What is welding?

 

Wikipedia defines welding as “a fabrication process that joins materials, usually metals.” This is done by melting the part of the materials to be joined and adding some additional molten joining material. When the molten material cools, it forms a strong bond or joint.

Welding is the most widely practiced way of joining metals together due to the efficiency and economy of the process. It has been estimated that approximately 50% of the Gross National Product of the USA arises from activities that are in some for or another related, perhaps remotely, to welding. As an example, farming may appear to have nothing to do with welding, but the equipment the framer uses to grow and harvest his crops will have used welding in their manufacturing process.

Until the advent of the 20th century, welding was confined to the blacksmith shops where two pieces of metal were heated to very high temperatures in a forge and then hammered together until the joining occurred. This is what is called forge welding.

With the introduction of electricity into industrial processes, welding became both quicker and easy, and also more economical. Today there are 4 types of welding techniques that are commonly used.

The most basic for is Arc Welding where the parts to be joined together are brought into contact with strong electrical current and heated. The molten parts are then joined together to form a weld. This is the low technology end of welding in its cheapest and least sophisticated form.

Gas Welding is generally used for repair work especially in the case hollow items like tubes and pipes. Hot gas is forced onto the surfaces to be welded. This procedure requires the parts to be subjected to less heat and is suitable for material that may be damaged by exposure to high temperature. For this reason it is used in the jewellery industry which has to work with soft metal with low melting points.

Resistance Welding requires that an additional sheet of material is used to cover the pieces that are to be welded together. This  provides great strength to a weld, but the process requires expensive equipment and also the use of additional material to encase the weld which makes it expensive and not suitable for all applications.

Laser Welding is the most modern technology available. High intensity lasers can be tightly focused and produce controllable heat on the surfaces to be welded very quickly. This is perfect for material which can be damaged by prolonged exposure to extreme heat. Laser welding is very accurate and can be used to produce even the smallest of welds. However, because of the high capital cost involved in purchasing this equipment, the cost of welding is also high.

Although the perception of welding is that of a simple process of heating and joining, it is a high technology industry with huge  amounts being spent of research and development to find stronger, more accurate and cheaper methods. The welding process plays a big role in metallurgy with a constant effort underway to find newer and more weld friendly alloys.

 

Sourced:  From www.welderworld.com

IMPORTANCE OF GOOD QUALITY WELDS IN TRAILERS

The topic of discussion today is one aspect of structural fabrication i.e welding to which the transporters do not give much importance to.  The general feeling in transporters is that welding is essential but it is  only as an ornamental requirement and does not deserve much skill and attention. This kind of mind-set is prevalent and shared by most of the transporters.  However it must be noted that the stability and the strength of the structure totally depends on the quality of the welds.

This aspect need not be discussed where both the parties i.e the manufacturer and the customer have a sound engineering background.  The problem arises where one of the parties does not have a sound engineering background and cannot appreciate the topic of discussion.

Let us understand what happens when a welding joint in a trailer or a semi trailer fails. 

1. It can lead to serious accidents.
2. It can cause distortion of structure and lead to unnecessary maintenance.
3. Tyre wear and tear.
4. Increase in down time of a productive vehicle.

The following pictures are classic example of inadequate welding and welding failure.

The  picture on the left shows a structural joint in which there is incomplete and poor quality of weld.  The picture on the right shows a failure of a weld joint due to a defect called as lack of fusion.  In this case the welder has failed to fuse the parent metals while depositing the filler material.  This type of defect shown in the picture is probably because of  low current setting coupled with inadequate skill of the welder.

The adjoining picture is a classic example of good fillet weld joint.












So in order to avoid failure and breakdown due to defective welding the following should be insisted upon.  The job of fabrication of a trailer body/frame is nothing short of structural fabrication and all the requirements relevant to fabrication and welding codes as per ASME should be insisted upon.  The following are the basic documents that the client should insist upon.

1. Material test reports for physical testing and chemical analysis  conforming to ST-42 or any other equivalent standard should be insisted upon. It is important to understand that while freezing a standard for the material to be used, the end application has to be kept in mind.
   
   
2. Once the materials to be used are tested and found satisfactory, the next step will be to establish a welding procedure.  There are standard formats in ASME sec IX which clearly define the parameters that have to be recorded. This procedure qualification has to be witnessed by an  welding inspector.  This process is called as establishing a “PQR”, the full form is “Procedure Qualification Record”.By carrying out this exercise we achieve the following. The material suitability of  the welding electrodes and the parent metal used in the structure is tested for physical and chemical properties.  The position of the weld joint and the welders skill in that position is both tested.  There are other intricate parameters which are also established like welding process, size of electrode, current, voltage, flow of gas in case of MIG/TIG, surface preparation, geometry of the weld joint, cleaning processes etc. The test sample of the welded material is sent to approved laboratories for non destructive and destructive testing as per relevant codes.
   
   
3. The next step is qualification of welders as per the established PQR and this process is called “WPS”.......

(To be continued……)

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

E-Mail:  jagdish@belcoengineers.com

SUSPENSION SYSTEMS IN SEMI-TRAILERS...

Suspension systems in semitrailers can be classified in various types.  

I am not going to blog on the type of suspensions or their classifications but what I am going to bring to the fore here is the inherent advantage of having a properly manufactured suspension systems such as York as compared to the indigenous ones which are so widely used by fleet owners but the following write-up will clear a lot of misconceptions.

