Power saving and security aspects of newly developed vibratory screens

A four deck Armstrong Vibratory Screen driven by two 0.5kw vibratory motors. Capacity up to 40 tons per hour for this 1 x 2 meter screen.
A four deck Armstrong Vibratory Screen feeding the four screened fractions over a divided single deck vibratory screen.

A four deck Armstrong Vibratory Screen driven by two 0.5kw vibratory motors. Capacity up to 40 tons per hour for this 1 x 2 meter screen.

The patented Armstrong vibratory screens are low powered, light weight efficient and have the following advantages when compared with conventional screens:

1.low power consumption – 10 to 20 % of the weight and the 10 to 20 % power requirements as compared to conventional screens.
2.the screening efficiency, using woven wire screen panels, is 60% more efficient than using polydeck panels.
3.the open spaces on woven wire screens are up to 40% more than the equivalent poly-deck screens.
4.the screens are compact, of low profile and can be accomodated into smaller spaces than conventional screens which make them ideal for installing in shipping containers where space is at a premium.
5.the screen frames and screens are easy to replace, simply undo the eight retaining bolts and remove the complete screen in an upward or downward direction.
6.it is quick and easy to replace the woven wire screen panels.
7.the screens have minimum pegging and are easy to clean and maintain.
8.the screen frames and frame bodies are factory produced on accurate jigs so as to be interchangeable.
9.the screens with their side mounted motors are easy to cover for security reasons or to protect the product against the weather.
10.the screen height and angle of operation is easily adjustable.
11.the screens can be produced as multi deck units.

Safety and Security aspects of Newly Developed Pipe Conveyors

 

1. The conveyor belt runs inside the pipe in both forward and reverse directions and belt on belt and belt on pipe friction is only a minimal consideration.The increased power require- ments are only fractionally higher than for conventional conveyors per tonnage conveyed.
   
2. The conveyor is stable in windy conditions as there is no external return belt and idler pulleys to create wind resistance, conveyor belt flapping, vibrations and conveyor instability. There is no external return belt to get wet when it rains which can result in wetting of dry material being conveyed.
   
3. The complete conveyor belt is quickly installed by pulling a continuous, accurately factory spliced belt through the pipe by hand or using the motorized drive pulley. Removal of the conveyor belt is done in the same way. There is therefore no necessity to join the belt into the conveyor system as with conventional conveyors and complete spare belts can be kept on site. In the case of the food or chemical industries PVC belts are considered a better option than rubber belts as they can be pulled into the pipes by hand and require less power to operate. Down time is therefore minimized during belt replacement.
   
4. The conveyors are supplied in three, six or twelve meter flanged lengths and are easy to assemble and dismantle into their component parts. The units are thus easy to containerize and transport.
   
5. The conveyors are completely safe and secure as they are supplied in completely enclosed units, hands off, eyes off units. This is of particular importance in the diamond industry or where other materials of high value are being conveyed. The conveyors are spillage free provided suitable feeder control systems are used.
   
6. The conveyors can be supplied in pipe diameters of 100 to 500mm and in lengths of up to 30 meters and can operate at angles up to 22° depending on the material being conveyed and the belt speed employed.
   
7. Pipe diameters up to 500mm have been tested up to tonnages of 130 tons per hour for alluvial gravels. Tonnages of 0.5 tons to 80 tons an hour are easily achievable for pipe diameters of 100 to 400mm in diameter for pipe conveyor lengths of up to 30 meters. The individual conveyors can be interlinked (piggy-backed) to form a continuous unit. The interlinked pipe conveyor system has the advantage that similar belt lengths can be used for each interlinked conveyor and where a belt has to be replaced it involves only one of the conveyor sections and not the belt for the entire conveyor system.
   
8. The pipe conveyors can be installed in situations where there are space restrictions and where conventional conveyors cannot be accommodated.
   
9. Pipe conveyors can be supplied as half pipes where an incorporated top walkway is required or where severe space restriction is a factor. These half pipe conveyors come at an additional cost and should only be considered where necessary.
   

