water washing machine uses the kinetic energy of hydraulic rotation and the reaction force of the screw rotation to achieve 360-degree stripping without dead angles. It has high working efficiency and does not damage the physical structure of the screw. It realizes new screw cleaning technology in an environmentally friendly, efficient and energy-saving way. It is suitable for forced stripping and removal of a variety of polymer materials, so it is a green processing technology with good cleaning effect.

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