How to reduce the loss of screen mesh

- Feb 16, 2018 -

How to reduce the loss of screen mesh

How to reduce the loss of screen mesh

Polyester mesh about 10 to 40 US dollars per yard, is one of the most expensive supplies in screen mesh printing. But they are vulnerable and vulnerable. If you waste 100 to 200 dollars a week (equivalent to 2 to 4 medium-sized screen meshs), the annual production cost of one mill will eventually increase by 8,000 to 10,000 U.S. dollars.

Take careless, poor storage place design, the printing process of the accident caused by screen mesh damage up to 20% to 30%. Although these problems can be prevented occasionally, in the unlikely event of an accident, you must prepare for screen mesh replacement, which is the inevitable cost of doing the screen mesh printing business.

However, most of the screen mesh damage is caused during the screen mesh production or as a direct result of the screen mesh production. The main reasons that cause the screen mesh to be damaged during screen mesh printing include, in order of importance, the following points:

Improper stretching

2. Lack of suitable test equipment, well-maintained stretching equipment and other tools;

3. The frame is not ready.

These problems can be avoided by properly training screen meshmasters and having a properly equipped screen mesh shop. You have to invest in new tools for the stencil making shop, which can incur training costs, but the total cost of these improvements is significantly less than the cost of wiping the screen mesh.


Tension of the screen mesh

Most screen mesh damage occurs during tensioning or as a direct result of stretching. Three major factors that lead to screen mesh damage include:

Tension and lack of time to achieve stability;

2. Tension value is incorrect;

3. The corners of the screen mesh are stressed.


Tension time

The tensioning process discussed in the following paragraph is based on what I call the "traditional" method. In the early 1990s, an alternative method, the fast tensioning method, developed by the Screen mesh Printing Technology Foundation, was designed primarily to increase screen mesh-making efficiency. With this method, the screen mesh can be tensioned one step at a time, just below its break point, thereby avoiding the tedium of repetitive tensioning in a few steps. Although this method has won some followers, it can not replace the traditional methods, mainly because it is a less tolerant approach, often resulting in the breaking of the screen mesh.

Although some screen meshs, especially those below 100 mesh / inch, can be tensioned to their maximum level in one tensioning step, the conventional approach is to tension the mesh in 3 to 4 small increments network. The screen mesh should first be tensioned to the initial tension level, which is a fraction of its final tension. Before proceeding to the next tension, the screen mesh should be placed 20min. Next, the tension of each tension should be 1/3 to 1/4 of the difference between initial and final tension. For example, if the initial tension is 15 N / cm and the final (maximum) tension is 24 N / cm, the tension for the next three tension steps should be increased by 3 N / cm each with a dwell time of 20 min between the two (Pause time should not be less than 15min no more than 30min, because too long the rest time seems to be no practical benefit).

Tension in the screen mesh to reach its maximum tension should be stable at least 24h, preferably 48h. During this time, the screen mesh will lose 3 ~ 6N / cm of tension due to "cold deformation", which is the normal state of polyester materials. Without this steady time to process the screen mesh and use it for printing, the image will be noticeably larger than it should be, and subsequent color registration will be difficult to maintain.


Tension value

The initial and final allowable tension of the screen mesh depends on the screen mesh specific cross-section (SCS) and its inherent strength. The SCS of a screen mesh is simply the sum of the cross-sectional area of each screen mesh per unit length (1 inch or 1 cm). If you know the screen mesh mesh (M c) and mesh diameter (D), you can calculate the specific cross-section screen mesh, in fact, these data can be found in the screen mesh specifications table. The calculation formula is SCS = π × Mc × D2 ÷ 4. Some charts, such as the screen mesh size comparison chart provided by ST Media Group, have calculated values for SCS.

Because the inherent strength of standard polyesters is relatively constant, SCS still determines what level of force the screen mesh will withstand and the appropriate initial and final tensile values, although higher than conventional polyesters in low stretch (LE) fabrics. Than the section is the only reliable data, it is used to measure the strength of the screen mesh.

To illustrate this point, I chose several plain weaves and classify them on a section-by-section basis (see Table 1). This table clearly shows that screen mesh mesh alone can not be used to determine screen mesh strength (although this is the main method recommended by many vendors). 420 mesh / inch, the mesh diameter of 35 μm (420/35) is larger than the section of 196/48, 230/40 or 280/40 mesh, so it can be tensioned to a higher value . The table also shows that the mesh of the same standard mesh is significantly different depending on the diameter of the mesh (eg 196/48 mesh can not be stretched as high as 196/55 mesh).

Based on empirical data and research from multiple vendors, I can relate the screen mesh's cross-section to its initial and maximum tension. The tension diagram shown in Figure 1 illustrates this relationship. Note that this chart was prepared based on the results of a medium to large (152 cm wide or more) screen mesh. Because of the "corner effect," if it is not impossible, a large halftone plate can not stretch to the same size as a small halftone plate.

The 25.4 cm × 25.4 cm screen mesh is so close to the corner that the entire screen mesh is easily tensioned to the same angle as the corner. However, as the large screen mesh farther and farther away from the corners, the difference between the tension in the corners and the tension in the middle portion becomes significant. The tension limits shown in Figure 1 are too low for a small screen mesh, but they are safe, regardless of the screen mesh size you are using.

