Crusher Hammer Made Using The Process

Field of the Invention:

The present invention relates to a manufacturing method for crusher hammers used in coal granulator. In particular, crusher hammer of any size, complex geometry, material flow difficulty, which are used particularly in coal granulator equipment for coal crushing which in turn is used for thermal power generation. These hammers are manufactured with forging process disclosed in the invention which results into better strength, wear resistant and quality product than the conventionally manufactured process like casting etc.

Background of the invention:

Typically the thermal power plant needs specific coal size requirement in huge quantity. The size of the coal received from mines is normally in-variable size, which may, however, depend on coal sources. The received coal is sized in crushers to the required shape and supplied to the furnace.

This crusher Hammer is also referred as ring type granulator. The input coal from mines is feeded to the granulator. The crusher hammers mounted on the shaft is rotated with certain RPM; these hammers break the coal through impact which flows through its path. Conventionally these hammers are manufactured using casting process. These hammers have low life due to high wear rate and it may increase cost of replacement in very early stage.

The invented process of manufacturing crusher hammers uses forging operation. The forging has been carried out in stepwise operation. The forged components have better quality, wear resistant, higher strength to weight ratio and continuous / directional grain flow lines.

Crusher hammers have been employed in coal granulator. For example, Pennsylvania Crusher corporation filed patent US 4343438 in 1982 titled "Ring Hammer" discloses design and manufacturing of ring hammer used in coal granulator by using forging process. This is more intent to product design aspect of crusher hammer. This patent does not disclose the detailed forging process. CN 101293274A the invention discloses a method for manufacturing a hammerhead of a crusher. The manufacturing process used in this is casting process followed with the treatment of water toughening or thermo quenching to the product. Whereas, the invented process uses forging as manufacturing method for crusher hammer and all properties including service life is improved 3-5 times than casting process.

It is evident that there remains a real and substantial need for crusher hammers with improved mechanical properties through innovative forging process. Summary of the Invention:

A process to manufacture crusher hammers by forging used in coal granulator of thermal power plant is disclosed. It uses step-wise forging operation to achieve final shape of crusher hammers, followed by unique heat treatment. The process starts with a preform made from a round billet and follows through with a upsetting followed by finisher forging, flash trimming and piercing operation. The forged components are further heat treated to get improved mechanical properties (strength, wear resistant, hardness, toughness etc.) and longer life. The hammers made using conventional processes have low life due to high wear rate and it may increase cost of replacement in very early stage. This problem is solved by the hammers manufactured by the process of invention.

Brief Description of Figures:

Figure 1 shows the process of the present invention.

Figure 2 shows the forged crusher hammer.

Detailed Description of the Invention:

The present invention is applicable to manufacturing of Crusher hammers used in coal crusher granulator of thermal power plants.

The key inventive feature of the present invention is the strength achieved due to forging and heat treatment operations carried out during manufacturing. As shown in Figure 1, the invented process of crusher hammer manufacturing typically involves the following steps:

1. Billet cutting into flat-faced billets and preparing billets for pancake formation

2. Pancake making to required size by upsetting with flat surface dies.

3. Forming a finisher forging process and treating the finisher by trimming and piercing.

The forged component is subjected to a unique heat treatment process.

The details of each step are provided below.

Billet Formation:

Billet identification based on heat code and heat number, the input billet is inspected dimensionally, material cleanliness and soundness criteria using ultrasonic testing.

- Billet heating in oil fired furnace at 1250 °C to 1270 °C temperature range.

Pancake Formation:

Pancakes are forged in flat dies using hammer equipment. Both top and bottom flat dies are lubricated before forging. The heated billets from the furnace are subjected to forging operation. It is ensured that the billet is kept on a flat die at the center vertical position and then gradually forged by number of blows. Pancake is maintained to required thickness. Finisher Formation by Forging:

The pancakes from flat upsetting dies are centrally positioned on a finisher die impression which is next to pancake position. Both the top and bottom dies of the finisher are lubricated before first blow. Numbers of blows are given using hammer for completely filling up of the finisher bottom die.

The forged finisher jobs are then proceeding towards trimming and piercing operation. The hot job is located centrally on trimmer impression and simultaneously flash trimming and piercing is done using mechanical press.

The invented forging process sequence results into better material compactness and directional grain flow lines along the contours of part geometry. This enhances component strength and life.

