Long time no talk all. Well it didn t take long before i came across another tasty little problem for us to get stuck into. Here Goes:
I ve got a limestone that recently failed testing for rail ballast on pretty much all the criteria.
1. gradings FAIL
2. Particle lenght FAIL
3. micro Deval Fail, and finally,
4. LA coefficent Fail.
Ok somew history. The rock passed last year with a LA of 23 and Micro Deval of 9. Also gradings were fine and Particle lenght wasnt a factor. This year they have changed the spec from MD of 7 and LA of 24 to MD of 7 and LA of 20.
The results of the recent test were MD 8.5 and LA of 24 with the gradings failing due to to much in the large particle fractions and to little in the small particle fractions. Also the particle lenght required was failed miserable with a maximum
allowed 4 %, and a result of 21.
this particle lenght requirement mean s that 4% of the sample must be less than 100mm in any one lenght.
The ballast tested was processed as follows; 6 inch down crushed using a jaw crusher run through a hammer mill at 500rpms with no grid bars fitted. the resaon for running at this speed was to produce as much stone as possible and a little as possible of under size (minus 30mm)
The gradings problem arised out of this i suspect. the feed material 6inch down was extremely slabby material or elongated material and with the mill running at such a slow speed i suspect that a high percentage of material ran straight through the mill with out any contact. The combination of both these crushers produced the bad shape problem i suspect.
My question is is there enough scope with the particle shape and grading to allow me get the MD and LA values down to spec. I propose to use a large impactor as primary crusher to produce a 6 inch or larger material which should be alot more cubical compard to the produce from the jaw crusher. this material will then be run through the hammer mill with increase rotor speed 1000rpm approx further reducing particle size but not affecting particel shape.
I also have the possibility of using a second impactor instead of the hammer mill but id rather not and dont think it would make a hugh difference when the mill is run at a higher speed.
Rail Ballast problem!!
Long time no talk all. Well it didn t take long before i came across another tasty little problem for us to get stuck into. Here Goes:
I ve got a limestone that recently failed testing for rail ballast on pretty much all the criteria.
1. gradings FAIL
2. Particle lenght FAIL
3. micro Deval Fail, and finally,
4. LA coefficent Fail.
Ok somew history. The rock passed last year with a LA of 23 and Micro Deval of 9. Also gradings were fine and Particle lenght wasnt a factor. This year they have changed the spec from MD of 7 and LA of 24 to MD of 7 and LA of 20.
The results of the recent test were MD 8.5 and LA of 24 with the gradings failing due to to much in the large particle fractions and to little in the small particle fractions. Also the particle lenght required was failed miserable with a maximum
allowed 4 %, and a result of 21.
this particle lenght requirement mean s that 4% of the sample must be less than 100mm in any one lenght.
The ballast tested was processed as follows; 6 inch down crushed using a jaw crusher run through a hammer mill at 500rpms with no grid bars fitted. the resaon for running at this speed was to produce as much stone as possible and a little as possible of under size (minus 30mm)
The gradings problem arised out of this i suspect. the feed material 6inch down was extremely slabby material or elongated material and with the mill running at such a slow speed i suspect that a high percentage of material ran straight through the mill with out any contact. The combination of both these crushers produced the bad shape problem i suspect.
My question is is there enough scope with the particle shape and grading to allow me get the MD and LA values down to spec. I propose to use a large impactor as primary crusher to produce a 6 inch or larger material which should be alot more cubical compard to the produce from the jaw crusher. this material will then be run through the hammer mill with increase rotor speed 1000rpm approx further reducing particle size but not affecting particel shape.
I also have the possibility of using a second impactor instead of the hammer mill but id rather not and dont think it would make a hugh difference when the mill is run at a higher speed.
Your help would be greatly appreciated on this.
Trev. ■