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Operational Requirements of Cemented Carbide Roll Rings |
| Author : Date : 2011-8-20 17:52:20 |
Operational Requirements of Cemented Carbide Roll Rings
Cemented carbide roll ring is a kind of tool material which consists of tungsten carbide and cobalt with high hardness and wear resistance.To take advantage of high wear resistance ,long life and high efficiency of cemented carbide roll rings durring the high speed rolling ,attention should be paid as follows when purchasing and using cemented carbide roll rings .
1)Grade selection
An overall understanding of the properties of cemented carbide grades is a basis for correctly selecting the grades for roll rings used in the stands of rolling mills and an optimal combination of grades is required for the various stands of rolling mills .
2)Roll rings installation
Sleeve mounting and assembly of roll rings should be strictly performed according to the precision required by the design process .Proper fitting is needed for the roll rings,roll mandrel for stands and conical sleeves ,which can not be over tight or loose .When it is too tight ,the roll rings are in a tensile state and more fluctuation of rolling force will make the roll rings break .When it is too loose ,it causes the roll rings ,roll mandrel and conical sleeve to slide relatively during rolling ,which scratches conical sleeves and roll mandrel resulting in cracks .Before running the mill make a check if the roll ring meets the needs and roll ring,the assembling faces of the conical sleeve and the roll mandrel need to be cleaned .it is forbidden to knock at the roll rings with a hammer or other hard materials when running the mill .It is forbiddemn for the roll rings to impact each other during the transportation and installation to prevent roll rings from damage .
3)Cooling and cooling water quality
Cooling is intended to reduce the influence on roll rings of thermal corrosion ,fatigue and stress during milling .It can prevent the roll rings from cracking and slow down the diffusion of cracks,prolonging the life time of grooves.It plays an important role in optimizing the performances of roll rings.The reference data for cooling are as follows :
a)The temperature of cooling water is below 25℃
b)The pressure of cooling water is 5~6 bar with a water volume of 24~30m3/hr/stand .
c)The water is jetted in a radial direction and angle between the water jet and the rotating direction of roll rings is 15~30 degree.
d)The width of the water column is 2 times than that of the groove and the water should be jetted directly into the grooves and the water should not be scattering or misty
Water Quality requirements
For alkali and acid vlue in water to cooling the roll rings is decided as per actual situation ,meanwhile ,the cotent of solid particles in the water <15milligram/litre.
4)Reasonable rolled quantity
During rolling ,the microcracks in grooves can not be avoided ,and they need to be reground when they are at a certain depth(normally controlled at 0.2mm).Excess rolling causes the depth of microcracks to extend rapidly and dangers of crushed rolls increase ,which should be prevented .The volume of material to be rolled normally after each regrinding is as follows :
a)Stands of pre-finishing rolling mill:(3500~4000)tons
b)1~2 stands of finishing rolling mill:(1800~2500)tons
c)3~4 stands of finishing rolling mill:(1800~2500)tons
d)5~6 stands of finishing rolling mill :(1500~2000)tons
e)7~8 stands of finishing rolling mill:(1500~2000)tons
f)9~10 stands of finishing rolling mill:(600~1200)tons
g)Stands of reducing diameters:(600~1200)tons
5)Regrinding of grooves
Miicrocracks will occur after the rolling of the groove for some time and when the microcracks extend to 0.2mm the roll ring has to be reground .Microcracks must be reground thoroughly when regrinding,otherwise ,the unground microcracks will make the microcracks extend more rapidly during the next rolling and probably make the roll ring crack.The recommended amount of regrinding after normal rolling is as follows :
a)Roll rings for stands 9~10 of finishing rolling mill(0.4~0.6)mm
b)Roll rings for stands 1~8 of finishing rolling mill(0.7~1.2)mm
c)Roll rings for stands of pre-finishing rolling mill(1.2~2.0)mm
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