With this chart, the tension value of any screen mesh can be determined if the specific cross-section of the screen mesh is known (ie determined by calculation). For example, if a 86/100 screen mesh is used, its cross-section is 0.00104 inches (ie, 1.04 x 10-3 inches). If you draw a vertical line through the X-axis of the table at 1.04 and note where this vertical line crosses the initial and maximum tension curves, you can read the corresponding values on the Y-axis of this table (21 N / cm and 38 N / cm). Use this chart to plot the initial and maximum tension values for medium to large screen meshs. Start by determining the screen mesh cross section and then draw a vertical line across this value on the X axis and past the initial and maximum tension curves. Find the tension on the left (Y-axis) that corresponds to the point at which the lines intersect each curve. Cross-section is better than the number of screen mesh mesh relative intensity index. The higher the cross-sectional value, the higher the strength of the screen mesh, the greater the tension it will sustain. With the same chart, the 280/40 or 196/48 screen mesh will give you initial and final tensions of 16 N / cm and 22 N / cm (both screen meshs have the same tension because they are nearly the same as the section).

I suggest that, to find all the frequently used screen mesh than the cross section, the second in the replica of the tension meter in Figure 1 marked with their values. Draw the vertical line at the appropriate point on the X axis and use a different color for each of the commonly used screen meshs. Where these vertical lines pass through the initial and maximum curves there will be a suitable amount of tension available. After you finish, you can post this chart in the screen mesh making workshop.

Also keep in mind that the maximum tension value is not the same as the screen mesh holding tension at printing. After 24 ~ 48h, the tension value will drop, lower than the maximum tension value reached when stretched. Finally, note that the tension chart in Figure 1 is suitable for both LE and normal screen meshs. The only difference is that the LE screen mesh allows the initial tension to be 2 to 3 N / cm higher than the normal screen mesh and maintains its tension longer than the normal screen mesh under the conditions of use.


Corner of the screen mesh

It is independent of the type of screen mesh used (ie self-tensioning, tensioning, etc.) and the type of screen mesh used. The screen mesh at the corner of the screen mesh must have as little tension as possible. Because taut forces appear to be perpendicular to each other, and because there is only a small amount of screen mesh between the two taut nets in the corner of the screen mesh, the tension increases rapidly to the breaking point of the screen mesh (see Figure 2). To avoid this problem, the corners must be "softened" by relaxing the mesh before or during the stretching process.


Instrumentation, tools and tensioning equipment

In order to do business without error, screen mesh makers must have the necessary instrumentation and equipment. In addition to manually stretching the screen mesh over a wooden frame, a tension meter must be used in all cases. Measuring microscopes and high power magnifiers are also necessary to verify the mesh size and mesh diameter and to evaluate the quality of the prepared screen mesh. Re-tensioning of the screen mesh frame requires a suitable adjustable wrench, and the pneumatic tensioning device requires the necessary controls to adjust the tensioning force smoothly and without jerking.

When using pneumatic clamps, the clamps should be periodically evaluated to facilitate smooth operation. When the clip in the stretched state, the use of rubber hammer gently tap it to see if it is tight. If the clip is moved (beaten) due to a beat, it should be cleaned, readjusted or replaced. When a pneumatic tensioning net suddenly applies too much force to the mesh netting, the mesh breakage often occurs due to the tendency of the tensioning force to balance. More often, clips are set incorrectly and do not move in a straight line during tensioning (see Figure 3). This problem also caused the clips to jam and suddenly bounce during tightening.

Dry preparation (Clean the mesh in the corner of the screen mesh frame to provide only a small amount of tensioning material for tautness.) Tension therefore causes the tension in these areas to be faster than the tension towards the center of the screen mesh Rise.If the screen mesh at the slack angle, the big box especially so, it will torn the screen mesh in the tension.Figure 2 screen mesh tension in the corner of the stress stress line and has been coated) screen mesh should In a screen mesh drying chamber at a temperature not exceeding 38 ° C (100 ° F). Above this temperature, the highly tensioned screen mesh breaks. Mesh frames and screen meshs have very different rates of expansion (aluminum nearly double the rate of polyester), a difference that causes the screen meshs to break during or after the drying process.


Mesh frame

The last important reason for screen mesh breakage is that the tightened mesh frame is not well prepared. Metal frames shall not have sharp corners or edges that touch the tensioned screen mesh. After each use, sanding or grinding with tighten the adhesive mesh often have repeated friction caused by sharp sharp edges or edges. Re-tensioning frames may have seemingly insignificant notches and burrs, but these notches and burrs will cause the screen mesh to suddenly under high tension.

Finally, tighten the mesh should be carefully placed and placed in a place not prone to accidents. Do not drop the mesh frame especially at an angle. Dropping at 1ft from the corners of the box almost always shakes a well-knit screen mesh.


Screen mesh production points

To reduce the number of faulty screen meshs and the amount of screen mesh waste, screen meshmasters should keep in mind the three basic rules of the screen mesh shop:

1. Stretching slowly when the network;

2. To know what the tension limit of all the screen meshs used is;

3. Take good care of tools, equipment and materials.

Carefully and repeatedly, pay attention to these suggestions and study the screen mesh-making process. The screen mesh-making workshop staff will benefit from the printed halftone screen mesh they produce. At the same time, your company saves hundreds and thousands of dollars each year on the cost of changing screen meshs, which you can use to improve other aspects of your operations.



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