NacoPax Asphalt Road Plants
Paxman Catalogue No 905
The text of catalogue No 905, issued c.1925/26, is reproduced below verbatim.
A history of this plant, order details and a further description are to be found on the page NacoPax Road Making Plant.
"NacoPax"
Asphalt Drying & Mixing Plant.
Designed specially for all types of Bituminous Macadam.
Manufactured by
Davey, Paxman & Co., Ltd
THE "NacoPax" Plant has been evolved after exhaustive study and consideration of present-day requirements by The Neuchatel Asphalte Company, Ltd., a firm with over fifty years' experience of asphalt work, and Messrs. Davey, Paxman & Co., Ltd., the well-known firm of engineers. It embodies the advantages both of permanent and portable plants, being designed with a view to very easy transport, and yet easily fixed on foundations or temporary supports, giving it 7 ft. headroom as the minimum for lorries, which should be provided on all plants, and is a matter of considerable difficulty to obtain with the ordinary type of plant mounted on wheels.
The "NacoPax" compares very favourably with any other plant on the question of drying and heating. While with many plants it is necessary to pass the aggregate through more than once to obtain the necessary dryness and temperature, the "NacoPax" is capable of dealing with this output at one operation under the very worst conditions and without involving the violent fluctuations in temperature which are a common feature of so many other plants.
"NacoPax" Plants are for the manufacture of road materials, consisting of bitumen and any specific aggregate for making synthetic asphalt roads. Synthetic asphalt is defined as the name applied to mixtures of either natural (e.g., Trinidad or Selenitza) or residual bitumen (e.g., Mexicantexan) with mineral aggregate of graded sizes including clinker from coarse broken stone down to the finest sand. The aggregate is dried and the bitumen is fluxed and melted. The specified materials are mixed and well stirred together and then spread out on the road with rakes and rolled down with steam rollers. The Plants are designed to manufacture all variations of bituminous carpet or macadam from 1½ in. wearing surface to the heaviest types of two coat construction whether natural or residual bitumen be used as the binding agent.
Capacity. The output of any asphalt plant must mainly be governed on the one hand by working conditions and the moisture content of aggregate to be handled, and on the other by ability of the plant to dry with the highest efficiency and to mix satisfactorily the maximum quantity of aggregate dried.
Economical operation in obtaining output will depend on the mechanical efficiency of plant, fuel consumption, and the ability to run without frequent breakdown and repair and, in general, sound design and construction.
To meet all requirements in these respects we unhesitatingly claim that the "NacoPax" Plant possesses outstanding superiority; claims which are based on actual working experience, and which we are prepared to substantiate at any time.
The "NacoPax" Plant is normally designated as a 10 ton plant, viz. : 10 tons of Carpet per hour or 80 tons per 8 hour day. This is an understatement of its capacity rather than the reverse. As a matter of fact, under ordinarily favourable working conditions, namely where supplies have been uninterrupted and motor transport adequate, our plants have maintained outputs in excess of 100 tons per day without difficulty.
We should be glad at any time to have the opportunity of supplying full details of our plant, which are briefly referred to in the following pages, and for this purpose would arrange for the attendance of one of our Engineers, having expert knowledge of this branch of engineering, to call upon interested parties.
Design. The main part of the plant is 23 ft. by 7 ft. 6 in. wide, and is easily carried on "crocodile" or boiler float. For export purposes the standard plant is so constructed that it may be almost completely dismantled into small parts and re-erected without riveting.
Erection. Special attention has been paid to this detail. All parts which are normally required to be removed and re-assembled when transporting the plant, are bolted together in small sections, the maximum weight of which is 2 cwts. (except the furnace for which special provision is made). A small crane is fitted to aid in the erection and may be used afterwards for raising cement, etc., for filler on to the platform, or for aid in changing the screen mesh, etc.
