How to achieve fast color change in extrusion blow molding

In the extrusion blow molding process, color change is an important and complex issue. The problems caused by color change include:

1. Decreased production

2. Loss of resin, masterbatch and energy consumption

3. Increased waste

4. Labor required for supervision

5. Risk of subsequent production instability

Regarding the last point, many people have encountered such a situation: after the color change, they thought that the production was normal, but 10 minutes later, there were traces of the old color.

So, how to minimize the interference and cost burden caused by color change? The key factors are:

1. Reasonable design and size of equipment

2. Thorough cleaning of equipment

3. Use the right resin for cleaning

Next, we will share some experimental results and discuss these and other factors.

"Switch directly from color A to color B, or purge color A with natural resin before switching to color B?"

Basic approach:

There are two basic methods of operation for color change in the extrusion blow molding process: one is to switch directly from color A to color B, and the other is to use the "circuit method" to switch from color A to uncolored or natural resin state, and then from natural resin to color B.

Clean up the entire production system

During the color change process, the entire process of the extrusion blow molding production system must be considered - from material mixing, feeding through the extruder, screw and die head, to flash conveying, crushing and re-feeding.
The first task of color change is to remove all old colors from all parts of the production system. The basic steps for cleaning are as follows:

1. Stop feeding

2. Drain the piping system until it is completely empty

3. Close all relevant hoppers and empty the extruder

4. Empty all relevant hoppers

5. Clean the hoppers with a vacuum cleaner if necessary

Purification system

After performing the above steps to clean the raw material handling system, you can proceed to the cleaning steps:

1. Replace the material with natural resin without masterbatch

2. Stop the regrind supply or switch to natural resin

3. Run the entire production system using only natural resin

"Hoppers, mixers, metal detectors, filters and pelletizers - don't forget to thoroughly clean these potential sources of contamination"

Steps:

1. Retract the filter pack and crushing plate

2. Clean out the molten material in the filter area

3. Remove the filter contaminated by the old color

4. Don't forget to thoroughly clean the filter holes - a wire brush is highly recommended

5. Insert the crushing plate or carrier and new filter - make sure to follow the correct order

6. Put the filter pack back into the working position of the extruder

Now, continue washing with natural resin. Once the final product is free of old color residue, the whole process is complete. Following the basic steps for switching from the old color to natural resin, now start switching from natural resin to the new color:
1. Stop the natural resin feed and continue running until the feed and discharge pipes are empty
2. Close all related hoppers and the extruder continues to work until it is empty
3. Replace with the new masterbatch formula and re-pneumatically extrusion process
4. Pneumatically blow the process with the new masterbatch
5. If the old color appears again, repeat the cleaning process
Don't forget the pulverizer
When you have completed the above steps and are ready to start the new color, it is the best time to clean. Clean the pulverizer thoroughly, if possible, use a vacuum cleaner. In addition, clean all conveyor belts, including the area inside the safety door of the blow molding machine. After completing these tasks, you can start production with the new color (including the pulverization system). After the production is stable, conduct a comprehensive quality inspection of the finished product. After the quality is qualified, start the final production.