Q&A

Both require "Solution Heat Treatment" and quenching first. The difference lies in the subsequent steps:

●T4: After quenching, the parts are placed at room temperature for "Natural Aging"

●T6: After quenching, the parts go into an aging furnace for "Artificial Aging" at a higher

temperature to accelerate the precipitation of strengthening phases, achieving the highest mechanical strength.

The solution treatment temperature of aluminum alloys is typically very close to their eutectic melting point (usually within a difference of only about 10°C to 15°C). If the furnace temperature is non-uniform, areas with higher temperatures will cause "Overburning" (Eutectic Melting, which causes surface blistering or grain boundary melting, leading to immediate scraping of the product). Conversely, areas with lower temperatures will result in incomplete solution treatment, failing to reach standard strength. Therefore, temperature uniformity requirements for aerospace or automotive-grade aluminum furnaces must often reach ±3°C to ±5°C.

●Too High: Leads to localized melting of grain boundaries (overburning), embrittling the material. This type of damage cannot be remedied by re-heat treatment.

●Too Low: Alloying elements cannot fully dissolve into the aluminum matrix. Consequently, sufficient strengthening phases cannot precipitate after quenching and aging, resulting in substandard hardness and tensile strength.

Quench Delay Time refers to the time required for the workpiece to travel from leaving the heating chamber to being completely submerged in the quenching medium (water or glycol coolant). If the delay is too long, alloying elements will prematurely precipitate along grain boundaries in the air, severely impacting final strength and corrosion resistance. For thin-walled parts or aerospace components, specifications usually require the quench delay to be under 10 seconds.

●Water Quenching: Offers the fastest cooling rate, yielding the best strength and corrosion resistance, but easily causes severe distortion in thin-walled or complex-shaped workpieces.

●Polymer Quenchant: By controlling the concentration and liquid temperature, the cooling rate is more moderate and uniform, significantly reducing workpiece deformation. It is the preferred choice for precision-machined parts, though it requires regular maintenance of the solution concentration.

To satisfy the extremely short "Quench Delay Time," a Drop-Bottom Furnace elevates the heating furnace chamber and positions the quench tank directly underneath. Once heating is complete, the bottom doors of the furnace open instantly, and the workpiece basket drops vertically via free fall or a high-speed winch into the water. This is currently the most stable furnace design for achieving a quench delay of under 7 seconds.

Aluminum has high surface reflectivity and is extremely poor at absorbing radiant heat (especially in low-temperature stages). Therefore, aluminum alloy heat treatment furnaces rely heavily on forced convection heat transfer. They must be equipped with high-volume, high-temperature-resistant circulation fans and precisely designed air flow baffles to ensure consistent heating rates across all areas in the furnace and to meet strict temperature uniformity requirements.

A Pit Furnace utilizes vertical loading into the furnace, allowing workpieces to hang naturally under gravity. This significantly reduces bending deformation under their own weight at high temperatures for long shaft parts (such as drive shafts, lead screws, gun barrels, etc.)—an advantage that is difficult to replicate with car-bottom or box furnaces.

The Muffle is mainly used to isolate the heating elements from the processing atmosphere and guide the hot-air circulation. During carburizing or gas nitriding processes, a sealed, heat-resistant steel muffle can precisely maintain the furnace atmosphere (carbon or nitrogen potential), preventing gas leaks or absorption by the insulation wool, while protecting the heating elements from soot erosion.

Modern pit carburizing furnaces typically use an Oxygen Probe inserted into the furnace to detect the oxygen partial pressure in real time. Combined with a microcomputer controller, the carbon potential is calculated. The system then automatically adjusts the inlet solenoid valves for enriching gas (such as propane or natural gas) and carrier gas (such as methanol cracked gas) to control the carbon potential at the set value (e.g., 0.8%–1.0% C).

Yes, Pit Nitriding Furnaces are very mainstream equipment. Ammonia gas ($NH_3$), or ammonia mixed with carbon dioxide/nitrogen (for nitrocarburizing), is typically introduced at around 500°C–580°C. These types of furnaces are equipped with an ammonia dissociation analyzer to control the nitriding case depth and compound layer (white layer) thickness.

In a bare-atmosphere pit furnace without a muffle, a protective gas (such as pure nitrogen or endothermic gas) can be introduced during the heating process to maintain a slight positive pressure inside the furnace, preventing external oxygen from entering. Alternatively, a "Pit Vacuum Furnace" design can be used, where the chamber is evacuated and then backfilled with protective gas.

There are two most common causes:

1. Thick and uneven Soot has accumulated on the fan blades, leading to a loss of dynamic balance.

2. The cooling water jacket is clogged with scale or lacks water, causing the motor bearings to overheat and wear out.

The equipment must be shut down immediately to clean the blades or replace the bearings;otherwise, it can easily lead to a fractured fan shaft.

The furnace is filled with flammable protective gases (containing $CO$ and $H_2$), which deflagrate upon coming into contact with air when the lid is opened. For safety design, before the lid opens, the system first ignites an Exhaust Flare at the furnace port. The moment the lid rises slightly to form an air curtain, it ignites the escaping gas. Operators must stand at the safe side-control panel and must never lean over to look down into the furnace.

Both are batch production furnaces. A Box Furnace is suitable for small-to-medium workpieces or low-volume, high-mix processes, where parts are typically loaded manually or via forklift. On the other hand, the bottom of a Car-Bottom Furnace is a movable car specifically designed to carry heavy, oversized workpieces (such as casting and forging parts weighing tens of tons), allowing for direct loading and unloading using an overhead crane.