Third in a series » Polymer quenchants, first introduced in the 1970s, have captured an increasingly large market share of quenchants at the expense of oil quenchants. In this series of articles, the quenchants (covered generally in the July 2024 issue) and individual polymer types will be examined in more detail.
In this installment, I will discuss polyethyl oxazoline (PEOX) type polymer quenchants, and their application.
Introduction
Polyethyl oxazoline-based products represent the second generation of polymer quenchants. Developed as part of a continuing program of product innovation and improvement, PEO technology is now covered by worldwide patents.
Polyethyl oxazoline (PEOX) is synthesized from the polymerization of ethyl oxazoline (Figure 1).
PEO-based products have similar characteristics of PAG quenchants commercially available and, as a result, are being used in a wide range of applications, ranging from induction hardening of steel and cast iron to tank quenching of high hardenability steel castings and forgings.
PEO chemistry is highly efficient in modifying quenching characteristics, and required properties are obtained at low polymer concentrations. This results in less drag-out than with other types of polymers and consequently great economy in use. Any polymer remaining on the surface dries to a hard, tack-free film, ensuring freedom from sticky residues.
Quenching characteristics of PEOX Quenchants
PEO-based quenchants exhibit inverse solubility at a temperature of 60-65°C. Hence, the quenching mechanism is very similar to that of the polyalkylene glycol-based products. Like all other types of polymer quenchants, the quenching characteristics are dependent upon polymer concentration, bath temperature, and degree of agitation.
PEO polymers can be used over a wide range of concentrations from 5-25 percent (Figure 2) depending upon the application. PEO products have the least stable vapor phase of all the polymer quenchants and this is particularly important during induction hardening and in the quenching of low hardenability steels.
Also, the very low cooling rate in the convection phase, where, at concentrations of 15-25 percent, the quenching speed is almost identical to that of quenching oil. This extends the range of applications to critical high alloy steels.
As with all polymer quenchants, as the temperature is increased, the effective cooling rate decreases. Because PEOX products have an inverse solubility temperature of approximately 63°C, it is important to ensure effective cooling of the bath, and to limit the bulk quench temperature to 40°C or so.
As with all polymer quenchants, the cooling effect is dependent upon the degree of agitation. However, the vapor stage with PEOX products is easily broken down and disappears completely with turbulent agitation. This is particularly important in the quenching of low hardenability materials.
As the agitation rate increases, the maximum cooling rate is increased, as with the temperature of maximum cooling.
Typical applications for PEOX quenchants
The flexibility of quenching speed, ease of breakdown of the vapor phase, low cooling rate in the convection stage, and freedom from sticky deposits enable the use of PEO-based products for a very wide range of applications.
Induction and flame hardening
Generally used at concentrations of 5-10 percent as a replacement for PAGs or oil in the treatment of steel and nodular cast-iron components. Typical applications include camshafts (Figure 3), crankshafts, and gears in the automotive industry, and drill pipe for the oil industry. The hard, dry residual film is of particular benefit to subsequent handling operations or where shot-blasting is required.
Quenching of low hardenability steels
The short vapor phase enables the development of maximum properties in low hardenability materials such as those used for fasteners. 10 percent PEO solutions are used successfully for the treatment of bolts and screws in continuous furnaces. Good agitation is required to minimize soft spots in these difficult-to-quench components.
Alloy steel forgings, bars and castings
Low cooling rates in the convection phase make PEO polymers suitable for higher hardenability alloy steel components which would normally be oil quenched. (Figure 4) Concentrations range from 15 to 25 percent, depending upon applications that include martensitic stainless-steel wire and rod AISI 4100 and 4300 series castings and forgings. High carbon-chromium grinding balls and liner plates, nodular and ductile iron castings have all been successfully quenched in PEOX quenchants.
Other applications
PEOX quenchants have been used in continuous mesh belt type furnaces for quenching small bearing races, as well as smaller link chain applications. The benefits of low residue and high cloud temperature result in a low drag-out product that can be readily washed off using cold or ambient temperature water.
While recovery of polymer is possible from rinse tanks by taking advantage of the inverse solubility and cloud point of PEOX polymers, the low residue and drag-out of PEOX polymers makes this possibly not economically feasible.
Conclusions
In this short column, we have discussed the use of PEOX type polymers and their applications. This type of polymer has a wide applicability to low and high hardenability steels, and different types of quenching. Spray and immersion type quenching is possible. It has applications from continuous type furnaces to large quench tanks quenching large forgings and castings.
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