Wheel mill

Typically, dry potassium nitrate is pulverized in a ball mill. Sulfur is milled into cellular charcoal to form a uniform mix in a separate ball mill. The nitrate and the sulfur—charcoal mix are screened and then loosely mixed by hand or in a tumbling machine. Magnetic separators may be used to ensure the absence of ferrous metals. The preliminary mix is transferred to an edge-mimer wheel mill with large, heavy cast iron wheels. A clearance between the pan and the wheels is required for safety purposes. The size of this gap also contributes to the density of the black powder granules obtained. Water is added to minimize dusting and improve incorporation of the nitrate into the charcoal. The milling operation requires ca 3 to 6 h. 

Ambient grinding involves the comminution of scrap rubber, including tires, at ambient temperatures, typically in a toothed-wheel mill, bench grinder, shear mill, or two-roll miU, to give particles... 

As with the modern fireworks industry, pressing is preferred over more forceful techniques, but even so, hres regularly break out in presses. Milling is not without hazard either, especially when the large wheel mills weigh several tonnes and the powder batch is around 150 kg. 

Mixing of insensitive ingredients of explosives also can be done in rotary drums, but if the components are not previously pulverized, the so-called pan mixers also known as1 wheel mills or edge runners are used. 

Water is added from time to time so as to maintain a moisture content of 3—6%. Usual charges were SO lbs in GtBritain, while in Canada and the USA, they milled up to 650 lbs (Ref 4, pi 3). In the wheel mill, described by Davis (Ref 5, p46), the charge was 300 lbs and the wheels, each weighing 10 tons, rotated for about 3 hrs at a rate of about 10 turns per minute (See also Ref 6, p249 and Ref 7, pi 214)... 

Dualine Stumping Powder (Canad). It was prepd in 1893 in Nanaimo, British Columbia, by incorporating 3 parts of BkPdr (previously pulverized by "wheel mill ) with 1 part of NG... 

Esplosivi molazzati- powdered explosives prepd by blending in a wheel mill , called molazze or macine, in Italian (see Figs 128 129, p 381 in Ref 8). This method of manuf has been used in manuf of BkPdr and some Dynamites... 

The dampened material is mixed with K nitrate (previously finely ground) and the moisture content adjusted to ca 4%. About 300 lbs of this mixt are placed in a Wheel Mill(such as described in Ref 11,p 46 Ref 18,p 69 or Ref 28,p 87) where the mass is processed during 3-6hrs. This operation is called Incorporation or Milling. The resulting material is called "mill cake , "clinker or "wheel cake . It... 

Corning Mill Dust. This is also called meal powder, or by the Fr pulverin. Corning mill dust is the finest and the most intimately incorporated BkPdr dust remaining in the mill after the "corning" or granulating operations. Various types of machines are used to manuf granulate BlkPdr, such as "Wheel Mill "Stamp Mill" illustrated by Davis (Ref 2), and "Corning Machines" illustrated by Marshall (Ref 1)... 

Incorporating or Milling. The usual wheel mill has wheels which weigh 8 or 10 tons each. It takes a charge of 300 pounds of... 

The French still make pulverin, for the preparation of black match and for use in pyrotechnics, by rolling the materials with balls, some of lead and some of lignum vitae, in a barrel of hardwood. They also sometimes use this method for mixing the ingredients before they are incorporated more thoroughly in the wheel mill. 

The black powder wheel mill is also used for reducing (under water) deteriorated smokeless powder to a fine meal in order that it may be reworked or used in the compounding of commercial explosives, and for the intimate incorporation of such explosives as the French schneiderite. 

Figure 20. Modem Wheel Mill for Making Black Powder. (Courtesy Atlas Powder Company.) The large wheels weigh 10 tons each.

The Schneiderite (Explosif S or /Sc) which the French used during the first World War in small and medium-size high-explosive shells, especially in the 75 mm., was made by incorporating 7 parts of ammonium nitrate and 1 of dinitronaphthalene in a wheel mill, and was loaded by compression. Other mixtures, made in the same way, were used in place of Schneiderite or as a... 

The oldest of the composite propellants is black powder that is produced by mixing the ingredients wet and then wheel-milling them. The tremendous pressures in the mill cause the sulfur to plasticize and flow. The product is then treated, dried, and screened to produce the various grades as a function of the particle sizes. The composite propellants are less vulnerable to initiate than nitrocellulose-base propellants [5]. 

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