Cutting consumable costs is authoritative for all mine operations, but not at the expense of quality. Grinding media represents abject hanging fruit for most miners. Most much, the grinding media in question are grinding balls. In some mid-cap mines, grinding media makes up ~10 % of total mine functional expenses ( OPEX ) and significant savings can be achieved .
Selecting the best-quality grinding media balls is considered a key dance step towards reducing mining costs. This post discusses grinding balls and quality master procedures that can be employed in order to select the best grinding balls for detail applications .
generator : Metso Grinding Media Brochure .
Comminution processes are department of energy intensive and energy ineffective. Some figures suggest that comminution is responsible for 1 % of ball-shaped energy consumption. As a result, it is authoritative to maximise the throughput for a given grinding undertaking. Comminution costs include electricity, grinding media balls, and liners. Choosing the best quality grinding media improves the efficiency of comminution.

Grinding balls form the major dowry of the consumable costs. They can account for 40 % – 45 % of the sum cost and directly affect a mill’s efficiency and break and tear. The musket ball charge consists of grinding balls of respective sizes and of different material qualities. Poor-quality grinding media balls have a negative affect on the entire grinding system. Low-quality grinding media balls are consumed faster, grind inefficaciously, and use more electricity .

GRINDING MEDIA APPLICATION

  • Grinding media steel balls are used to extract precious metals in ore mineral processing. They are most commonly used in copper and gold industries.
  • Ore particles must go through the communition process: grinding -> fine grinding -> ultra-fine grinding. They are ground down to liberate precious metals from gangue materials prior to concentration processes.
  • Grinding or communition is carried out in mills. The mills are partially filled with steel grinding balls or rods, commonly referred to as ‘grinding media’.
  • Mills need to be refilled continuously with new grinding balls as old ones wear out.
  • Choice and consumption of grinding media is related primarily to the volume and charecteristics of the ore (abrasiveness, particle size, and specific energy input).

Grinding Circuits. reservoir : Detour Gold

GRINDING BALL USAGE: MEDIA APPLICATION SUITABILITY:

  • Tower Mills: 0.5”-1.5” grinding balls are recommended. The normal top size of media used is 10-25mm, but even smaller grinding balls can be used for very fine grinding.
  • Isa Mills: <0.1” grinding balls are recommended. The Isa Mill is more efficient when using small media (i.e. high-chrome steel balls).
  • Rotary Mills: Small cylpebs (<1”) are effective in ultra-fine wet regrinding operations.
  • SAG Mills: 4”-6” forged-steel balls are recommended. Cast balls are not agood choice. Their outer crust is hard (typical Brinell hardness > 450). Cast grinding balls cannot sustain the high impact of SAG mill crushing forces. They are recommended for cement grinding and ultra-fine wet regrinding operations.
  • Ball Mills: 1”-4” grinding balls are recommended.

BALL CHARGE QUALITY

You should always test grinding media balls from a fresh source or supplier. This normally requires testing pilot-scale batches of grinding balls in an industrial mill using the marked-ball test. Compare their break rates with those of your current supplier. For the final evaluation, you may want to conduct full-charge operation trials on one or more milling circuits over a few months .

Types of grinding media

Factors used to determine grinding ball-quality operational use admit :

  • Frictional forces between liners and balls. 
  • Abrasiveness of feed material.
  • Impact forces in the mill.
  • Susceptibility to corrosion – especially in wet processes.

Simulations show that in some instances :

  • The use of forged-steel balls, compared to low-density cast-steel balls, increases throughput by 2%-4%.
  • Specific energy consumption is reduced by up to 3.5% (at constant feed/product size).
  • Forged-steel grinding balls achieve considerably better results iwhen tested against other gridning media, such as cylpebs, boulpebs, or high-chromium-cast balls, taking into account the total cost-calculation of the mill process.
  • Studies of SAG Mills performance show that poor quality cast grinding balls with porosity result in the production of a significant excess mass of steel scats in the SAG mill. If your milling operation is using this type of grinding ball, consider switching to higher quality balls. They offer more economic viability.
  • Worn out balls can be a source of iron, especially if the rate of wear is too high. This could result in the formation of iron sulphides, which may affect downstream metallurgical processes. Reduced wear rates are essential.