Lifting Gear. This is a very important feature which is peculiar to "Nacopax" Plants. Consisting of four light tripods fitted with self-aligning lifting screws, it permits the plant to be raised from the vehicle on which it travels to the working position, and allows 7 ft. headroom for lorries under the Mixer. The lifting to the necessary height can be done in a very short time and in one lift, When in position, steel trestles are clamped to the frame of the plant, and the whole of the lifting gear removed. This one set of lifting gear will serve several plants. With this gear it should be possible to erect a plant and have it ready for work in 24 to 30 working hours under favourable conditions. Reference to photographs on the opposite page will indicate that this statement is based upon working experience.
Foundations. When erected according to the method described above, sleepers on levelled ground are the only foundations required. The steadiness of the plant in operation is remarkable.
Outstanding Advantages of the "NacoPax" Plant.
Output.
Highest drying efficiency and better heat transmission.
Lowest fuel consumption.
Maximum mixing capacity.
Minimum radiating surface, and
Lowest radiation losses.
Lowest operating costs.
Highest mechanical efficiency.
30% to 40% less power for driving.
Heavy drives concentrated at one point.
Interchangeability of parts subject to wear.
Unique facilities for rapid erection and dismantling.
Easy portability.
No chain drives and consequent stoppages.
Short and rigid drum.
No long single drums liable to sag under overheat.
No heavy outboard drum bearing.
Material travels through drum independently of inclination.
Weighing under direct observation and control.
Extra large storage bins.
Sound design-Sound construction.
Simple drying may be effected without passing aggregate through bins by returning it close to dumps.
Cold Elevators. The cold material is raised into the feeding hopper by two elevators "A" extending on each side of the frame, an operated through bevel gearing from the line shaft which passes along the side of the machine on the opposite side of the main drive. The provision of two cold elevators instead of the usual single elevator more generally adopted, permits of a better distribution of the coarse and fine aggregate dumps.
From these elevators the material passes into the drying drum "B" through suitable chutes arranged through the outlet from the drum to the fan.
Fan. A fan "C" of ample dimensions, having a damper for regulating the draught, draws the hot gases from the furnace through the double drum in the opposite direction to the motion of the material to be dried thus carrying out the well-known "contra-flow" principle, in the most efficient manner. The fan discharges into a cyclone dust collector "D" from the top of which the exhaust gases finally escape to atmosphere.
Drying and Heating Drum. This is a very distinct feature and one of the most important parts of the plant. The drum is almost entirely enclosed in a brick-lined casing "E" over a furnace "F" of very large size. The furnace gases not only surround the drum, but pass through in two directions, meeting the mineral aggregate cascading and travelling in the opposite direction. By the special construction this drum is considerably shorter (although the distance travelled by the mineral aggregate is the same) while retaining the same diameter, than drums of the same nominal (though less actual) capacity, and since it is carried on rollers and friction driven, it requires no expensive spur gear ring, conical thrust rollers, nor water-cooled bearings. Standard firebricks are used throughout.
Owing to an ingenious arrangement of cascaders in both drums the gases come into intimate contact with the aggregate, across practically the complete sectional area of both drums, causing it to be completely dried and heated to the correct temperature before it passes from the drum into the boot of the hot elevator, a result which is impossible of achievement with a single drum type drier with equal efficiency. The fan and passages through the drum are so proportioned as to give the correct velocity at all points; a very important feature in drying. A very low fuel consumption is obtained by virtue of this arrangement which ensures that the maximum amount of heat is available for drying and heating the aggregate. Also, owing to the reduced length of the drum and consequently the casing, the radiation losses are reduced to a minimum.
Hot Elevator. From one end of the drum the dried and heated material falls by means of an enclosed chute into the bottom of the hot elevator "G" which is arranged to be easily detachable, and is raised by chain buckets to the screen "H" where it is screened and graded and delivered to the storage bins "J." The hot elevator runs faster than the cold elevators, thus giving an increased capacity to avoid choking.
Since the hot elevator, which is entirely enclosed to conserve the temperature of material, is detached for transport it is constructed in sections, thereby providing every facility not only for speedy erection, but also for packing. Both hot and cold elevators use identical chains, traction wheels and buckets. A special tightening device in each case permits the easy adjustment of all the elevator chains.
