Preventing Degradation of Quench Oils in the Heat Treatment Process

Originally Posted by Greg Steiger

1. Introduction

Because quench oil deterioration varies depending on the operating conditions, maintaining constant performance is difficult. Various phenomena occur in response to changes in the quench oil degradation. In this paper, we will examine how the oil condition, cooling performance, brightness and carbide growth are effected by various phenomena such as oil oxidation, thermal decomposition etc. In doing so we would like to introduce important points in managing and setting operating conditions to optimize the performance of quench oils.

2. Deterioration pattern of quench oil

Many production processes depend on a quality heat treatment operation. Therefore a stable quench oil is needed to improve efficiency and reduce failures due to thermal stresses or staining. In regards to the quench oils degradation in particular, we would like to explain the causes and solutions in dealing with deterioration of quench oil in real conditions.

Figure 1 shows the Deterioration phenomena and their causes:

Fig.1 Deterioration phenomena and their causes.

Fig.2 Degradation pattern of quench oil.

Figure 2 shows the on-site degradation pattern of a typical hot quench oil named High Temp Oil A.

The horizontal axis is kinematic viscosity, and the vertical axis are the H-values (hardenability factors). In general, the viscosity increases due to oxidation.  The initial increase in the oxidation of a quench oil will increase the H-values.  However, as oxidation increases to the point of oxidative polymerization, the H-values will decrease.  Pyrolysis and additive consumption will also decrease the viscosity.  The H-values are increased due to pyrolysis and decreased through additive consumption. In the actual use of quench oils, these phenomena are occurring simultaneously.  

3.  Failure to obtain as quenched hardness

A failure to obtain the proper as quenched hardness is a result of one or a combination of the following factors:

 ･ improper selection of quench oil

 ･ cooling change (oxidative polymerization)

 ･ change in cooling performance (pyrolysis)

･ consumption of additives

3.1. Oxidation test

In Japan, the oxidation test is JIS K 2514 Indiana Stirring Oxidation Test (ISOT).  Figure 3 shows the outline of the test. Figure 4 shows the results of the oxidation test of commercially available quench oil, High Temp Oil A.

When the oxidative degradation progresses, the acid value increases, and H-value also increases. However, as further oxidation occurs (96 hr. test period), oxidative polymerization begins and the H-value decreases.

Fig.3 Outline of the oxidation test. 

 Fig.4 Results of the oxidation test.

3.2. Pyrolysis test

There is no standard for the pyrolysis test. So, we introduce the Idemitsu proprietary sealed tube test. Figure 5 shows the outline of the test.

Fig.5 Outline of the sealed tube test.

 

Fig.6 Results of the sealed tube test.

 Fig.7 Change of cooling curve due to the addition of thermal decomposition products.

Figure 6 shows the results of the sealed tube test.

In only 24 hours, the viscosity is reduced by 20%.

Figure 7 shows the cooling curves of new oil and 10% addition of thermally decomposed oil.  Pyrolysis increases cooling performance.

4.  Uneven hardness

 In obtaining uneven hardness, the following causes should be considered:

 ･ uneven agitation

 ･ water contamination

 ･ deposition of sludge

4.1. Water contamination

Figure 8 shows the changes in the cooling curve due to water contamination. Cooling performance is increased as the amount of water contamination in an oil is increased. However, the water is considered not uniformly dispersed in the oil, therefore the cooling performance is not uniformly effected and this may cause uneven hardness. If the water content is more than 200 ppm, it is necessary to reduce the moisture content of the oil to ensure uniform cooling throughout the oil.

 

Fig.8 Cooling curve change due to water contamination.

 


Fig.9 Change in brightness due to oxidation deterioration test.

4.2. Deposition of sludge

Oil sludge is generated through intense oxidative degradation. The deposition of sludge on parts creates areas of uneven cooling.  Figure 9 shows a change in brightness due to oxidation deterioration and sludge deposition.  In general, sludge deposition causes a soft spot with low hardness. To prevent the sludge deposition, it is important to select a quench oil with high oxidative stability.

The proper care and usage of the quench oil is important and the following points should be considered:

･Avoid air contact at high oil temperatures, while stopping equipment, as entrained air will cause increased oxidation at elevated temperatures

･Avoid water contamination.

･Centrifuge operation can also be used to remove sludge.

･Do not mix new oil with degraded oil. Do not mix oil with that is dragged out on parts with oil in the quench tank.

5.  Quenching distortion

Quenching distortion is the most common quality defect in the heat treatment industry. Quenching distortion is classified as follows.

･Distortion increment

･Distortion variation

･Time dependent-change

Table 1. Shows the causes and solutions of quenching distortion.

Table.1 Causes and solutions of distortion

6.  Conclusion

This report focused on quench oil deteriorations depending on the operating conditions.

(1) The main causes of deterioration of quench oil are initial oxidation, oxidative polymerization, pyrolysis and additive consumption.

(2) Cause of failure in quenching hardness is the change in cooling performance, which is affected by the oxidative polymerization, pyrolysis and consumption of additives.

(3) Causes of uneven hardness are improper agitation, water contamination and deposition of sludge.

(4) Quenching distortion problems are classified as: distortion increment, distortion variation and time dependent-change.

Suitable solutions vary according to the cause.


Written by:  Katsumi Ichitani, Lubricants Department 2 Technical & Marketing Section 2, Idemitsu Kosan Co., Ltd., Tokyo, Japan, and Greg Steiger, Sr. Key Account Manager Quench Products, Idemitsu Lubricants America Corporation, USA.