Factors determining sand properties in green sand casting
In the use of high-density molding line there are two extreme misconceptions: one is that the automatic line and manual molding, general machine molding is no special difference; the second is that the automatic line is more high-grade, sand materials to use the best, brand new. According to years of practice in the enterprise, the open line sand and manual molding sand compared to a change in quantity, while the automatic line sand relative to the former is the quality of change. The former can be based on production experience, hand grasp, eye to determine whether the sand is suitable for production, while the automatic line sand is qualified to support the various indicators of data, the general foreign automatic molding machine on the sand of these indicators of data will be made provisions, some manufacturers will be very detailed provisions, part of the domestic automatic molding machine without any information in this regard, so that some of the initial contact with the automatic molding machine foundry manufacturers have no basis to rely on The data of these indicators will be specified.
Automatic molding line common indicators.1、compact rate 33 ~ 42%: is an indicator of the relative dryness and wetness of the sand, regardless of the amount of bentonite, coal dust and ash content in the sand, as long as the compact rate is controlled within the required range, the dryness and wetness of the hand is in the most appropriate state, it will affect the thickness of the sand, which is more obvious on the vertical line production. Confirmation of the final compact rate should be above the molding machine, generally in the sand mixer near the sampling, it is best to do several sand mixer and molding machine above the sampling comparison, to find out the difference between the two compact rates of the system, and finally determine the data sampled at the sand mixer to facilitate operation.
2、wet pressure strength 0.12 ~ 0.2MPa: wet pressure strength is an important indicator to ensure the normal process of molding and pouring, high strength sand can avoid collapse box, expansion box, leakage box, especially in the vertical production line sand to push the sand model made to move forward, pouring and no sand box to help withstand the pressure of the metal liquid, will require higher sand strength. Automatic molding machine in the vertical production line requires sand wet pressure strength 0.2 ~ 0.25MPa, a stage of its wet pressure strength between 0.17 ~ 0.18MPa, sand eye defects accounted for 70 ~ 80% of the scrap. Later, after adjustment, the wet compressive strength was 0.25-0.27MPa for several days, and the trachoma was reduced, and there was no trachoma for 4 consecutive days, but the porosity increased exponentially. This shows that the higher the wet pressure strength of the sand is, the better, because the wet pressure strength is too high will make the sand permeability decline, which will make the porosity defects rise, so that the cost increases, bringing difficulties in falling sand, etc. The placement of the test apparatus will have a greater impact on the data of wet compressive strength of the sand. Therefore, the test apparatus should be placed on a platform with a rigid connection to the ground, and the sample making machine should be disconnected from the placement plane of other test apparatus.
3、Breathability: Horizontal line 90～130, vertical line 70～120
In production, the pursuit of high permeability of the sand is the goal of many people who do not have a comprehensive understanding of the sand. Of course, low permeability increases the casting porosity defects, but too high permeability will also make the castings become scrap.
3.1 If a section of the horizontal production line more pores, and sand permeability has been stable at 110 ~ 130, but managers believe that the permeability is not high enough to abandon the size 70/140 original sand and replaced by 50/100 original sand, a week later, sand permeability gradually rose to 150 ~ 170, the surface of the casting gradually out of the burr, to a clump of burrs, individual castings have been unable to completely remove the burr The prototype of the casting can be restored, only to be awarded the waste.
3.2 If the vertical production line, sand permeability 90 to 130, the casting is located in the lowermost part of the sand burr clusters, when asked why not reduce the permeability, the product director that is not as high as the permeability of other production lines. He did not realize that the vertical and horizontal production lines are different due to the location of the pouring system in the cavity form, the requirements for sand permeability are different.
4、Moisture: horizontal line 2.8~3.4%, vertical line 3.3~3.7%
In the production, the determination of water commonly exists in two problems.
4.1 The weighing error of the sand moisture measured by using tray balance will be as high as ± 0.5%, it is better to use the electronic balance with a sensitivity of ± 0.01g, and the maximum weighing capacity is 200g.
4.2 When drying, the specimen should be completely cooled to room temperature before weighing. The old sand moisture problem, automatic line commonly use activated sodium bentonite, this bentonite mixed with water to achieve the best strength value takes a certain amount of time, and 80% of the effective bentonite in the sand are present in the old sand, so that the old sand moisture to keep in the sand moisture of about 60%, will make the sand better mixed grinding effect.
5、The brick content of sand: horizontal line 10-12%, vertical line 11-13% The brick content includes the effective bentonite, coal dust and dead ash, of which the effective bentonite and coal dust are stable under the condition of ensuring the performance of the sand. If the total gi content increases, it means the useless ash content increases, which makes the sand water higher, permeability lower and toughness lower, the quickest qualitative data to judge the gi content is the compactness/water of the sand, which should be 10-12. If this value is <10, the gi content is too high; if this value is >12, the gi content is too low. The dust removal ability of sand processing line is directly related to the control of gluing amount of sand.
