In critical product cleaning, achieving throughput means ensuring that residue is removed from parts in a short enough time and that the parts are sufficiently clean.
Barbara and Ed KanegsbergPart of the decision involves sizing the cleaning equipment for adequate throughput. Throughput also means assuring that manufacturing “traffic” flows smoothly – with no infamous Los Angeles-style traffic jams.
Cleaning Cycle, Sizing
Someone from a company selling the new cleaning machine may provide a throughput estimate. Throughput is provided in addition to the working dimensions of the chamber or the tank, or the conveyor belt width. Sometimes the phrase “sizing the equipment” is used. For batch cleaning, this involves estimating how many parts can reasonably fit in the process bath or chamber, then multiplying by the cycle time. For in-line (conveyor belt) processes, the equipment supplier may size the equipment based on the number of parts processed per unit time and the conveyor belt speed. The throughput estimate is essential information – but it is just that – an estimate. Consider a few more factors and avoid traffic jams, pile-ups, and complete freeway closures.
Bottlenecks
Selecting a cleaning system based on an estimated typical cleaning cycle alone is not a rational approach. For the best return on your equipment investment, consider additional factors. Be sure to ask, to question, and to look at your own manufacturing microclimate. Why are you cleaning? What do you expect to accomplish with the new cleaning equipment?
There can be bottlenecks. For example, estimating the cleaning rate per hour can be problematic if there are production peaks where cleaning must occur immediately after processing, or where the next manufacturing step must follow immediately after cleaning.
If a semi-automated cleaning system replaces hand-wiping by individual operators, the third shift may leave the product to be cleaned for the following day. We don’t mean to make fun of you, third shift people! Soil that remains on the part, even for a few hours, can be more difficult to clean. To address this problem, the third shift can learn to use the cleaning machine. If the third shift people (or anyone else) can’t do the cleaning step right away, a preliminary pre-cleaning step may be the best approach. This can be as simple as a wipe-down of the product or submersion of the parts in a hydrocarbon (subject to the permitting situation in your location). If the downstream process is the pinch point, perhaps a slower cycle time or a smaller cleaning system would be the right approach. Perhaps the downstream process could be made more efficient.
Where bottlenecks occur, the cleaned product must be stored to prevent recontamination.
Are You Removing the Soils?
That cleaning cycle has to remove soils effectively. Are you certain the new cleaning system will adequately remove all of the soils your facility is likely to encounter? Assumptions of cleaning effectiveness limit the best estimates of throughput. An effective process change team (yes, we have to remind you that process change is not a solo effort) tests the efficacy of cleaning. This means examining the cleaning agent used in the cleaning process alongside the soils on the parts. Coupon testing, in which soils are placed on a flat piece of metal and then run through the cleaning process, is inadequate. Flat coupons do not have the blind holes and tight spacing of most products. Also, the soil that is applied to a product is not the same as the residue. Residue includes a known, and often unanticipated, mix of dirt (particulate and thin-film) on the part after upstream processing, storage, and shipping. The actual cycle time is better estimated using real hardware and real residue. As always, we remind you to test new cleaning processes on scrap, not on customer hardware! Testing actual hardware with representative materials of construction can be eye-opening, as the default cleaning process may pose a materials-compatibility problem. A less aggressive cleaning process may be needed; therefore, it may take longer to remove soils and residue.
Fixturing and parts placement can become a bottleneck. To the extent possible, coordinate and consolidate the fixturing process. Managing the parts before, during, and after the cleaning process impacts throughput. You can’t (or shouldn’t) just toss the part over your shoulder and into the cleaning chamber or onto a conveyor belt. Parts must be placed appropriately for effective cleaning. We sometimes see situations where parts arrive at the cleaning system fixed from an upstream process. Then those parts have to be removed from the fixtures for the upstream process. Then the parts are placed in separate racks or fixtures for cleaning. Repeated fixturing, de-fixturing, and refixturing are labor-intensive and slow the overall manufacturing and assembly process while also increasing the risk of introducing new contamination. Conveyor belt systems, where the parts are sprayed in air, may also require parts fixturing. We see situations where electronic assemblies are so light that the force of the spray causes them to look like a multi-car accident, a bunch of assemblies pushed one on top of the other. Those in the middle of the stack don’t get cleaned properly. Sometimes the parts are driven off the conveyor belt and get stuck. This clogs up the works! Once the process is in place, the only solution may be to individually attach each assembly to the conveyor belt. In one memorable instance, the cleaning system for metal parts broke down due to insecure fixturing. The parts were hung from overhead hooks and moved through the immersion cleaning process. Sometimes, a part would escape and fall into the process bath. There, the parts sort of marinated, corroded, and generally degraded, contributing to a process that no longer cleaned effectively. More secure fixturing kept the problem from recurring.
