Sheet Rubbers:.
Natural Rubber in sheet form is the oldest and the most
popular type. Being the simplest and easiest to produce
on a small scale, small holders' rubber in most countries
is processed and marketed as sheet rubbers. Two types of
sheet rubbers are produced and marketed internationally
- Ribbed Smoked Sheets (RSS) and Air Dried Sheet (ADS).
Of the two, RSS is the most popular and is available for
volume consumption. ADS form only an insignificant percentage.
.
Ribbed
Smoked Sheet (RSS).
Ribbed
Smoked Sheets(RSS) are marketed based on visual assessment
of quality. To establish acceptable grades for commercial
purposes, the International Rubber Quality and Packing Conference
has stipulated the grade requirements and the details are
given in the Green Book published by the Rubber Manufactures
Association (RMA) inc., Washington D C, United States of
America.
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 grades:
-
Wet, bleached, under-cured and virgin rubber and rubber
that is not completely visually dry at the time of buyer's
inspection, are not acceptable (except slightly under-cured
rubber as specified for RSS 5)
- Skim
rubber made of skim latex shall not be used in whole or
in part in the production of RSS and for rubber marking
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.
Following
are the different grades of RSS
- RSS 1
- RSS 2
- RSS 3
- RSS 4
- RSS 5
Grade Description of R S S as per Green
Book
RSS1: The grade must be produced
under conditions where all processing operations are carefully
and uniformly controlled. Each bale must be packed free of
moulds 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, under cured, and over smoked, opaque and burnt sheets
are not permissible.
The rubber must be dry, clean, strong
and evenly smoked and free from blemishes, specks, rust, blisters,
sand, dirty packing and any other foreign matter. Small pinhead
bubbles if scattered, will not be objected to
RSS 2: Slight rust or a slight
amount of dry mould on wrappers, bale surfaces and interior
sheets, found at the time of delivery, will not be objected
to, provided these, either singly or in combination, do not
exist 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,
under cured, and over smoked, opaque and burnt sheets are
ruled out. The rubber must be dry, clean strong and free from
blemishes, blisters, sand, dirty packing and all other foreign
matter other than specified above as permissible.
RSS 3: Rust and dry mould on
wrappers, bale surfaces and interior sheets, found at the
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 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 are permissible. The
other parameters are the same as for RSS 2
RSS 4: Rust, dry mould on wrappers,
bale surfaces and interior sheets, found at time of delivery,
will not be objected to provide 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.
RSS 5: Rust, dry mould on wrappers,
bale surfaces and interior sheets, found at the 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.
Large bark particles, bubbles and
small blisters, stains, over smoked, slightly sticky rubber
and small blemishes are permissible provided they are not
present to a marked degree. Slightly under cured rubber is
also permissible but not weak, heated, burnt rubber, and those
with oxidized spots or streaks. The rubber must be dry, firm,
and free of blisters, except to the extent shown in the sample.
Dirty packing, sand and all other foreign matter other than
specified above are not permissible
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