We have articulated in past posts some of the benefits of configuring processing equipment in skid form. Generally, these advantages have to do with efficient execution, that is that a skid that supports a specific processing step is more thoroughly debugged at the OEM factory, installs quicker and is turned over to production faster with minimal interruptions.
Today we want to consider a skid application where the benefits go beyond those garnered from an efficient execution cycle. In the case of solution delivery skids, there are also manufacturing benefits and operating flexibility over a comparable hard installed system.
When we propose a solution delivery application, the functional need is to prepare and deliver a liquid coating solution to a production line that continuously conveys a flexible web (plastic film, paper, foil, etc.) through an application head, then a drying section, and finally a winding operation where the product sheet is wound into rolls.
This method of manufacturing, sometimes referred to as “Roll-to-Roll”, is favored for products that fit the thin web format and require value adding layers that can be dissolved, applied as a liquid, and then have the solvent removed in the drying step. This manufacturing approach is usually continuous, and results in low unit manufacturing costs for the high volumes of product that can be produced.
One significant challenge in roll-to-roll manufacturing is the inherent mismatch between the continuous flow of the web through the machine, and the batch-to-batch making of the coating solution. In most cases, the coating chemicals requires weight out of ingredients, a specific addition of chemicals into the solvent, mixing profiles, temperature control, assay of finished batch chemistry all prior to being coupled to the coating line and having the solution delivered and applied.
In order to service the continuous operation of the web line, redundant batch make capability must be provided, such that while one lot or increment of solution is being coated, another is being prepared, and must be ready to be coated ahead of the total consumption of the first batch.
The need to synchronize the making and delivery of the batch of solution to be coated with the continuously running roll-to-roll conveyance machine creates an opportunity to tap into the portability and flexibility of the skid based solution. The necessary solution make and deliver equipment, including a mix kettle (possibly jacketed) that can double as the delivery vessel, liquid and solids addition equipment, mixer, delivery pump, mass flow meter, even clean in place hook ups can all be built onto the skid.
Two skids, which are designed to be portable, will be required, sized according to coating flow rates and make cycles. While one skid is hooked up to the coating machine and is delivering its solution, the second kettle is off line being cleaned, charged, mixed and normalized to process conditions ahead of time. As the first kettle is being emptied, the second kettle is brought alongside, connected into the delivery line, and at the appropriate time the flow is cut over from the one skid to the other.
Some of the advantages of utilizing dual portable skids include:
- Ability to prepare solution in parallel with solution delivery and coat
- Minimize downtime and avoid time lost on fixed systems associated with purging, cleaning, and recharging
- Ensures accuracy, product assessment and instrument calibration can be done offline in parallel with coating
- Shortens start up time/time to good product as process conditions can be pre-set off line, portability of skid minimizes line lengths
- Avoids congestion around coating station attributed to space required for ancillary equipment (pumps, pipes, valves, etc.) in the fixed system model
Due to the self-contained nature of the solution skid, where all necessary equipment and devices are on board, we can see that the ability to prepare, condition, assay, and connect up in parallel enables a very short, smooth and robust changeover between batches. This is the highest value application of the skid concept, where the portability and flexibility are put to best advantage.
If you are in the roll-to-roll business, and struggle with the logistics of how you produce and deliver batches, we would highly recommend you consider a skid solution.