Heat treatment method of long flat steel wire spiral spring

Research on Heat Treatment Method of Long Flat Wire Coil Spring
Summary

This article introduces the use of resistance heating method to heat treat flat steel wire cylindrical spiral compression elastic yellow with a length of 50m and an outer diameter of ф60mm.

When selecting electric heating equipment and determining the basic calculation formula of the process parameters, the test results show that this method can meet the requirements of the spring hot

Management requirements, saving investment, simple and easy.

Preface

The heat treatment of a flat section cylindrical spiral compression spring with a length of 50m and an outer diameter of ф60mm is a foreign aid task we accept.

In foreign countries, this kind of spring is made by using oil-quenched and tempered steel wire to be wound into shape and then tempered at low temperature to eliminate winding stress.

In China, there is no professional factory that produces such flat section springs so far.

It is made of round steel wire rolled or drawn, wound into a spring and then quenched and tempered. Obviously quenching such a long spring

, Tempering treatment is very difficult. After investigation and analysis and a large number of experiments, we have initially explored the resistance method heating and quenching of this long spring.

The fire process has achieved relatively satisfactory results.

1. Determination of resistance heating process plan and equipment design

According to the longer characteristics and technical requirements of this spring, we compared the following three process schemes, namely flame quenching, high frequency

Quenching and resistance heating quenching. After analysis and comparison, it is believed that although the resistance heating quenching scheme also has certain technical difficulties, the most

The major feature is a professional equipment that does not require spring rotation during heating and does not spray coolant. Therefore, it is determined to use the resistance heating quenching method

experimenting. We derive the function of temperature change with time on the basis of heat and electricity, and derive the resistance heating process in turn

The change law of the heat of medium electric energy converted into thermal energy and radiant heat at any time, as a reference basis for determining the parameters of resistance heating workpieces

. Since the derivation is long and does not belong to the main content of this article, it is omitted here and only a brief introduction to equipment selection.

2. Test equipment and results

1. Test equipment

The equipment used in the test includes: (1) a ZUDG—253 salt bath furnace transformer; (2) insulation for spring heating and quenching

One set of fixing devices; (3) One cooling water tank; (4) One WGG2-302 optical pyrometer, one IRT-1200 infrared measuring instrument

; A stopwatch.

2. The main content of the test

Determine the quenching heating time and tempering time, select the quenching medium and observe the metallographic structure.

3. Test results

(1) The quenching heating time is determined according to the resistance heating is the internal heat source heating, and the temperature is a function of time. This test

A stopwatch, an optical pyrometer and an infrared thermometer are used to measure the continuous heating that the specimen can reach different temperatures under certain electrical parameters.

Time to determine the quenching heating time.

(2) For the selection of tempering time, use a stopwatch and infrared thermometer to test. The results show that the tempering heating time is 25—

30S is more suitable.

(3) The selection of quenching medium was tested according to the three quenching mediums of water and oil polyvinyl alcohol. From the test results

It can be seen that these three quenching media can meet the hardness and hardenability requirements, but the water-quenched specimens are obviously brittle, and the oil pollution is large.

Easy to catch fire. After a large number of experiments and comparisons, it is more appropriate to choose a polyvinyl alcohol quenching agent with a concentration of 0.5%.

(4) Metallographic structure. The test results show that this kind of spring is suitable for selecting electrical parameters and can ensure stable electrical parameters.

Under the quenching heating for 2 minutes, the temperature can reach 860-880℃, and the extremely fine quenched structure can be obtained.

Obvious characteristics of martensite needle-like structure can be observed. The tempering process is 380℃×28S, and the hardness can reach 39-43HRC. Metallographic Group

The weave is tempered troostite + a small amount of tempered aritite, and there is no obvious decarburized layer, so it has good comprehensive mechanical properties.

3. Analysis of test results

1. Resistance heating has a higher heating rate, which can refine the austenite grains when the steel is heated.

When the time is properly controlled, overheating will generally not occur. The relationship between oil quenching hardness and heating time is known: although the electrical parameters

Under stable conditions, the hardness requirement can be achieved by heating for 1.5 minutes, but considering the factor that the inner side of the coil is thicker than the outer side during winding

, So it is more appropriate to extend the heating time by 2 min.

2. In terms of resistance heating, time is very sensitive to temperature, so the material and cross-sectional dimensions are required to be uniform

Consistent. On the whole, the resistance method has a fast heating speed and proper time control will not cause overheating. But when the working section is obvious

When it changes, it may cause the local temperature to be too high, or even over-burning or even fusing, so when using resistance heating equipment to heat the workpiece

At the same time, especially when dealing with such special-shaped cross-section springs, it is necessary to prepare an air compressor for local cooling and reduce the temperature difference; at the same time

Before heating, the rust on the surface of the workpiece must be removed to prevent poor electrical heating from causing electrical sparks to burn the workpiece.

3. This test uses polyvinyl alcohol fire agent, which can meet the requirements of spring quenching hardness, and reduce the deformation and the phenomenon of opening out.

The cooling rate can be between water and oil, which can greatly reduce the thermal stress and transformation stress of the transformation from austenite to martensite