Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.) Technical Chapter 11: Other special techniques 11.1 Welding additives 11.2 Rubber tanks, flexible tanks 11.3 BY-Pass oil filters, by-pass micro-filters 11.4 Eccentric motor, vibrator, shaker

Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)

Technical Chapter 11: Other special techniques

11.1 Welding additives

Mine Workshop
Surface Mining Special Techniques

engl.:	protection against wear, wear-resistant materials
germ.:	Schweißzusatzwerkstoffe, Verscheißschutz, Panzerungswerkstoffe
span.:	materiales pare soldadura, proteccion contra desgaste, material de blindaje
Manufacturer:	Vautid

TECHNICAL DATA:
Dimensions:	for electric manual welding, cast or pressed round electrode rods, 2.5 - 8 mm, 350 - 450 mm in length
Power required:	90 - 320 A ave. current strength, whereby amperage increases with the diameter of the electrodes
Form of Driving Energy:	electric
ECONOMIC DATA:
Investment Costs:	electrode rods: approx. 20 - 60 DM/kg

CONDITIONS OF APPLICATION:

Operating Expenditures:	low |————|————| high
Maintenance Expenditures:	low |————|————| high
Personnel Requirements:	good welding skills required
Location Requirements:	power supply must be available
Regional Distribution:	worldwide in industrialized countries
Operating Experience:	very good |————|————| bad
Environmental Impact:	low |————|————| very high
Suitability for Local Production:	very good |————|————| bad
Lifespan of wear-resistant tools:	very long |————|————| very short
	this technique is applied to extend lifespan

Bibliography, Source: Vautid-Company information

OPERATING PRINCIPLE:

Available forms of welding materials are standard electrodes, filling wires, continuous cast rods and injecting powder. Various demands upon materials, such as abrasion by hard minerals or cavitation, impact or compressive stresses, temperature extremes caused by high ambient heat or friction, or corrosion by aggressive media can be counteracted by means of coating with the electrode material. Depending upon the requirements, alloys of Fe, Cr, Mn, Ni, W, V, Mo, Nb with Si, B, and C are applied.

AREAS OF APPLICATION:

Electrodes, for example against abrasion, contain in addition to other alloy elements, high proportions of chromium and carbon which form extremely hard chromium carbide during welding. They are used to increase resistance to abrasion of machine parts subject to wear in mining, beneficiation and energy production.

For mining equipment:	shovel bucket teeth, rail parts, pump blades, sand pump impellers, drilling and cutting tools
For beneficiation equipment:	crusher jaws, crusher rollers, crusher cones, grinder linings, linings in Chilean (edge) mills, chutes, cyclone linings, pump blades, agitators (stirrers) in flotation cells
For motors and engines:	turbine blades

REMARKS:

The coating of machinery parts with wear-resistant welding materials is, of course, work intensive, but extremely effective and especially important in developing countries, where it can substantially improve the quality of locally-produced machinery components for use in the mining industry. Low labor costs in developing countries enable this work-intensive solution to remain economical. A further significant advantage of this hand coating method lies In the fact that even complicated structures such as pump blades, etc., can be treated.

Depending on the electrode material, the goal is to achieve Vickers hardness values HV 10 from 230 - 2000, corresponding to Rockwell HRC values from 19 to about 70.

Welding materials can be used to coat the following materials:

- non-alloyed steel and cast-steel (magnetic, soft: test with magnet and file)

- alloy steel and steel with up to over 0.5 % C (magnetic, hard) after preheating at approx. 300 - 500° C

- manganese steel (non magnetic, hard), welded cold in water bath

- cast iron (magnetic, soft) possibly when thoroughly preheated (approx. 500°C)

- hard cast iron (magnetic, hard) should not be coated due to danger of cracking.

The electric current should not be too strong and welding should not be too slow in order to prevent too much mixing between the welding material and the melted base material which results in a reduction in hardness.

The maximum thickness of the coating depends upon the welding materials and ranges from 5 to 20 mm; greater thickness is achieved through multiple layers of thinner coatings.

Larger surface areas are sometimes reinforced only with individually welded beads or buttons.

During the hardening process, cracks develop in the coating materials which lower the stress and, as a rule, do not extend to the basic material underneath.

