- Dr Michael McDonagh
PVC Battery Separators – An overview of characteristics, manufacture & test methods.
PVC battery separators are microporous diaphragms placed between the negative and positive plates of lead acid batteries to prevent any contact between them to avoid internal short circuit but at the same time allow free circulation of the electrolyte. This kind of Separators has a maximum pore size of less than 50 micron meter and lower electrical resistance of less than 0.16 ohm / cm sq. PVC separators are uniform in quality, free from holes, broken corners, splits, embedded foreign material, surface rupture, physical defects, etc. These PVC battery separator have a very low electrical resistance which reduces internal loss saving on electric energy and improving battery performance. Their high porosity in the PVC battery separator ensures easy diffusion of electrolyte and movement of ions guaranteeing battery performance even at high discharge rates. Being completely non-reactive to acids, active metals and emitted gases, It enhances the active life of the lead acid battery and is an ideal choice for Tubular Gel Batteries with a designed battery life of 15 years – PVC battery Separators will not disintegrate unlike some other types of battery separators.
Because of these tremendous benefits the PVC battery separators are exclusively used in Plantè Batteries, Tubular Gel Batteries, Flooded OPzS cells and Flooded Nickel Cadmium Cells.
The OPzS Stationary Cells are in transparent SAN containers and are used for Telecommunications, Switchgear and controls & Solar applications, Power plants and substations, Wind, hydro & solar Photovoltaic, Emergency power- UPS Systems, Railway signaling.
Microtex PVC battery Separators are tested regularly and found to surpass IS Specifications IS: 6071:1986. The PVC battery separator was developed for the first time in India under the brand name MICROTEX with the company’s own know how and with indigenously designed machinery 50 years ago.The plant and machinery comprise sintering machines and other electrical installations, with own captive power generators, for the smooth and automatic production of over a hundred million separators per annum, the largest and most renowned manufacturers of PVC battery separators in India.
MICROTEX PVC battery separators are manufactured in both standard and custom sizes for automotive and industrial lead acid battery applications. Every PVC battery separator produced is visually inspected before being packed. Physical and chemical testing is done batch wise in our modern laboratory. Routine checks are made at key stages along the manufacturing process maintaining a high consistent quality.
MICROTEX PVC battery separator, combining the outstanding characteristics of low electric resistance, chemical cleanliness, higher porosity, Low pore size, superior corrosive resistance and with minimum level of oxidizable organics, make themselves extremely usable for automobile, traction Batteries, Inverter batteries, UPS & stationary, train lighting and all other lead acid batteries including the high end Tubular gel batteries with a designed life of over 15 years.
MICROTEX PVC battery separator have proven themselves over 50 years with loyal repeat customers. Five decades of experience and modern production methods and facilities have made MICROTEX the leading PVC battery separator supplier in India. The key to their leading position in the separator industry is technological innovation, quality and service.
MICROTEX PVC battery separator, combining the outstanding characteristics of low electric resistance, chemical cleanliness, higher porosity, Low pore size, superior corrosive resistance and with minimum level of oxidizable organics, make themselves extremely usable for automobile, traction, stationary, train lighting, Locomotive starting applications and all other lead acid batteries.
1.PVC Powder (Imported- Electro Chemical grade)
2. Powder Mix Process Ingredients (Special In House grade)
The Mixed PVC Powder is sieved and passed over the seamless belt and the die. The PVC powder takes the profile of the die and passes through various temperature zones of the machine and Sintered. The Finished PVC separator is cut to the customer required sizes. Each Separator is checked physically for Pin Holes, unformed area-thin and un-uniform profiles. The Inspected and Passed separators are packed, and the boxes marked for dispatch.
3.Types and sizes of PVC battery Separators manufactured by us: Sintered -Plain on one side with straight ribs on the other side and plain on both sides with minimum web thickness of 0.5mm and overall thickness up to 3.6mm. Length cut to the required dimensions.
Quality checks and record:
1) Raw material: Accepted as per Supplier Test results report which are within our standards.
2) Finished PVC battery separators are tested to IS spec parameters as below:
TESTS FOR PVC Battery SEPARATORS
A. Determination of percentage of volume porosity
A-1: Reagents: Distilled water.
