A clean paint shop is a profitable paint shop!
The problem of “paint dirt” in Class “A” paint finishing is a major concern. Paint dirt is one of the major causes of quality control dilemmas.
While there are many possible sources for paint dirt in a typical paint facility, some difficult to identify, there is one source that is as evident, and easy to fix as anyone could hope for.
When process technicians start to “de-bug” a process, spray gun/ bell washers are often identified as the actual source of these defects. They’re easy to see. Fixes are pretty easy to understand too, even though they’re often very time consuming.
Quality defects caused by gun cleaning stations, often referred to generically as “Cap cleaners”, run the gamut from a solvent drip, caused by a wet applicator while it moves over a part, to actual paint solids being dropped or blown onto a part. Splashing of cleaning solvent and/or waste can also happen if the cleaning vessel doesn’t drain efficiently or if solvent flowrate and pressure are less than optimal. Insufficient blow off while the gun/bell exits the wash station can also cause problems. The process is simple, but getting it right matters. The details matter.
I recently had the opportunity to talk with Gary Newbold of Hosco Fittings LLC.
Gary educated me on the merits of a properly designed and set-up gun/bell cleaning station. Gary has worked with customers to optimize this process, with really astounding Return on Investment figures.
He said “The quality control factors and other cost savings from a reduction in labor (to maintain and resolve issues) and solvent and air consumption will often pay for an optimized system very quickly. The key is in the details of the equipment design, set-up and use.”
Below are some of the symptoms he identified for a non-optimized applicator cleaner installation and/or its operation, relative to product quality impact.
Cause and effect of a dirty applicator and its effect on defect:
Solvent drips on product –
- Generally caused by insufficient blow off as the device exits the cleaning station.
- Plugged drains contributing to excessive fluid within the containment vessel.
- Overfeeding solvent during the wash operation, which can cause migration of solvent into cavities or surfaces that should not be exposed to the liquid cleaning fluids and are not addressed in the blow-off step.
Particles of agglomerated or dried paint left on the “cleaned” gun.
- Particles of crystallized paint fall into the wet film during the spraying steps for primer, color or clear-coat.
Droplets of paint, waste paint or solvent are splashed onto the product.
- In close proximity to the cleaning station during cleaning operation or during the evacuation or draining of the cleaning station, there’s potential for “splash” from a dirty, clogged or “over-full” containment vessel. Slow draining of the containment vessel is a potential factor
- Conductivity of the material being sprayed and electrostatic “wrap” are two major factors that affect the determination of cleaning intervals and conditions.
- Solids content and the individual material’s propensity to coagulate or agglomerate into larger particle sizes,
- Facilities and process factors such as environmental (humidity for example), mechanical (booth air flow, spray pressures/flowrates, material temperatures), etc.
- It is important to set up the frequency of automatic cleaning properly to prevent overloading the cleaning station’s ability to properly clean the applicator, and to also provide proper drain timing of the purge fluids in these short durations of applicator cleaning.
- If paint and purge material piping headers are employed in the station, this may be a deciding factor on the frequency of the cleaning process in order to be successful with gravity-based draining and collection systems.
What is needed to optimize performance of the applicator cleaner?
Air and solvent pressure and flowrate controls are critical-
Regardless of the brand or model of the applicator cleaner, it will involve some maintenance to optimize performance. Air and solvent dispense pressure, and flowrate controls are a principal factor in the performance of the cleaner. Both pressures and flowrate must be controlled to manufacturer’s specifications, accurately and consistently. Too high or too low of either pressure or flowrate will result in defects and inefficiencies.
Air & Solvent dispensing temperatures-
Using elevated temperature cleaning materials and drying air can significantly increase cleaning performance and potentially reduce solvent and compressed air usage and time in the cleaning step. Three important cost factors.
It is strongly recommended to investigate using elevated temperatures up to 130 F for both the purge material and drying air for the most efficient and effective cleaning.
Routine Maintenance of the Cleaning Stations-
The applicator cleaners must also be disassembled for thorough cleaning of the internals. This frequency is highly dependent on the specific materials running through the cleaner, the environment or location of the cleaner, and its use rate. A poorly set up and maintained applicator cleaner will cause as many defects as it prevents.
When it comes to removing defects or inefficiencies related to the applicator cleaner, Hosco is a recognized solutions provider with proven results. Hosco has been involved in applicator cleaning projects where repair/rework of spray defect, plus maintenance actions to keep the cleaning stations at even a minimum level of acceptability, has created well over “$2,000,000 of costs per year for a single high-volume plant.” Gary commented, “It is our belief, from our experience, that a mid-size paint shop in the assembly plant or a Tier One paint shop can incur an average of approximately $350,000-$950,000 of unnecessary costs to repair/rework on products detrimentally affected from an improperly set up applicator cleaner system. Off-shift maintenance and cleaning activities due to improperly installed or operated applicator cleaner system are a huge factor in cost impacts”.
How do you maximize effectiveness of the applicator cleaner and minimize maintenance?
The following steps for performance improvements of these applicator cleaners is summarized into logical feature areas with descriptions and related cost estimates. Gary stated, “Hosco has incorporated these features into our equipment to provide an optimal solution for our customers.”
Conductive PTFE Coating:
- Reduces the cleaning and disassembly frequency by changing the internal and external surfaces to shed overspray, splashes, and ultimately the waste sticking and drying onto those surfaces. It is important due to safety regulations to insure the coating applied is conductive to minimize electrical risks in the spray zone. This enhancement adds approximately $1000-2000 to the equipment cost depending on the surfaces to be coated.
- “We enlarged and relocated drains for absolute venting and quick removal of purged material during the cleaning or color change operation. Hosco recommends a 2” NPT port at the lowest section of the collection tank with JIC(F) couplings for easy make and break access during inspection and maintenance.”
Using Solvent Supply Recirculation with Heat applied to the Flush Solvent:
- Hosco recommends elevated temperature flush solvents in the 120-130 F range (140 F maximum) for waterborne purge materials (i.e.,deionized water with amine), to facilitate the cleaning cycle and minimize time and purge material used in this cleaning operation.
- If heated air is used at the applicator, we also recommend using this source of heated air to optimize the blow off performance of the applicator as it goes thru the drying step of the cleaning station operation.
Using Fluid Pressure and Fluid Flowrate control at the Cleaning station:
- In general, the supply pressure of the cleaning station should not exceed 80 PSI to prevent migration of solvent fluid into applicator areas that are not protected or could be harmed by the cleaning solvent.
- In general, the supply volume of cleaning solvent should not exceed 400 cc/min flowrates at any time during the spraying or wash down of the applicator and should be run at the lowest flowrate possible to perform effective cleaning.
I’ve been in hundreds of paint shops and I’ve seen just about every possible configuration of cleaning stations and I can concur with the issues, and their solutions raised by Gary. Details do matter in just about every facet of production processes. Taking the time to ferret out and fix the small problems will always pay big dividends in mass production scale processes. Not knowing what the problems are is often half the battle. Many process people get used to applying “band-aides” to a process, over and over again. Many are amazed when a permanent solution that actually works is presented. First pass yield is the most visible metric in paint shops. Quality defect is the make or break factor for first pass yield. Cleaning station optimization is low-hanging fruit when it comes to minimizing quality defects.
Contact Gary Newbold at Hosco Fittings.