This paper introduces the spray welding process of glass bottle can molds from three aspects
The first aspect: the spray welding process of bottle and can glass molds, including manual spray welding, plasma spray welding, laser spray welding, etc.
The common process of mold spray welding – plasma spray welding, has recently made new breakthroughs abroad, with technological upgrades and significantly enhanced functions, commonly known as “micro plasma spray welding”.
Micro plasma spray welding can help mold companies greatly reduce investment and procurement costs, long-term maintenance and consumables use costs, and the equipment can spray a wide range of workpieces. Simply replacing the spray welding torch head can meet the spray welding needs of different workpieces.
2.1 What is the specific meaning of “nickel-based alloy solder powder”
It is a misunderstanding to regard “nickel” as a cladding material, in fact, nickel-based alloy solder powder is an alloy composed of nickel (Ni), chromium (Cr), boron (B) and silicon (Si). This alloy is characterized by its low melting point, ranging from 1,020°C to 1,050°C.
The main factor leading to the widespread use of nickel-based alloy solder powders (nickel, chromium, boron, silicon) as cladding materials in the entire market is that nickel-based alloy solder powders with different particle sizes have been vigorously promoted in the market. Also, nickel-based alloys have been easily deposited by oxy-fuel gas welding (OFW) from their earliest stages due to their low melting point, smoothness, and ease of control of the weld puddle.
Oxygen Fuel Gas Welding (OFW) consists of two distinct stages: the first stage, called the deposition stage, in which the welding powder melts and adheres to the workpiece surface; Melted for compaction and reduced porosity.
The fact must be brought up that the so-called remelting stage is achieved by the difference in melting point between the base metal and the nickel alloy, which may be a ferritic cast iron with a melting point of 1,350 to 1,400°C or a melting point of 1,370 to 1,500°C of C40 carbon steel (UNI 7845–78). It is the difference in melting point that ensures that the nickel, chromium, boron, and silicon alloys will not cause remelting of the base metal when they are at the temperature of the remelting stage.
However, nickel alloy deposition can also be achieved by depositing a tight wire bead without the need for a remelting process: this requires the aid of transferred plasma arc welding (PTA).
2.2 Nickel-based alloy solder powder used for cladding punch/core in bottle glass industry
For these reasons, the glass industry has naturally chosen nickel-based alloys for hardened coatings on punch surfaces. The deposition of nickel-based alloys can be achieved either by oxy-fuel gas welding (OFW) or by supersonic flame spraying (HVOF), while the remelting process can be achieved by induction heating systems or oxy-fuel gas welding (OFW) again. Again, the difference in melting point between the base metal and the nickel alloy is the most important prerequisite, otherwise cladding will not be possible.
Nickel, chromium, boron, silicon alloys can be achieved using Plasma Transfer Arc Technology (PTA), such as Plasma Welding (PTAW), or Tungsten Inert Gas Welding (GTAW), provided the customer has a workshop for inert gas preparation.
The hardness of nickel-based alloys varies according to the requirements of the job, but is usually between 30 HRC and 60 HRC.
2.3 In the high temperature environment, the pressure of nickel-based alloys is relatively large
The hardness mentioned above refers to the hardness at room temperature. However, in high temperature operating environments, the hardness of nickel-based alloys decreases.
As shown above, although the hardness of cobalt-based alloys is lower than that of nickel-based alloys at room temperature, the hardness of cobalt-based alloys is much stronger than that of nickel-based alloys at high temperatures (such as mold operating temperature).
The following graph shows the change in hardness of different alloy solder powders with increasing temperature:
2.4 What is the specific meaning of “cobalt-based alloy solder powder”?
Considering cobalt as a cladding material, it is actually an alloy composed of cobalt (Co), chromium (Cr), tungsten (W), or cobalt (Co), chromium (Cr), and molybdenum (Mo). Usually referred to as “Stellite” solder powder, cobalt-based alloys have carbides and borides to form their own hardness. Some cobalt-based alloys contain 2.5% carbon. The main feature of cobalt-based alloys is their super hardness even at high temperatures.
2.5 Problems encountered during the deposition of cobalt-based alloys on the punch/core surface:
The main problem with the deposition of cobalt-based alloys is related to their high melting point. In fact, the melting point of cobalt-based alloys is 1,375~1,400°C, which is almost the melting point of carbon steel and cast iron. Hypothetically, if we had to use oxy-fuel gas welding (OFW) or hypersonic flame spraying (HVOF), then during the “remelting” stage, the base metal would also melt.
The only viable option for depositing cobalt-based powder on the punch/core is: Transferred Plasma Arc (PTA).
2.6 About cooling
As explained above, the use of Oxygen Fuel Gas Welding (OFW) and Hypersonic Flame Spray (HVOF) processes means that the deposited powder layer is simultaneously melted and adhered. In the subsequent remelting stage, the linear weld bead is compacted and the pores are filled.
It can be seen that the connection between the base metal surface and the cladding surface is perfect and without interruption. The punches in the test were on the same (bottle) production line, punches using oxy-fuel gas welding (OFW) or supersonic flame spraying (HVOF), punches using plasma transferred arc (PTA), shown in the same Under cooling air pressure, the plasma transfer arc (PTA) punch operating temperature is 100°C lower.
