article_evaluateion_fluid_performance_aistech19 by Quaker Houghton

Iron & Steel Technology A Publication of the Association for Iron & Steel Technology

A Publication of the Association for Iron & Steel Technology

August 2019

I IRON & STEEL TECHNOLOGY I AIST.ORG

• AIST 2019 North American Galvanizing Lines Roundup

AUG 2019

August 2019 Vol. 16, No. 8 Vol. 16, No. 8

• Cold Sheet Rolling, Processing, Coating & Finishing

A Publication of the Association for Iron & Steel Technology Featuring: AISTech 2019 Conference and Exposition Retrospective

Quaker_08_19.indd 1

9/19/2019 2:42:46 PM

AUG 2019

Technical Article

Quaker_08_19.indd 2

9/19/2019 2:42:48 PM

Technical Article

Evaluation of Fluid Performance for Thread Cutting of Premium Pipe Connections Using a Cut-Tapping Operation on AISI 4140 Steel Utilizing a Vertical Machining Center Machining of AISI 4140 steel serves as a useful method for assessing the performance capabilities of cutting fluids used for the thread cutting of P110- and L80-grade pipe connections. While it is difficult to reproduce the actual thread-cutting operation under laboratory conditions, the utilization of a tapping operation using AISI 4140 steel provides an effective means to assess fluid performance. This paper will discuss the application of a tapping test method and the performance parameters measured, which serve to provide an assessment of a fluid’s capabilities for use in pipe threading operations.

Edward Platt machining specialist, Quaker Chemical Corp., Conshohocken, Pa., USA platte@quakerchem.com Chelsea Good Quaker Chemical Corp., Conshohocken, Pa., USA

Discussion Thread-Cutting Fluids — Water-based thread-cutting fluids function by providing lubrication and cooling to the operation, as well as facilitating chip removal during and after the cutting process. There are two basic types of water-based fluids that are typically used for pipe-threading operations: oil-in-water emulsions and solution synthetic fluids. Each type of fluid offers certain strengths as well as certain limitations with regard to the threadcutting performance they provide. Further differentiation can be made within the class of emulsion type fluids whereby, based primarily on the size of the suspended oil droplets, a larger particle-sized macroemulsion can be used, as can a very fine, small droplet-sized translucent dispersion, often termed a microemulsion. The types of fluids and photomicrographs of each are shown in Fig. 1. Macroemulsions are opaque white or yellow-white liquids that consist of oil droplets suspended in a continuous phase of water. The oil droplet is of sufficient size (typically between 0.5 to 4 µm diameter) to scatter impinged light and thus give the opaque white

I IRON & STEEL TECHNOLOGY I AIST.ORG

Quaker_08_19.indd 3

of three fluids as well as the effects of the concentration of the fluid on thread-cutting performance will be discussed.

Robert D. Evans research scientist, Quaker Chemical Corp., Conshohocken, Pa., USA evansb@quakerchem.com

AUG 2019

ater-based metalworking fluids are often used to minimize cutting insert wear and improve thread quality in the cutting of highstrength API pipe materials. These metalworking fluids perform this function by providing lubrication and facilitating heat removal at the cutting edge, as well as enhancing the ease of chip removal and evacuation from the cutting area. It is often useful and beneficial to have capabilities to evaluate the performance properties of a given metalworking fluid under controlled laboratory conditions prior to use of the fluid in an actual industrial threadcutting operation. This enables a more data-driven selection of a given fluid for use and a higher probability of success with the fluid in the thread-cutting operation. The machining of AISI 4140 steel serves as a useful method for assessing the performance capabilities of cutting fluids used for the thread cutting of P110- and L80-grade pipe connections. While it is often difficult to reproduce the actual thread-cutting operation under controlled laboratory conditions, it has been found that the use of a cut-tapping operation using AISI 4140 steel provides an effective means to assess fluid performance. This paper will discuss the application of a cut-tapping method and the performance parameters measured, which serve to provide an assessment of a fluid’s capabilities. The performance

