|EP0899077||Method of manufacturing a porous tube with a strip of different material, apparatus for carrying out this method, tube obtained by this method and use of such tube for irrigation|
|EP1674503||Thermoplastic vulcanizate with high temperature processing aid|
|EP1741542||METHOD FOR MOULDING A THERMOPLASTIC POLYMERIC MATERIAL, DEVICE FOR CARRYING OUT SAID METHOD AND THE COMPOSITION OF THE THERMOPLASTIC POLYMERIC MATERIAL|
The invention relates to a peristaltic pump, a hose for such a pump and a method for manufacturing such a hose. The peristaltic pump is designed for circulating a medium, such as a liquid, a gas, a slurry, a granulate or a combination of two or more thereof, and comprises:
Such a peristaltic pump is known for instance from
Owing to the local compression, and thereby closing of the hose by the pressing elements, and the displacement of this local compression under the influence of the pressing elements driven along the hose, the medium present in the hose will be pushed along. After a pressing element has passed, the form of the hose is restored due to its elastic properties. Owing to this mechanism medium is drawn into the hose on the suction side.
Because it is ensured that the hose is always pressed shut locally by at least one locally acting pressing element, the pump operates as closing valve such that the delivery side and the suction side are separated from each other.
The hose is successively loaded locally in the peristaltic pump by the pressing elements passing under pressure. This causes fatigue in the material of the hose. A fatigue crack hereby occurring after a period of time can eventually result in breaking of the hose, whereby the medium which has been pumped and which is to be pumped can flow out of the hose, and lubricant possibly present on the outside of the hose can mix with pumped medium. Because the process of crack formation depends on many factors, the moment at which the break occurs is difficult to predict. A break causes the described technical disruptions, among others, and results in undesired maintenance at a non-predictable moment in time.
In the light of the foregoing it is an object of the invention to substantially increase the lifespan of the hose.
In addition, peristaltic pumps of the described known type are often not competitive with other displacement pumps because the pump capacity of peristaltic pumps is relatively small in relation to their dimensions and their cost price. Increasing the capacity by increasing the rotation speed could be considered, were it not for the fact that the lifespan of the hose would hereby be greatly shortened by the usual peristaltic pumps. It is therefore a further object of the invention to modify the known pump such that the lifespan of the hose is prolonged or the pump capacity is increased by increasing the rotation speed of the pump.
A pump known from
The problem which however occurs in this known hose is that, due to the continuously repeated compression and expansion, the pump is subject to premature delamination as a result of the strong shear forces occurring repeatedly each time. The hose hereby becomes unusable in a short time since the integrity of the PTFE layer is broken and the chemical resistance of the hose therefore becomes determined by that of the material of the carrier which is not specially designed or chosen for this purpose. The lifespan of this known pump hereby leaves a great deal to be desired.
With a view to the foregoing, the invention provides a peristaltic pump of the type stated in the preamble which has the feature that the hose is non-reinforced, non-layered and consists solely of a homogeneous thermoplastic vulcanizate (TPV).
It is noted that also
In no way whatsoever does this publication point in the direction of the possibility of the hose consisting solely of a homogenous thermoplastic vulcanizate as according to the teaching of the present invention. Attention is also drawn in this respect to the fact that this US patent refers to a hose with a layered structure, this even being wholly contrary to an important basic principle of the invention.
It must also be noted in this respect that the hose according to the invention, in accordance with the given definition, is free of any form of reinforcement such as embedded fibres with tensile strength, for instance in the form of a mat, as is known and usual per se for hose pumps.
In a further embodiment the peristaltic pump according to the invention has the feature that the pump is of the rotating type;
the pressing surface is curved and at least a part thereof takes the general form of circular arc with a central axis;
the pressing means are designed as a rotor;
the pressing element are placed at equal angular and radial positions; and
the rotor is rotatingly drivable around a central axis.
It is noted that while this rotating pump has a construction other than for instance a linear pump according to the invention, the principles implemented therein are nevertheless the same. The results of the teaching according to the invention can hereby also be easily realized in the rotating pump.
The invention further relates to a method for manufacturing a hose for a peristaltic pump of the specified type, according to which method a granulate consisting of a rubber and a thermoplastic plastic is pressed through an annular extrusion nozzle at increased temperature and at pressure, and the hose-like extrudate leaving the extrusion nozzle is cooled, and a hose of the desired length is separated from the thus obtained extrudate.
According to this method "new" material is used, i.e. material which in principle has not been previously used.
The stated material choice according to the invention is also suitable for recycling of for instance already used hoses of the type according to the invention. In this respect the invention also provides a method for manufacturing a hose for a pump, according to which method a previously manufactured and possibly already used hose is finely ground such that a granulate is obtained consisting of a rubber and a thermoplastic plastic, which granulate is pressed through an annular extrusion nozzle at increased temperature and at pressure, and the hose-like extrudate leaving the extrusion nozzle is cooled, and a hose of the desired length is separated from the thus obtained extrudate.
The invention further relates to a hose for a peristaltic pump of the type according to the invention. This hose has the feature according to the invention that the hose is non-reinforced, non-layered and consists solely of a thermoplastic vulcanizate (TPV).
There now follow three definitions for the purpose of elucidating the invention:
The invention will now be elucidated with reference to the only figure.
This figure shows a cross-section through a peristaltic pump 1 according to the invention of the rotating type.
The pump 1 comprises:
The indrawn medium is indicated with an arrow 13. The medium discharged under pressure is indicated with an arrow 14.
The construction of pump 1 is per se known. The invention lies in the choice of the material of hose 3. This material is a thermoplastic vulcanizate (TPV).
A very suitable material comprises ethylene propylene diene rubber (EPDM) and polypropylene (PP). This material has an excellent resistance to acids, bases, oxidizing substances, alcohols, aldehydes and non-fatty foodstuffs.
Another option is for the material of the hose to comprise nitrile rubber (NBR) and polypropylene (PP). An example is Geolast™ from Advanced Elastomer Systems, Belgium. This material is highly suitable for the pumping of oils, bases and diluted acids.
Yet another option is that the material of the hose comprises nitrile rubber (NBR) and polyvinyl chloride (PVC). An example hereof is Nitrovin™ from Vi-Chem Corporation, USA. This material is suitable for pumping oils and fuels.
Yet another choice is for the material of the hose to comprise polyacrylate rubber (ACM) and polyamide (PA). An example hereof is Zeotherm® from Zeon Chemicals, USA. This material is highly suitable for pumping hot oil, fuels and hydrocarbons.
Situated in pump space 15 is a liquid lubricant. Very suitable as liquid acting as lubricant and coolant is that commercially available from applicant under the name "Bredel Genuine Hose Lubricant". This is a liquid with a dynamic viscosity of about 600-700 mPa.s (20°C). This lubricant and coolant is registered in the United States at NSF under number 123204.
Tests have shown that the combination of the material for the hose according to the invention and a peristaltic pump according to the invention, wherein pressing surface 3, hose 4 and rotor 8 with pressing cams 9, 10 are situated in a lubricant, can have a lifespan which is three to seven times longer than:
Tests have also demonstrated that the combination enables a three to ten times greater pump flow rate by increasing the rotation speed of rotor 8.