Method for providing sheet metal stock with finely divided powder

A method of depositing very finely divided particles of resinous powder onto a metal substrate, comprising providing a mass of powdered resinous material within a retaining means having an opening therein, introducing pressurized fluid into the mass of powdered material to impart an agitating effect on the mass within the retaining means whereby the mass assumes a substantially unpacked state, allowing a stream of the unpacked mass to exit through the opening of said retaining means, conveying the mass while still in an unpacked state into a comminuting zone whereby said powdered material is reduced to very finely divided powder particles having an average diameter of about 10 microns or less, diffusing said finely divided powder particles to immediately cause a loss of momentum by passing said finely divided particles immediately after being comminuted directly and without interruption into a radially outwardly extending stream of fluid for delivery into a deposition chamber, said outwardly extending fluid stream flowing without a substantial restriction that may cause concentration and agglomeration of the particles along the path of travel between the comminuting zone and the deposition chamber, said chamber being provided with a substrate upon which particles are to be deposited, electrostatically depositing said particles onto said substrate, and coalescing the particles to form a uniform coating of about 0.5 mil in thickness.

A method of providing metal stock with a very thin, coherent and lubricous coating of resinous powder, comprising:

• providing an uncompacted supply of powder particles adjacent a coating zone, said uncompacted supply of powder particles being achieved by redistribution of a powdered mass;
• releasing the fluid energy of a compressed gas to impart sufficient momentum to said powder particles in a comminuting zone to reduce their average particle size to 10 microns or less and carry the finely divided particles in the flowing compressed gas;
• diffusing the flowing gas and reduced powder particles to provide an outwardly extending, substantially quiescent and slow-moving gas stream to maintain the reduced particles in a uniform segregated cloud and to carry said cloud directly to the coating zone, said diffusing of the flowing gas and particles being done at once and without interruption immediately after releasing the fluid energy to reduce particle size, said cloud of gas and finely divided particles flowing to the coating zone along a path that does not cause substantial concentration and agglomeration of finely divided particles;
• confining said cloud of reduced particles in the coating zone, said particles having a diameter-to-weight ratio such that they will remain suspended in the substantially quiescent atmosphere of the coating zone;
• moving sheet metal stock to be coated through the coating zone;
• providing an electric charging and depositing field terminating on the metal stock in the coating zone having a potential gradient sufficient to charge the finely divided powder particles and deposit said particles on the metal surface while the particles are in a repelling relationship with respect to one another thereby providing a uniform distribution of particles on the metal stock;
• and
• coalescing the particles to form a uniform coating of about 0.5 mil in thickness.

A method of providing metal stock with a uniform distribution of very finely divided particles of resinous powder, comprising:

• providing a supply of resinous powder particles adjacent a coating zone;
• releasing a gentle flow of gas through the supply of powder particles to permit the particles to flow freely and be redistributed to assume an unpacked state;
• delivering a substantially uniform flow of said unpacked powder particles to a comminuting site;
• releasing the fluid energy of a compressed gas to the flow of particles to impart sufficient momentum to said powder particles in the comminuting zone to reduce their average particle size to a very finely divided particle size of 10 microns or less;
• directly diffusing the thus-formed finely divided particles and gas to cause a loss of momentum immediately after being released to provide a substantially quiescent, slowly and upwardly moving gas stream to maintain the very finely divided particles segregated in a uniform cloud and to carry said cloud to the coating zone, said upwardly moving gas stream and cloud being directed to the coating zone over a path free of restriction that may concentrate the cloud and agglomerate the particles;
• confining said cloud of very finely divided particles in the coating zone, said very finely divided particles having a diameter-to-weight ratio such that they will remain suspended in the substantially quiescent atmosphere of the coating zone;
• moving sheet metal stock to be coated in strip form through the coating zone;
• providing an electric charging and depositing field terminating on the metal stock strip in the coating zone having a potential gradient sufficient to charge the finely divided particles and deposit said finely divided particles on the metal surface while the particles are in a repelling relationship with respect to one another thereby providing a uniform distribution of said finely divided particles on the strip;
• and
• coalescing the finely divided particles to form a uniform coating of about 0.5 mil in thickness.

A method of electrostatically coating finely divided particles of resinous powder onto a metal substrate, comprising:

• moving the substrate to be coated through a coating zone;
• providing a flow of air through the resinous powdered material to enhance its flowability and to render said powdered material in an unpacked state;
• feeding the flowable, unpacked powdered material to a comminuting zone adjacent to the coating zone;
• reducing the powdered material into finely divided particles having an average size of about 10 microns or less and delivering a flow of finely divided particles directly after being reduced in size to the coating zone, said delivery being into a zone of increasing cross section causing an immediate diffusion after particle size reduction and subsequent communication to the coating zone over a path of travel without restricted flow that may cause particle concentration and agglomeration whereby the finely divided particles gently flow in a subsequently quiescent cloud;
• electrostatically charging and depositing the finely divided particles onto the metal substrate;
• and
• coalescing the deposited particles to form a uniform coating of about 0.5 mil or less in thickness.