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   IndiaRubberDirectory.com > Rubber Engineering > Natural Rubber

Rubber Engineering - Composition and Structure of NR

GRADING AND PACKING OF RUBBER

Sunny Sabastian

The important marketable forms of natural rubber are:
1. Sheet rubber
2. Crepe rubber
3. Block rubber
4. Concentrated latex

The grading and packing of sheet rubber and various types of crepe rubber carried out as prescribed in the International Standards of Quality and Packing for Natural Rubber Grades-The Green Bock. The grading and packing of block rubber and concentrated latex are prescribed in IS 4588- 1977 and IS 5430 – 1981 respectively, published by the Bureau of Indian Standards.

Garding and packing of sheet rubber

The Green Book prescribes six grades for ribbed smoked sheet. They are RSS IX, RSS 1, RSS 2, RSS 3, RSS 4, and RSS 5. Nothing but coagulated rubber sheets, properly dried and smoked, can be used in making these grades; block, cuttings, or other Scrap or frothy sheets, weak, heated or burnt sheets, air dried or smooth sheets are not permissible.

No. IX RSS

The grade must be produced under conditions where all processes are carefully and uniformly controlled.

Each bale must be packed free of mould but very slight traces of dry mould on wrappers or bale surfaces adjacent to wrapper found at time of delivery will not be objected to provided there is no penetration of mould insides the bale.

Oxidized spots or streaks, weak, heated, undercured, over-smoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong, sound and evenly smoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong, sound and evenly smoked, and free from blemishes, specks, resinous matter (rust), blisters, sand, dirty packing and any other foreign matter. Small pinhead bubbles, if scattered, will not be objected to.

No official International Sample has been established for this grade.

No. 1 RSS

Each bale must be packed free of mould but every slight traces of dry mould on wrappers or bale surfaces adjacent to wrapper found at time of delivery will not be objected to provided there is no penetration of mould inside the bale.

Oxidized spots or streaks, weak, heated, undercured, over-smoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong, sound and free from blemishes, resinous matter (rust), blisters, sand, dirty packing and any other foreign matter, except slight specks as shown in sample. Small pinhead hubbles, if scattered, will not be objected to.

No. 2 RSS

Slight resinous matter (rust) and slight amounts of dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to, provided these conditions, either singly or in combination, do not exist to an objectionable extent on and in more than 5% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Small bubbles and slight specks of bark, if scattered, will not be objected to.

Oxidized spots or streaks, weak, heated, undercured, coversmoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong, sound and free from blemishes, blisters, sand, dirty packing and all other foreign matter other than specified above as permissible.

No. 3 RSS

Resinous matter (rust) and dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to, provided these conditions, either singly or in combination, do not exist to an objectionable extent on and in more than 10% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Slight blemishes in color, small bubbles and small specks of bark permissible.

Oxidized spots or streaks, weak, heated, undercured, over-smoked, opaque and burnt sheets are not permissible

The rubber must be dry, strong and free of blemishes, blisters, sand, dirty packing and all other foreign matter other than specified above as permissible.

No. 4 RSS

Resinous matter (rust), dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to provided these conditions, either singly or in combination, do not exist to an objectionable extent on or in more than 20% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Medium size bark particles, bubbles, translucent stains, slightly sticky and slightly over-smoked rubber and permissible to the extent shown in the sample.

Oxidized spots or streaks, weak, heated, undercured, over-smoked (in excess of the degree shown in the sample), opaque and burnt sheets are not permissible.

The rubber must be dry, firm and free of blemishes, blisters, sand, dirty packing and all other foreign matter other then specified above as permissible.

No. 5 RSS

Resinous matter (rust), dry mould or wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to provided these conditions, either singly or in combination, do not exist to an objectionable extent on or in more than 30% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Large bark particles, bubbles and small blisters, stains, over-smoked, slightly sticky rubber, and blemishes are permissible of the amount and size shown in the sample. Slightly under-cured rubber permissible.

Weak, heated, burnt, oxidized spots or streaks not permissible.

The rubber must be dry, firm, free or blisters, except to the extent shown in the sample, dirty packing, sand, and all other foreign matter other than specified above as permissible.

Packing of sheet Rubber

All ribbed smoked sheets shall be packed in rubber covered bales. Each bale belonging to a lot must be of uniform weight. Usually the weight of each bale is 50 kg.

