Operation snow removal : Strategies in order to increase the durability of wear pads

bladesScraper blades of snow removal equipment are originally considered as wear (spart) parts due to their degradation they face during their operational life. However, in order to prevent direct wear degradation of these parts while improving the equipment efficiency, manufacturers have worked on the modification and the design by adapting and fixing wear pads on the rear of the scraper blades in such a way to raise them slightly above the ground level. This way of proceeding protects the blade when these pads are wearing.

Aggregates of solid particles, asphalts, sand are ice that detach from the pavement and shoulder edges slide and scratch the underside surface of the wear pads during snow removal operations. Thus, the predominant wear mechanism in such a situation consists mainly of abrasion. The wear surface is characterized by various scratches of variable depth and parallel to the moving direction. The wear depends on pad material properties and the different operating parameters such as pressure, nature of ground, sliding distance or contact time, environment, etc.

In the light of greater amplitude of sliding movement, the wear debris are mostly evacuated from the contact zone (pad/ground), some other ones are embedded on the surface prior to detaching with the progression of wear. The damaged surfaces exhibit grooves and traces of plowing parallel to the direction of movement. Wear rate is becomes roughly steady over time. Wear volume increases with the applied load (pressure) and the travelled distance.

Wear pads: materials and fabrication:

Wear pads are generally made of either fully hardened steels or from hardfaced steel base metal. In fact, the hardfacing technique consists of his last option is considered as the preferred choice to confer a higher abrasion resistant to these critical parts, leading to increase their technical lifetime and also the equipment efficiency. According to the wear conditions described above, the materials that must be selected for hardfacing consists of ferrous alloys similar to high chromium white cast irons with the addition of strong carbides-forming elements (Nb, V, W). The typical microstructure of this type of hypereutectic alloys with a high fraction of primary carbides imbedded in matrix of austenite and secondary carbides. The high carbides concentration leads the abrasive particles to slide on the wear surface instead of indenting and abrading the matrix.

As per the previous experiences, it turns out that hardfacing deposited following a dot pattern have better spalling resistance in comparison with continuous hardfacing layers deposited on the same base metal. In addition, the selected hardfacing material must be compatible with the base metal. Welding must be carried out in a way to ensure a minimum penetration and to prevent the lack of fusion on the edges of prepared holes.

Preparation and welding

  1. Piercing of holes of 1/4” deep and 1/2 – 3/4” diameter as per a pattern of holes on the underside surface of the wear pad;
  2. Chamfering of the hole edges
  3. Filling and hardfacing with Sodel 2045 Plus, Sodel 2024 Plus or other products according to the base material and the recommended strategy

For hardfacing, proceed as follow :

  1. Preheat to 400°F;
  2. Strike the arc on the bottom of the hole and start to fill the hole with a circular movement from the edge towards the centre;
  3. Deposit an excess thickness of 2-3 layers after filling the hole;
  4. Let cool down to the room temperature;
  5. Grind out the outer periphery of the hardfacing to render it in the form of a rivet head.

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Khemici.badri@sodel.com

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PREVENTION OF POROSITY IN ALUMINUM WELDS

Porosite_aluminium.jpgPorosity is one of the main defects or discontinuities that may be encountered when welding aluminum and its alloys. The phenomenon is caused by the hydrogen gas that cannot escape from the molten metal, while still remaining entrapped in the microstructure after cooling. In fact, the hydrogen is very soluble in liquid pure aluminum with a concentration degree in the order of 2.2 (cm3 per 100 gr. of metal). However, this high concentration drops drastically to 0.069 cm3 per 100 gr at the boundary of the solidification before falling up to (0.036 cm3/100 g of metal) after cooling. The following graph illustrates the evolution of this phenomenon. It should be noted that the high thermal conductivity of aluminum, 210 W/m-K, promotes also the porosity formation especially in thick joint assemblies.

Hydrogen solubility in aluminum

Thus, since it is no longer soluble in solid aluminum after complete cooling, this free hydrogen will form voids air pockets, referred to as porosity. In function of the cooling conditions, the porosity mchartay be open to emerge on the surface and/or stay embedded in the metal. A coarse or clustered porosity may adversely affect certain metal properties such as tensile strength and toughness.

 

 

 

SOURCES OF HYDROGEN

The presence of hydrogen is originated primarily from humidity and contamination, and to a certain extent, fabrication condition and welding methods.

