Improvement in Productivity and Quality of Jute Bags
By
Pradip Kr. Choudhury
In- Charge, Geotech Cell
Indian Jute Industries’ Research Association
17 Taratala Road, Kolkata 700088, India
Abstract:
Bag manufacturing process in the jute industry is highly labour intensive and as a result cost of production goes high. The century old machineries used to manufacture bags are also of low speed and hence low productive. In the past IJIRA had done extensive study on improvement of productivity in sacking sewing and finishing. The results of study were highly encouraging and were implemented in the Indian jute industry. Productivity in the seaming sector has been increased by about four times. A few basic studies, like reduction of cut length of hemmed bags were also carried out to reduce the cost of production by about 4%. The major factors responsible for seam strength failure of bags were also investigated and appropriate remedial measures were established.
In fact, finishing and sack sewing section in the jute industry is most neglected. It is envisaged that by adopting the issues discussed in the paper, productivity and quality of jute bags can be increased significantly.
1.0 Introduction –
In the year 1858 jute commenced its journey in the packaging arena as an ideal material and has been enjoying the same till date in India, though, since last three decades there is a threat from synthetic bags made out of petroleum derivatives. Incidentally, UNO has declared the year 2009 as the year of natural fibre. Jute is a natural eco-friendly biodegradable fibre and annually renewable resource. The unique salient features of jute like, high tensile strength, low elongation, rugged texture, high frictional resistance, desirable thermal conductivity, adequate air permeability etc. have made it possible to establish as the most suitable packaging material. India, Bangladesh and many other countries uses this fibre to manufacture Sacking, Hessian and other type of bags for packing rice, wheat, sugar and number of different commodities and are popularly used world wide. Popularity of this material is not only due to its intrinsic characteristics but also due to its added advantages like, ease of handling, good stackability, reuses etc.
Since late seventies inroad of synthetic bags has become a challenge to jute bags. Some countries, including developed ones have started preferring the former without considering its eco-compatibility and non renewable reserves of the earth. The only reason of this preference is nothing but its cheapness. But fact remains- “cheap does not pay always”. Moreover it should be borne in mind that costs of bags are always paid by the consumers and not the manufacturers or suppliers. It is fortunate that a few of the literate personalities of the world have expressed their deep concern on the environmental impact of processing, using and disposing of such synthetic bags. For the obvious reasons it is expected that others will also raise their voice in the same line very soon.
However, it is not denying that cost of jute bag is higher as compared to synthetic bag. In fact, Sack Sewing & Finishing Deptt. of jute mills is highly labour intensive and machinery used are very old and low productive. Generation of sub-standard products, huge quantity of thread waste and gunny cuttings affect the profitability of the mills. Further, sack sewing section alone involves about 12 % of the total labour complements of the mill. Machine utilization in this are is also very low. In the early days jute bags were used to be seamed by hand sewing. After the invention of sewing machine in 1846 by Ilias Howe mechanized stitching of jute bags started. Since 1890 lock stitch (type 301) and single thread chain stitch (type 101) were used. These stitches were replaced by overhead sewing machine in 1910 for higher productivity and stronger seam. Overhead sewing system was again replaced by Herakle sewing machine ( Overedge chain stitch, type 502) in 1984 for further increase in productivity as recommended by Indian Jute Industries’ Research Association ( IJIRA ). Till date this system of seaming jute bags is in vogue where productivity level has been increased by more than 400%. Another study was done to improve the seam strength of bags like, hessian, sacking and the bags made from the fabric produced in shuttleless loom having nonconventional selvedges. IJIRA also undertook extensive R & D work on improvement of productivity and quality of jute bags including development of 50 kg carrying capacity food grain bags. IJIRA has also developed 50 kg carrying capacity light weight sugar bag which is awaiting standardization by BIS. Development of Food Grade Jute Bag by IJIRA is a land mark The findings of the study and recommendations discussed in the paper, if implemented would help to reduce the manufacturing cost of jute bags without impairing the functional performance of the end products.