Each bale must be wrapped on all sides and corners with equal or higher quality rubber of the same type. Double wrapper sheets must be used if wrapper sheets contain holes. No metal bands or wires or non-metallic binders shall be placed under wrapper sheets.

For No. IX, No.1, and No.2 Ribbed smoked sheets, the outside of the bales shall be lightly dusted with powder before applying the wrapper sheets to prevent sticking. Powder must not appear in any other part of the bale. For No.3, 4, and 5 Ribbed Smoked sheets, no powder shall be used on the inside of the wrapper sheet, nor in any other part of the bale.

To overcome adhesion in transit and also to provide proper background for stenciling of colored shipping marks, the outside of the wrapper sheet must be completely and entirely painted on all six sides with one coat of the official bale coating solution. No other bale coating solution may be used, except where such use has been specifically accepted by the buyer.

Preparation of bale coating solution

500g. clean rubber and 8 liter of hydrocarbon solvent (boiling point in the range of 140° to 210°C and sp. Quantities between 0.77 to 0.83) are taken and the rubber is allowed to swell in the solvent for at least 24 hours. 4 litrs of the solvent is again added and well mixed. The bale coating mixture is prepared by mixing the above solution with 8 ltrs. Of solvent 11kg. Of powder.

Note:- Powder used can be either talc or kaolin or whiting, 100% passing through 150 micro is sieve and 83% passing through 45 micron is sieve.

Crepe Rubber

The important types of crepe rubber available in our country are pale crepes and estate brown crepes.

Pale Crepes

These grades must be produced from the fresh coagula of natural liquid latex under conditions where all processes are carefully and uniformly controlled. The rubber is milled to produce crepe in thickness corresponding approximately to the pieces in the samples of Thick and Thin Pale Crepes, respectively.

No.IX Thick Pale Crepe
No. IX Thin Pale Crepe

Deliveries must consist of dry, firm rubber of Very light uniform colour.

Discoloration, regardless of causes, dust, specks, sand or other foreign matter, oil or other stains, or any evidence of oxidation or heat, not permissible.


No. 1 Thick Pale Crepe
No. 1 Thin Pale Crepe

Deliveries must consist of dry, firm rubber of light color with very slight variation in shade permissible.

Discoloration, regardless of cause, dust, specks, sand or other foreign matter, oil o other stains, or any evidence of of oxidation or heat not permissible.

No. 2 Thick Pale Crepe
No. 2 Thin Pale Crepe

Deliveries must consist of dry, firm rubber, slightly darker than No. 1 Thick or Thin Pale Crepe with slight variation in shade permissible.

Slightly mottled rubber, of the degree shown in the sample will not objected to, provided this condition does not exist in more than 10% of the number of bales included, the delivery, lot or tender as determined by the number of bales inspected.

Discoloration, regardless of causes, dust, specks, sand other foreign matter, oil or other stains, or any evidence of oxidation or heat, not permissible, other than those specified above as permissible.

No. 3Thick Pale Crepe
No. 3 Thin Pale Crepe

Deliveries must consist of dry, firm rubber of Yellow color with variation in shade permissible. Mottled and streaked rubber to the extent shown in the sample are permissible provided this condition does not exist in more the 20% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Discoloration, regardless of causes, dust, specks, sand or other foreign matter, oil or other stains, or any evidence of oxidation or heat, not permissible, other than those specified above as permissible


Packing of Pale Crepes

Each bundle belonging to a batch must be of uniform weight (usually 50 kg). Each bale must be wrapped on all sides and corners with equal or higher quality crepe. The surface of each bale must be lightly and evenly dusted with powder before application of the wrappers. Each bundle is them packed in hessian cloth.


Grading of Estate Brown Crepe (EBC)

The grades are made from lump and other high-grade scrap generated on rubber estates. Tree bark scrap, if used, must be preplanned to separate the rubber from the bark. Power wash mills are to be used in milling these grades into a form of thickness corresponding approximately to the pieces in the samples of Estate Thick and Thin Brown Crepes, respectively. Use of earth scrap, smoked scrap, and wet slab is not permissible in the preparation of Estate Brown Crepes.

No. IX Thick Brown Crepe
No. IX Thick Brown Crepe

Deliveries must consist of dry, clean rubber light brown in color.

