JPH0375352A - Activity restoring agent for salt bath for carbonitriding iron-based parts and its manufacturing method - Google Patents

Abstract

PURPOSE:To easily recover the activity of a salt bath for carbonitriding by adding the deammoniation polycondensation product of dioyandiamide when the activity of a salt bath for carbonitriding is deteriorated at the time of applying carbonitriding treatment to the surface of ferrous parts. CONSTITUTION:Carbonitriding treatment is carried out in order to improve the wear resistance, corrosion resistance, sizure resistance, and fatigue strength of the surface of ferrous parts. As a salt bath for carbonitriding, a salt bath composed principally of alkali cyanate and containing alkali cyanide or alkali carbonate as accessory component is used. The activity of the above salt bath is deteriorated because alkali cyanate as principal component is decomposed into active carbon and active nitrogen as the carbonitriding treatment for the ferrous parts proceeds and the alkali cyanate is reduced in content while being used for carbonitriding reaction. At this time, by adding dicyanamide while putting the granular deammoniation polycondensation product of dicyanamide as initial filling medium into a reaction vessel and performing heating up to 350-500 deg.C and also agitation, the deammoniation polycondensation product of dicyanamide as an activity recovering agent for the salt bath for carbonitriding can be easily produced.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a carbonitriding ability restorer used in a salt bath for carbonitriding iron-based parts, and more specifically, The present invention relates to a deammoniated polycondensate of dicyandiamide as a restoring agent for restoring its reduced activity, and a method for producing the same.

[Prior art] In order to carbonitride iron-based parts using a salt bath, a salt bath consisting of alkali cyanate as the main active ingredient has conventionally been used.The mechanism of action is as shown in the following equation. It decomposes when it comes into contact with parts, liberating nitrogen and carbon, and these activated nitrogen and activated carbon penetrate and diffuse from the parts surface.

4MCN0→2MCN + M, CO, + CO+ 2
[N] or 5MCN0→3MCN + MiCOs
+ GO□+2[N12MCN + 0□→2MCNO MCN+CO! →MCN0 + CO ゛2CO→can + [cJ However, M is an alkali metal, [N] and [CI represent active nitrogen and activated carbon, respectively.

Nitrogen and carbon from the generator of the above type enter from the surface of iron parts,
As a result of the diffusion, a compound layer containing 6 to 11% nitrogen and 0.5 to 1% carbon is formed on the surface layer of the component, and about 0.1% is formed directly below it.
A nitrogen diffusion layer is formed in which nitrogen is further permeated and diffused. As a result of the formation of these carbonitrided layers, the wear resistance, corrosion resistance, seizure resistance, and fatigue strength of iron-based parts are significantly improved.

However, on the other hand, the decomposed alkali cyanate is accumulated as alkali carbonate in the soil, reducing the carbonitriding activity.

As a means of restoring the activation power of a carbonitriding salt bath in a molten state, it is used as a restoring agent to restore the activation power of a conventional carbonitriding salt bath, in order to restore the alkali carbonate, which is an aging product, to an alkali cyanate. Various invention proposals have been made, for example, in Japanese Patent Publication No. 4892-1973, a molten product mainly composed of cyanuric acid or isocyanuric acid obtained by thermally decomposing urea, while in Japanese Patent Publication No. 42-7043, urea or other organic Nitrogen compounds are mentioned, such as biuret, dicyandiamide, melamine, melam, melon, ammeline, cyanuric acid.

The conventional patent publications mentioned above merely enumerate new substances that have a restoring effect, and do not disclose any problems or means for solving them when they are put into practical use industrially. .

[Problems to be Solved by the Invention] Conventional restoring agents have the following problems, which hinder their industrial use.

(1) When using a relatively low-molecular chain compound containing nitrogen-carbon-hydrogen and, in some cases, oxygen, such as urea, biuret, and dicyandiamide, as a restoring agent, the operating temperature of the carbonitriding salt bath is approximately 570 to 580. ℃ range, or even higher temperature, when the above-mentioned restoring agent comes into contact with the molten salt, it instantly decomposes and gasifies or sublimates, generating a large amount of white smoke containing decomposed ammonia, and The restoring agent itself scatters around the bath, significantly worsening the working environment.

