IL24575A - Asbestos cement filter tubes - Google Patents

Description

C O H E N Z E D E K & S P I S B A C H E G D . PATE NT ATT O R N EYS 24, LEVONTIN STR., P. O. B. 1169 T E L - AV I V P A T E N T S & D E S I G N S O R D I N A N C E 1384-0/65 SPECIFICATION A MS!EHQD 3Ρ0Ώ HAIIUFAS¾¾iffG ASBESTOS CBMSHT FIWER TUBES op.iOK-c3i.so iu'o mm»¾ "15.SBEEB BBS", tovarna eemen a in salonita, of Anhovo, Yugoslavia, DO HEREBY DECLARE the nature of this invention and in what manner the same is to be performed to be particularly described and ascertained in and by fhe following statement: The invention relates to a method of ■ male-iag asbestos cement filter tubes.

According to the invention, the same or similar inorganic hydraulic binding agents are used for bonding together the filter material itself and for joining it to the wall of the asbestos cement tube as are used for the manufacture of the tube itself, i an amount of to 20 # based on the weight of the filter material.

Hardening of the f lter tubes so made is carried out in the same way as is the case for hardening the asbestos cement tubes.

Insofar as, the autoclave method is used for the hardening of asbestos cement tubes or asbestos cement filter tubes, it is also applied to the method of manufacture of these tubes as is stated in the previous paragraph* except that the hardening is carried out in two stages, the first of which represents a partial hardening in air and the second of which represents a final hardening in the autoclave* This final hardening is carried out i an analogous way to the hardening in autoclaves of asbestos cement tubes themselves, viz* without any filter layer* Asbestos cement filter tubes are designed for use in pumping water from the lower earth strata or levels. ..·. For this purpose, seamless steel tubes were originally laid in previously-prepared and preferably wider borings, which steel tubes were divided, at the places where water levels were present, by means of perforated steel filter tubes. These perforated filter tubes were surrounded with a fine steel net. The whole bore, that is the space between the tubes and the earth strata, was filled with filter sand of a predetermined particle size range. The ground water which filtered in this way through the filter sand, so becoming purified, passed through the net and the perforations into the tube, from whic it was pumped up to the surface.

;The use of steel tubes for this purpose has several disadvantages. Above all, particularly in the presence of salt-containing and other mine waters, steel tubes are highly subject to corrosion and incrustation, which reduces their life-span, on the one hand, and involves operating difficulties by reducing their free width, on the other. Anti-corrosion protection with various coatings has not proved satisfactory. Also, the introduction of large amounts of filter sand into the bore (often several hundreds of tons) is very time-consuming and costly* In order to avoid the difficulties which result from corrosion, asbestos cement tubes were introduced, which in most cases are resistant to corrosion. Also, asbestos cement tubes are connected together with elastic couplings, which allow smaller tectonic movements without the suction inlet becoming displaced, which represents a further advantage over steel tubes.

Also, this solved the question of making a more rational use of filter sand, since it is unnecessary for the filter layer to be located along whole lengths of the bore or of the suntion duct; it is Sufficient for it to be surrounded by a few perforated tubes at those places where the duct is located in the regions where there is ground water or water strata. This problem was solved b fixing the layer of filter sand to the perforated tube by means of plastic adhesive agents, principally those based on formaldehyde and epoxy resins. This kind are still used today.

Although perforated asbestos cement tubes with plastic material filters represent a considerable advance in comparison with the previous state of the art, these filters still have certain disadvantages, since they are very costly* since their permeability is relatively poor and since the strength of the bonding between the filter layer of plastics material and the wall of the asbestos cement tube is low* It is an object of the invention to provide a method for manufacturing asbestos cement filter tubes provided with a filter layer, which tubes are not subject to the above-mentioned disadvantages.

These tubes should ensure adequate strength of the bonding between the filter material and the asbestos cement tube, they should be of good durability and, at the same time, their manufacturing costs should ensure their economic exploitation.

According to the method of the invention, this problem is solved thereby, that as a binding agent for bonding the filter material or the sand of corresponding particle size range, the same or similar hydraulic binding agents are used as were employed for manufacturing the asbestos cement tubes themselves, in which the same binding agent bonds together the asbestos fibres which impart to asbestos cement products their surprising properties with regard to strength. These binding agents effectively bond together the filter sand leaving, at the same time, sufficient free spaces to ensure that the filter layer has good porosity. Because of the fact that the substance of the asbestos cement tube is basically the same as the substance binding the filter sand, the bond between the filter layer and the asbestos cement tube is fully satisfactory as regards the compatibility of the substances.

It is essential to the method of the invention for the hydraulic binder to be selected both for its ability to bond together the filter sand and, at the same time, to join the filter layer to the asbestos cement tube. Other features of the method are optional, since they can be adapted without particular trouble to technological methods suited to modern economic conditions. For example, asbestos cement filter tubes can be made, by applying a moist layer of filter sand with admixed hydraulic binder to a perforated asbestos cement tube and carrying out the bonding and hardening in the moist atmosphere. Hardening can be carried out at normal temperature, . at elevated temperature (e.g. at about 40° to 70°c , in autoclaves (at temperatures over 100°C) or in such a way that two or all three of these possibilities are combined.

