Monday, September 10, 2012

Wednesday, June 10, 2009

Pipe Conveyors

Our pipe conveyors are operated up to an angle of 27°. 10 Tons an hour is no problem to convey. The longest conveyor we have supplied to date is 30 meters to Janel Construction for conveying diamond concentrate.
We have had enquiries for a 60 meter long conveyor from Exxaro South Africa to convey heavy mineral sand and from Fluor Australia for a 60 meter long conveyor for Argyle Diamond mine in Australia. These are on hold because of the present world recession. It is possible to pigiback the conveyors to achieve any required length and variation in inclinations as illustrated in the photos.
Our conveyors are in the initial stages of development and operation. We have supplied to the following conveyors thus far and we use them ourselves:
ADP Projects– Cape Town
Batemans Minerals & Metals – Johannesburg
Letseng Diamond Mine        – Lesotho
Mothae Diamond Mine         – Lesotho
Janel Construction              - Johannesburg

Monday, September 15, 2008

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. 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.

Sunday, September 7, 2008

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.

Saturday, June 7, 2008

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.

Friday, May 2, 2008

Armstrong Grease Tables

Plate 1

Plate 11
Plate 111

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.


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.

Tuesday, April 29, 2008

Grease Table


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


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.


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.


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.