  1. Humidity : the humidity comes from the following:
  • Hydrated oxide layer on the metal surface;
  • Storing conditions of welding consumable (covered electrodes, rods and filler wire);
  • Condensation in water-cooled welding torches (leaking joints and fittings)
  • Shielding gases pipes (defective or non-hermetic material);
  • Inadequate purity in shielding gases ;
  • Temperature change between the storing area of filler materials and the welding station (condensation- dew point)
  1. Contamination :

Hydrogen is the decomposition product of hydrocarbon products such as machining oil, grease, solvents, solid lubricants, dirt, etc. The latter products may be present either on the base metal or the filler metal, or on the tools reserved for cleaning and preparation. Naturally

  1. Fabrication conditions and welding parameters

 Fabrication :

  • The products or parts produced by die-casting has naturally a much higher porosity level as compared with those obtained by static casting or extrusion. As a result, the welded parts become unavoidably more susceptible to porosity in the weld joint or even in heat affected zone.
  • Welding parameters:
  • Welding near air draughts (open doors, fans, operating fans, etc.);
  • Excessive electrical stick-out or CTWD(Contact To Work Distance);
  • Insufficient gas shielding (low flow rate);
  • Turbulence in the molten pool due to a high shielding gas flow rate;
  • Short-Circuit (S) or Globular (G) GMAW transfer modes produce spatters and, eventually, more porosity than the other transfer modes.
  • Erratic wire feeding in semi-automatic welding process;
  • Splashes deposited inside the nozzle prevents normal flow conditions of shielding gas;
  • Too tilted electrode work angle to the normal;
  • Low heat input;
  • Number of welding layers: multipass welding (ex. thick joints) is more subjected to the phenomenon of porosity than mono-pass welding (thin joints).

 PRÉVENTION OF POROSITY

Porosity may be controlled by first making a diagnosis of the main incriminated factors of its occurrence prior to bringing the necessary corrective actions. This involves the control of the storing conditions of filler materials, the use of appropriate and clean tools and also the application of proper welding procedures. This is described below.

  1. Filler materials

Filler metals must be stored in a dry environment or under a relative humidity of 35% maximum with a temperature of 15°C minimum. They also must be conserved in their original packagings until their use

Covered electrodes having exposed to moisture can be reconditioned by a redrying at 100-120°C for 1 to 2 hours.

Filler wires and rods must be free from traces of solid lubricant that have been used during drawing to reduce friction.

  1. Tools, cleaning and preparation:
  • Use clean tools which are only reserved to aluminum such as stainless steel wire brushes or ceramic grinding discs to remove the oxide surface;
  • Select moisture-resistant gas-hoses, ex. From metal or neoprene;
  • Check the tightness of torch (joints, fittings);
  • Degrease and/or wipe the solid filler rods using solvents like acetone;
  • Wear clean gloves when handling metal filler materials and metal parts;
  • Place filler materials as well as base metal in the same location a hour at least prior welding;
  • Keep an interval time of 6h maximum between the cleaning and the start of welding operation. Otherwise, cleaning must be done again prior to welding;
  • Shielding and purging gases have to conform to the minimal purity degree as required by codes;

 

  1. Welding method
  • preheat the base metal (>1/4″ thick.) and the backing plate, when used, at 200°C (400°F);
  • use high-frequency alternating current HF-AC for TIG welding in order to get a better cleaning action on the base metal surface;
  • increase the heat input in order to produce molten pool with a good fluidity;
  • use a mixture gas Ar-He (He: 25-75%) instead of straight argon to get a hot arc while inducing more heat into the weld pool and the base metal;
  • avoid having turbulences in the molten pool by ensuring a constant wire feeding (GMAW);
  • reduce the cooling rate by reducing the travel speed;
  • keep the shortest possible distance between the nozzle and the surface to weld;
  • Weld with an angle of about 20° relevant to the vertical axis.

 

As mentioned above, residual hydrogen in liquid aluminum results in porosity during the cooling of the weld metal. Then, in order to get a sound and porosity-free weld metal, one should eliminate the different sources generating hydrogen in the weld pool such as moisture and contamination on one side, and adjust the proper welding parameters regarding the welding application on the other side.

It is concluded that ensuring a good control on the hydrogen sources leads to a considerable increase in the chance of getting a sound and porosity-free weld metals.

khemici.badri@sodel.com

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Jammed pin : we need it to move !

Tractor at a Construction SiteHeavy equipment maintenance can bring several challenges that could increase the downtime on this equipment. In this article, we will talk about a part that is often jammed and that could delay the maintenance time enormously on heavy equipment which are the pins. So, we will introduce you to a relatively easy solution to apply in order to avoid financial and productivity problems.

When a pin is stuck, it could be long and difficult before being able to remove it in order to resume the maintenance of the equipment. Some may try to lubricate the part and hit it, others will heat it or will use an hydraulic equipment, in order to force its extraction. Those solutions could work but at what price ? The lubrication followed by hitting the part could be extremely long and inefficient. While using the hydraulic equipment to extract the pin could cause major damage to the equipment and does not guaranty success, especially if the pin doesn’t move. Besides that, often, several employees participate in the extraction, so the longer the process takes the more expensive it will be for the company in non productive time.

