Moulding and Moulding Sands

DIPLOMA IN FOUNDRY TECHNOLOGY MOULDING AND MOULDING SANDS

SESSION 1 :  MOULDING SANDS

1.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  • Identify the various elements of silica sand
  • Explain how size distribution, grain shape and acid demand can affect the casting
  • Explain the effects of non silica sands on moulding processes
  • Understand how the general properties of the greensand will affect the casting
  • Explain the various types of bonding clays and their affect on the greensand
  • Explain how organic additions influence the greensand
  • Give examples of various types of mills utilized to produce greensand

Introduction

Most sand moulds and cores are based on silica sand since it is the most readily available and lowest cost moulding material. Other sands are used for special applications where higher refractoriness, higher thermal conductivity or lower thermal expansion are needed.

1.2      Non-silica Sands
1.3      Materials Used for Greensand Moulding
1.4      General Properties of Greensand
1.5      Raw Materials Used
1.6      Clay Types
1.7      Organic Additives
1.8      Bonding Clays for Foundry Moulding Sands
1.9      Preparation of Greensand
1.10   Types of Mills
1.11    Moisture Content of Sand
1.12    Maintenance
1.13    Homework

SESSION 2 :  BASIC TESTS FOR GREENSANDS

2.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  • Identify the types of tests carried out on greensand
  • Identify the pieces of equipment required for greensand testing
  • Explain the properties of each test and their influence on greensand
  • Explain the composition tests carried out on greensand
  • Explain the significance of these tests

Introduction

Physical testing of a greensand is needed to continuously monitor and control performance. Moisture content has the most effect on greensand properties and can be subject to rapid variations. The frequency of testing will depend on:

  • The type of sand plant used
  • The quantity of sand in the system
  • The mix of castings produced
  • Working practices of the foundry

The object of the tests is to control the moulding sand to keep it consistent, and not just to produce test results. The tests carried out on “greensands” include:

  • Moisture content
  • Permeability
  • Green strength
  • Dry strength
  • Shatter index
  • Compactability

When taking these tests, sand is to be taken after discharge from the preparation plant. Avoid sand that has dried out or stood for a time. If it is possible to do this safely, take a sample from the belt taking sand to the moulding station. Approximately 2kg to 3kg of sand is needed, and should be kept in an air-tight container; a polythene bag is ideal.

2.2     Sand Testing
2.3     Preparation of Standard Test Pieces
2.4     Determination of Moisture Content
2.5     Microwave Ovens
2.6     Determination of Permeability
2.7     Measurement of Greenstrength – SI Units
2.8     Measurement of Shatter Index
2.9     Measuring compactibility
2.10   Composition Tests on Greensand
2.11   Coal Dust in Greensand Moulding
2.12   Loss on Ignition and Volatile Matter
2.13   Homework

SESSION 3 :  OTHER TESTS FOR SANDS

3.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  • Identify further tests carried out on greensand
  • Explain the significance of these tests on greensand
  • Explain the consequences of working with “Hot Moulding Sand”
  • Define methods of cooling “Hot Moulding Sand”
  • Explain the need to record and display results obtained from greensand testing
  • Explain the reasons for mould compaction when producing moulds
  • Explain why sand degradation occurs after casting when producing moulds in greensand

Introduction

There are many tests devised for particular foundry problems and further control of a moulding sand. Four of these tests have particular applications in many foundries and are therefore worthy of consideration. These are:

  • Methylene-blue test for active clay in a sand
  • Wet-tensile test
  • Sintering properties of moulding-sands
  • Some specialized equipment is required for these tests, and details are included where relevant

3.2     Methylene-Blue Test
3.3     Wet Tensile Test
3.4     Sintering Tests on Foundry Sands
3.5     Cooling of Sand
3.6     Water Sprays
3.7     Recording and Feedback of Sand Test Data
3.8     Mouding-Sand Make-Up
3.9     Additions to Sand
3.10    Sand Control
3.11    Sand Testing
3.12    Recording Sand-Test Results
3.13    Degradation of Additives in Greensand
3.14    Compensation for Losses of Additions
3.15    Homework

SESSION 4 :  PRINCIPLES OF MOULDING

4.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  • Explain the principles of producing a mould
  • Explain why ‘machine moulding” has an advantage over moulds made by “hand”
  • Identify the forces required to produce greensand moulds
  • Identify different types of equipment for producing greensand moulds

Introduction

Having produced a greensand with the desired mouldings properties, we now have to produce a mould of sufficient strength to allow molten metal to be poured into it to produce a casting. The properties of the sand have to be such that after removal of the pattern which has been pressed into it, the sand retains the shape or imprint of the pattern.

The patterns used in the foundry industry are made in a number of different ways and can be solid, loose split or plated. The first and second alternatives are generally associated with hand-mouldings methods whilst the latter is associated with machine mouldings.

