- Author
-
Osterberg, L.
|
Gustafsson, H.
- Title
- Jordning av objekt vid lackering. (Abstract in English)
- Coporate
- Institutet for Verkstadsteknisk Forskning
- Report
-
IVF-skrift 90815
1990
49 p.
- Keywords
-
paints
|
safety
|
industrial plants
|
thickness
|
tests
|
electric potential
- Abstract
- When painting items electrostatically, which are imperfectly earthed, the items can reach an energy level high enough for a spark to develope and ignite a powder cloud or a solvent. This can also be the case when powder painting with tribocharging. It can happen when painting items of rather big sizes, in a normally shaped booth and at normal voltages. The safety at a painting plant can be secured when keeping the contact surfaces between hooks and items clean. A contactless earthing of the items and a suitable safety system for the equipments can also improve the safety of the plant. The thickness of the isolating paint alyer on ahook decides to what level the voltage of the charged items will reach. When the maximum voltage level is reached a spark is ignited. It goes from the item through the paint layer and to the earthed hook. The item is discharged. The spark will follow the path of lowest resistance. It can pass several centimeters in air before it finds a suitable way for example a pore. The voltage of the item can reach 50 kV or more for a thick isolating paint layer on the hook. There are some differences between the two types of powder painting, coronacharging and tribocharging. With tribo the maximum voltage, which the item can reach, can be higher. At tribo it is easier to compensate the charge of the item with contactless earthing. The tests have shown that a soluted paint layer as thin as 30 micron will negatively influence the paint result. Contactless earthening improves the paint result only when all items are isolated. The tribo equipment is less sensitive to imperfect earth. It is possible to monitor the earthing of the items before they go into the booth. This id sone in the following way. The items are charged. The remaining charge is measured at a fixed time later. A high remaining charge indicates an imperfect earth.