Protection and repair technology of machine tool guide rail according to different conditions-Shenzhen ZeTian CNC Machine Tool Co., Ltd.

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Protection and repair technology of machine tool guide rail according to different conditions

Number of views：2990 Time：2021-12-14

With the development of large machine tools in the direction of high speed, heavy load, high precision and automation, how to improve and maintain the precision of machine tool guide has attracted more and more attention. Cast iron guide rail has been the first choice of most machine tool designers because of its good vibration damping, wear resistance, stability and low cost. However, cast iron has weaknesses such as low hardness, loose structure and many blank defects. Large machine tools with heavy load are easy to cause wear and strain of guide rails, which reduces the accuracy of machine tools and affects the product quality. Therefore, it is necessary to improve the wear resistance of the guide rail surface and the rapid repair of surface defects. Practice has proved that surface quenching, brush plating to protect the guide rail and brush plating brazing to repair the damage of the guide rail are ideal means at present.

1、 Electric contact surface quenching of guide rail
The main principle of electrical contact surface quenching is that an electrode (graphite or red copper roller) is in close contact with the workpiece (Fig. 1), through the low-voltage strong current of the roller, resistance heat is formed on the contact surface between the electrode and the workpiece to rapidly heat the contact surface, and the workpiece surface is rapidly cooled by compressed air to ensure that very fine martensite and flake graphite are formed on the guide rail surface to achieve the purpose of surface quenching. At the same time, the roller moves forward at a certain speed, so that the whole guide rail can be cooled According to the actual test, the quenching layer can reach 0.3 ~ 0.4mm and the hardness is 59 ~ 61hrc. After quenching, the surface is polished with a grinder, which fully ensures the design requirements of the machine tool guide rail. At the same time, due to this method, the guide rail has small deformation, less investment, simple operation, fast speed and obvious economic benefits. At present, the flat guide rail and V-shaped guide rail of large machine tools of the group company adopt this quenching and grinding method, which is simple and effective. One quenching machine can complete the surface quenching of 3 ~ 5 machine tool guide rails with a length of 12 ~ 15m in one day.

2、 Protection of machine tool guide rail by brush plating
Brushing metal or alloy on the surface of the guide rail as the working layer can also strengthen its surface hardness, improve wear resistance and further reduce the roughness. Generally, quick nickel, nickel drill tungsten alloy and nickel tungsten D alloy are selected as the working layer. The electrodeposition speed of fast nickel alloy is fast, the hardness is equivalent to that of 45 steel, and the wear resistance is better than that of quenched 45 steel; The properties of nickel tungsten alloy and nickel tungsten D alloy are similar, Both have high hardness (58 ~ 60 HRC) and wear resistance twice that of No. 45 steel, but the electrodeposition speed is faster and slower. Therefore, for general medium and small machine tools, brush plating fast nickel can achieve the purpose of protecting the guide rail. For large machine tools or machine tools with high precision requirements, nickel tungsten D alloy or nickel drilling tungsten alloy working layer is ideal.

1. Brush plating formula
(1) Quick nickel formula: nickel sulfate 254g / L; fusinate 56g / L; acetate 23g / L; oxalic acid 0.1g/l; ammonia (25% ~ 28%) 105ml; specific gravity 1.15; power consumption coefficient 0.104a • H / DM2 • μ m。
(2) Nickel tungsten D alloy formula: nickel sulfate 393g / L; sodium tungstate 23g / L; boric acid 31G / L; citric acid 42g / L; sodium sulfate 6.5g/l; cobalt sulfate 2G / L; additive 2.8g/l; glacial acetic acid 20ml / L; sodium fluoride 5g / L; sodium dodecyl sulfate 0.01 ~ 0.001 g / L; pH value 1.4 ~ 2.4; power consumption coefficient 0.214 a • H / DM2 • μ m。
(3) Brush plating pretreatment process: Industrial gasoline cleaning guide rail surface → water sandpaper grinding → acetone fine washing → electrolytic degreasing (voltage 12V, machine tool connected to negative pole) → water washing → No. II electric cleaning (workpiece connected to positive pole, voltage 7V) → water washing → No. III electric cleaning (the workpiece is connected to the positive electrode with a voltage of 10 ~ 14V, and then the workpiece is connected to the negative electrode with a voltage of 6 ~ 8V) → water washing. Special nickel is used as brush plating transition layer, water washing, brush plating fast nickel or nickel tungsten D alloy or nickel tungsten alloy.