Armstrong Screen and Pipe Dryers

As it is advisable to feed the V.E. Machines with dry or damp material but not with material which is completely wet, both the screens and the pipe conveyors have been adapted to serve as material driers. In the case of the screens, 4 to 8 air fans are attached to the screen security cover and as the material passes over the screen the air blows any excess water through the screen and proceeds to dry the material. In the case of the pipe conveyors, two fans are fitted to the pipe. The first fan blows air into the pipe and the second pipe extracts the moist air together with any dust which may be generated during the drying process. With suitable fans an air speed of 40 km per hour can be generated through the pipe. Rubber deflectors are installed at suitable intervals along the pipe to deflect the material and enhance drying in rainy, humid or cold conditions. The pipe conveyor can be fed with hot air from a generator's exhaust through a suitable heat exchanger. This will considerably enhance the drying under adverse conditions.

Armstrong Grease Tables

Plate 1

Plate 11

Plate 111

Models

Mark II
This unit consists of a grease screen divided into 2 or 3 channels depending on the gravel fractions treated and the double or triple overlying screen employed. The screen has an overlying scrubber and a feeder bin. Underlying the grease screen screen is a water tank, a water heating system and a sand filter to keep the spray water clean and at the correct operating temperature of 20 to 24 degrees C. An electrical box housing the electrical operating system is supplied with the unit. All parts to be galvanized and painted and all fittings to be of stainless steel. An electrical box housing the electrical operating system is supplied with the unit.

The grease screen consists of a stainless steel screen pulled drum tight between a heavy duty rectangular tubing frame with underlying square tubing supports. The diamond grease is applied with a spatula in two strips from the underneath the screen and protrudes 1 to 2mm above the screen. This system allows for minimal grease removal when removing diamonds or when renewing the grease. Simply scrape the grease off the top of the screen and force a new layer up from underneath the screen.

See Plate 1

Mark III This unit is the same as for the Mark II but incorporates a built in triple deck vibratory screen to classify the gravel into three different size fractions after scrubbing. These fractions are fed similtaneously over the grease screen which is split lengthwise to accommodate the three separate size fractions.

Each of the above units are designed to be transported on the back of a SUV. The operative capacity of these units is 0.3 to 0.6 tons of concentrate per hour.

See Plate II

Mark IV This is a larger capacity unit which can handle up to 3 tons of concentrate per hour. It is equipped with a 4 deck vibratory screen to supply 4 separate size fractions to the grease screen which is split into 4 channels. It is equipped with a larger scrubber than the Mark II and Mark III units but has all the facilities of these units.

See Plate 111 excluding the scrubber

All units are assembled with plated high tensile bolts and nuts and all components are powdercoated to the customer's colour requirements.

Any of the units can be fitted into an insulated, airconditioned 20ft shipping container with landing legs if required at an extra cost.

Completely enclosed pipe conveyors can be supplied at an extra cost as follows:

6 metre  200mm φ    1.50kw

6 metre  150mm φ    0.75kw

12 metre 200mm φ   1.50kw

12 metre 200mm φ   0.75kw

Kw power requirements are minimal for the various units and are as follows:

Mark I   4.90kw

Mark III 5.08kw

Mark IV 7.64kw

All units are supplied ex works.

An optional extra is to have the equipment built into a shipping container.

Conditions of payment are 50% deposit on placement of order and 50% on collection from our factory premises.

Packaging, transport, field installation and commissioning is for the customer's account unless otherwise arranged.

Factory training can be provided if required.