A reworking of wear-resistant parts is usually only possible with SiC or corundum grinding wheels.

For large planar surfaces, pre-fabricated hardened compound plates, special threaded fittings, etc., are available on the market.

Armored and wear-resistant elements made of rubber can be recommended for various purposes, particularly when slow moving parts are exposed to abrasive materials (slurry) such as in spiral separation.

SUITABILITY FOR SMALL-SCALE MINING:

Wear-resistant materials are highly suitable and effective in greatly increasing the lifespan of locally-manufactured equipment and machine parts, and in reducing the frequency of maintenance and repairs.

11.2 Rubber tanks, flexible tanks

Surface Facilities General
Surface Mining Special Techniques

germ.:	Gummitanks, flexible Tanks
span.:	tanques de goma, cistern as flexopleglables, tanques flexibles
Manufacturer:	Arcotex, Continental

TECHNICAL DATA:
Dimensions:
from 700 1	over 10.000 1	up to 40.000 1	up to 100.000 1
2.00 × 1.25 m	4.80 × 3.20 m	8.5 × 5.30 m	10.1 × 10.5 × 1.3m
Weight:
12 kg	54 kg	130 kg	338 kg
Extent of Mechanization:	not mechanized
Form of Driving Energy:	not powered
ECONOMIC DATA:
Investment Costs:	5,000 I tank approx. 2000 US$ FOB Santiago de Chile

CONDITIONS OF APPLICATION:

Operating Expenditures:	low |————|————| high
Maintenance Expenditures:	low |————|————| high
Location Requirements:	due to their flexibility and collapsibility, empty tanks can also be transported through small doors in buildings or into the mine.
Replaces other Equipment:	brick tanks, tank-cars
Environmental Impact:	low |————|————| very high
Suitability for Local Production:	very |————|————| goodbad
Lifespan:	very long |————|————| very short

Bibliography, Source: Arcotex Company information, Continental Company information

OPERATING PRINCIPLE:

The flexible tanks have an interior lining which inhibits splashing of the fluid content, enabling transport by truck to meet supply requirements for mine water, gasoline, diesel, chemical fluids, etc. The collapsed empty tanks require very little space (less than 5% that of full tanks), allowing the trucks to be used for product and material transport on the return trip.

AREAS OF APPLICATION:

Transporting of fluids for mining, agriculture and industry.

SPECIAL AREAS OF APPLICATION:

Permanent stationary tanks.

REMARKS:

The tanks are filled without pressure, eliminating any need for filling pumps or similar equipment.

The tanks are made of a very strong nylon material which is coated on both sides with black synthetic rubber. The individual sections are joined by heat-cured (vulcanized) seams. To improve safety, additional nylon tarps are placed underneath the tank.

Flexible tanks are available on the market for the following fluids:

drinking water
gasoline, diesel and other common fuels
vegetable and mineral oils
hydraulic fluids and lubricants
waste water, salt water
alcohols
ethylene and various derivatives
leaches and acids up to medium concentration
formaldehyde, formamide, glucose, glycol, glycerin
carbon dioxide, corrosion-preventives, glue, soap buck, various inorganic salts and their leachates, etc.

The tanks are resistant to ageing and to reactions with the fluid content within a temperature range of -30° to + 70° C.

SUITABILITY FOR SMALL-SCALE MINING:

Flexible tanks are especially attractive as mobile tanks for the combined truck transport of fuels (to the mine) and of raw materials (from the mine). They are also suitable for short term application as stationary tanks.

11.3 BY-Pass oil filters, by-pass micro-filters

Open-Pit Mining General Surface and Under ground Vehicles
Surface Mining Special Techniques

germ.:	Bypass-Olfiiter, Nebenstrom-Feinstfilter
span.:	filtro de aceite-bypass, microfiltro secundario
Manufacturer:	Kleenoil

TECHNICAL DATA:
Dimensions:	0.15 m H, 0.15 - 0.25 m 0
Weight:	approx. 2.5 kg
Form of Driving Energy:	driven by oil pump pressure
Alternative forms:	for stationary systems, additional external manual pump
Throughput/Capacity:	approx. 100 I/h
ECONOMIC DATA:
Investment Costs:	approx. 640 DM without delivery and installation
Operating Costs:	approx. 40 DM per filter element

