The screening process can quickly become a slightly annoying “Goldilocks and the three bears” situation. Not too much, not too little, but just right.
Do you have problems with uneven spreading of mass on your screening machine? Not quite hitting the target curve? Then these tips are perfect for you.
Too much bounce
If the masses bounce over the screen too quickly, the screening process will not be effective. This can result in only a fraction of what should pass through the screen and miss the aiming curve. It is also a sign that the visibility is too fast.
In such a situation, it may help to remove imbalance weights to reduce g-forces. Specifically, this will result in less bounce in the screen deck. An added bonus of this is that your bearings will have a longer lifespan.
It is also possible to reduce the speed of the drive train to reduce the speed of the screening. This can work well in some cases. However, it is very important to note that you
never
do this without consulting the machine supplier first. This can have major and costly consequences if not done correctly.
Real-life example
The sight was supposed to cut at 22 millimeters, but sight analysis showed that 30% of what should have gone through just bounced past. In this case, it was because the speed was too high and there was too little mass on the screening machine. The solution was to reverse the direction of rotation of the drive to the sight. When turning the direction of rotation of the drive, the masses will bounce against the direction of travel. Because the screen cover is angled downwards, it will in practice only make the masses bounce over the panel more slowly, which in turn leads to an optimized screening process.
In this particular example, this was a good solution, but you should be a little cautious about doing this as you will increase the likelihood of plowing because you don’t have the same g-force to push the stones through the mesh. As a general rule of thumb, it’s worth remembering that you should always consult with your screen printing supplier before making any changes to the layout.
Too little bounce
If you have too little bounce on the screen panel, you will not get an optimal aiming process. You may experience problems with insufficient force to push the masses through the mesh in the screen panel. This can lead to you not aiming as much as you should, not hitting the aiming curve and problems with stones getting stuck in the mesh. This is because the visibility is too slow, so you lose too much g-force.
The solution to this challenge is to do the opposite of the previous example, i.e. increase the speed or add more imbalance weights. The same advice also applies here, do not do this without consulting the machine supplier first.
It may also be worthwhile to test alternative viewing screens to the one you’re having trouble with. Variation in hole size, material and hardness can have a major impact on the efficiency of the screening process.
Uneven spread on the screening deck
It is important to ensure even distribution of mass on the screening panel. Too little mass will lead to too much bounce on the screening panel which will drastically affect the screen curve. Without an overlying mass to push the fractions through the mesh in the screen panel, the mass will simply bounce off the panel.
Notice how the stones just bounce, and do not fall through when there is no even spread on the screen deck.
Are you struggling with voids on your viewing screen?
If you have problems with uneven spreading on the screen deck, a plow can be the solution. In practice, this means installing some PU strips in the box, which will help to spread the masses out evenly. A simple and affordable solution.
Tight meshes in the vision screener
The consistency and stickiness of the material, humidity, type of screening, number of strokes and speed of the screening machine are all factors that affect the properties of the screening panel.
When the top layer gets clogged, none of the fabrics do their job. There are an incredible number of screen panels in different thicknesses and materials. You have modular fabrics, Iseflex, finger screens, side-tensioned and long-tensioned fabrics, rubber, PU or steel to name a few.
The wrong fabric means more maintenance and lower quality of the end product.
We recommend that you carry out a screen panel analysis to find out exactly what type of panel is best suited to your work.
Quick tip at the start
If you’re struggling with challenges in the aiming process, it’s always worth testing. Remember that you always do one test at a time.
Allow some time to pass while you collect data and then look at the result. If you’re not satisfied, you can move on to test the next one, collect data, compare, and repeat.