Control of Weight of Beam Section

  • 1. Weight on the piece depends of the:
    • (a) Thickness of the web
    • (b) Thickness of flange
    • (c) Filling up of inside comer (<7) Taper of the leg
    • (e) Leg lengths (/) Width of the piece.

Roller lias veiy little control over (b), (c) (d) and (/). So to keep the weight within tolerance, Roller has to control the web thickness and leg length. If web thickness is decreased by pressing finishing and pre-finishing stand, then leg lengths also get slightly decreased and weight becomes less. On the contrary, with the increasing web thickness weight obviously becomes more.

Thickness of web and leg lengths can be decreased upto a certain limit, afterwards there is no other way, but to change pass.

Roller should see that passes should last long to give maximum possible life. Following parameters should be continuously monitored:

  • (a) Uniform load on the stand.
  • ( b) The temperature of the piece.
  • (c) Matching of passes, especially for passes of pre-finishing and finishing stand.
  • (d) Uniformity of the profile from every stand of the mill.
  • (e) Overfilling and under filling of passes should be avoided.
  • (/) Guards should be checked periodically to avoid marks in the passes,
  • (g) Pass should be changed when a slight mark is noticed on the pass.

To avoid the mark on the pass, it should be seen that guards should not press too much on the pass, may be due to more counter weight or with the use of heavy guards. Guard should not be too short and setting of the guards should not be such that, it may act as a cutting tool. The sitting of the guard on the pass should be made uniform; the material of the guards should not be too hard.

hi case of beam, roller has control over (?) web thickness and (if) leg lengths but does not have much control over leg thickness.

To control the web thickness and leg length the methods of control has been explained earlier. Here, roller should be borne in mind that alternate passes are close at top and open at the bottom. To control the leg length, both the top and bottom flange should be taken into consideration separately. When both flanges are found short and are required to be increased, then metal should be increased on flanges from roughing group. When bottom one side flange is to be increased, the top close pass rolls to be adjusted towards opposite side. Similarly, in case of one flange adjustment rolls should be adjusted as stated above.

Filling of comers is important. The top roll of previous stand should be shifted opposite to the comer and the top roll of the stand from which under filling is coming to be shifted towards the comer. In case of bottom comer the entry guides may be adjusted accordingly.

Special Precaution is to be taken during Beam Rolling

The sticker mark on the flange is noticed very often during rolling of beam profile. Sticker marks comes due to sticking of metal on the pass. This sticking is mostly due to wedging action in the pass. If the thickness of the flange is more from previous stand the wedging action will be more. If one side flange is having frequent sticker mark the probable reason is as explained above and that flange thickness should be reduced. If both flanges are found thicker than previous stand then pass should be changed immediately.

The second cause of sticking is due to loose portion of metal on the flange. This is probably due to scabby metal. If scabby metal is seen while it is passing through roughing and intermediate group it should be rejected.

Defects of Beam and its rectification

Defects of Beam

Fig. 10.36 Defects of Beam.

  • 1. Legs are short (both): This is due to less metal, coming out from roughing group. Too much hot metal and tension should be avoided. Metal on the leg should be increased, from the roughing group. If the pass of pre-finishing stand wears out beyond the limit, then also leg thickness will be more and legs will become shorter. The pass should be immediately changed.
  • 2. Legs are longer (both): This is due to just opposite action as mentioned in (1) above.
  • 3. Legs are unequal: This is due to mostly wrong setting of entry guides in first cutting pass, so guide should be set properly. Guides should move towards the shorter leg side. If setting of entry guide is correct, then the top roll is to be taken towards longer side.

When difference is less, the top rolls of finishing and pre-finishing stand should be shifted. If difference is more, then entry guides and rolls of roughing groups are to be adjusted. If necessary, one piece maybe rejected after the roughing group to check the flange lengths and adjustment are to be done accordingly. If the piece fed twisted to the stand after the tilter, then also, one leg may be become shorter and other gets longer.

