The defect in the common one, bearing ring quenching cooling process

Oil bearing parts are widely used as a quenching medium, the main reason for GCr15 steel bushing is the third stage of the process of oil in the cooling phase (convection) special slow cooling rate.Production use of the past 10, 20, machine oil between 650 ~ 500 ℃ for 20 ~ 50 ℃ / s.Convection period starting around 300 ℃, continued to room temperature, as it happens and the martensite turn temperature requirements of the bearing steel smaller cooling speed, so that the bearing parts in the process of quenching deformation and cracking tendency is greatly reduced.But in the way of operation is manual hoist will ring into the oil, the oil ring in the upper and lower movement of frequency and amplitude is controlled by the operator manually, it is difficult to meet the technological requirements, namely the ring in oil dynamic time not less than 3 s/mm.Therefore, in the process of cooling ring often appear the following quality problems: 1) poor hardness uniformity: the same ring divergence HRC hardness > 2, the same ring uniform hardness HRC > 1 or 2.2) ring surface area soft point or local soft point.3) for effective wall thickness > 7 mm ring, microstructure of 45 # steel bushing organization in mesh troostite.

After the heat treatment quality analysis in 1998, because of the furnace for quenching cooling adverse to repair tin bronze bushing fire repair rate of 51.5%, ring in the cooling process of defects, and results in the decrease of bearing stiffness, strength, abrasion resistance and fatigue resistance performance degradation.

For ring problems during cooling, had to take the following measures.

1. Without changing the cooling mode, and improve the quenching heating temperature of the ring (choose limit temperature), to increase the stability of the supercooled austenite in steel, so as to reduce the critical cooling rate of GCr15 steel.But with the improvement of heating temperature, the steel secondary carbides dissolve too much, cause the austenitic grain size grows larger, and hinder the martensite length greater role is abate, the fewer the same ring hardness difference is bigger, the biggest difference between HRC2, quenching and tempering in the organization still occasionally appear local there are a few small block troostite;Also began to have fine acicular martensite appeared at the same time, in 500 times metallographic microscope you can see the obvious acicular martensite (overheating).Quenching deformation has risen sharply, diameter change quantity rate rise by an average of less than 10% to more than 20%, parts mechanical properties relative degradation.

2. With fast cooling speed rapid quenching oil.Due to the limitation of objective conditions, in production, inevitable to enter a small amount of water in the tank, makes gradually emulsified oil in use process, performance changes, lose a good cooling effect, and make the quenching quality to reach the ideal effect.

Second, the bearing ring heat treatment study and application of new technology

The cooling capacity of quenching medium and hardening ability is an important factor affecting the quality of bearing ring heat treatment.Apparently and artifacts of metallurgical factors, the shape of the curve C on cooling and cooling conditions and so on.The cooling capacity of quenching medium, can make the work piece after quenching hardness higher or deeper hardening layer.In fact, the key of hardening is at the tip curve C cold speed should be enough big, but in martensitic transformation required cooling speed is relatively small.The application of new technology is adapted to this feature.By changing the workpiece and the relative speed of quenching oil, change the cooling of quenching medium and hardening ability, satisfy the workpiece formed under different temperature requirements of different cooling rate, thus obtain ideal quenching quality.

1. Cooling strength test analysis

Analysis after many experiments show that the new process change cooling mode, can improve the oil cooling intensity, thus improve the quality of heat treatment.The parameters of the cooling intensity H is the ability to reflect the cooling medium, H = alpha lambda / 2 (alpha as the interface heat transfer coefficient; lambda thermal conductivity of steel).Static water H value is 0.1.The more the cooling capacity of the H value, the greater the medium.In the experiment, according to quenching medium under the condition of different agitation, cooling intensity changes are shown in table 1, with strong stirring oil quenching, H value can reach 0.7, usually oil quenching H value is 0.3.

2. The organization analysis and hardness test

Ring in the process of testing the product model at 314/01, quenching temperature is 840.40 ℃, machine oil, coolant for 10 ring in static quenching and cooling conditions, through many experiments, it is concluded that ring troostite level changes in the microstructure, ring in static and dynamic cooling conditions, organization closely size differ about 5 ~ 10 times, under the condition of channeling dynamic cooling, fell to 0.5 hardness difference of the same race.
3. The application of new technology and equipment improvement

New technology is by changing the production facilities, the quenching oil and water jacket cooling circulation cooling, cooling with large flow pump the oil from the bottom of the quench tank after injection, to form the circulation under the funnel, uniform, again after a two layer oil column of orifice plate to form homogeneous swells up injection, boiled in oil tank are angled.And by changing the pump output flow, change the relative speed ring and oil, meet in the process of organization form to the requirement of different cooling rate, while the upper heat up the oil drain in time, make basic equilibrium in the oil tank, the lower the oil temperature.Not only makes the oil filter oil cooling system can fully cooling, and makes oil can get very good purification.New process which satisfies the requirement of GCr15 steel for high temperature cooling rate high request, to ensure the uniformity of quenching hardness and hardness, and can meet the workpiece under the low temperature austenitizing grain finer and low carbon, chromium content austenitic required critical quenching speed, refined martensite matrix organization, avoid quenching crack, the bearing ring quenching hardness stability control in HRC64 ~ 65.5, quenching microstructure of 2 ~ 3 grade.With 2 levels of multiple, outer diameter ￠above 100 mm ring diameter changes after quenching amount of super rate fell to about 7%, the workpiece surface after quenching brightness increased, the quality of all qualified, reduce the waste and loss of repair.

Production facilities improvement is hot quenching tank upper-middle-class oil overflow to the filtration unit, and then into a set of overhead of brass tube cooler in (place) in the cleaning cycle pool, and then after cooling in oil pump oil pump into the bottom of the quench tank, between two layers of aperture is ￠5 mm, pitch of 20 mm x 20 mm of porous plate, orifice on the second floor of a staggered, ensure uniform cooling oil on the rise.

Hunan Jintai Hardware and Machinery Co.,Ltd. is a professional manufacturer on various kind of bearings in China for over 15 years.We are making all kinds of sliding bearings including DU bushings,SF bushings,DX POM composite bushing,spherical plain bearing,bimetal bearing,ball transfer units ball bearing,wrapped bronze bushing,cast bronze bearings,guide slide bearing and wear plate bearing pad, sintered bronze bushing and sintering parts, graphite bearing, etc.

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