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NR in sheet forms are the oldest and the most popular type. Being the simplest and easiest to produce on a small scale, small holder's rubber in most of the countries are processed and marketed as sheet rubber. Two types of sheet Rubbers are produced and marketed in the international market, namely the Ribbed smoked sheets (RSS) and the Air Dried Sheets (ADS). Among these two types, Ribbed smoked sheet is the most popular and is available for volume consumption.

RIBBED SMOKED SHEETS (RSS)
Ribbed smoked sheets are marketed based on visual assessment of quality. To establish acceptable grades for commercial purposes, the international Rubber Quality and Packing conference, have stipulated the grade description and the details are given in the Green Book.
   
   
  Among these forms types, the first three are in the dry form and almost of the total NR produced in the world is at present marketed in these 3 forms.  
 
   
Sheet Rubber   Crepe Rubber   T.S.R
         
       
Preserved Latex        
 
     
 

THE INTERNATIONAL GRADE DESCRIPTIONS FOR RSS
Only deliberately coagulated rubber latex processed into rubber sheets, properly dried and smoked can be used in making RSS. The following prohibitions are also applicable to the RSS grade.
  • Wet, bleached, undercured and virgin rubber and rubber that is not completely visually dry at the time of buyer's inspection is not acceptable(except slightly undercured rubber as specified for RSS-No:5)

  • Skim rubber made of skim latex shall not be used in whole or in part in the patches as required under packing specifications.
Prior to grading RSS, the sheets are separated, inspected and any blemishes are removed by cutting with a pair of scissors.
 

GRADE DESCRIPTIONS

 
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 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 evenly smoked and free from blemishes, specks, rust, blisters, send, dirty packing and any other foreign matter. Small pinhead bubbles if scatters will not be objected to.
No: 1 RSS
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 the 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 from blemishes, rust, blisters, sand, dirty packing and any other foreign matter, except slight specks. Small pinhead bubbles, if scattered, will not be objected to.
No: 2 RSS
Slight rust, and slight amount 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 barks, if scatters, will not be objected to.

Oxidized spots or streaks, weak, heated, undercured, over smoked, opaque and burnt 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
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 clour, 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
Rust, dry mould on wrappers, bale surfaces and interior sheets, found at time 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 as permissible but should not be evident to a marked degree. Oxidized spots, or streaks, weak, heated, undercured 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 than specified above as permissible.
No: 5 RSS
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 30% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.