Moulds can be produced by two different methods:

  • By hand, generally termed floor moulding, bench moulding or stump moulding
  • By machine
  • A brief description of the procedures adopted to produce a mould are outlined below

4.2     Hand Methods of Mould Production
4.3     Machine Moulding
4.4     Mould Separation
4.5     Enhancements of Mould Making Practice
4.6     Disamatic Moulding Method
4.7     Homework

SESSION 5 :  MOULD SHAKE-OUT SYSTEMS

5.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  •  Explain the function of a shakeout system
  •  Explain the consequences of not wearing safety equipment at the shakeout area
  •  Define the difference between Punch-Up and Punch-Down shakeout methods
  •  Explain he problems encountered with dust and fume problems at the shakeout
  •  Explain how to keep the conveyor belt clean while transporting greensand
  •  Describe some typical features in the design of conveyor belt systems

Introduction

At a stage in the manufacture of castings in greensand moulds, the mould has to be broken up and the sand and castings separated. The methods used vary from the simple one of manually breaking the mould open on the floor to the sophisticated, fully automatic, acoustically enclosed shake-out, with facilities for cooling sand and castings.

Before looking at various knock-out methods in detail, it is necessary to consider initially what is required of the knock-out operation. Ideally a knock-out operation should accomplish the following:

  •  The separation of the sand, castings, and box, if used
  •  Cleaning from the boxes, if used, any adhering sand
  •  Removal of adhering sand from the casting surface
  •  Decoring of the casting
  •  Breaking-up of any large sand lumps

This operation needs to be carried out at a rate to suit production requirements, with no damage to the casting and with the minimum generation of dust and noise.

There are various pieces of equipment which may be used singly or in combination to perform the “knock-out” operation. The equipment used will vary, depending amongst other things on the production rate, the casting size, the mouldings methods used and the degree of mechanization within the foundry.

The most basic knock out is to break the mould open on the floor by parting the boxes, either manually or with the aid of a crane, and then retrieving the casting. This method is environmentally unpleasant, does not break up the sand lumps or clean adhering sand from castings. It is suitable only for very low production rates.

5.2     Vibratory Shake-Outs
5.3     Dust and Fume Problems in Greensand Plants
5.4     Dust Limits
5.5     Sand-Handling Plant Design
5.6     The Addition of Damp Sand
5.7     Knocking-Out
5.8     Homework

SESSION 6 :  SAND STORAGE AND HANDLING

6.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  • Understand the stages in the preparation of greensand
  • Identify the various pieces of equipment required for the preparation of greensand
  • Explain the storage and measurement of additions required for the production of greensand
  • Identify various casting defects and explain how they may be avoided
  • Explain the types of material used to produce castings in other metals

Introduction

Other sections deal with specific aspects of greensand production and the individual pieces of equipment such as sand mills and sand coolers. Important as these individual items are, it is necessary also to understand the requirements for the transport and storage of moulding sand and the materials used in its preparation.

The condition of the moulding sand varies significantly throughout any preparation system. The sand can be hot and “lumpy” after knockout and contain debris such as pieces of core and tramp metal. After screening it can be low in moisture content, therefore relatively free-flowing – but dusty. In storage, condensation can occur, worsening any tendency to stick in hoppers.

Prepared sand will compact if subjected to vibration or impact and its moisture content can be troublesome, even in short-term storage. It is important to note that the bulk density of the sand can vary considerably throughout the system.

The sand plant has to perform four main functions beyond the obvious transport of the sand. These define the design requirements of the system and can be listed as follows:

  • Cleansing the sand prior to re-use
  • Removal of excess heat energy transferred from the molten metal after casting
  • Homogenization of the materials in circulation, to stabilize the sand condition before reconditioning
  • Providing energy [in the form of mechanical work] to develop the desired bond properties
  • It is therefore necessary for the sand-plant designer to develop a “balanced” system, with due regard to the energy content of the materials being used

6.2     Sand Preparation
6.3     Storage and Measurement of Additive Materials
6.4     Types of Casting Defects
6.5     Avoidance of Casting Defects
6.6     Moulding of Other Metal Castings
6.7     Homework

SESSION 7 :  THE PATTERN

7.1   Introduction

Outcomes:

After you have worked through this section, you should be able to:

  • Describe the various types of patterns available to the foundry man
  • Explain the advantages and disadvantages of various materials used to produce patterns and core boxes
  • Explain the purpose of filtration when producing castings
  • Describe the three mechanisms which occur during the filtration of a casting
  • Explain the benefits of using filters while producing castings
  • Describe how chaplets are used in the production of castings which utilize cores

Introduction

The method of moulding, the number of castings ordered and the available moulding boxes determine the pattern and core box construction. The blueprint, now marked with the calculated weight of the casting, is handed to the patternmaker but before he can begin work he must know two things:

  • The number of castings required
  • The method of moulding to be adopted by the foundry

Carved blocks of wood are frequently received as working patterns but are merely models. They cannot be used for moulding operations because the woodworker has no idea of the foundry operations necessary to produce a Mould. A cheap pattern is in the long run, often more expensive than one correctly made, although initially more expensive. For quantity production, patterns made of metals such as brass, cast-iron, and aluminium alloys are advisable to secure dimensional accuracy and surface smoothness.

7.2     Pattern Types
7.3     Cope and Drag Pattern Plates
7.4     Special Patterns and Devices
7.5     Filtration
7.6     Types of Filter and Their Use
7.7     Filtration of Non-Ferrous Castings
7.8     Filtration of Ferrous Castings
7.9     Chaplets
7.10   Chaplets – Coatings
7.11   Uncoated Chaplets
7.12   Types of Chaplets
7.13   Homework