PRIMARY APPLICATIONS
Rock characteristics
According to French standards : - abrasion index less than 250 g/t - crushability more than 35%
- dynamic fragmentation more than 20%
- compressive strength less than 1 800kg/cm2 (test done with cylinder of rock 40 mm diameter and 80 mm high).
According to US standards :
- paddle abrasion index less than 0.0240 g - Los Angeles abrasion index more than 20 % - average impact work index less than 16
maximum impact work index less than 23.
Main kinds of rock : Limestones, dolomitic limestone, gypsum, talc, chalk, marbles, marl, schists, slates
Hammer materials in primary applications . Manganese steel
The property of this alloy is to be hardened superficially by the rock blows and to remain ductile in the heart.
This is the only kind of alloy enabling primary application use without breakage.
Hammer life duration is not easily predictable and of course the homogeneity of the quarry face (see life duration of wear parts) ; paddle abrasion index gives only an idea of what will be the wear parts life duration.
Results from sites shows that hammers can last 200 hours for abrasion index of 250 g/t (A.index. of 0.024 g) and up to more than 2 000 hours for not abrasive limestones. (See chart about estimation of hammer wear life).
. Other materials
In some application cases (i.e. with soft rocks, maximum feed size controlled to avoid too big blocks and no tramp iron,), it might be interesting to use martensitic steel or chrome iron hammers as far as life duration is concerned.
Chrome iron material is much more harder than manganese steel and then much more brittle.
This means that feed material must be well prepared and controlled as well as tramp iron otherwise breakages are bound to happen.
Martensitic steel material is in between manganese and chrome iron as far as ductility and hardness ; breakage might happen.
In case of abrasive material, it could be profitable, economically speaking and talking into account some breakages, to use such type of hammer material.
Improvement of life duration comparing to manganese:
1.2 to 1.5 times for martensitic steel 2 to 4 times for chrome iron
SECONDARY APPLICATIONS
Rock characteristics
According to French standards : - abrasion index less than 900 g/t - crushability more than 30%
- dynamic fragmentation more than 15%
According to US standards :
- paddle abrasion index less than 0.2100 g - Los Angeles abrasion index more than 15 % - average impact work index less than 20
maximum impact work index less than 26.
Horizontal shaft impactor has not to be used when more abrasive or tougher rock has to be processed.
Main kinds of rock : Same as for primary applications plus dolomite, some granites and basalts, sandstone, medium abrasive gravels and ores.
Hammer materials in secondary applications . Manganese steel
Used when paddle abrasion index is less than 250 g/t (A. index less than 0.024g.). Hammer duration life is from 200 hours up to more than 1 500 hours for not abrasive limestones.
. Chrome iron
When paddle abrasion index is more than 250 g/t, chrome iron hammers become necessary.
A secondary application top feed size allows the use of such material although a breakage might happen in case of tramp iron ; see performances chart for maximum top feed size when using chrome iron.
A protection by means of metal detector is necessary to prevent tramp iron to go through the machine.
Hammer life duration is from 150 hours up to more than 2 000 hours depending on rocks processed and on impactor working conditions.
IMPACTOR FEED
The quarry run is composed by 30% to 60% of rocks having half dimension of the maximum nominal size.
Bulk density is considered to be 1.6 g/cm3. Rule of thumb for quarry blocks:
- 3 dimensions represent the size of a bloc : thickness, the nominal size and length; thickness is about 0.6 times the nominal size and length is about 1.6 times the nominal size.
- See performances charts for weight of blocks and maximum top feed size.
MAXIMUM REDUCTION RATIO IN OPEN CIRCUIT
Refer to performances charts : the limit to get the final product size in open circuit is indicated.
MAXIMUM REDUCTION RATIO IN CLOSED CIRCUIT
Refer to performances charts :
In closed circuit, finer product size than indicated in the charts can be obtained but the recirculating load might be too large.
CAPACITIES IN OPEN AND CLOSED CIRCUITS
Refer to performances charts and average output curves.
N.B. a product size has 90% passing at the corresponding square opening.
POWER TO BE INSTALLED
Refer to performances charts : power mentioned is maximum power to install according to primary or secondary application.
ROTATION SPEED
Refer to performances charts.
ADJUSTMENT OF THE BREAKER PLATES
- Second breaker plate setting
To be adjusted to the nominal product size dimension.
- First breaker plate setting
Setting = (Top feed size + second breaker plate setting) / 4 + 20 mm.
- Example : top feed size : 1000 mm product size : minus 80 mm
Second breaker plate setting : 80 mm
First breaker plate setting : (100 + 80) / 4 + 20 = 290 mm.
- During commissioning
These above theoritical setiings have to be adjusted if required to get the final requested product.
HOW TO USE THE PERFORMANCES CHART
1- Choose the top feed size of the application.
2- Choose the final product size you want to get from the machine:
Several cases :
- You get directly the nominal product size in open circuit (OC), or you reach the impactor working limit in open circuit.
- You might want to get finer product then you have to use a closed circuit (CC) at an opening sieve equal to the nominal product size. In this case the output of the impactor will be the finer specified output you can get in open circuit.
Note:
Nominal size is with 90% passing at corresponding square opening; gradation curve will be found in the average output curves chart.
3- Capacities are basic capacities of the requested nominal product size obtained with the corresponding electrical power. For reduced outputs, the necessary power is proportional to the outputs reduction.
4- Rotation speed and tip hammer speed are indicated for each top feed size.