Drum screen printing process problems and solutions II

(b) Frames and stretch nets

1, the net frame

The frame is a frame used to support the screen. It is made of metal, wood or other materials and is divided into two types, fixed and adjustable. The most commonly used is the frame made of aluminum. The materials used to make the frame are designed to meet the tension requirements, and are sturdy, durable, lightweight, and inexpensive.

Square and rectangular frames are generally used for printing on the top surface of a drum. However, when printing on the circular surface of the barrel body, a frame adapted to its shape is generally used.

The cross-sectional thickness and shape of the frame material are also different due to the different methods of fixing the screen, its use, and strength. For example, when fixing a screen with an adhesive, angles and corners are generally used; in the case of physical fixation, a slotted frame is generally used. In the case of higher strength requirements, strengthen the ribs on the inside of the tube and use a certain thickness of the tube. In addition, some special frames themselves are equipped with stretching nets, which can be stretched without stretching the net. FIG. 2 is a cross-sectional schematic view of various shapes of the frame.

In order to ensure plate making, printing quality and other requirements, the frame can be selected based on the following conditions.

(1) Strong resistance to strain. The material of the frame should have enough strength to resist the tension of the mesh, because when the mesh is stretched, the mesh will produce a certain pulling force on the frame, and if the strength is not enough, the frame will flex and deform, so that no good print will be printed.

(2) It should be prestressed. After the netting, the bending deformation of the frame will affect the tension stability of the screen. To reduce this effect, the network box can be pre-processed. There are two methods for handling: First, according to the strength principle of the arched structure, the net frame is made into a convex shape, its deflection is about 4 mm/meter, each internal angle is slightly larger than 90°, or the metal frame that has been made, With a special tool to stretch this shape, this pre-deformation treatment can resist the impact of the screen tension. Another method is to do a pre-stress treatment while doing pneumatic pulling, that is, the front end of the drawer is tight against the outside of the frame, the net frame is bent by the top force, and when the net is fixed, the frame is subjected to force. Although the surface is moved from the outside to the top, the force direction and size are basically the same, so no more bending is added. Due to these advantages, the pneumatic stretching machine has become the most popular one at home and abroad.

(3) Suitable size. The production of different specifications of the network box configuration, use the size of the printing according to the size of the appropriate frame to determine, you can reduce waste, but also easy to operate.

The size of the frame should be larger than that of the printing plate. If the plate pattern is a × b, the inside size of the frame is 2a × 2b, which can be fully printed. The selection of the frame size is based not only on the printing area, but also on the needs of the squeegee and the start and end positions of the squeegee and the ink return plate at the time of printing; the need for printing ink on the plate; and the uniform screen tension at the plate of the plate is guaranteed. The need for silk screen printing in the squeegee printing stroke.

2, stretch net

The stretch net stretches the wire mesh to the frame, which is manually operated and mechanically operated. Manual stretch nets are simple and easy to use and are commonly used methods, while mechanical stretch nets are of good quality. Whether it is hand-stretched or mechanical stretched nets have to pay attention to the tension of the screen. It is not easy to stretch the tension of the screen too much. If it is too small, the screen tends to be loose (the stainless steel screen will also appear premature relaxation); if it is too large, the screen will break easily. In the actual stretching operation, the tension of the stretching net can be determined empirically, and while the screen is stretched, the screen is pressed with a finger until the screen has a feeling of elasticity. Commonly used stretching methods are:

(1) Manual stretch net The manual stretch net operation steps are as follows:

1 Cut a screen larger than the size of the outer net frame. Generally, the length and width of the screen are 40~60mm larger than the size of the outer net frame.

2 soak the screen in water.

3 The screen is placed on the frame. The latitude line of the screen is parallel to the frame (vertical). However, when used for high-precision printing or level printing, the latitude line is at an angle to the frame. It is 20°~45°.

4 Place the strip a, nail the frame A, and pull the screen toward the direction of E (see Figure 3). Then all the strips a nailed, fixed AB side.

5 Tighten the screen in the direction of F, put on the molding c, and then screw the C end. Then, while pulling the screen toward the direction of G, tighten the molding c so that the side of the CD is fixed.

6 In the same way, nail the bars b and d and fix the sides of BC and AD. At this point, the stretching operation is completed.
(to be continued)