2.0 Types and Specifications of a few Jute Bags –
Hessian and sacking are the two main varieties of jute bags where share of sacking bags is about 80 %. Jute bags are made generally either in hemmed or selvedge type for packing different commodities like rice, wheat, sugar etc. Economic dimension of each type of bag is mathematically designed to hold a particular type of material depending upon its weight and bulk density. The specifications of a few common type of bags used for packing different materials are given in Table I
Table: I. Specifications of a few types of Jute Bags
Sl No / Type ofbags / Dimension (inch / cm) / Porter x Shots / Ends x Picks per dm / Weight of fabric
( gsm) / Weight of bag
( gm) / Tensile strength wp x wft
( kgf) / Seam strength wft x wp
( kgf)
1 / B Twill –
(2/1 Sacking) / 44 x 26.5 / 112 x 67.5 / 6 x 8 /
76 x 31 / 643 / 1025 / 160 x 165 / 62
2 / A Twill –
(2/1 Sacking) / 44 x 26.5 / 112 x 67.5 / 8 x 9 /
102 x 35 / 750 / 1190 / 204 x 180 / 67
3 / 50 kg Food Grain –
(2/1 Sacking) / 37 x 22.5 / 94 x 57 / 6 x 7 /
76 x 28 / 577 / 665 / 160 x 145 / 50
4 / Hessian Bag
(1/1 Plain) / 40 x 20 / 101 x 51 / 11 x 12 /
47 x 47 / 305 / 350 / 112 x 120 / 34 x 36
5 / 50 Kg Sugar
( 2/2 Sacking) / 34 x 23 / 87.5 x 58.5 / 8 x 8 /
68 x 31 / 568 / 630 / 160 x 145 / 45
3.0 Comparative performance of jute and synthetic bags
A comparative study was undertaken by IJIRA to assess the comparative performance of jute and synthetic bag from end use point of view. Findings of the study has been tabulated (Table II ) where it is seen that jute bag is much superior to its synthetic counterpart in all respect except price.
Table: II (Observation based mainly on field trial performance)
Sl.No. / Properties / Jute bags / HDPE woven bags01 / Seam Strength / Strong / Poor
02 / Stack Stability / Excellent / Poor
03 / Storage space utilization / Excellent / Poor – Storage space utilization is affected due to low stack height (to avoid stack collaps).
04 / Resistance for Hooking / Fair / Poor – Hook holes generally irrecoverable.
05 / Drop Test performance (On dropping from minimum height of 16’) / Good (all bags survived) / Poor – All bags severally damaged.
06 / Surface Texture / Rough (Suitable for stack stability) / Smooth
07 / Operational Convenience / Good / Poor – Abrasive nature of bag causes palm injury during manual handling besides the griping inconvenience and laborers are prone to accident risks during stacking and destacking due to slippery surface texture.
08 / End-use performance (w.r.t. bursting damage spillage and replacement) / Good / Poor – bags are prone to irreparable damage resulting in spillage and replacement
09 / Grain preservation efficiency / Excellent / Poor – due to low air permeability and non hygroscopic nature.
10 / % seepage of cement during field trial / 1.18% / 1.16%
11 / Effect of atmospheric temperature and sunlight / Unaffected / Prone to rapid deterioration
12 / Dimensional Stability / Good / Poor
13 / Reusability / Excellent / Poor
14 / Weight / Heavier than HDPE woven bag. / Lighter
15 / Cost / Higher compared to HDPE bags but jute bags have attractive resale value / -
4.0 Process Flow for manufacturing Hemmed and Selvedge Bags –
The process flow generally followed for manufacturing the above two types of bags i.e., hemmed and selvedge are shown below:
Hemmed bags Selvedge Bags
Ex Loom cloth Ex Loom cloth
Damping/Unrollingg Damping/Unrolling
Inspection/Repairing Inspection/Repairing
Calendering Calendering
Cutting Cutting
Hemming Seaming
Seaming Branding (optional)
Branding (optional) Bundling
Bundling Packing (Baling)
Packing (Baling)
Though it is evident that in case of selvedge bag hemming operation is not required but cloth area required for making a selvedge bag is 2.5% higher as compared to hemmed bag of same dimension. Further, sacking cloths are manufactured from 37.5” (95.25 cm) R S loom which can not produce wider cloth.
