This paper introduces the craft characteristics of casting the shell of the gearbox, including the manufacturing of the resin moulding, the application of the hard sand core and so on.

针对变速箱壳体毛坯铸造的工艺特点，介绍了其树脂模具的制造、树脂自硬砂砂芯应用等关键环节的技巧和做法。

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Most sand is made of quartz, a hard silicon crystal.

VOA: special.2010.01.04

Most people are afraid to draw the hard lines in the sand for fear of angering a friend or losing a potential client or opportunity.

FORBES: No, You Can't Pick My Brain. It Costs Too Much

Senate Minority Leader Mitch McConnell drew a hard line in the sand after the election against any new tax hikes in the fiscal cliff showdown.

FORBES: Limiting Deductions Could Be The New Tax Hike In Fiscal Cliff Avoidance

While the hard ground - because of the underlying sand drying quickly - allows the ball to travel further from the tee, the ground off the fairway is far less forgiving.

BBC: Carnoustie