DIAMOND RECOVERY CRITERIA

For efficient diamond recovery over grease the following factors are essential:

1. The feed concentrate must be scrubbed efficiently to remove any coating on the diamond which may cause it to become non hydrophobic (this coating may be discernibly molecular or atomic by degree).
2. The concentrate must be efficiently screened into size ranges namely 1-2mm, 2-4mm, 4-8mm, 8-16mm and 16-32mm and passed over the grease in individual size ranges. Non compliance will result in larger non diamond wettable material dislodging smaller non wettable (hydrophobic) diamonds after they have stuck to the grease.
3. Screening and scrubbing of the feed concentrate should take place immediately prior to the feed concentrate being passed over the grease table. Retaining the above material in holding bins for any length of time prior to the grease recovery can result in the build up of coatings on the diamonds (at a molecular or atomic level) which could jeopardise the hydrophobic nature of the diamonds.
4. The scrubbed water must be removed after scrubbing and the concentrate washed with clean water before being passed over the grease table.
5. The water used on the grease table must be kept clean and of good quality otherwise minute particle build up on the grease surface may cause the grease to become ineffective. An efficient filtration system can be employed where water scarcity is a problem.
6. The grease table processing water must be kept at an operational temperature of between 20-24°C. At temperature below 18°C definite diamond loss will occur. At temperatures above 26°C gunge material will start sticking to the grease.
7. The material feed must be kept wet at all times as any dry material will immediately stick to the grease and clog the grease screen.

As you can see from the Gondwanaland Diamonds website we at present manufacture 3 different models.

Mark I
Here criteria 5, 6 and 7 are met for efficient grease diamond recovery.

Mark II
Here criteria 1, 5, 6 and 7 are met for efficient grease diamond recovery.

Mark III
Here all criteria 1 to 7 are met for efficient grease diamond recovery.

Mark IV
This is a larger capacity version of model Mark III.

---

Optional extras

1. A transparent removable glove box is built in between the multi deck screen and the grease table to make the diamond recovery operation more secure.
2. A camera is mounted inside the glove box for remote monitoring of the diamond recovery operation.
3. A grease recovery and diamond cleaning system operating within the glove box.
4. Suitable pipe conveyors for feeding and extracting material from the grease recovery units.

The prices of the above are dependent on customer requirements and are available on request.

The model most suitable will depend on your customer's facilities to efficiently feed the machine, to screen the material into the required sizes for treatment, etc as set out in requirement 1 to 7 for efficient grease recovery.
Whatever facilities your customer has in place will determine the model most suitable. If your customer has none of these, our recommendation would be model Mark III together with any optional extras he may choose.

Grease Table

GENERAL

The Armstrong Grease Table is a relatively light weight, large capacity machine with a large water recovery and temperature control system.

REQUIREMENTS

For efficient grease recovery the following factors must be adhered to:

1. Only good quality grease must be used. Diamond test the grease before regular use.

2. The spray water and the grease must be of the right temperature (22-24°C)

3. The spray water must be clean and contain less than 100ppm solids.

4. The spray water must contain less than 10ppm combined Na and Mg.

5. The material fed over the grease screen must be correctly sized i.e. 1-2mm, 2-4mm, 4-8mm, 8-16mm, 16-32mm fractions or smaller. This is so that the largest non-diamond particles in the size fraction will not dislodge the smaller diamonds. Larger non diamond particles will also force smaller non diamond particles into the grease if the variation in particle size is too great.

TECHNICAL DETAILS

The grease screen consists of a 1.5mm stainless steel mesh screen tightly suspended between an outer steel frame. The two vibratory motors are fitted to the sides of the frame which allows the water from the spray bars to pass directly into the underlying water tank for re-circulation. The water tank is fitted with baffles to allow for sedimentation and should be cleaned at regular intervals to prevent the build up of solids in the water. The water tank is fitted with a heater element and thermostat to control the water temperature to within the required limits.

OPERATIONAL DETAILS

Grease is applied with a spatula from underneath the screen through the screen cloth between the screen bottom transverse support bars in segments 2 and 4. Sufficient grease is forced through the screen so that the grease protrudes to 1-3mm above the screen. The grease is then smoothed over the surface as required to form a thin layer of grease on top of the screen. This thin grease layer together with any diamonds is easily removed with a spatula to leave a clean remaining layer of grease on the screen surface. Further grease is then forced up through the screen cloth using a spatula to form a new clean layer of grease 1-3mm thick as described above.

