Thai conveyor belt Co.Ltd. (TCB) has provided conveyor splicing service to RC 03 belt conveyor of XXXXXX Co.Ltd. on August, 22, 2009 for first splice at installation and November 25, 2009for second splice. The RC 03 receives the coal from the coal barge line and conveys to the storage warehouse for stock piling. After the conveyor operated for certain time the belt stretched until the fixed rope (counterweight hanging) reaches its fully tension.
RC 03 Conveyor Belt
This circumstance caused the take up counterweight does not work properly, consequently, the belt slips during starting and running the conveyor due to insufficient slack-side tension. Therefore, it is necessary to lower down the hanging rope to allow the counterweight freely move and the conveyor belt can get back to normal operation once again.
RC 03 Take up hanging rope
Currently, after free the hanging rope the take up still has small distance to reach its stop level. Therefore, it is necessary to plan the third cut and re-splice the belt (after first/second splice were done on mentioned date above) in order to bring the conveyor belt work properly as usual.
RC 03 during operation on January 11, 2010
It come to the XXXX worry that the frequently splice operation due to belt elongation effect to the reliability of their processing operation/related management as well as cause of other associated costs such as loss of output, idle worker/machine, schedule disruption and huge cost of barge delay. Therefore, XXXX required TCB to propose alternative belt selection to minimize the breakdown time and improve their reliability/safety of CV 03 conveyor system due to excessive fabric EP belt elongation.
2) Information of CV 03 provided by XXXXX
Handling Material : Coal
Design Capacity : 2,700 Ton/Hour
Current Operating Capacity ; 900- 1,200 Ton/ hour
Conveyor Type : 45 Degree Trough belt
Belt speed : 244 m/min
Belt Width: 1400 mm.
Horizontal length; 211.6 M.
Lifting: 4.0 M.
Bulk Density: 0.8 Ton/ Cu.M.
T (Maximum Tension : 4.8 Tons
Belt specification : EP 200x 3p x 5.0 /3.0
RC 03 Conveyor Structure
Observation of RC 03 during operation
3) Fabric (EP) ply V.S Steel Cord Conveyor belt Characteristics
TCB would like to illustrate some important technical characteristics of both fabric (EP) belt and steel cord belt for XXXX’s guidance in order to have sufficient information before making final decision. .
Steel Cord Belt Structure
Steel Cord Belt Cross Section
Fabric Belt Structure
Belt Stretch or Elongation (CEMA 6th. Edition)
Any conveyor can be expected to have stretch in conveyor fabric (EP) belt caused by elongation. Design for sufficient movement of take up distance to compensate these dimension change in overall belt length should be elaborately considered in order to accommodate acceleration or deceleration surges without having the take up strike against its stop level. Several types of stretch in fabric belt occurred during conveyor operation;
1) Elastic stretch: This is that part of the stretch which occurs in a conveyor belt during starting acceleration or braking deceleration. This stretch is almost entirely recovered when the applied pull or stress is removed.
2) Constructional stretch: This is due more to the type of fabric weave than to the textile material used. In a conventionally woven fabric, the warp strands which are crimped tend to straighten out as the load is applied. This results in belt growth, a portion of which is no recoverable.
3) Permanent length change: This includes changes in length caused by elongation in the basic fiber structure. It also includes that portion of the elastic stretch and constructional stretch which is no recoverable.
When consider only the working tension (max) = 4.8 Ton factor, to select the type of belt .It seems that the CV 03 conveyor span (211.6M-C/C) can accommodate with the current CV03 fabric belt EP 200x 3p x 5.0/3.0 very well. However, the fabric belt has the significant characteristic of elongation especially for the long span conveyor belt that has frequently splice affected to the process operation/related management as mentioned above. In general (CEMA 6th edition),it is necessary of the fabric(EP) belt to have automatic take up movement 1.25%-1.75% (C/C) while comparing with very little elongation 0.2% -0.4 % of steel cord depending on the rated tension.
In the YOKOHAMA conveyor belt technical information stated that the Elastic elongation and permanent Elongation of EP equal to 0.2%-0.5% and 0.5%-1.0 % respectively while for steel cord belt 0.03% – 0.06% for Elastic Elongation and 0.08%-0.13 % for permanent Elongation.
Therefore, in this particular case ,as for the elongation concerned, the fabric belt acquire belts spare length more than twice to re-splice the belt while the steel cord belt required only one or none. Furthermore, if fabric belt is still in use. it is necessary for the XXXX personnel to frequently observe and adjust the take up counterweight properly in order to allow the conveyor system smoothly operated as well as taken an inevitable risk in case of excessive elongation if there is no good record keeping of belt splice history.
Stress-Strain Curve for different belt carcasses
3.2)Troughability and speed: One of the damage of belt arises from edge damage due to crook running of belt. One of the causes is the poor troughability.Eventhrough, recently thin and strong fabric belt (EP) is used for general purposed belt and their trough ability has been improved. However when the long span of CV03 runs with its full capacity (2,700 ton/Hr.) .The designed fabric using should be strong enough (with considerable thickness ) to withstand the load .Therefore, the problem still remain in its troughability.
