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Cold-box technology: 16 small problems you can easily ignore

Sources:本站 | Release date: 2017-08-30 | Browsing volume:
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Cold-box technology: 16 small problems you can easily ignore
1 Use an acid scrubber for exhaust gas purification
Sulfuric acid is added to the clean scrubber and, if triethylamine is used, the solution must contain 23% strength sulfuric acid. If the solution to be prepared in the scrubber, then add water and then slowly add concentrated sulfuric acid, but also have good mixing, exothermic reaction.
If the amount of solution in the scrubber is reduced by evaporation, just add water to maintain the level. (Or use about 80% phosphoric acid concentration).
The pH value of the liquid should be checked frequently. When the pH is higher than 4.5, the acid will be wasted. The entire scrubber solution should be poured out and a new solution should be newly added. For example, it may take less time to add some concentrated sulfuric acid to temporarily use it.
2 sand core hardening time is too long
Sand core weight and ideal hardening time:
Different weights of sand cores have different hardening times because of insufficient amine supply for the amine generator. A 14-in. (889px) thick sand core is the same as the small sand core hardening time.
Hardening pressure:
Low pressure: 2PSI-9PSI (0.0138Mpa-0.062Mpa),
High pressure: 15-30PSI (0.1MPa-0.2Mpa).
In general, increasing the amount of amine, increasing the pressure on the core of the cartridge will reduce the hardening time.
Other: The ventilation system of the core box must fulfill its total ventilation area, inlet and exhaust area ratio and ventilation uniformity.
3 demoulding sand core is not hardened
For these non-hardened parts it is usually necessary to lengthen the hardening time; this is the result of the absence of amine gas in certain parts of the sand core. The remedy is to extend the hardening cycle or to improve as described above.
Amines did not pass through the non-hardened core sand site, while the non-uniform local sandy sand core did not cure. This was the reason that the two sand cores were not cured locally.
4 triethylamine dosage is too large
Which (1), (2) for two main reasons:
(1), improper core airway, the core part of the gas short circuit appears.
(2), the curing pressure is so low that the catalyst in the intake zone can not be diffused and pressed into every corner of the core.
(3), the level of the core box of the exhaust area is greater than the intake area will appear short-circuit gas phenomenon, resulting in gas through the core resistance of the smallest part of the formation of short-circuit channel. This can be overcome when more catalysts are used. (Side-blown sand, which is not important for balancing exhaust gas when it is blowing in. When the exhaust is set correctly, the sand creates a sufficient back pressure against the gas, allowing the gas to diffuse even if the exhaust area is greater than the intake area) .
(4), the negative pressure exerted on the exhaust side of the core box will further contribute to the short circuit and insufficient pressure in the core box. Although the purpose of applying the negative pressure is to remove the catalyst, it at the same time reduces the barrier effect of the sand on the gas flow. This reduces the ability of amine gas to diffuse to the side. Exhaust zone in the inflatable and high negative pressure, the best control in the + 1PSI (+0.006895Mpa) and -1PSI (-0.006895Mpa) range.
(5), parting surface leakage or positive pressure zone between the inlet and the core box leakage. The same phenomenon occurs due to the leak phenomenon caused by the poor sealing of the blow port of the side blown sand core box. The catalyst leaking into the air can not be used to harden the core. Leaks not only affect the normal pressure cavity, while polluting the working environment.
5 triethylamine odor is too large
1), generator leakage
2), tooling leaks;
3), after cleaning the remaining residual amine core. Evenly hardened and uniformly blown cores barely detect amine odor. The residual amine odor is primarily due to improper venting of the core cartridge followed by a large amount of amine with a small amount of clean air. This problem can be solved by increasing the blow-in time before correcting the tooling.
6 James mold
The so-called dip mold refers to a portion of the resin left in the core box, this phenomenon, plus more release agent can not be avoided.

Cause of: 

The factors that cause the sand core to be insufficiently compacted will cause the resin to remain on the core box when the sand core is released.