Authors

9/19/2019 2:42:48 PM

Technical Article Figure 1

viewed under high magnification. In considering the performance properties of these types of fluids, while there are exceptions, it is generally seen that larger-diameter macroemulsions offer higher levels of lubrication and frictionreducing properties with lower cooling and heat removal, while solution-type fluids tend to offer lower levels of lubrication and more efficient heat removal. Prior testing of these types of fluids in thread cutting of L80 and P110 pipe grades have shown that all three can be used effectively in thread cutting, with the opaque macroemulsion-type fluids offering slightly higher performance with regard to tool wear.9

AUG 2019

Water-based thread-cutting fluids.

appearance.1,2 Microemulsions are defined as a system of water, oil and amphiphile existing in a single phase and are thermodynamically stable.3–5 However, in a broader definition, microemulsions also can include stable transparent or translucent dispersions with very small-sized (<500 nm diameter) dispersed droplets.6–8 When viewed under high magnification, the droplets suspended in the water phase are too small to be observed. Solution synthetic fluids are typically comprised of 15–35% emulsifiers, rust inhibitors, dispersants, boundary lubricants and extreme pressure lubricants; 10–25% polymeric water-soluble lubricants; and 40–50% water. When mixed with water, such fluids give a stable, clear solution. Since all or the majority of the components of a clear solution synthetic fluid are solvated by the water phase, no observable droplets are seen when

Thread-Cutting Test: Machining Conditions — To provide a means for evaluating thread-cutting fluid performance under controlled laboratory machining conditions, a cuttapping test utilizing AISI 4140 steel has been developed. AISI 4140 steel is utilized since it offers a workpiece material comparable in composition and properties to those used for the production of L80 and P100 pipe connections. For each machining test conducted, using a Bridgeport GX-710 vertical machining center, 36 9.8-mm diameter holes are drilled to a depth of 33 mm, followed by reaming to a hole diameter of 10.2 mm in an AISI 4140 steel test block. These holes are subsequently tapped using an M12 x 1.75 cutting tap at a cutting speed of 18.29 m/minute and feed rate of 1.75 mm/rev. Details of the machining test, tool and test block, as well as the threads produced, are shown in Fig. 2.

Figure 2

Laboratory machining method for assessing fluid performance — cut-tapping of AISI 4140 steel.

Quaker_08_19.indd 4

9/19/2019 2:42:49 PM

5 Figure 3

Cutting Forces: The cutting power required during the tapping operation is measured over the 36 holes using an adaptive control and tool monitoring system. The signal obtained is shown in Fig. 4a. Following acquisition, the data is analyzed using MATLAB numerical computing to eliminate any contribution to the power demand resulting from non-cutting operations and also to separate the power measured during cutting from that measured during retraction of the tool. This then provides a clear measure of only the power required during the cut-tapping operation. Typically at the start of the tapping operation, high cutting power is obtained, which rapidly decreases down to a lower level after about five to 10 holes. This region is attributed to a period of run-in of the tool whereby the initial sharp edge of the tool gives high cutting forces. These high forces rapidly decrease as the tool wears slightly. As seen in Fig. 4b, which shows the cutting power measured using three different cutting fluids, this initial run-in regime is followed by a steady-state regime where the cutting power appears to level off. In this regime, the level of power demand and the consistency in the power measured from hole to hole are largely influenced by the performance of the metalworking fluid used and the ability of the fluid to provide lubrication and minimize tool wear. The significance of the measurement of cutting power is that, while it provides a measure of the energy demand of the cutting process, it also is largely influenced by the geometry and wear that occur on the tool. This is seen in Fig. 4c, which shows the relationship between the cutting power measured and tool wear.

Tool wear.

