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Articles - Rubber Technical Papers

N.R. Peethambaran

Extruded Goods

Extrusion procdess is one of the major manufacturing techniques of rubber industry and a large number of rubber products are produced by this technique.

1. Tread Rubber

The process of removing old worn out tread and replacing it with a new tread surface is called Retreating. Tread rubber is used to replace the worn-out tread. Tread rubber is used in "die size" or "strip" form. 'Die size' rubber is the rubber, which has been fed into the extruder and extruded into the shape desired. Die sises are given in three or more sets of numbers. The first two parts of numbers indicate the crown and base width in inches with the last number in each sequence indicating multiples of 1/8 inch. Each sequence of numbers after the first two indicates thickness of thread rubber in multiples of 1/32 inches. A die size of 52-76-13-11-13 means that the crown is 51/4 inches wide, the base is 7 3/4 inches wide and the tread has a valley contour with the tread rubber being 13/32 inch thick on each shoulder and 11/32 inch thick at the tread centre. As the die sizes are extruded a natural rubber cushion gum is applied to the ban of the tread rubber to provide a back surface so that the tread rubber will adhere to the buffed surface of the tyre.

A Retread compound (Camel back and slab) is expected to give the same performance as the original treads which it replaces. A retread compound is also expected to have long storage life. Typical compound recipes for a heavy-duty Truck Tyre and Cushion gum are given below.


Natural Rubber


Cushion gum

(RSSIV or ISNR-10) 80.0 100.0
Cis 1,4 polybutadiun 20.0 ---
Zinc oxide 5.0 5.0
Stearic acid 2.0 2.0
A.O. PBN 1.0 1.0
A.O. 4020 NA 0.5 --
GPF Black -- 30.0
HAF black 50 --
Pine tar 7 -- 7.0
Aromatic oil 5.0 --
Accelerator DZ 0.6 0.7
Insoluable sulfur 2.8 2.8

The rubber compound is prepared in a two roll-mixing mill and kept for maturation for 24 hrs. It is again pre warmed in the mill before feeding into the extrude.

Water Delivery Hose

Natural Rubber

Tube p.b.w.

Cover p.b.w

Tinc Oxide 100 100
Stearic acid 5 5
Hard clay 2 2
FEF black 180 100
Napthenic oil 20 50
A.O. PBN 18 15
P. Wap 1.5 1.5
CBS 1.0 1.0
TMTD 1.0 1.0
Sulfur 0.1
  2.4 2.4


II Calendered goods

1. Converyor belting

Conveyor belts transport materials at low speed and operate over big pulleys. A typical belt consists of a carcass and covers (top and bottom). The function of the carcass is to carry in load while the covers protect the carcass from wear and tear, shocks, deleterious effects of solvents, oils, heat, ozone and weathering. Typical compound formulations for the conveyor belt compounds are given below: -

General purpose Conveyor belt compound

Natural rubber 100 100
Tinc Oxide 10 5
HAF black 50 ---
SRF black -- 30
Stearic acid 2.5 2.0
PPTED CaCo3 -- 60
C.I. Resin 5 5
M.C.Wax 1 --
A.O.PBN 1 1
A.O.4020 NA 0.5 --
Accelerator CBS 1.0 1.0
Sulfur 2.4 2.4

2). Transmission Belts

Transmission belts transmit power and operate at high speeds over smaller pulleys in comparison with conveyor belts. Although flat belts and V belts both are grouped under a common heading the first type calls for high flexibility but total non-strechability to avoid loss of efficiency in power transmission. Compounds for V belts should with stand high speed flexing and heat while those for flat transmission belt should have good ageing resistance.

3). Rubber convered Rolls

Rubber convered Rolls find application in many industries notably paper manufacturing, steel processing textile processing metal coating and leather finishing. Most rolls are made of oil resistant rubbers and are generally vary in the range of 20-40 shere A. Most of them are produced by applying Calendered sheet on the rolls. Calendered rubber is carefully applied to the care and rolled down either by machine or by hand. Special care must be taken to prevent the incorporation of air into the roll. The built roll is then wrapped tightly with cotton for vulcanisation in an open steam or in an autoclave. In general printing rollers are made from nitrile rubber, paper rolls from natural rubber. Leather processing rolls are made from nitrile or EPDM or silecone rubber. Typical compound formulation for printing Roller is given below: -

Nitrile rubber 100
Zinc Oxide 5
Stearic acid 1.5
GPF black 15
Brown facties 40
Diochy lplhalal 60
TMTD 1.0
Sulfur 2.0

4. Hospital and Industrial sheetings

Hospital sheetings are of 3-4 mm thickness and width 36" and is manufactured by the calendering process. There are different types such as plain sheetings, fabric reinforced sheetings (Mackintosh) etc. Industrial sheetings are used for washers and seal, which are required in large number. These sheets are also available in both plain and fabric reinforced structure. A typical compound formulation for hospital sheeting are given below.

RSS IX 100
Zinc Oxide 10
Stearic acid 2
Barium Sulphate 100
China clay 80
Titanium dioxide 20
Napthenic oil 12
Paraffin wax 1.5
Antioxidant SP 1.0
White factie 5.0
Accelerator CBS 1.0
Sulfur 2.4

5. Tank lining: Calendered sheets are also used in tank and pipe linings in chemical industries.



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