Discoloration, regardless of causes, dust, specks, sand, or other foreign matter, oil or other stains, or any evidence of oxidation or heat, not permissible.

No. 2X Thick Brown Crepe
No. 2X Thick Brown Crepe

Deliveries must consist of dry, clean rubber brown light in color.

Discoloration, regardless of causes, dust, specks, sand, or other foreign matter, oil or other stains, or any evidence of oxidation or heat, not permissible.

No. 3X Thick Brown Crepe
No. 3X Thick Brown Crepe

Deliveries must consist of dry, clean rubber brown to dark brown in color.

Discoloration, regardless of causes, dust, specks, sand, or other foreign matter, oil or other stains, or any evidence of oxidation or heat, not permissible, except specks of bark of the degree shown in the sample which will not be objected to.

Packing of Estate Brown Crepe

Packing practices for EBC are similar to those for pale crepe, except that no packing in hessian cloth is done.

Block Rubber

In India block rubber is known as Indian Standard Natural Rubber (ISNR). Five different grades of ISNR are described in IS 4588-1977. Each bale of block rubber shall be free from skin rubber. The material shall be free from requirements in the following table.
CHEMICAL REQUIREMENTS FOR NATURAL RUBBER
 

Requirement for

Sl.No. Characteristic
Special
ISNR 5
 ISNR 5 ISNR 10 ISNR 20 ISNR50
1.

  Dirt Content,Percent
by mass,
Max
0.10

0.05  0.10  0.20  0.50
2.  Volatile matter,
Percent by mass,
Max 1.0
1.0 1.0 1.0 1.0
3. Ash, Percent by
Mass, Max0.6 0.75
0.6 0.1  0.6 1.5
4. Nitrogen, percent
By mass, Max 0.7
 0.7  0.7  0.7  0.7
5. Initial plasticity,
Min 30
30 30 30 30
6. plasticity
retention index
(PRI), Min 80
60 50 40 30


Packing

The crumb raw rubber shall be packed in 25 or 50kg. Bales. The material shall be wrapped in low density polyethylene sheets and shall be further wrapped as agreed to between the purchaser and the supplier.

Note:- Low density polyethylene sheets which are easily dispersible in rubber and of the following description, are generally found suitable:

Thickness, mm 0.030 to 0.038
Relative density 0.92
Melting poing 109°C

Grading of Concentrated latex

Three types of concentrated lattices are marketed-the high ammonia type (HA), medium ammonia type (MA) and low ammonia type (LA).

Type HA – Centrifuged natural rubber latex preserved with ammonia only or by formaldehyde followed by ammonia with an alkalinity of at least 0.6 percent.

Type MA - Centrifuged natural rubber latex preserved with ammonia and other preservatives as agreed to between the purchaser and the supplier with and alkalinity above 0.3 percent but less than 0.6 percent,

Type LA - Centrifuged natural rubber latex preserved with ammonia and other preservatives as agreed to between the purchaser and the supplier, with an alkalinity of not more than 0.3 percent.

The Chemical requirements for the three types of concentrated latex are given in
the table.

PEQUIREMENTS FOR CONCENTRATED AND PHESERVED NATURAL RUBBER LATICES
 

Requirement for
SI  No Characteristic Type HA Type MA Type LA
1. Dry rubber content, percent
By mass, Min
 60.0  60.0  60.0
2. Non-rubber solids, percent
By mass, Max
2.0 2.0 2.0
3. Coagulum content, percent
By mass of latex, Max
0.05 0.05 0.05
4. Sludge content, percent by
Mass of latex
0.10 0.10 0.10
5. Alkalinity as ammonia,
Percent by mass of latex
 0.6 AboveMin but below Max0.6  0.3  0.3
6. KOH number, Max 1.0 1.0 1.0
7. Machanical stability, s, Min 475 475 475
8. Volatile fatry acid number, Max 0.15 0.15 0.15
9. Copper content, ppm of total
Solids, Max
8 8 8
10. Manganese content, ppm of
Total solids, Max
8 8 8


Note: Test for mechanical stability shall be carried out at least 20 days of the packing or rubber latex.

Packing

Latex shall be packed in drum, so that each drum contaim 200±5 litrs. Each container shall have the following marking

a. Name. Of the producer/trade mark
b. Type of latex
c. Net weights, gross weight and tax weight and volume in litres.
d. Dry rubber content
e. Date of packing.


 

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