The improved asbestos cement filter tube manufactured according to the method of the invention is illustrated in the accompanying drawing, in which: Fig. 1 shows the asbestos cement filter tube in longitudinal section; Fig. 2 shows a section on the line A-A of Fig* l; Fig. 3 shows a perspective view partly in section of the filter layer and the asbestos cement tube.

In Figs. 1, 2 and 3» both layers of the asbestos cement filter tube can be seen, namely, the basic perforated asbestos cement tube 1 itself and the filter layer The method of the invention for manufacturing asbestos cement filter tubes is explained in the following example, which relates to the manufacture of a tube in which all elements of the method are suited to autoclave hardening, so that the example is only illustrative and the invention is not to be regarded as in any limited thereto..

The example relates to the manufacture of asbestos cement filter tubes having a free width (I.D.) of 400 mm, A newly-made asbestos cement tube 4 metres long with an internal diameter of 400 mm. and a wall thickness of 28 mm., was delivered from the pipe-making machine on a hardening conveyor at 100 relative humidity into a tunnel heated to 50°C. The tube was held in the tunnel for 5 hours. It was then sawn into two pieces each 2mm/ long and the tube ends were subjected to twining on a lathe so that these ends were appropriately shaped for eventual connection* The two metre long tube was then mounted in a perforating machine, in which 16 rows of holes with a diameter of 50 mm* were drilled, there being 17 holes in each row along the tube. Altogether* 272 holes 2 with a surface area of 0.533 m were drilled in the tube, so that the perforated surface amounted to 22 #* The perforated tube was then put into the upright position and surrounded with a mould, which was similar to the mould used for manufacturing concrete tubes having an internal diameter of 400 mm. but without an inner wall... In the asbestos cement tube, an insert of wood or, preferably, of expanded rubber (like an air hose) was introduced. The tube was enclosed in the mould in such a way that its two ends remained free for a length of 15 cm. , so that later connection or coupling to a pipe would be possible.

The space between the mould wall and the asbestos cement tube was filled with fresh filter material using a vibrator, in the customary way used in the manufacture of concrete tubes.

Fresh filter material, which basically consists of a concrete mix, was made in the same way and under the same conditions as is usual in the manufacture of concrete mixes.

For the tube mentioned in the example, the following quantities of components were employed: 330 kg. of washed quartz sand with a particle diameter of 2 to 3 mm* and a rounded surf ce; 50 kg. of cement of a quality suitable for autoclave hardening (from a mixture of 57 i° clinker, 40 quartz sand and 3 gypsum ground to a fineness of 2 to 3 i° of the remainder on a 4.900 screen; this same quality of cement was used for manufacturing the asbestos cement tube); 301* of water* The tube was left in the mould for 2 hours and then removed from the mould and allowed to stand in an upright position for 16 hours. The first stage of manufacture was thus completed.

In the second stage, the semi-prepared 2 metre long filter tube was placed on a carriage provided with cross-bars so that deformation of the tube under its own considerable weight (abou$ 500 kg. ) was prevented.

The carriage with the tube was guided into an autoclave, this was operated and, with the outlet valve, open, introduction of saturated steam started. When the air had been expelled, the outlet valve was closed and the steam pressure was increased for about one hour to 8 atmospheres (174°C).

In carrying out the autoclave hardening, account must be taken of the layer of condensate disposed over the length of the autoclave. At the pressure and temperature given, the tube remained in the autoclave for six hours and then the pressure was gradually reduced to atmospheric throughout one hour. The autoclave was then opened, the carriage removed and the tube allowed to cool. The tube is then ready for use* The filter layer of the tube had the following properties: Permeability - K — 0.6 cm/S Porosity . - 37 # Compression strength 2 (4x4x16 cm. prism) - 250 per cm Yield strength 2 4x4x16 cm. rism - 60 er cm The strengths are calculated according to JUS B.C. 1010.

Asbestos cement filter tubes are used in deep well bores which are effectively several hundred metres long. The boring of such wells has considerably increased in recent years. Th© examples of practical use of deep well borings are above all the location of drinking water in regions which have no available surface water or where it is unusable and also for lowering the ground water level in mine workings, particularly coal mines, for the purpose of easier working, as well as for the pumping of salt water from low lying levels.

The lengths of borings made annually for these purposes can be assessed at several thousand kilometres. Whe account is taken of the fact that this way has been used only for a few years and that the need of satisfactory drinking water is even greater now, a considerable increase in the lengths constructed can be counted on in the coming years.

Claims (4)

P.A. No.24575 ' ^ Pile No. 13840 Date t ±9. III. 6 . WHAT IS CLAIMED IS

1. Asbestos cement filter tubes, in which an inorganic hydraulic binder is used for bonding together the filter material itself and for joining it to the wall of the perforated asbestos tube, which binder is the same as or similar to those which are used as in the manufacture of the tube itselfm the amount of binder being 10 to 20$ by weight of the filter material.

2. Method of making Asbestos cement filter tubes according to Claim 1 , comprising the step of hardening of the filter material in the way used in the manufacture of asbestos cement tubes.

3. A method according to Claim 2 , in which hardening is carried out in a first stage at normal and/or elevated temperature in air and in a second stage in autoclaves, the times and temperatures of hardening being similar to those used in manufacturing asbestos cement tubes.

4. * Asbestos cement filter tubes, substantially as hereinbefore described with reference to the example given. DATED THIS 3rd day of