Assessment of Tapping and Fluid Performance â&#x20AC;&#x201D; Tapping performance and the effectiveness of the metalworking fluid in the operation are assessed by measurement of the cutting power during tapping, the tool wear and the quality of the threads produced. While these parameters are clearly interrelated, they each alone provide useful information on the performance properties of a fluid, and also can provide an effective means for differentiating between two or more closely performing fluids. Tool Wear: The wear occurring on the tool during machining is measured after completion of tapping of the 36 holes. Measurements are made under magnification using a Nikon stereoscope interfaced with digital imaging software. To obtain a measure of the level of wear, the area of wear formed on the rake face of the third and fourth cutting teeth (for the three flutes) is measured (shown in Fig. 3). This gives a total of six cutting teeth measured. The total wear value, which is a measure of the wear formed and is the wear parameter that is reported, is the summation of the wear area on the six cutting teeth measured.

Thread Quality: To further assess fluid performance, the quality of the threads produced is examined. With effective lubrication and cooling provided by the fluid, the resulting threads (on all three

Figure 4

AUG 2019

(b)

(c)

Tapping power signal for one hole (a), tapping power over 36 holes (b) and tapping power vs. tool wear (c).

Quaker_08_19.indd 5

I IRON & STEEL TECHNOLOGY I AIST.ORG

(a)

9/19/2019 2:42:49 PM

Technical Article Figure 5

Thread surface quality.

Figure 6

Thread-cutting fluids, with microphotographs of fluid at 6% concentration (400x).

Cutting power.

Thread-Cutting Fluid Performance — The application and utility of the cut-tapping test can be seen in the assessment of the performance of three threadcutting fluids currently used in industry. They are designated in this paper as Fluid 74, an opaque macroemulsion-type fluid; Fluid 75, a translucent microemulsion type fluid; and Fluid 27, a solution synthetic–type fluid (Fig. 6). Their performance capabilities when used at 6% concentration, as well as their effectiveness at a reduced 4% concentration, were studied. In addition, while it is generally accepted that the use of a lubricating fluid is essential for this operation, it was of interest to examine and confirm this. Therefore, testing was also conducted using only water. Cutting Power: The cutting power measured over the 36 holes tapped for the three cutting fluids, as well as water only, are shown in Fig. 7. As seen, the benefit, relative to the power demand, from use of a lubricating fluid is clear and significant. In looking at the three lubricating fluids, and how they differ in performance (Fig. 8), it can be seen that following the initial run-in period at hole 10, all three fluids show low and comparable cutting power. However, as tapping continues from hole 10 through

AUG 2019

Figure 7

major surfaces — root, flank and crest) will show no or minimal metal tearing, adhesion or metal smearing. In contrast, with insufficient lubrication in the cutting operation, the thread surfaces will show noticeable tearing and metal smearing on predominantly the crest and flank surfaces of the cut threads. This can be seen in Fig. 5, which shows the surface appearance of threads produced using both a highly effective cutting fluid as well as one that does not provide sufficient lubrication needed for the process. For each test, the quality of the thread surfaces produced is examined using optical microscopy and/or scanning electron microscopy.

Quaker_08_19.indd 6

9/19/2019 2:42:49 PM

7 Figure 8

hole 36, these fluids behave differently with regard to the rate at which power increases. A greater increase in cutting power as machining continues indicates a more rapid change in the geometry of the cutting edge, due to tool wear and possibly metal adhesion. Thus, while the tapping power is comparable with the three fluids at the start of the steady-state regime, the rate of increase in power seen from hole 10 to 36 provides a parameter useful for differentiating fluid performance. As seen, Fluid 74, the macroemulsiontype fluid, shows the lowest slope in cutting power throughout the steadystate regime, indicating a higher effectiveness in maintaining tool condition with lower levels of wear. Fluid 75 shows an intermediate level of performance, while Fluid 27, the clear synthetic fluid, shows the greatest increase in tapping power through the test.

Cutting power at 6% concentration.

Figure 9

Tool Wear: The large benefit offered by a lubricating fluid over unlubricated machining is also seen in the tool wear that occurs. In examining the tap wear that occurred using water only (Fig. 9), it is seen that significant abrasive wear, as well as chipping and fracture of the cutting edge, occurs on nearly all (five of six) of the cutting teeth examined. Under these conditions, a total wear value of 0.45 mm2 was obtained.

Tool wear â&#x20AC;&#x201D; water only.

