No, the problem is not so much with the inclination as that the cement is behaving in a fluid condition. Being a fine powder, cement is prone to aeration if agitated, particularly if warm for reasons of air viscosity. I suspect that the installation delivers the material to a short inlet in a dilated condition and it is just churning in the screw and behaving more or less in a hydrostatic manner up the casing.

As with the pulverised coal query in this forum, it indicates the difference between conveying easy bulk materials and the need for some experience when dealing with awkward products. The cost of lost production and rectification invariably outweighs the extra capital cost of purchasing from a specialists, but unfortunately it is usually too late.

Likewise, solutions are usually saught on the cheap or by brute force. My imutable laws on retrofits summerises many years of experience in this field. However, if the enquirer cares to send me full details of the application to lyn@ajax.co.uk, I will try to assist.

Lyn’s Ten Immutable Laws on Retrofits

1.Whilst time is invariably of the essence and in very short supply during the translation of a project from the conceptual stage to the design specification, there is all the time in the world for an inquest when things go wrong.

2.There is invariably far more interest in performance guarantees for retrofits than there was for the original equipment.

3.Money is far tighter for putting things right than for making it wrong.

4. Constraints of headroom and space, flexible at the start of a project, are cast in stone when retrofits are required.

5.The time spent in considering the problem before calling in someone new to correct it is inversely proportional to the time then available to produce a solution.

6.Far more time and money can be spent on assessing responsibility than on curing the problem.

7.The credit for correcting the blunder goes to the person who called in those who affected the change.

8.Retrofit contracts are very special during negotiations, but are treated as simple standard purchases once the order is placed.

9.If successfully completed, little credit is given to the supplying company as they are only supplying to order and the uncomfortable circumstances of the original incident and the user usually forgets its potential liabilities.

If not totally successful the supplier is hounded to secure the objectives not met when the equipment was first installed, the supplier’s reputation is in tatters on whom all subsequent expenses are expected to fall. ■

With regard to remedial action my response is frequently the Irish one -

"To be sure, if I was wanting to get to there, I wouldn't be starting from here!" ■

It is essential to either get rid of some of the excess air in the cement or deal with the material as a fluid. To consider a solution it is necessary to find out what the present situation is and what opportunities are available. How is the cement delivered to the conveyor inlet, how much space and headroom is available around the inlet, is it a continuous operation etc. A drawing of the installation is vital and, from this I may be able to see a way forward. Send an ACAD drawing to lyn@ajax.co.uk and I will examine the prospects or return with further questions.

Unfortunately, I cannot wave a magic wand. It is often much tougher to correct a situation than to make it right in the first place but there are techniques to de-aerate, force feed and deal with fluidised material. Finding the best answer is a balance between cost and time.

regards,

Lyn ■

Unfortunately this duty is not a standard kit, but has to be custom built for the installation. The basic technique is to utilise vertical tuned reeds to resonate at the natural frequency of applied vibration within an aerated bed. This acts to send compression waves through the product to stimulate air migration and provides short circuit routes for the escape of excess air, so that it does not have to perculate through the minute interstities of the void channels. With a bit of simple mechanics you can design your own. I am afraid that the forum is not a free design school, so this is as far as I can go. ■

I really think that Mr Bates has gone as far as he can.

Surely these forums are for free advice NOT free engineering.

Maybe you should now seek to employ a consultant to assist in solving your problem. ■

As with most awkward solids handling problems, the devil is in the detail. It is not practical to advise without knowing all the particulars of the installation and operation. This takes co-operation and time, which costs money. The question to put back is - does the extent of the problem justify the cost of expert advice. ■

Through 6 years of full time private initiative research within fluidisation and segregation processes occuring in vertical conveying, I am not either willing to design solutions for free.

These things about screws appears to be easy, that's why so many have problems. It's a 2200 year old invention and still there is far to go to in order to understand the process for every product, application and configuration.

Regards from Norway ■

My Book - 'Guide to the Design, Selection and Application of Screw Feeders', published by The British Materials Handling Board, may be a useful start for anyone looking at the basic principles of handling bulk materials by screws. ■