Semi-Solid Metal Casting to Reduce Costs

Semi-solid metal casting (SSM) is a virtually net shape production process which gives manufacturers and users of copper alloy parts a substitute and, in several cases, an economical way to manufacture bulk quantities of parts with superior component quality compared to conventional pressure die casting technique.

The capability to apply SSM casting or die-casting with metal in a semi-solid state is an outcome of the successful evolution of a high temperature nickel-base alloy die system. This high temperature nickel based alloy die system prolongs the die life in die casting metals and alloys with high melting temperatures. As the process requires easily available cold chamber horizontal die casting machines as the casting unit; it has the potential for far-flung applications and uses by existing casting professionals equipped with such machines and technology.

Semi-solid metal casting is made with metal at a temperature between the temperatures of liquid and solid state, with the fraction solid being in the range of 30-65 percent approximately. The semi-solid billet holds its form and shape and is suitable for loading into the shot sleeve of a traditional die casting machine. For the semi-solid metal to have adequately low viscosity, the structure at the working temperature should comprise of a globular primary solid state surrounded by the liquid state. The technical and economical feasibility of the Semi-solid metal casting process are ascertained, to a great degree, by the approach used to develop the starting stock with the necessary precursor structure.

Advantages of Semi-Solid Metal Casting
As an advanced casting technique, SSM casting offers huge potential in saving costs, energy, and material, and in reducing the environmental impact of casting. The advantages are -

• Virtually net shape processing
• Reduced thermal fatigue heat, reduced mold or die wear, and reduced solidification shrinkage as a result of the reduced feedstock temperature.
• Lower shear strengths of semi-solid slurries that are related with lower forming forces than fitting operations for solid metal
• Potential for superior tolerance control because of the inherently tight process temperature control related with SSM casting and reduced thermal cycling of dies
• Finer, more consistent, micro structures resulting in higher mechanical performance
• Control of viscosity, which may result in less turbulent mold and die filling that, minimizes the gas entrainment, shrinkage, porosity, hot tearing, and other solidification shortcomings
• Superior material utilization in making small components because of the productivity and accurate introduction of metal into the forming dies
• As alternative for sand casting, SSM cast parts production gets rid of the environmental costs and troubles of reclaiming and disposing of lead-contaminated sands
• Increased casting speed compared to liquid processing due to lower thermal demands on the dies
• Allows for the lead content of red brasses to be highly reduced and, combined with a semi-solid charge, should enable alloys usually prone to hot tearing to be die cast

Best Foundry Practices

The metal casting industry has been, and continues to be, an integral component of the industrial backbone of several nations across the world. The industry provides employment to a large number of people and supplies huge amount of castings thereby impacting almost every other industrial and commercial sector. The metal casting industry is also an important recycler of metal scrap, a major energy user, and an important pollution prevention partner in many countries.

Good foundry practices address critical technology deployment requirements that will help foundries in saving costs and increasing profits. These practices help in reducing the energy consumption and environmental impact of the metal casting industry and improve its competitiveness.

Given below are some of the good practices that can be adopted for cost savings and increase in profits:

Energy Saving Practices
By adopting following measures and practices, foundries can make big cost savings –

Set variable frequency drives on motors
Getting rid of voltage imbalances helps in reducing losses from vibrations, mechanical stresses, torque pulsations and overheating.

Switch off equipment and lighting when not in use
Specifically place a start-up and shut-down procedures to control energy usage spikes.

Install high efficiency lighting
Using fluorescent lighting with magnetic ballasts instead of older ballasts is always cost-effective. Install targeted lighting at inspection points rather than less efficient ceiling lights.

Cut down the compressed air pressure set point by 10 percent
Maintaining excess air system pressure is very expensive. Set points can be cut down with proper maintenance of system and continual repair of air system leaks.

Upgrade motor drive belts
Using energy efficient cog belts instead of drive belts help in reducing energy requirements. Cogged belts can function on existing v-belt pulleys, but at lower temperatures.

Adopt superior melting practices
Specific recommendations may vary depending on the type of melting system used by the foundry. Furnace manufacturers can be of great help in helping to identify good melting practices for energy savings. The use of preheated air/oxygen and optimized burner designs has found to be good for gas-fired furnaces.

Improved compressed air practices 
Compressor should be properly sized, it should not smaller or over-sized. Use air storage systems to limit idling of compressors. Reduce leaks at valves, couplings and pipe joints.

Short cycle heat treatment
Majority of the heat treatment practices followed by foundries are overly conservative and waste energy. High efficiency furnaces and furnace linings are usually cost saving.