2.7 About machining
Machining is a very important process in punch/core production. As indicated above, it is very disadvantageous to deposit solder powder (on punches/cores) with severely reduced hardness at high temperatures. One of the reasons is about machining; machining on 60HRC hardness alloy solder powder is quite difficult, forcing customers to choose only low parameters when setting turning tool parameters (turning tool speed, feed speed, depth…). Using the same spray welding procedure on 45HRC alloy powder is significantly easier; the turning tool parameters can also be set higher, and the machining itself will be easier to complete.
2.8 About the weight of deposited solder powder
The processes of oxy-fuel gas welding (OFW) and supersonic flame spraying (HVOF) have very high powder loss rates, which can be as high as 70% in adhering the cladding material to the workpiece. If a blow core spray welding actually requires 30 grams of solder powder, this means that the welding gun must spray 100 grams of solder powder.
By far, the powder loss rate of plasma transferred arc (PTA) technology is about 3% to 5%. For the same blowing core, the welding gun only needs to spray 32 grams of solder powder.
2.9 About deposition time
Oxy-fuel gas welding (OFW) and supersonic flame spraying (HVOF) deposition times are the same. For example, the deposition and remelting time of the same blowing core is 5 minutes. Plasma Transferred Arc (PTA) technology also requires the same 5 minutes to achieve complete hardening of the workpiece surface (plasma transferred arc).
The pictures below show the results of the comparison between these two processes and transferred plasma arc welding (PTA).
Comparison of punches for nickel-based cladding and cobalt-based cladding. The results of running tests on the same production line showed that the cobalt-based cladding punches lasted 3 times longer than the nickel-based cladding punches, and the cobalt-based cladding punches did not show any “degradation”.The third aspect: Questions and answers about the interview with Mr. Claudio Corni, an Italian spray welding expert, about the full spray welding of the cavity
Question 1: How thick is the welding layer theoretically required for cavity full spray welding? Does Solder Layer Thickness Affect Performance?
Answer 1: I suggest that the maximum thickness of the welding layer is 2~2.5mm, and the oscillation amplitude is set to 5mm; if the customer uses a larger thickness value, the problem of “lap joint” may be encountered.
Question 2: Why not use a larger swing OSC=30mm in the straight section (recommended to set 5mm)? Wouldn’t this be much more efficient? Is there any special significance to the 5mm swing?
Answer 2: I recommend that the straight section also use a swing of 5mm to maintain the proper temperature on the mold;
If a 30mm swing is used, a very slow spray speed must be set, the workpiece temperature will be very high, and the dilution of the base metal becomes too high, and the hardness of the lost filler material is as high as 10 HRC. Another important consideration is the consequent stress on the workpiece (due to high temperature), which increases the likelihood of cracking.
With a swing of 5mm width, the line speed is faster, the best control can be obtained, good corners are formed, the mechanical properties of the filling material are maintained, and the loss is only 2~3 HRC.
Q3: What are the composition requirements of solder powder? Which solder powder is suitable for cavity spray welding?
A3: I recommend solder powder model 30PSP, if cracking occurs, use 23PSP on cast iron molds (use PP model on copper molds).
Q4: What is the reason for choosing ductile iron? What’s the problem with using grey cast iron?
Answer 4: In Europe, we usually use nodular cast iron, because nodular cast iron (two English names: Nodular cast iron and Ductile cast iron), the name is obtained because the graphite it contains exists in spherical form under the microscope; unlike layers Plate-formed gray cast iron (in fact, it can be more accurately called “laminate cast iron”). Such compositional differences determine the main difference between ductile iron and laminate cast iron: the spheres create a geometrical resistance to crack propagation and thus acquire a very important ductility characteristic. Moreover, the spherical form of graphite, given the same amount, occupies less surface area, causing less damage to the material, thus obtaining material superiority. Dating back to its first industrial use in 1948, ductile iron has become a good alternative to steel (and other cast irons), enabling low cost, high performance.
The diffusion performance of ductile iron due to its characteristics, combined with the easy cutting and variable resistance characteristics of cast iron,Excellent drag/weight ratio
good machinability
low cost
Unit cost has good resistance
Excellent combination of tensile and elongation properties
Question 5: Which is better for durability with high hardness and low hardness?
A5: The whole range is 35~21 HRC, I recommend using 30 PSP solder powder to get a hardness value close to 28 HRC.
Hardness is not directly related to mold life, the main difference in service life is the way the mold surface is “covered” and the material used.
Manual welding, the actual (welding material and base metal) combination of the obtained mold is not as good as that of PTA plasma, and scratches often appear in the glass production process.
Question 6: How to do the full spray welding of the inner cavity? How to detect and control the quality of the solder layer?
Answer 6: I recommend setting a low powder speed on the PTA welder, no more than 10RPM; starting from the shoulder angle, keep the spacing at 5mm to weld parallel beads.
Write at the end:
In an era of rapid technological change, science and technology drive the progress of enterprises and society; spray welding of the same workpiece can be achieved by different processes. For the mold factory, in addition to considering the requirements of its customers, which process should be used, it should also take into account the cost performance of equipment investment, the flexibility of equipment, the maintenance and consumable costs of later use, and whether the equipment can cover a wider range of products. Micro plasma spray welding undoubtedly provides a better choice for mold factories.