Controlling Slot Thickening
Unlike other coating techniques, slot thickening is largely controlled by the delivery of solution. This is because the solution enters a narrow channel through the slot-die head, resulting in a pressure difference. The channel width and pressure drop are therefore critical for the smooth flow of the solution. This is a key reason why the design of the coat-hanger must be optimised to ensure an even flow rate across the slot-die head. It is also important to consider the viscosity of the solution. In some cases, aggregates or other particles may need to be filtered out of the solution. In addition, if the solution is highly viscoelastic, a change in the viscosity of the solution can cause a deviation in the idealized relationship between solution pressure and wet film thickness. <a href="https://lookups.api.uat2.mes.yeti.com/">slot server vietnam</a>
The first step is to control the flow of solution into the slot-die system. This is accomplished by shims. Shims are thin metallic pieces that are placed in a space between two heads. They prevent the solution from flowing out of certain areas of the slot-die head. They can also be used to set the coating width and thickness. They can be made of different thicknesses to accommodate for variations in the spacing between the heads.
Another method of controlling the thickness of the coating is by adjusting the pump rate. A simple peristaltic pump can be used to increase or decrease the flow rate of solution. This is especially useful for laboratory testing where small volume solutions are used. A higher flow rate will result in more material flowing upstream and a higher shear force. In addition, the higher the flow rate, the faster the substrate speed. The faster the substrate speed, the quicker the solution can shear the wet film.
An idealized relationship between the pressure and flow rates of solution is based on the Pouiselle Flow equation. The Pouiselle Flow equation describes how the fluid flows through a narrow channel. Specifically, it describes how the pressure drop is governed by the width of the channel, the flow rate, and the viscosity of the solution. However, this relationship is subject to significant deviations due to the non-ideal behaviour of various components of the process. It is also important to consider the drying effects. If the drying process is not effective, then the wet film may be thinner at the edge of the film.
The height of the slot-die head has a great impact on the quality of the coated film. In most slot-die systems, the height of the head is controlled by micrometers. In some advanced systems, it can be tilted in order to increase or decrease the distance between the front and the back of the slot-die head. This will reduce the appearance of neck-in defects and improve the accuracy of the coating pattern.
There are a number of processing steps that can be performed to destabilise the wet film coating bead. For example, introducing solvent at the exit of the slot-die can dilute the solution at the edge of the bead. When a bead is unstable, it can be distorted and the coating can be retracted, causing streaks or ribbing.