Figure 10 AUG 2019

(b)

(c)

Cutting edge wear â&#x20AC;&#x201D; thread-cutting fluids at 6% concentration: Fluid 74 (a), Fluid 75 (b) and Fluid 27 (c).

Quaker_08_19.indd 7

I IRON & STEEL TECHNOLOGY I AIST.ORG

(a)

9/19/2019 2:42:50 PM

Technical Article Figure 11

In examining the wear measured for the three thread-cutting fluids (Figs. 10 and 11), it can be seen that the use of all three fluids greatly reduced the level of wear relative to that formed without lubrication. Of the three fluids, and consistent with the cutting forces measured, Fluid 74 gives the lowest level of wear. This is followed by the microemulsion Fluid 75, and then Fluid 27, which gave the highest wear of the three fluids studied. Thread Surface Quality: The machined surface quality also reveals significant deficiencies when the cutting process is performed unlubricated. Fig. 12 shows a scanning electron micrograph of the threads produced when water alone was used. As seen, severe tearing and deformation of the thread crests occurs along with severe metal tearing and smearing on the flank surfaces. A backscatter image of the flank surface at higher magnification is shown in Fig. 13. The regions of smeared metal are clearly apparent on the surface. Such defects on the thread surfaces, along with giving poor thread quality, will also have significant detrimental effects

Tool wear at 6% concentration.

Figure 12

Figure 13

Figure 14

SEM of flank surface — water only.

Backscattering SEM image of flank surfaces of machined threads at 33x.

AUG 2019

Scanning electron micrograph (SEM) of cut threads — water only.

Quaker_08_19.indd 8

9/19/2019 2:42:51 PM

9 Figure 15

(a)

(b)

(c)

Backscattering SEM image of flank surfaces of machined threads at 200x: Fluid 74 (a), Fluid 75 (b) and Fluid 27 (c).

Figure 16

Fluid concentration effects on tool wear.

Figure 17

I IRON & STEEL TECHNOLOGY I AIST.ORG

Quaker_08_19.indd 9

Fluid Concentration Effects on Thread Cutting — It is often desirable and economically beneficial to be able to utilize a thread-cutting fluid at reduced concentrations. While the minimum recommended use concentration of a given fluid is often dictated by the threshold concentration needed for corrosion and/ or bioresistance, the fluids’ capabilities in the actual cutting operation can also determine the minimum use concentration for a fluid. To investigate this, the three fluids were tested at a concentration of 4% to determine the effects of reduced concentration on

AUG 2019

Fluid concentration effects on cutting power.

on the ease of repetitive breaks and remakes of the connections during use in the field. On examining the thread surface quality obtained with the three thread-cutting fluids, it is seen that while all three fluids tapped effectively, clear differences are produced in the quality of the thread surfaces. This is especially true on examination of the latter threaded holes for each test (holes 30–36), where the separation in cutting forces and tool wear is the greatest. Fluid 27, which shows the highest wear value, and also the highest slope in cutting power during the steady-state regime, as might be expected, shows more pronounced metal smearing and tearing on the thread flank surfaces as well as noticeable grooves formed in the machining direction of the flank surface (Figs. 14 and 15). The two emulsion fluids, Fluid 75 and Fluid 74, both giving lower wear values and lower cutting forces, show more uniform flank surfaces on the machined threads, with lower levels of metal tearing and smearing observed. Interestingly, although Fluid 75 gives slightly higher tool wear and cutting forces relative to Fluid 74, the uniformity and quality of the thread surfaces produced using the microemulsion fluid (Fluid 75) were the best of the three fluids tested.

