Quench tank

01

Size the agitation and flow through the load

In a 2024 Thermal Processing column, Quaker Houghton's D. Scott MacKenzie tabulates minimum agitation power by tank volume: for marine-type propellers at 480 rpm, 0.005–0.007 HP per gallon in oil and 0.004–0.005 HP/gal in water or brine; for modern airfoil impellers at 280 rpm, 0.003–0.004 HP/gal in oil and 0.002–0.003 HP/gal in water, noting airfoil impellers give about 40% greater flow efficiency at lower speed. [1]

In his worked case, a 3 m diameter, 6 m deep polymer tank (42.41 m³, about 11,200 gallons) with one 3.75 kW, 300 mm marine agitator in a draft tube gave only 0.015 m/s upward flow, a 'dead' tank; for the desired minimum 0.5 m/s through the load it needs about 3,534 L/s, met by eight 400 mm airfoil agitators around the periphery, which modelling showed gave about 1.0 m/s at the centre and 0.5 m/s at the edges of the work zone. Using 0.003 HP/gal, the minimum power is 33.6 HP. [1]

Editorial calculation: 3,534 L/s ≈ π × (1.5 m)² × 0.5 m/s, confirming the flow figure; 33.6 HP ≈ 25 kW, about 6.7 times the original 3.75 kW agitator. [1]

Give the supplier the quenchant type and volume, load size, weight and orientation, required flow velocity through the load, agitator type and power, heating or cooling duty and allowable temperature rise, fire protection, elevator or basket handling, and construction material.

02

Choose quenchant, fire safety and construction

L&L Furnace's QTS 124 portable agitated quench tank can be used with water or light polymer with rust inhibitor; its QTO124 version for quenching oil adds an explosion-proof motor and slide-on lid, and its QTW124 for plain water is stainless steel. L&L explains that agitation disperses vapour bubbles that form on hot parts, which would otherwise cause uneven quenching, and prevents localised overheating that could cause a fire with oil; the lid helps extinguish a quench-oil fire and keeps the medium clean. [2]

The QTS 124 holds 25 gallons in a 16 × 16 × 25 in tank with 12 × 12 × 24 in work space, double-welded 10-gauge steel with epoxy paint, a 1 in NPT drain, a 4 in 316 stainless impeller in a separate chamber behind a perforated screen, and a 120 V single-phase agitator of 1/4 HP (5.1 A) standard or 1/2 HP (7.6 A) explosion-proof; it is not designed for brine. [2]

Editorial calculation: 25 gallons ≈ 95 L; 1/4 HP for 25 gallons is 0.01 HP/gal, above the 0.005 HP/gal minimum MacKenzie lists for marine propellers in oil for his smallest band of 50–800 gallons (the 25-gallon tank is below that band). [2] [1]

The quenchant sets the tank's temperature duty. FUCHS lists its RENOQUENCH QH 35 MC (formerly THERMISOL QH 35 MC), a high-performance hydrocrack-based quenching oil for unalloyed, low-alloy and high-alloy steels in batch or continuous furnaces, at a bath temperature of 40–110 °C (maximum 150 °C), a flash point of 236 °C, kinematic viscosity of 37 mm²/s at 40 °C and density of 0.84 g/ml at 15 °C, for open and closed plants. [3]

Editorial calculation: at that oil's 150 °C maximum bath temperature the margin below its 236 °C flash point is 86 °C; heating, cooling and agitation must hold the bath within the 40–110 °C working range during each quench, and the tank's heat-removal capacity should be sized to the heaviest load's heat release per hour. [3]

03

OSHA alarm wording and unequal temperature differences

In the United States, OSHA's dipping and coating rule (29 CFR 1910.123 to 1910.126) applies to a dip tank holding a liquid other than water that is used to change the character of an object, and names quenching among the covered operations; it does not cover tanks that use only a molten material such as a molten metal, alloy or salt. [4] Section 1910.126(a) then sets additional requirements for hardening or tempering tanks: locate them as far as practicable from furnaces, on noncombustible flooring, with noncombustible hoods and vents to the outside whose ducts are treated as flues and kept away from combustible materials; fit each tank with an alarm that sounds if the liquid comes within "50°F (10°C)" of its flashpoint (the printed temperature differences are not equivalent; see the calculations below); where practicable, add a limit switch that shuts down the conveyor supplying work to the tank; fit a circulating cooling system if the liquid can exceed the alarm set point; and do not use air under pressure to fill the tank or agitate the liquid. A bottom drain may be combined with the oil-circulating system. [5]

OSHA 1910.126(a)(3) prints "50°F (10°C)". Editorial calculation: as a temperature difference, 50°F × 5/9 ≈ 27.8°C; the original parenthetical 10°C is not equivalent. Keep both readings visible and confirm the applicable interpretation with OSHA or the local authority. [5]

Editorial calculation: using the printed 10°C difference and the FUCHS oil's 236°C flash point gives 236 − 10 = 226°C. This is not a confirmed regulatory set point and is not an allowable oil bath temperature. Confirm with OSHA or the local authority. [5] [3]

Editorial calculation: using the printed 50°F as a temperature difference (approximately 27.8°C) and the same 236°C flash point gives 236 − 27.8 ≈ 208°C. This is not a confirmed regulatory set point and is not an allowable oil bath temperature. Confirm with OSHA or the local authority. FUCHS separately lists this oil's bath temperature as 40–110°C, maximum 150°C. [5] [3]

04

Quench-tank load, handling and cooling data

Ask any supplier for tank volume and dimensions, agitator type, number and power, expected flow velocity through the work zone, heating and cooling capacity, temperature control, fire protection (lid, extinguishing, explosion-proof motors), construction material and finish, and load handling.

05

Tank, screened impeller chamber and oil-fire lid

06

Quenchant limits and agitation data to specify

07

Send the quenchant, load and agitation data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Quenchant: [oil; polymer; water]
Load: [size; weight; orientation]
Volume: [L]
Agitation: [flow m/s through load; agitator type]
Thermal: [heating; cooling; temperature]
Safety: [lid; explosion-proof motors]
Construction: [steel; stainless]

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