  • 4. One leg is thicker and other is thinner: The top roll of finishing stand is to be taken towards thinner side.
  • 5. Both corners are blunt.
Both corners are blunt

Fig. 13.37 Both corners are blunt.

This is due to not filling up of comers of the pass of finishing stand.

This may be due to less metal from pre-finishing stand. In this case, the top roll of pre-finishing stand should be raised. If the finishing stand pass is not filled properly due to less reduction, then top roll of finishing stand should be pressed. If the turning of pre-finishing pass is not correct i.e., if comers are turned less, then the chances of blunt comer will enhance. To avoid this trouble, the pass of pre-finishing stand should be checked. If the pass of pre-finishing stand is too narrower than the finishing pass, the rounded comers are expected. In this case, wider pass for prefinishing stand or narrower pass of finishing stand is to be taken. Rounded comers may also be due to worn out pass of finishing stand, pass should be changed. Worn out pass of pre-finishing stand will help to fill up the comers.

  • 6. One side of corner is blunt: This may be due to above reasons and if the rolls of finishing or pre-finishing stand is cross. Top rolls should be moved towards blunt side in pre-finishing stand and opposite to blunt side in the finishing stand.
  • 7. Bend web: This is due to less reduction in finishing stand or more reduction in pre-finishing stand. Adjustment should be done accordingly. When the finishing stand pass is worn out, there is a chance of bend web. Pass should be immediately changed.
  • 8. Inside corners are not filled up: This is due to reasons explained in 5 and 6 above.
  • 9. Waviness of the web: This is due to unequal reduction between flange and web. Sudden more reduction in one web (pressing of top roll) will also result in this.

10. Wavy Flange: If there is excessive work on the flanges, they try to elongate more than the web. Because the web is holding them back, the extra length has to go somewhere so the flanges become wavy at the tips. At the extreme, the flange elongation can cause migration of material from the web to the extent of pulling holes in the web. This defect is generally obseived in universal rolling of beams.

Wavy Flange

Fig. 13.38 Wavy Flange.

Remedies are:

  • 1. Tighten rougher vertical rolls and/or
  • 2. Loosen rougher horizontal rolls or
  • 3. A combination of these depending on loads and finished bar dimensions
  • 4. At finisher, tighten horizontals and loosen verticals
  • 11. Under filling mark on the top: This is due to reasons explained at 5 and 6 above.
Under Filling Mark on the Top

Fig. 10.39 Under Filling Mark on the Top.

12. Worn out mark on the flange, web, and fire crack mark on inside corners: In case of less worn out mark on pass can be rectified by grinding and pass can be used again. The bottom roll grove of all stand gets heated up very quickly as accumulation of heat takes place at that point, water cooling of bottom roll should be very efficient, If ,it is not removed, then pass should be immediately changed.

13. Scratehes/Grooves

Scoring / scratching appearance on finished product. Beams are particularly prone to this problem.

Scratches

Fig. 10.40 Scratches.

  • • Mainly mechanical marking Remedies are:
  • • Check guides/tackle
  • • Check troughs, deflectors
  • • Check for scale build up in rolling line
  • 14. Holes in Webs: Result of web being stretched due to too much flange work

Possible causes

  • • Draughting ratios out of synchronisation between web and flanges
  • • Buckle appears due to either too much work on the flange or insufficient web work (inverse of web buckle).

Remedies

  • • Adjust roughing mill to allow more stock into finishing mill.
  • • Adjust finishing mill to balance web / flange ratio.
  • • Check for possible interstand tension in a continuous mill arrangement
  • 15. Off Centre Web: It is due to following reasons:

Off centre web is called, when top and bottom flange heights are different beyond permitted tolerance limit. Possible causes are:

  • • Rolling line is either too high or too low.
  • • Intermediate stock imbalanced on tongue and groove passes.
Off Centre Web

Fig. 10.41 Off Centre Web.

Remedies

  • • Adjust rolling line, addition of packers/running in plates or removal of stand and removing liners.
  • • Check roll alignment, guides and guard setting of roughing and intermediate group to get balance stock as best as possible.
 
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