2. Brush plating anode material and bath circulation
(1) Anode material. At present, graphite is widely used as anode in brush plating. Graphite has good conductivity and no other metal ions pollute the plating solution. However, due to the large brittleness of graphite, it is easy to collapse under high-density current. At the same time, graphite has low strength, it is difficult to make large electrodes, and metal is easy to form and has high strength. Therefore, high-purity metal can be used as anode, but metal can be used as anode It is easy to cause a large number of metal ions to be included in the electroplating solution, so the electroplating solution must contain a complexing agent with strong complexing force to complex excess metal ions, so as to ensure the stability of the electroplating solution and prevent the passivation of metal anode under high-density current. Electrolytic metal nickel is used as anode for brush plating of fast nickel, nickel tungsten D alloy or nickel drill tungsten alloy.
The fabricated anode shall be flat. The conductive plate and nickel plate shall be spot welded evenly with stainless steel electrode, and a 3mm plum blossom shaped small hole shall be drilled on the nickel plate at the bottom of the anode. The brush plated anode is shown in Figure 2.

(2) Circulation of plating solution. Closed method and intermittent pouring method can be adopted. Closed method: the plating solution is closed in the tank, and the anode is immersed in the plating solution for brush plating. At this time, all the brush coatings are immersed in the plating solution. The plating solution is not easy to be oxidized by air and affect the quality of brush plating. Generally, it is applicable to alloy plating solutions with expensive plating solution and slow electrodeposition speed. Intermittent pouring method: the plating solution It is poured on the anode intermittently to make it consume naturally. In order to reduce the loss of electroplating solution, a groove can be processed on the back of the anode, a small hole can be drilled at the bottom of the anode, and the plating solution penetrates from the small hole to the absorbent cotton for coating. This method has a lot of loss of electroplating solution, which is generally used for brush plating with high speed and cheap electroplating solution.

(3) Coating thickness control. Calculation formula of coating thickness: δ= I•t/C•S。 among δ Is the plating thickness（ μ m) , I is the current (a), t is the time (H), s is the area (DM), and C is the power consumption coefficient of the plating solution (a • H / DM2 •) μ m）。 The more uniform the coating thickness, the higher the precision of the guide rail. The coating uniformity is affected by the anode shape, the uniformity of anode cladding thickness and anode conductivity. Generally, the thickness of the plating layer is 0.05 ~ 0.08mm, and the non-uniformity can be controlled within 0.003mm.

3、 Repair of guide rail damage by brush plating brazing
Cast iron has high carbon content, loose structure and poor brazing bonding force directly on it. Therefore, nickel can be used as the transition layer and alkali copper as the intermediate layer, in which nickel can be used as the transition layer or the bottom layer has good bonding force with the matrix. Alkali copper can be used as the intermediate layer, which can be firmly combined with nickel and tin alloy of brazing layer, and tin alloy has low melting point, fluidity, toughness The wear resistance is good, and its hardness and melting point can be adjusted within a certain range according to the alloy composition. Combined with the actual situation, the specific process is formulated as follows:

1. Surface treatment
Guide rail surface treatment (oil and dust removal). Electrolytic oil removal → water washing → II electric cleaning → III electric cleaning → brushing transition layer nickel 2 ~ 3 μ M → water washing → brush plating alkali copper → water washing → pickling → brazing tin alloy → grinding the brazing layer → pretreatment before brush plating → brush plating.

It is particularly emphasized that before brush plating, the oil, ash and sand at the damaged part of the guide rail must be washed with gasoline and the serious fatigue layer shall be removed, otherwise the bonding strength of the welding layer will be seriously affected. When brushing the alkali copper layer, it is easy to oxidize, and the oxide layer will affect the bonding strength of the tin secret alloy of the welding layer. Therefore, wash the oxide film with hydrochloric acid before welding. At the same time, the hydrochloric acid cannot be coated too much, otherwise it will corrode the matrix and produce many pinholes in the tin secret alloy welding layer.

2. Nickel formula and process
Nickel sulfate 330g / L; Glacial acetic acid 30ml / L; Aminoacetic acid 20 ml / L, power consumption coefficient 0.42 a • H / DM2 • μ m； PH 0.8-1; The relative movement speed of anode and cathode is 10 ~ 25m / min; The voltage is 8 ~ 10V.

3. Alkali copper formula and process
Copper sulfate 250G / L; Ethylenediamine 250G / L; Aminotriacetic acid 150 g / L; Sodium sulfate 20 g / L; Nitric acid: 50g / L; PH value 7 ~ 8; The relative movement speed of anode and cathode is 10 ~ 20m / min; Voltage: 6 ~ 15V; Power consumption coefficient 0.18 a • H / DM2 • μ m。

The above methods can be applied according to different conditions of machine tool manufacturing or maintenance. The newly machined machine tool guide rail can be treated by surface quenching or brush plating; The damaged guide rail can be repaired by brush plating and brazing, and then the whole guide rail surface can be quenched or brushed with a layer of metal or alloy. This can not only solve the repair problem, but also protect the whole machine tool guide rail and prolong the service life of the machine tool guide rail. Atlas air compressor accessories and valves

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