More Flexibility for Green-Sand Molding Operations

Top and bottom sand-blowing system extends the Hunter expertise with a new option for foundries’ mold-filling needs.

The science of sand molding has not changed for centuries, but the process technologies involved in mold production are another matter. In that case, the changes are demand-driven. Molding machinery is developed to suit the production requirements of foundries, and foundries know where to turn for molding technology expertise.

Hunter Foundry Machinery Corp. has been innovating and refining molding machinery for more than half a century, famously with the Hunter HMP machine that introduced the "matchplate" concept that made green-sand molding faster, more reliable, and more cost-effective, and allowed foundries of all types to be competitive in terms of volume and product quality. It is a rugged, gravity-driven system that’s easy to operate and easy to understand; it is scalable to foundries’ available space; and it adapts easily to different foundries’ molding operations.

Various updates and modifications to the HMP system have been offered over the years, and Hunter extended its expertise to other molding process systems too — always adapting to the needs of green-sand foundries.

“We foresaw certain demand for a lower-speed, easier-operating, single-station molding machine,” company president and process developer Bill Hunter explained recently, referring to the latest process development. The patented HTTB machine — the acronym is for Hunter Top Bottom Blow —was introduced at CastExpo 2019 and GIFA 2019 events earlier this year.

Blowing sand to fill molds, rather than gravity-filling processes, allows the operators to achieve more customizable rates of speed.

Bill Hunter recalled how the company had designed a two-station blow machine called the Hunter Molding Center about 10 years ago. That machine is capable of producing molds for two different jobs at one time, “which is ideal for a high-production environment,” he noted.

About a decade earlier than that the company had designed a single-station blow machine — a system that’s still in operation. After researching foundries’ mold-production methods and needs, Hunter came to the realization that a single-station blow machine has some unique advantages — including lower investment requirements and high operating flexibility.

The new top/bottom blow-molding machine is a process alternative to complement Hunter’s gravity-fill molding systems. Using adjustable hydraulics, the HTBB delivers higher squeeze pressure and produces more consistent and uniform mold surface hardness, the developer noted. This improves casting finishes significantly, and reduces the requirements for finish machining.  It also reduces the amount of pattern spray consumption making it more environmentally friendly.

Further, the HTBB’s top/bottom blow process eliminates the shadow effect that is common in side-blowing machines. It allows foundries to produce more complex castings with deeper pockets. The variable mold height adjustment capability improves sand yield and casting quality.

In operation, a mold pattern is inserted into the HTBB machine between a cope and drag flask while being sprayed on both sides. The cope and drag flasks close simultaneously, with the pattern in-between. Next, sand is blown into the cope from above and into the drag from below, also simultaneously.

Once the mold is closed the high-pressure squeeze ensues, followed by drawing and removing of the pattern from the flasks, then placing cores, if needed, and discharging the completed mold from the machine.

Because of the volume and variety of customers’ molding requirements, Hunter aims to provide as much flexibility as possible for the new machine series. “Standard HTBB models are available to accept all existing Hunter pattern plate sizes,” Bill Hunter explained. In other words, there is a mold-filling process to suit any foundry’s process requirements. And it’s ready now.

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