A-2: Procedure: Exactly cut 127 mm long x 19 mm wide using scissor. Stack 5 strips and fasten them together by wrapping a length of copper wire around one end. Fill the graduated cylinder with approx. 85ml of the D.M water, record this volume(A). immerse the strips in the liquid, shake the strips within the cylinder few times to remove trapped air, place the stopper loosely on the top of the cylinder and let stand for 10 minutes. After the 10 min stand, record the increased volume of liquid (B). The volume of the solid material is the increase in volume of liquid, that is, B-A. Remove the stopper and withdraw the stripes from the liquid. Shake the strips lightly at the top of the cylinder to allow any excess water adhering to the surface of the sample to drain back into the cylinder. Record the volume of the liquid remaining in the cylinder C. This volume will be less than that of the original starting volume. Since we have extracted with the sample quantity of the liquid retained in the microporous material. This decrease in volume (A – C) represents the volume of the pores.
A-3. Calculation: % of Volume porosity = A – C X 100
B – C
B. Determination of Electrical Resistance in PVC battery separator
B-1: Reagents: Sulphuric Acid of Sp. Gr. 1.280
Set up the electrical resistance instrument. Measure the thickness of the Separators. Adjust the same thickness on the dial. Insert the separator sample in the baffle portion of the cell (before doing so ensure that the separators are soaked for at least 24 hrs. in Sulphuric acid of Sp.gr.1.280).
B-3: Calculation: The display on electrical resistant instrument will directly give the electrical resistance of the separators in ohm/Sq .cm/mm thickness.
C. Determination of Iron content PVC battery separator.
Sulphuric Acid (1.250 Sp gr.), 1% KMno4 soln., 10% Ammonium thiocyanate solution,std. Iron soln. (dissolve 1.404 gm of ferrous ammonium sulphate in 100ml of water. Add 25 ml of sulphuric acid of 1.2 Sp gr. followed drop by of potassium permanganate to slight excess. Transfer the solution. to a 2 lt. Flask and dilute to the mark. The soln. contain 0.10 mg of Iron/ml of Solution.).
Tear or shred 10 gm of Separator into a suitable small strip and put into a cleaned 250ml conical flask. Add 250ml of sulphuric acid and allow to stand for 18hrs. at room temperature. Transfer the acid to a 500ml graduated flask and make up the solution with distilled water upto 500ml and mix thoroughly. Pipette 25 to 30ml of the above solution into a beaker and heat to near boiling point and add KMnO4 solution drop by drop until the slight pink colour does not disappear after 3 or 4 mints. When the permanent colour is secured, transfer the soln. to a 100ml Nessler’s tube and cool under the tap. When cooled ad 5ml of ammonium thio cyanate soln. and dilute up to the mark. Cary out the control test if with the 60ml of std. Iron soln. using the same quantities of reagent without the separator sample. Compare the
colour developed in the two Nessler’s tubes.
The Iron in the separators shall be taken to be within the limit if the intensity of the colour produced in the test with the separators is not deeper than that produced in the test without separator containing the permissible quantity of iron as added from standard solution.
D. Determination of Chloride content in PVC battery separator.
Dil. Nitric Acid, Ferric Ammonium sulphate soln, Std. Ammonium thio cyanate soln. Std. Silver Nitrate soln. Demineralised water, Nitrobenzene.
Weigh 10 gm of finely shredded separator, transfer it into a 250ml conical flask and Cover with 100ml of boiling D.M water, stopper and shake occasionally while letting the contents cool for 1 hr. Decant the extract into a 500ml volumetric flask. Make up to 500ml with distilled water. Transfer 100ml of the aliquot into a 600ml conical flask. Cool and add exactly 10ml of Std. Silver Nitrate soln. Add a few ml of Nitrobenzene and shake to coagulate the ppt. Of Silver chloride. Titrate the excess of Silver nitrate with Std. Amm. Thiocyanate using FAS as indicator. The end point of the titration is a faint permanent brown colouration which is difficult to see without considerable experience. If any doubt is felt about the end point, it should be compared against a similar solution containing dil. Sulphuric acid, Nitrobenzene, FAS and 1 drop of Std. Amm. thiocyanate which gives the colour of the end point.
