Improving the adhesion resistance of injection molding machineextruder screw to
2018-09-12 10:11:35
The screw is the key part of injection molding machine and extruder. With the rapid development of plastics raw material industry, various reinforced and modified engineering plastics raw materials are constantly introduced. The traditional screw can not meet the needs of processing these reinforced and modified materials. The main manifestations are as follows: the screw working surface has low resistance to high temperature adhesive wear and corrosion, the screw working surface is rapidly worn out, losing transportation The conveying capacity greatly reduces the service life of the plastic machine. For this reason, many plastic machine equipment manufacturers use a variety of ways to strengthen the working surface of the screw, trying to improve the durability of the screw, but with little effect. Conventional surface strengthening treatment, due to a variety of defects, such as carburizing in hot-dip plating material selection is narrow, wear resistance is not enough; nitriding layer is too thin; chromium plating, thermal spraying, surfacing, hardening layer wear resistance, although good, but with the substrate bond is low, wear-resistant layer is easy to fall off, etc., can not meet customer requirements.
In this paper, a laser alloying technology with high cost performance, high temperature adhesion and wear resistance and excellent corrosion resistance is proposed to strengthen the surface of screw to meet the requirements of molding reinforced plastic materials. Based on the mechanism of screw wear failure, a laser alloying composite coating was formed on the worn screw surface by using high-tech nano-ultrafine alloy powder. The effects of laser alloying material selection, laser alloying process control and main technological parameters on laser alloying quality were studied. By means of microhardness test, metallographic microstructure observation and wear contrast test, the quality of alloying was qualitatively and quantitatively analyzed, and the optimum technological parameters of laser alloying were determined.
1 experimental materials and methods
The screw material of the original injection molding machine is 40C R, and the heat treatment method is nitriding. In order to conform to the actual use, 40 C r was selected as the matrix material, and the chemical composition of the sample was as shown in Table 1.
According to the working conditions of the screw and the results of wear failure analysis, C 2 Ultrafine alloy powder (1-5 micron), A 1 ultrafine alloy powder (1-5 micron) with good adhesion and wear resistance, and carbon nanotube composite alloy with a mass ratio of 1:1:1, were selected. W, C o, C R, N I M O and so on.
Before the test, the sample surface was decontaminated and degreased to remove the stains and oxides on the sample surface. In laser alloying, there are usually two ways to supply alloyed materials: pre-deposition and synchronous powder feeding. Because the alloying material used in the test is ultra-fine auto-soluble alloy powder, which has good compactness and low porosity, it is easy to pre-deposit by manual brushing method. Therefore, the sample is pre-coated on the surface to be treated. The ideal pre-deposited layer should have uniform thickness, low porosity, good adhesion with the substrate, and no harmful effect exists in laser interaction. In the experiment, a self-made absorbent coating was used to enhance the absorption of CO2 laser on the surface of the material. The absorbent coating and alloy powder were applied to the surface of the sample by pre-coating. A proper amount of alloy powder was added to the absorbent coating, stirred evenly, and mixed together with paste or paste on the surface to be treated. The selected absorbable coating is good in adhesion and volatile.
A 7 kW C O2 transverse flow laser with a laser wavelength of 10.6 micron was used in the experiment. The laser head, worktable and workpiece were controlled by a 6-axis 4-linkage NC machine tool to do multi-axis motion. In the preparation of the sample, the workpiece is fixed and the laser head moves in a straight line. In the laser alloying treatment of the screw, the laser head is fixed and the screw rotates.
