self lubricant enamel

Hi
In wire enameling process we use self lubricant top coat . This self lubricant must have a Coefficient of friction about 0.04 to 0.05 (according to the manufacturer declaration). But in practice we face to coefficient of friction about 0.07 to 0.08. Therefore we have to use additional paraphin layer on self lubricant surface. Why this phenomela happen? and how can we decrease COF of self lubricant? What are self lubricants disadvantages?

Process informations:
copper wire 0.30 and 0.32 mm diameter
enamel: 661/42A Under coat and one pass Tongmid 595 MBL self lubricant for top coat both from Elantas.
oven temperature : 610 oc
wire speed : 300 to 310 m/min

Thanks
Nima

Mr. Rahati,
My first thought would be that perhaps you are not getting sufficient coverage of the Tongmid 595 MBL. Typically this product is the second or third coating placed upon the wire. It is sometimes little more than a wash but it is essential that the coating completely cover the wire. Even though the amount of placed on the wire, it normally would take multiple passes through the applicator to obtain complete coverage.
Hitachi developed a similar product and has patented it. I am not a chemist, but my biggest concern is that this material utilizes Silane Coupling Agents: silicon-based chemicals that contain two types of reactivity – inorganic and organic – in the same molecule. A typical general structure is (RO)3SiCH2CH2CH2-X, where RO is a hydrolyzable group, such as methoxy, ethoxy, or acetoxy, and X is an organofunctional group, such as amino, methacryloxy, epoxy, etc.

A silane coupling agent will act at an interface between an inorganic substrate (such as glass, metal or mineral) and an organic material (such as an organic polymer, coating or adhesive) to bond, or couple, the two dissimilar materials.

Initially they used it for inverter wire where they put on a base coat, then a heavier intermediate coating that include silica sol (silica in solution). This coating has microscopic or nano slilica particles in it to essentially make a ceramic coating. The final coating was the self-lubricated polyamideimide enamel.

Most wire enameling systems today utilize a precious metal coated metallic mat(s) as a catalysts to convert the solvents released by the cutting process into heat energy. Today’s enameling systems depend upon this released energy to maintain the operating heat of the enameling oven. The metallic catalytic mat is coated with platinum or palladium and other precious metals so that a reactive surface is created. When the solvent vapors come in contact with this surface there is a catalytic reaction which release the heat energy that is in the solvent vapor.

When enamel is heated, the solvent vapor evaporates and as it evaporates it carries some of the solids of the enamel with it. (note when you see smoke what you are seeing is either the vapor or an accumulation of minute particles of solids in the vapors.) Along with the various resin particles there are silicon or silica particles entrapped in the vapors and as they pass through the catalysts, the solvents will burn but the solids either become a very fine ash, go up the stack, or in the case of the silicon/silica they stick to the catalyst and over time will form a glass like coating on the catalyst mat. This means that the catalysts will not work, your electrical consumption will increase, your emissions or pollutants will increase, and in some cases you will not be able to maintain oven operating temperature and or operating speed.

I have seen this occur in as few as three days with some enamels!