Rust is a predictable Chemical Reaction. The rate of reaction is influenced by many different process parameters or Key Performance Indicators that need to be managed, maintained and then adjusted when certain KPI’s are out of our control ie. higher temperature and humidity through the summer months.
The rate of corrosion is impacted by several different factors
Process optimization is about identifying all the Key Performance Indicators that can negatively or positively impact the manufacturing process, understanding how they inteact with one another, controlling the KPI’s you can adjust, and then making deliberate changes to your control plan based on the process parameters that are out of your control. The more tightly you can manage your control plan, the lower the risk of a rust related event and the better you are able to manage your costs.
Controlling rust is no different. Rust is a predictable and repeatable chemical process. The rate of corrosion is impacted by several different process parameters which can change significantly over time. Since the rate of reaction increases significantly as temperature and humidity go up, its essential to adjust the corrosion inhibition techniques used to slow the process back down.
Below are just some of the KPI’s that need to be built into your dynamic control plan in your efforts to minimize rust risk at the lowest cost possible.
In a machining application, the pH of the metalworking fluid is a critical factor in controlling corrosion. The optimal pH range varies depending on the metal being maintained, for instance a pH greater than 9, will protect ferrous metals but can adversely affect the corrosion control of non-ferrous metals, such as aluminum, brass and bronze
High Water hardness can significantly increase the rate of corrosion as divalent ions react with soaps, wetting agents and emulsifiers to form compounds with limited solubility. The formation of these in solubles depletes rust inhibitors, and can lead to rusty parts and machines.
Chemicals in the make-up water can increase the rate of corrosion. Waters containing more than 100 ppm chlorides, 100 ppm Sulfates of 50 ppm nitrates are considered to be aggressive water. By breaking down the protective barriers that MWF’s create in their effort to delay corrosion, chlorides, sulfates and nitrates significantly increase the rate of corrosion.
High Bacteria levels in metal working fluids can be a direct root cause to corrosion. Bacteria can consume specific components in the metal working fluid that results in the depletion of specific components. By-products from bacterial growth are acidic in nature and can cause the pH of the system to drop significantly putting the process at further rust risk. Bacteria can also create emulsion stability issues as discussed below.
Work In Progress or WIP can significantly impact the amount of time that temporary rust prevention measures need to stay effective. Corrosion is a chemical reaction that naturally occurs, with time and temperature being two of the critical catalysts to the rate of reaction. Where aluminum corrodes at a pH above 9, ferrous materials corrode in our natural environment and as more time is allowed to pass, the more likely that corrosion will be visible on manufactured goods prior to the application of a permanent rust preventative solution being applied.
Coolant instability can cause rust. If the coolant/water emulsion breaks, or separates, the rust inhibitors in the coolant are no longer able to protect the part. Emulsion instability can result from excessive bacterial contamination, water hardness, poor concentration control, excessive tramp oil ingress etc.
And Many others….
Bi-metallic Corrosion, part to part contact, poor packing procedures, part handling or fingerprint corrosion, high Total Suspended Solids, spontaneous combustion, a highly corrosive atmosphere, low concentration, etc
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To manage both rust risk and total process cost, its essential to determine what set of parameters is causing rust to occur in your process. Unless true root cause is determined and then built into a sustainable and dynamic control plan, plants are forced to “Contain” their rust events. Containment actions occur when companies use higher concentrations or aggressive PM schedules to mask the real problem. Starting from scratch (ie fluid dump and recharge) or raising the concentration can positively impact the rust protection built into the manufacturing process, however it definitely increases operating costs and can leave the process at risk since the true root cause is not identified.
This guide is designed for Parts Manufacturers that would like to follow a step by step process to first identify, validate and then implement sustainable process control related to the formation of rust. Filled with tools and support to speed the identification process, this guide is meant to structure the problem solving process to quickly and efficiently identify corrective vs containment action.