For BlackHawk’s energy sector customers, component machining presents extraordinary challenges such as high-temperature metals and ultra-precise specifications. Today we consider two examples from heat exchangers. Our guest expert is Patrizio Cresta, Global Product Manager for Holemaking at WIDIA, a BlackHawk partner supplier.

Anatomy of a heat exchanger

Heat exchangers are used wherever temperature transfer is required between two separate fluids. They are most commonly associated with oil/gas/petrochemical applications, but heat exchangers are also widely used by the pharmaceutical and food processing industries.

Structurally, a heat exchanger is a long horizontal cylinder, typically with one fluid reservoir at each end and a separate center chamber between them. The end reservoirs are capped by circular tube sheets and connected by a series of pipes that mount to the tube sheets. A “hot” fluid flows from an inlet in one reservoir and is drawn through the tubes to the opposite reservoir, then exits via an outlet. In the exchange process, a “cold” (lower temperature) liquid – often water — is pumped into the center chamber around the hot tubes. The two fluids never mix. The flow time of the exchange is regulated by a series of baffles placed inside the tube framework for flow control and additional structural strength. The thermodynamic effect is that the cold fluid draws heat from the hotter fluid, cooling it. Hence, a heat exchange.

For our purposes, the two key components are the tube sheets and the baffles.

According to Patrizio, under current pandemic conditions, the primary objective for machinists is to lower the cost of the component as opposed to improving productivity or increasing output.

Patrizio explains. “Machine time represents about 90% of the component cost. So to lower that cost, you have to lower time on the machine. To do that you must raise your feed rates. And to raise feed rates, you need tools that are precise, reliable and long lasting.”

Machining tube sheets

Tube sheets are giant circular “coins” in which hundreds or even thousands of holes are drilled to anchor the network of tubes. “A two meter diameter tube sheet can have up to 2000 holes, one per tube,” explains Patrizio. “Precision is critical because the final assembly cannot have any leaks. The seals have to be leak-proof, so the holes must be perfect.” Depending on the end usage, tube sheets are made from low carbon steel (OP&G uses) or stainless steels and titanium (food processing). They may be plated with alloys. “Low carbon steel creates large chips, so you use long drills,” says Patrizio. “For stainless and titanium you need tools that can handle multiple materials and high temperatures.” In either case, the machinist’s mission is to maximize feed rates with unerring accuracy.

Machining baffles

Baffles create a different challenge, as they are typically drilled in stacks of 2-5 stock pieces. “Baffles are usually made from low carbon steel, so they are softer and easier to drill, but abrasive, so they create longer chips,” says Patrizio. “Also, they are thin — anywhere from 10 to 22mm (< one inch) thick — so machinists stack them, sandwich style. That creates the potential for the stack to wobble or shift during drilling, or to snag on the tool and break it. Stability of the set-up is critical because you don’t want any movement.”

Boosting feed rates. Firm grips. True cuts. What’s the answer for the machinist?

WIDIA TDMX drills — interchangeable solution

Introduced in 2019, the WIDIA TDMX line of interchangeable drills has proven to successfully tackle the challenge of these heat exchanger components. As Patrizio notes, “The modular TDMX design is a hybrid. It combines the high-feed and larger size options (16-40mm) of a solid drill with the flexibility of an indexable drill. The solid carbide cutting insert can be changed out quickly without removing the steel body from the machine, cutting downtime.”

TDMX offers unique design features that are ideal for machining heat exchanger parts and for similar applications:

• Tapered pocket seat for a snug, secure insert fit with no movement
• 45° angled clamping screw tightens on notched insert shaft to anchor insert
• A second perpendicular screw is turned to push up shaft and remove insert

“Even if you push the feed rates, the TDMX stays in place with no movement. You get a true hole every time,” says Patrizio.

Optimal TDMX geometries are 140 point for tube sheets and 180 for baffle stacks of 3-5 pieces.

Patrizio sums up, “Security. Stability. Reliability. These TDMX tools offer everything you could want for accurate, high-feed performance.”

View all WIDIA products available from BlackHawk here.

Adapted from the WIDIA webinar, Tech Talk: Drilling Operations in the Energy Market hosted by Patrizio Cresta, July 23, 2020.