Belt Thoughability Test
In this particular CV 03, with the trough angle of 45 degree of carriers (which considered large trough angle) still has potential to create the problem whereas, the steel cord belt is quite advantageous because there is no transverse reinforcing element to spoil troughability. The absence of transverse reinforcing in steel cord belt provides the ability to trough empty at virtually any trough angle irrespective of belt strength or width. Consequently, there is no trouble due to poor troughability as well as better improve belt alignment.
In addition, the steel cord belt is very good for high speed conveyor belt than the EP fabric .The design speed of CV03 is 244 M/min which is greater than CEMA (6th. edition) recommendation (152 M/min.) for coal fired power plant (consider of material degradation and the hazards associated with spillage, leakage and dust generation).Therefore the use of steel cord belt instead of fabric is most beneficial.
3.3) Service Life: Since the tension of steel cord lies on a single plane, the adhesion between the steel cord and rubber is excellent THEREFORE, THE STEEL CORD GIVE SUPERIOR IN ITS flexural fatigue resistance. The carcass of fabric belt consist of laminated EP which can be ply separated due to flexural fatigue and decreasing of tension strength of fabric will be caused due to water/chemical penetration from the injured portion , which result in overall width cut-off. Consequently, much longer life can be expected from steel cord belt than fabric belt.
Tension Member of Steel Cord forms one single ply
Adhesion between steel cord and cushion rubber is excellent
Fabric Belt with laminated EP carcass
3.4) Life of splicing part: A remarkable characteristic of steel cord belt is that the life of the splicing part is long and the safety property of the belt is very high. In case of a fabric belt, it usually consists of overlapped fabric plies, and when it is bent at the pulley, the outer ply is expanded, while the inner ply is compressed. Accordingly, when this movement is repeated for a long period and added with repeated shocks, the rubber between plies, particularly in the splicing part, becomes fatigued making it easily separable.
Overlap Carcass preparation for fabric belt splice
Steel cord belt, however, having parallel steel cord embedded lengthwise in cushion rubber which forms only a single ply. Due to the tension member of steel cord act as single ply. Therefore, it almost entirely free of such fatigue and make the splice has tensile strength and service life same as the belt as a whole. In addition, internal inspection using X-rays can be conducted on steel cord belt without any adverse affect on the splicing section, but this is not possible with fabric belts, so a very high degree of safety can be ensured with steel cord belt.
Outer fabric EP in tension while inner in compression causes belt fatigue
For general purpose belt, YOKOHAMA belt design manual use 7 and 12 safety factor for steel cord and fabric belt respectively. Therefore, it is indicated that the steel cord belt has more reliability than fabric belt.
3.5) Repair of the belt: In case the steel cord belt is damaged, an adequate treatment can be taken because the degree of injury can be clearly found by means of X-ray photograph etc. Yet, there is almost no fear, in the case of little degree of injury, that the injury will be further expanded, thus making the belt highly safe. Consequently, if the subsequent maintenance and control are performed satisfactorily, the belt can be used very safely.
Particularly, in case of longitudinal tear accident, which is the most fearful injury for a conveyor belt, it is quite vital for a fabric belt, whereas it can be temporarily repaired, in the case of ST BELT, without the fear of decreasing its strength. Further, it is possible to make a permanent repair for steel cord belt to yield the same strength as the old one.
In conclusion, steel cord belt is the safest belt because the danger of being injured is very little if the facilities and management are satisfactory and it is easily repaired even when it is injured.
4) Recommendation: Steel cord belt has much longer life and more reliability than fabric belt and it is very often recommend using for the main conveyor line. In the near future XXXX suppose to use CV 03 to convey the coal in maximum capacity (2,700 Ton/Hour) while currently carrying only 900-1,200 ton/Hour. It is anticipated that the fabric belt shall be inevitable encounter excessive elongation problem as currently happened.
RC 03 Running at 900-1,200 Ton/Hour
Therefore XXXX needs to have the high reliability/safety conveyor belt to minimal breakdown time and save the associated costs as aforementioned. Base on the excellent operating performance of the steel cord than the fabric belt .TCB would recommend XXXX to use steel cord belt, regardless of cost consideration, to replace the existing fabric belt in order to minimize the existing problem encounter and improve reliability/safety of XXXX’s conveyor system. Anyway steel cord belt is worth for the alternative selection for long term investment especially when reliability, maintenance and service life issues are put into consideration.
Special advice for XXXX consideration
1) Belt specification: TCB would recommend the FR (Fire resistance or Fire extinguish) belt grade to use for coal carrying to comply with safety purpose in case of fire. (XXXX uses FR belt for all their conveyor belt lines.) Please check your existing belt used whether it is FR belt or not.
2) Belt speed: The design speed of CV03 is 244 M/min which is greater than CEMA (6th .edition) recommendation (152 M/min.) for coal fired power plant (consider of material degradation and the hazards associated with spillage, leakage and dust generation). Therefore, the use of steel cord belt instead of fabric is most beneficial especially for this high speed with large volume carrying circumstance.
Hope that this report would be satisfactory to XXXX to have sufficient information for making decision. If there is any query, please do not hesitate contact TCB .We are prompt to support you at any time.