9/19/2019 2:42:53 PM

Technical Article

AUG 2019

Figure 18

wear) begin to occur. In contrast, for the other two cutting fluids, a more substantial increase in wear occurred at the reduced 4% concentration, with both fluids giving wear values above the failure criterion, thus suggesting that the lower concentration of 4% would not be a suitable use concentration for these two fluids. The tapping power measured for the three fluids at the 4% concentration were consistent with the tool wear results obtained. Fluid 74 maintained low tapping forces at 4% while the other two thread-cutting fluids showed a noticeable increase in cutting power as their concentrations were reduced from 6% to 4% (Fig. 17). With the macroemulsion Fluid 74, in maintaining low cutting forces and low tool wear at the reduced concentration of 4%, it would be expected that little Microphotographs of thread flank surfaces — 4% fluid concentration. to no change in the surface quality of the machined threads would be seen relative to that obtained at 6%. Upon examination of the thread surface qualcutting power, tool wear and thread surface quality. ity produced at 4% (Figs. 18 and 19), it can be seen In looking first at the effects of reduced concentrathat relatively smooth thread surfaces are obtained. tion on tool wear (Fig. 16), it is seen that with a This is consistent with the results of both tool wear reduction from 6% to 4% concentration, the macand cutting power, and further supports a conclusion roemulsion Fluid 74, while showing a slight increase that this fluid offers the potential for use at lower in wear value, maintains a low and acceptable level concentrations. Also, as expected from the wear and of wear. This is based on a wear failure criterion power results, the thread surfaces obtained using the of 0.24 mm2, which is the level of wear at which, in other two fluids at 4% show a higher level of surface this test, it is seen that more catastrophic changes defects. to the tool (such as fracture, chipping and crater

Figure 19

(b)

(c)

(a) Scanning electron microphotographs of thread flank surfaces — 4% fluid concentration: Fluid 74 (a), Fluid 75 (b) and Fluid 27 (c).

Quaker_08_19.indd 10

9/19/2019 2:42:53 PM

11 Conclusions A machining test has been presented that offers the ability to evaluate the thread-cutting performance properties of a given metalworking fluid under controlled laboratory conditions prior to use of the fluid in an actual industrial thread-cutting operation. The use of a cut-tapping operation using AISI 4140 steel provides an effective means to assess fluid performance and to compare the performance of different fluids for a given thread-cutting operation. The measurement of tool wear, cutting power and thread surface quality is used for assessing performance. In the study presented, three thread-cutting fluids were evaluated. While all three performed effectively and would be considered suitable for use at a fluid concentration of 6%, it is seen that the macroemulsiontype fluid, Fluid 74, provides the highest level of performance and also the potential for use at a reduced concentration of 4%.

Robert Evans, Ph.D. is a research scientist and Edward Platt is a Machining Specialist in North America for Quaker Houghton 901 East Hector Street Conshohocken, PA 19428 USA 800.832.4000 www.quakerhoughton.com

References 1. W. Clayton, The Theory of Emulsions and Their Technical Treatment, 4th ed., The Blakiston Co., New York, N.Y., USA, 1943, p. 1. 2. P. Becher, Emulsions: Theory and Practice, 2nd ed., Reinhold, New York, N.Y., USA, 1966, p. 2. 3. I. Danielsson and B. Lindman, Colloids Surfaces, Vol. 3, No. 391, 1981. 4. G. Gillberg, H. Lehtinen and S.E. Friberg, J. of Colloid Interface Sci., Vol. 33, No. 40, 1970. 5. K. Shinoda and S.E. Friberg, Adv. Colloid Interface Sci., Vol. 4, No. 281, 1975. 6. S.E. Friberg, Colloids Surfaces, Vol. 4, No. 201, 1982. 7. M. Podzimek and S.E. Friberg, J. Dispersion Sci. Technol., Vol. 1, No. 34, 1980. 8. K. Shinoda, H. Kunieda, T. Arai, and H. Salto, J. Phys. Chem., Vol. 88, No. 5126, 1984. 9. R.D. Evans, E. Platt, F. Hoogendoorn, E. DeMeter and S. Shtub, Iron & Steel Technology, Vol. 13, No. 8, 2016, pp. 135–141. F

AUG 2019 IRON & STEEL TECHNOLOGY AIST.ORG

Quaker_08_19.indd 11

9/19/2019 2:42:54 PM

AUG 2019

Technical Article

Quaker_08_19.indd 12

9/19/2019 2:42:55 PM