'New diamond prospective area in Greenland

A test run with part of the modular plant: a high capacity, vibrating grease table, developed for Avannaa by Gondwanaland Diamonds, South Africa. Courtesy: Avannaa Resources

Avannaa Resources Ltd, operating in Greenland via its fully owned subsidiary Avannaa Exploration Ltd, reports 18 February 2008 (Nicholas Rose, CEO) that it has diamond- tested a dyke in the vicinity of Ataa Sund, central West Greenland, within its licence area no. 2007/52. The 39 kg sample was analysed for its diamond content by SGS Lakefield, Canada, and yielded 102 diamonds with a total weight of 0.013 carat. One stone can be characterized as a macrodiamond with dimensions of 0.83 x 0.66 x 0.53mm, translucent and white with graphite inclusions, while the remaining 101 stones all are microdiamonds. In terms of colour, 95 stones are white and 7 are off white, and in terms of clarity, 62 stones are transparent and 60 translucent. The majority of the stones (76) are crystal fragments suggesting a high probability that larger stones are present. The discovery significantly extends the regional extent of diamond-prospective bedrock in West Greenland, which has primarily focused on the Maniitsoq - Sarfartoq belt 300 kilometers to the south of the Ataa region.

Avannaa will follow up on this discovery in 2008 by bulk sampling the diamondiferous dyke itself and by detailed evaluation of an alluvial diamond target also within its 2007/52 licence area including sampling of up to 500 tonnes of channel facies sands and gravels of the Atane Formation on eastern Disko. The company will also be prospecting for other dykes and plugs of kimberlitic affinity in the Ataa Sund region, where Avannaa has applied for an exploration licence via a newly formed subsidiary Avannaa Diamonds Ltd. The company's other activities in 2008 are targeted at gold and nickel in several existing and new licences in West Greenland. To process sands and gravels on its alluvial diamond project, Avannaa has acquired a light modular plant specially designed for the Atane Formation sediments by Gekko Systems, Australia. This includes a 2 ton/hr in-line pressure jig (IPJ600) equipped with a 5 ton/hr feed trommel and concentrate sorting screens. A high capacity vibrating grease table, with a pre-cleaning scrubber, designed for Avannaa by Gondwanaland Diamonds (South Africa), will make a final processing of the concentrate before delivery to SGS Lakefield for diamond identification and characterisation. The combined processing plant will allow recovery of 0.6 to 12 mm diameter diamonds.'
Copied from MINEX No. 32 - February 2008

Gondwanaland Diamonds

GAVIN ARMSTRONG

The Armstrong vibratory screen system cuts conventional system's power usage.



Gavin Armstrong MD of
Gondwanaland Diamonds

MATERIALS HANDLING

'Vibratory screen system cuts conventional system's electricity usage

By: Leandi Rostoll

Published: 10 Apr 08 - 8:57 in Mining Weekly

Plant, equipment and accessory manufacturer Gondwanaland Diamonds South Africa MD Gavin Armstrong said this week that the company had developed a vibratory screen that could cut conventional screen systems' electricity usage by up to a quarter of the electricity.

The system was developed to be a cost and space effective option, he said in an interview with Mining Weekly.

The Armstrong screens were lighter than conventional screens, had a low profile and could be placed in confined spaces.

The Armstrong conveyor belt, which transports the raw materials to the vibratory screen, was a new concept that completely runs in a pipe protecting the belt and the material transported on the belt from natures elements, he said.

"The belt is easy to replace. By just removing the pulley, the belt can be removed and replaced within ten minutes."

