if your fabrication practices are not done right the first time you will always have problems.

If you are using motors that are running to fast you will have problems.

If you are overloading your screens you will have problems.

Any good metalurgist will solve your problems as far as diagnosing damage from operations.

If you do not describe your assembly process I am unable to help you. ■

Screen sidewall failures are quite common. Many split between the shaft housing & the nearest available stress raiser. I have put chalk lines along my anticipated crack lines & always been within 25mm of the actual developed crack.

Your failure source seems to be the other one. A mild steel plate vibrating backwards & forwards will distort dynamically according to the prevailing forces & frequencies. These distortions are resisted locally by the crossmembers through their connections, some manufacturers even weld the frame up, by bolts. If you provide external plating at the joints you can then use more bolts and thereby reduce the fluctuating tension in each bolt. It would also be helpful for you to stiffen the sideplates according to good structural practices so that they can better sustain the localised lateral deflections resulting from the dynamic behaviour of the beam webs.

By all means ream the holes. ■

Sandeep: How are you doing? Some points to consider:

1. Is this a circle throw inclined screen or?

2. All mfrs use FABRICATION JIGS.......HIGHLY important to maintain absolute squareness when welding various components

3. IF unsquare at all - the screen box will BREAK APART

4. We had 6 big machines....6x20 horizontals a long time ago, brand spanking new that BLEW APART....All of them the same way. The factory had installed a WASH trough across the width of the machines (a V shaped plate 3/8" thick) the factory did NOT install Reinforcing GUSSETS to the underside of these troughs and when the machines started up the troughs began to FLUTTER at its own frequency and cracked the sideplates out at the point where they were bolted to the sidewalls.

5. Any member operating at its own frequency will BREAK the sidewalls quickly.

6. If any welding is done on internal cross members MFRS always RELAX the welds prior to assembly TO avoid torquing up a screen box with a WARPED, TWISTED, NON SQUARE shape which will always BREAK a sideplate out.

7. IF welding corners of frames and or longitudinal support bars to cross members, care MUST be taken NOT to overweld all the way around corners and all the way around pipes, AS this will cause the welded area to be too RIGID and they will tear apart.

We had to SONIC relieve the cross member welds on a screener in QUEBEC because of this problem. Took us a long time to discover this problem also.

8. REINFORCING around the connection area ....is also commonly done. A lot of forces at the weakest spot in the body....the biggest bore or hole in the screenbox.

9. We have the shaft assembly housings done outside specially..due to the HIGH importance of sweating the TUBE ENDS onto the cross pipe absolutely SQUARELY as we know full well the result if not machined perfectly square...sidewalls crack.

GOOD luck ■

On the otherhand, lets talk about feed for a moment:

1. What is top size of the feed? If too big we could be SHOCK loading the screen box...ABUSE = broken sidewalls

2. What is the DROP height measurement from the feed conveyor headpulley to the screen cloth? If dropping too far, SHOCK LOAIDING.

3. Is there a FEED BOX which you are feeding onto or are you feeding right onto the WIRECLOTH? = ABUSE.

4. iT Might just be running too fast, that is always an excellent way to RIP a sideplate apart. What is the speed and the stroke. If over a certain accelerating G Force. = ABUSE.

5. When whoever picked the screen box off the TRUCK, did they use spreader bars OR just pick it up and lay the steel cables on the sideplate (happens all the time) = it will run untrue and erratic = ABUSE.

6. Have you done a physical STROKE check and measured it? It should POINT you right to the source area on the screener box that is running MOST Erratic and hence guide you to the area to look closely at and fix.

7. IS the wirecloth in TIGHT or loose? ■

In the good ole days.........don't ya love that phrase?

OUr shop always used REAM FIT holes when assembling screener boxes. You know why? For a nice SNUG TIGHT fit of the bolt into the hole....the idea is to have all parts vibrate as ONE....vs many different frequencies.

- Also used to use Ntl fine thread hardware, why.....for a nice TIGHT fit.

- Torquing of bolts to proper VALUES for the size is important

- Huck bolts will all be fastened at an equal torque value.

But, the sidewall should NOT be DIMPLED or concaved when installing sidewalls to cross members. This applies stress to that area and is subject to CRACKING when under VIBRATION.

- ■

Sandeep

Dear moderators and members,

in one of my last post i was telling you about a problem when 3 screens in one of the plants we operate ripped apart on the same day,

we had to replace the sidewall plates again. now i can see streach and stress marks on the side wall plates again near the huckbolts where the cross beams are bolted.

i guess this is due to

"irregular size of the cross beams" - WHAT DO YOU MEAN BY THAT? YOU ARE NOT KIDDING?

due to whihch the plate is getting bent and stressed.

and this probably might be the reason why the plates crack up often.

Can you please guide me on good fabrication practices for manufacturing the screens and these fabrication practices.

do we need to machine all flanges or frames before we bolt them up with the side wall plates - YES YOU DO

Should we always have tight tolerance holes for bolting etc. - YES BY ALL MEANS

kindly guide me on the fabrication practices and tolerances followed by major manufacturers - FABRICATION AND TOLERANCES ARE PRETTY STANDARD, WHAT YOU NEED IS A PROPER DESIGN, ASSEMBLY AND TESTING PROCEDURE

REGARDS

ziggy ■