When the thickness of the hardened layer is not thick enough and the applied high-pressure curing gas is long, a layer of resin is applied around the air vent and separated from the other cores. This occurs in any parting pattern , The reason is that excess curing gas to the resin near the vent holes;
The phenomenon of sticking is related to the grain composition of the sand. The tendency of the sand grains to be polygons rather than circles is more increased. The resin is uniform on the surface of the round sand grains and is covered with excess resin in the concave corners of the polygonal grains. Blockage of the exhaust plug, so that the entire cavity of the core cavity are attached to a layer of resin film, this phenomenon is very common, the solution is to clean the core box with detergent (or dry ice cleaning). The phenomenon of sticking mold is also related to the distance from the grit nozzle to the impact point and the pressure of the grit injection. The closer the distance is, the larger the pressure of the grit injection is, and the greater the tendency of sticking mold is.
Solution to the problem of sticking mode:
(1) to improve the resin composition, adding internal release agent;
(2) too late to replace the resin, in the core box easy to stick to the site of affixing transparent tape, because the relationship between wetting angle, after the sticky tape is not stained, this method is simple, immediate, but to be solved Good shot after the tape edge tilt problem, which provides us with a coating on the mold coating to solve the problem of the feasibility of sticking ideas.
7 bright carbon defects
According to Li Chuan-tang, a founding member of the Foundry Association of China, "This defect easily occurs along the first strand of hot metal entering the cavity and is also prone to occur near the gate and often on the side and top of the stream." If the casting system used If turbulence occurs in the chamber, it is possible to punch the film into the casting to form a sub-dermal layer, which can penetrate the casting if the film is sandwiched between two streams. " Castings in the following figure as a flaw surface cracks is bright carbon.
Measures to prevent bright carbon defects
If bright carbon defects are found in the castings, some precautions may be taken to prevent such defects in cases where it is not convenient to switch to a resin with a lower carbon index.
(1) Increasing the pouring temperature can strengthen the oxidizing atmosphere in the filling process, and can effectively oxidize the hydrocarbons generated by pyrolysis so as to reduce or eliminate the bright carbon defects. Experiments show that pouring temperature increased to 1480 ℃, can completely eliminate this defect.
(2) to increase the casting rate, shorten the casting time, can reduce the amount of pyrolysis resin filling process, which can effectively reduce the bright carbon film precipitation.
(3) increase the mold vent, the resin pyrolysis products discharged, but also can effectively reduce the bright carbon defects.
(4) In the surface sand by adding iron red powder (Fe2O3) 2%, can completely eliminate the bright carbon defects. But the resin sand by adding 2% iron red powder, the mold strength will be significantly reduced. According to foreign research reports, with aluminum sulfate instead of iron red powder, add the amount of just 1%, that is, the same effect, in this case, the impact of resin sand is small. "
8 waste core rate is high and the storage and transportation process is damaged
(1), the dialing slope problem; (2), the mold is not stable; (3), the initial strength (mold strength) is too low; Sand pressure or correction tooling to keep the sand and exhaust in balance. Tooling design to consider the liquidity of cold core sand.
Low local hardness is often caused by low density at that location, whereas low overall sand core hardness can result from under-stirring core sand or due to low gas pressure during hardening. Sand core mixed grind is not good, or is not fully stirred, or less resin or raw sand water high, compressed air moisture, sand temperature below 10 ℃, low viscosity resin temperature, sand fineness and Angular coefficient, clay content and micropowder content are also influencing factors.
9 pulse pattern and sintering
The main reason is:
At 573 ℃, the change of volume of quartz sand causes the swelling stress to cause the sand or core to crack. Quartz sand particle size more concentrated, the greater the risk of cracking the sand core. The higher the silica sand silica content, the bigger the core cracking probability. The grain shape is more rounded, fine grain size quartz vein generated tendon pulse grain shape than the polygons, coarse grain size quartz sand to be serious.
