Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

62.1 ELECTROSTATIC ATOMIZATION METHOD

 

· The Blade Method 9Ransburg's No. 1 process),

  1. - no spraygun used
  2. - a straight sharp edge is used charged to about 90 KV
  3. - the work is grounded
  4. - the paint is slowly pumped onto the blade, it spreads out, and by the time it reaches the tip it comes off as small charged droplets.
  5. - the shape of the workhead encourages a linear dispersion pattern
  6. - advantages,
    1. - high efficiency/low wastage
    2. - simple controls
    3. - suited to flat surfaces
  7. - disadvantages,
    1. - limited dispersion patterns
    2. - least cost effective and flexible

 

 

 

· The Bell Method (Ransburg's No. 2 process)

  1. - uses a rotating bell or funnel to disperse the paint
  2. - the bell head is about 1 ft. from the workpiece
  3. - a potential of 90-100 KV is applied to the head while the work is grounded
  4. - the head rotates at 900 r.p.m. to cause good paint dispersion
  5. - advantages
    1. - good coverage for rounded surfaces
    2. - better efficiency than blade method
    3. - suited to spherical irregular shapes
  6. - disadvantages,
    1. - extra power/equipment to run motor

 

 

 

· ASIDE: the edge effect in electrostatic phenomenon leads to higher concentration of charges at corners and edges.

 

· The Disk Method (also Ransburg's No. 2 process)

  1. - similar to Bell method except that a flat disk is used.
  2. - the geometry of the disk allows a much wider spray coverage
  3. - advantages (compared to bell),
    1. - wider coverage area
    2. - well suited to irregular and long parts

 

· Rotating Bell handgun

  1. - can be used for manual/movable spraying
  2. - is well insulated to prevent shocks
  3. - well suited to complex shape because of operator aiming
  4. - most effecient and cost effective method

 

· Consider the comparative tables [source unknown],

 

 

· Air/Hydraulic Electrostatic Spraying

  1. - Type I
    1. - large negatively charged (100KV) electrodes are placed at the side of a spray paint line
    2. - work on the central conveyor is rounded,and uncharged paint is sprayed in.
    3. - the sprayed paint enters the electic field, becomes negatively charged and is drawn to the work.
    4. - can be upgraded to a full electrostatic method easily
    5. - a higher paint wastage results.
  2. - Type II
    1. - a typical spray gun head is modified to deposit a high voltage charge on the paint particles
    2. - the paint is sprayed with a negative charge, and it is attracted to a grounded workpiece
  3. - Type III
    1. - the paint is charged before passing through the spray head

 

· Control systems (power supplies) for spraying a resistive/non-resistive. Resistive systems use resistors to limit the maximum current that can be drawn, thus protecting the users. Non-resistive sysems require added safety precautions and are best suited to automate systems.

 

· The edge phenomenon can result in uneven distribution of paint near edges and corners.

 

· The Faraday cage effect will result in recessed areas that get less paint coverage.

 

· Safety issues include electrical shocks, ventillation (most paints are solvent based), and arcs from poor grounding or unexpected metal contact.

 

· Some automation issues are,

  1. - part recognition on a conveyor
  2. - color changes
  3. - booths are costly, but provide safety and process advantages