Analysis of Common Problems in Resin Sand Casting Process

Nov. 04, 2020

Due to the Resin sand casting, Resin sand casting parts has produced the casting surface quality and dimensional accuracy is high, the rejection rate is low, wide applicable scope, low requirement to the workers technical level, greatly reduce the labor intensity of the workers and improve the working environment, etc, so more and more companies in China (or enterprise) choose self-hardening Resin sand casting method. Although the self-hardening resin sand casting technology is mature, there are still many problems in the production process.

OEM Metal Parts Manufacturer introduces you to several foundry processes that require the following considerations.

One, always pay attention to the operation of the equipment

The operation of equipment has a direct impact on the casting production cost and casting quality. Therefore, in casting production, attention should be paid to the operation of equipment frequently and the following two aspects should be paid attention to when abnormal operation is found:

1. Pay attention to the operation of dust removal equipment.

The stand or fall of dust removal equipment, a direct impact on the reclaimed sand regeneration cost and casting quality, in casting production, dust removal equipment operation anomalies are often difficult to find, but if the bad effects of dust removal equipment, not only affects the working environment, air pollution, more important is affecting the reclaimed sand powder content, its direct result is increased when the amount of resin sand and increase the casting scrap rate due to poor permeability.

2. Pay attention to the operation of sand mixing equipment.

The quality of sand mixing is directly affected by the normal operation of the sand mixing machine, among which the amount of liquid material (resin, curing agent) is the most critical. Under normal circumstances, the addition amount of the resin is voltage by the control gear pump motor, is for the amount of curing agent of voltage by the control of diaphragm pump motor, due to the change of season, weather, causing the change of the liquid viscosity, under the condition of the same voltage, the liquid will produce fluctuations, the dosage and curing agent are prone to crystallization, valve and pipe blockage, therefore, should be per shift to clean liquid pipeline, the addition amount of liquid for testing every week, to ensure the accuracy for the amount of liquid.

Second, we should pay attention to the correctness and rationality of the production process

Whether the production process is reasonable or not directly affects the yield of casting, casting quality, and casting cost. The following items should be paid attention to when the production process is formulated:

1. Determine the LOI value of the appropriate reclaimed sand

The LOI value namely calcination reduction is an important index to measure the rate of the reclaimed sand to, also is the appearance of porosity and gas evolution of molding sand and casting defects is closely related to the indicator of iron castings, generally USES the furan resin sand production practice shows that the LOI value control around 3% can completely meet the production requirements, and makes little sense to reduce the LOI value too much.

2. Determine appropriate casting process parameters

(1) Determine the appropriate final strength

Generally, after mixing resin sand, after 24 hours or so of self-hardening, it can reach the highest strength that is the final strength. Due to the different production conditions and production scale of each enterprise, the time interval between molding and pouring is not necessarily more than 24 hours, so the determination of the final strength should be determined by the enterprise. A 24-hour final strength standard may be adopted for small-scale enterprises that implement a one-furnace system for several days; For enterprises whose casting curing time does not exceed 24 hours, the final strength standard shall be the strength achieved before casting. At the same time, there are two tendencies to be overcome in production: on the one hand, to ensure the quality, blindly increase the strength, resulting in higher casting cost, resulting in waste; On the other hand, lowering the strength to protect the cost will result in unstable quality and wide fluctuation range, and the casting quality will be greatly affected by the raw materials and operators.

(2) Determine the appropriate ratio of sand to iron

Due to its high strength, molding after curing, and flat parting surface, self-hardening resin sand eats less sand than clay sand, but its ratio of sand to iron also has certain requirements. If the ratio of casting sand to iron is too high, resin and curing agent will be wasted in the production process, and the large waste sand block will be produced, which will aggravate the burden of reactivation, reduce the stripping rate, increase the LOI value, and increase the possibility of casting porosity. If the ratio of sand to iron is too low, it is easy to produce running fire and deformation of casting. According to our experience, the ratio of sand to iron should be 2.2~ 3:1.

(3) Determine the appropriate casting system

Furan resin sand is poorer, the thermal stability of the materials is introduced, the amount of resin in the resin sand from 1.4% to 1.6%, its thermal stability is best, but in general, the amount of resin at about 1.2%, therefore, the design principle of gating system for the liquid metal in the thermal stability of resin time to ensure the rapid and full of mold cavity smoothly, so, when determining the gating system, should use the ceramic tube, as far as possible and make the gate and more scattered.

Resin Sand Casting

Resin Sand Casting

Three should pay attention to the choice of raw materials

The choice of raw materials has a great impact on casting production, because the quality of raw materials, on the one hand, affects the casting quality, on the other hand, affects the amount of various materials added and consumption. Therefore, the following aspects should be considered:

1, the choice of the original sand is divided into ordinary sand, washing sand, scrubbing sand, etc., because the silt content in the scrubbing sand is already very small, it can greatly reduce the waste of resin, should be the first choice, then choose washing sand, but must not use the raw sand without treatment. When selecting molding sand, one should follow the principle of nearby selection to reduce transportation costs, and the other should try to choose the raw sand with a low angular coefficient.

2. Selection of resin

The choice of resin directly affects the casting quality. If you choose the poor quality of the resin, not only increased the amount of resin, and affect the quality of the molding sand, casting scrap increases, so the selection of raw materials, not only according to the manufacturers to provide technical data to determine, and deal with the manufacturer's production equipment, production process, and quality control methods, and try to examine each index of the resin or please have a good reputation of the test in the inspection department, or from the experience of similar use manufacturer or choose a better credit well-known large enterprise products.

3. Selection of other raw materials. Other raw materials include curing agent, coating, binder, mold release agent, sealing mud strip, etc. The choice of these raw materials should consider not only their quality, but also their matching with the main materials, such as procurement, convenient transportation, and other issues. The influence of these raw materials on casting quality is not the main one, but the influence on casting cost cannot be ignored. For example, the different amount of curing agents can not only affect the production cost due to the influence on the production efficiency of molding process, but also affect the material cost.In a word, as long as we pay attention to the above aspects, we can not only produce castings that meet customers' requirements, but also reduce casting costs and bring development and benefits to the enterprise.