The Christy & Norris NPK pulverizer was developed especially to reduce the particle size of materials which become sticky if subjected to a temperature rise during the grinding process. No screens are used. The principle of size reduction employed is to use one high speed rotor and one slow speed drum type rotor. The high speed rotor is fitted with flails and rotates in the opposite direction to the slow speed drum. A scraper is fitted under the drum so that any material which tends to stick to it is removed.

Drives
The high speed rotor is driven through vee belts from the main motor. The drum type rotor is driven from a worm gearbox through a chain drive. It is possible to drive either end of both the high speed and slow speed shafts so the two drive motors can be positioned in any one of eight combinations to suit the layout. See schedule for speeds.

Method of particle size selection
The double rotor pulverizers do not use built-in screens so that the whole of the stream of material fed into the machine passes straight through. This means that all the reduction in size is carried out during the brief period that the material is passing through the machine. For this reason there is likely to be certain amount of oversize material in the ground product. It is normal to incorporate a screening device after grinding and to re-circulate the oversize material back to the double rotor pulverizer. The size of the finish product depends upon the material, its tendency to stickiness, moisture content, temperature, and the adjustment between the high and slow speed rotor, and the speed at which the high speed rotor is driven. This can be varied to obtain the optimum balance between particles size reduction and build up of sticky material in the machine.

Materials
The double rotor pulverizers are used very extensively through the world for size reduction and compound fertilizers. Details of outputs of these form various size of machines are shown in the scedule. These materials can be delt with at a temperature of up to 100ºC. The machines can also be used to replace the particle size of such a sticky material as clay for brick making. We would be pleased to advise on whether these or another of our range of machines are suitable for any particular product.

The Christy Brton 380 and 660 are HIGH SPEED DUEL ROTATION HAMMER MILLS and are ideal for grinding cereals for animal feeding stuffs, for reclaiming waste food and by-products. Available in models from 55 to 150 kW, these robustly constructed machines are noted for trouble-free performance and high output / energy consumed ratios.

Christy Briton Mills are high speed dual rotation machines always supplied for direct coupling to the electric motor. The 6mm thick beaters rotate at 360 km/hour and the feature of "dual rotation" reduces the frequency of beater changing by two-thirds, thus saving time on maintenance. The change of rotation is made by the use of reversing started coupled to a timer.
The Mill body is of a heavy cast iron construction, accurately machined to provide rigid bearing surfaces on which are mounted heavy duty high speed self-aligning ball bearings.

The unique lobe-type rotor is made up of rotor plates securely mounted to a large diameter shaft.

Christy & Norris heavy-duty pulverizers grind a wide variety of materials from steel swarf, limestone, ceramics, wood hogging and many more. The extremely rugged construction ensures a long life with minimum maintenance, easy to install, and economical to run. Material is fed in at the periphery to minimise air pressure under the pulverizer, greatly reducing the dust problem.
For some material suitable ventilation is recommended. By introducing air on the discharge side of pulverizer, this will prevent a dusty atmosphere at the inlet.
Heavy section, specially hardened alloy steel swinging beaters ride heavy shock loads and return to the grinding position. The beaters are secured to the heavy-duty sectional rotor by nickel chrome steel transverse pins.
The shell is lined throughout with either cast iron or manganese steel according to the size of pulverizer and duty required.
Semi-circular, interchangeable screens which determine maximum particle size of product are inserted through the top front doors and slide in grooves cast in the sides of the pulverizer.
A tramp trap, incorporated in certain models, allows solid items to be thrown out of the grinding chamber to avoid damage to beaters and screens and prevents contamination of finished product. When fed automatically, the machine can be safely left to work unattended. We can provide a pulverizer to reduce almost any material to the size required.