What Is a Purging Compound?
A purging compound is a cleaning agent used in resin molding machines when changing materials. It removes resin and carbides from metal surfaces. Normally, a resin molding machine is operated by changing the color of the resin or the type of resin. However, if the cleaning process is omitted, residual material from the previous material will be mixed in, reducing the yield rate. As a result, not only does resin waste increase, but labor and other costs are also reportedly incurred. Therefore, purging compounds are used to prevent yield loss. In recent years, many purging compounds have used boric acid as the main ingredient, allowing cleaning without damaging the molding machine.
Uses of Purging Compounds
Purging compounds are used to clean resin molding machines when changing materials or colors. When changing material type or color, it is necessary to clean the previous material adhering to the molding machine. Specifically, it is not always necessary to clean, but if subsequent materials are fed without cleaning, they will mix with the previous material, resulting in lower yield and material loss, which is time-consuming and costly. It is also possible to remove carbides and black spots that adhere to molded products. However, the appropriate purging compound varies depending on the resin used and must be confirmed in advance.
Principle of Purging Compounds
This section describes the cleaning process using purging compounds. Note, however, that it may vary depending on the material and molding machine used before and after.
- Discharge all pre- and post-materials
Ensure discharging the pre-material since a high cleaning effect cannot be achieved with residual pre-material. Also, discharge hoppers and supply lines in the same manner.
- After cleaning the hopper section, feed in the purging compound
The specified amount of purging compound is fed, but the amount and frequency of feeding need to be devised since the cleaning effect will be lower in uneven areas.
- Cleaning by rotary purge after considering various conditions
To increase work efficiency, back pressure should be increased and injection speed should be set higher. Also, the cleaning temperature should be maintained at the molding temperature of the previous material.
- Confirm that the pre-material or pre-color has been removed.
Visually confirm that all previous material has been removed and stop the molding machine.
- Change to molding temperature of post-material
After changing the molding temperature of the post-material, load the material.
- Discharge with rotary purge
Perform the same operation as during cleaning to discharge the purging compound completely. After confirming that the purging compound has been completely removed, move on to the normal molding operation.