6、the effective coal dust content: generally to determine whether the amount of coal dust is appropriate to the type of sand sand gassing, high-density molding line sand generally 1g of gassing volume in 16 ~ 24ml. effective bentonite content: 5 ~ 9%.
Case 1.
In the vertical parting automatic line, the production of small and medium-sized castings, 4 pieces per case, there was a period of the lower 2 pieces, because the whole body full of long burrs, had to plug the gate, each type from 4 pieces into 2 pieces per type, in the discussion of the casting of the lower two castings will be full of burrs, found that its sand permeability of ~ 170, and the vertical line because the casting in the pouring position is placed up and down, the iron is poured into the casting from above, the cavity The bottom of the cavity will be under great pressure. The sand permeability of 170 means that the pores on the surface of the sand cavity are large, and under the action of heat and gravity of the iron, the high-temperature iron penetrates into these pores and forms a serious mechanical sticky sand, resulting in a scrap without other defects. Its sand using high-quality bentonite, coal dust, the original sand grain size 50/100. after research found that the problem lies in the original sand grain size. Because the sand SiO2 content ~ 83%, the use of the process of heat and various mechanical forces, easy to break, and automatic line sand composition of the original sand is generally 1% to 2%. The proportion is small, so that the type of sand will not be in a high permeability state. If the sand SiO2 ~ 90%, type sand particle size is still used 50/100 original sand, it makes the type sand permeability rose to ~ 170. program is to change the green sand to 70/140 original sand, permeability down to ~ 140, for fine sand did not timely replenishment, and the use of 50/100 original sand for two days, type sand permeability and return to 170, just better some castings, sticky sand situation and intensify, while catch The amount of coal dust in the sand feel not much, and the castings sticky sand heavier, the amount of gas to do the sand only 13, 14ml, and the ingredient list of coal dust content of 0.45%, not too low, and the actual situation does not match. Looking deeper into the reasons, it is found that the weighing of pulverized coal on the electronic scale, there is always a residual amount of 5Kg, so that the amount of pulverized coal added for a long time at a low level, in the process of talking with the sand management personnel, talking about why the rapid rise in permeability, did not take timely measures, the original understanding of the management personnel is the higher the permeability the better, and even some people think that a type of the upper two pieces of non-sticky sand because of high permeability, the lower two pieces The sticky sand is caused by the bad exhaust condition.
Case 2.
Vertical parting production line production of small and medium-sized castings, casting grit scrap serious, sand: compact rate: 27%, wet compressive strength: 0.26MPa, permeability: 55, water: 3.75% grit content: 18.05%
The grain size of the original sand used is 70/140, and the grain size of the composite sand used in the core is also 70/140. The low compacting rate will reduce the toughness of the sand and make it easy to form a sand eye. From the analysis of the above data, the compact rate of the sand is too low, indicating that the water in the sand compared with the effective water-absorbing material, water should be increased, but at this time the wet compression strength is already very high, and the water is in the upper limit, if the compact rate is increased to 36-37%, the strength will increase, the main thing is that the water will rise a lot, which is extremely detrimental to the control of casting porosity, after research found that
(1) observation of castings without shot blasting cleaning, 40-50% of the surface of each casting has been removed from the sand, revealing a gray-blue surface.
(2) sand treatment dust control is divided into five gears, when only open in three gears.
(3) The original sand will not replace the origin in the short term.
(4) The amount of bentonite added was 1.4%, and the amount of coal dust added was 0.4%.
Combined with the above reasons, the following recommendations were given.
(1) sand treatment dust removal to the highest grade, to maintain the strongest dust removal capacity.
(2) the amount of bentonite added to ~ 0.9%, the amount of coal dust added to less than 0.2%.
(3) Use 50/100 raw sand.
After 20 days, feedback information.
Compaction rate: 36%, wet compressive strength: 0.19MPa, permeability: ~60 Moisture: ~3.5% Cement content: 13.2%, effective bentonite: 8.3%, effective coal dust: 6.2%
Among them, the permeability is still very low because the original sand of 70/140 is not used up, the coarse sand is not replaced, and the addition of the original sand is very low, other properties are more ideal, and the casting quality has been greatly improved.
Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of Green Sand Molding Line,Self-hardening sand molding line,foundry machines,Sand molding machine,Sand casting equipment,sand mixer,GS high efficiency rotary mixer,Resin sand mixer,no-bake resin sand mixer,Jolt squeeze molding machine/Jolt-squeezing moulding machines,Multi- Piston Moulding Machine/Hydraulic multi-piston moulding machine,sand casting molding machine,sand reclamation equipment，foundry molding machine,flaskless moulding machine,shot blasting machine,dust collector,according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.