Well-designed, high-quality fixtures are important for achieving optimal throughput. Make sure fixtures are designed so parts can be easily placed and removed. Consider purchasing extra fixtures and factor in enough time and money to ensure there are enough trained and educated people to load and unload parts.
Managing Extremes and Outliers
Consider the difficult extremes in selecting the right-sized equipment. Difficult extremes include worst-case parts, worst-case residue, very large parts, and very small parts. Complex parts with very adherent residue are likely to require different process parameters than usual. We have seen too many instances where a small percentage of difficult parts require repeated cleaning. Very large parts may be better cleaned manually. Very small parts may take up a significant amount of time in the parts cleaner. For small parts, it may make sense to purchase a separate, smaller benchtop cleaning system. Very small “widgets” can often be cleaned with ultrasonics. When there are a number of small parts that require different cleaning agents, the parts can be placed in beakers that are then placed in the tank. The tank is filled with a dilute surfactant solution.
Are the parts adequately rinsed? Is the product too hot to handle? Be sure to consider the number of rinse cycles and drying time when estimating throughput. Drying complex metal parts, parts containing plastics, and other non-metal parts is time-consuming. Drying time is often underestimated. Do you need two drying steps? Cool-down time slows the process flow.
Location
A large, centralized cleaning system is usually easier to control than smaller or cell-based systems. It’s easier to control process parameters and to monitor process baths. The system can be designed to minimize air emissions and to institute engineering controls that protect workers.
Where is the cleaning system located relative to other manufacturing steps? When considering throughput with a centralized cleaning system, account for how long it takes assemblers to move the part to and from the cleaning machine. Having assemblers trudge all the way across the facility to the cleaning machine, then repack and carry the cleaning product to the next step, can be a schlep (that’s a technical term). The time required to move product constitutes a hidden increase in cycle time.
Downtime
During downtime, the process flow is zero. Downtime can be relatively short, and it may occur regularly. Aqueous cleaning systems must reach the operating temperature. It takes a significant amount of time and a lot of energy to heat water. Ultrasonic tanks must be degassed, or cavitation will be ineffective.
Regular equipment maintenance is a must for all cleaning machines, and unexpected breakdowns can occur. There are strategies to minimize downtime. Suppliers of cleaning equipment may offer remote monitoring either by you or by the manufacturer. Breakdowns happen. We encourage clients to have spare parts in-house. We also encourage them to scope out who can repair the system and how responsive they are. Sometimes, in-house staff at your company have the skills and talent to handle repairs.
Always, always, always get the Safety/Environmental folks involved, and get them involved early in the game. Even if you think they will say “no,” get them involved. They can stop a process dead in its tracks. In one extreme example – before you ask, this was NOT in California – new cleaning equipment was sitting alone and unused in a corner of the facility. Why? The safety group vetoed use of the cleaning machine. To avoid zero throughput, the facility was forced to use a slow, ineffective cleaning system. Safety/Environmental could have and should have implemented worker safety and environmental controls.
Solvent and water management can derail the process for days. The Safety/Environmental person on your team may be able to help during the planning stages with issues related to the storage and removal of hazardous waste. Details in cleaning equipment design can make the difference. A solvent that you can keep using is a solvent that doesn’t have to go to a hazardous waste facility. In aqueous processes, the liquid in the wash and even the rinse tanks must be replaced. The spent process baths may have to be treated as hazardous waste.
Consider alternative cleaning options, particularly where high volume, continuous cleaning throughput is required. If possible, have another cleaning system available. Consider contract cleaning at an outside facility that has been pre-qualified.
It’s a Process, Not a Purchase
In the final analysis, estimating cyclic time and equipment sizing requires more than simple arithmetic. We’ve provided a few examples of what to look for. In our experience, it is wise to factor in downtime, changes in upstream processes, and less-than-expected cleaning efficacy. Also, factor in success – allow a little room for production increases.
Your specific manufacturing environment is probably not the same as that of another company or even another facility within your company. While there are no guarantees, understanding the factors that affect throughput will markedly improve your chances of avoiding traffic jams and coping with shutdowns.
Changing the cleaning process is itself a process. In upcoming episodes of this series, we will provide you with more food for thought, more ammunition to ask the right questions, make the best decision, and grow.
Barbara and Ed Kanegsberg founded BFK Solutions in 1994 as a critical cleaning consulting service and the go-to resource for eliminating cleaning, surface quality, and contamination problems — or, even better, preventing them altogether. Barbara, widely known as “The Cleaning Lady,” is an expert and trusted adviser in critical cleaning. Ed is known as “The Rocket Scientist.” They write Clean Source, an approximately monthly e-newsletter that provides practical ideas to improve cleaning, contamination control, and product quality. They are co-editors and contributors to the acclaimed two-volume “Handbook for Critical Cleaning,” CRC/Taylor & Francis, 2011. Visit https://bfksolutions.com
