Pros and cons you must to know about resin sand casting ...

The name of self hardening furan resin sand comes from the English furan no bake process, which means that the sand can be self solidified at room temperature without baking or hardening gas. Usually referred to as "cold hard resin sand", or even "resin sand".

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The advantages are:

1. The surface of the casting is smooth, the edges and corners are clear, and the dimension accuracy is high.

2. High modeling efficiency, improved productivity and site utilization, and shortened production cycle.

3. Resin sand mold (core) has high strength (including high temperature strength), good formability, low gas generation, good thermal stability and good air permeability, which can greatly reduce casting defects such as sand sticking, sand inclusion, sand hole, air hole, shrinkage cavity, crack and so on, so as to reduce scrap rate, and can produce complex and key parts that are difficult to be made with clay sand.

The disadvantages are:

1. Higher requirements for the original sand, such as grain size, grain shape, Si02 content, micro powder content, alkali metal salt and clay content.

2. The temperature and humidity have great influence on the hardening rate and the strength after curing.

3. Compared with inorganic binder, resin sand has a higher gas production rate. If the measures are improper, it is easy to produce gas pores.

4. Because the hardening mechanism is dehydration condensation type, the hardening reaction needs a certain time, the turnover rate of single pattern is low, and multi pattern is suitable for the production of large quantities of castings.

5. Compared with clay sand, the cost is still high.

6. For castings such as nodular iron or Low-C stainless steel, poor spheroidization or carburization may be caused due to sulfurization or Carburization on the surface.

1. RESIN HAS NOT HARDENED AFTER THE INDICATED TIME

If resin has not hardened after the indicated time has elapsed, there may be several causes. Here are
the most common ones:

• Double-check the usage ratio indicated in the instructions. An incorrect or approximate combination may affect the catalysation of the product. It is very important that you never add a greater amount of hardener than the specified one.
• Never cast the second layer without ascertaining first that the previous one has completely hardened. Pouring another layer over a surface that has not catalysed may cause overheating and compromise your work.
• If you work in an environment where the temperature is relatively low, the curing time of the resin will increase significantly. For example, if you go from 25° [77 F] to 15° [59 F], the curing time will double. Use an external heat source (stove, radiator, etc.) to increase the ambient temperature or apply a hardener suitable for working at low temperatures.
• Most of the problems concerning the failure to harden of the resins can be traced back to
  incorrect mixing. Make sure to carefully mix your product for at least two minutes,
  meticulously scraping the bottom and the walls of the container used. Never be inattentive in this very important stage.
• Add the additives (pigments, dyes, etc.) only after mixing resin and catalyst.
• Use the catalyst you find packed together with the resin you are going to work with. The use of &#;unrelated&#; catalysts may vary the final result.

2. RESIN DOES NOT STICK WELL

• If you want to use resin as a bonding agent or to create River Tables, you may run into some problems related to the stickiness of the product.
• If you are working on a very porous surface, this will absorb the product very easily, making a second layer of resin necessary particularly on the edges of the material you are going to glue.
• If you work on wood, make sure to clean and smooth the surface. A rough cleaning may nullify the adherence of the resin.
• Another problem might relate to the width of your worktop. A large surface of resin alone
  may in fact not guarantee a perfect seal. To deal with this problem, all you need to do is add material to reduce the workload of the resin.
• Make sure that the resin is evenly distributed over the entire surface.

3. RESIN LOST ITS SHINE

If your resin has taken on an opaque and unpolished colour, the causes are most likely due to climatic conditions of your working environment.
Many times the opacification may be caused even just by a normal change of season.
Use an external heat source to remove moisture and to foster polymerization.

4. A STICKY FILM HAS FORMED ON THE SURFACE

Once the resin has hardened, a sticky film may form on the surface. This problem can be easily reduced by wiping a sponge soaked in hot water on your surface.
However, if you want to avoid film formation, employ the following precautions:

• Always try to work in an indoor environment, preventing sudden changes in the room temperature.
• Avoid working with too small quantities, since the smaller the mix dosages, the more you risk to enhance the formation of impurities in the compound.
• Remember that film formation does not depend only on moisture but also on the
  presence of CO2, thus limit the use of thermal guns during the catalysis process.
• Remember that using a container limits the interaction of the resin with the air molecules.
  Try to keep your product as isolated as possible.

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5. AFTER YEARS OF STORAGE, THE HARDENER HAS TAKEN ON A REDDISH COLOR

It is quite normal that, after a few years, the hardener takes on a reddish colour and loses its transparency.
This colour variation does not in any way affect the quality of the resin, which can still be safely used unless a completely colourless product is required.

6. THE RESIN SURFACE HAS AN &#;ORANGE PEEL&#; EFFECT

If the resin surface features bulges or an &#;orange peel&#; effect after hardening, this is probably due to the temperature of your working environment as well.
There are a few solutions that you can try to reduce this problem:

• If the product has not yet completely hardened, use a roller to &#;smooth&#; the surface, this procedure will remove the several bulges on the resin surface.
• If the resin has not yet completely catalysed, you can try a repair casting of maximum 2 mm [0,07&#;].

• If the resin has completely catalysed, sand it with a sheet of 100 grit abrasive paper and finish it with a layer of glossy polyurethane spray paint.

7. THE APPLIED VARNISH DOES NOT STICK TO THE RESIN

If the varnish you have chosen to finish the resin does not stick well to the product, you may have made some mistakes in the preparatory stage:

• The resin may not yet be fully cured. Let the product dry for another 24 hours before applying the varnish
• Make sure that the varnish you are using is compatible with the resin. Do not use varnishes that are not compatible with your products.
• Verify that no sticky film has formed on your resin surface. If so, remove it as described in step 4.

8. RESIN CURES TOO QUICKLY

Besides the hardening problems, you may also experience issues related to a too fast polymerization of your product.
Again, the reasons are linked to the temperature of your working environment: if it is too high, the product may catalyse too quickly and compromise your work.
It is therefore advisable to keep the temperature at around 20°-25° [68-77 F] and not to mix excessive doses of product.

9. AIR BUBBLES HAVE APPEARED ON THE SURFACE OF THE RESIN

The appearance of air bubbles is one of the most common problems when working with resin.
To avoid this process, make sure to mix the product carefully and slowly, in order to prevent air admission into the compound.
If, during the curing process, the resin features small bubbles on the surface, these can be easily removed with the use of a heat gun that you will have to move quickly over the surface at 10-minute intervals.
Remember that once the product has hardened, bubbles can no longer be removed unless you decide to make a further casting by using colouring agents.

10. RESIN, COMBINED WITH FIBREGLASS, FEATURES MICRO-HOLES

It may happen that, by using resin and fibreglass, some micro-holes can appear. In this case, the solution is very simple: fill these holes with resin using a spatula, let it dry and put down a second coat of resin.

11. RESIN IS NOT COMPLETELY CLEAN

If resin is not completely clean, the reasons may be certainly related to the cleanliness of the environment.
You must be very careful when cleaning the work tools, the container you are going to use (remove any oil or grease from the inside of the wall) and the room you are going to work in.
An extreme cleaning will minimize the risk of contamination of the resin by external agents.

12. WHAT IS AN EPOXY RESIN?

An epoxy resin is a particular type of resin that catalyses thanks to a specific hardener and without requiring any particular climatic condition.
This kind of product has excellent adhesive and mechanical properties, it is completely non-toxic and it can be used to create a wide range of artifacts.

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