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A Holistic Approach to Finishing -Step 4

16. December 2019 21:14

By: Joe Baggett, Innovative Wood Process Solutions

One of my favorite movies is the old western John Wayne and the Cowboys. There are two scenes in the movie that would hold true to the journey of Holistic Finishing. When the Cowboys which in this instance are truly teenage boys are getting ready to go on the cattle drive, they must turn in all arms to the wagon/trail boss.

One particular young man steps up to turn in his pistol and can barely unholster it due to its size. Surprised by the large pistol from the small boy John Wayne asks him is he had every fired it before, to which he reluctantly replied no. If you know the movie then by the end the young boy learned to use it well and did so to recover the stolen herd of cattle from rustlers and drive them to the end of the trail drive.

The current and developing technology of applying and curing coatings in the wood finishing arena is a powerful tool or weapon if you will allow the analogy. The challenge in most applications is the context in which to use the technology to create strategy and value to win. The application and curing technology have improved commensurately with the chemical technology in the coating that we alluded to as in the formulation phase of step II in this Holistic Finishing Process. To get the most value out of the technology in the chemical development of the coatings many times cutting edge technology in the application and curing is required.

When looking at the application and curing technology that will enable and enhance the formulations from step II there are important questions to ask. All chemical formulations apply and cure differently. Too many times a very general approach is taken to the application and curing. When looking at the total internal cycle time when shops and factories it is common to have the most amount of time in the plant taken by finishing. Sometimes this is due to color changes, no forced curing, space for WIP in between finish lines, the sequencing of work going into and coming out of the finish lines, and coordination of preparation of the coatings based on demand of the product being finished, and the amount of time required for color approval before beginning or continuing finishing of production. The amount of internal cycle time dedicated to finishing can usually be reduced if the right application and curing technology can be identified and implemented. Here are the main questions to ask:

What is the most efficient way to apply the coatings from the formulation phase? 
Transfer efficiency is the missing link in many finishing operations. It is best to set target transfer efficiency and then track performance against the target. This is just as important as the yield of hardwood or plywood in the mill. It is not uncommon to see the application equipment be selected for the lowest up-front cost but the lowest transfer efficiency. If you aren’t currently tracking transfer efficiency, we encourage all wood finishers to start immediately. Many other finishing problems and defects are caused by ineffective transfer efficiency, this is why it is a good metric not only for saving money but as a general litmus test of the overall effectiveness of the finishing operation. It requires good processes and adherence to those processes to achieve and maintain high transfer efficiencies so when the transfer efficiency drops it is usually due to a process failure. Applying the target film builds no more and no less is one of the main performance factors of the successful finishing operations. I want to show how to transfer efficiency correlates to finishing from a holistic approach. If a finishing operation is permitted a certain amount ton in emissions and they improve the transfer efficiency by 15% then usually reduce their emissions proportionately creating the ability to produce more volume without additional permitting or permit amendments. The more that compressed air is used as the atomizing method the less transfer efficient the spray application becomes ( compressed air expands at about a 10:1 ratio as it leaves the gun creating overspray and pressuring spray booths. Also, the compressed air introduces a cold gas into the coating which can increase flash and cure time. Instead of compressed air, heated and ionized nitrogen improves these negative effects in all the spray application technologies listed in the chart below, it also increases the sealer sand ability of sealer and in between coats.

What is the most effective method for curing the coatings?
Curing of coatings is often misunderstood and when typical finish lines run out of budget money the election of low costing curing methods winds up increasing the internal cycle time in the finish department and the plant. Let me say that forced curing it one of the best ways to reduce costs and eliminate problems in the finishing area. Let me also say that when internal lead times increase the cost to cash cycle tying up cash. Curing coatings in the least amount of time reasonably possible holds value in several ways other than reducing cycle time. The forced curing of coatings in the shortest cycles possible using ovens will help in the following ways. It will reduce the amount of time the coating sits wet on the substrates reducing the possibility of contamination of dust and other foreign material. It will get the coating closest to the final appearance before it leaves the factory. Depending on the formulations, the forced curing parameters vary based on the solvent line up and the resins and binders and then the catalyst/hardeners and photoinitiators (if it is UV cured). All solvents including water are volatile (this means they evaporate) the way they evaporate, and how fast they evaporate and how they react with the remaining chemistry is the important first step. The temperature of the wood substrate to which the coating is being applied, the temperature of the coating as it is being applied and the temperature of the air whether it is ambient or forced heated is where the curing process begins.

