Updated technical tips and information
Subject: When should I automate?
The question always arises when to switch from manual painting to automatic painting in your manufacturing facility. Issues concerning improved quality, increased productivity and solutions to operator health/safety problems indicate that you should be evaluating your painting system. Below, I would like to outline the three basic areas which determine the right time to consider automatic painting equipment and the impact an automatic system could have on your bottom line operating costs:
The quality issue covers several areas on the painting line. I would like to discuss those issues directly related to the comparison of manual spray painting to automatic spray painting. Before I make these comparisons I should identify the issues.
GUN TO TARGET DISTANCE, is the distance the tip of a spray gun is from the surface on which paint is applied. A change in gun to target distance on a part dramatically affects the appearance and sometimes the adhesion of paints and similar materials to the surface or substrate.
BNH tech tips:
* Most spray applicators are designed for a twelve (12) inch nominal gun to target distance. This is the distance from the surface at which the paint being sprayed/atomized provides the best overall appearance, adhesion, film build and transfer efficiency.
* Typical maximum distance is fourteen inches (14"). Most times if a part is sprayed with a gun to target distance greater than fourteen inches (14"), dry spray and poor adhesion is encountered.Also, OVERSPRAY is increased and therefore transfer efficiency is decreased resulting in more paint usage to achieve the same film build on a part with less than optimum appearance (this is a triple penalty on your process - adhesion/appearance/transfer efficiency).
* Typical minimum distance is eight inches (8"). Most times if a part is sprayed with less than eight inches (8") of a gun to target distance, the finish quality is reduced due to non uniform thickness (paint film build) and heavy paint. The curing of heavy paint can trap solvents/water which may cause differences in color and appearance as well as reduced weathering resistance. Also the color match of metallic paints is much more difficult because metallics rely on uniform thickness and flow-out of the paint during the curing process for uniform metal flake alignment and therefore color/appearance matching. This is again directly affected by proper and uniform film build .
GUN TIP VELOCITY, is the speed the tip of the spray gun moves across the surface being painted. A change or variation in gun tip velocity directly affects the film build of paint or similar materials being applied on the substrate. One foot per sec (1 ft/sec) to four feet per second (4 ft/sec) are typical gun tip velocities for most painting applications. Any variations outside of this window should be carefully researched prior to application on your production line.
BNH tech tips:
* Most conventional spray applicators are designed for a two to three feet per second gun tip velocity. With a proper gun tip velocity the atomization of the paint particles is optimized as it relates to film build on the part being sprayed. This means optimum appearance, adhesion, film build and transfer efficiency.
* Typical maximum gun tip velocity is three feet per second (3 ft/sec). Most times if a part is sprayed with a gun tip velocity exceeding 3 ft/sec the fan pattern integrity is compromised. This means that the fan pattern of the gun is not uniform and inconsistent paint deposition across the fan pattern occurs. The film build across the part is non-uniform, which will affect color match and surface appearance. The fan pattern may also experience what is known as brooming at high gun tip velocities. This is when the shape of the fan pattern is bent or not in a straight line with the tip of the gun because the tip of the gun is moving too fast. Typically the transfer efficiency is also reduced at high gun tip velocities which costs the company money. Because more paint is required to paint the same amount of surface area on a part as compared to more efficient gun tip speeds.
* Typical minimum gun tip velocity is one foot per second (1 ft/sec). Most times if a part is sprayed with a gun tip velocity less than 1 ft/sec the film build is too heavy and the optimum atomization settings for the paint being sprayed have to be adjusted to less efficient ranges.
REPEATABILITY is the key to success for any paint system. With the dozens of painting parameters affecting the quality of the paint job a system must first and foremost be repeatable and consistent. Following is a list of just a few of the variables in a paint system that must be controlled in order to achieve a consistent quality paint job:
paint composition (% solids)
gun tip velocity
gun to target distance
booth air flow
booth air temperature
Without repeatable manufacturing controls for each of the above parameters a production paint job is inconsistent at best, and many times is out of control both in the process and in the quality area.
As you can see there are many variables in the painting process.
Typically one manual painter per spray booth and therefore one spray gun per man is all that is possible on the production line. Manual painters may be added and multiple shifts needed to achieve increased production throughput. When a production paint line is required to produce quality parts in large quantities limitations on film build per pass and flash times between coats also affect system output capability.
An automatic machine can be equipped with multiple applicators in one spray booth and is designed to operate on three shifts, 7 days a week. With minimal daily cleanup and monthly maintenance an machine like the BNH 4000 (Long Stroke Reciprocator) will run efficiently for years. This increase in productivity is dramatic when compared to a manual sprayer.
I saved the safety issue for last because it is so important in todays work environment. Many of the latest paint coating formulas have changed and some are known carcinogens (such as CARC paints and other isocyanate catalyzed materials). Not only are we morally obligated to ensure a safe working environment for the employees, it makes good business sense to eliminate any potential health hazards or situations for todays workers. An automatic machine is impervious to solvents and overspray. It is compatible with nearly all coatings and materials. Again, the manual painter must be protected with respirators, gloves, and sometimes breathing-air suits. For health and safety reasons an automatic machine is the logical choice.
Consistency, allows a manufacturing process and therefore QUALITY, to be monitored and improved. An automatic machine is precisely repeatable and can eliminate a large number of the variables involved, we have the technology.
If additional manpower or shifts are needed to achieve your required PRODUCTIVITY, an automatic machine can work all three shifts and carry more atomizers when compared to a man.
If your work environment is hazardous to the health or SAFETY of a man. The man should be removed to safe working conditions, and an automatic machine implemented.
If you were to attach a dollar value to any one of the three categories QUALITY, PRODUCTIVITY, SAFETY, the return on investment (ROI), by installing and automatic machine in place of a man is usually less than six (6) months. Given all three...... the choice is easy.
The man should be outside the spray booth, maintaining proper process and system operation, working in concert with the tools management provides. An automatic machine is just a tool, a tool designed to improve QUALITY, PRODUCTIVITY and the SAFETY of your operation.
Information and comments provided by:
Charles A LaPointe BSME with over 30 years experience in robotic and automatic painting systems