D-3: Calculation: Wt. of chlorine = ( Vol. of AgNO3 – Vol. of NH4CNS) x 500 x 100
Vol. of aliquot x wt. of separators
E. Determination of Manganese content PVC battery separator.
1.84 Sp. Gr. con. H2SO4, Orthophosphoric acid (85%), solid potassium periodate, std. Manganese sulphate soln. (Dissolve 0.406gm of MnSO4 crystals in approx. 20ml of water). Add 20 ml of con. Sulphuric Acid followed by 5ml of orthophosphoric acid. Add 3gm of potassium periodate and boil the soln. for 2 minutes. cool, dilute to 1 lt. (1ml=0.01 mg of Manganese). The soln. is stored in cool dark place). Std. KMnO4 soln. (Dissolve 0.2873 gm of Kmno4 in lt 1 lt. Of water to which 1 ml of concentrated H2SO4 has been added. Dilute 100 ml of this solution. to one litre so that 1 ml=0.01mg of manganese).
Select at least 8 separators at random and break them in to small pieces. Weigh accurately 10gm from the piece and place it on a silica dish. Dry the sample for 16 hrs. at 105 ± 20C. Ignite the material in a muffle furnace at a dull red heat for approx. 1 hr. Stir the ash for complete combustion. Cool the ash in desiccators, moisten with water, add 2 to 3 ml of con. H2SO4 followed by 0.5ml of con. H3PO4. Add 10 ml of water and heat the dish and its contents on a boiling water bath until all the material is dissolved. Cool and filter into a 100ml beaker, add 0.3gm of Potassium periodate, boil the soln. for 2 minutes. And after cooling make it up to 50 ml depending upon the colour developed. Compare by a suitable comparator with the std. Manganese sulphate soln. Conduct control determination on the reagents.
E-3: Calculation: Express the amount of manganese present as mg/100gm of oven dry sample.
F. Determination of Max. Predominant pore size in PVC battery separator.
F-1: Reagents: n-propanol.
The maximum pore size is determined by measuring the air pressure necessary to force the first bubble of air through a separator wetted by abs. Alcohol. The separator is fixed in the holder and alcohol is allowed to stand on the separator to a depth of few mm. Air pressure is applied from underneath the surface. It is gradually increased till air bubbles appear on the surface of separator. Sometimes an individual pore may be quite large to develop an air bubble at quite a low pressure. This pressure is neglected and the pressure at which the bubbles appear over the whole surface in sufficiently large number is noted. This is taken as an indication of the predominant max. Pore size.
The pore size is calculated from the following formula.
D = 30g X 103
Where D = diameter of pore in micrometer,
g = Surface tension of liquid in Newton per meter (0.0223 for absolute alcohol) at 27oC
P = Observed pressure in mm Hg
G. Test for Wettability in PVC battery separator
G-1: Reagents: Sulphuric Acid of Sp.gr.1.280
Place a drop of 1.280(270C) Sulphuric acid soln. with a pipette (10cc) on the surface of the separators at room temperature. The drop shall be absorbed by the separators within 60sec. The test shall be carried out on both the surfaces of the separators.
The test shall be taken to have been passed if the separator absorbed the acid drop within 60 sec.
H. Test for Mechanical strength in PVC battery separator
H-1: Reagents: Nil.
The specimen separator shall be clamped in the jig with ribs, if any, being on the lower side. A steel ball of 12.7mm dia. Weighing 8.357 ± 0.2gm is dropped vertically from a height of 200mm. The ball shall fall between the ribs.
The test shall be taken to have passed if the separator shall not break or fracture due to impact of steel ball.
I. Life Test for PVC battery separator
I-1: Reagents: 1.280 Sp. Gr. Sulphuric Acid.
The separator under test (50×50 mm) is interposed between two lead blocks kept in Sulphuric acid (Sp. Gr. 1.280) and connected to the positive and negative terminals of a direct current source. If the separator is ribbed, the ribbed side should face the positive of the dc source. The lead blocks should be stoppered off with lacquer except for the porton, which is in direct contact with the separator. A few more lead blocks are added to the block to make a total weight of 1 Kg, so as to impress a pressure of 4 Kg/dm2 of the separator an ampere hour meter is connected in series in the circuit to record the total current passed and to calculate the number of hours of life under constant current conditions. A constant current of 5 amperes is passed (current density 20 amperes per dm2) between the two lead blocks. When the separator fails, the lead blocks become shorted and the voltage across the separator drops to nearly zero. This voltage difference is taken account of by an electronic relay which cuts off the dc source.
From the ampere hour meter reading the life of separator in hours is calculated by dividing the AH meter reading by 5.
TEST RESULTS: All the relevant test results shall be recorded in the standard lab report.
This article gives information relevant to testing of PVC battery separators. Please feel free to write to us for further information.