Heat Treatment:

The forged component is processed to a controlled heat treatment cycle, which will improve the strength and microstructure of the component to appreciable extent. The heat treatment cycle of the invention comprises the steps of normalizing followed by hardening. The step of normalizing consists of heating the forged component at 800 °C to 900 °C followed by air cooling to ambient temperature. The normalized component which is now at the ambient temperature is subject to hardening which consists of austenitising the forged (normalized) component at 800 °C to 880 °C in a furnace with soaking time of 1 to 2 hours. The austenized component is quenched into agitating oil and cooled up to 100 °C followed by double tempering with temperature range from 540 °C to 640 °C. This is followed by cooling the double tempered part to ambient temperature.

The controlled heat treatment cycle results into good amount of tempered martensite with pearlite structure and less amount of ferrite structure. This in turn results into better hardness and wear resistant.

The invented forging and heat treatment process results into component with better strength and life. Advantages of the invention:

The conventional process of manufacturing crusher hammers produces component with low strength; which will results into less life of crusher hammers, frequent replacement of parts, poor quality of crushed coal and higher cost. The invented step wise forging process will make high strength crusher hammers having at least 3 to 5 times more life than conventionally manufactured component.

The invented forging process sequence results into better material compactness and directional grain flow lines, along the contours of the component geometry. This enhances component strength and life.

The crusher hammer manufactured using invented process has better strength, less wear rate, which yields better performance in its service life. Also this forging process sequence helps to make the product defect free. Hence the use of said forging process sequence resulting into good quality and economical product.

It is evident from the foregoing discussion that the invention has a number of embodiments as detailed below.

1. A process manufacture of crusher hammers by forging characterised in that said process comprises the steps of:

cutting a billet into flat-faced billets and preparing billets for pancake formation

making pancakes to a required size by upsetting with flat surface dies

forming a finisher by a forging process

treating the finisher by trimming and piercing

2. A process as disclosed in embodiment 1, characterised in that said step of inspecting it dimensionally, for material cleanliness, and for soundness using ultrasonic testing, further followed by the step of heating the inspected billet in an oil fired furnace at a temperature range between 1250 o.

'C and 1270 °C.

3. A process as disclosed in embodiments 1 to 2, characterised in that said step of making pancakes further comprises the steps of forging said heated billets obtained at the end of the process of claim 2 in in flat dies using hammer equipment, wherein both top and bottom flat dies are lubricated before forging and maintained at the center vertical position, and wherein forging blows are applied gradually.

A process as disclosed in embodiments 1 to 3, characterised in that said step of forming a finisher further comprises the steps of centrally positioning said forged pancakes on a finisher die impression wherein both the top and bottom dies of the finisher are lubricated, followed by completely filling up the finisher dies with blows using a hammer.

A process as disclosed in embodiments 1 to 4, characterised in that said step of trimming and piercing further comprises the steps of positioning said finisher centrally on a trimmer impression and simultaneously flash trimming and piercing using a press, leading to a trimmed and pierced component.

A process as disclosed in embodiments 1 to 5, characterised in that the trimmed and pierced component is subjected to a controlled heat treatment cycle, said heat treatment cycle comprising of the steps of, in sequence, normalizing, hardening, quenching, double tempering and cooling.

A process as disclosed in embodiment 6, characterised in that said step of normalising comprises heating said trimmed and pierced component to a temperature between 800 °C and 900 °C followed by cooling the heated component to room temperature, leading to a normalised component. 8. A process as disclosed in embodiment 6 and 7, characterised in that said step of hardening comprises austenizing the normalised component to a temperature of 800 °C to 880 °C with a soaking period of up to 2 hours, leading to an austenized component.

9. A process as disclosed in embodiments 6 and 8, characterised in that said step of quenching the austenized component is carried out using agitated oil to cool said austenized component to a temperature of up to 100° C, leading to a quenched component.

10. A process as disclosed in embodiments 6 and 9, characterised in that said step of double tempering is carried out to raise the temperature of the quenched component to 540 °C to 640 °C, leading to a double tempered component.

11. A process as disclosed in embodiments 6 and 10, characterised in that said step of cooling the double tempered component brings the temperature of the double tempered component to ambient state.

12. A crusher hammer manufactured using the process of any of embodiments 1 to 11, characterized in that said hammer has continuous grain flow lines.

While the above description contains much specificity, these should not be construed as limitation in the scope of the invention, but rather as an exemplification of the preferred embodiments thereof. It must be realized that modifications and variations are possible based on the disclosure given above without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.