Our field experience has demonstrated that the utilization of equipment that could pierce a hole and heat the part at the same time allows a quicker extraction of the stuck part. The use of «exothermik » cutting & piercing tubes is a very sensible choice that could make you save a lot of time in maintenance (hour per employee) and increase your benefits.

Here is the procedure to use with the proper equipment and the « exothermik » tubes in order to proceed with the extraction of the pin on the heavy equipment.

  • Start piercing the part while taking care to create a flow space (red arrowcylindre on the picture), in order to allow the melting metal to get out easily and to facilitate greatly the job of the operator.
  • Continue the piercing until you get through the pin.
  • griz1As soon as the hole is completed, immediately sprinkle cold water on the pin with a water hose. The extremely hot part will contract in contact with cold water
  • Extract the pin manually or mechanically.

In order to extract a jammed pin, several techniques can be used but if the extraction doesn’t work with your usual strategies and the clock is ticking, it could payoff to try the Sodel Vulcain-Grizzly duo.

For more information or to receive a demonstration contact us.

Support@sodel.com / www.sodel.com

See the Sodel Vulcain-Grizzly duo in action

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WELDING METHOD CAN EFFECT THE FERRITE NUMBER

WeldingLast week we had a question from a customer that had to weld a 304H stainless steel part using a 308H electrode. The contract specification was requesting a ferrite number between 3 and 6 on the weld beads. They tough that they would be in line with specifications in using a 308H coated electrode with a ferrite number of 5,5 (calculated from WRC 1992 diagram). What was the final result when analyzing with the Ferritscope probe ? A ferrite between 0 and 2 FN; how could it be possible ?

One of the most powerful chemical elements affecting ferrite level is the dissolved nitrogen in the weld bead. For evaluating ferrite level, welding rod manufacturers consider an ideal nitrogen level of 0,06% in any stainless steel (300 series) weld metal. This is the nitrogen content you should get if you weld their rods using prescribed parameters. It is important to understand that nitrogen is not added intentionally in the coated rods. As a matter of fact, nitrogen which dissolves in the austenitic stainless steel comes from the ambient atmosphere. To obtain this low ideal nitrogen level of 0,06% in the weld metal, you have to maintain a very short arc.

In the present case, the project requested to realize 308H weld beads containing 94 to 97% of austenite and 3 to 6% of ferrite. If the customer uses a too long arc, he should obtain a dissolved nitrogen level in the weld bead over 0,06%. Nitrogen being a powerful austenitizer (a chemical element which stabilizes austenite to the detriment of ferrite), that’s why the measured ferrite number is lower than expected. In this situation you have two possible ways to obtain the requested ferrite : shorten the arc length using the same rod rated at 5,5 FN or keep a long arc using a rod rated at 8 or 9 FN. If you choose the second solution, the long arc will give you higher nitrogen content which should lowers the weld metal ferrite to the requested range. Because a higher than normal nitrogen level can have an effect on the weld bead mechanical properties, you should carefully consider this last solution.

support@sodel.com   / 1-800-363-1821

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How to have acceptable welds with copper filler metal

Copper breweryThere is mainly four causes that explain why the welds might not be acceptable when welding with copper filler metal : the thermal conductivity, the welding position, the sensitivity to hot cracking and the tendency to make porosity.

To counter the thermal conductivity, it is important to use a procedure (preheating, heat input, protective gas) enable to transfer enough heat to the welding joint.

Molten copper is very fluid and has to be welded in the flat position. On fillet weld, it is possible to weld it in the horizontal position.

Copper is sensitive to hot cracking when it is cooling down to the solid state. This is mainly occurring with tin bronze, copper-nickel and alloys containing lead. You can improve your chance of success by buttering the face of the chamfer and by peening the weld bead while they are still hot.

Copper reacts easily with oxygen to form porosities, so it is important to ensure of the adequacy of the gas protection.

Here is some reminder on welding with copper alloys

  • Weld in flat position whenever possible because of copper’s high fluidity
  • Using a support plate will help keep the parts on for better penetration
  • Good cleaning before and during welding will help to produce a quality weld
  • If there is arc blow while welding dissimilar metals, increase the preheat temperature
  • If the part is held in place by a vise or other metal device, preheating such devices will help maintain the temperature of the workpiece when preheating is required
  • Heat losses during preheating can be prevented by using a non-flammable, insulating material such as Sodelfix and by placing the workpieces on insulating refractory material.
  • When welding dissimilar metals, use the minimum welding currents recommended, whenever possible to minimize dilution
  • To join cast iron to copper alloys with Sodel 661, use small diameter electrodes and make small, discontinuous beads.

support@sodel.com / 1-800-363-1821

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HARDFACING STRATEGIES TO PROTECT YOUR BUCKET

hardfacing_snowIn order to choose the right alloy for your hardfacing application you first need to determine the composition of the base material (the material that you will weld on) and then the service condition that the weld deposit will have to face (impact, abrasion, etc). Once you have done your homework and you know which alloy is the best for your application, you can now select the hardfacing strategy that will give an optimal protection to the area for which you want to increase the durability.