Molten metal infiltration into the formation of veins, sand core and hot metal interface temperature is higher than the solidus temperature of iron, so that penetration will continue from the beginning, only the penetration of molten iron front solidification, infiltration to stop, so that the liquid metal The so-called sand core sintering, ie metal-permeable mechanical sticking sand, is formed by sand core cracks or pores penetrating the entire cross-section of the core. It turns out that this metal infiltration is impossible to clean out, so castings have to be scrapped. To avoid or reduce the veins and impermeable metal infiltration, it is necessary to overcome the cracking of the sand core and to inhibit the infiltration of molten metal into the crack.
Solution:
In the sand or core sand by adding some concessional additives can reduce the expansion stress of the sand to reduce the tendency of veins, the choice of low silica sand, the choice of 4 sieve or even 5 sieve sand can reduce the tendency of veins; improve the sand core at high temperature strength And toughness to ensure that its surface by the thermal phase-change stress through its own deformation can ease the trend of cracking; the use of sintered coating painted on the surface of veins easy to produce veins, but also to make the sand core in high temperature hot metal hot impact Under the effect of producing high temperature toughness and high temperature strength. From another point of view, when the molten metal contacts the surface of the sand core to form a heat zone, if this part of the heat is diffused and transferred to the sand core by the technological means on the one hand, the temperature of the surface of the sand core is as short as possible On the other hand in the liquid metal contact, the impact of the sand core surface, if the sand core surface of the liquid metal cooling, to speed up the contraction of the role of rapid solidification of liquid metal, together with the sand core The surface of the hot ductile effect of the formation of high temperature, so that more effectively prevent pulse pattern.
Add 5% -10% of the pulse of the stars can effectively prevent pulse defects.
Another: use special sand.
Prevention of fissure-like nitrogen holes
When the amount of carbon-silicon is low, the solubility of N in molten iron increases, the thin-walled parts control N <0.013%, the thick-walled parts control: N <0.008%
Hot metal in the content of Ti: 0.02% -0.025%, the use of Ti nitrogen fixation can eliminate fissure-like nitrogen pores. Of course, iron oxide powder in the sand is one of the ways.
11 water-based paint or alcohol-based paint, application time
Water-based paint preferred, because alcohol-based paint penetration depth, the impact of the strength of the sand core.
Apply water-based paint Time: timely application, timely drying, it is recommended to complete the application within half an hour and immediately dried. Do not apply more than 2 hours after the core, because the solvent evaporates after 2 hours, the solvent can prevent the paint from penetrating into the sand core.
Application of alcohol-based paint Time: due to various reasons have to use alcohol-based paint, the core should be put after a while before applying, the best is applied after 8 hours, or 4 hours after the application, because alcohol The penetration of the coating leads to a decrease in the strength of the sand core. Of course, the actual production of a core immediately after the application, but it is helpless, not recommended.
12 cold box casting cavity cavity sand scarring defects
Towards this end, Yu Mingdao, Xing Qimin, Xu Zhixin and Niu Benqing of YTO Group have detailed analysis and discussion. Here do not repeat, focusing on several teachers under the "bad thermal effects of sand core" effect, see below: Many manufacturers are "slipped into the water" to eliminate, scarring problems to be solved.
13 Cold-core box sand core shooting mouth opening problem
A lot of units of the cylinder round mandrel core set up a shooting nozzle.
14 cold core box overall core dip coating problems
Group core group to what extent, the cylinder water core core coating paint cleaning, sand core drying, sand core coating overflow tank before drying.
15 cold core machine for the template when the template erected on the device
Quickly change the mold can be set up on the template to facilitate maintenance and cleaning devices.
16Cold core machine shot blasting head of the security angle of the problem
Consider the core making machine is not big enough and want to shoot a larger sand core or stroke is too small lead to the shot horn angle is too large, may be due to the mixture angle of rest led to the furthest nozzle in the first and second molded core No sand, this time should be set shot sand guide sand block.
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