Vertical Screw Sampler


I'm looking for some advice on a vertical screw system that our company presently uses to sample material from bulk bags that we receive. The system presently in use uses a spear (3" OD, DOM tubing) with a vertical screw that draws the material up and into a sample bag as the spear is inserted into the bag. The screw specs are: 2"OD, 1" Shaft , 1.5" pitch and the material is drawn up a distance of 48".

We are having two problems:

1) The sample size is too large. After doing a lot of research I think a variable pitch screw would be the best solution for this but I would appreciate any comments/suggestions in this regard.

2)The sampler is unable to draw sticky, compacted material (much like clay). I am aware that ribbon screws are well suited for this but am not sure if they are ever used in a vertical configuration or in this small of an outer diamter.

Any comments or suggestions would be most appreciated and please let me know if I can provide more info.

Sampling Screw

Posted on 14. Dec. 2007 - 10:27

Small screws of ribbon construction can be used vertically. A coreless screw would also work and be better for sticky material. However, the screw has to be strong enough to transmit the torque required over the length of the unit, so a ribbon screw with a small centre shaft is probably best.

A sticky material would stay in the tube when the sampler was withdrawn, so you may consider lifting out the sampler and reversing the screw as required into the sampler vessel to secure a suitable size of sample, rather than extracting in situ.

Re: Vertical Screw Sampler

Posted on 14. Dec. 2007 - 05:53

Thanks for the reply. One of the reasons for this type of design is to minimize dust issues, which shouldn't be that much considering the water content of the material, but I agree that the operator should at least be able to time the reversal of the screw as it is withdrawn to empty the sampler. This would also be a more representative sample as this procedure is repeated over several bags, thus minimizing cross contamination between bags.

BTW, has anyone heard of this type of system being used before?

Any thoughts on the vertical variable pitch screw in order to sample more free flowing materials?

Thanks again for any comments.

Re: Vertical Screw Sampler

Posted on 15. Dec. 2007 - 05:45

Sounds like you need to look at what soil samplers do.

I have seen appartus that looks like a pipe which is pushed into the ground and then withdrawn and the "core" is pushed out.

Seems simpler than trying to screw it out then clean out the screw tube, particularly since you will never be going more than 3 ft or so. An overhead monorail with two cylinders to push in the sample tube then push out the core might be all you need.

Re: Vertical Screw Sampler

Posted on 16. Dec. 2007 - 01:46

I'm with JD.

My only question is: where did the screw come from in the first place?

John Gateley

Re: Vertical Screw Sampler

Posted on 17. Dec. 2007 - 07:35

I appreciate both your replies, and it's funny that you ask. The screw sampler was supplied several years ago by Heath & Sherwood. I actually have been looking at soil samplers, as you mentioned, that have vibrators mounted to them so they can easily be pushed into the soil, and I have mentioned this idea to my supervisor. Although he liked the idea at the time, he has been having me focus on trying to improve the screw concept. I think this is a case of wanting to stick with what's already there, despite the fact that another design may be more appropriate. This is somewhat frustrating as I agree with JD and john that the "tube" design seems much more feasible. In terms of sampling ease and the quality of a representative sample. Also, I didn't mention that the sampler has to be portable (presently it is mounted on a front end loader and driven by the hydraulic system) as the bulk bags are usually distributed over a fairly large area. I do like the two cylinder idea though and I will pursue that further and see if I can incorporate it into a portable design. Very good insights though, and again I appreciate all the comments thus far and welcome any more.

Re: Vertical Screw Sampler

Posted on 18. Dec. 2007 - 04:03

There was an article in Bulk Solids a few years back describing a tyre mounted sampler for assessing the vermin content in the European Grain Mountains. It would help you if you could trace it.

As I remember the author(ess) was from East Anglia, for a geographic search Norfolk, Suffolk, Essex, Lincolnshire or Cambridgeshire: although I'm pretty sure it was Suffolk.

Good luck!

John Gateley

Re: Vertical Screw Sampler

Posted on 18. Dec. 2007 - 05:12

Since you have mentioned Heath & Sherwood, I now see that you are also from Ontario.

A mobile unit in this case might consist of a Fluidpak or similar hydraulic unit as would be used on a truck mounted snow plough. Depending on the push force required, (ie frozen or non frozen bags) it might even be mounted in the bed of a pickup truck with a jib or Hiab style arm.