Low Cost Technology Practices
By adopting following measures and practices in various technical domains, foundries can save costs –

Melting
Melt cold, pour hot, pour fast – This will reduce the consumption of melting energy to minimum, while at the same time improves the quality of melt and reduces disfunctioning. It is usually much economical in the long run to completely preheat ladles than to melt hot and admit high temperature drops during the transfer of metal.

Molding
Upgrade the sand testing quality assurance – good control of sand systems ensure superior mold quality and reduction in scrap. Make consistent use of sand supplier testing capabilities. In several cases, improved molding practices can help reduce the biggest single contribution to casting scrap.

Scrap Reduction
Improved reporting and analysis of scrap – The single effective way to reduce scrap is to identify the scrap and its root causes in a proper manner. Lack of attention to detail in reporting of scrap may badly affect the bottom line; for instance, it is crucial to identify ‘sand’ or ‘slag’ as the causes of scrap instead of simply grouping them together as 'dirt'.

Lighting
Good housekeeping & lighting results in improved quality – A little extra KW of energy use, specifically in inspection areas, actually results in money savings. Good housekeeping leads to pride among workers and improved quality of products.

Data Collection
Decisions should be based on sound data collection - Make sure that the data, which you have collected has sufficient gage R&R; it is useless to collect data if you are not going to use it. Employees will be much more accurate and efficient collection of data if they know how that data is going to be used.

Training
Training helps in enhancing the skills and productivity of employees – Make use of all internal and external training resources to improve the work skills of your employees. If production employees are better trained they are found to be better problem solvers.

Profitability
Superior costing & pricing systems – This is essentially a challenge especially in the jobbing foundry, but is essential to ensure the long term success of an organization.

Metal Piles at China Ports indicating sluggish growth

A reddish-gray mountain range is springing up across China’s eastern seaboard, casting a shadow over the nation’s economy.

The mountains are iron ore, a crucial import which’s a lifeline to the world’s largest steel producer, and their size has become a telling, even if imperfect, signal of the Chinese economy’s sharp, sudden sputter.

Iron ore stockpiles at Chinese ports this week reached an all-time high of around 120 million tons, a senior analyst for Beijing’s Umetal.com told China Real Time on Thursday. The high supply level is not a good indicator: It suggests steelmakers aren’t in a hurry to produce, signaling a weak appetite across the industry that is heavily dependent on China’s all-important real-estate sector.

It’s not just iron ore.  China is the world’s largest buyer of just about every industrial commodity, so an economic slowdown since April in the world’s second largest economy is a reason for concern in global trade.

Coal stockpiles this week also reached a 2012 peak, rising 40% compared to a year earlier at 8.7 million tons, according to analysts at a research agency affiliated with the National Development and Reform Commission. High stock levels also extend to agricultural commodities, with the state-backed China National Grain and Oils Information Center warning last week that “recent soybean arrivals at ports have been on the higher side.”

As far as iron ore is concerned, however, the rising port stock levels aren’t necessarily a harbinger of doom, said Zhang Jiabin, research director for Beijing-based steel consultancy Umetal.com. While higher inventories normally point to slower downstream demand, Zhang said it would be too simplistic to say consumption is going down. “The ore stock level has been fairly steady this year, and although there has been some output reduction among smaller steel mills, there have not been large-scale production cuts,” he said.

Iron ore spot prices began to increase in the last week of May after sliding 9% from mid-April, signaling that steel makers have resumed bargain hunting.

Still, if ore inventory consumption is measured and compared in terms of how many days’ port stocks can last, it’s clear the industry is languishing. Stock levels surveyed in a sample of 50 smaller mills over the last 2 weeks have remained around 29.9 days-of-use, Macquarie Commodities said in a report published Wednesday. In comparison, mills were holding about 20-28 days’ worth of stocks last year, Macquarie said.

Steelmakers are also facing more problems obtaining bank loans. “It’s an open secret that banks are now more restrictive toward loans for steel mills and fluctuating prices have reduced the ability of trading houses to use imported steel as collateral,” Zhang said.

In some cases, analysts have already started projecting that rising quayside supply will dent China’s import appetite. Macquarie estimated that refined copper imports in May could fall 25 percent from April as Chinese consumers opt to run down high levels of domestic stocks. Copper stocks are estimated to have risen sharply this year to around 1 million tons. Iron ore imports have shrunken for 2 successive months.

Bouts of high port inventories don’t always tell the story of a slowdown that’s here to stay. China’s steel mills have been known to pause buying as a collective tactic to secure cheaper ore prices. But if the freighters calling at Chinese ports need any early indication of what’s going on, they need look no further than the record high right at their offloading berths.