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Nestled in the heart of Ridgway, Pennsylvania, which claims the title “powder metal capital of the world”, Allegheny Blending Technologies (ABT) specialises in custom blending of ferrous and non-ferrous powder metals that are sold to moulders of powder metal parts.
These blends of iron powder and additives (copper, nickel, graphite, manganese sulphide and dry lubricants) play important roles in products and equipment. In the US automotive industry, nearly every car has about 12 kg of powdered metal parts ranging from timing gears to anti-lock breaking mechanisms. Powdered metal parts are also found in the drive gears and motors of lawn mowers, snow throwers, and other gardening tools, as well as in home appliances such as washers and dryers.
ABT have been blending custom powder metal batches from 227 to 4536 kg since 1997. Four double cone blenders handle the 227 kg, 1134 kg, 2268 kg and 4536 kg batches. A 12 kg capacity double cone blender handles samples. “With double-cone blenders, we find it’s best to match the load to blender capacity for optimal homogeneous mixing,” said Paul Reed, president of ABT. “Under loading a double-cone blender reduces mixing action efficiency. The material tends to roll around in the barrel rather than blend thoroughly together.”
When customers requested blended batches of 20 412 kg truckload lot sizes, rather than purchase another double cone blender, Reed chose a Munson 700-250 HD rotary batch mixer for high bulk density materials. “A double cone blender for this capacity would not meet our needs,” said Reed. “Higher weight loads increase the friction the powder particles experience during blending, affecting the final properties of a mix. In addition, double-cone blenders of that capacity are tall, requiring a ceiling height of more than seven metres.”
The rotary batch blender is a physically compact piece of equipment. “ I had also heard that rotary blenders’ mixing action is more gentle than that of double cone blenders and of shorter duration,” continued Mr Reed. “These features will reduce particle rounding caused by friction between the metal powders, maintaining our high quality product.”
In addition, the rotary batch system can be under loaded down to 10 per cent with no effect on batch uniformity or cycle times, handl ing batches from 20 412 kg down to 2 041 kg with equal efficiency.
The blending process begins when iron powder arrives at ABT in loads consisting of 2268 kg palletised cardboard boxes. Forklift s load the boxes into a powder dumper, which tilts and dumps the contents into a steel hopper positioned above a fine-mesh screener .
Additives arrive in either small bulk containers or paper sacks and are poured into individual hoppers that rest on coarse mesh screens. “We sift everything prior to blending,” said Reed. “We ensure contaminants such as wood slivers from the pallets or bits of cardboard or plastic do not enter the mix, as foreign material could compromise the finished powdered metal part.”
After screening, three floor scales weigh the powders before they are loaded into the blender. The iron is weighed on a 4536 kg scale in 2268 kg loads. The 227 kg scale weighs the nickel and copper additives. A 91 kg scale provides the greatest accuracy needed to weigh graphite and dry lubricants.
The iron powder is gravity fed one box-load at a time from the steel hopper into the blender. Before the last 1134 kg load is added, the hopper containing the additives is raised into position by a forklift for gravity discharge into the blender.

The rotary mixer consists of a horizontal, rotating drum with a stationary inlet at one end and a stationary outlet with a discharge gate at the other. A self-adjusting face seal at the inlet allows dust-free operation. Internal baffles (mixing flights) and lifters create a four-way mixing action that tumbles, turns, cuts and folds material throughout the filling, mixing and discharging phases, achieving 100 per cent batch uniformity and preventing the separation of ingredients of varying particle sizes.
The mixer can achieve 100 per ecnt batch uniformity in three minutes, but ABT mix 20 250 kg loads for about 15 minutes depending on the properties required for specific powder metal mixes. “The rotary batch mixer saves us time and ensures a quality product,” said Reed. “A double cone blender for this size load would take more than 50 minutes to blend because the material tends to roll around rather than mix together. Plus, the long blend time builds more heat within the mix. When the mix gets hot, then you know you’re rounding the particles, reducing the mixture’s green strength.”
After loads are mixed and the plug gate is opened, the flights and baffles in the rotating drum elevate and discharge the entire contents of the batch, with no residue, into hoppers that are transferred to the packaging area. “We found that if we let the blender run for a few minutes after full discharge, only minute amounts of dust remain,” said Mr Reed. “If we stop the blender too quickly, maybe one-quarter to one-half kilogram of material remains. We use a shop vacuum to remove any remaining dust, but even then, clean-up is quick and easy."
 Uniformity of powdered metal blends is crucial to the performance of the finished part. “Even though our customers’ parts typically weigh only a few grams to 7.7 kg, they need repeatability and consistency to meet tight dimensional tolerances,” he added, “so they see the benefits of our homogeneous product.”
Sampling ensures homogeneity, but it is done primarily on new blends to obtain blending times. “Once we’ve mastered a blend’s mix and mixing time, there’s no need to sample. But, if a customer has an order for a specific feature in a blend, such as apparent density, we will sample to ensure we meet that specification,” said Mr Reed.

“Most parts manufacturers get their metal powders preblended now, and no longer do it themselves so green strength is something we measure for our customers,” continued Paul Reed. “We mould test bars of green metal that are about 38 mm long, 13 mm wide and 6 mm thick and break them in a tensile tester to assess a blend’s strength. We have found that green parts from material blended in the Munson unit have a higher green strength than parts moulded of material from double-cone blenders.”
Paul Reed says, “We’re providing a more consistent, homogenous, less degraded material; that’s all a benefit for our customers. They like what they’re getting from us.”

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