The only advantage one can gain from using a indigenous or plate fabricated type of suspension system is that the initial cost is less but 

obviously this cheaper option has a very high maintenance cost.  The transporters who opt for this type of fabricated suspension systems ultimately incur loss.

Reasons for failure of the indigenous type of suspension:

• The general wear tear is more in case of the fabricated type of suspension as compared to York manufactured  suspension because the material of construction of the fixed and move-able joints are all made up of forged steel where as the indigenous suspension components are fabricated out of mild steel plates.
• All the joints in a York manufactured suspension are provided with suitable bush so that the main components do not get damaged in the general course of usage.  During a maintenance cycle only the bushes have to be replaced and the job is done.  However in case of the fabricated type of suspension no bushes are provided.  The mating components are fitted with pin type of bolts directly with out any bush.  In due course of time the joints wear out damaging the main plates and thereby causing  play in the joints.  This results in misalignment and tyre wear & tear.  The only option during repairs will be to replace the primary supporting plates which is a costly option.
• In case of York suspension the balance rod has an option for adjusting its lengths so that alignment can be done in-situ, whereas the indigenous suspension have fixed type of balance rods where no adjustment is possible.

I hope this write up will throw some light on the suspension systems to be used so that cost cutting can be done and will help the transporter choose the right type of suspension system especially because there is stiff competition and therefore it is important to take into consideration the running and maintenance cost if we really have to cost effective ........ competitive!!!


Regards,

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

E-Mail:   jagdish@belcoengineers.com

Reinforcing Primary Members In Semitrailers

The topic I have taken today is very important and relevant.  The manufacturers have to understand that all approved designs take into consideration the rated load to be carried and also a factor of safety is added along with the corrosion allowance depending on the climatic conditions of a place where the fleet is to be operated.

This results in a structure which is optimal in weight and the transporter also ends up getting more payload for a prime mover of a particular capacity.  But this market of manufacture of trailers is highly competitive and is also customer driven.  Sometimes the design of a vehicle is altered to suit the customer's whims and fancies flouting all engineering norms. 

A case in point is if we consider the transporters operating over dimensional cargo with over load.  They insist that the primary member be reinforced with an additional flat which is welded on the bottom flange of the main beam.  The point I am trying to make is here is that the flat is welded in such a location that it does not affect the moment of inertia in any way, moreover the thickness of the flat welded for reinforcing is three times the thickness of the bottom flange or the primary members.  After welding such a flat to the beam it only results in increase in stresses due  to heavy welding.  Failure due to heat affected zone is evident and the purpose is defeated!!  A classic example of failure is shown in the pictures above.

This factor must be considered by the transporters because it affects the rated payloads and the fabricator ends up using more steel without acheiving the objective of strengthening.

REINFORCEMENT OF PRIMARY MEMBERS AT OUR WORKS

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

E-Mail:  jagdish@belcoengineers.com

IMPROVEMENT IN DESIGN FOR SEMITRAILERS - LOW BED TYPE

We have modified the neck design of the low bed semi trailer by providing additional support as shown in the above picture so that  sharp bends are avoided in primary structural members.

Actually when there are sharp bends the weight acting per unit area is more.  This becomes a weak zone where the structure can shear.  The area near the neck is more vunerable for one more reason i.e while fabricating this neck a lot of heat input is given in terms of welding and cutting the members to achieve the given shape of the low bed trolley. 

This heat input induces stresses in these areas. When subjected to load the primary members fail because of the heat affected zone; this problem could have been addressed by stress relieving techniques.  However the cost of the trailer would go up and this becomes a prohibitory factor.

In the said scenario our design will take care all the above factors.  This will help us avoid use of additional steel that is wrongly used by local fabricators to strenthen the primary members while manufacturing trailers.

Written by:

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

-Mail:  jagdish@belcoengineers.com

A SEMITRAILER FOR THE TATA PRIMA 4928..... The World truck

As I write this I am very proud to inform that we have delivered two semi-trailers for the Tata Prima 4928, world truck shown in the above picture.  This prime mover is manufactured to compete in international market and the quality of the product is on par with any international brand. 

It was a honour when we were asked to manufacture a low bed semitrailer 45 feet long with triple axle.  We went back to the drawing board to modify the structure for the low bed semi trailer.  The challange here was to design a structure for this prime mover which is equipped with the state of the art common rail diesel engine.

The major difference in this prime mover and the conventional prime movers is that the speed to weight  ratio is very high.  This necessasiates a structure which has good resistance to impact loads because the road conditions in India have still to reach international standards and on the other hand making the structure too heavy to withstand these impact loads reduces the payload available to the transporter; making his operations un-viable.  Both the requirements are contradictory and it was a challange to arrive at a optimal design to take care of both these conflicting requirements.

I am glad we have achieved this and I would certainly like to thank our clients M/s Reetu Logistics & Roadlines Pvt Ltd; who showed a lot of confidence in our capability.  I feel my team has definitely done justice and come out with a product which will match its powerful prime mover.

Congratulations to all concerned.

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

-Mail:  jagdish@belcoengineers.com

Introductory Blog.

Dear readers,

I have been blogging for quite some time now though on a personal level.  However this blog will be an interface between Belco Engineers and clients, consultants, employees, vendors and of course well wishers who are connected with the company.

I look forward to a very fruitful sharing of thoughts and ideas.  I hope this becomes a good platform for interacting.

Regards

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

E-Mail:  belco@belcoengineers.co.in