PROPERTIES OF STEEL GRINDING BALLS IN CHINA

Steel grinding balls are produced from a compass of alloys. Grinding media suppliers in China purchase bars from large-scale steel mills such as the Laiwu Steel Group. These bars offer different characteristics based on their severity and sum of alloying required by the end user .

Alloys Description
High carbon (C) and high manganese (Mn)China Specs (B2, 60Mn, No. 45 steel) Steel with alloying elements such as molybdenum (Mo), chromium (Cr) or nickel (Ni). These balls are especially made for ball mills and are uniformly through-hardened to 60-65 Rockwell C. They represent the highest quality of all metal grinding balls. Most operators insist on using them. 
Cast nickel alloy  These grinding balls are also very popular. They are basically a white metal ball, and cause less metallic staining than other types of grinding media. The principal objection to these grinding balls is their rough outer surface and projecting nubs, typical of most cast balls. They require a long conditioning period before being placed into general use. 
Stainless steel  Because of its high cost, stainless steel is only used for special work that requires an acid resistant, non- magnetic ball. 
Forged low carbon steel  Chill iron and low carbon steel grinding balls are the cheapest metal grinding balls. They are recommended for rough grinding only, where metallic contamination is not a problem. 

CHEMICAL PROPERTIES & HARDNESS: ACCEPTABLE GRINDING MEDIA QUALITY

COMPOSITIONAL EFFECTS

Steel grinding balls are produced from a range of carbon/iron ( Fe/C or Fe-C ) alloys. The alloy systems used include AISI 1020 mild steel, high carbon low debase forged steel, forged martensitic stainless sword, forged austenitic stainless steel sword, Ni-Hard, 20 % chromium, 27 % chromium and 30 % chromium white vomit irons .
By increasing the carbon paper content to produce cast irons, both the unfeelingness and wear resistance are improved significantly. The high carbon content of hurl sword leads to a microstructure consisting of primary carbides rather of austenite or one of its transformation products ( i.e. pearlite, martensite, etc. ) as a primary phase.5 Usually, the C contented of the steel balls is kept between 0.70 % and 0.80 %. besides, the Cr content should not be less than 0.5 % in order to ensure a minimal unfeelingness gradient .
The balance of the composition is Fe with only attendant impurities, such as sulphur ( S ) and morning star ( P ). Mn is added to supplement the Cr subject, particularly in larger diameter balls. A high C content ( i.e. > 0.85 % ) in forged sword balls reduces formidability, which normally causes spalling. This is due to an increased inclination to retain austenite in high carbon steels .

Ball Type Elements   Hardness
C Cr Mn (HB)
 
Cast Steel ~3.50 ~3.0 1 max 530
Forged steel 0.80max 1.0max 1 max 675
         

GRINDING MEDIA STEEL BALL HARDNESS

For the best performance, sword testis unfeelingness must be consistent from airfoil to core. The unfeelingness of cast or forged labor balls is measured on the Rockwell or Brinell Scales. Hardness tests can be performed in conformity with the manufacturer ’ second specification. Minimum severity for grinding balls varies based on the material, desired stamina by the end drug user, and the ore being prime .
The hardness influences the grinding resistance of grinding balls. In order to obtain the needed unfeelingness, grinding balls should be heat treated and cooled properly to achieve good impact underground .
Factors that lead to premature breakage of balls:  

  • Pre-existing flaws that concentrate stress (quench cracks, gas and shrinkage cavities,centreline shrinkage in continuous cast bar before forging, and forge laps in surfaces).
  • Poor forging and heat treatment processes. These lead to high retained austenite content.
  • Lack of quality control.