One of the biggest opportunities to reduce and improve curing is the pre-heating of the substrate and the coating before using forced curing ovens or even ambient curing. It is helpful to heat the substrate up 100 degrees or so immediately before spraying and then curing as well as the coating to the level that is doesn’t begin to pre-cure in the delivery equipment. This will not only reduce the curing time be it will help the coating flow out quickly and flash the solvents out from the bottom up more efficiently.

As an example, water-based coatings typically need to be brought to a board surface temperature of about 118°F to begin to force out the water beyond ambient evaporation pre-heating the substrate reduces the load from the oven to raise the board surface temperature. These physical and chemical properties vary by solvent and coating. Flashing out the solvents in way that allows for flow and good surface tension without pre-cure and bubbles and grain raise is important. This is especially important for UV cured coatings. Then for coatings that are assisted by raising the board surface temperature to higher levels helps cross-link and snap cure (acid cure, and 2K and pre-catalyzed coatings) the curing methods should reach and hold the board surface temperature to enable the best cross-linking possible. This will ensure the highest level of hardness when the parts come out of the curing ovens and cool off as the coating finishes it’s curing process.

What is the most repeatable and productive method for applying the coatings?
It is important to answer the first two questions first as they carry more weight than the last question. Right now, many want to scale their business for growth and alignment with the changing workforce and employment conditions. So, what does this look like in setting up finish lines? The repeatability of consistently putting a finish out that is a game-changer/difference-maker is important. The repeatability includes the ability to produce it in a regular scenario with the same group of people and information and in the same cost. Some repeatably produce a finish but the cost and time to do so vary a lot. The line and equipment to produce it should be repeatable in time, materials and cost on a normal day to day scenario with the same group of people. Finishing lines are sometimes the highest dollar item that is frequently abandoned the soonest out of all the equipment in factory or shop.

Click to opening Complete List and Descriptors of Finishing Systems.pdf (111.77 kb)

If I had a little money for every time I hear “that finish lines doesn’t work” I would have more money in the bank. The next step after achieving repeatability is productivity. What is the most productive scenario for the new finish? The ability to quickly change colors without creating waste is important especially as paints have outpaced stains. The basic lines are in the chart below. This chart deals with spraying, roll coating, and vacuum coating and then the oven and or curing. The sealer sanding in between coats is also an important component to increasing the productivity there are stand-alone and inline automatic sealer sanding technologies that can increase productivity and improve quality. How these integrate with the delivery and curing technology and equipment in the chart below is very configurable to application. That said there is no technological issue preventing the finishing operation from reaching high levels of productivity. Digital Printing is also an up and coming technology to which we will devote a special article separately.

Hopefully, this is empowering with some of the more important questions to ask the context and perspective with which to answer them. For step IV in this Holistic Approach to Finishing we encourage people to engage multiple coatings and equipment suppliers with the same questions and do a significant amount of testing with the chemical formulations from step II.

We also encourage the design of the lines to be done in AutoCAD with process equipment, delivery equipment, operators, carts, material handling etcetera. Then draft the flow of the process giving space to work in process and other process variables. The ovens, lines speeds, cure time, spray rates, sealer sanding and other process constraints should be taken in to account. Establish targeted theoretical costs in material labor and overhead for the finishing operation. This is the best opportunity to make the operation cost-effective during the design phase, this is all about game-changing/difference-making finishing. 

 

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