5.0 Machine speed and production
Machine parameters followed by different jute mills are discussed here and the production level along with scope of improvement are shown in table III.
5.1 Damping
Ex loom rolled cloth is manually fed into damping machine to unroll the cloth. The machine runs at a speed about 180-200 yds/min (165-183 m/min) without spraying water through nozzles excepting in dry spell.
5.2 Inspection/ Repairing
The weaving faults present in the cloth are inspected and repaired manually. Inserted cop present, if any, is removed to avoid major damage supposed to occur during calendering. Production at this stage varies depending upon major and minor weaving faults present in the fabric.
5.3 Calendering
Cloth is fed into machine applying proper tension through the rails and passed around all the iron and paper bowls of a 5-bowl calender machine. The central bowl is a steam cylinder that supposed to admit steam at a pressure of 25 to 30 psi. Proper calendering action takes place under adequate tension, temperature and pressure. 60” (152 cm) or 90” (228 cm) wide calender machine run at a speed of about 25 yds/m (23 m/min). Repairing of the defective cloths is also done after calendering stage in some mills.
5.4 Cutting
Normally Rotary and Guillotine type machines are used to cut the cloth into pre fixed piece lengths depending on the dimension of the bag. Machine speed is around 20 strokes/min.
5.5 Seaming and Sewing
In bag manufacture Stitchlogy plays an important role so far productivity and quality is concern. Stitchology or stitching technology is the study of basic stitch formation of all the machine made stitches, their properties and applications. To calculate production of bag in sewing machine following formula was evolved by IJIRA-
Production/mc./shift = Stitches/min x 60 (min) x 8 (hrs) x efficiency%
Stitches/dm x total length of stitches in a bag
5.5.1 Hemming
In order to arrest fraying of weft yarn from raw edges each of the two raw edges of cloth piece is folded twice individually to insert the raw edge inside the fold followed by stitching through hemming machine. Double locked chain stitches (type 401) is employed for the purpose using 8lbs (276 tex) jute single sewing thread with a stitch density of 10 SPDm. Machines run at a speed of about 1600 SPM.
5.5.2 Seaming
Seaming is the most vital sewing operation in bag manufactures. Two ends of the same piece of cloth are placed one above other and stitched for seaming (joining) with Herakle sewing machine that produces Overedge Chain Stitches (type 502) that runs at a speed of 1600 SPM.10 lbs (345 tex) x 3 ply jute sewing thread is used for stitching maintaining the stitch density of 10 SPDm and seam bight of 10 mm.
5.5.3 Safety Sewing
In bags, like A Twill an additional line of stitches is incorporated for safety purpose for preventing seepage of fine grains like sugar from the seam zone of the bag. Double locked chain stitches (type 401) is employed for the purpose using 9 lbs (310 tex) X 2 ply jute sewing thread with a stitch density of 10 SPDm with a speed of about 1700 SPM .
5.5.4 Branding
As per buyer’s requirement bags are branded manually by screen printing technique. Branded bags are kept on the floor for sometime to facilitate drying of the dye staff used for branding.
5.5.5 Bundling
As per BIS guide line 25 or 50 bags, depending on the quality of bag, are arranged one above the other and tied up with jute twine to form a bundle. 4% joined bags are placed in a bundle and loose ends, if any are trimmed off. As per recommendation of IJIRA providing knot or corner stitching has been eliminated.
5.5.6 Packing (Baling)
Required number of bundles are stacked on the platform of a hydraulic press (water or oil) and is compressed after covering with pack sheet and placing required number of iron hoops (hot or cold roll) on its top. When the stack height is reduced two ends of each hoop are anchored with pin and buckle. Loose ends of pack sheets are joined by hand sewing. Bags packed in the form of bale is pushed off the press and marked as per specification. The bales thus formed are stored in mill’s godown to offer for inspection and dispatch to the customers.
Based on the snap and time study conducted by IJIRA productivity in different sections of sack sewing and finishing department were estimated which are shown in Table III.