Research Of The Technology And Performance Of The Finned Tube Blade Surface Modification Treatment

Copper finned tube for heat dissipation was widely used in the area of air conditioning.Its' surface was processed by the rotation of low carbon low alloy steel blade with a special shape.To make finned tube surface a larger surface area and heat dissipation capacity,the blade used for processing was highly required for good processing properties,toughness,high hardness and wear resistance.The present condition of the enterprise was that the blade has poor hardness,wear resistance and low service life.To solve the problems above,this paper adopt the surface modification technology(QPQ treatment)to prepare a composite layer in the surface of the blade.Preparation technology and dry silding friction and wear performance of the composite layer were systematic studied.The optimal process parameters given by the orthogonal experiment was 560?nitriding for 150 min and 430? oxidation for 40 min.The micro-topography,element distribution and phase composition of the layer were analyzed by the methods of OM,SEM,EDS and XRD.Using the micro-hardness tester and binding force test to analyze the performance of the layer.The results showed that the thickness of the composite layer under the optimal process was about 20.9?m and consisted of the oxide film(Fe3O4),the compound layer(Fe2-3N)and the diffusion layer(Fe4N)from outside to inside.The permeability layer was uniform and compact.Its' cross section hardness was about705.6HV0.05 which was nearly three times higher than that of matrix.The layer and matrix presented a good metallurgical bonding.Ball-disc dry sliding friction and wear experiments showed that the wear resistance of the layer was better than that of the matrix in quenched and tempered state under different loads,rotation speeds and temperatures.Permeability layer had low friction coefficient.The wear rate and grinding crack depth were an order of magnitude lower.Wear mechanism analysis showed that under normal temperature,wear mechanism of the quenched and tempered samples transformed from oxidation wear to peeling wear and oxidation wear,accompanied by severe plastic deformation increased by loads.Effect of the wear of composite layer changing by load was small and was mainly fatigue wear,accompanied by material peeling off.When the load increased to 20 N,as a result of the compound layer wear out and a reduction of hardness,the wear of the layer transformed to oxidation wear.Wear mechanism of the quenched and tempered samples transformed from oxidation wear and plastic deformation to peeling wear and oxidation wear,accompaniedby severe plastic deformation.Effect of wear mechanism of composite layer changing by rotate speed was small and was mainly fatigue wear,accompanied by material peeling off.Under high temperature and the load and rotation speed was constant,the wear mechanism of the quenched and tempered samples transformed from peeling wear which was given priority and accompanied by oxidation wear to oxidation wear given priority,accompanied by peeling wear and adhesive wear.The wear surface microstructure of the layer was similar under different temperatures.The main wear mechanism was oxidation wear and abrasive wear appeared at 250?.In general,after QPQ surface modification treatment,the blade surface obtained a uniform thickness composite layer and improved its hardness and wear resistance.It would be very beneficial to the improvement of the surface life of the blade.