CONDITIONS OF APPLICATION:

Operating Expenditures:	low |————|————| high
Maintenance Expenditures:	low |————|————| high
Personnel Requirements:	periodic changing of filter
Replaces other Equipment:	recycling of lubricating oil can drastically reduce mining equipment oil consumption, and especially minimizes of used-oil disposal problems
Regional Distribution:	in industrialized countries
Operating Experience:	very |————|————| good bad
Environmental Impact:	low |————|————| very high
	technique is environmentally advantageous
Suitability for Local Production:	very good |————|————| bad
Under What Conditions:	good metal workshop, filter candles can be made from suitable types of toilet-paper rolls
Lifespan:	very long |————|————| very short

Bibliography, Source: Kleenoil information

OPERATING PRINCIPLE:

A microfilter functions by pressing oil through a filter cartridge which removes:

- particles > 1 ym (common oil filters separate above 5 ym), and
- water (for example, condensed water from combustion) down to < 0.05 %.

This results in greatly reducing the abrasiveness of the oil, and substantially inhibits the development of acids from contact between the condensed water and combustion gases. The filter cartridges are made of tightly wound, long fibrous conifer-wood cellulose, held togother by a cotton sleeve.

AREAS OF APPLICATION:

Applicable either as by-pass filters in secondary oil circuits or as stationary microfilter systems.

In secondary oil circuits in engines, they can be installed, for example, on the pressure (delivery) side at the oil-pressure sensor using a tee-piece, or on the return side at the oil pan. The advantage of this installation is that the oil-change Interval no longer needs to be observed, with only an occasional change of filter cartridge being required.

Employed as stationary microfilters, the oil is pumped from the engine's oil pan during periods of non-operation (engine off) through a microfilter unit.

REMARKS:

Following longer periods of operation between oil changes, the oil normally contains up to 4-5 % impurities. With the use of filter cartridges, these impurities are already partially removed during engine operation, so that the time interval between oil changes (i.e. oil lifespan) can be increased ten to fifteen-fold.

90 % of machine wear is caused by acids which develop when acidic by-products combine with water in the oil.

The crucial problems of waste-oil disposal can be largely minimized through application of such filters, which reduce the volume of used oil to around 10 %.

Stationary filter types can also be used for cleaning of hydraulic oil.

Used filter cartridges can be burned, during which the production of smoke is minimal due to the high proportion of vegetable fibers contained in the filters.

SUITABILITY FOR SMALL-SCALE MINING:

Fine oil filters, either as stationary or by-pass filters, can help solve the disposal problems associated with used oil by substantially extending the lifespan of lubricants.

Fig.: Operating principle of a by-pass oil filter in secondary oil circuit. Source: Kleenoil Company information.

11.4 Eccentric motor, vibrator, shaker

Open-Pit Mining Mine Workshop
Surface Mining Special Techniques

germ.:	Unwuchtmotoren, Ruttler
span.:	motores con contrapeso, vibrador
Manufacturer:	Bosch, Italvibras, Netter, Schenck, AEG, Jost

TECHNICAL DATA:
Dimensions:	depends on type and capacity, from 5 × 5 × 5 cm to 8 × 8 × 65 cm
Weight:	approx. 100 g to more than 100 kg
Extent of Mechanization:	fully mechanized
Power required:	electric alternating-current vibrator: 0.03 - 11 kW; electric direct-current vibrator 0.2 kW (12V)
Form of Driving Energy:	electric with direct and alternating current
Alternative forms:	pneumatic
Technical Efficiency:	vibration frequencies:		depending on form of drive electric
	low frequency,	900 - 3000 min-1
	high frequency	6000 - 12.000 min-1
	mechanical	600 - 35.000 min-1
	centrifugal force:	pneumatic vibrator	10 N - 70 kW
		electric vibrator	40 N - 120 kW
ECONOMIC DATA:
Investment Costs:	350 to 400 DM for 12 V - external vibrator

CONDITIONS OF APPLICATION:

Operating Expenditures:	low |————|————| high
Maintenance Expenditures:	low |————|————| high
Equipment which can be driven:	conveying chutes, delivery (feed) chutes, discharging chutes, proportioning chutes, vibrating screens, vibrating sorting units, drainage systems
Regional Distribution:	vibrating devices are being increasingly employed in conveying, sorting, feed-proportioning and drainage equipment.
Operating Experience:	very good |————|————| bad
Environmental Impact:	low |————|————| very high
	low noise pollution and possible resonance vibrations
Suitability for Local Production:	very good |————|————| bad
Lifespan:	very long |————|————| very short

Bibliography. Source: Company Information

OPERATING PRINCIPLE:

For use as vibrators or shakers, motors are equipped with unbalanced rotating weights which can be adjusted In order to vary the centrifugal force. An alternative system is the pneumatic piston vibrator, which is characterized by its high adjustability of vibrational frequency and amplitude. Shakers and vibrators can be used as external vibrators mounted to the machine exterior, or as internal vibrators shaking the material directly inside the machine.

AREAS OF APPLICATION:

For loosening or jarring, the vibratory motion reduces the friction forces or breaks down the adhesive attraction, causing the material to loosen and attain flow-like properties. For conveyance, the flow of material can be maintained with the help of vibrations inducing minute forward-advancing movements.

For compressing or compacting, an artificial "flow" of the material, similar to that produced for loosening or jarring, is induced by vibrating whereby the material particles are deposited as densely as possible and the volume of air or water pores is minimized.

REMARKS:

Through the use of an eccentric motor, the machine is shaken by rotational vibration forces. The use of two counter-rotating eccentric motors of identical frequencies produces a resonance due to linear vibration (see diagram below).

Fig.: Operating principle of a single centrifugal vibrator (Fig.1); two counter-roatating eccentric motors (Fig.2); and a linear vibration system with foundation determining the direction of vibration (Fig.3).

Vibrators should always be fixed at the most rigid (reinforced) part of a machine to allow optimal transmission of imposed vibration. In the event that no reinforcements exist, they must be added to the construction in the area where the shaker is to be attached.

When the entire machine is subject to a low-frequency vibrating, it should be mounted, depending on the weight, on rubber. metal fixtures, screws or leaf springs.

The following approximation formula can be used to obtain a rough advance estimate of the dimensions for vibrators based on their centrifugal force:

Centrifugal force = (3 to 5) × (weight of the machine to be vibrated + 0.2 × weight of material to be vibrated)

Additionally, the following rough calculation can also be used (by Italvibras):

centrifugal force = amplitude of vibration × total weight of system to be shaken × ( rpm)² / 900.000

with centrifugal force:	kg	weight: kg
work moment:	kg mm	amplitude: mm
rpm:	min-1

Low-voltage direct-current shakers permit operation with energy supplied from solar cells.

SUITABILITY FOR SMALL-SCALE MINING:

Imported vibrators and shakers, incorporated into locally-manufactured mining and beneficiation machines with high "local content", can increase both the efficiency and technical quality of such equipment. In beneficiation machines, for example, vibrators increase the selectivity of the sorting processes.

Selection of the required frequency range is facilitated by the following table according to Bosch company information
	Areas of Application and Vibration Frequency/min.
PROCESSES AND MATERIALS:	normal frequency			high frequency (HF) + compressed air
	1000	1500	30000	6000	12.000
COMPRESSING/ COMPACTING of light, normal, and heavy concrete			forms + casings for pre-poured concrete parts, vibrating tables, vibrating frames, battery casings, in-situ-concrete casings, slip form paver, stone forming machines
of bulk materials of all kinds, molding sand, graphite, powdered quarzite, food stuffs		foundry machinery, packing machinery furnace lining, production of electrodes,
LOOSING of bulk materials, e.g. sand, lime, cement, coal, grain, etc.		emptying of silos, bunkers, containers, casting boxes, forms, settling grids
CLEANING		filter equipment, amongst others
CONVEYING of bulk materials, such as sand, gravel, crushed stone, granulates, concrete; of piece goods, such as castings, packages, chips/cuttings	conveyor chutes, discharge chutes, conveying pipes, ducts, vibrating chutes, spiral conveyors
SCREENING dewatering	vibrating (jigging) screen, classifying (sizer) screens, dewatering screening through ceramic sieve