What you will find in this article
In this article, you will learn about molding sand, also called sand casting method. Due to its reliability and quality finishes, it is one of the most used casting solutions in the overall industry. Gamarra has been working with this method since the early beginning of our history. We have become experts in the matter. Before getting into details about what is molding sand, if you don’t need the complete information or you are short of time, Gamarra has prepared a list of the main knowledge you need to have regarding molding sand.
Main details about molding sand
- It is a casting solution that utilizes sand as the mold to form pieces and components
- It stands out for its versatility, low-cost, endurance and sustainability
- At Gamarra, we use two different casting solutions: green sand casting and chemical sand casting
- The process consists of several phases: patternmaking, coremaking, molding, melting and pouring of the metal, cleaning (trimming) and testing
What is molding sand?
Molding sand (also called sand casting) is a sand casting method that utilizes sand as a mold to form several pieces. This method is very versatile and can be used to obtain detailed components of many sizes . They can range from a few ounces to several tons. It is one of the oldest casting processes, dating back to 1000 B.C. The ability to mold metal without machining allows for mass production of components and parts that result both inexpensively to produce and durable in the long-run. Nowadays and after centuries perfecting the process, over 60% of all casting solutions are produced through this method. It is only produced in specialized foundries and factories such as Gamarra.
Our molding sand casting solutions are present in a wide range of products of different industries. These include railway, automotive, defense, ship construction, oil&gas, hydraulics, wind energy, machining and construction equipment and many more. Through the years, we have been helping these sectors to create the best components and pieces for their respective activity.
What are the advantages of molding sand?
This process has some perks that are very valued in the industry, which makes molding sand a widely used method to obtain components and pieces.
Low-cost. Its raw materials, which (of course) includes sand can be very inexpensive. Also, the cost of the required equipment is low, as it usually only involves the sand and reusable patterns that were previously designed.
Sustainability. The sand of the mold produced to obtain casting is reusable for making new molds. This way, we can minimize the environmental impact of our activity.
Endurance. Molding sand is a method that can hold out against extremely high temperatures that we subject the molten metal in. Furthermore, it is one of the fewly available processes that can endure metals such as nickel, steel and titanium, which have extremely high melting points.
Versatility. The molding sand method can be utilized for low, medium and high production means that can be manufactured quicker than with other methods such as investment casting. This makes this process versatile, ideal for short production runs, flexible and efficient.
Types of molding sand solutions
At Gamarra we offer both sand casting solutions:
Green sand casting. This is the traditional sand casting process. It is made with an aggregate of sand, bentonite clay, and water. It is the most environmentally friendly casting process and an industry favourite because it is low cost and performance. And, why is it called “green” sand casting? “Green” refers to the moisture present in the mixture. Also, the sand is recyclable and there are no chemical additives (just sand, clay and water). It is indeed very eco-friendly. This method is very reliable due to its permeability, reusability and collapsibility.
Chemical sand casting. This process is more modern and similar to green sand casting. However, the difference is that it contains chemical additives that make it harder, thus offering greater geometric stability of the molds.
Steps involved in the sand casting process
There are few steps involved in the process, which in summary are design and patternmaking, coremaking, molding, melting and pouring of the metal, cleaning (trimming) and testing of the final pieces and components. Below, we explain the full sand casting process for you to comprehend what we do at Gamarra.
Our skilled team of pattern makers design a mould which will be slightly oversized and larger than the final product, as the metal will shrink during the cooling phase of the process. In order to make a detailed and professional pattern, it requires a know-how and several skills that at Gamarra we have been perfecting with years of experience. Once the design is finished, we construct the pattern usually with wood, resin or aluminium.
2. Coremaking and molding
The sand mould is divided into two halves, which when united will create the mold. Top half is called the “Cope” and the bottom part is called the “Drag”.The sand is placed in the pattern to create a half mold. Then both parts are assembled to create the desired mold.
3. Pattern extraction
The pattern is removed. Pattern extraction is made carefully to avoid breaking it or distorting the mold cavity.
4. Melting and pouring
Next step is pouring. The mold cavity is quickly filled to avoid early solidification with cast metal, which at that point it has an extremely high temperature. For that reason, if we want the casting to be successful, the mold cavity has to maintain its shape until the molten metal has fully cooled and solidified.
5. Cooling and trimming
The metal is left to cool down to later remove the sand casting. The desired cooling time can be estimated based upon the wall thickness of the casting and the alloy. However, if the cooling process of the molten metal is too quick, the component may exhibit shrinkage, cracks or incomplete sections. This process, which can be removed manually or by automated machinery, or removing the sand from the castings is called shakeout. The surface finish, when it just left the mold, is poor and so must be cleaned by shotblasting to obtain a smooth surface.
The desired piece is obtained and, at Gamarra, we test the pieces for the dimensions, surface, mechanical properties and other requirements together with offering other services such as machining, welding or painting.
In conclusion, the sand molding sand process is an economic, versatile, sustainable and reliable process to obtain high-quality pieces and components for many industrial markets.