In addition, this also caused the problem that the efficiency of restoring carbonate to cyanate using a restoring agent was extremely low.

(2) In the case where an organic cyclic compound containing nitrogen-carbon-hydrogen such as cyanuric acid or isocyanuric acid, melamine, or melam, and optionally oxygen is used as a restoring agent, it is almost the same as in case (1), and these restoring agents comes into contact with the high-temperature bath, causing decomposition, gasification, sublimation, etc., producing a large amount of white smoke containing ammonia, and the scattering of the restoring agent itself, resulting in a deterioration of the working environment and a reduction in restoration efficiency. .

(3) On the other hand, in the case of polycyclic compounds containing organic nitrogen-carbon-hydrogen such as melem and melon, which have a higher degree of polycondensation than melamine and melam, the degree of polycondensation (11,
(Problems like 21 will gradually be resolved.

However, although these polycyclic compounds with a high degree of polycondensation have excellent performance as restoring agents, their production costs are high and there are economical problems in their industrial use.

The present invention solves the above problems, causes no problems in the working environment,
The purpose is to provide a restoring agent that has high restoring efficiency and is economically viable.

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention conducted extensive research to obtain a restoring agent that has good performance as described above and is easy to manufacture. As a result, the present invention has been completed.

First, as a result of various studies, it was discovered that dicyandiamide was the most suitable starting material for a restoring agent having such characteristics.

When dicyandiamide is heated under normal pressure, at a temperature exceeding its melting point of 270°C, a rapid exothermic reaction occurs accompanied by the generation of ammonia, instantly producing melamine and a small amount of a polymer compound higher than melamine. When the heating temperature is further increased, the melamine in the product further reacts and changes into a higher-order polycondensate.

When the heating temperature is 420-450°C or higher, the proportion of melamine in the reaction product starts from a few percent and gradually approaches O.If ammonia is sufficiently released at the final heating temperature, the desired restoration is achieved. You can get the drug.

In the above heating process, the exothermic reaction of dicyandiamide just above the melting point can be effectively used as heating energy, and this is one of the reasons why dicyandiamide was selected as a raw material that can be used to produce a restoring agent at a low cost. . If the final heating temperature during production of the above-mentioned restoring agent is 350°C or less, when used as a restoring agent, the generation of white smoke, which was a target for improvement as described above, will gradually increase as the heating temperature decreases, and the restoration efficiency will decrease. do.

Further, when the final heating temperature is 500° C. or higher, both the generation of white smoke and the restoration efficiency are good, but the degree of improvement is small and the energy cost increases, which is not preferable.

Therefore, the temperature at the end of the reaction should be in the range of 350°C or more and 500°C or less, preferably in the range of 420 to 450°C.

In addition, when heating dicyandiamide as a raw material to cause a polycondensation reaction, if the raw material is in contact with the heat transfer surface of the reactor, the reaction product will stick to the heat transfer surface as the reaction progresses, and the reaction product will form lumps. The particles solidify into solid shapes, inhibiting a smooth reaction and making it difficult to remove the reaction product.

In order to solve this problem, the inventors put the restoring agent in particle form after one reaction into a reactor as an initial filling medium, raised the temperature to the final reaction temperature with stirring, and maintained it at that temperature. During this time, dicyandiamide as a raw material is added onto the initial filling medium at a rate that does not lower the reaction temperature and allowed to react. As a result, the raw materials undergo a polycondensation reaction without causing problems such as reaction inhibition due to nodular solidification and difficulty in taking out the reaction products, and the amount of product increases, making it easy to take out a part of it.

[Effect] When the restoring agent obtained as described above is added to a deteriorated salt bath prepared with a salt bath agent for carbonitriding iron-based parts containing alkali cyanate as the main active ingredient, whitening is achieved. The generation of smoke,
There was no scattering of the restoring agent and no contamination of the working environment was observed.

In terms of restoring ability, it is superior to any other substance that has restoring ability.

