When cutting a thick steel plate, the temperature decreases downward from the upper surface. At the beginning of cutting, the oxygen pressure gradually increases and finally reaches the same in the thickness direction of the steel plate. This leads to inconsistent combustion in the thickness direction of the steel plate at the cutting start position, and defects appear at the cutting start end of the workpiece, as shown in figure 1.
To avoid defects, the following methods can be adopted:
(1) adopts circular arc feed to increase the length of lead-in line and avoid directly entering the point. This method has good effect and is widely used in production. Its disadvantage is that it wastes materials.
(2) Use ignition match. The method is to add a steel plate close to the thickness of the steel plate at the entrance point, and there can be no gap near it. The cutting knife should be cut into the fire bar, and ignition match will guide the flame of the cutting tool to the bottom of the steel plate, so that the burning speed of the steel plate can be consistent from top to bottom, and the best cutting section can be obtained. Ignition match can be replaced by chips. This method reduces the distance between the workpiece and the edge of the plate, reduces the generation of scrap, and effectively improves the utilization rate of the plate. Ignition match is more practical when cutting extra-thick steel plates.
Second, the main points that should be paid attention to in forging and cutting
Because the oxide scale on the surface of forgings is thick, and the ignition point of the oxide scale is higher than the melting point, cutting is easy to be interrupted, which leads to the decline of cutting quality and working efficiency. Therefore, when cutting forgings, the oxide scales on the upper and lower surfaces in the cutting area should be removed before cutting to improve the cutting speed and quality.
3. Key points to prevent cutting deformation of cold bed tooth plate of rolled blank
The tooth plate layout is shown in Figure 2. The toothed plate has a total length of 8 meters, a width of 0.4 meters and a thickness of 40 millimeters, and belongs to a slender strip-shaped cut finished product. How to control the deformation of the workpiece is very important in cutting. If the cutting route is arranged according to the routine, the workpiece will be deformed out of tolerance, even if it is reshaped, it will be difficult to meet the size requirements, and the product will eventually be scrapped. Therefore, it is very important to arrange the gas cutting route reasonably: set the cutting point at A, about 30 ~ 40 mm away from the head, and make hooks to prevent deformation. 1 part is cut from part a, and the workpiece is gradually separated from the substrate by counterclockwise cutting. Parts 2 and 3 are cut in the same way as parts 1. Next, cut part 6. The tangent point is set at B, and cut counterclockwise. At this time, the deformation of the component 6 is small due to the wider base material. Finally, the workpiece 5 and the workpiece 4 are cut. The deformation of the workpiece 5 is limited by the workpiece 6 and the uncut workpiece 4, and the deformation of the workpiece 4 is limited by the workpieces that have been cut on both sides, so that the cut workpiece can be guaranteed to be qualified.
Fourthly, the experience of improving cutting surface quality.
Improving the quality of oxygen and acetylene is the fundamental guarantee to obtain high quality cutting surface. When 99% bottled oxygen and acetylene produced by acetylene generator are used for numerical control flame cutting, the cutting surface quality is low, which is characterized by rough surface, frequent phenomena such as melting of the upper edge of the incision, serious slag hanging and discontinuous cutting. For steel plates with a thickness of 6mm-30mm, the cutting speed can only reach 60%-90% of the standard; 30 meters
The cutting speed of steel plate with thickness exceeding m is only 20%-60% of the standard.
When used, the purity can reach 99.
When more than 5% liquid oxygen is used for cutting, the quality of cutting surface is obviously improved due to the stable pressure, and there is less slag hanging and the cutting speed is greatly improved. When bottled acetylene is used for centralized gas supply, there will be no intermittent cutting because of its high purity and stable pressure. Method of increasing oxygen pressure (increasing pressure to 0.
1MP-0。 3 million pounds
A) Smooth cutting of thick plate and verticality of cutting surface are ensured, and the quality of cutting surface is improved to some extent. In addition, the corrosion of steel plate surface and the smooth ventilation of cutting nozzle also have great influence on continuous cutting. Therefore, incoming steel plates shall not be piled up in the open air, and shot blasting shall be carried out before cutting. The cutting mouth should be used correctly and cleaned frequently.
V. Measures to reduce cutting deformation
Severe cutting deformation will make the size of parts out of tolerance, affect the welding of subsequent assembly, and even cause scrap. Therefore, in order to reduce the cutting deformation and improve the dimensional accuracy of the cut parts, the following measures are taken:
1. Choose a reasonable cutting sequence, cutting direction and cutting starting point when programming. When cutting and blanking multiple parts, the principle of "cutting small parts first, then cutting large parts" should be followed. When cutting, the cutting deformation trend of the parts should be analyzed according to the shape and position of the parts on the steel plate, and the reasonable starting point and cutting direction should be determined.
Generally speaking, under the same thickness, the cutting deformation of parts with large external dimensions is smaller than that of parts with small external dimensions; The cutting deformation of small aspect ratio parts is smaller than that of large aspect ratio parts; Parts placed near the middle of the steel plate have smaller cutting deformation than parts placed at the edge. Therefore, in the process of cutting, the last cutting edge of the part should be connected with the steel plate that is not easy to shift as much as possible.
For some narrow parts with large length and width, it is still impossible to effectively control the deformation only by considering the cutting sequence when programming, and discontinuous cutting methods should also be considered. That is, more than two temporary non-cutting points are set on the same cutting edge of the part. This point connects the parts with the steel plate into a whole during cutting, and then cuts these points after cutting other parts. This can reduce the shrinkage deformation of the component in the length direction.
2. For rectangular parts with large aspect ratio and width greater than the minimum distance between cutting torches, they can be cut in a centralized way, and several cutting torches can be used to cut into an arch shape at the same time, and two adjacent parts can use one incision, which can not only effectively reduce cutting deformation, but also improve cutting efficiency and steel utilization rate.
3. Whether the bracket supporting the steel plate is stable directly affects the cutting quality. The contact surface between the support part of the bracket and the steel plate should be smaller, and the contact points should not be too many. It should be balanced and horizontal. Tilting and shaking easily make the steel plate shake, which affects the cutting size and the verticality of the incision. Therefore, the support should not only consider the flatness of the steel plate, but also consider the walking safety of the operator and the convenience of lifting, and should be adjusted regularly.
Six, narrow and long hole cutting quality control
If the general starting point piercing method is adopted, the parts are easy to be cut when piercing, and serious defects such as melting of the cutting surface are easy to appear at the starting point after cutting by the flame cutting machine, resulting in the quality not meeting the requirements. Therefore, a new starting point piercing program is established. The starting point cutting vector length is defined as 5mm, the preheating time is controlled, the cutting speed is adjusted, and the starting point position and cutting direction are reasonably determined, that is, on the premise of ensuring the cutting penetration, the preheating time is shortened and the cutting speed is accelerated, the piercing flame is cut at an included angle of 30-45, and the piercing point is selected at a distance of 30-50 mm from one end of the hole. This can reduce the accumulation of blown slag on the uncut board surface during perforation. If the perforation point is close to the end of the groove, when the cutting torch returns to the vicinity of the perforation point, a small amount of slag accumulated near the perforation point is still in a molten state, which is more prone to oxidation, resulting in continuous adhesion and cutting interruption.