Dry Sand Moulding

Dry Sand Moulding Introduction

What are the basics one must know before learning the dry sand moulding process?

Small to medium-size casting can be manufactured using a green sand moulding process but when it comes to producing heavy, accurate casting of larger-size dry sand mould is preferred over green sand mould.

Moisture content in this mould is negligible making this moulding process very suitable for producing heavy casting with better close tolerance, surface finish and dimensional accuracy.

There is high flexibility in adding chemical bonds and additives to the moulding sand.

Casting products produced from this mould have negligible gas defects such as porosity defects, open hole casting defects, blowholes and pinhole defects.

The dry sand moulding process is also called dry sand casting.

It can produce complex shape, thin-section design casting products better than the green sand casting process in automobile, aerospace and agricultural sectors using all metals.

I have explained below this process which includes advantages, disadvantages, diagrams and applications of the mould.

{tocify} $title={Dry Sand Moulding Table of Content }

Dry Sand Mould

What is the dry sand moulding process?

The process of dry sand moulding starts with mixing sand and binders together to make mould. After mixing sand and binders this mixture is placed in the oven to take out all moisture to produce dry sand mould for producing dry sand casting.

A metal flask is used which holds the mould during the baking process in the oven.

Mould is heated in an oven for up to 48 hours at 300 ℃ removing all moisture and making it dry completely and strong.

This mould is created with a mixture of binders + sand is heating up to 360℃, the temperature in the oven should not exceed 400℃ to retain the quality of the binders.

After all moisture is taken out mould will look as shown in the diagram below, dry sand mould is made up of dry sand as shown below in diagram (a)

(a) Dry Sand Mould

The strength of dry sand mould in the dry sand moulding process depends upon binding materials such as resin, flour, molasses and clay.

Sand used in the dry sand moulding process should have dry strength and hot strength properties to make a high-quality sand mould.

Dry sand mould has less erosion and has higher strength than green sand mould.

The downside of this mould is that it takes longer to produce and is more expensive than green sand mould.

During the baking of mould, mould can go through distortion and deformation due to high heat.

Handling dry sand mould is easier than green sand mould as it has less possibility for damage.

Medium to large-size casting can be manufactured using this mould, this process is most suitable for producing casting slabs in the construction industry.

The cost of making this mould is higher than green sand mould and is mostly used in large-size foundry only.

In the dry sand casting process, mould is wholly dried; in skin-dried moulding, only the mould's skin is dried.

There is no time duration when the dry sand mould should be used in the foundry unless and until the dry sand mould is kept dry.

The requirement of skim core and stainer reduces in the dry sand moulding process as erosion of the sand is lowest as compared to green sand moulding.

The initial stage and steps of making dry sand mould are similar to green sand mould with additional steps of baking green sand mould in the oven making this process time-consuming.

What is the difference between green sand and dry sand in the casting process?

The major difference between green sand and dry sand is that green sand has a moisture content of up to 5% which is used along with clay to bind the mould together. While in dry sand all the moisture present is evaporated by heating the green sand in the oven.

Dry sand is made from green sand by removing all moisture from the sand and mixing it with other binding agents to make dry sand moulds.

Dry sand is used in the dry sand casting process while green sand is used in the green sand casting process. A combination of both sands is used in the skin-dry casting process.

Before pouring molten metal into this mould, dry compression strength tests and green compression strength tests are carried out on the mould to determine the compression and shear ability of the sand during the moulding process.

Advantages Of Dry Sand Mould

What are dry sand casting advantages in the casting process?

Strong mould as compared to green sand mould as dry sand chemical binders bind together better than clay.
Chances of damage during handling dry sand mould are reduced.
The surface finish and dimensional accuracy of casting produced from dry sand mould are better than casting produced from green sand mould reducing the secondary manufacturing process.
The opportunity to use mould wash in dry sand mould is more giving better quality sand casting.
Fine sand can be used with less additives in this moulding process.
Close tolerance, surface finish, complex patterns, larger sizes, shine, accuracy and accurate dry sand casting shape can be achieved with this mould.
The larger size of dry sand casting products can be manufactured as dry mould has lower erosion of sand, has higher refractoriness and can withstand the heavy flow of molten metal in the cavity.
Collapsable dry sand cores can be made having better hot tearing and reduction in casting stress tendencies improving the potential of making intricate casting.
The number of vents required to exhaust gases and vapours is less as compared to skin-dried casting.
Molten metal can be confidently poured into the mould cavity as the possibility of flow interruption is low as mould is strong and erosion of sand is minimalistic.
The surface roughness of final casting is lower than green sand mould because of lesser course grains being used.
Heavyweight larger-size casting can be easily produced in large boundaries using both ferrous and non-ferrous material.
This mould is best suitable for cope and drag patterns, match plate patterns, gated patterns and multi-piece pattern casting.
Solidification rate and cooling efficiency are better controlled using this mould.
Erison of the mould, mould material defects and gas defects in this mould are less as compared to dry-skin and green sand moulds.
Run-out defects are less prominent in dry sand mould due to mould being stronger than green sand mould.

Disadvantages Of Dry Sand Mould

What are the dry sand casting disadvantages in the casting process?

Casting is more prone to hot tearing during the process because of the low moisture content in the sand during the pouring operation and molten metal cooling process.
The time required for producing dry sand mould increases with the additional step of baking mould in the oven.
Dry sand moulds are subjected to distortion in the oven during the baking process. If mould is baked faster dry sand is more prone to cracks.
Tools and equipment required for producing dry sand casting are more than for producing green sand casting process.
Dry sand moulds are more expensive than green sand moulds and skin-dry sand moulds. This mould is not cost-effective for producing smaller-size casting.
Floor space, movement of mould in the foundry, operators, energy and skills required for making this mould are more.
Not suitable for mass production of moulds as the process is time-consuming reducing mould production rate.
Less environmentally friendly than green sand moulding because of the use of chemical binders in the mould.

Application Of Dry Sand Moulding

What are dry sand moulding applications and dry sand moulding generally used for?

Large engine blocks and cylinders.
Alloy pump casting.
Motor body, housing and casing.
Cast iron bowel bore.
Bronze cylinders.
Round liner cast iron casting.
Stainless steel impellers.
One-piece sculptures, figurative and statues.
Iron roller mills.
Aluminium wheels.
Pulleys and heavy metal bars.
Large spur gears.
Ship engine casing.

Dry Sand Moulding | Dry Sand Casting | Advantages | Disadvantages | Application | Dry Sand Mould | Mechgrace |