Impact toughness of grinding media forged steel balls.   Proper hotness treatment can improve the impact tire resistance ( IFR ) of grinding balls. The shock fatigue resistance decreases with increasing amount of retained austenite ( Áret ). ideally, the retained austenite content should be less than 10 % for high impact wear conditions .
drop tests can be performed on the balls to evaluate their resistance to impact break. These tests involve dropping a testis from a acme of 3.4 m onto a 500 millimeter diameter by 150 mm thick hardened steel anvil .
Abrasive wear of grinding media forged steel balls. In comminution, high grinding media wear rates represent identical high production costs. The costs should be minimised by proper materials selection, particularly for grinding balls. ideally, wear rates should be less than 1kg/ton. Marked ball tests can be performed to check the harsh wear rates of particular grinding balls .

 

PRODUCTION OF GRINDING MEDIA (STEEL FORGED BALLS)

production overview by Vitkovice Cylinders- Manufacturer based in the Czech Republic .

Steel Forged Balls fabricate process : Roll forged & Rotary roll

output video : production of Grinding Media Forged steel balls. By Air Hammer.

  • A steel bar is cut into shots, then reheated and hammered at least 30 times to compact and harden it.
  • In order to maximise the throughput in the milling process, the correct grinding media is selected.
  • The bar undergoes a process of hot rolling followed by rapid cooling, reheating, and hammering. This changes the microstructure from pearlitic to martensitic.
  • In the forging process, the structure of the steel grain aligns and stretches.
  • Stronger, more compact steel is created. This is used to make the grinding balls. The bars are heated to make them malleable enough to form near-perfect spheres.
  • Finally, the balls are quenched and reheated for tempering and relieving stress.

DROPBALL TEST

Global capacity of the grinding media industry
There are many ball-shaped players in the labor media industry. The total capacity is more than 5 million tons per year of grinding balls and other grinding media .

Region Capacity (tons)
China 2.3mill
North America 700,000
South America 750,000
Europe 500,000
Russia & CIS 500,000
Middle East, SE Asia 500,000
Australia 450,000
Africa 350,000

The grinding media market’s global players

China is home to many grinding media suppliers and manufacturers ; from coal-fired foundries to state of the art production facilities. The quality from China varies widely. Some of the poorest grinding media is produced here, as is some of the best. Chinese-produced grinding balls have replaced big identify brands from some of the largest grinding media circuits worldwide. In some mill industrial tests of chinese steel forged SAG balls, wear rates were found to be 19 % better than Scaw Metal, West african Forgings ( WAFO ), Corvus and approximately 6 % better than MolyCop .

GRINDING MEDIA STEEL BALL SUPPLIERS LIST

If you are a manufacturer and would like to be added to the list above, please electronic mail here .
Grinding Media Price Drivers
Depending on the location of the supplier, prices are formulated according to the keep up principles. price can be fixed and re-negotiated quarterly or every 6 months .

  • Pricing is generally based on an agreed price formula relative to the CRUspi or Scrap indices
  • Freight (generally paid and managed by the supplier.) Seen as a key part of the price equation (thus proximity to the customer is often important.)

General pricing formula for China:
1. Steel Price Adjustment: When the price apparent motion of the MySpic composite steel index published on www.mysteel.net exceeded an allowance of 2.5 % in the previous six months, the price of the intersection shall be adjusted for the surveil six months period according to the surveil recipe : ( If the steel index does not adjust by more than 2.5 % in the former six months, no adjustment to the sword price is made. ) A= [ B/MySpic ( 0 ) ] XMySpic ( 1 ) Where, A : Updated price ( FOB Price with packages )
initial Price ( FOB Price with packages )
MySpic ( 0 ) : initial MySpic steel composite index published on www.mysteel.net MySpic ( 1 ) : value of leaden average of MySpic steel composite index published on www.mysteel.net of former six months movements .
2. Adjustment as a result of Rate of Exchange Fluctuations:  Should the version of the average exchange rate for a specific six months period ( compared to the previous six months ) between USD and RMB published by Bank of China exceed 2 %, the Rate of Exchange will be adjusted according to the succeed formula : C=D X ( E/F )
C : Updated price ( FOB Price )
d : adjust USD price according to the above price Adjustment Formula .
vitamin e : initial Exchange rate ( Middle Rate ) on www.boc.cn
F : Exchange Rate ( Middle Rate ) in the date of adaptation on www.boc.cn
3.Freight cost from departure port to destination port:  Should be adjusted according to commercialize monetary value and added as-is to the FOB price to make up to CFR Price .