Here are few examples of strategies you can use depending of your particular situation :

DOTS STRATEGY

plate_tetonsWhen to use it : When your parts are subjected to several impacts, like in crushers.

How to depose it : You need to make a dot the size of about a 2$ coin and the distance between the dots must be half the diameter of the dot. So, if your dot has a diameter of 1’’, the distance between the circles must be at 0,5’’. You must use the same pattern that you find on a dice for the number 5.

Which Sodel products to use : The kind of products to use could be different depending of the base material of your part to be protected, the kind of rocks or soil where your equipment is working and the kind of resistance you are looking for. Contact the Sodel technical team in order to have the right products for your application.

CIRCLES STRATEGY

plate_beigneWhen to use it : On the side of buckets in a way that the soil stays stuck inside and around the circles to protect the steel. Very useful for city works.

How to depose it : You need to make a circle of about 1” diameter and the distance between the circles must be half the diameter of the circle. So, if your circle has a diameter of 1’’, the distance between the circles must be at 0,5’’. You must use the same pattern that you find on a dice for the number 5.

Which Sodel products to use : The kind of products to use could be different depending of the base material of your part to be protected, the kind of rocks or soil where your equipment is working and the kind of resistance you are looking for. Contact the Sodel technical team in order to have the right products for your application.

LINES STRATEGY

plate_lignesWhen to use it : Lines can be used to facilitate the flow or to avoid the material from coming out of the bucket depending on their orientation..

How to depose it : When you are mainly working in rocks, the lines are welded along the flow and their spacing depends on the size of the rocks. While when you are mainly working in fine material (sand, soil, small rock, etc.), the lines are welded perpendicular to the flow to retain the material in the bucket.

Which Sodel product to use : The kind of products to use could be different depending of the base material of your part to be protected, the kind of rocks or soil where your equipment is working and the kind of resistance you are looking for. Contact the Sodel technical team in order to have the right products for your application.

DIAMONDS STRATEGY

plate_croiseeWhen to use it : It can be use for multiple situations, it is a combination of the lines and circles strategies.

How to depose it : The lines are welded to make a diamond shape and their spacing depends on the size of the material.

Which Sodel product to use : The kind of products to use could be different depending of the base material of your part to be protected, the kind of rocks or soil where your equipment is working and the kind of resistance you are looking for. Contact the Sodel technical team in order to have the right products for your application.

You can contact our technical support team anytime in order to get the right product and procedure for your application. (support@sodel.com) / 1-800-363-1821

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ROADS AND BRIDGES CONSTRUCTION

Multiple roads, bridges and maintenance projects have been undertaken for several years. Contractors are oftenModern dredge on a background of the new bridge working on tight budgets, so the used equipment has to be in operation and constantly productive. There are big challenges ahead for the equipment that will be used to manipulate the soil (excavation) or to break rocks (drilling). The soil varieties and the hard rocks encountered must be taken into consideration in order to suggest the optimal welding filler alloys for the situation. One type of soil could be much more abrasive than another one, whereas there are different kinds of rocks with their own size and hardness which make them unique.

Sodel has several solutions that will allow you to increase the productivity of the equipment in terms of durability and reduction of maintenance time and costs. Sodel has a complete line of hardfacing welding alloys that adapt to the working situation of your tools and equipment. Here are some of the most popular ones :

Sodel 325 will be useful where there is a direct jolt with rocks ; this alloy has an excellent impact resistance. This exceptional impact resistance is due to the quick hardening of the deposit’s microstructure under shock stress. The hardfacing of hammers and crusher jaws constitutes one of the major applications that will require the use of this alloy.

Sodel 2045 will protect the parts against abrasion when drilling. This product has a superior resistance to fine abrasives. This intrinsic property is due to the multiplicity and the concentration of hard compounds forming in the deposit’s microstructure in the as-welded condition.

Sodel 2024PLUS is to be used on parts facing abrasion under low impacts. This product has an excellent abrasion resistance and a moderate impact resistance. With its unique structure meeting the requirements for resistance to abrasion and impact, this product is very efficient and has brought great satisfaction in regards to its performance on several machinery components (Agriculture machinery, mining equipment, forestry equipments, dredging equipment, public work, etc.).

Please take note that the ideal product to use may vary from one project to another depending on the working condition of the equipment. It is for this reason that the Sodel product line includes more than 50 hardfacing products.

(support@sodel.com) / 1-800-363-1821

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