PRODUCT DIVISION 2

OPERATIONAL SUGGESTIONS FOR CARBIDE RINGS

RING ASSEMBLY

  1. In a tungsten carbide set, the diameter differences among the rings should not be more than 0.1mm.

  2. Carbide rings when moved around must avoid contact with each other and also with other tools; the assembly must be done with clean surfaces.

  3. For the ring mounting preparation, clamping sleeves should be at a similar temperature than the shaft or mandrel where they will be housed.

  4. The carbide ring manufacturers' assembly instructions must be strictly followed according to the pressure and assembly method, because a too tight or loose fitting will cause cracks and breakages of the rings.

  5. After assembly, the conditions of the guide elements and cooling water must be observed making sure they will not interfere with the ring channels and that the water can enter the rolling channel.

  6. It is recommended to standardize the rings (channels) wear in order to have well controlled parameters of rolling, machining and product quality.

COOLING REQUIREMENTS

The cooling is designed to reduce corrosion, fatigue and thermal stress wear in the carbide rings during rolling. 

Formation of cracks will always occur in carbide rings during rolling, but a correct water cooling application will delay their emergence and will stop their propagation, thus prolonging the life of the channels. 

Although carbide rings are designed to have resistance to corrosion, fatigue and thermal stress, the cooling conditions must meet certain requirements to obtain their best performance such as: 

1. Water pH control at 7.2 to 7.5 

2. Work should only be done with treated water with a maximum suspended particles of 70ppm; 25ppm is recommended. 

3. Minimum volume of water per stand at 24m3 / hour 

4. Minimum pressure of 5 bars or 70 psi. 

5. Water temperature should be uniform and preferably not exceeding 6°C at room temperature. 

6. The water application must be done with a minimum angle of 15° (degrees) from normal. 

7. The water applied must cover the width of the channel in excess and the largest volume of water must be applied close to the exit of the bar at a distance of 20mm to 25mm.

PERFORMANCE AND MACHINING OF GROOVES

As we know during rolling, micro-cracks emerge in the ring channels and cannot be avoided; these micro-cracks are what determine the performance of the finishing and pre finishing stands. It should be noted that with good cooling water these micro-cracks can be reduced, but not ruled out. 

From experience in rolling mills, the performances of carbide rings are 8 to 10 times higher than that of cast iron qualities, however it is the particular rolling mill operating conditions that will determine these performances. 

It should be considered that as the emergence of micro-cracks is constant, the machining of carbide rings must also be constant in order to make the cracks disappear. Based on operational practices and performances set by the mill production team, the machining of the ring channels, as a general rule, should be a function of the of the micro-cracks depth which can reach 0.4mm. However, if a greater depth is reached it would jeopardize the integrity of the rings as micro-cracks would spread uncontrollably and eventually result in the ring breakage. 

It is always suggested to use penetrating inks for good control after machining of the rings and to have a machining pattern which should be double or triple the micro-cracks depth; up to 0.6mm for finishers and 1.2mm for pre-finishers. 

In the case of rolls, cracks can be deeper and deeper machining up to 2.0mm is recommended.