Screen and Storage Bins. The screen "H" is placed over storage bins "J" at the top of the plant where it is entirely enclosed. It is of a parallel type of simple construction, suitable for the use of either perforated plate or wire mesh. The mesh can be made to suit any specific requirements and is easily removed and replaced. The Screen is driven by vertical shaft and gear wheels from main drive below (no chain drive being used).
The screened material then falls into storage bins which are of large capacity and designed for rapid erection and dismantling. They are usually made in two compartments of 2 and 4 tons capacity, but other divisions and proportions can easily be arranged in conjunction with modification of screen mesh. Overflow and tailings pipes are provided and suitable bin gates are fitted operated by levers in a very accessible position on platform.
Weighing Gear. From the bins, the stored material is delivered to the weighing skip "K," which is suspended on an adjustable scale and is situated immediately under the discharge doors of the storage bins. The scale is arranged so that multiple grades of aggregate may be weighed consecutively for each batch, the setting of the weight being effected on a single beam by a simple hand lever, the action after the adjustment of the gear to the required weights being semi-automatic. This system is much simpler than the arrangement of multiple beams usually adopted and is much less liable to confuse the operator. When weighed the batch is discharged by easily manipulated discharge door direct to mixer "L" underneath.
Bitumen Weighing Skip. This is a tipping skip "M" of sufficient capacity to hold the maximum charge of bitumen for the mixer. It is suspended on a suitable beam scale generally arranged for attachment to a trolley running on an overhead rail, carried over the Bitumen Boiler for easy charging. The bitumen skip can, however, be arranged in a permanent position directly over the mixer where an air lift or other means is used for elevating the hot bitumen.
Mixer. This is of the twin-shaft Pug Mill type, of unquestionable efficiency, and having a working capacity of 12 cwts. This type is most successful for turning out a well-coated and uniform mixture, whether natural or residual bitumen is employed as a binding agent. Special attention has been paid to the need of changing the paddles from binder to carpet type and vice-versa, and by means of complete spare shafts with paddles, gears, and bearings, together with a special construction of mixer, the time required for this operation has been reduced to a minimum - at the most one hour. Discharge from the mixer to lorry underneath is effected by means of a sliding door operated by hand lever fitted with special gear designed to overcome troubles due to sticking in action.
Driving Gear and Transmission. Special attention has been paid to this most important feature. The whole of the heavy drives are concentrated at one point which is close to the platform at the mixer end and under observation, the main driving pulley is thus situated in the most convenient position for driving from an independent portable engine.
Power is transmitted throughout by strong toothed wheels. No chain drives whatever are employed.
With the exception of the belt drive to the fan all the transmission is by shafting carried in Double Row Self-Aligning Ball or Roller Bearings. By this means trouble due to chains breaking, a feature of certain other plants, is entirely obviated, friction is reduced, while the self-aligning feature of these bearings renders the gearing practically fool-proof during erection. All main driving gears are enclosed, thus preventing any possibility of accidents to operator.
Owing to the use of self-aligning ball bearings throughout the mechanical efficiency of the plant is very high. Special attention has been paid to the ball bearing housings, which are so constructed as to be absolutely dust and grit proof. Provision is made for all bearings to be packed with suitable lubricant.
Dog clutches are fitted to both cold and hot elevators. The mixer can be declutched at will.
Interchangeability of wearing parts has been one of the most important considerations in the design of this plant. All the operating shafts with the exception of the main driving shaft and mixer shaft are of the same diameter and consequently all the self aligning ball bearings and housings on these shafts are of the same size. The mitre wheels are also interchangeable. Ample facilities are allowed for adjustment and consequently the upkeep charges are reduced to a minimum.
Accessories. When required we supply air lift for elevating hot bitumen from boilers to bitumen weighing skip, consisting of air compressor, steam jacketted piping and cocks, and the necessary receivers. Also cold bitumen hoist consisting of winch and runway for bitumen boilers. For driving purposes we recommend the use of one of our Compound Portable Engines, illustrated on page 24. We also supply a small Portable Engine for the purpose of supplying power for driving bitumen boiler agitator gear, and for driving bitumen winch.
Page created: 07 FEB 2006