How to Improve Grinding ball Quality in your Supply Chain

The impact of low quality grinding balls on  milling

  • Ball chips from flaked, poor quality grinding balls result in shorter operational life of pumps, hydro-cyclones, and recirculating pipes.
  • Grinding balls may be too light to have the sufficient kinetic energy to break rock. 
  • Mill flow rates are reduced. Inferior grinding balls cause peening when they are hammered against the discharge rate. This cushions the rocks being hammered and causes ineffective breakage.
  • Energy consumption increases. The lightweight balls are pinned to the mill shell and carried to a point before leaving the shell on its trajectory, adding more load to the motor.
  • Steel consumption is increased. This generates iron ions detrimental to flotation, which in turn depresses sulphide minerals, and increases sodium cyanide consumption.

EFFECTS OF BALL SCAT REMOVAL ON SAG MILL PERFORMANCE

Ball scat is fragments of grinding balls that result from using holey grinding balls. 30t of scats were removed from a total charge warhead of 70t. Surveying and modeling the mill revealed that the breakage rates had increased dramatically at the coarse end of the size distribution. An increase of over 10 % in mill throughput was achieved by removing the ball scats from a single-stage SAG mill. This solve highlights the importance of maintaining a competent ball charge in a grind .
referee : “ Starting Effect of Ball Scats Removal on SAG Mill Performance ”

 

How to Select the Best Supplier for Grinding Media

If you want to get the best crunch ball for your money, determine prize by examining ball performance and price per unit, a well as the surveil factors :

  1. Quality. Grinding media steel balls should offer consistent and superior wear rate performance compared to alternative products. Don’t assume that a low price is a good deal, however. Some suppliers offer reduced prices by supplying poor quality grinding media. This can increase production costs through downtime or faster wear of cyclones and piping.
  1. Supply Assurance. Since grinding media is a key consumable, mines need flexible and timely product delivery. Significantly longer supply chains may increase the risk of substantial delays. Many suppliers are able to offer VMI services that eliminate long delivery times. VMI also increases unit costs, however. With careful planning, end users can import grinding media directly from overseas sources. 
  1. Technical support. Most mines require technical support –these may include ball mill inspections, grinding media consumption monitoring, etc. This service is normally provided for free, as a value added service.  

 

Delivery of Grinding Balls and Other Grinding Media

Grinding balls and early grinding media are by and large delivered in one of two packaging types :

  • In steel drums with content of approx. 900kg net on wooden pallets.

  • In UV resistant PP bulk bags with the content of approx. 1,000kg net.

Conclusion

Grinding media is not a commodity. It represents a bombastic assign of your total grind cost and has a meaning impact on your OPEX. Select your grinding balls with improved grind performance and efficiency in mind, but besides look for the lowest sustainable cost and maximize mill handiness. A full moon chemical psychoanalysis, unfeelingness profile and microstructure analysis can help you choose cost-efficient grinding media balls. Implement a good quality control condition broadcast to ensure consistency in the supply chain, equally well .
Kemcore assists mining executives in cutting costs without cutting corners. We offer mining companies a full compass of grinding media from acme producers in China. Contact us now to find out how we can help you increase your profitableness. Click here to learn more about our range of grinding balls and other grinding media .

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