The Armstrong vibratory screen and conveyor belt has been in production for three years and have been used in the diamond mining industry, but can be adapted for other mining industries as well.'
Reproduced here with the permission of Creamer Media's Mining Weekly online

Armstrong Vibratory Screen

The Armstrong vibratory screen, patents 2003/4539 and 2004/9572, consists of a heavy duty 25x75mm rectangular frame to accommodate a standard 2300x920mm woven wire screen. The screen is attached to a square tubing blocked out frame by means of posi-drive screws and rubber-lined metal washers. The vibratory motors are attached to the sides of the screens for maximum screening efficiency and to allow easy fitting of security covers or a cover carrying a number of air fans which converts the screening arrangement into an effective drying screen, with minimum power requirements. The screen can be easily converted into a double or multi deck screen by adding additional decks and larger vibratory motors. This screening system has the following advantages over conventional screens:

1. The screening efficiency is ±60% greater than for poly-deck screens of equivalent size and aperture.

2. The open spaces on the woven wire screens are up to 40% more than that for equivalent poly-deck screens.

3. The screen weight is less than one third that of poly-deck screens of equivalent surface screening area.

4. The power to drive the screen is less than a quarter required for driving the conventional poly-deck screen of the equivalent surface screening area.

5. The screen is compact, of low profile and can be accommodated into smaller spaces than conventional screens which make for ideal use in shipping containers where space is at a premium.

6. The screen is easy to replace, simply undo eight retaining bolts and remove the frame holding the screen in an upward or downward direction. Clean or replace the screen cloth and refit the frame or fit a frame with a new screen mesh. The screen frames and frame bodies are factory produced on accurate jigs so as to be interchangeable.

7. The screens with their side mounted motors are easy to cover for security reasons.

Vibratory Screens

Pipe Conveyors continued

7	The uniform nature of the spliced belt allows for a segmented spring loaded scraper to be used for a belt running on a straight or crowned pulley, copyright. This scraper is highly effective.
8	The conveyor system can be supplied in multiple flanged lengths of 6 or 12 meters and of various pipe diameters and motor sizes.
9	The conveyor system is easily transported and installed. 3 x 12 meter conveyors can be transported on a trailer setup using the conveyors as the trailer chassis and using a 4 wheel SUV or small truck. http://www.gondwanalanddiamonds.com/conveyors.htm

Pipe Conveyors

Armstrong Pipe Conveyor and Belt Scraper

From practical experience over the past three years while developing and operating a diamond recovery plant, the following pipe conveyor system, Patents 2002/00644 and 2006/3646 have been developed.

The entire conveyor belt both in the forward and reverse or return direction is arranged to run within the conveyor pipe. With this system the following advantages over conventional conveyors are achieved.

1	No guide rollers are required to support the belt as the belt is supported within the pipe. This results in the conveyor being more stable in windy conditions as there is no external return belt to create wind resistance, conveyor instability and vibration.
2	There is no appreciable increase in power required to drive this conveyor even when under load.
3	The complete rubber belt is installed by pulling an accurately hot-spliced complete belt into the pipe by using the motorized drive pulley. Removal of the belt is done in the same way. There is therefore no necessity to join the belt into the conveyor system as previously required. A PVC belt can be used which can be installed and removed by hand.
4	No conveyor belt guide pulleys are required except for the entry and exit guide pulleys which keep the belt clear of the pipe ends. The pipe takes over the function of any guide pulley assemblies.
5	The cradles on both the drive and idler pulleys are both easily adjustable with additional fine adjustment on the idler pulley. Once the belt is adjusted to run in the center very little if any adjustment is required.
6	Where conveyor belts are joined on site an attachment is available to grind the splice to the exact thickness of the belt patent 2006/3646. Conveyors

Gondwanaland Diamonds

Gondwanaland Diamonds is a developer and manufacturer of diamond prospecting and recovery equipment and diamond polishing equipment such as precision ground scaives and polishing benches. We build mobile diamond recovery plant and related equipment, such as vibratory screens, driers, pipe conveyors and belt scrapers. The manufacture of portable jigs and milling and screening units for use in the diamond prospecting industry will be continued. Details of the above mentioned plant and equipment presently being manufactured appear here.