The Reasons Of Rust Return Between The Pretreatment Processes

The problem of rust return between the pretreatment processes of the workpiece has become the most concerned issue for customers. After the workpiece is rusted, it directly affects the pre-treatment film quality, which in turn affects the coating effect. Therefore, how to do rust prevention between processes is one of the key tasks in pretreatment.

Typical process flow of phosphorus-free pretreatment process (including pickling process):

Pre-degreasing-main degreasing-water washing 1-(pickling)-water washing 2-(water washing 3)-Silane/ceramic treatment-water washing 4-water washing 5-drain-electrophoresis/dusting/painting

The main reasons for the return rust between processes are as follows:

One, after the main degreasing, the water is washed and the overflow water is too large.

Analysis of the cause: If the overflow water is too large before the workpiece enters the silane/ceramic tank, the pH of the bath may be weakly acidic, causing the workpiece to return to rust.

Countermeasures: Adjust the flow rate of the overflow water appropriately, control the pH of the bath; add a rust inhibitor as appropriate.

Second, there is a pretreatment process in the pickling process, washing 2 is not sufficient

Analysis of the cause: If the water wash 2 is insufficient before the workpiece enters the silane/ceramic tank, the acid remaining on the surface of the workpiece will cause the workpiece to rust.

Countermeasures: Add a rust inhibitor as appropriate.

Third, the workshop temperature is too high

Analysis of the cause: If the temperature in the workshop is too high in the summer, the water temperature in the washing tank will rise. When the temperature exceeds 35 °C, flash rust will appear on the surface of the workpiece.

Countermeasures: keep the workshop ventilated and dry, keep the temperature within 35 °C; appropriately increase the flow rate of the overflow tank of the washing tank, reduce the water temperature; appropriately add rust inhibitor

Fourth, the main degreasing after washing time is too long (3 wash)

Analysis of the cause: The summer temperature is very high, the humidity is large, and 3 washes are taken. If the workpiece is exposed to humid air for a long time, it may cause rust.

Countermeasures: Add a rust inhibitor as appropriate.

Fifth, the draining time is too long

Analysis of the cause: Excessive draining time causes the workpiece to be exposed to humid air for a long time, causing the workpiece to rust.

Countermeasures: increase the blowing device in the draining area, or reduce the residence time of the workpiece in the draining zone; add a small amount of rust inhibitor to the washing 5

Sixth, emergency stop line

Analysis of the cause: When the emergency line is stopped, the workpiece is exposed to the air for a long time, causing rust.

Countermeasures: When the production is resumed, the surface of the workpiece is rusted, manually polished and reprocessed.