[Example] (1) Manufacturing test The particulate product of the present invention was placed in a reactor as an initial filling medium, and while the stirring blade was rotated at a speed of 660-18 Orp, the temperature inside the reactor was adjusted to 430 °C using a temperature controller. °C so that the initial filling medium is evenly heated and the temperature is 43°C.
When the temperature reaches 0°C, dicyandiamide as a raw material is added from the raw material supply hopper.

It was fed on top of a bed of particulate product which was kept under agitation in the reactor.

When the raw material dicyandiamide thus supplied is uniformly dispersed in the heated particulate product, it undergoes a self-heating reaction and receives the heat retained by the product, completing the polycondensation reaction in a short time.

Increments of product were removed through an automatic discharge valve attached to a product discharge vibrator at the bottom of the reactor.

During this time, the temperature of the product layer in the reactor is 420° to 450°C.
The resulting restoration agent as a product had a uniform appearance and restoration efficiency.

(2) Restoration agent sample of the present invention prepared according to Restoration Performance Test Example (1) +11
and urea (
CI), melamine (C2), commercially available dicyandiamide (C3)! The restoring ability was tested for a total of 5 samples, 3 and 4 of the reaction product (C4) of dicyandiamide at a reaction temperature of 300°C.

To the carbonitriding salt bath with a suitable control value of alkali cyanate CN0-36%, assuming a deteriorated state, alkali carbonate, which is a degrading component, was added and adjusted to CN0-31.9%, C
A salt bath with a composition of N-0.8% was prepared.

2.5 kg of this salt bath was divided into 5 small pots,
While maintaining the temperature at 0.06C and stirring with ventilation, 15g of each restoring agent was added. Restoration performance was measured using an automatic potentiometric titration device [COMTITE- manufactured by Hiranuma Sangyo Co., Ltd.] for samples before and after addition of restorant.
101] and indicated by the amount of increase in CN0-,
At the same time, we observed the occurrence of factors that affect environmental pollution. The results are shown in the table below.

[Effects of the Invention] The restoring agent of the present invention can improve the activity of a salt bath for carbonitriding iron-based metal parts whose main active ingredient is alkali cyanate when its activity decreases during use as a salt bath. Restoration performance as a restoration agent for restoration.

It is superior to any other restoring agent that has been used or proposed to date.

In addition, when used as a restoring agent, there is almost no generation of white smoke or scattering of dust, and the amount of ammonia generated is the least compared to other restoring agents, which is preferable from the viewpoints of labor safety, hygiene, and industrial pollution.

On the other hand, in terms of manufacturing technology, there are no problems that hinder production, such as sticking of the product to the heat transfer surface or clumping, and it also makes it possible to reduce energy costs by effectively using reaction heat. It has greatly contributed to the field of carbonitriding salt bath industry.

Claims (5)

[Claims] 1. This is an activity restoring agent for salt baths for carbonitriding iron-based metal parts that has cyanic acid as the main active ingredient.It is a polycondensation agent that uses dicyandiamide as a starting material and reacts by heating it to a temperature above its melting point under normal pressure. An activity restoring agent for carbonitriding salt baths obtained as a deammoniated polycondensate of dicyandiamide by sufficiently releasing ammonia gas generated in the process. 2. The above heating temperature is 350 to 500°C, preferably 42°C.
The activity restoring agent according to claim 1, which has a temperature of 0 to 450°C. 3. 3. The activity restoring agent according to claim 1, wherein the salt bath for carbonitriding iron-based parts has an alkali cyanate as a main active ingredient and an alkali cyanide and/or an alkali carbonate as a secondary ingredient. 4. Activation of a salt bath for carbonitriding, which uses dicyandiamide as a starting material and reacts it by heating it to a temperature above its melting point under normal pressure, and sufficiently releases ammonia gas generated in the polycondensation process to produce a deammoniated polycondensate of dicyandiamide. Method for producing force restoring agent. 5. When reacting the dicyandiamide at a temperature above its melting point, a part of the product of the activity restoring agent is made into particles and placed in the reactor as an initial filling medium, and heated to 350 to 300 ml while stirring.
While raising the temperature to 500° C., preferably 420-450° C. and maintaining the temperature, the raw dicyandiamide is added onto the initial charging medium and allowed to react at a rate of addition that does not reduce the reaction temperature. 5. The method for producing an activity restoring agent according to claim 4.